When Does Biomechanics Matter?
I am a biopsychosocialist.
I believe that biomechanics often matter for those in pain.
These two statements do not conflict.
Below I will lay out an opinion of situations where biomechanics contributes to pain or injury. Essentially, When Biomechanics Matters (WBM). I think there are video lecture versions of this on the web out there but I don’t keep track of all my propaganda. Most of these situations below will overlap and some will even mitigate the influence of others. You might also have your own way to categorize – but these are mine.
WBM #1: High Load Activities
Relevant Variables: Technique/movement quality, strength, ROM, preparedness.
The Gist: When an external loads exceeds the ability of tissue to tolerate stress than an injury might occur.
Examples of this are seen with hamstring strains. High loads seem to be required to tear a hamstring and strength of the hamstring seems to be a factor in moderating risk. The same could be said for almost any muscle tear. Basic strength seems important but we recognize that it is not the only variable but certainly a good example of when a biomechanical attribute (strength) is important.
A related example could be non-contact ACL tears. Strength is a mitigating factor but so might technique or movement quality. Most people could tolerate low load dynamic knee valgus or even high load dynamic knee valgus with greater than 25 degrees of knee flexion but under some conditions dynamic knee valgus is capable of “overloading” the ACL and an injury might occur. This is a nice example where one biomechanical variable (strength) may be protective and “allow” one to ignore another biomechanical variable (technique or preparation or muscle timing). A proof of principle would be the ACL FIFA-11 prevention programs. These have been shown to reduce injury risk but when researchers measure the variables that might mediate that risk reduction we don’t see a change in joint kinematics/technique. Thus the individuals might still do the offending movement quality yet they can somehow cope.
WBM #2: Performance
Yes, how you move can influence your performance. This is probably the area when biomechanics matters the most. Jumping, lifting, throwing etc can all be influenced by movement quality. But pain and injury are other stories
WBM #3: Preparation trumps quality – The Importance of the Acute to Chronic Workload Ratio (ACWR)
Relevant Variables: Adaptability and the limits of adaptability
You need to prepare for what you will expose yourself to. We assume that people can adapt to the stresses placed upon themselves and that stress is not an inherently bad thing. We see this in all aspects of the biopsychosocial stressor realm.
The Acute to Chronic Workload Ratio suggests that large changes in acute loads are tolerated when they are preceded by a consistent and slowly progressing history of workload or stressors. This is fundamental to being a human. We respond positively to stress. If the biomechanical loads exceed what we are prepared for then we may be more likely to get injured.
However, our adaptability is finite and the speed of that adaptability is limited. We see this in occupational settings where total cumulative load can increase your risk for low back pain (interestingly, this was not mediated by how you lift the load) and in the area of muscle tears where high absolute running loads might increase your injury risk, albeit with a poor ability to predict injury at an individual level.
What is interesting with this adaptability model is that it is not just about mechanics and physical workload. Our adaptability and response to the physical workload or our “preparedness” would be influenced by other psychosocial stressors. This is well discussed in recent paper by Soligard.
WBM #4: Temporary movement modifications to desensitize
Relevant Variables: motor control, strength, ROM, movement analgesia
Again, this interrelates with other variables. Sometimes, we are in pain and we just need to give our body/ourselves a break. We assume that stress is a good thing and elicits adaptation but often we might want to back off of the load.
Our challenge as therapists is to answer the question “Expose or Protect”. Expose suggests the person needs some new stimulus to cause a positive adaptation and Protect suggests that the removal of stimulus is more important. Or perhaps the person is not “prepared” for the exposure.
Examples of this are often seen in the symptom modification approach to treating painful conditions. You can have an acute strain of tissue and protection with some loading might be the right stimulus or you could have a persistent pain condition where moving differently teaches that person that they can control their pain and resume activities of daily living that they might be missing.
- A runner has knee pain for 6 months. They have taken time off, done exercises and slowly tried to build back up. Their knee still hurts. You tinker with their stride and increase their step rate 7.5%. This can influence the load on the knee about 10-15% and for some reason it helps them run an extra 2 km pain free. Super. Keep it up.
- A patient has low back pain. It is not disabling. They have very little kinesiophobia. They aren’t afraid of the pain. They are just tired of it. It seems to consistently hurt when they flex forward when they squat. They feel better in a neutral spine and you were able to teach them how to squat, jump and do other meaningful activities with less spine flexion and for them, less pain. You explain that this is temporary desensitizer. Spine flexion is not inherently bad for them but for some reason they kept flexing and kept sensitizing themselves.
- A patient has shoulder pain with overhead arm raising. They do this a lot because they ask questions in class and paint walls for kicks. They have less pain when they shrug their shoulder and then lift their arm. As part of a comprehensive capacity shoulder program they do this simple and temporary modification when they lift their arm.
In general, this is a symptom modification approach used by many therapies. It hurt to do this so you do something else for a bit. It might help some patients control their pain and might help them start doing things that they miss. Or may or may not be a necessary part of treatment. But it can be helpful.
What it’s not saying is that there is a “correct” way to move. Rather, there is a way to move that is less painful for them at this point in time. Simple.
Nor should we think that it is the biomechanics alone that is the reason for less pain. The biomechanical change might have a greater impact on the psychosocial factors. We’ve just always explained our treatment in a biomechanical framework. Perhaps making movement modifications is a cognitive challenger – it confronts them with their own strength and leads to them discomfirming their view of their pain.
The RISK: When we teach people to move differently to control their pain there is a risk that we might create unhelpful safety behaviours. We can go too far. Symptom modification could lead to some pretty extreme interventions like ring-shifting or SI corrections. We don’t want our patients thinking they need to align their ear lobes because of potential distortions in their fascial fucking net. Or that they feel they can’t do certain movements without making elaborate corrections and a checklist of how to move. In my opinion, we explain this as a temporary change.
Last, symptom modification driven kinematic changes might be a bad idea in those with fear avoidance and more movement withdrawal. This group may have been avoiding and the treatment is actually to expose to the painful movement or the feared movement. Again, its this tough decision that we make. We can poke the bear but we probably shouldn’t hump the shit out of it.
WBM #5: Movement Habit Interruption
Relevant Variables: Motor control, strength, ROM
This is very similar to #4. It is the notion that sometimes when in pain we keep doing the same thing that aggravates us. Perhaps without realizing it or perhaps because of an impairment in a biomechanical variable that doesn’t permit us to avoid it. Goes back to too much bear poking/humping.
Further, its rooted in the idea that we are mostly self correcting. When you sit and your butt starts to hurt you move. We assume that nociception is occurring and it catalyzes movement before there is pain or even damage. When you can’t correct and move then damage can occur (think of pressure sores).
Or you might have a patient who continues to move in a way that is sensitizing them based on a faulty belief about their predicament. They might think that their spine should not flex and they should always be bracing their core 20% when sitting and keeping an upright neutral spine. In this case, their habit of movement might be sensitizing them because they are avoiding healthy slouching and movement variability.
Another example might explain when things like strength or flexibility matters. In the video below you will see my daughter do back handsprings and bridges. She has very little hip extension yet a lot of back extension and her habit it to always use her back extension. If she had some back pain that was aggravated with extension it would be very difficult for her to do her sports with different technique that might give her back a “break” for a few days. She might keep sensitizing it. A runner who consistently forefoot strikes and develops achilles pain, forefoot pain or calf pain might benefit from running with a flat foot strike but if they don’t have the skill to make this simple change it could be more difficult to keep running with this symptom/load modifier.
A case study/RCT of this can be seen here in rowers. What is great about this is that the spine kinematics were changed based on symptoms but they did NOT have to remain changed.
An example of movement habits being influenced by a biomechanical variable could be hip abduction strength. Many of us can run with a increased pelvic drop or hip adduction. It is not an injury sentence to have running related to pain. But, trying to address that pelvic drop when someone has new pain is a viable option to help someone. Strength may be a variable that contributes to a contralateral pelvic drop in runners (here and here.) Thus addressing the strength deficit may help someone move in a different way that can be associated with less pain and recovery.
There are a lot of “could’s, possibly’s and maybe’s” in here. The idea being that biomechanics are an option, but rarely the only solution,for helping people in pain. Changing biomechanics or having a “biomechanical” approach can be helpful. But, it may not even be necessary. I would suggest that as loads become higher and tissue injury becomes more of a factor than biomechanics become much more important and may be something that become more of a “requirement” than an option. I would also suggest that movement preparation, optimizing training and load response are more important than changing biomechanical technique for influencing our response to those external loads that are sometimes related to injury.
Part Two (whenever that will be) might explore the converse of this. Common cases where biomechanics become less important.
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