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Pain and Biomechanics in Running: Determining Causation

FACT: Pain often exists independent of tissue damage

FACT: Pain can exist WITHOUT tissue damage

FACT: Pain often develops independent of specific biomechanics

Many runners view pain as a one-way street in which biomechanics and training loads are the direct causes of pain.  While it is certainly true that certain biomechanical qualities are risk factors for pain, it is a mistake to automatically assume causation runs only run direction.  Pain results for many reasons and is often the force driving biomechanics.  

I recently presented at a clinic in which one presenter was peddling orthotics touted to cure pain caused by “misalignment.”   Naturally, she was able to prey on the faulty notions like “I am in pain because my foot pronates...” or “My alignment is causing pain because I felt my back out of alignment.” 

The truth is that sometimes motor control changes due to pain, while other times pain results due to specific biomechanics. But you can’t assume anything.  Literature has consistently shown that pain leads to altered motor control.   Note, this doesn’t mean that biomechanical changes aren’t part of a solution to pain, but rather that chasing a strict ideal of biomechanical gait as antidote to pain leads many runners astray.  

Since our focus in this post is running, I’ll mostly review studies relevant to gait, though we’ll also cover the low back and one study from on the arms.   

Henricksen (2009, 2011, 2011) presented three studies on experimental pain in the lower extremities.  Experimental pain involves creating pain artificially such as by saline injection.  Studies were unanimous in showing motor control changes in response to pain.    

***2009 - Experimental pain results in significant changes in knee mechanics during lunging.  Pain not only resulted in reduced quadriceps muscle activation during the movement, it resulted in reduced muscle activation after pain had subsided. 

***2011 - Hamstring pain (again experimental) led to changes in pain resulting in “unloading of the painful muscle.”  Authors concluded “musculoskeletal pain is a protective signal leading to changes in movement patterns that serve to unload the painful tissue.” This may seem obvious to anyone who’s had a leg injury, but note that pain this case had absolutely nothing to do with previous biomechanics.  In real life, we might call this “favoring one leg.”  Now imagine you have leg pain and some coach is giving you drills on a track to cure your pain with “correct form,” yet the reason you don’t have “correct form” is that you were in pain....See the problem there?                    

***2011 - Achilles pain. “Experimental Achilles tendon pain causes widespread and reduced motor responses with functional effects on the ground reaction force.”  

Arendt-Nelson (1996) found similar results using experimental to induce low back pain.  “Chronic low back pain patients showed significantly increased EMG activity in the swing phase; a phase where the lumbar muscles are normally silent. These changes correlated significantly to the intensity of the back pain…The clinical and experimental findings indicate that musculoskeletal pain modulates motor performance during gait probably via reflex pathways.”  Ervilha (2005) found significant alterations in muscle activation of the biceps and triceps during elbow flexion and extension after experimental biceps pain.

Conclusion

This post is not to completely dismiss biomechanics and alignment.  Instead, it’s critical to recognize these relationships as a tangled web.  There’s no doubt medicine often neglects the specialized needs of repetitive use athletes, which is why well-intentioned coaches often try to fill the void.  But caring and good intentions are proxies for competence.  Understand that pain drives motor control, often independent of biomechanical laws.  We can utilize these laws as robust protectors of pain, but once pain sets in, the rules of the game change.

References

Henriksen M, Rosager S, Aaboe J, Bliddal H.  Adaptations in the gait pattern with experimental hamstring pain. J Electromyogr Kinesiol. 2011 Oct;21(5):746-53. Epub 2011 Aug 6.

Arendt-Nielsen L, Graven-Nielsen T, Svarrer H, Svensson P.  The influence of low back pain on muscle activity and coordination during gait: a clinical and experimental study.Pain. 1996 Feb;64(2):231-40.

Ervilha UF, Farina D, Arendt-Nielsen L, Graven-Nielsen T.  Experimental muscle pain changes motor control strategies in dynamic contractions.Exp Brain Res. 2005 Jul;164(2):215-24. Epub 2005 Jun 11.

Henriksen M, Alkjaer T, Simonsen EB, Bliddal H.  Experimental muscle pain during a forward lunge--the effects on knee joint dynamics and electromyographic activity. Br J Sports Med. 2009 Jul;43(7):503-7. Epub 2008 Aug 21.

Henriksen M, Aaboe J, Graven-Nielsen T, Bliddal H, Langberg H.  Motor responses to experimental Achilles tendon pain.  Br J Sports Med. 2011 Apr;45(5):393-8. Epub 2010 Jun 11.

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