Dominic Stone
Muscle excursion refers to the distance between a muscle's maximum elongation and maximum shortening. Excursion is important in regulating sarcomere number in growing animals, and it plays a role in muscle contracture after tendon injuries. During tendon transfer surgeries, muscles are often overstretched, and limb lengthening can cause muscle fibers to stretch beyond their initial length. While it is assumed that muscles will adapt to the stretch, there is a lack of functional measurements to support this. Muscle excursion is also relevant in the context of tendon repair, as preserving muscle length and excursion can impact the progression of muscle contracture.
| Characteristics | Values |
|---|---|
| Definition | The distance between maximum elongation and maximum shortening |
| Purpose | To allow the joint to move through its entire range |
| Factors | Serial sarcomere number, contraction velocity, and physiological cross-sectional area (PCSA) |
| Regulation | Excursion regulates sarcomere number in growing animals |
| Adaptation | Immobilizing muscle in stretched or shortened positions affects sarcomere number |
| Growth | Increased muscle excursion may lead to increased longitudinal muscle growth |
| Tendon Injury | Preserving muscle length and excursion can prevent muscle contracture after tendon injury |
| Tension | Tension is the force within a muscle, combining passive and active tension |
| Contractile Components | Skeletal muscles generate length and velocity-dependent forces for movement or stability |
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What You'll Learn
- Muscle excursion is the change in muscle length to produce a full range of joint motion
- Excursion is important in regulating sarcomere number in growing animals
- Muscle excursion is proportional to contraction velocity
- Excursion length can be used to evaluate muscle contracture after tendon injury
- Muscle excursion is determined by a range of muscle lengths where active tension is >50% of Po
Muscle excursion is the change in muscle length to produce a full range of joint motion
Muscle excursion is the change in muscle length required to produce a full range of joint motion. It is the distance between maximum elongation and maximum shortening, and it allows the joint to move through its entire range. Typically, a muscle can be shortened to about half its normal resting length and stretched up to twice its normal resting length.
Muscle excursion is important in regulating sarcomere number, particularly in growing animals. Sarcomeres are the contractile units within a muscle, and their number is influenced by the working length of the muscle. Immobilising adult skeletal muscles in stretched or shortened positions can increase or decrease sarcomere number, respectively, with the muscle adapting to near-optimal sarcomere lengths at the immobilised length. In growing animals, increasing muscle excursion leads to increased sarcomere addition, while decreasing excursion has the opposite effect.
Studies have shown that muscle excursion is significant in the context of tendon transfer surgeries. During such procedures, muscles are often overstretched, which can result in decreased muscle function. However, it is assumed that muscles will adapt to the stretch over time, leading to functional recovery. Nevertheless, there is a lack of functional measurements to support this assumption, highlighting the importance of investigating muscle adaptation to chronic length changes.
Additionally, muscle excursion plays a role in muscle contracture after tendon injuries. Experimental studies have demonstrated that preserving muscle length and excursion can help prevent irreversible muscle contracture following tendon injuries. These findings have implications for the management of acute tendon injuries and neglected tendon ruptures.
Overall, muscle excursion is a critical aspect of muscle biomechanics, influencing muscle function, adaptation, and recovery. Understanding the relationship between muscle excursion and sarcomere number, as well as its role in surgical and injury contexts, is essential for optimising muscle health and performance.
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Excursion is important in regulating sarcomere number in growing animals
Excursion is the change in muscle length required to produce the full range of joint motion. It is important in regulating sarcomere number in growing animals. The number of sarcomeres in series in skeletal muscle fibres or fascicles (sarcomere number) is influenced by mechanical signals, which remain speculative. However, studies have shown that increasing muscle excursion results in increased serial sarcomere addition in growing animals.
A procedure assumed by Crawford (1954, 1961) to increase muscle excursion was found to increase longitudinal muscle growth in young animals. This procedure involved releasing the tibialis anterior (TA) tendon from its restraint at the ankle joint in 3- to 4-week-old rabbits. After 4 months, the muscle belly length was 20% longer for the released tendon compared to the control tendon. This suggests a potential relationship between increased muscle excursion and increased sarcomere number.
Studies have also shown that immobilizing adult skeletal muscle in stretched or shortened positions produces increases or decreases in sarcomere number. The adaptations in sarcomere number appear to produce near-optimal sarcomere lengths at the immobilized muscle length. These results indicate that the working length of the muscle is important in regulating sarcomere number.
In growing animals, muscle excursion may play a significant role in regulating sarcomere number. Immobilizing growing muscle in a stretched position decreases sarcomere number relative to the control muscle. This is in contrast to the results observed in adult animals.
Furthermore, tendon transfer surgeries often involve overstretching the muscles, which can lead to limb lengthening and muscle fibers being stretched beyond their initial length. While surgeons assume that muscles will adapt to the stretch, there is limited experimental evidence to support this. Normal skeletal muscle exhibits a relationship between serial sarcomere number and muscle excursion, but this correlation has not been consistently demonstrated in stretched muscles.
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Muscle excursion is proportional to contraction velocity
Muscle excursion refers to the distance between a muscle's maximum elongation and maximum shortening. Generally, a muscle can be shortened to about half of its resting length and stretched twice its resting length. The muscle excursion is important in regulating the number of sarcomeres in skeletal muscle fibres or fascicles.
The force of a muscle contraction is proportional to the contraction time. The longer the contraction time, the greater the force of contraction. The force-velocity relationship relates to the speed at which a muscle changes its length, usually regulated by external forces such as load or other forms of resistance.
The force generated by a muscle contraction is also dependent on the amount of overlap between thin and thick myofilaments. The greater the overlap, the larger the contraction force. The length-tension relationship relates the strength of an isometric contraction to the length of the muscle at which the contraction occurs. Muscles operate with the greatest active tension when close to their ideal length, which is often their resting length.
While muscle excursion is important in regulating sarcomere number, it is important to note that there is a disconnect between the functional and structural properties of muscles. Specifically, muscle excursion was found to be significantly lower in transferred muscles compared to controls, even though serial sarcomere numbers had increased. This suggests that muscle excursion does not directly correlate with increased serial sarcomere numbers after muscle adaptation to stretched tendon transfer.
In summary, muscle excursion is related to contraction velocity and the number of sarcomeres in series, with longer contraction times resulting in greater contraction forces. However, the relationship between muscle excursion and serial sarcomere numbers is more complex and may vary depending on the specific muscle and its adaptation to external factors such as tendon transfer surgeries.
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Excursion length can be used to evaluate muscle contracture after tendon injury
The distance between maximum elongation and maximum shortening of a muscle is referred to as its excursion length. Excursion length is important in regulating sarcomere number, which is the number of contractile units in a muscle. In the case of tendon injury, muscle contracture can occur if the tendon repair is delayed, leading to intramuscular fibrosis and irreversible muscle contracture.
A study on the effect of muscle length and excursion on muscle contracture after tendon injury in rabbits found that preserving muscle length and excursion can help prevent muscle contracture. The study had five experimental groups, with different approaches to managing the tendon. The groups that maintained half the excursion or preserved maximal muscle length showed better results in preventing muscle contracture within 4 weeks of tenotomy. However, after 8 weeks, the group that maintained excursion was the most effective in preventing muscle contracture.
Another study by Takahashi in 2012 investigated muscle functional adaptation to chronic length changes after tendon transfer surgery. It was found that muscle excursion was significantly lower in the transferred muscle compared to controls, even though serial sarcomere numbers had increased. This suggests that muscle excursion does not directly correlate with increased serial sarcomere number after muscle adaptation to stretched tendon transfer.
The findings from these studies indicate that excursion length can be a useful parameter in evaluating muscle contracture after tendon injury. By understanding the relationship between excursion length and muscle function, clinicians can make informed decisions about tendon injury management and prevent irreversible muscle contracture.
Furthermore, the concept of excursion length is closely tied to muscle biomechanics, which involves the study of muscle function and the forces generated during movement and stability. Clinicians can utilise this understanding to optimise patient management through techniques such as passive stretching and plyometric exercises.
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Muscle excursion is determined by a range of muscle lengths where active tension is >50% of Po
Muscle excursion refers to the change in muscle length required to produce the full range of joint motion. It is the distance between maximum elongation and maximum shortening. Typically, a muscle has sufficient excursion to allow the joint to move through its entire range.
The maximum value calculated from the polynomial equation for active tension is defined as Po. The muscle length where the muscle generates Po is defined as the optimal muscle length.
Functional muscle excursion is determined by a range of muscle lengths where active tension is >50% of Po. This means that muscle excursion is determined by the range of muscle lengths where the muscle generates more than half of its maximum active tension.
Muscles can be shortened to about half of their normal resting length and stretched about twice their normal resting length. The force generated by a muscle depends on the amount of overlap between thin and thick myofilaments. As muscles shorten, the probability of interaction between actin and myosin decreases, leading to a decrease in force. This is particularly notable at high shortening velocities.
Studies have suggested that optimal muscle function may be achieved by increasing muscle length, length extensibility, passive elastic stiffness, mass, and strength. This is supported by observations of increased muscle length in immobilized muscles, which may be due to an increase in collagen content and reconfiguration of collagen arrangements.
Additionally, increasing muscle excursion has been linked to increased serial sarcomere addition in growing animals. Sarcomere number may also be influenced by muscle excursion, with potential implications for muscle force-length and force-velocity properties. However, the relationship between muscle excursion and sarcomere number has not been conclusively established, and further experimental investigation is warranted.
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Frequently asked questions
Muscle excursion is the change in muscle length required to produce the full range of joint motion. It is the distance between maximum elongation and maximum shortening.
Muscle excursion is important in regulating sarcomere number. Increasing excursion results in increased serial sarcomere addition, while decreasing excursion results in decreased serial sarcomere addition.
Preserving muscle length and excursion can help prevent muscle contracture after a tendon injury. In a study on rabbit soleus muscles, it was found that maintaining maximal muscle length (Group B) was initially the most protective in preventing muscle contracture, but after 8 weeks, maintenance of excursion (Group A) became more effective.
