Injury

Why runner’s knee is sexist

Ladies, this one’s for you. Just when we thought the feminist movement was winding down and full gender equality was within reach, we discover that running injuries are still discriminating. That’s right, patellofemoral syndrome – that familiar knee pain known not-so-affectionately as “runner’s knee” – is much more common (an estimated 25% more 1) in women than men. Researchers at East Carolina University examined the source of the injury gods’ apparent sexism in their new paper 2 entitled “Male and female gluteal muscle activity and lower extremity kinematics during running”.

No need to remind the female readers that we women possess several unique physical characteristics, particularly in our hip and behind region. These structural gender differences, along with prior research suggesting that hip or gluteal (butt muscle) function can contribute to knee pain, prompted the authors to focus on these areas.

They enrolled twenty male and twenty female healthy, young, recreational runners who reported no recent running injuries and were running at least ten miles a week. They geared up the runners with reflective markers attached to their pelvis and legs to monitor the participants’ leg motion as they ran down a short runway. They also attached electrodes to the runners’ behinds to measure the timing and degree of glut muscle activity during running using electromyography.

Their structural measurements showed that women have a wider pelvis to femur (upper leg bone) ratio, confirming that – no surprise – women do have nice wide child-bearing hips. Great, but how do these differences relate to running function? Compared to the male runners, the women ran with not only distinct form, but also unique muscle activation patterns. Specifically, the ladies tended to activate their gluteus maximus muscles more (40% peak , 53% average activation increase over males) and, during the stance phase, rotate their hips inward (adduct) and their knees outward (abduct) more than the men.

Considering that this study’s motivation was the imbalanced prevalence of patellofemoral syndrome between genders, it’s curious that the researchers controlled, rather than investigated, this factor. It would have been interesting to see two additional groups tested – men and women with patellofemoral pain – to examine whether these female-specific features were exaggerated in the knee-pain cohorts. As is, we can only speculate whether the observed biomechanical effects might increase susceptibility for knee pain … which is precisely what the authors do. They propose that greater glut engagement in women may lead to earlier fatigue, predisposing them to aberrant kinematics and consequently excess stress on the knee. While this is certainly a reasonable hypothesis worthy of further testing, nothing in this study directly supports it. In fact, given that participants only ran along a 20-meter runway and did not run to exhaustion, it seems quite unlikely that these women were simply tired and running with sloppy form. While any causal relationship between their findings and knee injuries is absent within this study, they offer solid support from prior studies associating patellofemoral pain with greater glut activity, hip adduction and knee abduction 3,4.

So what can we learn from Willson and colleagues? Men and women are built differently and hence, run differently. Their results are backed by sound methods, a reasonable interpretation and even a relatively convincing argument that these effects are the source of the gender bias behind runners’ knee injuries. But ladies, before you blame that shapely booty for one more woe, let’s wait for that follow up study proving causality.

References

    1. Boling M et al. 2010. Gender differences in the incidence and prevalence of patellofemoral pain syndrome. Scand J Med Sci Sports 20:725–30.
    2. Willson JD et al. 2012. Male and female gluteal muscle activity and lower extremity kinematics during running. Clin Biomech.
    3. Souza RB & Powers CM. 2009. Differences in hip kinematics, muscle strength, and muscle activation between subjects with and without patellofemoral pain. J Orthop Sports Phys Ther 39:12–9.
    4. Myer et al. 2010. The incidence and potential pathomechanics of patellofemoral pain in female athletes. Clin Biomech 25:700–7.

ResearchBlogging.org
Willson JD, Petrowitz I, Butler RJ, & Kernozek TW (2012). Male and female gluteal muscle activity and lower extremity kinematics during running. Clinical biomechanics (Bristol, Avon), 27 (10), 1052-7 PMID: 22948078

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