Setting the tone

Chris Smith explains muscle tone.

What is Cerebral Palsy?

There are many definitions for cerebral palsy. One of the most useful definitions for me is that it’s a physical injury to the developing brain that occurs before, during or shortly after birth. Cerebral palsy is not a genetic condition, it is acquired through an injury to the brain. There are many ways such an injury can occur, such as a bleed in the brain, a car accident or a lack of oxygen during birth. In a child with cerebral palsy the brain injury doesn’t increase with time. However, it often impacts on further development so that the effect of the injury is not unchanging, it ripples throughout the child’s further development.

What is muscle tone?

Most caregivers of children with cerebral palsy are familiar with the language around muscle tone, having had several years of reports from paediatricians, orthopaedic surgeons, physiotherapists and other professional reports describing their child’s condition. However, when I speak with families, they are often familiar with the terms but not the actual meaning. In order to be specific, professional medical language can be a lot of jargon and not easy to understand for many caregivers. Many can quote terms such as spasticity, dystonia or hypertonicity but many don’t understand how this presents and specifically impacts onto their child’s movement disorder.

Children with cerebral palsy don’t drop into neat categories, most have a range of challenges associated with their brain injury which is not just difficulty with movement. Many children will have issues around swallowing or speech, understanding and communicating their needs. This is often specific to the nature, size and location of the brain injury. These physical, sensory, emotional and cognitive difficulties often impact a child’s ability to perform activities of daily living (ADLs) and subsequently how they participate in society as a whole.

When it comes to describing the way children with cerebral palsy move, professionals will often refer to some of these characteristics. Such as hypertonicity (high muscle tone), hypotonia (low muscle tone), spasticity (difficulty moving a joint quickly) or dystonia (movement that happens on its own).

These are often associated with injury to specific parts of the brain relating to the injury. It might be useful to clarify these terms by first starting to talk about typical muscle tone.

So, what is ‘typical muscle tone’?

This term has been widely used within the fitness industry and in a way, has made it difficult for parents to relate it to their child. Firstly, muscle tone has nothing to do with how strong “Children with cerebral palsy don’t drop into neat categories” or weak you are but is all about how ready you and your body are to move, the resting tonus or tone. In a typically developed individual our brain and body work together to get the muscles to put in just the right amount of effort to maintain our posture or move as we wish. This coordination of brain and body provides the correct muscle tone for the movement. Both the front and back muscles of each joint work reciprocally to ensure that one side lengthens and the other shortens. We call this reciprocal innervation and the amazing thing is that we don’t even have to think about it as it’s automatic.

For example, if we are standing on one leg, the supporting limb joints are working harder, so the brain/body recognises this and increases the muscle tone around those joints. This isn’t hypertonicity, it’s simply the body responding to increased demand for stability. Alternatively, if a person is laid on the floor the body doesn’t require such a high level of muscle tone and so reduces it significantly. Again, this isn’t hypotonicity this is the brain/body responding appropriately to the demand, which is less.

What are the effects of less movement?

An individual without a brain injury is able to move and quickly change their muscle tone automatically in response to need. This is often not the case for children with cerebral palsy as the brain injury causes excessive co-contraction of muscles which prevents movement. This results in less movement, less activity. The knock-on effect from this is the child develops learned disuse and muscle weakness. We all need a little bit of success to motivate us to learn and this becomes difficult to achieve for a child with cerebral palsy. Movement opportunities need to be carefully developed often with the support of a physiotherapist. A typical 18 month’ old child will walk over 2300 steps a day (Adolf et al, 2012), but a child with cerebral palsy misses a lot of this movement practice and it’s the role of a Physiotherapist to help address this.

What are hypertonia and hypotonia?

These terms often refer to the underlying state of the muscle tone. Hypertonia means the resting tone is higher than it needs to be and so movement is stiff and difficult to achieve. Hypotonia means the resting muscle tone is lower, so it can be hard to recruit enough effort to move and as a result the joints can struggle to keep their position and be very floppy.

What are spasticity and dystonia?

Parents and new therapists alike often tell me that they struggle to tell the difference between spasticity and dystonia. They are very different in terms of the location of the brain injury but they both can prevent the muscles moving in a typical way. Dystonia is involuntary movement, and it is something that you will see, with the child moving in a way which is not effective. Spasticity is something that you will feel. Spasticity is an exaggerated response to a stretch and is speed dependent, in as much as when you try to move the muscles around the joint they will stop at a certain point. This is often called the ‘catch’. In the foot it is often possible to move the toes up slowly but with increased speed you feel the catch preventing movement. This is a particular problem in function when walking as the foot swings through it moves from toes down to toes up quickly and so spasticity prevents the foot coming down and heel touching the ground first.

Muscle strength – ‘My child has cerebral palsy but is strong and I can’t move his legs apart when standing.’

A common misconception is that some children with cerebral palsy have strong muscles. Muscle weakness has long been identified as one of the key features of Cerebral Palsy. When caregivers perceive their child as strong it is often when they are trying to move the child. This can be explained by a child presenting with either spasticity or general hypertonia which makes it difficult for the child to be moved due to the excessive co-contraction discussed earlier.

What’s the best way I can help my child learn to move?

The great news is that children learn movement and pretty much anything else faster than adults. Progress can be made by getting your child’s muscles stronger and practising activities.

We learn best by doing fun things that have meaning to us, repeatedly. Try to make any exercises engaging, functional and have a muscle strengthening component. It is possible to make great progress with the support of your child’s rehabilitation team.