Histochemical and physiological correlates of training- and detraining-induced changes in the recovery from a fatigue test

Program in Physical Therapy, Irene Walter Johnson Rehabilitation Research Institute, Washington University School of Medicine, St Louis, MO 63110.

BACKGROUND AND PURPOSE. The primary purpose of this study was to evaluate the effects of endurance training and detraining on the development of and recovery from fatigue induced by isokinetic exercise. It was our hypothesis that the rate of recovery from fatigue would correlate with maximal oxygen uptake (VO2max). A secondary purpose was to determine whether changes in the development of fatigue and in the time course of recovery that occur with alterations in training status correlate with shifts in the proportions of type IIa and type IIb muscle fibers. SUBJECTS AND METHODS. Four subjects with no regular endurance exercise training participated in a 12-week program of intense endurance exercise training, and 6 endurance-trained subjects stopped all exercise training for 12 weeks. In addition, 11 subjects performed a single isokinetic fatigue test with recovery and a graded treadmill or bicycle ergometer test to determine VO2max. RESULTS. Maximal oxygen uptake increased 24% (SD = 10%) in response to the exercise training program and decreased 17% (SD = 6%) with detraining. The percentage of type IIa and type IIb muscle fibers changed with endurance training and detraining. The percentage of decline in torque during a 60-second isokinetic exercise test was unaffected by endurance training or detraining; however, there was a significant change in recovery of torque. CONCLUSION AND DISCUSSION. The results demonstrate a positive correlation (r = .75) between the percentage of reduction in torque at 30 seconds of recovery and the change in the proportion of type IIb fibers with both training and detraining. The results also demonstrate a high, negative correlation (r = -.84) between the percentage of reduction in torque at 30 seconds of recovery and VO2max. These results suggest the recovery of muscle torque reflects both the training- and detraining-induced changes in the proportion of type IIa and type IIb muscle fibers and maximal aerobic exercise capacity.

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