Response of Resistance Exercise-Induced Muscle Protein Synthesis and Skeletal Muscle Hypertrophy Are Not Enhanced After Disuse Muscle Atrophy in Rat

Abstract

Skeletal muscle disuse rapidly decreases muscle mass. Resistance training (RT) is believed as the most effective way to gain muscle mass via an increase in mTORC1 activity and muscle protein synthesis (MPS). However, it remains unclear whether muscle atrophy by disuse alters the mTORC1 activation and MPS response to an acute resistance exercise (RE) and chronic RT-mediated skeletal muscle hypertrophy. This study investigated the influence of disuse muscle atrophy on the response of mTORC1 activation and MPS to an acute RE. We also evaluated whether disuse muscle atrophy affects the response of RT-induced muscle mass gain. Thirty male Sprague-Dawley rats were randomly divided into control (CON) or hindlimb suspension (HS) groups. A 14-day HS via the tail was used as the model for gastrocnemius muscle disuse in the HS group. Unilateral lower limb muscle contraction using by percutaneous electrical stimulation was used to mimic the stimuli of RE. Ten bouts of RE were performed in 3-week as chronic RT. Our results showed that MPS and mTORC1 activity was unchanged after HS at basal state. However, the ribosomal RNA (rRNA) level was reduced in HS rats compared to that in CON rats at basal state. MPS and rRNA increased in both HS and CON rats in response to acute RE to the same extent. However, the level of mTORC1 activation in response to an acute RE was significantly higher in HS than that in the CON group at 12 h after exercise, even though no difference was observed at 3 h after exercise. The 10-bout RT significantly increased gastrocnemius muscle mass in both CON and HS rats. The response of muscle hypertrophy did not differ between the groups. Therefore, MPS in response to acute RE and muscle hypertrophy in response to chronic RT were unaltered after disuse muscle atrophy.

Reversible Effects of Functional Mandibular Lateral Shift on Masticatory Muscles in Growing Rats

“…Muscle atrophy and hypertrophy, in terms of muscle mass and fiber size, occur in response to mechanical stimuli, as shown in past studies that used several in vivo and in vitro experimental models [ 32 , 33 , 34 ]. This study demonstrated the effects of FMLS on the two main masticatory muscles, i.e., MM and TM [ 35 ].…”

Molecular Regulation of Skeletal Muscle Growth and Organelle Biosynthesis: Practical Recommendations for Exercise Training

“…Chronic exercise promotes cellular adaptations leading to improvement of mitochondrial function, reducing oxidative damage and attenuating the rate of skeletal muscle mass decline. A recent study examined the effects of disuse muscle atrophy on mTORC1 activation and muscle protein synthesis during a single bout of resistance training, and whether disuse muscle atrophy could interfere with muscle mass and strength gains after a resistance training protocol [ 247 ]. In this work, a 14-day hindlimb suspension decreased basal rRNA level, but not mTORC1 activity and muscle protein synthesis in rats.…”

“…In this work, a 14-day hindlimb suspension decreased basal rRNA level, but not mTORC1 activity and muscle protein synthesis in rats. Importantly, the response of muscle hypertrophy did not differ between the groups [ 247 ], showing that disuse muscle atrophy does not alter muscle protein synthesis in response to acute resistance exercise and muscle hypertrophy in response to chronic resistance training. Consistent with these data, another study on disuse atrophy showed that intermittent loading with protein ingestion prevents atrophy during hindlimb unloading probably through mTORC1 signaling pathway [ 248 ].…”

Combined effects of functional overload and denervation on skeletal muscle mass and its regulatory proteins in mice

“…Recently, researchers have shown that percutaneous electrical stimulation‐induced muscle contraction partially ameliorated muscle atrophy associated with hindlimb suspension (Kotani et al, 2022 ). In addition, mouse skeletal muscle atrophy associated with hindlimb suspension demonstrated a protein synthesis response to electrical stimulation‐induced resistance exercise after the period of suspension comparable to that of the non‐atrophied muscle (Ato et al, 2020 ). Thus, it is suggested that overload stimulation of skeletal muscle is effective to maintain skeletal muscle mass even during inactivity.…”