Effects of a 24-week same-session combined endurance and strength training program on physical performance and serum hormone levels in recreational endurance runners

Abstract

Combining endurance (E) and strength (S) loadings into the same training session might be an efficient time-saving strategy for endurance runners that want further develop performance thanks to the benefits obtained by adding strength training. However, performing strength training repeatedly after prolonged runs may generate a superior degree of stress on both neuromuscular and endocrine systems that, especially at high training frequencies, may compromise long-term strength training adaptations. This, in turn, might have important implications on endurance running performance. This study investigated the longitudinal changes in the acute responses to a same-session combined endurance and strength training and their influence on the long-term physical performance and serum hormone levels in recreational endurance runners. Eleven male recreational endurance runners (32±5 years) completed a 24-week periodized combined training program consisting in 2 combined endurance and strength training sessions (E+S) and 3-4 endurance-only training sessions per week. Basal measurements of endurance performance (Vpeak, blood lactate at submaximal running speed), neuromuscular performance (MVC, 1RM, F500ms, CMJ) and endocrine function (testosterone, cortisol, GH, TSH and SHBG) were performed in the first week of training (week 0), after 12 weeks (week 12) and at the end of the training period (week 24) under controlled conditions. Acute neuromuscular and hormonal response to the combined training session and early recovery phase were also assessed in the same weeks of basal measurements with a specifically-designed training session, before E (PRE), after E (MID), after E+S (POST) and after 24 and 48 h of recovery. The combined training session lead to significant (p<0.05) decreases at POST in neuromuscular performance (MVC, F500ms and CMJ) both at week 0 and 24 but not in power capacity (F500ms, CMJ) at week 12. Significant (p<0.05) increases occurred in testosterone, cortisol, GH at MID at week 0, 12 and 24, however, a longitudinal reduction was observed in the acute cortisol and TSH response at POST during the intervention period. Whereas MVC, F500ms and CMJ were recovered at 24 h, cortisol and TSH remained (although not always significantly) depressed at 24 and 48 h at week 0, 12 and 24. No long-term improvements in neuromuscular performance were detected during the study period. Significant increases in Vpeak (p<0.01) and blood lactate at 15 km h-1 (p<0.05) occurred in the last 12 weeks of training. Significant correlations were observed between F500ms at MID and Vpeak (r=0.663, p<0.05) and F500ms at MID and blood lactate at 15 km h-1 (r=-0.673, p<0.05) but only at week 12. The present study confirmed that, training strength always after endurance may lead to an augmented stress to the endocrine system that may take several days to recover. Despite minor adaptations, this training design may impede strength and power development, counteracting the benefits of strength training on endurance performance.