The limitations of all movement screening and the FMS by default

Originally published at Medbridge Health (a great online CE source)

I've used movement screens in the past and still use movement testing of patients to look at how they move. If you use the Functional Movement Screen (FMS) you will probably pick up some limitations in how your patients move. Some of these limitations have even been linked to future injury in specific populations. The limitation of these “screens” is that they might not even be “screens” at all. A screen should catch everything (i.e. have more false positives and FEW false negatives) but I’m afraid that movement screening tests don’t actually screen for anything beyond the movement that you are testing.

I see two big concerns with movement assessment testing and screening:

  1. Can “screening” using very simple tests actually miss the movement “flaws” or “dysfunctions” that we are interested in?
  2. Does screening for “flaws” just expose normal human movement variations/options and are we too quick to label something as dysfunctional?

By far, the most popular and successful screen is the Functional Movement Screen (FMS). I respect the thought and great work that has gone into developing and researching the FMS as well is its clinical cousin the SFMA. The Selective Functional Movement Assessment can be seen here being taught by Kyle Kiesel. This post is not an attack on the FMS or other movement screens (MCS out of New Zealand for example). It is more about the limits of all of our tests in assessing for movement dysfunction, trying to predict injury risk and treating pain. Their work deserves a lot of respect and I intend to give it.

Some background on Physical Function Screening

“Screening, in medicine, is a strategy used in a population to identify an unrecognized disease in individuals without signs or symptoms. This can include individuals with pre-symptomatic or unrecognized symptomatic disease. As such, screening tests are somewhat unique in that they are performed on persons apparently in good health.” (Wikipedia)

Physical Function Screens have a few purposes:

  1. Identify individuals at a greater risk of injury based on how they move
  2. Give insight into how people move that is greater than the sum of its parts
  3. Give insight into the mobility or stability of specific body regions
  4. “Clear” certain areas of function. The screen functions as a “triage” to help the assessor determine where other assessments take place

The very strength of the FMS is its simplicity, which leads to its lack of sensitivity

Injury Prediction Limitations

The ability of movement screening to predict injury has been dissected numerous times with much of the research being conducted by the creators of the screen. A review of the research on the FMS can be seen here and an interesting podcast discussion can be heard here. Injury prediction is so complicated and difficult, it is not really fair that we ask the FMS or other screens to be able to do this. Rather, as its creators suggest, it should be part of a complete battery of testing. I would go so far as to suggest that instead of using simple screens of physical function, we need to expand the screen and delve into all the parts the make up all the movements, plus a battery of tests addressing the entire human (e.g. cognitions, psychosocial profile etc). So if a movement screen becomes part of a battery of testing, is it really still a screen? To me, it just becomes another series of good tests that provide some information. If you expand your screening to include other more detailed tests, do you still need that screen? To me, each test in the screen now becomes valuable in its own right but NOT as surrogates for other realms of function.

Limitations associated with current physical function screening

Screens must be Sensitive

Perhaps the screening test itself is not that important. It is what the screening test exposes that is important. It is the alteration in form or the movement anomaly that we are looking for. We assume that there are better ways to move, and certain flaws will increase our chance of injury. So to be a good screen, a test must expose the “flaw” assumed to be related to injury. This is where I feel most screening tests can miss things. They miss some limitations in function. Some examples:

Limitation #1: Screens can miss simple aspects of altered function

Let’s just assume that limited ankle dorsiflexion is a risk factor for injury in runners. A screening protocol should expose that flaw. Most screening battery tests use some form of squat test to look at this function. The FMS uses an overhead squat test. If the athlete cannot squat to depth without significant back rounding or the arms coming forward, it is assumed that something is wrong. The FMS does not tell you why that person can’t squat. You now have to do breakouts and see if they have limited hip flexion, poor thoracic extensions, a motor control issue or perhaps limited dorsiflexion. You then go and do additional testing to figure out which it is. The problem here is you don’t need a lot of dorsiflexion to squat deep if you have good lumbar and thoracic extension, if you have a greater proportion of anterior body mass relative to your lower body (think toddlers, their big heads balance their butts). Here is a case where the screen misses the flaw that we want to find. This would hold true for most other testing in the FMS as well. You would have to add the Y-balance scale to give a better idea of ankle dorsiflexion. The tests are still great because they tell us something is not right with the movements, but the job of screening is to be comprehensive.

Limitation # 2: Screens can miss movement flaws even in similar tasks

I like the single leg squat test. I think it gives me insight into how the hip controls the knee. I like to think that it might also give insight into hip strength, control of the knee during running, or control of the knee during jumping. The problem is it probably doesn’t. Same holds true for an overhead squat, a lunge, or a step-over test. My favourite screening test is not that good of a screen because it may not tell me about the flaw I am trying to expose (dynamic knee valgus during sporting activities). I have 3D kinematic equipment for analysing runners. I would guess that more than half the time a runner has increased hip adduction during running, they will have normal hip adduction during the single leg squat.

Limitation #3: Lack of transferability with load and speed

One good thing that the FMS has always taught is that movement testing is more than the sum of its parts. It gives insight into how people choose to move (motor control) that can’t just be predicted from manual muscle testing or joint goniometers. What we have seen lately is this lack of consistency between table tests and movement tests may be a double-edged sword. Meaning, the tests we perform in the clinic (e.g. squats, single leg squats etc) may not reflect how someone moves in their ADLs, in their sport, or under different load and speed conditions. David Frost and Stu McGill highlighted this in their paper here.

To me, the point of the tests are to expose flaws. If a single leg squat test or any tests of the FMS miss a flaw that occurs during other functional tasks, then that test is not a screen. It missed the flaw. Screens by definition are overly sensitive. You should have way more false positives than false negatives. The screening tests might only tell us about how an individual performs that test, nothing about their movement at other times and in different contexts. It still provides valuable information when the athlete fails the test, but it’s not a screen.

Limitation #4: Screens aren’t surrogates for assessing all aspects of joint function

If I recall correctly, one of the points of using movement assessment tests was to get away from simple tests of muscle strength or endurance. However, I often hear utilizers of screening tests suggest that someone fails a screen because they are weak in the hips or spine or that they don’t have “stability”. Hell, I thought this myself. A poor single leg squat means you are weak in your hips right? Nope. We assume that if a pelvic tilt occurs, there might be weakness in the hip abductors. Amazingly, this isn’t related. A recent paper paralyzed the hip abductors (mirrored in a similar paper here) and there was no change in hip kinematics suggesting the Trendelenburg is not a good screen. A second paper assessed the one leg squat and found that hip adduction was not correlated with hip strength. If we think hip strength, in and of itself regardless of movement technique, might be protective of injury our screening tests miss this. We therefore need more tests. The hip adduction motion in that study was correlated with Gluteus Maximus recruitment suggesting that movement pattern was a motor control issue (as the FMS people consistently teach), thus the test still has value in and of itself. It’s just not a surrogate.

We know that movement screens aren’t surrogates for tests of performance or for tests of joint strength, ROM, etc. Isn’t some of this information important? Is core endurance important for your athletes? Is the ratio of hip abductor strength to adductor strength important in hockey players? Do you want high levels of strength in the hip abductors of running? Probably yes. Movement screens give no insight into this. If you simply leave your testing at the level of the screen you miss this information.

Failing a single leg squat test (or a lunge, overhead squat etc) can still be valuable. I won’t throw these tests totally out. But now they just become tests and not screens. I would argue that a movement “screen” is really just a test separate to itself. Those movement assessments are independent entities. Addressing those tests specifically might be valuable. But I can’t say that the test is a surrogate for other functions and for other contexts. Thus it is limited as a screen and is just another test.

Stop being so critical – Screens are still helpful

It’s not fair or just to only point out limitations. I use parts of all of these movement screening tests. The ideas behind the movement screens (i.e. the flaws they expose) even help me create my own (e.g. every exercise can be an assessment). I’ve suggested that movement screening might miss movement flaws, give basic information about strength/endurance, and not always accurately test the mobility of joints. But the tests themselves do tell us something. If someone “moves poorly” on a test in an unloaded position, we could argue many times that they certainly can’t do that type of movement under weight or speed. These tests certainly give information about how people choose to move. That in and of itself could be valuable for exercise prescription.

Alternatives to physical function screening

Make testing less about the test and more about flaw. Test for comprehensive capacity. We need to know more about what physical limitation or form deviations are predictive of injury for different sports, activities, and people. For example, if we think that lateral spinal tilting is a risk factor for injury in a certain sport, then our job is to try to expose this risk factor. The FMS can be a great launching pad for that. But don’t just stop when someone has “passed” a test. If you agree that the screen might be capable of missing something, then you have to test everything. If you agree that the screening tests might not reflect what happens to function during when load or speed is placed on the body, then you have to modify the tests to try to expose these flaws under those conditions. If your athlete is a runner, then your screening test should be running. You can make up your own screens. Your job is to expose flaws.

The limitation of all movement testing: When is a “flaw” a “flaw”

I use the word flaw like it’s a given. We assume that certain movements are more related to injury. Unfortunately, the research is not that robust. Our biggest difficulty and challenge in research and in the clinic is to figure out when a “flaw” is truly a flaw that increases the risk of injury. One alternative to viewing movement “flaws” as flaws is to view them as different movement options. You’ve seen these people. People who move with “terrible form” yet still perform well and are injury-free. How do they do this? Perhaps they are well trained to tolerate those positions.

Take Home Points

  1. Movement screens probably aren’t best viewed as screens since they lack sensitivity. Movement screens are good at exposing how someone chooses to move during specific tests. Unfortunately, we can’t generalize these movement patterns to other contexts. So in effect, passing a movement screen only tells us that the flaw we are hoping to expose doesn’t occur during the test, but can still occur during everyday movements.
  2. Movement screens aren’t surrogates for other areas of physical function. Screens aren’t well correlated with spine “stability” measures, trunk endurance/strength, physical performance, or basic measures of joint kinesiology. All of these metrics may hold some value in injury prevention.
  3. Perhaps movement screens should just be viewed as movement assessments in their own right. If they lack transferability to other tasks and aren’t surrogates for other functions, then we should view them as distinct. There can still be value in seeing how someone moves during these tests (they are now tests and not screens).
  4. You can make up your own movement assessments: the ideas behind the screens (i.e. exposing a “flaw”) in movement can be useful. If you believe that flaws/movement dysfunctions are relevant to injury risk or current injuries, then every test, movement, exercise, or performance can be an assessment. Learning from the professionals that teach the FMS can be helpful in you creating your own assessments. Go buy the book Movement by Gray Cook. It’s very well done in terms of teaching, pictures and explaining their rationale.  You can disagree with them but I think its very important to still respect their work.

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Blog, 2014Greg Lehman