Effects of Exercise Sequence and Circadian Rhythms on Molecular Mechanisms of Muscle Hypertrophy and Mitochondrial Biogenesis in Obese Rat

PURPOSE: This study aimed to investigate whether endurance and resistance training sequences and circadian rhythms affect muscle hypertrophy and mitochondrial biogenesis-related molecules in obese rats.METHODS: Rats were randomly divided into five groups: the obesity control group (OCG), aerobic-resistance exercise in the morning group (ARMG), resistance-aerobic exercise in the morning group (RAMG), aerobic resistance exercise in the evening group (AREG), and resistance-aerobic exercise in the evening group (RAEG). The exercise groups performed endurance and resistance exercises for 8 weeks according to their circadian rhythms and exercise sequences.RESULTS: We evaluated specific muscle hypertrophy and mitochondrial biogenesis markers in the flexor pollicis longus and soleus muscles using western blot and immunofluorescence techniques. The body weight was significantly decreased in the ARMG, RAMG, AREG, RAEG compared to the OCG after intervention. The soleus muscle fiber cross-sectional area and muscle hypertrophy markers p-Akt and p-mTOR were significantly increased in the AREG group compared with those in the OCG, ARMG, RAMG, and RAEG groups after exercise intervention. Most mitochondrial biogenesis-related markers were significantly increased in the RAMG group than in the other groups after exercise intervention.CONCLUSION: Our findings provide new evidence that muscle hypertrophy might be upregulated by resistance exercise after evening endurance exercise. In addition, morning resistance exercise followed by aerobic exercise, might promote mitochondrial biogenesis.