Effects Of High Intensity Interval Training/moderate Intensity Continuous Training And Detraining On Skeletal Muscle Mass And Lipid Deposition In Rats By High Fat Diet

Objective:Skeletal muscle is an important component of the motor system and an important endocrine regulator of the body’s glucolipid metabolism,and low muscle mass and high lipid content are strongly associated with health risks.Studies have confirmed that High Intensity Interval Training（HIIT）and Moderate Intensity Continuous Training（MICT）are effective in increasing skeletal muscle mass and improving skeletal muscle lipid deposition.However,long-term adherence to exercise is less likely in real life,and detraining for various reasons can result in partial or complete loss of exercise effects.In this study,we investigate the effects of HIIT/MICT on increasing skeletal muscle mass and reducing skeletal muscle lipids in rats fed a high-fat diet and the regression after 6 weeks of detraining.Methods:Fifty-four female SD rats aged 7 weeks were randomly divided into a no exercise group（CON）,medium intensity continuous training group（MICT）and high intensity interval training group（HIIT）after 8 weeks of high fat feeding.MICT and HIIT groups were subjected to equidistant treadmill exercise（5 days per week）,with MICT exercising at 50%～70%VO_2peak intensity for 45 min and HIIT exercising at 85%～100%VO_2peak intensity for 1 min,50%～70%VO_2peak intensity for 2 min repeatedly.After 10 weeks of training,9 rats in each group were randomly selected to be killed and the other 9 rats were taken after detraining and continuing high-fat diet for 6 weeks.Body weight,mass of soleus and gastrocnemius muscles were measured;the cross-sectional area of skeletal muscle fibers was calculated by HE staining;the triglyceride content of skeletal muscle was measured by GPO-PAP method;the lipid deposition of skeletal muscle was observed by transmission electron microscopy.A3×2 two-way ANOVA was used to analyze the main effects and interaction effects of"training"and"detraining",and the LSD method was used for multiple comparisons after ANOVA.Results:（1）The effect of HIIT/MICT and detraining on body weightThe main effects of"training"and"detraining"on the body weight of rats were highly significant（p<0.01）,and the interaction effect between the two factors was not significant（p>0.05）.The body weight of rats in the HIIT and MICT groups was significantly lower than that in the CON group（p<0.01）,and there was no difference between the two exercise groups（p>0.05）;After 6 weeks of detraining,the body weight of all three groups increased significantly,and there was no difference in the increase of each group.（2）The effects of HIIT/MICT and detraining on skeletal muscle mass and muscle fiber cross-sectional area（1）The main effect of"training"and"detraining"on the soleus muscle mass of rats was highly significant（p<0.01）,while the interaction effect of both factors was not significant（p>0.05）.Soleus muscle mass in the HIIT group was significantly higher than that in the MICT and CON group（p<0.01）.There was no difference between the MICT and CON groups（p>0.05）;After 6 weeks of detraining the soleus muscle mass of rats in all three groups increased significantly,and there was no difference in the increase of each group.（2）The main effect of"training"and"detraining"on the cross-sectional area of rat soleus muscle fibers was highly significant（p<0.05）,and the interaction effect of the two factors was not significant（p>0.05）.The cross-sectional area of soleus muscle fibers in the HIIT and MICT groups was significantly higher than that in the CON group（p<0.01）,and that in the HIIT group was significantly higher than that in the MICT group（p<0.01）;After 6 weeks of detraining,the cross-sectional area of soleus muscle fibers of all three groups increased significantly,and there was no difference in the increase of each group.（3）The main effect of"training"and"detraining"on gastrocnemius muscle mass in rats was not significant（p>0.05）,and the interaction effect of the two factors was not significant（p>0.05）.（4）The main effect of"training"and"detraining"on the cross-sectional area of gastrocnemius muscle fibers in rats was highly significant（p<0.05）,while the interaction effect of both factors was not significant（p>0.05）.The HIIT group was significantly higher than the MICT and CON groups（p<0.01）,and there was no difference between the MICT and CON groups（p>0.05）;After 6 weeks of detraining,the cross-sectional area of gastrocnemius muscle fibers of all three groups increased significantly,and there was no difference in the increase of each group.（3）The effect of HIIT/MICT and detraining on the triglyceride content of skeletal muscle tissueThe main effect of"training"and"detraining"on the triglyceride content of soleus and gastrocnemius muscles of rats was highly significant（p<0.05）,and the interaction effect of the two factors was not significant（p>0.05）.The triglyceride content of soleus muscle and gastrocnemius muscle in HIIT and MICT groups was lower than that in CON group（p<0.01）,and there was no difference between the two exercise groups（p>0.05）;After 6 weeks of detraining,the triglyceride content of soleus muscle and gastrocnemius muscle of all three groups increased significantly,and there was no difference in the increase of each group.Conclusion:1、HIIT increased soleus muscle mass in rats fed a high fat diet,and the effect of HIIT on soleus muscle mass was maintained after 6 weeks of detraining;HIIT and MICT did not affect gastrocnemius muscle mass in rats.2、Both HIIT and MICT inhibited lipid accumulation in soleus and gastri-cnemius muscles caused by high fat diets,and the effects of HIIT and MICT in inhibiting lipid accumulation in soleus and gastrocnemius muscles were maintained after 6 weeks of detraining.