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How do muscles grow?

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Quick answer

Muscles grow when exercise creates tiny tears in muscle fibers, and the body repairs them slightly bigger and stronger. With enough protein, rest, and progressively harder training, this repeat-and-rebuild cycle gradually builds muscle size and strength. Hard exercise causes tiny tears in muscle fibers.

Step by step

  1. Hard exercise causes tiny tears in muscle fibers.
  2. The body repairs them thicker and stronger.
  3. Protein supplies the building blocks.
  4. Rest and progressive overload drive growth.

People also ask

How do muscles grow?
Exercise damages muscle fibers slightly; the body repairs them bigger and stronger, given protein and rest.
Why is rest important for muscle growth?
Muscles rebuild during recovery, not during the workout itself, so rest is when growth happens.
Does protein build muscle?
Protein provides the amino acids needed to repair and grow muscle, supporting the process alongside training.

Part of the guide: How Your Body Works →