Adaptation to Repeated Eccentric Exercise in Males and Females

Abstract

Unaccustomed eccentric exercise results in damage to skeletal muscle ultrastructure. One bout of eccentric exercise can induce adaptations in skeletal muscle, such that if the bout is repeated indices of muscle damage are attenuated. However, little is known about the pathways mediating these "protective" adaptations. The purpose of this thesis was to further characterize adaptations to repeated eccentric exercise and to investigate the hypothesis that increased stress protein content is associated with attenuated indices of muscle damage following the second exercise bout. Untrained male (N = 8) and untrained female (N = 8) subjects performed two bouts of unilateral, eccentric leg press and unilateral, eccentric knee extension exercises separated by 5.5 wk. Biopsies were taken from the vastus latera/is of the exercised and control (rest) leg. Blood samples and strength data were also collected. Following the second exercise bout the rise in serum CK activity, the post exercise force deficit and the extent of ultrastructural disruption as characterized by Z-disk streaming were attenuated, however ubiquitin conjugated protein content was elevated. Serum CK activity was lower in females as compared to males and ubiquitin conjugated protein content was greater in males as compared females. No gender difference was detected in the extent of Z-disk streaming or the relative magnitude of post exercise force deficit. Muscle macrophage counts were elevated over resting values 24 h post exercise bout 1 and 2 in both males and females. Whereas, neutrophils counts were only elevated over resting values following the second exercise in females. HSP72 protein content did not change in response to eccentric exercise, but it tended to be greater in males as compared to females (p=0.053). HSP27 protein content increased in response to exercise in males only, although females had greater basal content. Following the second exercise bout bcl-2 protein content was greater in females as compared to males. In conclusion, adaptations to repeated eccentric exercise are associated not only with attenuated serum CK activity and force deficit as previously described, but also with decreased ultrastructural damage, increased ubiquitin conjugated protein content and changes in stress protein content.