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Mechanical energy of the centre of mass of the body while running to and jumping over an obstacle

When running on the level, the motion of the centre of mass of the body (COM) can be compared to the movement of a spring–mass system bouncing on the ground (Cavagna et al. 1988). During the contact phase, mechanical energy is partially stored and recovered in the contracted muscles and the tendons. The contact phase is followed by an aerial phase during which the elastic model is no more valid, since the vertical acceleration is constant. The duration of this latter phase depends on the vertical velocity of the COM at take-off. For jumping over an obstacle, the runner has to increase his/her vertical velocity at the end of the contact period in order to increase the vertical movement of the COM and the duration and the length of the aerial phase. The purpose of this pilot study was to analyse how the bouncing mechanism of running adapts to achieve this goal. Therefore, we studied the mechanical energy changes of the COM during the three steps preceding the jump over a 0.85 m high barrier, while running at a fast speed (18 km h).