Research Paper Volume 15, Issue 2 pp 308—352

Figure 2. The effect of long-term endurance exercise on soleus skeletal muscle weights and contractile force. Endurance exercise resulted in hypertrophy of soleus muscles in all body weight groups in both 18 mo and 22 mo old mice. Endurance exercise also increased absolute force output in all body weight groups, while force normalized to muscle size was not changed in both 18 mo and 22 mo old mice. (A) Soleus muscle weight (left) and muscle weight/body weight (MW/BW) ratio (right) for 18 mo mice. (B) Soleus muscle absolute maximal force (left) and specific maximal force (right) in 18 mo mice. (C) Soleus muscle absolute submaximal force (left) and specific submaximal force (right) in 18 mo mice. (D) Soleus muscle weight (left) and muscle weight/body weight (MW/BW) ratio (right) for 22 mo mice. (E) Soleus muscle absolute maximal force (left) and specific maximal force (right) in 22 mo mice. (F) Soleus muscle absolute submaximal force (left) and specific submaximal force (right) in 22 mo mice. ^*: p < 0.05, ^**: p < 0.01, ^***: p < 0.001, and ^****: p < 0.0001. VWR vs. CTRL mice. Abbreviations: CTRL: control group; VWR: voluntary wheel running group; CBW: Combined groups (18 mo: n = 16 CTRL, n = 17 VWR; 22 mo: n = 8 CTRL, n = 8 VWR); LBW, Low body weight group (18 mo: n = 8 CTRL, n = 10 VWR; 22 mo: n = 4 CTRL, n = 4 VWR); HBW, High body weight group (18 mo: n = 8 CTRL, n = 7 VWR; 22 mo: n = 4 CTRL, n = 4 VWR).