Control of energy dissipation when landing from a jump

Purpose: Landing from a jump is a complex task requiring precise postural motor control in order to dissipate the energy accumulated during the jump without falling, losing balance or rebounding. The purpose of this study is to investigate the modifications of the motor control of landing, by examining the biomechanics and the lower leg muscles activity as a function of the amount of energy to be dissipated. Methods: Ground reaction forces and muscular activity (tibialis anterior; gastrocnemius lateralis; biceps femoris, vastus lateralis) were recorded on fifteen subjects jumping from a box of different heights (10; 20; 30; 40; 50; 60cm) to change the amount of energy to be dissipated. Results: In landing, the lower limb muscles act as a spring and as a damped harmonic oscillator whatever the height of the jump. More precisely, when the amount of energy to be dissipated increases, the spring properties remain constant while the damped harmonic oscillator properties are modified. Whereas muscle pre-activation seems independent of the height, muscle activity during landing increases as height increases. A similar coordination is observed between agonist/antagonist muscles, whatever the energy to be dissipated. The tibialis anterior, a foot dorsiflexor, seems to be the one most influenced by the change in height. Conclusion: Throughout landing the lower limb properties are modified and are influenced by energy constraints. The tibialis anterior appears to act as a key muscle in the control of the landing