Using leg muscles as shock absorbers: theoretical predictions and experimental results of drop landing performance

Abstract

The use of muscles as power dissipators is investigated in this study, both from the modellistic and the experimental points of view. Theoretical predictions of the drop landing manoeuvre for a range of initial conditions have been obtained by accounting for the mechanical characteristics of knee extensor muscles, the limb geometry and assuming maximum neural activation. Resulting dynamics have been represented in the phase plane (vertical displacement versus speed) to better classify the damping performance. Predictions of safe landing in sedentary subjects were associated to dropping from a maximum (feet) height of 1.6-2.0 m (about 11 m on the moon). Athletes can extend up to 2.6-3.0 m, while for obese males (m = 100 kg, standard stature) the limit should reduce to 0.9-1.3 m. These results have been calculated by including in the model the estimated stiffness of the 'global elastic elements' acting below the squat position. Experimental landings from a height of 0.4, 0.7, 1.1 m (sedentary males (SM) and male (AM) and female (AF) athletes from the alpine ski national team) showed dynamics similar to the model predictions. While the peak power (for a drop height of about 0.7 m) was similar in SM and AF (AM shows a +40% increase, about 33 W/kg), AF stopped the downward movement after a time interval (0.219 +/- 0.030 s) from touch-down 20% significantly shorter than SM. Landing strategy and the effect of anatomical constraints are discussed in the paper.

Designing, building, measuring, and testing a constant equivalent fall height terrain park jump

“…However, Fig. 7 shows clearly that, even though it takes longer (about 0.25 s) for the jumper COM velocity vector to become tangent to the landing surface as a result of the landing being cushioned by the leg muscles (Minetti et al [30]), eventually the EFH experienced by the board and COM are the same. Figure 8 shows how the EFH experienced by the jumper varies with landing position along the surface.…”

“…Minetti et al [30] have shown that the maximum value of EFH an elite jumper's legs can absorb is only 1.5 m. Clearly EFHs greater than this cannot be considered to be safe. Therefore this value was adopted by the USTPC [31] as a landing design limit.…”

“…For this proofof-principle experiment, we designed a medium-sized constant EFH jump of about 14 m (horizontal) length, with a takeoff angle of 10 and a constant EFH of 0.5 m. The terminal conditions y L ðx F Þ used to integrate the constant EFH differential equation (Eq. 1) were tuned until the resulting jump surface intersected the parent slope at around 14 m and the angle of the landing surface at that point was less than 30 (assumed to be the practical limit for the snowcat). The profile of the resulting jump design is shown below in Fig.…”

Landing errors in the men’s floor exercise are caused by flight characteristics

“…Minnetti et al [10] discovered that dynamic characteristics of landings from different heights are dependent of muscle activation.…”

“…The influence of preactivation on the landing success and the foot stability has been investigated by several researchers [3]. The greatest activity of the lower extremities muscles occurs when hips start to drop [10].…”