Effects of aerobic interval exercise training on mouse slow and fast twitch skeletal muscles

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2015-12

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The Ohio State University

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Abstract

Aerobic exercise training (AET) is a well-established approach to improve aerobic capacity, cardiovascular function and metabolic efficiency. However, the benefits of exercise have been shown to differ based on the unique modalities of the exercise regimen. We sought to specifically investigate the effects of aerobic interval exercise training on skeletal muscle. For this purpose, 2.5 months old FVB/n male mice (n=6) were subjected to an aerobic interval exercise-training program on a six-lane mouse treadmill for 6 weeks at a maximum speed of 16mts/min/10° incline for 60mins, 5 days/week. Age matched sedentary controls (n=6) were familiarized to the treadmill twice/week at 10mts/min for 10mins. No significant differences were observed in body weight between the sedentary and exercised mice (SED= 30.96±0.656 gms vs EX=31.59±0.610 gms). At the end of the training program, aerobic exercise capacity was determined by subjecting the mice to a graded maximal exercise test on a modular treadmill connected to a CLAMS metabolic unit. Critical markers of whole body aerobic capacity including maxVO2 measurements (SED=4965.518±139.355 and EX=6295.406±60.71ml/kg/hr) and maximum running speed (SED=33±1.22mts/min; EX=46.8±0.547mts/min) were increased in the trained mice compared to the sedentary controls. Blood lactate levels, measured within 15secs of the exercise test were decreased in trained mice relative to untrained sedentary controls (SED=13.26±0.676 and EX=11.78±0.660mMol/L). Our study indicates that our specific aerobic interval exercise improves overall aerobic capacity indicated by 5.3% increase in VO2 max and 1.5mMol/L decrease in blood lactate. The Soleus and Plantaris muscles were selected as examples of a slow and fast twitch phenotype respectively. Muscle to body ratios were not significantly different. Fiber type switching in response to the exercise regimen was assessed by Myosin heavy chain (MHC) isoform expression. After 7 weeks of AET, MHC 1 isoform decreased in Soleus by 16.12% while it increased by 79.77% in the Plantaris compared to untrained sedentary control muscles. On the other hand, MHC IIb increased by 56.72% in Soleus while it decreased 5.92% in the Plantaris after AET. Thus our protocol, which included aspects of both aerobic as well as endurance training, induced shifts in both slow and fast MHC isoforms in the Soleus and Plantaris muscles. Interestingly, we find that the same exercise protocol shifted the Soleus to favor a faster phenotype and the fast Plantaris towards a slower phenotype. The shifts in MHC isoforms in these two muscles studied may indicate the effects of a combined aerobic and endurance demand whereby both muscles may have reached a level of higher efficiency by acquiring a new ratio of slow and fast capabilities.

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Muscle, Mice, Exercise, aerobic, fiber types

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