Effect of aerobic exercise on the contractile function of gastrocnemius myosin heavy chain

Objective To study the effect of 4-6 weeks’ treadmill training of male SD rats on the contractile function of their gastrocnemius myosin heavy chain (MHC). Methods Forty male SD rats were randomly divided into control group and training group. The treadmill training of the training group rats was incessantly performed for 4-6 weeks at an intensity of about 75% VO2max (18.5-24 m/min,gradient of 0°,each training session lasting 50 minutes,twice a day). The content of gastrocnemius MHC mRNA was tested by reverse transcription polymerase chain reaction (RT-PCR),and the changes of muscle fibre and its cross-section area (CSA) were measured using immunohistochemistry. Electric stimulation tests were used to determine the maximal tension of isometric contraction of the post-training gastrocnemius. Results ① After continuous treadmill training for 4-6 weeks,we found that the content of the total MHC,MHC Ⅰ,MHC Ⅱx,MHC Ⅱa mRNAs was 105%,105%,109% and 108% of that in the resting control group,respectively,and the MHC Ⅱb mRNA content did not change significantly. The percentage of MHC Ⅰ mRNA in the total MHC mRNA increased while that of MHC Ⅱ mRNA decreased after aerobic training. ② The slow type of fibre type Ⅰ was the main part of the MHC after training and the CSA of the muscle fibres increased simultaneously. ③ The maximal tension of isometric contraction by pulse stimulation of square wave in the training group increased significantly compared with that in the control group (P<0.01). Conclusion The findings indicate that aerobic exercise may promote an increase in the contractile function of MHC.