Low Muscle Tone
What is low muscle tone?
Muscle tone is the tension/tightness provided by your muscles when they are relaxed. It can also be thought of as the amount of resistance to movement a muscle has. Muscle tone helps muscles contract and work to move the body. Low muscle tone (also known as hypotonia) means that there is decreased tension and resistance to movement provided by the muscles in the body. Babies and children with low muscle tone require more effort to activate their muscles compared to a child with normal muscle tone.
The Muscle Tone Spectrum
Muscle tone exists on a spectrum ranging from severe low tone to severe high tone. Severe low tone means that muscles have minimal tension and require a great deal of effort to contract. Severe high muscle tone is when muscles have extremely high levels of tension and tightness. Muscles with high tone are also difficult to contract efficiently due to their high resistance to movement. Muscles with normal levels of muscle tone have moderate tension and resistance to movement, leading to efficient and easier muscle contractions when compared to muscles with low or high tone. Muscle tone that is considered normal also has both a low-normal end and a high-normal end.
Causes of Low Muscle Tone
Low muscle tone may be due to hundreds of different medical conditions and syndromes. These conditions include diagnoses such as Down Syndrome, Cerebral Palsy, chromosomal abnormalities, and many more. Low muscle tone can also occur without any known underlying condition. This is called Benign Congenital Hypotonia. Additionally, babies born prematurely are more likely to have low muscle tone than babies born full term.
Low Muscle Tone and Muscle Strength
Low muscle tone does not equal low muscle strength. Low muscle tone often means that it is harder to contract muscles from rest, but a child with low muscle tone can still have strong muscles. Muscle tone is the resistance to movement, whereas muscle strength is the ability to generate a force against resistance. A child can have strong muscles, but may have low tone and have a harder time activating those muscles to perform a muscle contraction. Once a child with low tone activates their muscles to start a motion, they can still have good strength during that motion. Since it is harder to activate muscles and move, babies and children with low muscle tone often do have muscle weakness because they don't move around as much as children with normal muscle tone, but they can gain strength with intervention.
Signs and Symptoms of Low Muscle Tone
The signs and symptoms of hypotonia vary based on severity and a child's age, but you may notice the following:
Poor head control
Difficulty with tummy time, rolling, and other motor milestones
Delayed gross and fine motor skills
Difficulty with swallowing and feeding
Difficulty initiating complex movements
Interventions for Low Muscle Tone
Babies and children with low muscle tone often benefit from physical, occupational, and/or speech therapy based on their presentation and developmental milestones. Physical and occupational therapy will often focus on strengthening and stabilization activities for the whole body, along with working on age-appropriate motor milestones. If needed, speech therapy may address any issues with feeding, swallowing, or speech production.
A common finding in both babies and children with low muscle tone is core weakness and difficulty properly activating core muscles during activities. A few core strength/activation activities a physical or occupational therapist may work on are: bouncing and perturbations on an exercise ball, baby/normal planks, pull-to-sit/sit-ups, and animal walks that work the core such as bear and crab walking.
Children with more severe low muscle tone may also benefit from pre- or custom-made orthotics to help support their feet and legs in proper alignment.
Prognosis for a Child Diagnosed with Low Muscle Tone
Low muscle tone is a condition a child will have for life; they do not grow out of it as they get older. With the appropriate interventions, babies and children with low muscle tone can improve their strength, endurance, muscle activation, stabilization, and motor milestones. Depending on severity and cause of low muscle tone, one child may be able to catch up with their peers and complete age-appropriate activities, while a different child may remain delayed compared to their peers. A child's hypotonia may appear to improve and become less apparent as they get older, stronger, and learn to coordinate their body more, but they will still have underlying low muscle tone. However, with extra work and therapy, a child with low muscle tone can still live a meaningful life full of activity!
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2. Aculbertson. How To Explain Hypotonia With A Rubber Band. Surestep. https://surestep.net/blog/hypotonia-with-a-rubber-band/. Published 2018. Accessed August 19, 2021.
3. Palisano R, Orlin M, Schreiber J. Campbell's Physical Therapy For Children.; 2018.
4. What is Hypertonia (and Hypotonia)?. Birthinjuryhelpcenter.org. https://www.birthinjuryhelpcenter.org/hypertonia.html. Published 2021. Accessed August 19, 2021.
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