The term muscle tone refers to two aspects of muscles' structure and function:
- The inherent stiffness of a muscle - its resistance to being stretched and firmness when palpated (squeezed).
- A muscle's (or groups of muscles') readiness for action - the muscle's responsiveness to signals from the brain and to sensory feedback.
The term low muscle tone is used when the muscles' stiffness is less than usual (ie it is low) and the readiness for action is also low (muscles respond slowly).
How is a muscle's firmness (tone) tested?
The clinician may make a judgment about a muscle's firmness and inherent stiffness by:
- Squeezing the muscle to feel the resistance to compression
- Lifting up and moving the limbs and feeling the resistance to this movement
The trouble with these tests is that they are not reliable and do not provide any useful information.
What determines a muscle's firmness?
The firmness of a muscle is determined by its inherent stiffness and this in turn depends on the stiffness in the connective tissue sheaths that encase each muscle fiber, hold the bundles of muscle fibers together and connects the muscle to the tendons.
In children with hypermobile joints the connective tissue is less stiff than usual. (It has more give and is more easily stretched).
This tendency for less stiff connective tissue which results in hypermobile (lax) muscles and joints is genetically determined. About 10-15% of people are hypermobile.
The other very important structure that that determines a muscle's firmness and resistance to being stretched is the giant molecule titin.
Titin is a very large elastic molecule found within the muscle cell. The size and strength of the titin molecules is determined by the amount of work a muscle is made to do on a regular basis. Strong muscles have larger and stiffer titin molecules - and this makes the muscle firmer and stiffer. The muscle has better tone.
Generally speaking, strong muscles are firmer and have better tone. It is a common fallacy that you can have strong muscles which are also "low toned". Strengthening a muscle makes it firmer and changes the form of the titin which is component of a muscle fiber which provides the tension and recoil in the muscle.
Strong muscles always have good "tone"
There is a common misconception that a muscle can be strong and low toned. This is not correct. Strengthening a muscle increases it resistance to being lengthened and readiness for action. The elastic muscle protein titin increases in size with training - this makes the muscle less resistant to being lengthened (stretched) and increases its stiffness. Training also increases the strength of the connective tissue components of the muscle as well as the strength and stiffness of the tendons.
Muscle tone, alertness and readiness for action
The term muscle tone is also used to describe the a muscle's readiness for action. This is set by the child's alertness, general level of arousal and readiness for action.
The brain primes the muscles for action by sending signals to the muscles’ sensory receptors. In effect the sensory receptors become more alert and provide more effective sensory feedback and respond more quickly. This allows for the rapid adjustments needed for maintaining balance and postural stability.
- When a child is alert and engaged, the muscles are primed for action. The muscle tone is good and the posture is erect.
- When a child is over-aroused, the muscles may become twitchy and overactive. This makes the child less able to focus attention on a task.
- If a child is anxious, finds a task difficult and is having trouble focusing his attention, the normal alertness for action signals do not reach the muscles. They become less responsive and provide less sensory feedback. Muscle tone is lowered and the child's posture becomes less erect and alert..
SfA Fitness and Coordination Training Guide
All the information you need to be your child's coach and advocate
Subscribe here for $20
Disclaimer The content on this site is provided for general information purposes only and does not constitute professional advice. All liability is excluded to the fullest extent permitted by law in respect of any loss or damage whether direct, indirect or consequential that arises in connection with the use of or reliance upon any content forming part of this site.
