Abstract
Skeletal muscle fibers have a unique capacity to adjust their metabolism and phenotype in response to alternations in mechanical loading. Indeed, chronic mechanical loading leads to an increase in skeletal muscle mass, while prolonged mechanical unloading results in a significant decrease in muscle mass (muscle atrophy). The maintenance of skeletal muscle mass is dependent on the balance between rates of muscle protein synthesis and breakdown. While molecular mechanisms regulating protein synthesis during mechanical unloading have been relatively well studied, signaling events implicated in protein turnover during skeletal muscle recovery from unloading are poorly defined. A better understanding of the molecular events that underpin muscle mass recovery following disuse-induced atrophy is of significant importance for both clinical and space medicine. This review focuses on the molecular mechanisms that may be involved in the activation of protein synthesis and subsequent restoration of muscle mass after a period of mechanical unloading. In addition, the efficiency of strategies proposed to improve muscle protein gain during recovery is also discussed.
Highlights
Skeletal muscles play fundamental roles in the human body, including locomotion, posture maintenance, generating heat, venous blood flow, and breathing control
Recovery of wet skeletal muscle mass is normally complete after 14 days of reloading following 14-day mechanical unloading [103,104,105,106], whereas processes related to fiber cross-sectional area (CSA) recovery after prolonged hindlimb unloading (HU) can extend up to 5 weeks [107]
Over the past decade considerable progress has been made in our comprehending the molecular mechanisms underlying the recovery of skeletal muscle mass following a period of disuse/mechanical unloading
Summary
Skeletal muscles play fundamental roles in the human body, including locomotion, posture maintenance, generating heat, venous blood flow, and breathing control. The most important event in the process of skeletal muscle recovery from unloading is the upregulation of anabolic processes followed by an increase in muscle mass and subsequent recovery of muscle performance In this regard, it is very important to understand the changes in the activity of key intracellular signaling pathways that regulate protein synthesis in skeletal muscle. It is known that after an eccentric load, there is a sharp activation of anabolic signaling in skeletal muscles fibers [22,23,24], it can be assumed that during the initial period of reloading, components of the mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling system may be involved, leading to an increase in the rate of protein synthesis. The efficiency of strategies proposed to improve muscle protein gain during recovery is discussed
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