Athletic footwear, leg stiffness, and running kinematics.

CONTEXT: The leg acts as a linear spring during running and hopping and adapts to the stiffness of the surface, maintaining constant total stiffness of the leg-surface system. Introducing a substance (eg, footwear) may affect the stiffness of the leg in response to changes in surface stiffness.

OBJECTIVE: To determine if the type of athletic footwear affects the regulation of leg stiffness in dynamic activities.

DESIGN: Repeated-measures design.

SETTING: Motion analysis laboratory.

PATIENTS OR OTHER PARTICIPANTS: Nine healthy adults (age = 28 +/- 6.8 years, mass = 71.6 +/- 12.9 kg) free from lower extremity injuries.

INTERVENTION(S): Subjects hopped at 2.2 Hz on a forceplate under 3 footwear conditions (barefoot, low-cost footwear, high-cost footwear). Subjects ran on a treadmill at 2 speeds (2.23 m/s, 3.58 m/s) under the same footwear conditions.

MAIN OUTCOME MEASURE(S): Limb stiffness was calculated from forceplate data. Kinematic data (knee and ankle angles at initial contact and peak joint excursion after contact) were collected during running. We calculated 1-way repeated-measures (stiffness) and 2-way (speed by footwear) repeated-measures analyses of variance (running kinematics) to test the dependent variables.

RESULTS: A significant increase in leg stiffness from the barefoot to the "cushioned" shoe condition was noted during hopping. When running shod, runners landed in more dorsiflexion but had less ankle motion than when running barefoot. No differences were seen between the types of shoes. The primary kinematic difference was identified as running speed increased: runners landed in more knee flexion. At the ankle, barefoot runners increased ankle motion to a significantly greater extent than did shod runners as speed increased.

CONCLUSIONS: Footwear influences the maintenance of stiffness in the lower extremity during hopping and joint excursion at the ankle in running. Differences in cushioning properties of the shoes tested did not appear to be significant.