As muscles grow larger, the same weight used in training applies less force to individual molecular components called titin, which may reduce the signal that tells the muscle to keep growing. To...
Mechanism
Synthesis from 1 study
Lifting weights pulls on a special protein in your muscles called titin, which turns on a signal that tells your muscle to build more protein-making machines. More machines mean bigger muscles over time. But as your muscles get bigger, the same weight pulls less on each titin, so the signal weakens...
Most probable mechanism
When you lift weights, the muscle fibers stretch and pull on a giant protein called titin. This pull activates a part of titin that starts a chain reaction inside the muscle cell, leading to more protein-making machines (ribosomes) being built. More ribosomes mean more muscle proteins are made over time, making the muscle bigger. But as the muscle gets bigger, the same weight pulls less hard on each titin molecule, so the signal gets weaker — you need to lift heavier to keep the signal strong and keep growing.
Mechanical tension during muscle contraction stretches titin, applying force to its kinase domain at the M-band of the sarcomere
Force induces a conformational change in the titin kinase domain from a closed to an open state, enabling ATP-dependent phosphorylation
Phosphorylated titin kinase recruits nbr1 to form a signaling complex that activates serum response factor (SRF)
SRF activation increases transcription of genes involved in ribosome biogenesis
Increased ribosome density overcomes steric hindrance from the myofilament lattice, enabling sustained synthesis of sarcomeric proteins
Accumulation of sarcomeric proteins increases myofibrillar cross-sectional area, resulting in muscle hypertrophy
As muscle size increases, the same absolute load reduces force per titin molecule, diminishing the mechanosensory signal amplitude
Evidence from Studies
Supporting (1)
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Why exercise builds muscles: titin mechanosensing controls skeletal muscle growth under load
Contradicting (0)
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