Muscle damage and regeneration: Response to exercise training

Abstract

Exercise training influences the function of skeletal muscle, modifying fibre structure, metabolism and promoting the release of growth factors and other signalling molecules. The number of satellite cells under the basal lamina of type I and type IIA muscle fibres increases during endurance training and under the basal lamina of both type II fibres during resistance training. An increase in satellite cells is related to several factors expressing different genes and type II muscle fibre hypertrophy. Insulin-like growth factor-I has a role in the hypertrophy of muscle fibres through the stimulation of the differentiat ion of satellite cells. The increased mitochondri al biogenesis via adenosine myophosphate-activated protein kinase is accompanied by the suppression of myofibrillar protein synthesis through pathways mediated by mitogen-activated protein kinases and the nuclear factor kappa B. Insulin-like growth factor-I expression is high er in type I fibres. Myostatin, the expression inhibitor of muscle hypertrophy, is higher in type II fi bres. The proteasome-, lysosome- and Ca 2+ -m ediated protein degradation is more intensive in fibres with higher oxidative capacity. Both, oxidative capacity and satellite cells number in muscle fibres play important roles in skeletal muscle regeneration. In this review, we explore the regeneration capacity changes in different types of skeletal muscle fibres in response to resistance, endurance and overtraining.