Core stability and pain: Is it time to stop using the word stability to explain pain?

sidebridge feet
sidebridge feet

Purpose: To cherry pick a few research articles to suggest that even though our knowledge of core stability is very impressive its link to pain is poor. Nutshell summary: People in pain have spines that function differently than those not in pain.  Many treatments can influence pain.  The spine stability model of low back pain does not explain how people have pain and takes an overly mechanical view of the pain experience.  No test has ever shown that a spine is unstable or how "increasing stability" would lead to a decrease in pain.  Thinking that our spines need more stability or control may be the completely wrong path in explaining how people have pain or how our exercises help them.   Our treatment "corrections" occur not via one specific "corrective" mechanism (e.g. improving stability) but rather through global non-specific mechanisms that our better explained by our understanding of pain neuroscience.  Making the shift from believing that "stability" is the issue with pain can thus free up to choose completely different exercise programs.  Exercise and treatment prescription thus become simpler.  We have preliminary evidence to support this view with the clinical studies that show benefits with the various exercise conditioning programs that train different schools of thought on stability or the just as effective programs that completely ignore any concepts of stability.

Caveat of Ignorance

The purpose of this post is to question things that we say about exercise, low back pain and of course "spine stability".  This is an informed opinion piece and everything I say can be challenged strongly...that's why I write it.  I am also going to put out some "notions" on how I think exercises can help with pain and function.  These are certainly subject to debate and will probably change with time.  I have also ended the piece with a general overview of what I do in Part Two.

A BRIEF and not complete background on spine stability across two hemispheres

Two schools of thought regarding spine stability and low back pain emerged in the 1990s.

The Australians and their inner muscles - Train the local muscles first

The first was based on Bergmark's classification of muscles into "segmental" stabilizers and others into "global" movers.  Segmental stabilizer muscles were often considered to be tonic (constantly on) while the others were phasic (on intermittently to create movement).  This idea of muscles having different roles was suggested decades earlier by Janda.

Low back pain was assumed to occur when the segmental stabilizer muscles were inhibited and the global muscles took over.  The research supporting this idea came from the great work of Paul Hodges (A nice review of Paul Hodges and Motor control can be seen a Todd Hargroves site bettermovement.org).  In early studies, Paul showed that in healthy subjects the transverse abdominis and the multifidus muscle (two local muscles) should fire in a feedforward manner when someone is asked to lift their arm.  Lifting the arm is a perturbation to the body and muscles in the trunk and legs must turn on for us to keep our balance (some call this "stability').  Dr. Hodges showed that the "Tranny" and MFD turn on before or within 50 milliseconds of the deltoid muscle.  Since the muscles become active  before the deltoid we can assume that the brain did some motor planning to prepare the body for the arm raising - muscle activation was NOT a reactive response to the movement of the arm.

With low back pain Dr. Hodges showed that this feedforward (or motor control planning) was delayed in the Tranny and the MFD.  And BINGO a whole  industry was born and the misapplication of science ran hogwild over common sense.  So that's it.  All Paul showed was that in those with pain you got a DELAY in firing.  No one showed that the tranny was weak, no one showed that the muscle was turned off and no one involved in the research said that the Tranny was the most important muscle on the planet.

But somehow physiotherapists, chiros and personal trainers started telling everyone to suck in their stomach when they did squats because the muscle was erroneously deemed to be super important for spine stability.  This was never what the research suggested and caused fits in the North American Spine researchers who really railed against this simple idea.

The other school of thought - Train general core stability (a brief simple version)

birddog1
birddog1

Fortunately, I was innoculated against this because of my MSc with Dr Stu McGill in the late 1990s.  Dr. McGill and Dr. Sylvain Grenier were excellent in challenging the supremacy of the Tranny.  I view their research as less a repudiation of Paul Hodges' ideas and more of an attack of the misuse of Paul Hodges' research.  What McGill and his colleagues had always advocated and also modeled with their biological fidelitous spine model was that spine stability (aka the ability of a system to return to its normal position after a perturbation) was most robust when all of the muscles worked together in the trunk - all muscles were important for stability.  This was again nothing new and we knew this from other joints.  Muscles co-activate, create joint compression and the cost of compression is assumed to be offset by the benefit of stability.   This North American model of stability assumes that all muscles of the trunk work together to balance the stability demands of the spine.  Hence rehabilitation from low back pain should train all the muscles of the trunk in a manner that creates stability but does not do so at a huge compressive cost or adverse tissue loading cost.

Dr. McGill was a leader and pioneer in this.  He was the only one actually evaluating exercises and measuring stability and measuring the compressive/shear loading on the spine to determine which exercises might be "safe".   Dr. McGill was able to classify exercises in to ones which were "safeish" (lower compressive or shear loading on the spine) and others which might have a high compressive penalty but an individual got a good workout (i.e. lots of muscle activity).

The clinical relevance of both the North American and the Australian views are founded on a number of assumptions and unknowns.

What both views assume is that exercise training will make the spine more robust in terms of stability (not more stable, as we know a system is either stable or unstable - you don't make it more stable) and this will lead to less pain and perhaps decrease your injury risk.

Faulty research extrapolations to people in pain and other random stability issues

Below are a number of points regarding the limitations of the relationship between spine stabiliy and pain

1. We do not know why people have low back pain. We do not know what tissue is actually cranky/irritated, fires off a volley of nociception that may ultimately result in the production of pain in the brain (if it even is coming from some cranky/irritated nerve embedded in tissue and is not wholly a production of pain from the brain in response to some perceived threat).  We can not say that a disc is pissed off, a muscle is cranky, a facet joint is upset or if some ligament wants a vacation.  Damage in the spine has a poor correlation to pain. So if you can't identify what tissue is the source of nociception (and we can't) what is the mechanical basis for the prescription of any stability exercise?  How would changing the stability of the spine decrease nociception? If you think spine stability exercises actually change stability parameters by what mechanical means does this change nociception? If you think spine stability exercises help your patients and clients but you can't explain it via a mechanical explanation (but you know it works) do you think there might be  something else going on besides stability issues that you are affecting to influence the perception of pain?

2. Who cares if a muscle is delayed 50 milliseconds?  Really, what relevance does this have.  The muscle turns on eventually and does its job during a task.  Why is a delay of 50 ms relevant in terms of biomechanics.  Is this delay a defense or a defect?  Is the problem in the spine (unlikely) or more a symptom of "something is up" with the brain (more likely, and this is where Dr. Hodges is doing most of his work now yet in popular clinical culture we are stuck at the level of spine). I will go into Hodges work later in another post because I think his work on motor control and the brain may be extremely relevant.  Big point here, Hodges never measured stability.  Just muscle activation in all the muscles that make up the trunk cylinder (side note: he did a wonderful job here, I think his research is excellent, he is an excellent researcher and his contributions to our understanding in the area of motor control are without par.  I would also prognosticate that his future research might bridge the gap from mechanical views of spine and pain neuroscience).  Everyone just jumped on the stability wagon and assumed that it was compromised.  Maybe there is something else going on here besides stability.

3. The argument for the motor control camp against bracing and planking - "Don't brace or do planks because your spine becomes rigid" is a wee bit weak.  This is the argument against the North American model of spine stability and is used to justify"motor control" or low level exercise. It suggests that if you do a bunch of planks you will become rigid and activate your muscles too much. I disagree with this puppetry view of the body. Doing planks will not somehow carry over to rigidity in our activities of daily living.  We aren't puppets where we can tighten and loosen the strings of our spine. This is catastrophizing against a therapy rather by the patient.  These exercises aren't that powerful both in a negative or a positive way.  However, if you actively brace and assume a rigid posture as a choice during all of your normal activities then you can make this argument.  Don't blame the exercise blame the conscious choice of movement.

4. Do you think your patients are really "unstable"? Patients are in pain.  They move differently, you might perceive them to have "tight" muscles.  But is their spine really unstable? Is there a vertebrae in there sloshing around, sliding this way and that, pinching on stuff.  Is the spine really buckling?  We can have patients with high levels of spondylolithesis and their spines are not unstable.  I think we might want to reconsider telling our patients that their backs are unstable and they need stability exercises.  How much fear do you think this creates?  No one has ever shown that a patient with persistent low back pain has funny uncontrolled movements at a segmental level in the spine.

5. But my SI joint needs force closure, I need to train my Tranny or MFD or some bloody fascial sling.

How  is your SI joint unstable?  What wonky movement do you really think is happening in there?   I believe that there is less than 2 degrees of movement and a few millimetres of slide in that SI joint but how is having a delay of 60 milliseconds in one muscle changing this movement?  If it does change that movement why does this cause pain? And so what if the joint slides too much.  Other joints slide around and they don't create nociception.  And if you have a delay in the tranny won't the big, bad global muscles be on at the same time and thus increase force closure and shut down the movement.

These global muscles certainly have the architectural requirements to create force closure.  None of this makes sense. Oh wait, those global muscles are on too much and that causes too much compression in the joint and that causes pain.  Oh, gotcha that makes perfect sense.  But guess what, no consistent research actually suggesting that this happens.   The studies showing increases show increases that are extremely subtle and again how this would cause pain is never laid out in any logical or supported manner.   Well what if that joint is fused?  That seems like a lot of compression.  Should that not be painful yet its not? And why would compression from muscles be painful? Would someone not be better lying down and not lifting weight, walking, running if compression was so nasty for the SI.  More compression on a joint is not necessarily bad and does not lead to pain.  There is something else going on here.

childs pose
childs pose

5. Is it really that bad to get away from the neutral spine? I agree that a neutral spine is generally stronger when the spine is undergoing maximal compressive and shear loading.  Maintaining a neutral spine when deadlifting, doing kettlebell swings, squats and picking up your sofa makes some sense to me.  But do I really need to never bend or twist my spine.  It has a certain amount of movement built into it.  Why would I not use it?  Motion is lotion.  We would never tell another body part to not move.  Taking away movement is how we torture in Guantanomo.  The majority of spine pain does not occur because of we have overloaded it to an extent where it reaches the limits of tissue injury capacity.  This may be one of those issues where we can confuse injury with pain.  Neutral spine bracing can probably help with injury and performance when under high loads but is it necessary to decrease pain in someone getting up from a chair with low back pain?  I will grant that sometimes when you brace and move with a neutral spine and get out of a chair you have less pain.  In other people it gets worse.  Maybe there is something else that explains this besides stability.

6. Patients get better with all types of spine exercise programs.

We have clinical efficacy trials showing that a motor control program (e.g sucking in your belly and then progressing with more global exercises) and a global exercise program helps for low back pain.  So do general exercise programs.   We know that exercise for the spine can help but perhaps it does not matter which exercises we do.  When we get similar results from two different theoretically supported exercise regimes perhaps there is something about the two different programs that is similar.  Perhaps it is that similarity that leads to improvements in pain.  A recent paper by Mannion et al (2012) championed a similar idea.  In other words, we get results but not for the reasons that we think we get results.

7. I think we scare the shit out of people when you tell their spine needs stability

This the default word that many of us tell our clients.  "You're unstable, you can't "control" your movement and that is why you are in pain".  Its so defeatist and catastrophizing and really has little support.  I say we stay away from these words...See my previous post here on this same topic (The words we use can harm)

Recap

You can rehab a patient using the two different schools of thought on spine stability.  You will probably have similar results.  Conversely you could just have patients exercise their entire body and they will also show improvements. You will also have good results if you just teach people about pain and give them the confidence to keep moving and not get worried about their "bloody lack of stability" that some therapist told them they once had.

Stability is probably the most inappropriate word we can use to describe our patient's spines that are in pain.  No one has documented that patients in pain have unstable spines nor is there any reliable clinical test for it...yet we have been using this word for twenty years.  That is crazy yet so many of us think that we have to "increase the stability of the spine" in those with low back pain.  No one has shown how any dysfunctions related to "stability" actually cause pain. Again, crazy.  Yet we tell patients they need stability exercises to correct some mysterious bogeyman.   When we get results with completely different movements or exercises that totally conflict in terms of spine stability theory this tells me that the reason our treatment is effective probably has nothing to do with stability.

In part two, I will layout how the spine function is different in people in pain and also give some theories on what treatment does to help our patients.

Form, footwear and footstrike: an e-book on running mechanics review with injury insights

This post is a link to a pdf ebook on the presentation I gave for the MSK-Plus course November 25, 2012.  Below I give a brief intro into the confusion that surrounds these topics.  If you note a huge amount of uncertainty, a whiff of grey and lack of simple answers than your interpretation is correct.

 

The pdf file is form footwear and footstrike running mechanics ebook nov20 2 2012.

Related posts

1. Barefoot running and footstrike style overview

2. Gait modifications to influence impact loading

3. Barefoot running and running economy

4. Running in the backseat: lack of hip extension and its possible relationship to injury

5. What we know and don't know about running injury prevention

Overview

We can change the following variables of running:

1. Kinematics or changing the position of the body (e.g. trying to not let your knees collapse inwards) or the timing of events (e.g number of strides per minute)

2. Footstrike style

3. Footwear: barefoot, "barefoot shoes", minimal shoes, traditional cushioned shoes with an attempt to "correct" something

We also hope that changes in mechanics will occur.  Some variables that may be related to injury:

1. Rate of impact loading

2. Joint forces

3. Muscle loading, timing or activation levels

4. Joint kinematics

 

We assume that making one change will result in positive changes in other variables. The big assumption is that we know what is bad in running.  It sounds so simple, but in practice it is not. Especially when we deal with something like pain and injury.

What you will see in the attached e book is that nothing is that simple.  Changes in many variables related to running often don't result in the "positive change" in some running variable that we hope for.

 

Below is a brief introduction to the modifiable variables and their relationship to running mechanics and to a less extent injury.  The attached pdf file goes into a little more detail.

 

Modifiable variables during running

Run barefoot or run minimal

I wish it were this simple.  We have some data suggesting that some barefoot runners will run with a forefoot strike, reduced stride length and other changes and thus they will have a decreased rate of impact loading.  We have no data suggesting that making this change reduces injury and the link between rate of impact loading and injury is a wee bit murky.  We also have a number of research studies showing that just changing to barefoot is not sufficient to result in decreases in the rate of impact loading.

In Lehman's terms, we may want to be cautious about any blanket statements

 

Lose the cushioned shoes and run in flats

I do this but I certainly don't think its the answer for everyone. I also run in cushioned shoes because I think variety is important.  As for mechanical changes when going to flats there is not a lot of robust data out there that supports this in terms of biomechanics.  The assumption is that if you lose the heel on your shoes and the cushion you will automatically start to run with a softer gait.  Again, this is not supported in the literature and research exists showing increases in rate of loading and joint loading with racing flat like shoes.  Again, we need to reserve our blanket statements.

 

Convert from a heel strike to a forefoot or midfoot

The assumption is that heel striking is bad.  Again, not strongly supported in the literature.  Research is mixed with some work showing decreases in the rate of impact loading when going to midfoot or forefoot but we also have conflicting work showing the opposite.  Again, blanket statements are not cool.  The epidemiological research is also in its infancy, is correlational in nature and correlation data sucks for implying causation.

Decreasing stride length and increasing stride rate

This modification may have the most support and may be a common variable in other interventions.  For example, I think that someone might strike the ground with a forefoot strike and have a large rate of impact loading if they have a long stride, while another individual might convert to a forefoot strike and also decrease the length of their stride.  We might initially conclude that the forefoot strike was the variable that resulted in the decrease in the rate of impact loading but really it was just having a shorter stride.  This may also be a factor with barefoot interventions.  Barefooters tend to stride shorter...maybe those barefooters with higher impact loading rates failed to decrease their stride length.  BUT, and there is always a but, we do have a well designed study that showed no changes in impact loading when increasing stride rate (Giandolini 2012).  I am not even sure how that is possible but that was their finding.

 

Kinematic variables

The ebook does not touch on this but these would be things like increased frontal plane projection angle, hip valgus, hip internal rotation, pelvic obliquity, lack of hip extension, increased anterior pelvic tilt, prolonged pronation, lack of pronation, uneven arm swing, lack of trunk rotation etc.  Surprisingly, we have very mixed data on this.  Even the biggies like increased hip internal rotation and hip valgus.  Sure there is some correlational data that shows that some runners with knee pain have greater amounts of hip valgus when compared with controls but the predictive data is much weaker.  We also have data showing no relationship between assumed gait flaws and any current injury.

We don't know if pain begets gait flaws (e.g hip weakness) or if the biomechanical flaw caused the pain.  What might surprise you is that we can often rehab a patient, get them running injury and painfree and they still present with the initial "biomechanical flaw".  My concern with assuming that some biomechanical variables are faulty is that this views the body as being inherently weak and we forget about its amazing variability and strength.  You will see lots of runners with huge amounts of hip valgus/knee collapse.  You will shudder in horror at this.  But sometimes that is just that person's little idiosyncrasy .  They have always done it and they have adapted.  You will try to fix them under the assumption that they are faulty.  But this a massive assumption.

I am working on a large post on the kinematics of gait and injury.  I will go into a lot of detail on this topic

 

OK.  So everything is grey.  What do I do?

 Warning: Opinions ahead.

Gait modifications can help with an individual in pain:  We have good data that a slow return to running with modifications to form can help.  I don't necessarily believe that this is always related to biomechanics in the sense that we are changing mechanics to be closer to an ideal.  I think we are changing mechanics and it is the act of change that is important.  Variability and novelty is important to me in all my rehab programs.  Changing your gait loads the body differently and is also different for the brain.  Different gait patterns may avoid certain physical stressors on the body and may not activate our pain neurotags because of the novelty.  Further, most gait re-training is a slow, gradual return to running.  This exploits our innate adaptive abilities.

 

How should people run if not in pain?

Please note, the suggestions below only relate to running form.  There are a lot of things we can do to reduce the risk of injury.  Below is not comprehensive.

If I have to go out on limb I would suggest four things:

1. Novelty and variety: different shoes, different surfaces, different speeds, different distances.

2. Check your cadence: if you are running a five minute kilometer than  your steps per minute should be greater than 170 per minute.  If  you are "loping" and don't have a quick turnover consider increasing your cadence.  What you are trying to avoid is landing with the foot extremely far in front of the body and this is associated with a close to straight knee at footstrike

3.   With reservation and many exceptions, a midfoot to forefoot strike with the occasional heel strike thrown in:  this one is tough for me to say and I have some hesitancy. If you are novice runner I would probably suggest running with a midfoot strike. I think the bulk of the research suggests that running with a midfoot strike is the way to go.  I know that there is research suggesting heel striking is fine especially if it is not associated with overstriding.  I totally get this.   As  I said, I have some hesitancy - I treat a lot of heelstriking runners and would not consider changing their gait so this suggestion is obviously not a blanket for everyone.  Many heelstrikers have their feet land close to their body and their gait is soft and quick. However,  I also think that thinking about midfoot striking will also help with your cadence.  Last, for slower runners (10 minute miles) I doubt footstrike matters as much.  One caveat, I also think many runners would benefit from using different footstrikes during the same run provided their cadence is not too low.  This is consistent with my views on variety.

4. Gradual increase in running or in changes in form.  This one is obvious.  The body adapts over time we just have to give it some time to adapt.

 

My bottom line

I would be hesitant to change things about someone's form if they have no injury or past history.  If they have had a series of past injuries or currently have an injury this is where I think we can help the most with changes in form.  What you will see in the e-book is that there are so many exceptions to our commonly held beliefs about certain running related variables.  These exceptions make me quite cautious in just trying to change runner's form when you don't actually know what you are causing when you try to make a change.  I am lucky in that I have access to 3D motion capture equipment.  I can see what happens with different changes in form.  But I don't have force plates and I can make no comment on changes in joint loading or impact loading.  And the "running expert physio" dude with one camera (or who just eyeballs a runner from behind) can't say what changes in force (e.g rate of impact loading are occurring) and is also probably wrong about a runner's kinematics should be a little cautious in just making changes based on one or two cherry picked research papers.  What the research in this e-book shows is that many changes we assume to be good end up resulting in elevated levels of impact loading or joint loading.  Thus, I advise caution.

 
 
 
 

 

 

 

What is a functional exercise for runners and athletes?

clamshell open
clamshell open

A recent discussion was sparked by Mike Reinold's thoughts on the Clamshell exercise. I found myself defending the lowly clamshell exercise for runners. I was discussing with other physios whether the clamshell exercise was less "functional" than a band walk exercise (where you put elastic bands around your knees/ankles and walk forwards, sideways or backwards).  I suggested that both were NOT (or equally) functional but agreed that both had their uses. I can tell  you, I convinced no one :)

The consensus against me was that the clamshell sucked and that the band walk exercise was superior.  I tried to argue that this might be true but  not because the Bandwalk was more functional.  We essentially just babbled back and forth with no resolution for 20 minutes. The problem was the word "functional".

What the hell do you mean by 'functional".

When I heard someone say the bandwalk exercise was more "functional" than the clamshell I immediately thought malarky.  Because my knee jerk reaction to hearing "functional" was my brain translating this to "movement specificity" or kinematic specificity.  Meaning the exercise you are training matches the kinematics (specifically the displacements or joint angle motion) of the athletic task (in this case running).

Using kinematic/movement specificity to judge a Bandwalk or a Clamshell was a no brainer.  In terms of function (using the kinematic specificity definition) they both suck.  No runner lies on their side and lifts their leg up (e.g. the clamshell) but no runner runs sideways with a bloody elastic band around their knees.

So lets define "functional"

My knee jerk translation of "functional" to being "kinematically specific" is a little narrow. Our discussion exposed this.  Function to me means that the exercise has some sort of relevance to the task the athlete hopes to accomplish.  Viewing it this way then exercises can be functional or relevant thru a number of different means:

1. Movement specific: this means the exercise task somehow looks like the athletic task it is trying to train.  This means your exercise has similar form (due to motor control) to the goal task.  Further more, it suggests that the neuromuscular recruitment pattern is similar to the exercises (e.g. muscle onsets, offsets, ratios etc) For example, squats are great functional exercise to get out of a chair.

2. Muscle or joint specific: this means the exercise is training similar muscles to the muscles that are being used in the goal task.

3. Velocity specific: this means if your goal task requires you to move fast than you should probably train fast.  Exercises are therefore "functional" if they lead to some sort of carryover to the goal task's speed demands.  We know that you don't actually have to move fast to get this carryover, sometimes just the intention to move fast will garner improvement

4. Movement direction:  if your goal task requires a lot of deceleration than you should probably train the eccentric loading capability during your exercise.  For a runner, you might think they have increased hip adduction during the impact phase of  running which occurs for less than 100 milliseconds.  Thus you should probably train this deceleration ability over that specific time frame for it to be functional.

5. Context: the exercise should be similar to the context of the goal task.  The context might the exercises relationship to gravity or even to a societal or performance context (e.g you train to shoot free throws while people are screaming at you).

So what is more functional the lowly clamshell or Bandwalks?

Trick question! You can't answer this.  There is no functional scoresheet.  The better question is what is more useful to the runner or athlete.   You have to be able to answer why  you are prescribing an exercise in the first place. What is your intention with each exercise? What do you hope to accomplish?  If you prescribe an exercise because it is "functional' than this is just begging the question. Functional isn't enough it has to lead to some specific gain.  And if you think it is functional why is it beneficial?

A case example in the limits of functional justification: The BandWalk

I think most people would argue that the Bandwalk is more "functional" for the runner because it appears to train the muscles used in running in a more similar manner kinematically and more of the muscles that a runner uses when they are running.

But does it really do this?  How much of the previous "functional" components does the band walk satisfy?

Movement Specificity: No runner runs with a band around their knee, they don't run sideways or backwards. On its surface it certainly isn't very similar in terms of joint angles and displacements.  If you think movement specificity is important or practice makes perfect than training a movement that is so dissimilar to running can't be justified in this manner.

Movement Direction: Lateral band walks do not train the hip abductors in the manner that they are used during running.  Eccentric control occurs over very short period under high impact loads when running.  Band walks are extremely dissimilar to this. They are slow. They have an external force that is extremely different to the force vectors that create joint torques during running.  We don't satisfy a movement specificity or even a velocity specificity argument.  Considering this is the Bandwalk still functional?

Context? The band walk looks better than the clamshell that is for sure.  The athlete is standing and shifting weight.  But are they standing a shifting weight like a runner shifts weight? Nope. Is just standing and having weight shift enough to make it functional?  Why not do dumbbell curls while standing and shift your weight back and forth.

Motor Control:  No way.  Doing bandwalks are nothing like the motor patterns used in running.  Timing would be way off, no impact, no feedforward activation of muscles to damp vibration, hardly any storage of elastic energy.  Do you think the "extensor paradox" occurs during a band walk.  Not a chance.  These two tasks are completely separate beasts.  There is no way you can argue you are engraining some motor pattern during the band walk to enhance running.

Is the BandWalk Garbage?

Nope.  It can certainly help runners.  I don't use it but I still think it is reasonable for a runner to train with it. Because it satisfies our simplest category of "function".  It trains a group of muscles that runners need.  These exercises build the capacity of those muscles and this probably transfers over to increased mechanical efficiency and maybe even some injury protection. However,  if you think that it is functional enough to actually change a runners form than you might end up getting some poor results.

The problem with this last justification for strength coaches and rehab people is that it is too simple.  As therapists we want to think that we have some special knowledge about special exercises.  We don't.  There are no special exercises.  Train hard, train smart, get strong, build power, build tolerance, build capacity, build endurance, build the ability to absorb load, dampen vibration, produce strength at all ranges etc.  Have a generalized, good all around program and you will probably have good results. Maybe through in some assessments to see where your athlete is lacking and then train the hell out of that and you will do better. But, there are no running exercises.  And that is what both the research suggests and gurus suggest.  Pick an expert in a field of strength and conditioning (powerlifting, olympic lifts, corrective exercise, pilates, yoga, core stabilizinationists etc) and they all swear by their success with runners.   They are all probably right.

OK, so is the clamshell better?

No way! The clamshell sucks most of the time.  I got started blogging a lot because of Mike Reinold's post on a research study in JOSPT that looked at EMG in the hip abductors. The clamshell was a touted exercise and  I hated it. I thought runners should never do it.  I thought it was remedial and "non-functional".  My comment is on Mike's site.

The clamshell works fewer muscles, has the person lying down, looks kinematically different than running and doesn't satisfy many of the functional principles I laid out earlier.  BUT, it does train some muscles substantially different than the bandwalk.  This is where it can be a useful exercise.

The clamshell sees the hip flex to 90 degrees and has the patient externally rotate the hip.  At 90 degrees, because of changes in the line of pull of many hip muscles (GMax, GMed, Piriformis) the only muscles that externally rotate the hip are the deep external rotators.  So training the capacity of these muscles might carryover to running.

I used to abhor the clamshell.  Then I started testing more runners with the clamshell. A number who tested strong in many positions would tremble during the clamshell.  Crazy, they had a lovely one leg squat, strong hip abduction but had trouble with 10 or 15 clamshells.  What does that tell me?  Such a massive deficit in function.  Would you suggest clamshells here or something to address that specific movement?  This seems like a case where I would suggest clamshells.  If a runner can't do them I would want to address that deficit.

But, do I want to see every runner doing them as part of a "functional" program. Of course not.  They suck for that.  This is a case a where the exercise prescription is "functional" because it addresses a specific limitation in a specific runner.

OK. What do you suggest?

I have no exercise that addresses all of the components of "Functional" but that's why runners should get a comprehensive program. If I have a bias I lean to training "Comprehensive Capacity".  This means you train runners like they are athletes.  Big multijoint-compound exercises that train strength, high load power (e.g cleans), low-load power (ploymetrics), variable range exercises and unilateral exercises.  The thing with the word "functional" is that is so broad to be meaningless to justify an exercise.  Choose exercises based on some other specific capability of the neuromuscular system you hope to improve.

The Key Question: Why are you training what you are training?

For runners, I only think that we are training the muscle, joint, tendon and nervous system's capacity to tolerate stress that running imposes.  This makes runners more powerful, mechanical efficient and may make them less injury prone although with hip abductor training the research is a bit dodgy.

Do exercises help change running form?

This is seems to be the underlying idea behind an exercise that kind of looks like running (eg. the clamshell).  That training in that manner will improve your running form.  But there is some evidence to suggest that this does not occur (Willy 2011). We probably aren't training form.  We aren't correcting the biomechanics of running by choosing certain exercises.  We aren't engraining some motor programs that carryover to running.  If you want to do any of these things you have to do that while running and with some form of feedback.  Our bodies are not puppets where muscles can be tightened or loosened to obtain some different posture or form. That is a motor control skill not something that changes with other exercises.

So why are you prescribing the exercises you prescribe for your runners?

Please let me know what other rationales are out there.  I don't think this brief article really addresses everything

Greg

PS

This discussion was also quite serendipitous.  I was just finishing a pictorial post of bunch of hip exercises that people can use for their patients.  The pictures are all high quality and the idea is that you download them and put them into handouts or your website and what not.

Hip Centricity: A pictorial of hip exercises

 Related Posts:

1. The relationship between functional tests and athletic performance: Part I – The single leg balance test.

2. Can we treat our patients like puppets? Changing posture through exercise?

3. Running Injury Prevention: What we know and more of what we don't

4. Runner's Strength: Some simple exercise videos for runners.

Hip Centricity: A pictorial of hip exercises

Audience: Patients Purpose: I recommend a lot of  hip exercises and consider variety and novelty important for people in pain and for athletic injury rehabilitation.   This is just a catalog of pictures.  Please don't do them and don't consider these to be the be and end all for exercises.  Many other exercises can also be chosen to achieve your goals.  Below is a catalog of a number of exercises that you can use to train/stress your hips.

backbridge
backbridge

BackBridge

backbridge leg elevated
backbridge leg elevated

One Leg BackBridge

squat with band around knees
squat with band around knees

Basic Squat

Sit backwards into your heels to start this movement.  We want the stress to go through the hips to a greater extent than the knees.

You can add a strap around your knees and push outwards if you want to increase the hip challenge

deadlift start1
deadlift start1
deadlift down
deadlift down
hipthrust end
hipthrust end
hipthrust start
hipthrust start

One Leg Lateral DeadLift

lateral deadlift end
lateral deadlift end
end of lateral deadlift side view
end of lateral deadlift side view

One Leg Squat with lateral leg lift

one leg squat
one leg squat

Lateral Shift Bird Dog (Like a kneeling Hip Airplane)

birddog with leg out and hip dropped downwards
birddog with leg out and hip dropped downwards

Hip Airplane

hip airplane closed behind
hip airplane closed behind
hip airplane behind open
hip airplane behind open

What is missing and is to come

Variations on the bridge series

Hip Flexor Training

Olympic Lifts

Fascia Science: Stretching the power of manual therapy.

Purpose:  Fascia is everywhere, provides a fantastic structural support for the body and has the ability to transmit force from force generating muscles.  But we as therapists tend to get ahead of ourselves and make statements about treatments and the body's function that I am not sure make sense and haven't made sense for the past decade that I've questioned it.

The fascial treatment fallacy.

Fascia is laid out everywhere in the body... we can even use some sharp scissors to dissect it in such a way to create lines of fascia that show how muscles that follow a limb or the trunk are connected.  We can even give these lines names and call them trains.  I think this stuff is really neat.  But then we go and suggest that we can actually influence that line with our hands or some tool.  Without a doubt I would support the idea that strength training tensions this connective tissue  and we would expect adaptations in the fascia.  Super, nothing new there.  But then we might get in trouble with what we say we can and should do with manual therapy.  Two examples...

Two examples of things I wish were true but probably aren't when it comes to fascia therapy

1. If we "rub, pin, release, contact, shear or roll-out" fascia while pressing our digits/utensils against the skin we can somehow modify fascia.

We also assume that if we palpate the skin we can find "restrictions, adhesions or scar tissue" in the fascia.  As if the normal response to activities of daily living or strength training is to build "restrictions, adhesions or scar tissue" in this important connective tissue.  Why do we think that rubbing through skin will somehow make fascia change?  How is this even possible?  Does mechanotransduction work this way?  Mechanotransduction is typically meant to refer to how the forces produced within body (e.g strength training) might yield some biological changes in tissues.

Mechanotransduction refers to the many mechanisms by which cells convert mechanical stimulus into chemical activity

But rubbing on skin and hoping that this is influencing fascia is not the same as strength training.  No one would suggest that if you rub a muscle it will hypertrophy and become stronger.  Yet, we postulate a theory of mechanotransduction to influence fascia that no one would even consider if we applied it to muscle.  And what is more responsive to change?  Muscle or fascial connective tissue? Why muscle of course.  So the more responsive tissue to mechanotranduction would not get stronger after your rub it but fascia, the less responsive soft tissue, will naturally warp and bend to your genius hand wishes.  Makes sense to me.

2. If you have pain in one part of the body you have to follow that fascial line/link/chain/train and treat the whole thing.

Lets forget about the questionable possibility of even influencing the mechanical properties of fascia with your hands (if you talk neural properties of the nervous system I will listen) lets just look at the idea that everything is connected and you need to treat that bloody chain.  I have two biomechanical questions/issues with this:

a. Why just follow that fascial line that you read about in a book?  Fascia seems to be continuous and some brighter than I anatomist even suggests that our fascial lines are just arbitrarily created during dissection (link here).  For example, if you have a patient with bicep pain someone might tell you that you have to treat the entire anterior arm line because it is "all connected".  But with fascia I was under the impression that we really know that it is all connected and if you follow this reasoning you should just treat everything around the arm.  And why stop there, just treat the whole body since it is one fascial web.  Again, this assumes that you can influence it. Good luck.

b. So you  have picked the fascial line that you want to treat.  You've been told that the problem in the biceps could be coming from some "problem/restriction/adhesion" in the fascial line somewhere down or up the chain.  Lets assume you even have some reliable way of detecting this.  How would a fascial dysfunction 30 cm away from the biceps pain mechanically influence that biceps? I am not talking about regional interdependence when you can make a case based on link segment mechanics. I am talking about the fascial "butterfly effect" which assumes you will be treating dysfunction down the fascial chain because of some "dysfunction" up stream.  I don't know how this works.  From the studies that have actually looked at the force transmission of fascia and how different muscles seem linked through fascia (e.g the glutmax and opposite latissimus dorsi) we know that the force transmission along these fascial lines is minimal and only transmits force a few centimeters.  Therefore a dysfunction up the chain has limited biomechanical reach.  Lets look at the thoracodorsal fascial research in greater detail.  Because one, it will illustrate my point and two, it is very cool research.  See, I don't hate fascia.  I think its amazing.  Its how we extend our reach in our explanations that I hold issue with.

 Thoracadorsal fascia - how far can the effects of tension be seen

The thoracolumbar fascia partially links the gluteus maximus with the contralateral latissimus dorsi.  Fascially fantastic!  Vleeming (1995) did some very interesting cadaver dissections and then pulled on different parts of those dead bodies to show that movement occurred elsewhere in the body.  Neat-O.  First, lets looks at this beautiful study and some related research.

Vleeming (1995) and Van Wingerden (2004)

JOA_1511_f14
JOA_1511_f14

The Vleeming study showed us how different muscles attach to the superficial layer of the thoracodorsal fascial.  Contracting these muscles will then tension the fascia and the authors propose that this leads to increases in stability.  The authors looked at what would happen when they tractioned different muscles to the movement in the superficial fascia.  They found the following displacements in the superficial lamina:

- tug on lat dorsi and get homolateral movement of 2-4 cm

- tug on the caudal part of the lat dorsi and get midline displacement of 8-10 cm

-traction of the glut max and get some movement of 4 to 7 cm

-traction the trapezius and you're lucky to get 2 cm of displacement

Stretching the clinical relevance of this research

This wonderful research shows how limited the fascial reach is.  The largest change was only seen 10 cm (4 inches) downstream.  Your wife might think four inches is big but that's an illusion dude.  Even if you think biomechanics of fascia is important the biomechanical research suggests that it is not.

Where I believe these clinical observations become extended too far is when we make claims that this link between the two muscles (and muscles or joints further down this extended chain) and the possible implications for dysfunction are somehow more robust than they are.  The research above shows a minor connection between the two muscles where tugging on one muscle lead to a small amount of strain 7-10 cm at a distance from where the tug started.  This is interesting but maybe we run a little too far with this in our clinical application.  Tugging on the glutes did not cause the shoulder to extend.  Yet, if you are a fly on the wall in a clinic this is what you will hear.   Nor does any other work suggest that dysfunction in one muscle will lead to dysfunction in the other muscle along its entire length and how that muscle works. Yet, that is how this research is extended.  At its simplest some guru will tell you that "it is all connected" so they ended up rubbing the butt of someone with shoulder pain and this study or Anatomy Trains will be held up as the "scientific reasoning".

As for function...yes we will see the Lats fire at the same time as the opposite glutes during some activities (not really walking but running).  But does this mean that the fascia is the communication system linking the two and that there is a special relationship between two?  I would suggest that there is a special relationship between the glutes and ALL the muscles of the trunk that are involved in spinal rotation not just the lats.  But because we have this interesting fascial link between the two and pretty pictures we put a greater emphasis on the lats:glutes relationship rather than the glutes:erector spine or glutes:obliques relationship.  These aren't linked in a beautiful fascial manner but they sure are linked functionally.

One big issue with fascia - What is the dysfunction?

Adhesions, adhesions, scar tissue, scar tissue, restrictions, restrictions.  I have heard this for over a decade and I still don't get it.  The use of the word "adhesion" sounds identical to the use of the word "subluxations" in chiropractic land.  Believe it or not there is more research behind subluxation than there is behind an adhesion.  I don't know what an adhesion is.  It makes no sense.  If it is scar tissue than there is no way you are breaking it up with your hands.  Not possible.  Surgeons use knives for this.  Is it some stickiness between tissues.  Well don't worry about it.  When you move, warm up, strength train it will go away.  Welcome to viscosity land.

And why do we get adhesions?  Sure, we can get scar tissue after some major trauma or surgery.  But why would be get adhesions with regular working out.  And this is what we hear.  We hear that adhesions follow because of microtrauma.  You know the same microtrauma that we create everytime we work out.  The same microtrauma that causes us to adapt, get stronger, jump higher, have a better immune system, stronger bones, denser tendons, better functioning nervous system.  But somehow this wonderful tissue stress causes the Hobgoblin "Adhesion".  This makes no sense.  What a shitty evolutionary adaptation.  So those fit, strong, healthy people who have never had any "body work" must be riddled with adhesions.  Poor souls.

Recap of salient points

1. Is it reasonable that activities of daiy living or strength training result in "adhesion or scar tissue formation" in fascia.  Is the body that stupid?

2. By what means can your hands actually mold, shape or cause some change in fascia?  Why can't they do this in muscle - the far more responsive tissue to stress.

3. If fascia is everywhere and connects everything why should you let your treatment be guided by arbitrary lines of fascia?

4. The reach of fascia is limited.  While structures may be connected biomechanical studies show that displacement along a fascial line may only be 10 cm maximum

I'm open minded: please change me

I would like nothing better than to say with confidence that my hands are breaking down adhesions and that these fascial chains are relevant in manual therapy.  This is a beautiful model and easy to explain to patients.  I would also love to write about "the four best exercises to prevent low back pain" but both of these wishes just seem to be made of fairy dust.  So, if you have some research that addresses two areas I would love to see it. My two wishes:

1. Any work showing the existence of an adhesion and how this relates to pain or dysfunction (The langevin study on the back is not an adhesion)

2. Once you find an adhesion show some work that shows that you can manually change this fascial adhesion

3. Any work that shows you can change fascia (there is some out there that shows that fascia is ridiculously strong and is not modifiable except with a back hoe: blog links here and here)

Caveat

Treatment away from the location that a patient feels pain can be justified.  "Fascial" treatments can also 'work".  But they probably work for different reasons than what we attempt to justify with molding fascia with our hands.  So to conclude I am not Knocking any results that people get with their treatment.  A lot of fantastic therapists explain their treatments with this model.  What I am questioning is the model itself.  I want a better model.

This just in...

just read a link to Paul Ingraham's (at saveyourself.ca) further insights on fascia with Dr. Schleip at Paul's site here:  This stuff is great and suggests that I'm saying nothing that is really that new....http://saveyourself.ca/blog/0415.php

Alice Sanvito has a great blog post on this similar topic.  Also read her comment section where good questions are posed and she responds quite well.

Some related links (if you have interesting links please let me know)

1. Saveyourself.ca with Schleip's interactions

2. Saveyourself.ca wonderful, indepth analysis of fascial ideas (Does fascia matter?)  click here

3. Todd Hargrove at Bettermovement.org and his fascial ideas on foam rolling click here

4. Todd Hargrove again at Bettermovent.org peering at fascia under the microscope: click  here.

5. Greg Lehman on foam rolling the IT Band

6. Greg Lehman critiquing the research on foam rolling at Bret Contreras's blog

7. Dr. Andreo Spina from Functiona lAnatomic Palpation Systems writes a detailed comment in the comments section below.  Please have a look.  Dr Spina was also kind enough to post his comments as a blog post on his own website.  I think his comments are a great standalone post worthy of discussing so have a look there.

Basic Runner's Strength Training: Program One

deadlift-down.jpg
deadlift down
deadlift down

Audience: Runner's looking to start a simple resistance exercise program who still want most of their time spent running Background

You can justify strength training for runners via performance enhancement and injury prevention.  Surprisingly, the evidence for performance enhancement is much stronger than injury prevention.

Components of a Good Strength Training Program

You can do thousands of different training programs.  Don't let someone tell you they have the best one or there is one best exercise for you.  I recommend that all good programs build comprehensive capacity.  Meaning you want a program that trains everything (or close to it)...you don't want to neglect a movement, a body part or some function (e.g. speed, power, strength) in a year round program.  If your program satisfies this simple goal then it is a good program.  You might be a fan of pilates, exercise ball training, kettlebell training, TRX, Olympic lifts or Yoga.  All of these can help and can be part of your conditioning.

What I am recommending below is just one introductory component of a year round program that you can do for 10-15 minutes before or after your runs.

Why should runners strength train?

Performance Enhancement

We have a great amount of research showing that lower body strength training, power programs, plyometric work and even some simple "core" work can improve mechanical efficiency during running.  The reason for this is debatable.  It is unlikely that strength training programs that see athletes doing a few sets of  10-15 repetitions translate to improvements in our physiological endurance capabilities.  Yet somehow strength and power programs lead to increased efficiency.  One theory is that strength training may slightly increase our muscular and connective tissue stiffness or even train the nervous system to modulate such a change.  In other words, strength training builds a better spring and running is nothing if not built on good springs.  Runners bounce they don't push.

Don't worry about becoming muscle bound.  This won't happen.  Putting on muscle mass is difficult and and even if you do it won't lead to a loss of performance

Injury Prevention

This is something we have been recommending for years but in all honesty we actually have little published research linking strength training with decreases in injury rates.  Sure, poke around on the internet and you will read about runners with weak glutes, weak hip abductors (I'm guilty of this) and weak hips in general and how these deficiencies are linked with current injuries.  The rub is that this is just a link in time (i.e. a correlation) and we actually suck at predicting future injuries.  Regardless, it is scientifically plausible that if we can increase the tolerance to tissue loading via strength training in a  novel and different manner from how we normally load our tissues (e.g. running) then we might expect some increases in the resiliency of our tissues to the repetitive stresses associated with injury (disclaimer: chronic, persistent pain is a whole other mess).  If you are in pain, strength training is a novel movement.  This novelty can sneak under our pain radar and modulate the brain's production of pain and even help resolve a painful running "injury".

Warning: Runners often train like endurance athletes instead of just athletes.  You need to choose exercises that make you tired before 15 repetitions.  You need to struggle and you need to push yourself.  If you can do 30 squats then you need to either get under a barbell or do one legged squats.  You are training strength not endurance.  Push yourself goddamnit.

Last Caveat: The exercises that might become easy can then be performed as a warmup or as  cooldown.

Alright enough preamble.  Below is the program.

6 Exercise Program:  All exercises are coupled with another exercise

I use exercises in pairs (couplets) and sometimes in threes (triplets).  This called a superset.  It is more efficient and decreases the downtime associated with the rest you need between exercises.  The exercises that are usually paired train muscles or even sides of the body (front versus back, push versus pull).

When, how much, how often?

  • before or after your run
  • two to three sets of 10-15 repetitions (if you aren't tired at 15 reps than you have to find another exercise)
  • this can be performed 3 times per week

Couplet One: High Knee Drive to Squat

1high knee lift
1high knee lift

Standing High Knee Drive

Standing tall drive your knee upwards. Brace through your spine.  This exercise can be preceded by a front scale.

Another option is hold your hip flexed (knee above hip) and perform a 6 inch knee lift with the hip already flexed.

Use resistance: add tubing around your knee or perform this on a 4-way hip machine

deep squat
deep squat

Deep Squat

Thats it. Squat deep.  One option is to shift your weight back and forth once you get deep.

You can combine these exercises by squatting, driving up and driving your knee upwards.  Then drop back into the squat.

Tip: vary the speed

Tip 2: add weight

Couplet #2: Core Couplet

front bridge
front bridge

The most popular exercises on the planet.    Bridging or planking.  Whatever you want to call it.

These exercises you work your front, your side and even your back.

You can do these exercises separate from one another or you can roll from one hold to the other.

sidebridge feet
sidebridge feet

You can hold the positions for 2-3 seconds or go nuts and hold for 30 to 60 seconds.  You will get benefit either way.  Your goal is to feel tired.  When you feel that your form starts to weaken then you can wrap it up.

Options: lift a leg, rock up and down, roll a little bit

Couplet #3: Single leg squat to lateral birddog (aka birddog hip airplane)

one leg squat
one leg squat
birddog with leg out and hip dropped downwards
birddog with leg out and hip dropped downwards

Lateral Birddog Hipairplane: this exercise is a modification of the good old birddog where you lift your leg to the back and your arm to the front.  The modification sees you lifting your leg out to the side and then dropping your hip that has the knee on the ground out to the side.  You will feel increased pressure in the outside of the hip.  Let your other hip drop to the ground and then lift it back up.  To really stress things swing other leg side to side.

One leg squat: you can do this with your leg out to the side like in the picture or you can have your leg out back.  I recommend hinging forward at your hip and NOT trying to keep your trunk upright.  Let it bend forward to increase the strain on your butt.

Go through that circuit.  Twice.  Its easy, takes 10-15 minutes and is good for us runners who really only want to run but know we should do something else.  You can do this one day a week and on two other days make up your own strength couplets.  Or just do this 3 times a week but in 4-6 weeks you should mix things up.  Add some speed, more weight, different exercises...train variety build capacity.

Related Programs

1. Runner's Strength Videos

2. Patellofemoral Pain Rehab Sheets

3. Bridging Variations

4. Stu McGill's Big Three

5. Hamstring Tendinopathy Strength Training Videos: Hint not just for hamstrings

A Summary of Techniques to Change Impact and Joint Loading During Running

Purpose: To review some of the data on ground reaction forces during running, the significance of this physical loading and how loading can be modified. WARNING: this post is massive.  It is meant as a working and evolving repository of much of the research on this topic.  It is a compilation that I would like to update as more work is added. I use a post like this as a living reference library so I don't have to search through an entire article to get the gist of it.  It is not meant to win a writing award. Skip to the bottom for a summary.

What is in this post

1. Ground reaction forces (GRFs) overview

2. Relationship between GRFs and Injury

3. Modifying loading with step rate

4. Modifying loading with foot strike style

5. Modifying loading with shoe wear or going barefoot.

What are ground reaction forces and impact loading?

When the foot strikes the ground during running the ground produces a force back against the foot.  The force can be broken into three directional vectors:

1. Vertical

2. Forward - Backwards (e.g. "braking" and then "push off")

3. Side to Side.

Most of the research has focused on the Vertical loading so I will too.  Vertical loading looks like this:

The first peak in force is termed the impact peak and results from the collision of the foot with the ground.  We can also look at how quickly this force rises and when that peak occurs.  This is called the rate of loading.

The second peak is called the active peak.  It corresponds to the point when the energy absorption has stopped (the center of mass is at its lowest) and when we start to "push" off against the ground.

Relationship between ground reaction forces (GRFs) and injury

The relationship is contentious.  It is simple to assume that less load or less stress on the body leads to a reduction in injury risk.  But this does not always pan out.  The human body has the ability to adapt and the variability across runners' ability to adapt is huge. Simply, we don't know how much load is bad for an individual person.  You can even argue that loading is good in that this is what stimulates an adaptation in the runner (e.g. stronger bones, stronger soft tissue, a better nervous system?).  What the cutoff is between good loading leading to adaptation and too much loading leading to injury is our Holy Grail of Injury Prevention.  The concept of loading and loading rate on injury in runners could be a long post itself - I will just link to some articles below and briefly touch on this area.

There is some suggestion that the rate of impact loading is related to stress fractures in runners.  See this post here and the abstract here.   We also have some suggestion that decreasing peak loading can influence stress fracture risk (abstract here and here)

We also have some great research by Dr Irene Davis linking higher impact velocity (e.g rate of loading) with stress fractures (link here).  Dr. Davis has also published case series showing changes in loading rates with feedback during running (abstract here).

Some links to follow for more information on this.

Davis and company (here, here, here, an outlier here)

Other researchers showing no relationship with loading and injury ( here and here)

So How Can We Modify Loading During Ground Contact?

In the following sections we will take a look at three methods that are used to change loading during foot strike:

  1. Changing step rate
  2. Changing type of foot strike (i.e. rearfoot versus midfoot)
  3. Changing footwear (or foregoing footwear altogether)

In an upcoming post I will review what other changes occur when we attempt to make these changes to impact loading.  Changes don't exist in a vacuum.  They could lead to changes in running economy, muscular activation or other unintended consequences that could affect performance and maybe injury risk.

The Bottom Line before the bottom

All three techniques are able to change impact loading and joint loading in some individuals but not in all individuals.  What we see in the research is variability and this leads to conflicting results across studies.  This is because there are other factors than the three above that influence the ground reaction force.  For example, you can change to a midfoot or forefoot strike and still overstride (see a neat video and case on this here).  The stiffness in our limbs can all influence impact.  This is what happens to some extent with kinematic changes with aging.  Older runners can have similar stride rates but still have greater impacts (for a brief review see here).  But lets look at some research.

A. Changing step rate

We can increase the number of steps we take while running.  Heiderscheit et al (2011) did such a thing (for detailed review of the study look here and here).  He increased step rate by 5 and 10%.  This is some of what they found:

At both 5 and 10% increases in cadence

  • decreased step length
  • decreased Center of Mass vertical excursion (less bouncing up and down)
  • decreased horizontal distance from the center of mass to the foot (i.e. less overstriding in front of you)
  • less knee flexion (excursion) during the foot contact (i.e. increases stiffness)
  • decreased energy absorption and energy production at the knee
  • decrease in the impact transient occurrence (there were times when runners did not have that sharp spike in ground reaction force plot)
    • decreased braking impulse

At a 10% increase in cadence only

  • decrease in foot inclination angle at contact (toes point down more)
  • decreased stance time duration
  • increased rating of perceived exertion
  • less hip flexion and adduction
  • increased knee flexion at initial contact
  • decreased peak vertical ground reaction force
  • decreased energy absorption at the hip

A note on the ankle

There was no change in the amount of ankle energy absorption when increasing cadence yet a huge decrease in the amount of energy absorbed at the knee.  This is most likely due to a lack of change in the ankle kinematics and how the foot struck the ground.  I would guess that changing cadence was not enough to change the type of foot strike.  If an individual went from a rearfoot to a mid or forefoot strike we would probably see more energy absorption at the ankle.  Take home point, is that a lot variables can influence impact loading.

A note on the initial impact loading and loading rate

The authors found that reducing step length decreased the occurrences of that sharp initial bump in the ground reaction force.  This is the impact transient and is what we most see in runners who heel strike - it is essentially the collision force with the ground. However, it was rarely seen (0-1 times in every 5 strides) only 56% of the time when increasing step rate by 10% (this lack of impact transient was seen 22% at preferred step length).  So notice this is just a trend in some runners.  If you notice with the study the authors did not calculate the average loading rate across all runners.  This is how we typically compare loading rates across interventions.  I would guess with the variability across the subjects we would not end up with a statistically significant change in loading rate.  Presenting the data in this way shows us that sometimes we get a change in the impact transient just not always.  As a refresher here is a lovely video of the loss of the impact transient with forefoot running.

http://youtu.be/XO4MruQov4Q

Hobara (2012 -abstract here ) had athletes run at 2.5 meters per second and also modified step frequency (increasing huge amounts of 15 and 30%).  They found decreases in:

  • vertical impact peak (VIP),
  • vertical instantaneous loading rate (VILR) and
  • vertical average loading rate (VALR).

The only issue with this study is how practical it is to have such a huge change in stride rates.  It is great for a proof of principle but we should question whether we want to do this in terms of running economy and even injury risk (i.e. you are taking a lot more strides thus increasing repetitions).

...and the other side of things (nothing is ever that simple)

But, these findings were mildly contrasted with another neat study that looked at changing a number of things (step rate, foot contact style and type of shoe) and the loading response.   Giandolini (2012)found the following when increasing cadence 10%:

  • no change in the rate of impact loading
  • no change in the impact transient
  • no change in the time that your foot is on the ground
  • a decrease in the aerial time (time you are in flight)
  • increase in stiffness (vertical)

These authors looked at the group average for changes in rate of impact loading.  They don't show their raw data so it is possible that there may have been some individuals who decreased their rate of impact loading and perhaps lost the impact transient during initial foot strike.  This would be consistent with the Heiderscheit study.

In this comprehensive study, these authors were also able to change a number of loading and kinematic variables with other interventions.  They did two other things - put runners in a racing shoe (versus a big bulky cushioned shoe) and had the runners switch from a rear foot strike to a mid foot strike.  They also combined all three changes (COMBI).    So why don't we take a look at this neat-o study along with other relevant studies that look at changing footstrike style.

B. Switching to a Midfoot Strike

The research suggesting changing foot strike influences loading variables

This simple change provided some pretty drastic results.  Giandollini et al (2012) found:

  • loss of the impact transient when switching (also found in the COMBI)
  • greater than 50% decrease in the rate of loading (also found in COMBI)
  • interestingly no change in step rate (this is of interest because we often assume that this happens with a midfoot strike.  We typically assume that running midfoot versus the heel naturally shortens the stride - suggesting that we can get changes in loading rates without decreasing stride length)
  • an increase in Gastroc (calf muscle) and Tibialis Anterior (shin muscle) muscle activity was found just before impact but not during impact.  However, the authors did not account for the electromechanical delay (i.e. the muscle turns on immediately but it takes time to take up the slack of the muscle to create force against the bones) that occurs with EMG muscle activity so we shouldn't conclude that the muscles are not creating less force during impact.  With the delay these muscles are creating force and are mostly likely contributing to the buffering of the impact loading response.

You can see a video version of this response in the video above from Dr. Lieberman.

...again it is never that simple.  Similar research has found different conclusions

Laughton, Davis and Hamill (2003) investigated fifteen habitually rearfoot strike runners and then converted them to a forefoot strike pattern in a single session.  The authors found:

  • increased average peak vertical ground reaction force
  • increased Anterior to Posterior GRF
  • Increased Anterior to Posterior loading rates
  • no difference in average or instantaneous GRF loading rates

some other findings:

  • increased dorsiflexion and calcaneal eversion excursion
  • decreased centre of mass excursion during foot contact
  • increased knee flexion at initial contact
  • decreased knee flexion excursion
  • increased knee and leg stiffness
  • decreased ankle stiffness

WHOA...this is very conflicting.  Sure is.  It again stresses that changing a single variable is not sufficient to change other variables. Changing to this type of forefoot strike pattern either increased peak loading, no change in loading rates, increased braking forces and increased knee and leg stiffness.  We don't know if stride rate changes but the increased anterior-posterior forces suggest that the forefoot striking may have been related to overstriding.  Last, in this particular study the forefoot strikers were not permitted to let their heels hit the ground.  They essentially ran on their toes.  The Giandollini suggests that converting to midfoot strike can be beneficial (in terms of impact and force variables) but there may be a correct way to do this.  i.e. don't just run on your toes

Further research showing variable impact loading with changes in footstrike

Becker et al (2012) in an abstract presented at the ASB 2012 concluded that foot strike pattern does not predict loading rates during shod or barefoot running.  With a subject population of 11 (this study was reported as ongoing so it looks like it may be more robust in the future).  The authors measured vertical impact loading rate and strike pattern in the runners when they ran either shod or barefoot.  What they were able to evaluate was how footstrike pattern related to VILR in quite a novel way.  The participants were not told to attempt to change their foot strike pattern.  Rather, they had people either run with their shoes or in barefoot and measured their footstrike pattern with something called a Strike Index while also measuring their VILR.  With these two measures in hand they determined how foot strike pattern related to VILR because some people would naturally change from a rearfoot pattern while shod to a forefoot pattern while barefoot.  So, there were few permutations on what could happen.  Here is a sample of what I see as relevant and check out the chart below for all the details.

Lets look at those instances where people RFS while shod but ended up switching to a forefoot strike while barefoot:

  • 12/16 switched from a RFS to MFS/FFS while 4/16 remained RFS while barefoot
  • of the 12 that switched 5 of them significant increased their VILR while 7 had no change.
  • of the 5 that showed changes when going to a MFS/FFS while barefoot all of them showed increases in loading rates while non showed decreases.
  • Figure 1 below shows no loss in the impact transient in subjects running with a midfoot strike

The flow chart below shows what happens to the vertical loading rate to individual runners when they either change to a midfoot/forefoot strike (MFS/FFS) while barefoot or remain heel striking (RFS)

The bottom line from this study is that a mere shift to a MFS/FFS is not sufficient to get less VILR.  This study is also confounded with the shift from the shod to barefoot but it again suggests that is not a sufficient condition to automatically assume you will get less loading rates.  Big limitation: there was no training or time allowed for habituation.  This is short term study and may not reflect what happens with motor learning over time. 

C. Impact and loading changes when we change our shoes

 I will cut right to the chase here.  Changing your shoes is not always enough to get changes in loading variables.  Big bulky shoes are knocked under the assumption that the ass of the shoe gets in the way and forces runners to land on their heels and overstride.  We assume that replacing these shoes with lighter shoes (and less of a heel to toe drop)  will lead to a change in how we run to avoid heel striking  (due to pain) and overstriding.  Lets look at the research on what happens in different shoes.

Possible Study Outcome #1: Traditional versus minimal shoes lead to variable changes in loading

Goss et al (2012) Accuracy of self-reported footstrike patterns and loading rates associated with traditional and minimalist running shoes (ASB 2012).

These authors looked at 57 runners who ran in either traditional running shoes (n=22) or minimalist running shoes (n=35).  There were no details on what these minimal shoes were.  The authors measured ground reaction force and were classified into either a rearfoot or forefoot runner.  This gave three categories of people: 1. rearfoot striker with traditional shoes (TSR) 2. Midfoot striker in minimal shoes (MSA) and 3. rearfoot striker in minimalist shoes (MSR).  Before doing the assessment they also asked the runners how they thought they struck the ground.  Here is what they found:

  • 1/3 of experienced minimal shoe wearing runners misclassified their running footstrike - they thought they were midfoot but they were hitting their heel.
  • the MSA group (midfoot minimal) had the lowest average vertical loading rates (52.8 BW/s), traditional shoe rearfoot strikers were next (68.6 BW/s) and the rearfoot strikers with minimal shoes had the highest loading rates (107.8 BW/s).
  • there was no change in peak ground reaction force across groups
  • vertical ground reaction force curves were different between groups.  Noticeable there is less of the impact transient in minimal shoes regardless of footstrike but midfoot striking with minimal shoes leads to the gentlest of loading rates.  See chart below.

Possible Study Outcome #2: Shoes versus barefoot lead to increases in joint loading

Kerrigan et al (2009) looked at the influence of running shoes on lower extremity joint torques in standard running shoes and barefoot (n=68).  They found increases in the following joint torques when going from barefoot to shod:

  • hip adduction
  • hip external rotation
  • knee flexion, knee varus, knee internal rotation
  • ankle internal rotation

In terms of ground reaction forces there were increases with shod running in:

  • medial to lateral GRF and Vertical GRF

with a decrease in the minimum anterior to posterior GRF

Stride length was found to increase from 2.15 meters (barefoot) to 2.29 meters (shod) although the authors suggested that this accounted for only a small percentage of the changes in joint torques.

Possible Study Outcome #3: Minimal shoes lead to increases in joint loading

Logan et al (2012 - ASB Abstracts here) GROUND REACTION FORCES BETWEEN RUNNING SHOES, RACING FLATS AND DISTANCE SPIKES IN RUNNERS

The authors compared the three different shoes and aspects of the ground reaction force (Impact peak (BW), loading rate (BW/s), peak braking and propulsive force (BW), peak vertical force (BW), stance time (s), and vertical stiffness (BW/m)) in runners (n=18) who were all habitual rearfoot strikers.  Further, these runners were college track athletes running between 5.67 -6.7 meters/s.  This is fast considering that running around a 5 meter/second pace will have you run 5 km in 16:40.   They found:

Impact peak and vertical stiffness significantly increased between running shoes and spikes. Differences between stance time and loading rate approached significance with trainers being lower

This again is interesting.  I don't know if these runners changed their foot strike with any of the shoes but it reiterates that changing shoes to a more minimal shoe is enough to positively lower loading variables.  In this case it increased them.  I would assume that these runners were still heel strikers despite the change in shoe.    This group shows that you can have less of an impact peak, less vertical stiffness and a trend to having less loading rate with a trainer than with more minimal shoes.  Take home point here is that our movement patterns involve motor learning...motor learning involves effort, time and conscious attempt to change how we move.

Possible Outcome #4: Shoe differences are minimal but going barefoot decreases loading variables.

...and now a contrary view Hamill et al (2011  with a detailed review here) in a study titled "Impact characteristics in shod and barefoot running".  The authors compared barefoot running with running shod in three different shoes of different sole thickness (1. A shoe with a 4mm heel and 0 mm forefoot; 2. a shoe with 12mm heel and 8mm forefoot and 3. a shoe with a 20mm heel and 16mm forefoot). The authors looked at the immediate response with these different shoes.  Again, there was no training or attempts repatterning a gait stride. Their results in a nutshell were:

  • switching to barefoot leads to an anterior footstrike pattern
  • barefoot leads to less 50% of the loading rate of all footwear conditions
  • impact peaks are still common with minimal shoes (a 4mm drop and very little thickness)
  • there is a trend to decrease loading rate with decreasing shoe midsole thickness
  • in general, shoes of different midsole thickness did not have different loading variables as runners in all shoes did not change their footstrike pattern

Possible Outcome #5: Minimal shoes show no effect on impact loading

The Giandollini (2012) study compared standard cushion shoes with a racing shoe (important note: the racing had a large heel to toe drop of 10.8 mm - thus some may not call this a minimal shoe despite there being less mass).  The authors trained the participants and had them run at the same speed with the two different shoes on.  The authors found no difference in loading rate, time to peak vertical load and peak vertical loading. The authors suggest that individuals continue to use a heelstrike style of running and that the minimal shoe did not coerce the runner into changing their running style.  What I find interesting is that even though the racing shoe is much lighter with less cushioning there are no adverse consequences to running with a similar style compared with the  normal cushioned shoe.  Below is a nice graphic representation of all of Giandolinni's interventions on the vertical ground reaction force.

Brief Summary of changing gait variables to influence impact loading

All methods can influence of impact and joint loading but not consistently.

Increasing step rate can decrease joint loading but does not always lead to a reduction in the impact transient or rate of impact loading

Changing to a midfoot strike does have evidence to change impact loading variables but again in some individuals we won't see any change

Changing to a midfoot strike may also result in other factors that increase the strain on the tibia (link here for a start to this interesting idea).  We can't say with certainty that everyone should be doing this change.  A follow up post must and will address this area.

Changing your shoes to lighter weight or minimal shoes also has variable effects.  Most importantly, instances can exist where your loading can increase when going to lightweight, minimal shoes.  Most likely due to maintaining the running style that you have adopted when running in your previous cushioned trainers

The Giandollini et al (2012) study is really quite lovely.  They look at as many variables and interventions that you can reasonable look at.  They show how many techniques of what we think might change impact don't consistently change impact and they also provide insight into the "whys" of this.  I also like their conclusion (probably because it agrees with something I wrote last year on barefoot running and foot strike style and I need reinforcement :) ) where they write:

our results show that running "barefoot-like", i.e. with a midfoot strike pattern may be an effective solution to reduce the magnitude of impact, as quantified through the loading rate

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