We’ve been playing hide and seek with the topic of muscle tone for a lot of years; I even had one instructor who refused to discuss the topic of tone because we couldn’t agree on a definition.  I don’t recommend that approach, but I certainly understand her frustration.  So I read with interest a recent research article that discussed muscle tone in children with CP (1).  This study confirmed that it was difficult to distinguish clinically between spasticity and passive muscle stiffness.  This is absolutely what we see as clinicians.

Personally, I think that there are at least 3 components of muscle tone: the neurological component, the mechanical component and the dynamic holding component.

The neurological component is the spasticity piece of the puzzle.  The mechanical component is the passive stiffness that develops as a result of the decreased active contraction/relaxation of the muscle.   Finally, there is the dynamic holding component.  We know that our clients learn to use their muscles in any way they can for function.  The children learn to use their spasticity and/or stiffness to create stability.  This active recruitment of the spastic/stiff muscle is dynamic holding.  It is also the component that can change dramatically as our clients develop central stability strategies.  As their central stability improves, their need to actively hold distally decreases and the dynamic holding decreases. And as dynamic holding decreases, so does some of the mechanical stiffness in those muscles.  We haven’t changed the neurological component but muscle tone as a whole can change.

As Physical Therapists we are constantly assessing postural control and movement throughout our sessions.  We are uniquely positioned to provide information and education to parents and physicians about how a child moves, why they move the way they do and the impact of certain interventions for each child.  The more we have conversations about muscle tone, its complexity and its interaction with movement, the more it will lead to better care for our clients.

PRACTICAL APP:

Make note of which muscles you consider as having the most muscle tone in your client.  As you watch that child in function, notice which of those muscles are working hardest for stability. Then try to gently change the alignment so that the muscle working hardest is in a slightly lengthened range. If that muscle relaxes with a change in alignment then there is a dynamic holding component to the muscle tone.

1.  Willerslev-Olsen M, Kirebtzeb H, Sinkaer T, Nielsen JB.  The muscle properties are altered in children with cerebral palsy before the age of 3 years and are difficult to distinguish from spasticity.  Dev Med Child Neurol.  2013; DOI: 10.1111/dmcn.12124

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