Muscle Tone Explained

Muscle tone is a word you will hear often in pediatric therapy, and it can mean different things to different people. You will hear that your child has low tone or high tone, floppy muscles or stiff ones, and those words will shape the therapy you are offered. This post explains what muscle tone is, what low and high tone mean, how tone is measured, and what the research says about whether therapy can change it.

What muscle tone is

Muscle tone is traditionally defined as the tension in a relaxed muscle, or the resistance felt by an examiner when a joint is moved passively while the muscles are at rest. That is the definition used in a 2021 peer-reviewed review of muscle tone physiology by Ganguly and colleagues in the journal Toxins, which notes that behind that simple bedside definition sits a complex system: tone reflects signals from the brain, the spinal cord, and the muscle spindle. The review describes two parts to tone: a passive part that comes from the stretchiness of muscle and the connective tissue around it, and an active part driven by the nervous system. It also describes postural tone, the background muscle activity that holds the body up against gravity, which shows most in the muscles along the trunk.

Low tone and high tone

Low tone is hypotonia: reduced resistance to passive movement, muscles that feel soft or floppy at rest. High tone is hypertonia: increased resistance to passive movement. Both are findings, not diagnoses; they describe what a clinician observes, and neither explains why. Hypertonia comes in two main forms. Spasticity is velocity-dependent: the resistance jumps when the limb is moved quickly, often described as a catch. Rigidity feels the same regardless of speed and in both directions of movement. The distinction matters because the treatments differ. Low tone can start in different places; Ganguly and colleagues note, for example, that lesions in the cerebellum can produce hypotonia. Finding the cause is a medical question, and this site's hypotonia guide covers what to ask about it.

How tone is measured

Tone is graded at the bedside with scales that ask an examiner to move a joint and rate what they feel. A common one is the Modified Ashworth Scale. In the 1987 paper that tested it, Bohannon and Smith each graded elbow flexor spasticity in 30 patients with brain lesions and agreed on 86.7% of their ratings; they called the results positive enough to encourage further trials, while noting they covered only the elbow flexors. The Cochrane stretching review names the Ashworth and Tardieu scales as the usual ways spasticity is measured. Scales like these rely on what the examiner feels, which Ganguly and colleagues note opens the door to subjective variation. For children, a 2018 systematic review by Goo and colleagues found 21 assessments with tone items across 97 studies, all part of broader developmental exams; only four showed at least moderate validity or reliability for both resting and active tone, and the authors called for more research, especially for older children. A tone grade describes what the examiner feels in a resting muscle. It is not a test of what your child can do. Tone is one input into a therapy plan, not the plan itself.

What DMI says about tone

DMI's own materials talk about tone in two ways. The official DMI FAQ lists hypotonia among the diagnoses it says may benefit, and it lists "Modifying tone" among the ways it says the therapy can help. A DMI blog post on Down syndrome lists low muscle tone first among the reasons babies with Down syndrome are often delayed in gross motor milestones, and describes tone as "like a setting in the brain" that keeps muscles ready to contract. DMI's Clinical Commentary says the therapy focuses on eliciting new neural connections, and may strengthen synaptic connections, through novel exercises that provide strong sensory input and prompt active postural responses, and it adds that further research is needed. No controlled study has yet tested whether DMI changes tone.

What the research shows about therapy and tone

The research on therapy and tone is mixed, and the answer depends on the child's condition and the treatment. Novak and colleagues' 2013 "state of the evidence" review in Developmental Medicine & Child Neurology, a review of systematic reviews, graded the evidence from 166 articles covering 64 interventions for children with cerebral palsy. It gave its green "do it" rating, for at least one outcome, to medical and surgical treatments including botulinum toxin, diazepam, and selective dorsal rhizotomy, and also to therapy approaches such as casting, goal-directed training, and constraint-induced movement therapy. A Cochrane review of 49 trials with 2,135 participants found high-quality evidence that stretching for less than seven months had no clinically important effect on joint mobility, and the few studies that measured spasticity could not rule an effect in or out. For low tone, a 2018 systematic review of 37 studies of interventions for young children with central hypotonia (Paleg and colleagues) found green-light evidence for treadmill training to help walking, and for massage to positively affect muscle tone, motor development, and use of vision, in infants with Down syndrome; it rated both as possibly effective for other children. None of this says therapy is pointless for a child with tone differences. It means a useful question for any program is what your child will be able to do, and how progress will be measured.

What it means for your child

When a provider says your child has low tone or high tone, they are describing a finding, not a diagnosis and not a verdict. A tone grade describes what an examiner feels, not what your child will learn to do. It also means you can hear claims about tone accurately. If a program says it will change your child's tone, ask what evidence it has for children like yours and how the change will be measured. A program that says it will work on active responses, strength, and skills, given the tone your child has, is describing goals you can watch and track.

What to ask

• Ask what finding the provider is describing: low tone, high tone, spasticity, or something else.
• Ask whether tone was formally assessed, and with which scale, if the answer will change the treatment plan.
• Ask what the provider expects therapy to change: tone itself, or function and skills in the presence of tone differences.
• Ask what specific milestones or skills the program targets, and how progress will be measured.
• If your child has low tone and no explanation for it, ask whether a medical workup is warranted before or alongside therapy.

Where it appears on this site

The term runs through this site. The hypotonia guide explains low tone as a finding that needs a diagnosis rather than just therapy; the cerebral palsy guide covers spasticity and the two registered DMI trials in spastic cerebral palsy; the Down syndrome guide discusses low tone and loose ligaments; and the DMI therapy guide notes that children with extreme low tone need extra precautions. The atlantoaxial instability explainer covers a related neck precaution for children with Down syndrome.

Sources

• Ganguly J, Kulshreshtha D, Almotiri M, Jog M. Muscle Tone Physiology and Abnormalities. Toxins. 2021;13(4):282. Full text on PubMed Central
• Goo M, Tucker K, Johnston LM. Muscle tone assessments for children aged 0 to 12 years: a systematic review. Developmental Medicine & Child Neurology. 2018;60(7):660-671. PubMed
• Bohannon RW, Smith MB. Interrater reliability of a modified Ashworth scale of muscle spasticity. Physical Therapy. 1987;67(2):206-207. PubMed
• Novak I, McIntyre S, Morgan C, Campbell L, Dark L, Morton N, Stumbles E, Wilson SA, Goldsmith S. A systematic review of interventions for children with cerebral palsy: state of the evidence. Developmental Medicine & Child Neurology. 2013;55(10):885-910. PubMed
• Harvey LA, Katalinic OM, Herbert RD, Moseley AM, Lannin NA, Schurr K. Stretch for the treatment and prevention of contractures. Cochrane Database of Systematic Reviews. 2017;(1):CD007455. Cochrane Library
• Paleg G, Romness M, Livingstone R. Interventions to improve sensory and motor outcomes for young children with central hypotonia: a systematic review. Journal of Pediatric Rehabilitation Medicine. 2018;11(1):57-70. PubMed
• DMI Parent Resources and FAQ. DMI Therapy. dmitherapy.com
• Down Syndrome: A Physical Therapy Perspective. DMI Therapy. dmitherapy.com
• DMI Clinical Commentary. DMI Therapy. dmitherapy.com