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Tonic and phasic muscle theory was popularized by Dr. Vladimir Janda, a Czech neurologist and physiotherapist, in the late 1960s. Phasic muscles are those that are only active when deliberately called upon and quickly return to a relaxed state. They are designed primarily for movement and are easily fatigued due to their reliance on anaerobic metabolism. These muscles are not responsive to gravity and can be strengthened through training. Phasic muscles include the abdominals, gluteals, and rhomboids. Understanding the differences between tonic and phasic muscles can help address muscle imbalances caused by inactive lifestyles.
| Characteristics | Values |
|---|---|
| Type of muscle fibres | Fast-twitch, type II |
| Metabolism | Anaerobic |
| Fatigue | Easily fatigued |
| Activation | Activated on demand |
| Response to overuse, underuse or trauma | Lengthen and weaken |
| Purpose | Designed for movement |
| Endurance | Low endurance |
| Relationship with gravity | Not responsive to gravity |
| Activity | Insufficiently active |
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What You'll Learn
- Phasic muscles are available on demand but are not responsive to gravity
- They are easily fatigued and contain fast-twitch muscle fibres
- They are responsible for movement and are activated by the brain
- Phasic muscles are insufficiently active and may exhibit false paralysis
- They are prone to lengthening and weakening in response to overuse, underuse, or trauma
Phasic muscles are available on demand but are not responsive to gravity
Tonic and phasic muscle theory was developed in the 1960s by Dr. Vladimir Janda, a Czech neurologist and physiotherapist. Using electromyography (EMG), Dr. Janda discovered that some muscles are always active and resistant to fatigue, while others are only active when called upon and quickly return to a relaxed state.
Phasic muscles are those that are available on demand but are not responsive to gravity. They are easily fatigued and contain a high density of fast-twitch muscle fibres. These fibres rely on anaerobic metabolism to fuel their contraction and can be fatigued as they do not use oxygen, instead relying on the body's glycogen stores. Phasic muscles are designed primarily for movement and are therefore more suited to rapid and intense movements of short duration. They are prone to inhibition and have a lower endurance threshold than postural muscles.
Postural muscles, on the other hand, are always active and help to oppose gravity and keep us upright. They contain mostly slow-twitch muscle fibres and have a greater capacity for sustained work. These muscles are responsible for holding you upright and are constantly active, even during normal activities and at rest.
The two types of muscles influence each other and are not created equal. Variations in structure, function, and physiology are well-known. A sedentary lifestyle, insufficient body movement, or improper training can skew the innate functional patterns of these muscles.
Understanding the differences between tonic and phasic muscles is important for improving the body's function and preventing or correcting muscle imbalances. Phasic muscles, when under-used, can lengthen and weaken, leading to faulty movement patterns and chronic pain. Therefore, it is essential to train phasic muscles to allow the tonic muscles to relax and prevent musculoskeletal imbalance and joint instability.
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They are easily fatigued and contain fast-twitch muscle fibres
Phasic muscles are those that are only active when deliberately called upon. They are easily fatigued and contain fast-twitch muscle fibres.
The concept of phasic muscles was first introduced in the late 1960s by Dr. Vladimir Janda, a Czech neurologist and physiotherapist. He used electromyography (EMG) to discover that some muscles are always active and resistant to fatigue, while others are only active when called upon and easily fatigued.
Fast-twitch muscle fibres are involved in rapid and intense movements of short duration, such as weightlifting, throwing a ball, or sprinting. They rely on anaerobic metabolism, which does not use oxygen, to fuel their contraction. This reliance on a metabolic process that does not use oxygen contributes to the muscles' high fatigability.
Phasic muscles are designed primarily for movement. For example, the glutes help to extend the hip and leg when walking. Leading a sedentary lifestyle can cause these muscles to weaken and atrophy.
Imbalances between postural and phasic muscles can lead to musculoskeletal imbalance and joint instability. This can result in faulty movement patterns and chronic pain.
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They are responsible for movement and are activated by the brain
Phasic muscles are designed primarily for movement. They are activated by the brain and are available on demand, but they are not responsive to the pull of gravity. They are easily fatigued and don't have the endurance that postural muscles have. They contain a high density of fast-twitch muscle fibres, which rely on anaerobic metabolism to fuel their contraction. This means they are relying on a metabolic process that does not use oxygen, such as the body's glycogen stores.
The tonic and phasic muscle theory was originated in the 1960s by Dr. Vladimir Janda, a Czech neurologist and physiotherapist. Using electromyography (EMG), Dr. Janda found that some muscles are always active and resistant to fatigue, while others fatigue easily and are only active when called upon. The hyperactive group of muscles, responsible for holding us upright, were called "'postural" (now known as "tonic"), while the languid group, which only fire up when necessary, were labelled "phasic".
Phasic muscles include the abdominals, gluteals, deep neck flexors, and rhomboids. These muscles seldom act alone but typically act in relation to postural muscles. For example, the glutes help to extend the hip and leg when we walk. If we lead a sedentary lifestyle, these muscles can easily become weakened and atrophy.
The body is a dynamic system and adapts to the things it is asked to do. If we are constantly sitting at a desk all day, the body will default towards using postural muscles. This can lead to musculoskeletal imbalance and joint instability when postural and phasic muscles are located on opposing sides of the agonist-antagonist relationship.
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Phasic muscles are insufficiently active and may exhibit false paralysis
Tonic and phasic muscle theory was developed in the 1960s by Dr. Vladimir Janda, a Czechoslovak neurologist, physiatrist, and physiotherapist. Using electromyography (EMG), Dr. Janda discovered that some muscles are always active and resistant to fatigue, while others fatigue easily and are only active when called upon. The former group was dubbed "postural" muscles, while the latter was named "phasic" muscles.
Postural muscles, also known as tonic muscles, are always active in the background and help to hold the body upright. Phasic muscles, on the other hand, are activated on demand and are primarily responsible for movement. They are easily fatigued due to their high density of fast-twitch muscle fibers, which rely on anaerobic metabolism for contraction. This means they operate without oxygen, relying on the body's glycogen stores. Examples of phasic muscles include the abdominals, gluteals, deep neck flexors, and rhomboids.
Phasic muscles can become weakened and atrophied due to a sedentary lifestyle. They also have a tendency to lengthen and weaken when paired with over-used tonic muscles. This can result in musculoskeletal imbalance and joint instability, leading to faulty movement patterns and chronic pain. Insufficient activity in phasic muscles may even lead to a form of false paralysis, despite no actual injury being present. This false paralysis is a result of the muscles being insufficiently active, rather than a nervous system problem, which is the usual cause of paralysis.
Paralysis occurs when nerve signals cannot reach the muscles, resulting in an inability to make voluntary movements. It can be partial, where some muscle control is retained, or complete, where all muscle control is lost. False paralysis, or paresis, differs from true paralysis in that the individual still has some control over the affected muscles, but the movements are weaker than normal. This is due to nerve damage, which impairs muscle movement. Treatment for paresis focuses on addressing the underlying causes and improving quality of life through physical and occupational therapy.
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They are prone to lengthening and weakening in response to overuse, underuse, or trauma
Phasic muscles are designed primarily for movement. They are easily fatigued and have poor endurance. They contain a high density of fast-twitch muscle fibres, which rely on anaerobic metabolism to fuel their contraction. This means that they are relying on a metabolic process that does not use oxygen, such as the body's glycogen stores, and can therefore be easily fatigued.
Phasic muscles are also prone to inhibition and are seldom active in isolation. They are only active when deliberately called upon and quickly return to a relaxed state. They are available on demand but are not responsive to the pull of gravity.
In contrast to tonic or postural muscles, phasic muscles tend to lengthen and weaken in response to overuse, underuse, or trauma. This is the opposite response to that of tonic muscles, which shorten and tighten in response to these stimuli. This can lead to musculoskeletal imbalance and joint instability when the two types of muscles are located on opposing sides of the agonist-antagonist relationship.
For example, a person who sits at a desk for long hours may try to sit up straight but finds themselves slouching. This is because their overused tonic muscles, such as the pectoralis minor and upper trapezius, are pulling their underused phasic muscles, such as the rhomboids and mid/lower trapezius, into an excessively lengthened position. This can result in faulty movement patterns and chronic pain.
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Frequently asked questions
Phasic muscles are those that activate when deliberately called upon and quickly return to a relaxed state. They are designed primarily for movement and contain mostly fast-twitch muscle fibres, which rely on anaerobic metabolism to contract.
Phasic muscles include the abdominals, gluteals, deep neck flexors, and rhomboids.
Postural muscles are those that are always active and resistant to fatigue, helping to sustain posture and oppose gravity. Phasic muscles, on the other hand, are easily fatigued and are activated only when necessary.
A sedentary lifestyle can lead to weakened and atrophied phasic muscles. This can result in musculoskeletal imbalance and joint instability, as phasic muscles lengthen and weaken in response to under-use.
To strengthen phasic muscles, specific training is required. Rest intervals are important, as phasic muscles need to be trained more to allow the tonic muscles to relax.
