Effect of concurrent strength and endurance training on skeletal muscle properties and hormone concentrations in humans

The purpose of this study was to investigate the effect of concurrent stren gth and endurance training on strength, endurance, endocrine status and mus cle fibre properties. A total of 45 male and female subjects were randomly assigned to one of four groups; strength training only (S), endurance train ing only (E), concurrent strength and endurance training (SE), or a control group (C). Groups S and E trained 3 days a week and the SE group trained 6 days a week for 12 weeks. Tests were made before and after 6 and 12 weeks of training. There was a similar increase in maximal oxygen consumption ((V ) over dot O-2max) in both groups E and SE (P < 0.05). Leg press and knee e xtension one repetition maximum (1 RM) was increased in groups S and SE (P < 0.05) but the gains in knee extension 1 RM were greater for group S compa red to all other groups (P < 0.05). Types I and II muscle fibre area increa sed after 6 and 12 weeks of strength training and after 12 weeks of combine d training in type II fibres only (P < 0.05). Groups SE and E had an increa se in succinate dehydrogenase activity and group E had a decrease in adenos ine triphosphatase after 12 weeks of training (P < 0.05). A significant inc rease in capillary per fibre ratio was noted after 12 weeks of training in group SE. No changes were observed in testosterone, human growth hormone or sex hormone binding globulin concentrations for any group but there was a greater urinary cortisol concentration in the nomen of group SE and decreas e in the men of group E after 12 weeks of training (P < 0.05). These findin gs would support the contention that combined strength and endurance traini ng can suppress some of the adaptations to strength training and augment so me aspects of capillarization in skeletal muscle.