The use of treadmill ergometers for extensive calculation of external work and leg stiffness during running

Recently, new treadmill ergometers have been designed to measure the ground reaction forces during numerous successive steps. From ground reaction forces measured in track running, it has been shown to be possible to compute external mechanical work ( W(ext)) and leg stiffness ( k) of a bouncing spring-mass system. However, to the best of our knowledge, there is still no study reporting the inter-stride coefficient of variation (CoV) of W(ext) or k parameters calculated from many successive steps. The aim of this experiment was to investigate the intra-and inter-individual variations of W(ext) and k while running at different speeds on a treadmill ergometer. Thirteen healthy runners ran at 12, 14, 16 and 18 km h(-1) during 3 min. Ground reaction forces were measured and recorded during the last 20 s of each exercise (50-62 steps). From these forces, average values and CoV of W(ext) and k were calculated. W(ext) significantly increased while k decreased with speed (both P<0.001). The mean values of these parameters were in agreement with data already reported and the CoV was less than 6% for all the parameters, showing almost no variation with speed. Therefore, this method of calculation, based on the extensive measurements of ground reaction forces, can be used to extensively study the mechanical parameters of treadmill running, and especially the inter-stride variability.