Limb length discrepancy is considered a source of injury for heel strike runners, but not for forefoot runners. One detailed suggestion about why limb length discrepancy might be more problematic for heel strike runners and that is the role of pronation.
Limb Length Discrepancy More Problematic for Heel Strike Runners
Pronation duration of the foot is longer in heel strike running because ground contact time is longer as compared with forefoot running.
- Normally, pronation of the long leg helps compensate for the mechanical stress caused by a limb length discrepancy.
A leg length inequality can result in the long leg side ankle already being pronated at heel strike [1] –this limits the ankle’s impact attenuate ability by fully pronating, resulting in higher loads transferred proximally through the kinetic chain [2,3].
Forefoot Running is Safer
In forefoot running, pronation pattern is also different as compared with heel strike running.
- Forefoot runners tend to pronate less which minimizes mechanical stress on the leg, preventing overloading, especially if a limb length discrepancy is present.
(Check out what a forefoot strike looks like here).
The Take Home Message
The chief bonus of forefoot running is the reduction of high impact loads as well as shorter ground contact time –these are evolutionary forces of natural selection which have contrived to ensure our ancestors remained injury-free while they ran barefoot.
Because natural selection promoted forefoot running over heel strike running to contribute to survival, leg length discrepancy, which is and has always been extremely common, would induce less danger for runners.
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References:
[1]. Langer S. Structural leg shortage. J Am Pod Ass, 1976;66:38-40.
[2]. D’Amico et al. Limb length discrepancy: an electrodynographic analysis. J Am Pod Med Ass, 1985; 75:639-43.
[3]. du Plesis MP. Stress fractures and overuse syndromes. SA Mediese Tydskrif, 1980;41:670.
Bretta Riches
BSc Neurobiology; MSc Biomechanics candidate, ultra minimalist runner & founder of RunForefoot. I was a heel striker, always injured. I was inspired by the great Tirunesh Dibaba to try forefoot running. Now, I'm injury free. This is why I launched Run Forefoot, to advocate the health & performance benefits of forefoot running and to raise awareness on the dangers of heel striking, because the world needs to know.
If you have a leg length discrepancy and run forefoot on minimalist shoes, do you still need to correct the discrepancy with an inlay?