title: Effects of fatigue on kinetic and kinematic variables during a 60-second repeated jumps test.
abstract: OBJECTIVE
  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 flexion and ankle dorsiflexion 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.
authors.affiliation: Department of Physical Education, Health, & Recreation, Eastern Washington University, Cheney, WA, USA.
authors.forename: Jeni R
authors.initials: JR
authors.lastname: McNeal
authors.forename: William A
authors.initials: WA
authors.lastname: Sands
authors.forename: Michael H
authors.initials: MH
authors.lastname: Stone
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004576:Electromyography; D005080:Exercise Test; D005260:Female; D006801:Humans; D007700:Kinetics; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D012737:Sex Factors