Henneman size Principle

The Henneman Size Principle (Original: “Henneman Size Principle” after the American neurophysiologist Elwood Henneman) describes the cooperation of neurons in the respective motor units. Furthermore, the cooperation of the motor units among each other and each other in the skeletal muscles . Henneman developed the size principle of the same name through special experiments over a period of 25 years. His findings were published in the Journal of Neurophysiology .

The CNS activates the different motor units in a targeted manner, depending on movement and task.Elwood Henneman Recognized this as early as 1957. He Summarized his research results under the “Henneman size principle” named after him. This means that engine units are recruited on the basis of their size.

The Henneman Size Principle


Engine units

A motor nerve not only supplies one single muscle cell (muscle fiber, myofibrils). Rather, muscle cells are always supplied by a nerve in a group – the so-called motor unit. Within a motor unit there is always one child of muscle fiber types .

Small engine units

The nerve of a small motor unit innervates about 200 muscle cells.These consist of slow, fatigue-resistant fibers – the so-called tonic muscle fibers, also known as slow switch fibers. The small engine units are recruited at low force requirements. This results in a small muscle tension.

Large engine units

The nerve of a large motor unit innervates about 2000 muscle cells. These consist of almost, quickly tiring fibers, the so-called phasic muscle fibers, also known as fast-switch fibers. The large engine units are recruited for high strength requirements. This results in a high muscle tension.

How the Henneman Size Principle Works – and how it works is created by this


  • In a contraction the small (tonic, slow-twitch) motor units fire first and cause a small increase in muscle tension.
  • If the contraction becomes stronger, larger (phasic, fast-twitch) motor units are included. Accordingly, muscle tension increases.
  • This allows a controlled, qualitatively finely graded movement to take place.
  • This method results in a fine tuning of small to large movements.

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William C. Hilberg
As an author, Mr. Hilberg has published several papers on health issues that have gained international recognition. He is close to nature and loves the seclusion and activity as a freelance journalist. In his function as editor William C. Hilberg manages the entire content of PENP. Our team greatly appreciates his expertise and is proud to have him on board.