How do muscles grow, and is it really from damage?
Muscles mostly grow by enlarging the cells they already have rather than by making new ones, and the old idea that tiny tears drive it is now doubted.
βΆ Start the storyMuscles grow mainly by making each existing muscle cell bigger, not by adding new cells. Scientists call this muscle : an increase in the size of skeletal muscle through growth in the size of its component cells. Inside each fibre, extra contractile proteins appear to be added to the existing , the chains of sarcomeres that do the pulling. There seems to be a limit to how large a myofibril can become, and at some point it splits.
What triggers this? The theory researchers currently accept is mechanical tension, set off by what is called , the practice of gradually asking a muscle to do more. Tension is known to switch on pathways such as mTOR, which is responsible for , and building protein is a mechanism that directly contributes to growth. The precise mechanisms, though, are not clearly understood.
Step 1:
A muscle is asked to do progressively more
Step 2: Mechanical tension
Tension activates pathways such as mTOR
Step 3:
More contractile proteins are made
Step 4: Bigger cells
Existing muscle cells grow larger
You may have heard that muscles grow because training tears them and they rebuild bigger. That is one theory: the body responds to by overcompensating, replacing damaged tissue and adding more. But more recent research has cast doubt on it. Microtrauma does occur, yet it correlates poorly with how much a muscle grows, and muscle damage itself does not appear to be the primary driver. In one study, was not directed to growth until the damage subsided.
There is also a surprise about strength. Most strength progression is largely due to neural adaptations, meaning the nervous system learns to recruit and fire the muscle more efficiently, and the muscle tissue itself expands after that initial period. So a person can get stronger before the muscle looks any bigger.
Genes matter too. A twin study estimated that about 53 percent of the variance in lean body mass is heritable.
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Recap
Muscles grow by enlarging cells, not adding them, and mechanical tension, not damage, is the accepted driver.
π‘ A trick to remember it Β· Think of inflating a balloon rather than buying more balloons: the same muscle cells just get bigger.
Surprising fact Β· Microtrauma correlates poorly with how much a muscle grows.
Sources (1)
No source, no claim. Every fact in this lesson (17 claims) cites at least one of these.