Henneman's size principle

Henneman's Size Principle (also known as the size principle) is a neurophysiological postulate proposed by Elwood Henneman and his colleagues in the late 1950s. It describes the recruitment order of motor units in response to increasing strength of voluntary muscle contractions.

Overview

The size principle states that motor units are recruited in a fixed order from smallest to largest. This is due to the different threshold levels of motor neurons. Smaller motor neurons have lower threshold levels and are therefore recruited first. Larger motor neurons have higher threshold levels and are recruited as the force requirement of the muscle increases.

Implications

The size principle has significant implications for motor control, muscle fatigue, and physical therapy. It helps to explain why fine motor tasks can be performed without fatigue for extended periods, while larger, more forceful movements result in rapid fatigue.

Criticisms and Limitations

While the size principle is widely accepted, it is not without its criticisms and limitations. Some researchers argue that the principle is too simplistic and does not account for the complexity of motor unit recruitment in real-world tasks.

See Also

• Motor unit
• Motor neuron
• Neuromuscular junction
• Muscle contraction