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Tonic and phasic muscle theory was developed by Czech neurologist and physiotherapist Dr. Vladimir Janda in the 1960s. Tonic muscles, also known as postural muscles, are those that are always active and resistant to fatigue. They are responsible for holding us upright and opposing gravity. Phasic muscles, on the other hand, only activate when necessary and quickly return to a relaxed state. In vertebrates, skeletal muscle is one of the three types of muscle tissue, along with cardiac and smooth muscle. Skeletal muscle fibres are typically classified as either slow (type I) or fast (type II), with slow fibres capable of sustaining longer contractions. Tonic fibres, or slow fibres, are found in varying proportions across different vertebrate species.
| Characteristics | Values |
|---|---|
| Definition | Tonic muscles are "background" muscles that act with little or no stimulus. |
| Activation | Tonic muscles activate with little or no stimulus, whereas phasic muscles only activate when we insist that they do. |
| Contraction Speed | Tonic muscles contract slowly and have great endurance. Phasic muscles contract quickly. |
| Twitching | Tonic muscles do not generate spikes and do not "twitch", whereas phasic muscles do. |
| Response to Overuse/Underuse/Trauma | Tonic muscles shorten and tighten in response to overuse, underuse, or trauma. Phasic muscles lengthen and weaken. |
| Examples | Tonic: Multifidus, pectoralis minor, upper trapezius. Phasic: Biceps Brachii, rhomboids, mid/lower trapezius. |
| Receptors | Tonic receptors adapt slowly to a stimulus, providing information on the duration of the stimulus. Phasic receptors adapt rapidly and do not provide information on duration. |
| Examples of Tonic Receptors | Pain receptors, the joint capsule, muscle spindle, and the Ruffini corpuscle. |
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What You'll Learn
- Tonic and phasic muscles work together in a cycle of contracting and relaxing to bring about movement at a joint
- Tonic muscles can be thought of as background muscles, acting with little or no stimulus
- Tonic muscles contract slowly and have great endurance
- Tonic fibres are slow fibres, a term also used to refer to mammalian fibres
- Tonic fibres do not generate spikes, unlike phasic fibres
Tonic and phasic muscles work together in a cycle of contracting and relaxing to bring about movement at a joint
Phasic muscles, on the other hand, are action muscles that use force when needed. They activate when we insist that they do. These muscles lengthen and weaken in response to over-use, under-use, or trauma. Phasic muscles include the rhomboids and mid/lower trapezius.
The tonic and phasic muscle theory, created by Dr. Vladimir Janda in the late 1960s, categorises muscles based on their predominant characteristics. However, it is important to note that muscles never work in isolation, and any given muscle or muscle group can exhibit both tonic and phasic behaviours depending on the stimulus and conditioning.
The two types of muscles work together in a cycle of contracting and relaxing, which can be likened to a conversation between two people. When one muscle contracts, the other relaxes and lengthens, allowing for movement at a joint. This partnership is crucial for maintaining proper posture and preventing musculoskeletal imbalances.
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Tonic muscles can be thought of as background muscles, acting with little or no stimulus
Tonic and phasic muscles work together in a cycle of contracting and relaxing to bring about movement at a joint. Tonic muscles can be thought of as "background" muscles, acting with little or no stimulus. Tonic muscles are responsible for holding you upright. In a deconditioned or improperly trained body, it is common for tonic muscles to shorten and tighten in response to over-use, under-use, or trauma. Phasic muscles, on the other hand, lengthen and weaken in response to these conditions.
Tonic muscles contract slowly and have great endurance, but they are also prone to overactivity. They are closer to the joints and are stabilisers. Phasic muscles, such as the biceps brachii, are fast-twitch muscles designed for brief bursts of activation. They are farther away from the joints and are used for actions, movements, and gestures.
The differing responses of tonic and phasic muscles to improper stimuli can lead to musculoskeletal imbalance and joint instability when these muscles are located on opposing sides of the agonist-antagonist relationship. For example, a person with a desk job who spends long hours sitting at a desk may find themselves constantly slouching, partly because their over-used tonic muscles (pectoralis minor and upper trapezius) are pulling their under-used phasic muscles (rhomboids and mid/lower trapezius) into an excessively lengthened position.
The concept of muscles being tonic or phasic arose from 19th-century physiological studies of frog muscles. In "tonic" states, fibres displayed prolonged contractions in response to a nerve stimulus. Tonic fibres have since been called slow fibres, a term also used to refer to mammalian fibres. Slow-tonic is a slow-twitch fibre that can sustain longer contractions.
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Tonic muscles contract slowly and have great endurance
Tonic muscles are slow-twitch muscle fibres that can remain contracted for extended periods. They are slow to respond to stimuli, taking a longer time to reach full activation and relaxation compared to phasic muscles. Tonic muscles are also known as slow fibres, a term that includes mammalian fibres, although mammalian slow fibres differ from non-mammalian slow fibres. For example, tonic fibres in frogs do not generate spikes, whereas mammalian slow fibres do.
Tonic muscles are closer to the joints and bones, and they play a crucial role in maintaining posture and keeping us upright against gravity. They have excellent endurance due to their ability to sustain prolonged contractions. This is in contrast to phasic muscles, which are fast-twitch fibres designed for brief bursts of activation. Phasic muscles contract rapidly and have poor endurance, quickly tiring due to their distance from the joints.
The interplay between tonic and phasic muscles is essential for joint stability and overall body movement. Tonic muscles are the dominant muscles, prone to overactivity and tightening, while phasic muscles are their antagonists, tending to be relaxed and lengthened. When tonic muscles are overactive, they can cause joint misalignment, leading to pain and potential injury.
Understanding the unique characteristics of tonic and phasic muscles is vital for fitness professionals and personal trainers, as it helps them design effective exercise plans to prevent and address postural issues in their clients. By employing strategic flexibility exercises to relax tonic muscles and activation or strength training to stimulate phasic muscles, fitness professionals can improve joint stability and overall body mechanics.
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Tonic fibres are slow fibres, a term also used to refer to mammalian fibres
Tonic fibres, also known as slow fibres, are one of the two types of muscle fibres that make up the skeletal muscle system in vertebrates. The concept of slow and fast fibres was first introduced in the 19th century following studies on frog muscles. While fast fibres were further divided into two or three subtypes, slow fibres were initially believed to be a homogeneous group. However, it was later discovered that slow fibres could be further categorised into two distinct groups based on their ability to generate action potentials: those without action potentials (AP-less fibres) and those with action potentials (type I fibres).
Tonic fibres, specifically those found in frogs, are classified as AP-less fibres as they do not generate spikes or action potentials. In contrast, mammalian slow fibres, or type I fibres, are capable of firing action potentials. This distinction is important as it highlights a key difference between tonic fibres in different species.
Tonic fibres are characterised by their prolonged contractions in response to a nerve stimulus. They are often referred to as "background" muscles as they act with little or no stimulus. Tonic fibres play a crucial role in maintaining posture, opposing gravity, and keeping us upright. They are resistant to fatigue and are always active, even when not deliberately activated. This is in contrast to phasic fibres, which quickly return to a relaxed state and only activate when necessary.
While tonic fibres are typically associated with slow contractions, it is important to note that they can also exhibit a combination of tonic and phasic characteristics. The behaviour of these fibres can vary depending on the stimulus and conditioning. Additionally, the specific functions of tonic fibres can differ between species, with mammalian slow fibres exhibiting twitching capabilities, also known as "slow-twitch" muscles.
In summary, the term "slow fibres" is used to describe tonic fibres, which are characterised by their slow contraction properties and their ability to maintain prolonged contractions. These fibres are essential for maintaining posture and opposing gravity. While tonic fibres are generally slow, the specific characteristics and behaviours of these fibres can vary across different species, highlighting the complexity of muscle physiology in vertebrates.
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Tonic fibres do not generate spikes, unlike phasic fibres
Tonic and phasic muscles are two types of muscle fibres that are present in the skeletal muscle system of vertebrates. The concept of muscles being slow and fast or tonic and phasic arose from physiological studies of frog muscles in the 19th century. Tonic fibres are slow fibres that display prolonged contractions in response to a nerve stimulus, while phasic fibres are fast fibres that display rapid twitches.
An important distinction between tonic and phasic fibres in frogs is their ability to fire action potentials. Tonic fibres do not generate spikes, unlike phasic fibres, which propagate them. This means that frog tonic muscles do not exhibit "twitches", unlike phasic muscles. However, it is important to note that mammalian slow fibres do fire action potentials, and mammalian slow muscles are capable of twitching.
The difference in the ability to generate spikes between tonic and phasic fibres in frogs was observed through electrical measurements. In tonic fibres, there was a delayed rectification in about 95% of the fibres, while anomalous rectification and generation of spikes were found in only about 5% of the fibres. This is in contrast to phasic fibres, which showed a linear current-voltage relationship for both outward and inward currents not exceeding 0.75 microA.
In the context of the human body, tonic muscles are responsible for holding posture and act with little or no stimulus. They can constrict and tighten, making it challenging to achieve and maintain correct posture. Phasic muscles, on the other hand, are used for dynamic movement and can weaken and lengthen, leading to slouching if they are not adequately strengthened.
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Frequently asked questions
Tonic muscles are ""background" muscles that act with little or no stimulus. They contract slowly and have great endurance. Tonic muscles are responsible for holding you upright.
Tonic muscles contract slowly and have great endurance, while phasic muscles contract quickly and have poor endurance. Tonic muscles are prone to overactivity and tightening when overactive, whereas phasic muscles lengthen and weaken in response to over-use, under-use, or trauma.
Tonic and phasic muscles work in a cycle of contracting and relaxing to bring about movement at a joint. Tonic muscles are typically shortened and tightened, while phasic muscles are lengthened and relaxed.
