Fatigue of the knee extensor muscles following eccentric exercise.

The purposes of this study were to determine the time course of muscle fatigue in the knee extensor muscles following an eccentric exercise protocol, and to determine if the position of the subjects during assessment affected the measurement of muscle fatigue. Twenty-four female subjects were assigned to three groups. All subjects completed baseline measure (pre-exercise test) of a power spectrum analysis of the vastus medialis, rectus femoris and vastus lateralis muscles. Following an exercise protocol of 300 eccentric repetitions of the knee extensors, power spectrum analysis was repeated at two, four, 20, 24, 48 and 72 hours for group one, at 0 hour (immediately following the exercise) and two hours for group two, and at 0 hour for group three. Groups one and two were tested in sitting, while group three was tested supine. The slope of the median frequency of the vastus lateralis muscle changed significantly over time (p < 0.001) for group one, but there were no significant changes in the slope of the median frequency of the vastus medialis muscle, while the rectus femoris muscle showed an increase in the slope of the median frequency when the subjects were in the sitting position. Further testing, in supine (group three), indicated that the position of the hip joint influenced the power spectrum analysis of the rectus femoris muscle but not the vasti muscles. In addition, fatigue occurred immediately post-exercise with recovery within 24 hours.