Fatigue after eccentric quadriceps femoris work produces earlier gastrocnemius and delayed quadriceps femoris activation during crossover cutting among normal athletic women.

Athletic women are at greater risk of anterior cruciate ligament (ACL) injury than men. Twenty, healthy, athletic women were evaluated for the effect of preferred stance limb isokinetic quadriceps femoris and hamstring fatigue from eccentric work compared with controls on the activation onset of vastus medialis, rectus femoris, vastus lateralis, the medial hamstrings, biceps femoris, and gastrocnemius muscles. Following 3 weeks of crossover cut training, subjects were tested for fatigue effects (5 subjects/week, 3 conditions, 1 condition/day, order effect controlled) on muscle activation onsets prior to crossover cut landing heelstrike (mixed model, ANOVA, P < 0.05). Fatigue from eccentric quadriceps femoris work produced delayed vastus medialis (P = 0.03), rectus femoris (P = 0.007), and vastus lateralis (P = 0.03) activation onsets compared with control, but did not differ compared to hamstring fatigue. Neither hamstring nor quadriceps femoris fatigue produced differences (P > 0.05) in medial hamstring or biceps femoris activation onsets compared to control. Quadriceps femoris fatigue from eccentric work produced earlier gastrocnemius activation onsets (P = 0.048) than control, but did not differ for hamstring fatigue. The gastrocnemius appears to provide synergistic and compensatory dynamic knee stabilization in closed kinetic chain function during quadriceps femoris fatigue. This finding in a normal group at high risk of ACL injury while performing a maneuver with a high ACL injury risk supports gastrocnemius inclusion in knee rehabilitation and conditioning programs and suggests the need for comparative evaluations of knee injured/reconstructed subjects.