Effects of Immobilization and Subsequent Low and High Frequency Treadmill Running on Rat Soleus Muscle and Ankle Joint Movement

Abstract

To investigate the effects of low and high frequency treadmill running on immobilization-induced soleus muscle atrophy and ankle joint limitation, we performed morphological and histochemical analyses. Fifteen 8-week-old female Wistar rats (weight: 195.1 ± 6.2 g) were used in this study. After 2 weeks immobilization, rats were randomly assigned into 3 groups for 6 weeks exercise, such as free cage activity for the free remobilization (FR) group, once-a-week treadmill running {low frequency running program (LFR group)}, six times a week running {high frequency running program (HFR group)}. Two weeks of immobilization significantly reduced the soleus muscle wet weight, type I and II fiber cross-sectional areas, and range of ankle joint movement, and it increased the type II fiber ratios compared with the contralateral side. Some of these changes were not corrected by free remobilization, whereas in the LFR and HFR groups the changes were clearly restored toward normal levels, the effect being more beneficial in the HFR group for muscle recovery. In addition, LFR and HFR groups had improved range of ankle joint contracture in comparison with the FR group. These findings indicate that immobilization-induced muscle fiber histochemical alterations and the decrease of range of ankle motion in rats, to a great extent, is a reversible phenomena, especially if remobilization is intensified by physical exercise. High frequency running is more beneficial for recovery of the immobilization-induced muscle atrophy and joint contracture than no running or low frequency running.