To investigate biochemical, histochemical and contractile properties associated with strength training and detraining, six adult males were studied during and after 10 weeks of dynamic strength training for the quadriceps muscle group of one leg, as well as during and after a subsequent 12 weeks of detraining. Peak torque outputs at the velocities tested (0-270 degrees X s-1) were increased (p less than 0.05) by 39-60% and 12-37% after training for the trained and untrained legs, respectively. No significant changes in peak torques were observed in six control subjects tested at the same times. Significant decreases in strength performance of the trained leg (16-21%) and untrained leg (10-15%) were observed only after 12 weeks of detraining. Training resulted in an increase (p less than 0.05) in the area of FTa (21%) and FTb (18%) fibres, while detraining was associated with a 12% decrease in FTb fibre cross-sectional area. However, fibre area changes were only noted in the trained leg. Neither training nor detaining had any significant effect on the specific activity of magnesium-activated myofibrillar ATPase or on the activities of enzymes of phosphagen, glycolytic or oxidative metabolism in serial muscle biopsy samples from both legs. In the absence of any changes in muscle enzyme activities and with only modest changes in FT fibre areas in the trained leg, the significant alterations in peak torque outputs with both legs suggest that neural adaptations play a prominent role in strength performance with training and detraining.
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