Logan Steele
Muscle compliance is a critical factor in the control of movement and has implications for various clinical problems such as the control of orthotic/prosthetic devices and functional electrical stimulation. It refers to the ability of muscles to distend and increase volume in response to increasing pressure or force. This phenomenon is influenced by the interaction between muscle activation and muscle-tendon compliance, which can alter optimal muscle lengths and force-generating capacities. The role of muscle compliance in movement control is evident across various physiological mechanisms, including the neuromuscular system. Additionally, muscle compliance is associated with cardiac remodeling in endurance athletes, contributing to their ability to generate high cardiac outputs during exercise.
| Characteristics | Values |
|---|---|
| Definition | Compliance is the ability of a hollow organ (vessel) to distend and increase volume with increasing transmural pressure or the tendency of a hollow organ to resist recoil toward its original dimensions on the application of a distending or compressing force. |
| Reciprocal | Elastance |
| Importance | Compliance is of particular significance in cardiovascular physiology and respiratory physiology. |
| Influencing Factors | Muscle length, joint torque capacity, muscle tendon compliance, and activation level. |
| Implications | Muscle compliance influences motor function and must be considered at every level of motor function. |
| Areas of Relevance | Control of orthotic/prosthetic devices, functional electrical stimulation, and the effects on muscle tone of neuromuscular pathologies. |
| Compliance and Relaxation | Compliance accelerates relaxation in muscles by allowing myosin heads to move relative to actin. |
| Compliance and Exercise | Exercise can improve cardiac compliance, with endurance athletes exhibiting superior ventricular diastolic compliance and distensibility. |
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What You'll Learn
Muscle compliance's influence on movement control
Muscle compliance is a critical factor in movement control, influencing both normal voluntary movements and reactions to external forces. It refers to the ability of muscles to deform or stretch in response to pressure or force. This compliance is not an inherent property of the muscles themselves, but rather emerges from the combined operation of many physiological mechanisms.
The degree of muscle compliance has significant implications for muscle and locomotor performance. For instance, muscle length affects muscle force and joint torque capacity. Even in “isometric” (fixed-end) contractions, muscle fibers will shorten due to tendon stretch, an effect that is more pronounced at higher activation levels due to greater forces. This results in a shift in the operating ranges for muscles with compliant tendons on the force-length curve. Additionally, muscle compliance plays a role in muscle relaxation. Stretches during the linear phase accelerate relaxation, while shortening movements slow it down.
The interaction between muscle compliance and activation on muscle operating lengths has been demonstrated, but the exact mechanisms remain unclear. While muscle-tendon compliance is a factor, activation can also alter optimal muscle lengths, even in the absence of compliance. The relative contributions of these two factors and their simultaneous influence on force-length operating ranges require further systematic exploration.
The compliant behaviour of muscles has clinical relevance in areas such as the control of orthotic/prosthetic devices, functional electrical stimulation, and the effects on muscle tone of neuromuscular pathologies. Additionally, muscle compliance is important in cardiac performance, with endurance athletes exhibiting superior ventricular diastolic compliance and distensibility, facilitating high cardiac outputs during exercise. Furthermore, exercise interventions have been shown to improve cardiac compliance, particularly when initiated at a younger age.
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Muscle-tendon compliance
Muscle compliance is a term used to refer to the compliant properties of the neuromuscular system, which influence and must be considered at every level of motor function. In other words, muscle compliance is the ability of a muscle to respond to external forces and the implications for normal voluntary movements.
To investigate this theory, researchers have attached artificial tendons of varying compliance to muscle fibre bundles in vitro and measured power output and mechanical efficiency during stretch-shorten cycles. The results of these experiments have shown that peak power, average power output, and efficiency all increased with increasing tendon compliance. This is presumably due to the tendon acting to minimise muscle energy use by allowing the muscle fibres to shorten at optimal speeds.
The maximum efficiency for compliant tendons was found to be similar to the highest value measured under constant velocity and force conditions. This suggests that tendon compliance can maximise muscle efficiency under certain conditions. These findings have implications for the control of orthotic/prosthetic devices, functional electrical stimulation, and the effects on muscle tone of neuromuscular pathologies.
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Muscle compliance in orthotics and prosthetics
Muscle compliance is the ability of a muscle to experience pressure or force without disruption. In the context of orthotics and prosthetics, muscle compliance plays a crucial role in the control of movement and the management of various clinical conditions.
Orthotic devices are used to improve the efficiency of function during injuries or neurological changes. They can be used to stabilise bony fragments, address tendon or ligament injuries, and provide support after surgical repairs. Orthotics can be ready-made or customised, depending on the patient's needs. For instance, a patient with a peripheral nerve injury may require a specific type of orthosis to address the resulting hand deformity and improve thumb function. Orthotics can also be used to manage neuropathies and provide functional assistance for weak muscles or deformities. For example, a balanced forearm orthosis enables trace movements at the shoulder to control arm movements.
Prosthetics, on the other hand, are artificial limbs designed to replace missing or amputated body parts. In combination with orthotics, prosthetics can assist in restoring human locomotion and enabling individuals with impairments to regain physical function. Technological advancements have led to the development of wearable robotic prosthetic and orthotic devices that can interface with the user's sensory-motor control system.
The compliant properties of the neuromuscular system influence motor function at every level. Therefore, muscle compliance must be considered in the control of orthotic and prosthetic devices. For instance, functional electrical stimulation (FES) can be used in conjunction with orthotics to actuate the user's muscles and facilitate their participation in locomotive tasks. However, one challenge with FES is the precise placement of electrodes over the muscles, which may require assistance.
In conclusion, muscle compliance is integral to the successful application of orthotics and prosthetics. By understanding and characterising compliant behaviour, healthcare professionals can develop effective strategies to control these devices in harmony with the user's intentions and improve their quality of life.
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Muscle compliance and exercise
Muscle compliance is a property of the neuromuscular system that influences motor function. It is the ability of a muscle to change length under tension. The degree of muscle compliance is determined by the interaction between muscle activation and muscle-tendon compliance. The force–length (F–L) relationship of muscles has important implications for muscle and locomotor performance. Muscle length affects muscle force and, therefore, joint torque capacity.
Compliance is a measure of the ability of a hollow organ (or vessel) to distend and increase volume with increasing pressure or resist a return to its original dimensions when a compressing or distending force is removed. Compliance is of particular significance in cardiovascular physiology and respiratory physiology. In the context of muscle compliance, it refers to the ability of a muscle to change length under tension.
The compliant properties of the neuromuscular system influence and must be considered at every level of motor function. For all but the slowest movements, three mechanical properties must be taken into account: the ability to produce force, the ability to transmit force, and the ability to change length under tension (muscle compliance).
Exercise has been shown to improve muscle compliance. For example, vigorous exercise initiated in middle-age can improve cardiac compliance. Additionally, exercise training increases CRF (cardiorespiratory function) and cardiac output, which leads to improved ventricular compliance and distensibility. However, the dose and intensity of exercise are important factors in eliciting a response, and interventions later in life may have more modest effects on muscle compliance.
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Muscle compliance in the heart
Compliance is the ability of a hollow organ (vessel) to distend and increase volume with increasing transmural pressure or the tendency of a hollow organ to resist recoil toward its original dimensions on the application of a distending or compressing force. The degree of compliance is influenced by the structural properties of the muscle fibres and connective tissue, as well as the state of contraction and relaxation. The term is of particular significance in cardiovascular physiology.
In the context of the heart, compliance specifically refers to the ability of the heart chambers or blood vessels to expand when filled with blood. This is influenced by the structural properties of the heart muscle, such as the orientation and thickness of the muscle fibres, as well as the presence of connective tissue. For example, ventricular hypertrophy leads to decreased ventricular compliance due to increased ventricular wall thickness, resulting in higher ventricular end-diastolic pressure (EDP) at any given end-diastolic volume (EDV).
The compliant properties of the neuromuscular system are important in the control of movement, including the ability to catch errors under load uncertainty. Additionally, muscle compliance has implications for the control of orthotic/prosthetic devices, functional electrical stimulation, and the effects of neuromuscular pathologies on muscle tone.
With aging, the heart undergoes myocardial fibrosis, leading to increased stiffness, decreased cardiac compliance, and impaired ventricular filling. This can contribute to diastolic heart failure and induce lethal arrhythmias. Myocardial fibrosis is characterised by the crosslinking of ECM proteins due to glycation, which increases the rigidity of the heart tissue. In diabetic rats, for instance, reduced compliance of the left ventricle has been observed.
Pharmaceutical interventions, such as rapamycin, have been shown to decrease heart dimensional measures and attenuate cardiac fibrosis, thereby improving age-related measures of heart function.
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Frequently asked questions
Muscle compliance refers to the ability of the neuromuscular system to respond to external forces and the implications for normal voluntary movements.
The compliant properties of the neuromuscular system influence motor function at every level. Clinically, muscle compliance is relevant to the control of orthotic/prosthetic devices, functional electrical stimulation, and the effects on muscle tone of neuromuscular pathologies.
Muscle length has important implications for muscle and locomotor performance. Longer muscles can exert more force and therefore have a greater joint torque capacity.
Compliance accelerates relaxation in muscles by allowing myosin heads to move relative to actin. Stretches imposed during the linear phase quickened relaxation, while shortening movements prolonged the time course.
Exercise has been shown to increase muscle compliance, particularly in younger individuals. However, the effects of exercise on muscle compliance in older individuals are modest.
