The effect of endurance training on muscle strength in young, healthy men in relation to hormonal status.

The objective of this study was to establish the effect of moderate intensity endurance training on muscle strength in relation to hormonal changes in the body. Fifteen young, healthy men took part in 5 week endurance training performed on a cycloergometer. Before and after training program, exercise testing sessions were performed involving all participants. Training program significantly increased V(O2 max) (P<0.05) and time to fatigue at 50% of maximal voluntary isometric contraction (TTF 50% MVC), P<0.03, but it did not affect maximal voluntary isometric contraction (MVC). This was accompanied by an increase (P<0.001) in total plasma testosterone (T) and free testosterone (fT) concentrations, whereas a decrease in sex hormone-binding globulin (SHBG) (P<0.02), growth hormone (P<0.05), free triiodothyronine (P<0.001) and free thyroxine (P<0.02) concentrations was observed. No changes were found in plasma cortisol (C) and insulin-like growth factor-I (IGF-I) concentrations. Additionally, MVC was positively correlated to T/C, fT/C and IGF-I/C ratios after the training, whereas time to fatigue at 50% of MVC was closely positively correlated to the SHBG concentration, both before and after endurance training. We have concluded that moderate intensity endurance training resulting in a significant increase in V(O2 max), did not affect the MVC, but it significantly increased time to fatigue at 50% of MVC. This index of local muscular endurance was greater in subjects with higher concentration of SHBG, both before and after the training.