Research Paper Volume 15, Issue 2 pp 308—352

Figure 6. Effects of endurance exercise on skeletal muscle fiber type, cross-sectional area and number in 18 mo old mice. Endurance exercise induced fiber type switching from Type II to Type I in the soleus (SOL) but a reduction in Type IIB in the EDL in 18 mo old mice. Endurance exercise increased fiber cross-sectional area (CSA) in SOL, but not EDL in 18 mo old mice. No significant differences were found in the total fiber number of both skeletal muscles. (A, B) SOL fiber typing. (A) Pie charts showing all mice (CBW) in the CTRL and all in the VWR groups with the representative images. (B) The effect of VWR on each fiber type in different subgroups, CBW, LBW and HBW mice. ^*: p < 0.05, ^**: p < 0.01, and ^***: p < 0.001, VWR vs. CTRL mice. (C) The effect of VWR on SOL fiber CSA and number with representative images. ^*: p < 0.05, ^**: p < 0.01, and ^***: p < 0.001, VWR vs. CTRL mice. (D, E) EDL fiber typing. (D) Pie charts showing all mice (CBW) in the CTRL and in the VWR with the representative images. (E) The effect of VWR on each fiber type in two different subgroups, LBW and HBW mice. ^*: p < 0.05, VWR vs. CTRL mice. (F) The effect of VWR on EDL fiber CSA and number with the representative images. No significant differences were found. Abbreviations: CTRL: control group; VWR: voluntary wheel running group; CBW: Combined groups (18 mo: n = 12 CTRL, n = 12 VWR); LBW: Low body weight group (18 mo: n = 7 CTRL, n = 6 VWR); HBW: High body weight group (18 mo: n = 5 CTRL, n = 6 VWR).