Girard, O., Micallef, J.-P., &Millet, G. P. (2010). Changes in spring-mass model characteristics during repeated running sprints. Presentation 695 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

This study investigated fatigue-induced changes in spring-mass model characteristics of the legs during repeated sprint running. Ss (N = 16) performed 12 x 40 m sprints interspersed with 30 seconds of passive recovery. At 5-10 m and 30-35 m, vertical and anterio-posterior ground reaction forces were measured with a force platform integrated into an indoor athletic track from which two consecutive steps (one stride) were extracted for analysis. Force data were used to determine stride parameters (contact time, stride length, and stride frequency) and to calculate spring-mass model characteristics (leg and vertical stiffness).

Stride frequency, push-off, and braking forces decreased significantly from the first to the last repetition, at 5-10 m and 30-35 m, respectively. Contact times increased. Stride length and peak vertical force did not change significantly. Leg stiffness decreased with fatigue throughout the set but to a lesser extent than vertical stiffness.

Implication. Repeating 40 m sprints deteriorated leg-spring behavior, as evidenced by the reduction in lower leg and vertical stiffness values measured both at 5-10 m and 30-35 m distance intervals. Procedures that help preserve stiffness (cooling?) might sustain sprint performance.

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