Hip extensor fatigue alters hip and knee coupling dynamics during single-limb step-downs: A randomized controlled trial.

Impaired hip muscle function may cause movement coordination deficits that increase lower extremity injury risks. We examined whether hip and knee coordination is altered during single-limb step-downs following a hip extensor fatigue protocol. Forty participants in this randomized controlled trial performed 20 single-limb step-downs before and after completing either a fatigue protocol or a sham fatigue protocol. Means and SDs of sagittal and frontal plane hip and knee kinematics were measured. Nonlinear measures of coupled hip and knee coordination were examined with cross recurrence quantification analyses. Pre- to post-fatigue change scores were analyzed inferentially (α = 0.05). The fatigue protocol induced 22.2% strength reduction in the fatigue group, versus 4% reduction in the sham group. Neither the magnitude nor variability in sagittal and frontal plane hip and knee kinematics changed following the fatigue protocol (P > .05, small effect sizes). Participants in the fatigue group, however, performed post-fatigue step-downs with greater cross determinism (P = .046, effect size = 0.71) and mean line (P = .038, effect size = 0.74) in sagittal plane hip and frontal plane knee coupling, whereas participants in the sham-control group performed step-downs with reductions in those measures. In the fatigued state, participants performed repeated step-downs with subtle increases in cross determinism and cross mean line, which implies they performed the task with greater predictability of hip and knee coupling and less adaptability. The findings may provide insight into coupled movement patterns and their reflection of motor control.