Quantitative and spatial aspects of degenerative changes in rat soleus muscle after exercise of different durations.

The aim of the present study was to investigate the effect of exercise duration on the amount of histological change (degeneration and cellular response), the number of affected muscle fibres, the segment over which muscle fibres were affected and the spatial distribution of affected muscle fibres in the rat soleus muscle after submaximal uphill running. Male Wistar rats ran on a treadmill (10 degrees incline, 1840 m/h) for 1.5 or 2.5 h. Three days postexercise the left and right soleus muscles were removed. Serial transverse sections were cut from proximal to distal, so that individual fibres could be followed over their entire length. Histological changes were quantified morphologically. With increasing exercise duration, an increase in the histological changes was found, as were a greater number of affected fibres and an increase in the mean length over which fibres were affected. Beside occasional minor clustering, affected fibres were distributed randomly throughout the muscle.