Altered muscle tone is a common problem that wheelchair prescribers face when assessing for wheelchairs and seating. Altered muscle tone can negatively impact function and affect the way a user interacts with their wheelchair equipment.
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What Is Muscle Tone?
A state of tension that is maintained continuously - minimally - even when relaxed - and which increases in resistance to passive stretch.
Dictionary of Sports and Exercise Science (2008)
We need normal muscle tone for postural stability as muscles work in surrounding joints to stabilize body segments to enable function. This tone enables us to maintain certain positions for longer periods without fatigue. When we increase the muscle tone by activating or contracting those muscles either side of a joint (co-contraction), we can achieve greater stabilization.
Low Muscle Tone
Reduced muscle tone is also known as hypotonia and can occur in two ways. Either as a congential condition (e.g. benign congential hypotonia) or more commonly, it is seen as a generalized symptom in cerebral palsy, muscular dystrophy, or spinal muscular atrophy. The person can appear 'floppy' and unable to maintain an upright functional seated position. Individuals with low tone require seating that offers greater support of body segments:
- Seat cushions - greater contouring or use of positional components to increase stability (e.g. medial, lateral knee guides, and hip guides).
- Back supports - often require lateral thoracic support commonly placed symmetrically as no compensatory scoliosis is present.
- Tilt in space is a feature that is commonly employed for wheelchair users to assist with low tone, as tilting the user backwards allows gravity to assist rather than decrease postural stability.
High Muscle Tone
Elevated or increased muscle tone limits joint movement and is characterized by muscles that are stiff and difficult to move. It occurs when there is overload of signals to the muscles and can occur when the brain or spinal cord have been damaged. It is also known as hypertonacity or hypertonia. There are two types: spastic and rigid hypertonia. In spasticity, the tone increases with increased speed and movement of a limb through the joint range and is felt as increased resistance as the limb is extended or straightened. This is common with cerebral palsy and acquired brain injuries. Rigidity is increased muscle tone that is not dependent on direction or speed of movement. Commonly the limb is extremely difficult to move and common in conditions such as acquired or traumatic brain injury or Parkinson's disease.
- Seat cushions need to have variable contouring that can match the user's leg and pelvic position and be changed in response to altered body position due to an increase in hypertonacity.
- Back supports need to not only have options of contact surfaces to meet an individual's specific needs, but also have lateral thoracic supports that can be symmetrically or asymmetrically placed.
Some users can present with mixed tonal patterns and this can prove challenging for the prescriber as scoliosis and pelvic asymmetry are common. Cerebral palsy is the most common condition where this occurs and requires seat cushions to be able to accommodate abnormal pelvic position but also offer increased postural support.
Having a complete understanding of your client's medical history and current postural presentation, including muscle and the type(s), is a vital piece of the evaluation and equipment provision process. As mentioned above, there are various techniques that can be utilized to address different types of muscle tone. Be sure to explore the options of wheelchair cushions, backs, and frames in the Sunrise Medical family of brands for examples of equipment to meet the needs of your clients.
Matt Eveleigh is an Occupational Therapist from the United Kingdom. He has worked for Sunrise Medical since 2013 and his current role is as a European Power Product, Market and Training Manager within the European Product Management Team. Prior to this, Matt was the Clinical Specialist, STEPS Clinical Educator, and JAY Product Specialist for the UK and Éire. He is a Clinical Specialist Occupational Therapist by background and has specialized in wheelchairs and seating for over 15 years.