The speed with which all four phases of a short sprint (start, acceleration, maximum speed, and deceleration) are completed depends upon the amount of force applied during the pushing action away from the ground (ground reaction force – GRF) each foot strike, and the speed with which force is applied (rate of force production – RFP). With correct form and technique, a maximum amount of force can be applied at exactly the right time, in the right direction, and in the shortest possible ground contact time.
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A study by Nagahara, et. al. (2017) examined the association of sprint performance with ground reaction forces during the acceleration and maximum speed phase
Eighteen male athletes performed a 60-m sprint with GRF measured at every step over a 50-m distance from the start. Accelerations at 55%, 65%, 75%, 85%, and 95% of maximal speed, and running speed during the maximal speed phase were determined as sprinting performance variables. Ground reaction impulses and mean GRFs during the acceleration and maximal speed phases were selected as independent variables. Stepwise multiple regression analysis selected propulsive and braking impulses as contributors to acceleration at 55%–95% (β > 0.724) and 75%–95% (β > 0.176), respectively, of maximal speed. Mean vertical force was a contributor to maximal running speed (β = 0.481). The current results demonstrate that exerting a large propulsive force during the entire acceleration phase, suppressing braking force when approaching maximal speed, and producing a large vertical force during the maximal speed phase are essential for achieving greater acceleration and maintaining higher maximal speed.
Coaching Application: This study supports the findings of numerous other researchers on the contribution of both horizontally- and vertically-directed GRF to acceleration and maximum speed. While horizontal force requirements increase in linear fashion during the start and acceleration phase, nearly 100 percent of force requirements at maximum speed are in a vertical direction. The main factor preventing an increase in the maximum (mph) speed of athletes is the inability to exert additional vertically-directed ground reaction force. Strength training programs (weight room, plyometrics, sprint loading) must contain exercises that increase GRF in both a horizontal and vertical direction and mimic the movements of a sprinter during the acceleration and maximum speed phase.
Reference
Ryu Nagahara, Mirai Mizutani, Akifumi Matsuo, Hiroaki Kanehisa, and Tetsuo Fukunaga. 2017. Association of sprint performance with ground reaction forces during acceleration and maximal speed phases in a single sprint. Journal of Applied Biomechanics. https://doi.org/10.1123/jab.2016-0356
