Knee and ankle external joint moments and kinematics pre - and post-fatigue during drop jumps in female university soccer players

Background: Non-contact knee injuries are common in soccer, with female players at greater risk than males. Fatigue is frequently proposed to increase injury risk, yet findings are inconsistent, and ankle biomechanics under fatigue are less well understood.

Purpose: To compare dominant-leg ankle and knee joint angles and external joint moments at initial contact and mid stance during a drop jump before and after fatigue in female university football players.

Methods: Twelve female players (age 20.4 ± 1.2 years; height 167.4 ± 5.8 cm; body mass 66.2 ± 8.4 kg) completed three drop jumps pre and post fatigue. Three-dimensional motion capture using a CAST lower body marker set quantified ankle and knee kinematics and kinetics. Fatigue was induced using a lower limb exercise circuit continued until a rating of perceived exertion of 9 on the 0 to 10 Borg scale (mean sets completed 10.3; most participants completed 4 to 10 sets; one participant completed 44 sets). Normality was assessed using Shapiro Wilk tests and pre to post comparisons were analysed using paired samples repeated measures statistics.

Results: Single legged countermovement jump height decreased from 11.9 ± 3.9 cm to 9.9 ± 2.8 cm, a 16.6% reduction (P = .002). No significant pre vs post fatigue changes were observed for ankle or knee angles or external moments in any plane at initial contact or mid stance (all P > .05). For example, knee flexion angle at initial contact was 28.48 ± 5.48 degrees pre fatigue and 28.9 ± 6.2 degrees post fatigue (P = .7), ankle dorsiflexion angle at mid stance was 32.6 ± 3.4 degrees pre fatigue and 30.8 ± 5.5 degrees post fatigue (P = .16), and external knee flexion moment at mid-stance was 9.3 ± 3.2 %BW.h pre fatigue and 8.9 ± 3.5 %BW.h post fatigue (P = .58). i

Conclusion: Although the fatigue protocol reduced single-legged countermovement jump performance, no statistically significant pre- to post-fatigue differences were detected in ankle or knee angles or external joint moments during the drop jump in this sample. Given the small sample size and variability in fatigue response, these findings should be interpreted cautiously and do not rule out fatigue related changes. In addition, because the drop jump is a controlled laboratory task that differs from soccer specific jumping and landing demands, future work should use larger, adequately powered cohorts and more soccer-representative tasks and fatigue protocols.