Peak biomechanical variables during bilateral drop landings: comparisons between sex (female/male) and fatigue (pre-fatigue/post-fatigue)

Abstract

Background: Although anterior cruciate ligament (ACL) sprains usually occur during the initial phase of the landing cycle (less than 40° knee flexion), the literature has focused on peak values of knee angles, vertical ground reaction force (VGRF), and muscle activity even though it is unclear what occurs during the initial phase of landing.

Objectives: The objectives of this study were to determine the effects of sex (male and female) and fatigue (prefatigue/post-fatigue) on knee flexion angles at the occurrence of peak values of biomechanical variables [knee valgus angle, VGRF, and normalized electromyographic amplitude (NEMG) of the quadriceps and hamstring muscles] during a bilateral drop landing task.

Methods: Knee valgus angle, VGRF, and NEMG of the quadricep and hamstring muscles were collected during bilateral drop landings for twenty-nine recreational athletes before and after a fatigue protocol.

Results: Peak values of knee valgus, VGRF, and NEMG of medial and lateral hamstring muscles occurred during the late phase of the landing cycle (>40° of knee flexion). Females in the post-fatigue condition exhibited peak VGRF at significantly less knee flexion than in the pre-fatigue condition. Males in the post-fatigue condition exhibited peak lateral hamstring muscles NEMG at significantly higher knee flexion than in the pre-fatigue condition.

Discussion and conclusion: Peak values of biomechanical variables that have been previously linked to ACL injury did not occur during the initial phase of landing when ACL injuries occur. No biomechanical variables peaked during the initial phase of landing; therefore, peak values may not be an optimal indicator of the biomechanical factors leading to ACL injury during landing tasks.

Figure 1.

Participant with markers and electrodes preparing to perform a drop landing.

Figure 2.

Occurrence of peak values in the landing cycle: non-fatigued males

Figure 3.

Occurrence of peak values in the landing cycle: fatigued males

Figure 4.

Occurrence of peak values in the landing cycle: non-fatigued females

Figure 5.

Occurrence of peak values in the landing cycle: fatigued females

Figure 6.

Knee flexion angle at occurrence of peak vertical ground reaction force

Figure 7.

Knee flexion angle at occurrence of peak lateral hamstring muscles normalized electromyographic amplitude