Spasticity is one of the most controversial and poorly defined terms in neurology, but forms one aspect of hypertonia, or high tone, which are commonly present of injury to the central nervous system.
To begin to understand spasticity, first we must know about normal muscle tone. The muscles in your body are made up of thousands and thousands of individuals muscle fibres, which are called into action via messages from the brain and spinal column. When you’re at rest your muscles still have a little bit of background activity happening – this is muscle tone and it serves to keep your body ready for movement. Tone is a continuous trait and muscle tone can range from very low to very high, with a broad spectrum of what is considered normal. When muscle tone if low, usually to the point that it interferes with function it is called hypotonia, and when it is too high it is called hypertonia. Spasticity is one form of hypertonia, along with other features such as spasms, clonus, dystonia, and rigidity.
The most commonly used definition of spasticity was determined by Lance in 1980, and describes spasticity as:
“A motor disorder characterised by a velocity dependent increase in tonic stretch reflexes (muscle tone) and increased tendon jerks resulting from disinhibition of the stretch reflex, as one component of the upper motor neurone lesion”.
This means that the muscle becomes very active in response to it being moved quickly, but is less active when moved slowly. It is still unclear exactly how spasticity is caused. The central nervous system uses a variety of very complex pathways to modulate muscle tone and activity and how it responds to various stimulus. Based on what we currently know about the pathways involved in spasticity, a newer definition by a group called SPASM is more accurate, but less specific:
“Disordered sensori-motor control, resulting from an upper motor neuron lesion, presenting as intermittent or sustained involuntary activation of muscles”.
Because of the wide variations in the understanding and definitions of spasticity amongst healthcare professionals, it’s really important to be specific about what features are used to define spasticity. Some research shows that people who have been clinically diagnosed as having spasticity actually don’t have spasticity at all, but instead have an increase in passive muscle stiffness, which is entirely different. It’s important to make this distinction as medication used to treat spasticity (such as baclofen) only work on the hyper-active stretch reflex, but will not influence passive muscle resistance.
Spasticity has long been considered the main limitation on function in people with neurological conditions of the central nervous system such as stroke, MS, HSP and brain injury, however research is now showing this is not the case. Weakness is the biggest predictor of loss of function after stroke. In the past, strength training regimes have been avoided in those with spasticity, as they were believed to increase spasticity. Research in the last 20 years has shown that this is not the case and strength training does does not increase spasticity, it actually more likely to improve underlying muscle strength and improve spasticity.
If you feel that you have spasticity and are finding it difficult to manage, please call us. We are specialists in determining the right way to improve not just your spasticity, but your entire muscle function.