The bounce of the body in hopping, running and trotting: different machines with the same motor

摘要

The bouncing mechanism of human running is characterized by a shorter duration of the brake after'landing' compared with a longer duration of the push before 'takeoff'. This landing–takeoff asymmetryhas been thought to be a consequence of the force–velocity relation of the muscle, resulting in a greaterforce exerted during stretching after landing and a lower force developed during shortening before take-off. However, the asymmetric lever system of the human foot during stance may also be the cause. Here,we measure the landing–takeoff asymmetry in bouncing steps of running, hopping and trotting animalsusing diverse lever systems. We find that the duration of the push exceeds that of the brake in all the ani-mals, indicating that the different lever systems comply with the basic property of muscle to resiststretching with a force greater than that developed during shortening. In addition, results show boththe landing–takeoff asymmetry and the mass-specific vertical stiffness to be greater in small animalsthan in large animals. We suggest that the landing–takeoff asymmetry is an index of a lack of elasticity,which increases with increasing the role of muscle relative to that of tendon within muscle–tendon units.