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Runners adjust leg stiffness for their first step on a new running surface

PainSci » bibliography » Ferris et al 1999
Tags: running, exercise, self-treatment, treatment

Six articles on PainSci cite Ferris 1999: 1. Is Running on Pavement Risky?2. The Complete Guide to IT Band Syndrome3. The Complete Guide to Patellofemoral Pain Syndrome4. Complete Guide to Plantar Fasciitis5. Shin Splints Treatment, The Complete Guide6. Are Orthotics Worth It?

PainSci notes on Ferris 1999:

This simple experiment showed that runners adapt to changes in the hardness of the surface they are running on with amazing speed — just a single step — as measured in terms of maintaining the height of their centre of mass. Importantly, this nearly instantaneous adaptation only occurs with an expected change on familiar surfaces, but we are probably pretty quick with unexpected and unfamiliar surface changes as well.

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

Human runners adjust the stiffness of their stance leg to accommodate surface stiffness during steady state running. This adjustment allows runners to maintain similar center of mass movement (e.g., ground contact time and stride frequency) regardless of surface stiffness. When runners encounter abrupt transitions in the running surface, they must either make a rapid adjustment or allow the change in the surface stiffness to disrupt their running mechanics. Our goal was to determine how quickly runners adjust leg stiffness when they encounter an abrupt but expected change in surface stiffness that they have encountered previously. Six human subjects ran at 3 m s(-1) on a rubber track with two types of rubber surfaces: a compliant soft surface (ksurf = 21.3 kN m(-1) and a non-compliant hard surface (ksurf = 533 kN m(-1). We found that runners completely adjusted leg stiffness for their first step on the new surface after the transition. «The first step—wow!» For example, runners decreased leg stiffness by 29% between the last step on the soft surface and the first step on the hard surface (from 10.7 kN m(-1) to 7.6 kN m(-1), respectively). As a result, the vertical displacement of the center of mass during stance ( approximately 7 cm) did not change at the transition despite a reduction in surface compression from 6 cm to less than 0.25 cm. By rapidly adjusting leg stiffness, each runner made a smooth transition between surfaces so that the path of the center of mass was unaffected by the change in surface stiffness.

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