Relation between stature and contact or flight time in running

According to a well known study, the variation coefficients (=VC) of stride times (or stride length) were 5.9-6.0% in the range of running speeds between 3.15-4.12 m/s. Such data refer to 21 subjects ranging from 1.69 to 1.83 m. The correlation coefficient between stride time and stature (H) was not significantly different from zero (1). We measured contact time (Tc) and flight time (Tf) during treadmill running at different speeds up to the maximal one maintained for at least 5 s. Rest pauses were inserted between 0.28 m/s incremental steps to avoid fatigue. The 21 subjects’ height was 1.77±0.15 (1.52-1.98) m. Maximal attained speed was 7.5±0.7 (6.1-8.9) m/s At 4.17 and 6.11 m/s step lengths (Ls) were 1.450 m±6.9% (= ±VC) and 1.834 m ±8.1%, respectively. Ls was significantly related to H (R^2=0.42-0.37). The forward movement of the centre of gravity (=CG) during contact (Lc) was related to H (R^2=0.56-0.57) while the movement during flight was completely independent (R^2=0.00-0.00). In 90% of the subjects Lc plateaued over 5 m/s and was strictly related to H (R^2=0.79). At the fastest speed the unexplained difference of Ls from linear regression ranked from +0.19 to –0.20 m. It is unknown if these differences are due to anthropometric characteristics not taken into account like body mass, muscle fibre distribution and length or mass of leg, thigh, shank, foot. Nevertheless, in cycling the dependence of freely chosen cadence on muscle fiber type is an open question (2). The vertical velocity (Vv) at the beginning of Tc can be computed from Tf (Vv=9.81*0.5*Tf). Assuming a half time of Tc as pushing time and a linear increase of vertical velocity up to the take-off, the vertical displacement of the CG and vertical work may be obtained. Assuming a decrease of forward speed in the first half of Tc independent of average speed (3), the changes of kinetic energy in forward direction may be obtained. The computed vertical and horizontal powers are a good approximation of values obtained by force-platforms and imaging analysis. A positive relationship between horizontal power and H was found but the p value was only 0.025.