2001 Volume 46 Issue 2 Pages 195-205
Vertical component of ground reaction force (GRF) in rhythmical hopping motions of seven male subjects was recorded to analyze the stiffness of mm. triceps surae based on a simple mass-spring model. Hopping motions were performed only with plantar flexion, with knee and hip joints kept as straight as possible. Human body was modeled by a simple model, which was composed of a mass and a linear spring, which corresponded to human. Averaged difference between recorded GRF and theoretically predicted GRF based on the model ranged from 10 to 14% of the peak value of GRF, which was regarded as small. From the length of the phase in which GRF was larger than the body weight, value of the spring constant was estimated based on the simple model. The value ranged from 2.4 × 10^4 to 10.4 × 10^4 N/m, varying with the change of the hopping frequency. The reproducibility of the estimated stiffness, which was measured in different days, was quite high (CV ranged from 2.2 to 4.4%). Furthermore, predicted jump height, which was calculated from estimated spring constant, matched well to actually measured jump height. These facts supported the validity of the simple mass-spring system model.
