Dominic Stone
Fusiform muscles, also known as strap muscles, are a type of muscle with a parallel-fibre arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle. This muscle architecture is found in muscles where the fibres are parallel to the force-generating axis. Fusiform muscles are generally associated with a greater range of motion and joint velocity compared to muscles with a different fibre arrangement but the same cross-sectional area. Examples of fusiform muscles include the biceps brachii, sartorius, and brachioradialis muscles.
| Characteristics | Values |
|---|---|
| Definition | A muscle that has a spindle shape, being wider in the middle and narrowing towards both ends. |
| Muscle fibres | Arranged parallel to each other and the long axis of the muscle. |
| Range of motion | Fusiform muscles have a greater range of motion and joint velocity compared to muscles with a different fibre arrangement but the same cross-sectional area. |
| Force | The force produced by fusiform muscles is concentrated into a small area. |
| Examples | Biceps brachii, sartorius, brachioradialis, and sternohyoid muscles. |
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What You'll Learn
Fusiform muscles have a greater range of motion and joint velocity
A fusiform muscle, also known as a strap muscle, is a type of muscle with a parallel-fibre arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle. The fibres run the entire length of the muscle, narrowing at each end to form a spindle shape.
Fusiform muscles are generally associated with a greater range of motion and joint velocity compared to muscles with a different fibre arrangement but the same cross-sectional area. This is because the parallel arrangement of the fibres allows for the greatest degree of shortening, enabling the muscle to produce a quick and wide range of motion.
The shape of a muscle is an important indicator of its specific action. For example, long, strap-like fusiform muscles typically provide large ranges of motion, whereas thick, short muscles typically provide large forces. Triangular muscles, such as the gluteus medius, have large proximal attachments that provide a well-stabilized base for generating force. Rhomboidal muscles, such as the rhomboids or the gluteus maximus, have expansive proximal and distal attachments that make them well-suited for stabilizing a joint or providing large forces.
In contrast, fusiform muscles have a smaller cross-sectional area than pennate muscles, which have a feather-like shape with many muscle fibres. Despite this, fusiform muscles are still able to generate sufficient force for their specific functions. For example, the hamstrings are a fusiform muscle group that is specialized for fast contractions, and the gastrocnemius is a fusiform muscle that facilitates ankle plantarflexion, knee flexion, and subtalar inversion.
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They have a parallel-fibre arrangement
A fusiform muscle, also known as a strap muscle, is a type of muscle with a parallel-fibre arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle. This arrangement results in a spindle shape, with the muscle fibres running parallel to each other and narrowing at each end. The thickest part of the muscle is typically near its middle.
The parallel-fibre arrangement in fusiform muscles provides unique functional characteristics. The force produced by these muscles is concentrated into a small area due to their shape. An example of this is the biceps brachii, which has a fusiform architecture type. The biceps brachii flexes the forearm and produces a large range of motion.
Compared to other muscle types, fusiform muscles generally exhibit a greater range of motion and joint velocity for a given cross-sectional area. This is because the parallel arrangement of muscle fibres allows for efficient force transfer along the length of the muscle. As a result, fusiform muscles are considered versatile due to their ability to change the direction of pull by adjusting the contraction of the fibres.
It is important to distinguish fusiform muscles from other muscle shapes, such as triangular or convergent muscles. Convergent muscles, like the pectoralis major, have a broader nature as their fibres converge at one end and spread out at the other. This broader shape results in a weaker pull on the attachment site compared to the concentrated force of fusiform muscles.
In summary, fusiform muscles, with their parallel-fibre arrangement, offer a unique set of mechanical advantages. The spindle shape and fibre alignment contribute to their range of motion, joint velocity, and force concentration capabilities. Examples of fusiform muscles include the biceps brachii, sartorius, and brachioradialis, each demonstrating the ability to produce quick and wide ranges of motion.
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They are also known as strap muscles
A fusiform muscle, also known as a strap muscle, refers to a type of muscle that has a parallel-fiber arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle. Fusiform muscles are generally associated with a greater range of motion and joint velocity compared to muscles with a different fibre arrangement but the same cross-sectional area. This is because the strap-like arrangement provides the greatest degree of shortening, enabling the muscle to produce a quick and wide range of motion.
The shape of a fusiform muscle is like a spindle, being wider in the middle and narrowing towards both ends. The thickest part of the muscle is usually near its middle, with the tendons that attach the muscle to bones restricted to the ends. The force produced by fusiform muscles is concentrated into a small area.
Examples of fusiform muscles include the biceps brachii, sartorius, and sternohyoid muscles. The biceps brachii is an example of a fusiform parallel muscle and is responsible for flexing the forearm. The sartorius muscle is a flat sheet that expands at the ends to make broad attachments.
Most skeletal muscles in the body have a parallel fibre arrangement. Parallel muscles can be further divided into fusiform and non-fusiform types based on their shape. Fusiform muscles are more spindle-shaped, while non-fusiform muscles are more rectangular with a constant diameter.
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Examples include the biceps brachii
A fusiform muscle, also known as a strap muscle, is a type of muscle with a parallel-fiber arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle. Fusiform muscles are generally associated with a greater range of motion and joint velocity compared to muscles with a different fibre arrangement but the same cross-sectional area.
The biceps brachii is a large, thick, fusiform muscle on the upper arm's ventral portion. As the name implies, this muscle's proximal attachment has two heads. The short head is sometimes referred to as "caput breve", while the long head is also called "caput longum". The biceps brachii is also an important landmark for locating the brachial artery during physical examination and ultrasound-guided arterial cannulation.
The biceps brachii functions as a powerful supinator of the forearm, i.e. it turns the palm upwards. This action, which is aided by the supinator muscle, requires the humeroulnar joint of the elbow to be at least partially flexed. If the humeroulnar joint is fully extended, supination is then primarily carried out by the supinator muscle. The biceps are involved in tasks such as lifting, sports involving throwing and racket use, and gesturing.
The biceps brachii is one of the most variable muscles in the human body. In 10% of cases, it has a third head arising from the humerus, and four, five, and even seven supernumerary heads have been reported in rare cases. The biceps brachii is also one of three muscles that flex the elbow and it does this work along with the brachialis and brachioradialis.
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They are less powerful than penniform muscles
Fusiform muscles, also known as strap muscles, are a type of muscle with a parallel-fibre arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle. They are called fusiform muscles because they narrow at each end, forming a spindle shape. The thickest part of the muscle is usually near its middle.
Examples of fusiform muscles include the biceps brachii, sartorius, and sternohyoid muscles. Fusiform muscles are generally associated with a greater range of motion and joint velocity compared to muscles with a different fibre arrangement but the same cross-sectional area. This is because the strap-like arrangement of fusiform muscles provides the greatest degree of shortening, enabling the muscle to produce quick and wide ranges of motion.
However, despite their advantages in range of motion and joint velocity, fusiform muscles are less powerful than penniform muscles. This is because the force produced by fusiform muscles is concentrated into a small area. The shape of a fusiform muscle, with its tapered ends, means that the force generated by the muscle fibres is focused on a narrower region. In contrast, penniform muscles have a broader structure that allows them to generate force over a larger area, resulting in greater overall power.
Additionally, the type of muscle fibre also plays a role in force production. There are three main types of muscle fibres: Type I, Type IIa, and Type IIb. Type I fibres have a slow rise in force and an overall low force production. Type IIa fibres exhibit fast contraction and a fast rise in force, maintaining some of their force production with repeated activity due to moderate fatigue resistance. Type IIb fibres have extremely large force production but are easily fatigued and cannot maintain force for more than a few contractions. The specific combination and arrangement of these muscle fibres within a fusiform or penniform muscle can further contribute to the difference in power between the two muscle types.
In summary, while fusiform muscles excel in providing a greater range of motion and joint velocity due to their parallel-fibre arrangement and strap-like shape, they are less powerful than penniform muscles. This is a result of the force concentration in a smaller area for fusiform muscles and the broader structure of penniform muscles, as well as the specific types and arrangements of muscle fibres within each muscle type.
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Frequently asked questions
Fusiform muscles, also known as strap muscles, are a type of muscle with a parallel-fibre arrangement. This means that the muscle fibres are arranged parallel to the longitudinal axis of the muscle.
Fusiform muscles are spindle-shaped, wider in the middle and narrowing at both ends.
Examples of fusiform muscles include the biceps brachii, sartorius, and brachioradialis.
Fusiform muscles generally have a greater range of motion and joint velocity compared to muscles with different fibre arrangements but the same cross-sectional area. However, they are not as powerful as penniform muscles.
