2-Adrenergic receptor downregulation and performance decrements during high-intensity resistance exercise overtraining

Fry, Andrew C., Brian K. Schilling, Lawrence W. Weiss, and Loren Z. F. Chiu. 2-Adrenergic receptor downregulation and performance decrements during high-intensity resistance exercise overtraining. J Appl Physiol 101: 1664–1672, 2006. First published August 3, 2006; doi:10.1152/japplphysiol.01599.2005.—Previous research on overtraining due to excessive use of maximal resistance exercise loads [100% 1 repetition maximum (1 RM)] indicates that peripheral muscle maladaptation contributes to overtraining-induced performance decrements. This study examined the cellular and molecular responses of skeletal muscle to performance decrements due to high-relative-intensity (%1 RM) resistance exercise overtraining. Weight-trained men were divided into overtrained (OT, n 8) and control (Con, n 8) groups. The OT group performed 10 1 at 100% 1 RM daily for 2 wk, whereas the Con group performed normal training 2 days/wk. Muscle biopsies from the vastus lateralis muscle, voluntary static and dynamic muscle performances, and nocturnal urinary epinephrine were assessed before (pre) and after (post) overtraining. Overtraining occurred as indicated by a decrease in 1-RM strength for the OT group (mean SE; OT pre 159.3 10.1 kg, OT post 151.4 9.9 kg, Con pre 146.0 12.9 kg, Con post 144.9 13.3 kg), as well as a 36.3% decrease in mean power at 100% 1-RM loads. Normal training could be resumed only after 2–8 wk of training cessation. Muscle 2-adrenergic receptor ( 2-AR; fmol/mg protein) density significantly decreased by 37.0% for the OT group and was unchanged for the Con group ( 1.8%). Nocturnal urinary epinephrine for the OT group increased by 49%, although this was not significant (effect size 0.42). The ratio of nocturnal urinary epinephrine to 2-AR density suggested a decreased 2-AR sensitivity for the OT group (2.4-fold increase). Overtraining occurred based on decreased muscular force and power. Desensitization of the 2-AR system suggests that this may be an important contributor to performance decrements due to excessive use of maximal resistance exercise loads.