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Training

Size Principle

Motor units are recruited from smallest to largest as force demands increase.

The size principle (Henneman's size principle) states that motor units are recruited in order from smallest to largest based on force requirements. Low-force activities use only small motor units; high-force activities recruit progressively larger units. This is why heavy training is needed to fully recruit and train all motor units, including high-threshold ones.

Examples

  • Walking uses small motor units
  • Maximal lifts recruit all motor units
  • Why heavy training builds strength

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