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Muscle tone refers to the amount of tension a muscle has at rest. All muscles have a normal resting tone, which helps the body move freely against gravity and is needed for overall posture. Extensor muscle tone is the tension in the extensor muscle groups, which can be lost temporarily and intermittently, resulting in muscle cramps. Extensor muscle tone is important in maintaining stability, balance, and function. Increased extensor muscle tone can lead to contractures or a permanent shortening of the muscles. Spasticity, rigidity, and dystonia are the three main subtypes of increased muscle tone.
| Characteristics | Values |
|---|---|
| Definition | Extensor muscle tone is a part of normal human muscle tone, which is the natural and continuous slight contraction of a muscle. |
| Function | It helps the body move freely against gravity and is needed for overall posture. |
| Abnormalities | In some cases, people may experience a loss of tone in extensor muscle groups, resulting in muscle cramps. |
| Treatment | Muscle cramps can be treated with muscle relaxants or quinine. |
| Assessment | The assessment of muscle tone is critical for diagnosing and treating movement disorders such as Parkinson's disease and dystonia. |
| Types of Abnormal Tone | Rigidity, dystonia, and spasticity are subtypes of increased muscle tone. |
| Rigidity | Resistance to movement, fast or slow, resulting in a uniform increase in muscle tone. |
| Spasticity | Velocity-dependent resistance to passive stretch, resulting in increased muscle tone during quick movements. |
| Impact on Function | Increased muscle tone can affect ambulation, gross and fine motor control, stability, balance, trunk and head control, feeding, swallowing, and other functional activities. |
| Seating Considerations | Increased muscle tone impacts seating positions and strategies, with Dynamic Seating being a useful intervention. |
| Neurological Causes | A lack of inhibition from the central nervous system (brain and spinal cord) can cause increased muscle tone or hypertonia. |
| Presentation | High muscle tone may present as rigidity, particularly in muscles responsible for flexion, with joints slightly bent. |
| Low Muscle Tone | Hypotonia, or low muscle tone, can result in weakness and loss of superficial reflexes. |
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What You'll Learn
Extensor muscle tone and spasticity
Muscle tone refers to the natural and continuous slight contraction of a muscle. It varies along a bell-shaped curve, with low tone being perceived as "lax, flabby, floppy, mushy, [or] dead weight" and high tone being perceived as "tight, light, [or] strong". Extensor muscles are those that counteract flexor muscles, and they are crucial for maintaining stability, balance, and posture. For example, to sit up straight, one must balance the flexors and extensors in their trunk.
Spasticity is a velocity-dependent increase in muscle tone in response to passive movement. It is a symptom of certain neurological conditions and can affect movement, speech, and gait. Spasticity causes certain muscles to contract all at once, and the faster the muscle is moved or stretched, the greater the resistance to stretch or elongation. This creates an inability to stretch muscles or coordinate movements effectively. Spasticity can vary in severity, ranging from a mild feeling of muscle tightness to severe, painful, and uncontrollable muscle stiffness and spasms.
Spasticity can be distinguished from rigidity, another form of hypertonia, by its velocity-dependence. Rigidity is velocity-independent resistance to passive stretch, meaning there is a uniform increase in tone whether the joint is moved quickly or slowly. In contrast, spasticity exhibits greater resistance to faster movements. Additionally, rigidity affects all muscles surrounding a particular joint equally, whereas spasticity does not.
The management of spasticity is important, as some patients rely on aspects of it to maintain enough tone for functions such as standing or walking. Treatment options include physical therapy, medication, and local injections of botulinum toxin (Botox) or phenol into spastic muscles. These injections selectively reduce tone in muscles causing tightness or spasms, improving comfort, positioning, and function.
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Extensor muscle tone and rigidity
Muscle tone refers to the amount of tension a muscle has at rest. All muscles have a normal resting tone, which helps the body move freely against gravity and is needed for overall posture. Extensor muscles are responsible for extension, the straightening of a limb at the joint, and are often used to describe muscles in the legs and arms. For example, the triceps are extensor muscles that extend the arm at the elbow.
Extensor muscle tone is the tension in the extensor muscles at rest. In some cases, people may experience a loss of tone in the extensor muscle groups, which can result in muscle cramps. This can be treated with muscle relaxants or quinine. However, these medications reduce tone in both the flexor and extensor groups. The cause of muscle cramps is still unknown, but the stimulus may originate in the cerebral cortex, spinal cord, or the muscle itself.
High muscle tone, or hypertonia, is characterised by an increased state of active muscle contraction, even at rest. It is often difficult to move and may involve muscles responsible for flexion more than extension. In the leg, this may present as a slight bend in the knee, while the wrist and fingers are often clenched. High muscle tone can impact a person's ability to engage in explosive movements, such as sprinting or high jumping. Additionally, high muscle tone can impact functional activities such as feeding and swallowing, as well as fine and gross motor control.
Rigidity refers to resistance to movement, whether fast or slow, and is independent of velocity. It gives rise to uniform resistance to passive stretching in all directions, known as the 'lead pipe' phenomenon. Rigidity can be of the leadpipe type, where there is resistance throughout passive movement, or the cogwheel type, where resistance is jerky. It is important to distinguish between different subtypes of increased muscle tone, including rigidity, dystonia, and spasticity.
Dynamic Seating can be a useful intervention for people with increased extensor muscle tone and rigidity. Additionally, certain exercises can help manage high muscle tone in children. For example, the child's pose position may prevent increases in tone if the child is in a heightened state. Providing increased input to each major joint through gentle compressions can also help, as can gentle rocking over a therapy ball.
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Extensor muscle tone in ophthalmology
Muscle tone refers to the continuous and passive partial contraction of muscles, or the muscle's resistance to passive stretch during a resting state. It is important in maintaining posture and balance, and can be affected by factors such as age, disease, and nerve damage. Extensor muscles, along with flexor muscles, play a crucial role in maintaining this muscle tone while at rest.
In ophthalmology, muscle tone, or tonus, is a key consideration in eye surgery, particularly when manipulating extraocular muscles to correct strabismus, also known as crossed eyes. Strabismus can be present in infants and is associated with tonicity aberrations, where the eyes are not properly aligned and may appear turned or crossed. This condition is caused by issues with the oculomotor system, specifically the innervated myotendinous cylinders of the extraocular muscles.
Extraocular muscles are responsible for eye movements and are controlled by the oculomotor nerve. In patients with strabismus, these muscles may exhibit '"overaction", leading to abnormal eye positions and movements. The exact pathophysiological processes behind this "overaction" are still being studied, but it is believed to involve the innervation of the extraocular muscle pulleys.
The treatment for strabismus often involves surgery to adjust the extraocular muscles and restore proper eye alignment. This procedure requires a precise understanding of muscle tonus and the ability to manipulate the muscles without causing further tonicity aberrations. The goal is to achieve a balance between the extensor and flexor muscle groups, ensuring that the eyes are aligned and functioning correctly.
Additionally, tonicity aberrations in ophthalmology have been linked to various eye diseases such as Adie syndrome. These conditions can affect the muscle tone of the eye, impacting the patient's vision and eye movement. Thus, the assessment and management of muscle tone are crucial in ophthalmology, both in surgical interventions and in the diagnosis and treatment of eye disorders.
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Extensor muscle tone and movement disorders
Muscle tone is the natural and continuous slight contraction of a muscle. The amount of muscle tone depends on the velocity of movement: the more rapid the movement, the greater the resistance; the slower the movement, the less the resistance. The tone in the flexors and extensors of a limb is not balanced, which commonly causes characteristic resting postures of that limb.
Extensor muscles are those that cause the body to straighten during movement. Extensor muscle tone is, therefore, the resistance to passive stretch in these muscles. Extensor muscle tone can be assessed by passive limb manipulation in the awake state with muscles fully relaxed.
Abnormal extensor muscle tone can result in movement disorders. Extensor muscle tone abnormalities can be caused by damage to the central nervous system, namely upper motor neuron lesions. This damage impairs the ability of motor neurons to regulate descending pathways, resulting in disordered spinal reflexes, increased excitability of muscle spindles, and decreased synaptic inhibition. This leads to abnormally increased muscle tone in symptomatic muscles.
Spasticity, rigidity, and dystonia are the three main subtypes of increased muscle tone. Spasticity is velocity-dependent resistance to passive stretch, meaning that the resistance to movement depends on the velocity of the stretch. It is caused by an upper motor neuron disease and can result in involuntary muscle hyperactivity. Rigidity is velocity-independent resistance to passive stretch, meaning that there is uniform resistance to movement whether it is slow or rapid. It is a severe state of hypertonia and can result in stiffness, decreased range of motion, and loss of motor control. Dystonia is also a form of hypertonia and is characterised by muscle resistance to passive stretching and a tendency of a limb to return to a fixed involuntary posture following movement.
The treatment of abnormal extensor muscle tone aims to decrease hypertonia and provide a sensation of normal position and movement. Therapeutic interventions are individualised to particular patients, but some common methods include icing and other topical anesthetics, inhibitory pressure, and promoting body heat retention and rhythmic rotation. Physiotherapy, exercise, and patient education are also important for a more permanent state of improvement.
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Extensor muscle tone and the central nervous system
Muscle tone refers to the amount of tension a muscle has at rest. All muscles have a normal resting tone, which helps the body move freely against gravity and is needed for overall posture. Extensor muscles are responsible for extension, the straightening of a limb at the joint, and work in opposition to flexor muscles, which are responsible for flexion, or bending.
Extensor muscle tone is influenced by the central nervous system (CNS), which comprises the brain and spinal cord. The CNS plays a critical role in regulating muscle tone by balancing excitatory and inhibitory signals to the muscles. When there is a lack of inhibition from the CNS, it can result in excessive contraction of the muscles or increased muscle tone. This can be due to damage in the brain or spinal cord, leading to a loss of inhibitory drive to the muscles.
Spasticity and rigidity are two types of increased muscle tone that can occur due to CNS dysfunction. Spasticity is velocity-dependent resistance to passive stretch, meaning that moving a joint quickly will elicit increased muscle tone, while moving it slowly may not. It is characterised by exaggerated tendon jerks and is commonly associated with upper motor neuron syndrome. Rigidity, on the other hand, is velocity-independent resistance to passive stretch, resulting in uniform increased tone regardless of the speed of movement. Both conditions can impact extensor muscles and lead to difficulties in movement and coordination.
The assessment and management of extensor muscle tone are crucial, especially in individuals with CNS disorders such as cerebral palsy, stroke, or Parkinson's disease. Physiotherapy interventions may include exercises to improve strength, flexibility, and range of motion in the affected extensor muscles. Additionally, seating strategies and dynamic seating interventions can be employed to optimise positioning and comfort for individuals with increased extensor muscle tone.
In summary, extensor muscle tone is intricately linked to the functioning of the central nervous system. Disorders or injuries affecting the CNS can result in abnormal extensor muscle tone, impacting an individual's movement, posture, and overall functional abilities.
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Frequently asked questions
Extensor muscle tone refers to the amount of tension in extensor muscles at rest. Extensor muscles are responsible for extension, or straightening, of body parts. Extensor muscle tone is critical to several movement disorders, such as Parkinson's disease and dystonia.
High extensor muscle tone, also known as hypertonia or hypertonicity, refers to an increased state of active muscle contraction even at rest. This can lead to potential issues with movement and posture.
Low extensor muscle tone, also known as hypotonia, is the opposite of hypertonia, and is perceived as "lax, flabby, floppy, mushy, dead weight". Low tone increases flexibility and decreases strength.
