Muscle tension and time under tension are critical for muscle protein synthesis and increases in muscle mass and strength. Skeletal muscle is a highly-reactive tissue that increases in size in response to overload, such as strength training, and atrophies in response to inactivity.
Researchers from the University of Maryland, in a review of literature, summarized the effects of muscle tension and training load on muscle protein synthesis. Mechanical loading (weight training) turns on muscle protein synthesis by activating the mTOR-signaling pathway. Muscle tension also increases the movement of amino acids into muscle cells, which form the building blocks for making new muscle tissue. Muscle tension also activates muscle growth factors, such as IGF-1 to stimulate protein synthesis. Sensors in the muscle cell membranes detect muscle loading, which trigger chemical pathways that make new muscle protein.
Muscle tension, along with the availability of key amino acids and other nutrients and hormones, are key ingredients for promoting muscle growth.