Victor Forge
The tonic and phasic muscle theory, created by Dr. Vladimir Janda in the 1960s, categorises muscles based on their function and response to stimuli. Tonic muscles, or postural muscles, are responsible for maintaining posture and balance, while phasic muscles are involved in movement and are activated when needed. Phasic muscles tend to lengthen and weaken in response to overuse, underuse, or trauma, while postural muscles tend to shorten and tighten. Imbalances between these muscle types can lead to musculoskeletal issues and joint instability. Understanding the differences between phasic and postural muscles is essential for designing effective exercise routines and preventing injuries.
| Characteristics | Values |
|---|---|
| Activation | Phasic muscles activate when we want them to. |
| Response to over-use, under-use, or trauma | Phasic muscles lengthen and weaken in response to over-use, under-use, or trauma. |
| Response to inactivity | The brain will disconnect from phasic muscles if the body is inactive. |
| Type of muscle fibres | Phasic muscles contain mostly fast-twitch muscle fibres. |
| Fatigue | Phasic muscles fatigue more easily. |
| Prone to | Phasic muscles are prone to inhibition. |
| Suited to | Phasic muscles are more suited to movement. |
| Colour | The fast-twitch muscle fibres in phasic muscles are white or pale due to their low oxygen stores. |
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What You'll Learn
Phasic muscles are activated voluntarily
The theory of tonic and phasic muscles was created by Dr. Vladimir Janda in the 1960s, through EMG experiments that revealed which muscles are resistant to fatigue and which are activated when called upon. Phasic muscles are predominantly Type II fast-twitch muscles, while postural muscles are mostly slow-twitch muscle fibres.
Tonic muscles are prone to shortening and tightening in response to over-use, under-use, or trauma, while phasic muscles lengthen and weaken in response to these stimuli. This can lead to muscle imbalance and joint instability, especially when the muscles are located on opposing sides of the agonist-antagonist relationship.
Postural muscles are designed to keep us balanced and upright, and have a high threshold for sustained contraction and fatigue. However, they can easily be overused. Phasic muscles, on the other hand, are more suited to movement and are more easily fatigued.
In terms of training, phasic muscle training focuses on increasing the stability of the joint by using phasic muscles. Stability here refers to the stability of the joint rather than the ability to balance on an unstable surface.
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They are prone to lengthening and weakening
Phasic muscles are more prone to lengthening and weakening than postural muscles. This is because they are mostly made up of fast-twitch muscle fibres, which are more suited to movement and have poor endurance. When phasic muscles are weak, they lengthen, and this is made worse by the tightening of an overactive antagonistic postural muscle about a joint.
Postural muscles, on the other hand, are more likely to shorten and tighten in response to over-use, under-use, or trauma. This is because they are mostly made up of slow-twitch muscle fibres, which have a greater capacity for sustained work and are prone to hyperactivity.
The imbalances between these two types of muscles can lead to musculoskeletal problems and joint instability. For example, people who sit at desks all day are constantly asking their bodies to use postural muscles, and this can lead to the body defaulting to using these muscles when exercising, which can cause pain and injury.
The tonic and phasic muscle theory was created by Dr. Vladimir Janda in the late 1960s. Tonic muscles can be thought of as "background" muscles that act with little or no stimulus and are responsible for holding you upright. Phasic muscles, on the other hand, only activate when we insist that they do.
It is important to understand the differences between these two types of muscles to address muscular imbalances and improve overall movement and stability.
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Phasic muscles are mostly extensors
Tonic and phasic muscles are two different types of muscles, categorised by their characteristics and functions. Phasic muscles are activated when we want them to be, whereas tonic muscles can be thought of as "background" muscles that act with little to no stimulus. Tonic muscles are responsible for holding us upright, while phasic muscles are responsible for movement.
When a muscle is overused, underused, or traumatised, a tonic muscle will shorten and tighten, while a phasic muscle will lengthen and weaken. This can lead to musculoskeletal imbalances and joint instability, especially when the two types of muscles are located on opposing sides of an agonist-antagonist relationship.
The concept of tonic and phasic muscles was created by Dr. Vladimir Janda in the late 1960s through EMG experiments. It is important to understand the differences between these two types of muscles to address muscular imbalances in the body and to design effective exercise routines.
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They are responsible for movement
Phasic muscles are responsible for movement. They are activated when we want them to be and contain mostly fast-twitch muscle fibres, which are more suited to movement.
When weak, phasic muscles lengthen and weaken further, which can lead to musculo-skeletal imbalance and joint instability. This is especially true when phasic muscles are located on opposing sides of the agonist-antagonist relationship with postural muscles.
Postural muscles, on the other hand, are designed to keep us balanced and upright. They contract slowly and have great endurance. They are prone to overactivity and tend to tighten when overactive.
When postural and phasic muscles are in balance, the body is better able to perform functional movements. For example, the hamstrings and glutes are mostly phasic muscles, while the erector spinae (lower back muscles) are postural. When performing squats, the body should recruit the phasic muscles as the prime movers. However, after years of sitting in a chair, it can be difficult to activate the glutes and hamstrings, leading to soreness in the lower back.
To address imbalances between postural and phasic muscles, it is important to strengthen weakened muscles and stretch tightened muscles. This can be achieved through targeted exercises and stretching protocols.
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Phasic muscles are Type II fast-twitch muscles
Phasic muscles are those that activate only when we want them to. They are the opposite of tonic muscles, which act with little or no stimulus and are responsible for holding us upright. Phasic muscles lengthen and weaken in response to overuse, underuse, or trauma.
The tonic and phasic muscle theory was created by Dr. Vladimir Janda in the 1960s. EMG experiments revealed which muscles are active and resistant to fatigue and which ones fire up only when called upon. Most tonic muscles are flexors, and most phasic muscles are extensors. Many tonic and phasic muscles have agonist-antagonist relationships, meaning they oppose one another.
Imbalances between tonic and phasic muscles can lead to dysfunction, especially when combined with poor posture, flexion-focused activities, and gravity. For example, a person who sits at a desk all day may try to sit up straight but finds themselves slouching because their overused tonic muscles (pectoralis minor and upper trapezius) are pulling their underused phasic muscles (rhomboids and mid/lower trapezius) into an excessively lengthened position.
Phasic muscles are fast-twitch muscles. There are two types of fast-twitch muscle fibers: type IIA and type IIB. Type IIA muscle fibers are called upon last to do their job, after slow-twitch type I and fast-twitch type IIB. Type IIA fibers are red to pink in color, while type IIB fibers are white/pale due to their low oxygen stores. Type IIB fibers are also called fast glycolytic (FG) fibers and have fast contractions, fatiguing more quickly than the others. Type IIA fibers, on the other hand, are resistant to fatigue and use oxygen as a fuel source, much like slow-twitch fibers.
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Frequently asked questions
Phasic muscles are those that activate when we want them to. They contain mostly fast-twitch muscle fibres and are therefore more suited to movement.
Phasic muscles contract quickly and have poor endurance. They are prone to lengthening when they are weak, and this can lead to musculo-skeletal imbalance and joint instability.
The hamstrings and glutes are mostly phasic muscles.
Postural muscles act predominantly to sustain your posture in the gravity field. They contract slowly and have great endurance. Phasic muscles, on the other hand, are more suited to movement.
Tonic and phasic muscle theory focuses on muscles that predominantly function according to the characteristics of each group. Tonic and phasic muscles often have an agonist-antagonist relationship, meaning they oppose one another.
