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This study aimed to evaluate the influence of combined intermittent fasting (IF) and high-intensity interval training (HIIT) on morphology, caspase-independent apoptosis signaling pathway, and myostatin expression in soleus and gastrocnemius (white portion) muscles from healthy rats. Sixty-day-old male Wistar rats (n = 60) were divided into four groups: control (C), IF, high-intensity-interval training (T), and high-intensity-interval training and intermittent fasting (T-IF). The C and T groups received ad libitum chow daily; IF and T-IF received the same standard chow every other day. Animals from T and T-IF underwent a HIIT protocol five times a week for 12 weeks. IF reduced gastrocnemius mass and increased pro-apoptotic proteins apoptosis-inducing factor (AIF) and endonuclease G (EndoG) in soleus and cleaved-to-non-cleaved PARP-1 ratio and myostatin expression in gastrocnemius white portion. HIIT increased AIF and apoptosis repressor with caspase recruitment domain expression in soleus and cleaved-to-total PARP-1 ratio in gastrocnemius muscle white portion. The combination of IF and HIIT reduced fiber cross-sectional area in both muscles, increased EndoG and AIF expression, and decreased cleaved-to-non-cleaved PARP-1 ratio in gastrocnemius muscle white portion. Muscle responses to IF and HIIT are directly impacted by the muscle fiber type composition and are modulated, at least in part, by myostatin and caspase-independent apoptosis signaling., (© 2024 The Author(s). Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Creatine has been used to maximize resistance training effects on skeletal muscles, including muscle hypertrophy and fiber type changes. This study aimed to evaluate the impact of creatine supplementation on the myostatin pathway and myosin heavy chain (MyHC) isoforms in the slow- and fast-twitch muscles of resistance-trained rats. Twenty-eight male Wistar rats were divided into four groups: a sedentary control (Cc), sedentary creatine supplementation (Cr), resistance training (Tc), and resistance training combined with creatine supplementation (Tcr). Cc and Tc received standard commercial chow; Cr and Tcr received a 2% creatine-supplemented diet. Tc and Tcr performed a resistance training protocol on a ladder for 12 weeks. Morphology, MyHC isoforms, myostatin, follistatin, and ActRIIB protein expressions were analyzed in soleus and white gastrocnemius portion samples. The results were analyzed using two-way ANOVA and Tukey's test. Tc and Tcr exhibited higher performance than their control counterparts. Resistance training increased the ratio between muscle and body weight, the cross-sectional area, as well as the interstitial collagen fraction. Resistance training alone increased MyHC IIx and follistatin while reducing myostatin ( p < 0.001) and ActRIIB ( p = 0.040) expressions in the gastrocnemius. Resistance training induced skeletal muscle hypertrophy and interstitial remodeling, which are more evident in the gastrocnemius muscle. The effects were not impacted by creatine supplementation.