FORCE PARAMETER VARIABILITY IN RESPONSE TO LOWER EXTREMITY DYNAMIC FATIGUE922

Abstract

Neuromuscular fatigue has been associated both with decrements in human performance and increased incidence of musculoskeletal injury. The purpose of this study was to assess force parameter variability associated with fatigue-related decreases in continuous maximal vertical jumping performance. Limited information is available characterizing the kinetic changes associated with dynamic fatigue. Four healthy adults [mean (± sd) age: 30.4± 7.5 yrs, height: 173 ± 15 cm, weight: 711 ± 233 N] performed two bouts (with sufficient recovery time between bouts) of continuous maximal vertical jumps to self-identified fatigue. Mean number of jumps per bout was 30.8 ± 6.5. Jumps were performed on a force platform sampling force records at 1000 Hz. Data were statistically evaluated using a repeated-measures ANOVA with Scheffe test comparisons among means. Selected unfatigued jumps (UJ) at the beginning of each bout were compared to those fatigued jumps (FJ) made just prior to the end of each bout. Flight times confirmed significant (p<.01) fatigue-related decrements in performance between UJ (420 ± 51 ms) and FJ (306 ± 85 ms) trials. Significant differences (p<.05) were found between UJ and FJ trials on measures of impulse (Ft) duration, absolute and body-weight-normalized vertical impulse and average impulsive force. Force profiles showed a landing peak force (LP) and a propulsive peak force (PP), both of which were significantly (p<.03) lower in the FJ compared to the UJ trials (LP: 2014± 616 N vs. 2602 ± 983 N; PP: 1502 ± 410 N vs. 1764± 495 N). Results show force parameter variability associated with fatigue-related performance decrements and may prove to have important training implications.