Effects of Fatigue on Kinetic and Kinematic Variables During a 60-Second Repeated Jumps Test

Purpose: The aim of this study was to investigate the effects of a maximal repeated-jumps task on force production, muscle activation and kinematics, and to determine if changes in performance were dependent on gender. Methods: Eleven male and nine female athletes performed continuous countermovement jumps for 60 s on a force platform while muscle activation was assessed using surface electromyography. Performances were videotaped and digitized (60 Hz). Data were averaged across three jumps in 10-s intervals from the initial jump to the final 10 s of the test. Results: No interaction between time and gender was evident for any variable; therefore, all results represent data collapsed across gender. Preactivation magnitude decreased across time periods for anterior tibialis (AT, P < .001), gastrocnemius (GAS, P < .001) and biceps femoris (BF, P = .03), but not for vastus lateralis (VL, P = .16). Muscle activation during ground contact did not change across time for BF; however, VL, G, and AT showed significant reductions (all P < .001). Peak force was reduced at 40 s compared with the initial jumps, and continued to be reduced at 50 and 60 s (all P < .05). The time from peak force to takeoff was greater at 50 and 60 s compared with the initial jumps ( P < .05). Both knee fexion and ankle dorsifexion were reduced across time (both P < .001), whereas no change in relative hip angle was evident ( P = .10). Absolute angle of the trunk increased with time ( P < .001), whereas the absolute angle of the shank decreased ( P < .001). Conclusions: In response to the fatiguing task, subjects reduced muscle activation and force production and altered jumping technique; however, these changes were not dependent on gender.