Biomechanics of sprint running

Sprinting involves a quick acceleration phase followed by a velocity maintenance phase. During the initial stage of sprinting, the runners have their upper body tilted forward in order to direct ground reaction forces more horizontally. As they reach their maximum velocity, the torso straightens out into an upright position. The goal of sprinting is to reach and maintain high top speeds to cover a set distance in the shortest possible time. A lot of research has been invested in quantifying the biological factors and mathematics that govern sprinting. In order to achieve these high velocities, it has been found that sprinters have to apply a large amount of force onto the ground to achieve the desired acceleration, rather than taking more rapid steps.

Human legs during walking have been mechanically simplified in previous studies to a set of inverted pendulums, while distance running (characterized as a bouncing gait) has modeled the legs as springs. Until recently, it had been long believed that faster sprinting speeds are promoted solely by physiological features that increase stride length and frequency; while these factors do contribute to sprinting velocities, it has also been found that the runner’s ability to produce ground forces is also very important.

Weyand et al. (2000) came up with the following equation for determining sprint velocity:

where ${\displaystyle V}$ is the sprint velocity (m/s), ${\displaystyle f_{\text{step}}}$the step frequency (1/s), ${\displaystyle F_{\text{avg}}}$ the average force applied to the ground (N), ${\displaystyle W_{\text{b}}}$ the body weight (N), and ${\displaystyle L_{\text{c}}}$ the contact length (m).

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