HISTOCHEMICAL AND PHYSIOLOGICAL CORRELATES OF TRAINING-INDUCED AND DETRAINING-INDUCED CHANGES IN THE RECOVERY FROM A FATIGUE TEST

Background and Purpose. The primary purpose of this study was to evalu ate the effects of endurance training and detraining on the developmen t 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 determ ine whether changes in the development of fatigue and in the time cour se of recovery that occur with alterations in training status correlat e with shifts in the proportions of type IIa and type IIb muscle fiber s. Subjects and Methods. Four subjects with no regular endurance exerc ise training participated in a 12-week program of intense endurance ex ercise training, and 6 endurance-trained subjects stopped all exercise training for 12 weeks. In addition, 11 subjects performed a single is okinetic fatigue test with recovery and a graded treadmill or bicycle ergometer test to determine Vo2max. Results. Maximal oxygen uptake inc reased 24% (SD = 10%) in response to the exercise training program and decreased 17% (SD =6%) with detraining. The percentage of type IIa an d type IIb muscle fibers changed with endurance training and detrainin g. The percentage of decline in torque during a 60-second isokinetic e xercise test was unaffected 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) b etween the percentage of reduction in torque at 30 seconds of recovery and the change in the proportion of type IIb fibers with both trainin g and detraining. The results also demonstrate a high, negative correl ation (r = -.84) between the percentage of reduction in torque at 30 s econds of recovery and Vo2max. These results suggest the recovery of m uscle torque reflects both the training- and detraining-induced change s in the proportion of type IIa and type IIb muscle fibers and maximal aerobic exercise capacity.