The Effect of Exertion and Sex on Vertical Ground Reaction Force Variables and Landing Mechanics.

The purpose of this investigation was to determine how exertion and sex affected a variety of vertical ground reaction force (VGRF) parameters during a jump-landing task, including peak VGRF, peak VGRF asymmetry, loading rate, and loading rate asymmetry. Additionally, we wanted to determine whether landing mechanics changed after exertion as measured by the Landing Error Scoring System (LESS). Forty recreationally active participants (20 men and 20 women) completed jump landings from a 30-cm-high box onto force plates before and after repeated bouts of an exercise circuit until a specific rating of perceived exertion was achieved. Three-way (sex × time × limb) analyses of variance were used to analyze variables pre-exertion to postexertion. No significant 3-way interactions were observed for peak VGRF (p = 0.31) or loading rate (p = 0.14). Time by sex interactions were observed for peak VGRF (p = 0.02) and loading rate (p = 0.008). Post hoc analysis revealed that men increased landing force and loading rate after exertion while women did not. Landing mechanics, as assessed by total LESS score, were worse after exertion (p < 0.001) with increased frequency of errors for knee flexion <30° at initial contact, lateral trunk flexion, and not flexing the hip during landing. Women may be more resistant to exertion compared with men and use different joint controls' strategies to cope with VGRF after exertion. However, VGRF asymmetry is not affected by sex and exertion. Limiting peak VGRF and addressing landing postures, especially after exertion, should be components of injury prevention strategies.