Effects Of Intermittent Fasting And High Intensity Training On Regulators Of Muscle Mass And Metabolism

Abstract

Diet-induced obesity can lead to higher intramuscular fat deposition and inflammatory cell accumulation, ultimately having a negative impact on skeletal muscle morphology and function leading to mitochondrial dysfunction and insulin resistance. Intermittent fasting (IF) and high intensity interval training (HIIT) are both effective strategies for losing weight, specifically fat mass. However, the effects on skeletal muscle, specifically genes that regulate mitochondrial function, energy homeostasis, and muscle atrophy are unknown. PURPOSE: To investigate the effects of IF and/or HIIT on molecular markers of skeletal muscle mass and metabolic function in diet-induced obesity. METHODS: Eight week old mice (C57BL/6, n=39) had ad libitum access to an obesogenic diet (60% fat, 30% sugar) for 12 weeks. They were then randomly allocated to three intervention groups: IF (fasting for 2 alternate days/week), HIIT (3 days/week), combined IF+HIIT (2 alternate fasting days and 3 days HIIT) or control (CON) for a further 12 weeks. Extensor digitorum longus (EDL) muscle weight and expression of PGC1α, AMPK, citrate synthase (CS), muscle atrophy F-box (MAFbx), and muscle RING Finger-1 (MuRF1) genes were measured at the end of the intervention period. Data was analysed using ANOVA. RESULTS: Muscle weights were similar between groups at the end of the intervention period (CON: 9.5±1.3mg, HIIT: 9.2±0.8mg, IF: 9.2±0.4mg, IF+HIIT: 9.7±0.8mg, p>0.05). PGC1α and CS gene expression was significantly lower in the IF group compared to the CON (PGC1α: 0.8±0.1 vs 1.0±0.2, CS: 0.8±0.2 vs 1.0±0.4, p<0.05). AMPK gene expression was also significantly lower in the IF group, but only compared to the IF+HIIT group (0.9±0.1 vs 1.0±0.1, p<0.05). MAFbx and MuRF1 gene expression was significantly higher in the HIIT group (1.7±0.8 & 2.2±0.9) group compared to CON (1.0±0.4 & 1.0±0.2), IF (0.9±0.2 & 0.8±0.2), and IF+HIIT (1.4±0.3 & 0.9±0.2, p<0.01).groups. CONCLUSIONS: Intermittent fasting reduced gene expression markers of mitochondrial biogenesis and energy homeostasis, while HIIT appeared to increase markers of atrophy at the end of the intervention period. The combination of IF and HIIT did not show any synergistic effects within the muscle.