This was originally posted on Dr Peter Malliaras’ blog and shared here with permission. It is co-authored by Peter’s PhD student, Igor Sancho. It was prompted by lots of interesting twitter talk about kinetic chain involvement in Achilles pain (credit to Tom Goom on that too) – enjoy!
Many patients are told they have weak and poor gluteals that are causing everything. Their Achilles pain, their back pain, and perhaps thereby gluteal ‘weakness’ is the cause of their general dissatisfaction with life! Stop therapy, just strengthen your gluteals.
Are the gluteals to blame? Let’s unpack our question with a little critical thinking.
Question 1: Am I sure the gluteals are REALLY ‘weak’?
Weak and strong muscles are difficult to define. In this context, I am referring to poor gluteal clinical test findings eg endurance or static resisted strength tests or sometimes activation tests. i.e. the common clinical gluteal tests that are out there. The question of whether someone is really weak or testing poorly on these tests is about reliability and validity.
Reliability is about finding the same thing on repeated testing
Let’s take a classic test. Ask someone to push against your hand into abduction as hard as they can and they push really weakly. Does this mean they are weak? If you repeat the test 30 seconds later will they be stronger? Most likely. They have warmed up and are more familiar with the test. Perhaps they gained confidence after realising it did not hurt as they thought it would.
To achieve reliability, you need to consider warm up, performing several trials, the order of your clinical assessment, etc. These are hard tests to get reliable in a lab setting, let alone the clinic when time is limited!
The likely within person random variability (e.g. I feel great today so will push harder), as well as systemic variability (I feel more confident this time so will push harder) associated with these tests is likely massive in a clinical context. Ie the measurement error or slop is pretty massive. Therefore, we need to accept that we need pretty crap ass test findings to have any confidence that there is something going on. I call this a major or unequivocal finding.
Validity is about measuring what we think we are measuring
Are my clinical gluteal tests actually measuring gluteal ‘strength? If my hip abductor strength test was getting the patient to match the maximal force of my little finger, then a vast majority of people would pass it every time. It is reliable, but it is not measuring strength in the correct range and therefore is not a valid measure of gluteal strength.
Another example is gluteal activation in a single leg bridge. Even if we assume we can assess it reliably, does it have any relationship on gluteal activation or function in running? My guess would be very little for most people. This would mean gluteal activation in bridging is not a valid assessment of gluteal function in running.
We all have our clinical hunches but really little is known about what many clinical glutel tests out there are actually telling us. So my simple clinical rule of thumb is keep it simple, and only get concerned about the major and unequivocal findings. Confucius says, he who cannot do one single leg bridge = not going to win any gluteal strength contest.
Remember also that both sides may be affected. We cannot rely on side to side differences to tell us someone has an issue. It comes down to again our clinical hunch (given lack of evidence in most cases) of what they should be testing at. So this concept of focusing on major or unequivocal findings becomes even more important.
Question 2: Can the ‘gluteal weakness’ be fixed?
Most of us would agree that with appropriate loading interventions, most people can achieve improvement in gluteal output eg force generation, torque, rate of force development, etc. This question is probably more relevant for other so-called kinetic chain deficits that are commonly picked on. E.g. anterior pelvic tilt kinematics in running. Sometimes if the underlying reasons are structural it cannot be changed. Consider whether what you want to change can be changed. Pick your battles.
Question 3: If the gluteals are ‘weak’, should I worry about it?
Assuming we do believe the findings of our tests and they are major and unoquivocal (question 1), and we are confident we can do something about it (question 2), when should we care?
So is gluteal weakness a cause of Achilles pain? (our original question)
If you believe gluteal weakness is a risk factor for Achilles pain, then obviously you would address gluteal issues. But is it? My PhD student Igor Sancho just completed a systematic review synthesising biomechanical (kinematics, kinetics and neuromuscular) changes during running among people with AT vs controls – see figure below. Habets et al. 2017 have also shown that people with AT may have reduced gluteal torque output. Two important points about this literature; first = all findings are from cross sectional studies so there is a good chance they occurred after the onset of pain. Second = there are not many studies and they for damn sure need to be replicated given the science truism – ‘different studies often find different things’. Overall, this evidence is so far limited and not convincing.
But hang on, isn’t it patently obvious that weak gluteals could lead to increased Achilles load? I’m not so sure. Gluteus maximus forces are relatively low compared to vasti and soleus, regardless of running speed (see figure below showing bodyweights of force from a modelling study by Dorn 2012). So maybe if the gluteals are not pulling their weight there is subtle load redistribution, that would perhaps be an issue for an Achilles tendon that is very sensitive to small changes in load (e.g. an older tendon, or a tendon attached to a body that has hormonal or metabolic challenges). The adjacent joint scenario is easier to argue for and more common clinically e.g. classic example is long term painful/post-surgery knee contributing to Achilles or gluteal tendinopathy.
Is it worth addressing gluteal ‘weakness’ among people with Achilles pain?
Most clinicians (unless you work in sport) are in the business of treating rather than preventing Achilles pain. So, when someone presents with Achilles pain is it enough just to manage the pain if we assume that many of the gluteal changes going on are secondary to pain? Probably. Especially when people have had short term pain, gluteal dysfunction seems to be related to limb apprehension/guarding/fear. Other times the gluteals may need a bit of help to get going again. One of these times is when there is evidence that the gluteal dysfunction precedes pain, e.g. they have had a major prior injury or surgery in the area.
I like to give the patient the benefit of the doubt if not sure. E.g. try and manage their pain and load the Achilles-calf for a week or two if not sure, and see if the gluteal ‘weakness’ improves. You may even add some general kinetic chain loading to recondition the lower limb generally.
This approach brings up another interesting question…is it essential to load the local muscle-tendon unit? I.e. the Achilles-calf for someone with Achilles pain. I would say yes, if they have evidence of dysfunction or a load intolerance. Some Achilles patients have the former (dysfunction), but pretty much all have the latter (load intolerance). A key point is the mechanisms for improving pain with loading may not include strengthening or restoring function at all for some people, although this may still be important.
Here is a flow diagram of the clinical reasoning in this blog. Have removed Q2 for this example as we can assume we can address gluteal weakness.
More questions than answers, as usual. But some take home messages:
- There is no evidence that gluteal ‘weakness’ causes Achilles pain
- Cross-sectional studies show gluteal weakness/activation changes in people with Achilles pain
- There is a good chance they develop after the onset of pain
- Still may be worth addressing gluteal ‘weakness’ to recondition the limb
- Focus on major and unequivocal issues since our gluteal tests are limited
- Also, ask yourself whether the gluteal ‘weakness’ may resolve when you treat pain
- If you’re still convinced, work your gluteal magic!