March 2024 Special Needs Living Magazine

Muscle Tone

BY BECKY ALLEN

Muscle tone is a bit like the internet. No one really understands how it works but we all use it. Tone is hard to explain and very few people understand it. Muscle tone is extremely complicated because so many parts come into play when determining one’s tone. For this reason, I am going to ATTEMPT to explain it in a way that is understandable, but not 100% accurate because, quite frankly, that would take a novel. Abnormal muscle tone is not actually a deficit of muscle but a neurological problem.

To explain muscle tone, first, we need a brief anatomy lesson. Our muscles are made up of a bunch of muscle filaments called sarcomeres. These sarcomeres are like strands of a rope. When a nerve signals the muscle sarcomeres to tighten the muscle will contract. When the nerves tell the sarcomeres to move farther away from each other or stretch out past the resting state the muscle will elongate. At rest, there is a tension or pulling force between each sarcomere. This resting tension is called tone. Even when we are sitting on the couch completely relaxed our muscles still have tension.

If the nerves are signaling too much and the sarcomeres are being pulled on tightly, the muscle has high tone, and this is called hypertonia. Think of a brand-new hair rubber band that is hard to stretch around your hair. If the muscle fibers are too loose and the tension is low, this is called hypotonia. Think of an overstretched hair tie that is loose and flimsy. Typical tone has muscle fibers that are spaced out exactly right creating the perfect tension and optimal starting point for a muscle contraction. That last part is important. Typical tone, or tone that is in the middle of the spectrum is the OPTIMAL starting point for a muscle contraction.

When a muscle contracts the muscle fibers always must first go to the “optimal” tension or starting point. So, in a muscle with high tone, first, the fibers need to relax back to optimal tension and then contract. This requires extra energy and effort. For a muscle with low tone, the muscle fibers must first tighten all the way from its over-relaxed position to the optimal starting point and then it can contract. All this extra work requires extra energy and effort. So, children that have low or high tone will utilize more energy than those typical tone. This is one reason children with abnormal tone fatigue easily and have difficulty moving their body.

We are all born with a specific amount of tone that cannot be changed. The diagnosis of hypertonia or hypotonia occurs when a person’s tone is out of the normal range. Our muscles can get stronger or weaker, but the tone will remain the same. The ligaments and connective tissues that hold our body together may get looser or tighter, but our tone will remain the same. With time and practice a child may learn to move their body more effectively and efficiently, but the tone will remain the same.

Strength is often confused with tone. People often assume that low tone means weaker muscles and high tone means stronger muscles. But muscle strength is the amount of force an active muscle can produce against resistance. Whereas muscle tone is the level of tension at rest. Tone is passive. A person with low tone can still actively produce force against resistance and still create a strong contraction. And conversely, children with high tone can have weakness, especially in the areas of range that they do not use often.

This brings me to common issues that arise in children with abnormal tone. The biggest issue for hypertonia is a loss of range of motion of the joints. It is the use it or lose it theory. When our ligaments/tendons/capsules do not regularly stretch to their full available length they become stiff and brittle which contributes to joint contractures. When this happens, we typically need intervention to regain full range of motion. Consistent physical therapy, bracing, medications like Botox or Baclofen, or a combination or even a surgical intervention may be necessary. Children with low tone have difficulty with postural control and are often considered “slouchy” or “floppy.” They often require bracing to assist their body for support against gravity or weight bearing.

A common issue for children with either low or high tone is that they may have difficulty “grading” movements. Meaning they have trouble making small, controlled movements. They tend to often under or overestimate the amount of force needed to produce movements. This is because the “receptors” or the sensors in our body that tell our brain exactly how much force is needed are located in the muscle and its tendons.

Treatment for children and adults with atypical tone is truly a juggling act between therapy, pharmacological, and neurosurgical involvement. Communication between doctors, the patient, and the patient’s caregivers is an important and often overlooked component. And because a person’s tone never changes, interventions may be necessary throughout a person’s lifetime.