The mechanisms of increased insulin sensitivity in rat skeletal muscle following low-intensity prolonged exercise

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Exercise increases insulin sensitivity of glucose uptake in skeletal muscles. However, the constituent (duration, intensity, volume) of exercise which determines post-exercise insulin sensitivity is uncertain. The mechanism(s) of exercise-induced increase in muscle insulin sensitivity is also not clear.We examined the effects of low-intensity prolonged swimming (LIS; 3h) or high-intensity short-term swimming (HIS; 160 sec) on rat fast-twitch epitrochlearis muscle. Although both LIS and HIS increased muscle insulin sensitivity as compared with resting control, LIS which intensity (50% VO2max) is around lactate threshold increased muscle insulin sensitivity to higher level than HIS which intensity (140% VO2max) is far above lactate threshold. Thus, it is suggested that total volume of exercise is important determinant of post-exercise insulin sensitivity.Furthermore, in our present study, we exercised rats for 90-360min by treadmill at 6m/min or 9m/min and examined post-exercise insulin … More sensitivity in slow-twitch soleus muscle. The intensity of these treadmill walking is less than lactate threshold. Treadmill walking at 9m/min, but not at 6m/min, enhanced insulin sensitivity in rat slow-twitch soleus muscle. Thus, very low-intensity exercise which intensity is less than lactate threshold can increase muscle insulin sensitivity. However, it is probable that minimum exercise intensity is required for increasing post-exercise insulin sensitivity in rat slow-twitch soleus muscle.In our present study, LIS but not HIS increased Sirt1 mRNA expression in rat epitrochlearis muscle. Therefore, it is likely that Sirt1 gene expression in skeletal muscle increases in accordance with the increase in exercise volume. Since Sirt1 is known to regulate muscle insulin signaling, it is possible that LIS-induced enhancement of muscle insulin sensitivity is mediated by increased Sirt1 gene expression. Furthermore, we found that increased gene expression of Sirt1 occurred in skeletal muscles recruited during exercise. Thus, exercise-induced increase in Sirt1 gene expression is mainly due to muscle contractile activity. Less