The orientation of the ground reaction force (GRF) vector is a key determinant of human sprint acceleration performance and has been described using ratio of forces (RF) which quantifies the ratio of the antero-posterior component to the resultant GRF. Different methods have previously been used to calculate step-averaged RF, and this study therefore aimed to compare the effects of three calculation methods on two key “technical” ability measures: decline in ratio of forces (D_RF) and theoretical maximal RF at null velocity (RF₀). Twenty-four male sprinters completed maximal effort 60 m sprints from block and standing starts on a fully instrumented track (force platforms in series). RF-horizontal velocity profiles were determined from the measured GRFs over the entire acceleration phase using three different calculation methods for obtaining an RF value for each step: A) the mean of instantaneous RF during stance, B) the step-averaged antero-posterior component divided by the step-averaged resultant GRF, C) the step-averaged antero-posterior component divided by the resultant of the step-averaged antero-posterior and vertical components. Method A led to significantly greater RF₀ and shallower D_RF slopes than Methods B and C. These differences were very large (Effect size Cohen’s d = 2.06 – 4.04) and varied between individuals due to differences in the GRF profiles, particularly during late stance as the acceleration phase progressed. Method B provides RF values which most closely approximate the mechanical reality of step averaged accelerations progressively approaching zero and it is recommended for future analyses although it should be considered a ratio of impulses.

地面反作用力 (GRF) 矢量的方向是人类冲刺加速性能的关键决定因素，并且已经使用力比 (RF) 进行了描述，力比 (RF) 量化了前后分量与合成 GRF 的比率。以前曾使用不同的方法来计算步平均 RF，因此本研究旨在比较三种计算方法对两个关键“技术”能力测量的影响：力比下降 (D _RF ) 和理论最大 RF 在零速度 (RF ₀）。24 名男性短跑运动员在完全配备器械的赛道（串联的力量平台）上完成了从阻拦和站立起跑的最大努力 60 m 冲刺。RF 水平速度剖面是根据整个加速阶段测量的 GRF 确定的，使用三种不同的计算方法来获得每一步的 RF 值：A) 站立期间瞬时 RF 的平均值，B) 步平均前后分量除以阶梯平均合成 GRF，C) 阶梯平均前后分量除以阶梯平均前后分量和垂直分量的合成值。方法 A 导致显着更大的 RF ₀和更浅的 D _RF斜率比方法 B 和 C。这些差异非常大（效应大小 Cohen's d = 2.06 – 4.04）并且由于 GRF 曲线的差异而在个体之间变化，特别是在加速阶段进行的后期站立期间。方法 B 提供的 RF 值最接近于逐步接近零的步进平均加速度的机械现实，建议用于未来的分析，尽管它应该被视为脉冲的比率。