The effects of rest interval length and training on quadriceps femoris muscle. Part I: knee extensor torque and muscle fatigue.

AIM: The purpose of this study was to examine the effects of rest interval on quadriceps femoris (QF) muscle strength and fatigue during short-term, high-intensity training.

METHODS: Fifteen healthy males were assessed for isokinetic QF strength, via peak torque (PT), work (WK) and power (PW), at a pre-set angular velocity of 180 deg x s(-1). Quadriceps femoris muscle fatigue was evaluated as the decline in isokinetic work and power (slope) across 30 maximal concentric contractions. Subjects were randomly assigned to 1 of 3 groups: Group 1 (short rest interval), Group 2 (long rest interval), and Group 3 (control-no training). Subjects in Group 1 received a rest period of 40 s in between exercise sets corresponding to a 2:1 rest:work ratio. Subjects in Group 2 received a rest period of 160 s corresponding to an 8:1 rest:work ratio. Groups 1 and 2 performed isokinetic knee extension contractions at 180 deg x s(-1) 2 days per week for 6 weeks.

RESULTS: The results demonstrated a significant increase in QF muscle PT across the 6 week training period in the long rest interval group, and no significant changes in the short rest interval and control groups. Quadriceps femoris muscle work and power were observed to not change significantly across the training period in all 3 groups. The reduction in QF muscle work across the single set of 30 repetitions was observed to decrease significantly in the control group across the 6 week duration; no other significant changes in QF muscle fatigue for work and power were observed.

CONCLUSION: The major findings of this study suggests that the possibility of different physiological mechanisms of adaptation exist for QF muscle peak torque, work and power, while changes in muscle fatigue resistance may be present when assessed across multiple, rather than a single, bouts of activity.