Skeletal Muscle Mitochondrial Oxidative Injuries Induced By Overtraining In Rats

Objective Investigate the cell biologic mechanisms of injuries to the skeletal muscle caused by a one-week repeated overtraining.Methods Sixteen SD male rats were divided randomly into two groups: control(C) group(8) and exercising(E) group(8). Exercising group took repeating exhausting run on the treadmill for one week. After training, the quadriceps femoris muscle was obtained from each of the rats to isolate the mitochondria, and SOD and cytochrome C oxidase activities were determined. Assessment of the broken mitochondrial DNA was performed with FADU method.Results (1) Overtraining caused the decrease of the mitochondrial protein in quadriceps femoris. (2) The malonic acid(MDA) content of quadriceps femoris mitochondria were more than the control group. (3) A reduction of the absorption coefficient of cytochrome C was observed. (4) Overtraining could disrupt the mitochondrial DNA strands, reducing the content of double strand DNA. (5) Morphologic changes in early stage of apoptotic cell could be seen under transmission electron microscope(TEM), such as the aggregation of chronosome, the expansion of nuclei cistern and the contraction of nucleus.Conclusions Overtraining may lead to free radical-mediated injuries to the rats' skeletal muscle, cause apoptosis and necrosis as well.