Effects of Chronic Stretching on Soleus Muscle of Wistar Female Rats

Abstract

The purpose of this study was to evaluate the chronic effects of stretching exercise on soleus muscle histomorphology and histomorphometry of young and aged rats. Thirty-eight female rats were divided into young control group (YCG, n=10;274±50 g); young stretching group (YSG, n=8;274±12 g); aged control group (ACG, n=10;335±39 g); and aged stretching group (ASG, n=10;321±32g). A mechanical apparatus was used to stretch muscle in 4 repetitions, 60 s each, 30 s interval between repetitions in each session, 3 times a week for 3 weeks. Twenty-four hours after the last stretching session, soleus muscle was removed for micromorphology and immunostaining analysis. Data analyses were performed with one-way ANOVA, post-hoc Tukey, or Kruskal-Wallis tests for parametric and nonparametric, respectively (p≤0.05). Muscle fiber cross-sectional area (MFCSA) of ACG was lower (18 %) compared to the YCG. Stretching increased MFCSA comparing YSG to YCG (5,681.15± 1,943.61 µm 2 vs 5,119.84±1,857.73 µm 2 , p=0.00), but decreased comparing ASG to ACG (3,919.54± 1,694.65 µm 2 vs 4,172.82±1,446.08 µm 2 , p=0.00). More serial sarcomere numbers were found in the YSG than YCG (12,062.91±1,564.68 vs 10,070.39±1,072.38, p=0.03). Collagen I and collagen III were higher in YSG than ASG (7.44±7.18 % vs 0.07±0.09 %, p=0.04) and (14.37 %± 9.54 % vs 5.51 %±5.52 %, p=0.00), respectively. TNF-a was greater in ASG than YSG (43.42 %±40.19 % vs 1.72 ± 2.02 %, p=0.00). Epimysium was larger in the YSG compared to YCG (201.83±132.07 % vs 181.09±147.04 %, p=0.00). After 3-week stretching the soleus muscles from aged rats were smaller than their younger counter-parts. Interestingly, while stretching appeared to positively affect young soleus muscle, the opposite was detected in the muscle of the aged rats.