A medical dictionary will show the following or similar definition:

Muscle tone is a physiological and neurophysiologic phenomenon that gives firmness and proper shape to muscles. The continual firing of ‘motor units’ within a muscle causes muscle tone. Motor unit 'fire' (input and output) is a function of the central nervous system (CNS). Motor units provide muscles with the ability to expand and contract, causing movement or stability in any part of the body, from the small muscles of the eye to the large and powerful leg muscles.

The brain is the source for the transmission or communication, which determines ‘tone’ whether it is ‘high’, Hypertonicity (causing spasticity) or ‘low’, Hypotonia ('soft', ‘floppy’ or ‘squishy’.) There are various degrees of tone in between. The emotional state of an individual can affect muscle tone (i.e. a hypertonic child may experience increased spasticity and a hypotonic child may have a ‘meltdown’ when excited or tantruming.)

When this motor unit ‘fire’ is compromised (too much, too little, or not synchronized) a muscle cannot perform a specific task adequately. Consequently, a child may not have the 'power' to perform what we would consider a simple or routine task (i.e., holding an object or crawling). The muscles may provide enough support for the initial movements of the task then run out of energy to complete the activity. At these times, large muscles will assist the small muscles, or the child may develop other compensation techniques. This can be seen in a child who often leans or slouches, who must prop his or herself to do writing tasks, or whose entire upper body becomes tense while writing. Children with low tone often present over extended finger joints when holding a pencil or pen, and hold the item with a very powerful grip. When writing they may push excessively hard, or so light the print can barely be seen, because the feedback or input from their fingers and hand is compromised.

Low muscle tone impairs the sense of touch in respect to how or where to move the body; this causes motor planning and body awareness problems. In the classroom, their written work will look fine at the start and then quickly deteriorate, often looking as though a different child completed the document. This is due to the quick fatigue of the muscles.

Hyperextension of the joints or joint instability is a result of low muscle tone. Resistance to applied pressure is minimal. This can cause injuries during games and sports activities. They will tire more quickly, and recover more slowly than children with normal tone.

Muscle tone cannot be changed by intervention; it is a function of the Central Nervous System. However, strength and endurance can be increased over time and with consistent regular activity. Children with low muscle tone learn compensation techniques and most are able to achieve skills commensurate to their IQ or age level.

Although there is no 'cure' for low tone, staying physically fit is critical to the function of low tone children. It gives them the best possible opportunity for normal function. When an OT identifies a child with low tone, daily exercise is usually suggested for the child's optimal performance. However, care providers must be cautioned, just as it is true of other physiological developments, each human has his or her own time line. We can not make the mustache grow sooner, change the height, or hormonal development of a body, nor can we ‘cure’ a child with low tone by pushing them beyond their limits.