Training Dictionary
Motor Unit
Definition: A motor unit consists of a motor neuron and the muscle fibers it innervates.
In general, each motor unit consists of only one type of muscle fiber, either fast twitch or slow twitch. When a motor unit is signalled to contract, it is completely activate or completely inactive. 1
The number of muscles in a motor unit range from a few in delicate movements as seen in the control of the eyeball to thousands as seen in the large muscles in the leg. When a motor unit recieves a signal, all the muscle fibers connected to the motor unit contract.2
An expanded view including a network of motor units would include many light bulbs, each hooked up to a different circuit. Each motor unit contracts in a coordinated pattern and in a sequential order. Learning this information is vital for undertanding the size principal.
Each motor unit contracts in a coordinated pattern and in a sequential order. Learning this information is vital for undertanding the size principal.
Sources:
1 American College of Sports Medicine,2006. ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription. 5th Edition. Lippincott Williams & Wilkens, Philadelphia: 60-61 pp.
2Nicholls, Martin, Wallace, & Fuchs, 2001. From Neuron to Brain. 4th Edition. Sinauer Associates, Sunderland, MA 449 p.
