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Human resting muscle tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties. Resting muscle tone is considered the passive tension in our muscles when not loaded or in use, helping to maintain enough tension to quickly respond to a stretch and to maintain postural stability in balanced equilibrium positions. This passive tension is the CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells. Muscle tone varies along a bell-shaped curve, with low tone perceived as lax, flabby, floppy, mushy, dead weight and high tone perceived as tight, light, strong. Disorders of muscle tone can arise from dysfunction in these pathways and manifest as hypertonia or hypotonia.
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What You'll Learn
- Resting muscle tone is the passive tonus or tension of skeletal muscle
- It is a CNS-independent component resulting from intrinsic molecular interactions
- Resting muscle tone helps maintain postural stability in balanced equilibrium positions
- Physical disorders can result in abnormally low (hypotonia) or high (hypertonia) muscle tone
- Muscle tone is an adaptive function of the neuromotor apparatus
Resting muscle tone is the passive tonus or tension of skeletal muscle
Resting muscle tone, also known as Human Resting Muscle Tone (HRMT), is the passive tonus or tension of skeletal muscle. It is an intrinsic viscoelastic tension exhibited within the body's kinematic chains. This passive tension is a CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells. CNS-activated muscle contractions generate far greater tensions transmitted by fascial elements.
HRMT is a passive myofascial property that operates within networks of tensional tissues, or biotensegrity. It functions inseparably from fascial (myofascial) tissues and ligamentous structures. The word "tone" has been used to convey varying clinical and physiological features that have led to confusion and controversy.
Resting muscle tone is the passive tension in our muscles when not loaded or in use. This helps maintain enough tension in the muscles to quickly respond to a stretch and to maintain postural stability in balanced equilibrium positions. This is different from strength or co-contraction of muscle, which would be what a muscle can do when not at rest, though this can often build off the baseline resting muscle tone. For example, if you were to jerk someone’s elbow straight, quickly stretching the bicep muscle, it would often tighten up to prevent injury or overloading of tendons and ligaments at the end-range of motion for that joint. This often happens automatically without any input from the Central Nervous System (CNS) or brain.
Resting muscle tone varies along a bell-shaped curve. Low tone is perceived as "lax, flabby, floppy, mushy, dead weight" and high tone is perceived as "tight, light, strong". Muscles with high tone are not necessarily strong, and muscles with low tone are not necessarily weak. In general, low tone does increase flexibility and decrease strength, and high tone does decrease flexibility and increase strength, but with many exceptions. Physical disorders can result in abnormally low (hypotonia) or high (hypertonia) muscle tone.
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It is a CNS-independent component resulting from intrinsic molecular interactions
Human resting muscle tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties. It is a CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells.
HRMT is the vital low-level, passive tension, and resistance to stretch that helps to maintain postural stability in balanced equilibrium positions. It is important to note that this passive tension is not a result of conscious effort or input from the Central Nervous System (CNS) or brain. Instead, it arises from the intrinsic properties of the muscle itself, specifically the interactions of the actomyosin filaments within the muscle fibres.
The CNS-independent nature of resting muscle tone means that it is always present, even when the muscle is at rest or not actively being used. This passive tension allows the muscle to maintain a baseline level of tension, which helps it to quickly respond to any sudden stretches or movements without having to start from a completely relaxed state. This is particularly important in maintaining stability and preventing injuries.
While the CNS-independent component of resting muscle tone is essential, it is also important to consider the overarching CNS-activated muscle contractions, which generate far greater tensions. These CNS-activated contractions are what we typically think of when we consider muscle strength or co-contraction, and they build upon the baseline resting muscle tone. The interplay between the CNS-independent and CNS-activated components of muscle tone allows for a dynamic range of motion and stability in the human body.
Research into the CNS-independent component of resting muscle tone has important implications for clinical practice and a better understanding of muscle disorders. By studying the intrinsic molecular interactions that contribute to resting muscle tone, clinicians can gain a deeper insight into the mechanisms underlying muscle function and dysfunction, leading to more effective treatments and interventions. This interdisciplinary approach to understanding HRMT promises to enhance the effectiveness of clinical practitioners and the productivity of investigators.
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Resting muscle tone helps maintain postural stability in balanced equilibrium positions
Human resting muscle tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties. Resting muscle tone is considered the passive tension in our muscles when not loaded or in use. This passive tension is the CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells.
The CNS-activated stretch reflex theory of muscle tone predominates in the literature. However, it overlooks clinical and experimental research supporting resting muscle tone in intact animals and humans. The absence of EMG evidence of muscle contractile activity of normal resting muscle indicates that clinically recognized tone is caused by intrinsic viscoelastic properties.
Resting muscle tone is important for maintaining postural stability in balanced equilibrium positions. It helps to maintain a relaxed standing body posture with minimal energy costs, often for prolonged durations without fatigue. This is different from strength or co-contraction of muscle, which would be what a muscle can do when not at rest, though this can often build off the baseline resting muscle tone. For example, if you were to jerk someone's elbow straight, quickly stretching the bicep muscle, it would often tighten up to prevent injury or overloading of tendons and ligaments at the end-range of motion for that joint.
Resting muscle tone varies along a bell-shaped curve. Low tone is perceived as "lax, flabby, floppy, mushy, dead weight" and high tone is perceived as "tight, light, strong". Muscles with high tone are not necessarily strong, and muscles with low tone are not necessarily weak. In general, low tone does increase flexibility and decrease strength, and high tone does decrease flexibility and increase strength, but with many exceptions.
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Physical disorders can result in abnormally low (hypotonia) or high (hypertonia) muscle tone
Human resting muscle tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties. Even when relaxed, muscles have a small amount of contraction that gives them a springy feel and provides some resistance to passive movement. This passive tension is a CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells.
Hypertonia, on the other hand, is abnormally increased muscle tone. It is often associated with damage to the central nervous system, specifically upper motor neuron lesions, which result in disordered spinal reflexes, increased excitability of muscle spindles, and decreased synaptic inhibition. Hypertonia can manifest as spasticity, rigidity, or dystonia. Spasticity causes certain muscles to contract all at once, affecting movement and sometimes speech. Rigidity is associated with basal ganglia injuries and is often seen in Parkinson's disease. It affects all muscles surrounding a particular joint equally. Dystonic hypertonia refers to muscle resistance to passive stretching and a tendency for a limb to return to a fixed involuntary posture following movement.
There are various treatments available for hypertonia, including local injections of botulinum toxin (Botox) or phenol to relax spastic muscles, physical therapy to stretch and reduce motor neuron excitability, and inhibitory pressure and rhythmic rotation to promote relaxation.
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Muscle tone is an adaptive function of the neuromotor apparatus
Human resting muscle tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties. It is a CNS-independent component resulting from intrinsic molecular interactions of the actomyosin filaments in sarcomeric units of skeletal muscle and myofibroblast cells. This passive tension helps maintain postural stability in balanced equilibrium positions.
The motor system must generate movements that are adaptive and aligned with the goals of the organism. These goals are set by high-order areas of the brain, and the motor system transforms these goals into the appropriate muscle activations to achieve the desired movements. For example, moving a hand from a pocket requires coordinated activity at the shoulder, elbow, and wrist. The motor system determines the necessary forces and coordination at each joint to produce a smooth motion.
Additionally, the motor system must adapt to changing circumstances. As an individual grows, the motor commands required to raise a hand will differ between an infant and an adult. The system must adjust its output over time to accomplish the same goals, enabling the acquisition of complex motor skills. This adaptability is facilitated by complex neural circuits that process the "nuts and bolts" of motor control, allowing higher levels of the hierarchy to focus on planning and coordinating movements without needing to encode the details of each muscle contraction.
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Frequently asked questions
Resting muscle tone, or HRMT, is the passive tonus or tension of skeletal muscle that derives from its intrinsic molecular viscoelastic properties. It helps maintain postural stability in balanced equilibrium positions.
Resting muscle tone is the passive tension in our muscles when not loaded or in use. Strength or co-contraction of a muscle refers to what a muscle can do when not at rest, which can build off the baseline resting muscle tone.
Resting muscle tone varies along a bell-shaped curve. Low tone is perceived as "lax, flabby, floppy, mushy, dead weight" and high tone is perceived as "tight, light, strong". However, muscles with high tone are not necessarily strong, and muscles with low tone are not necessarily weak.
Physical disorders can result in abnormally low (hypotonia) or high (hypertonia) muscle tone. Hypotonia can present as muscle flaccidity, with floppy limbs and decreased stretch reflex responses. Hypertonia can present as spasticity or rigidity.
Muscle tone may reflect a state of preparedness to move and can be defined as the constant muscular activity necessary as a background to actual movement. It is an adaptive function of the neuromotor apparatus that responds to commands from upper levels of movement construction.
