The number of muscle fibers in a motor unit varies from effector to effector. In the hand and eye, fewer than 100 muscle fibers occupy a motor unit; in the lower leg, a single motor unit may contain as many as 1,000 muscle fibers (Buchthal & Schmalbruch, 1980).

How many muscle fibers do small motor units have?

The smallest motor units are in muscles that must produce very fine gradations of force: lumbricals: 100 fibers/unit.

How many muscles does a motor unit have?

For example, a motor unit in the soleus (a muscle important for posture that comprises mostly small, slow units) has an average innervation ratio of 180 muscle fibers for each motor neuron.