HORTOBÁGYI, T., J. A. HOUMARD, J. R. STEVENSON, D. D. FRASER, R. A. JOHNS, and R. G. ISRAEL. The effects of detraining on power athletes. Med. Sci. Sports Exerc., Vol. 25, No. 8, pp. 929–935, 1993. We investigated the effects of 14 d of resistive exercise detraining on 12 power athletes. In comparing performances pre- to post-detraining, there were no significant (P> 0.05) changes in free weight bench press (-1.7%), parallel squat (-0.9%), isometric (-7%) and isokinetic concentric knee extension force (-2.3%), and vertical jumping (1.2%). In contrast, isokinetic eccentric knee extension force decreased in every subject (-12%, P < 0.05). Post-detraining, the changes in surface EMG activity of the vastus lateralis during isometric, and isokinetic eccentric and concentric knee extension were −8.4%, −10.1%, and −12.7%, respectively (all P > 0.05). No significant changes occurred in knee flexion forces or EMGs (P > 0.05). Percentages of muscle fiber types and the Type I fiber area remained unchanged, but Type II fiber area decreased significantly by −6.4% (P < 0.05). Levels of plasma growth hormone (58.3%), testosterone (19.2%), and the testosterone to cortisol ratio (67.6%) increased, whereas plasma cortisol (-21.5%) and creatine kinase enzyme levels (-82.3%) decreased (all P < 0.05). Short-term resistive exercise detraining may thus specifically affect eccentric strength or the size of the Type II muscle fibers, leaving other aspects of neuromuscular performance uninfluenced. Changes in the hormonal milieu during detraining may be conductive to an enhanced anabolic process, but such changes may not materialize at the tissue level in the absence of the overload training stimulus.
©1993The American College of Sports Medicine