Dominic Stone
Muscle contractions are the activation of tension-generating sites within muscle cells. Muscle shortening occurs when there is sufficient muscle tension to overcome the load, and the muscle contracts and shortens. This occurs when the force generated by the muscle exceeds the load opposing its contraction. However, it is important to note that muscle contraction does not always result in muscle shortening, as muscle tension can be produced without changes in muscle length. For example, holding something heavy in the same position can produce muscle tension without shortening. The shortening of muscles can occur in concentric contractions, where the muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. This can be observed during activities such as a bicep curl or standing up from a squatting position.
| Characteristics | Values |
|---|---|
| Definition | "To undergo an increase in tension, or force, and become shorter." |
| Concentric contraction | Occurs when there is sufficient muscle tension to overcome the load, and the muscle contracts and shortens. |
| Eccentric contraction | Occurs when the muscle works to decelerate a joint at the end of a movement as opposed to pulling a joint in the direction of the contraction. |
| Adaptive shortening | A physiological process where muscles and connective tissues generally shorten their length or become "tight" over time as a result of being chronically held in shortened positions. |
| Isometric contraction | A type of muscle contraction that generates force without changing the length of the muscle. |
| Muscle relaxation | The return of muscle fibres to a low-tension state. |
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What You'll Learn
Muscle shortening is not synonymous with muscle contraction
Muscle shortening and muscle contraction are not one and the same. Muscle contraction refers to the activation of tension-generating sites within muscle cells. When a muscle contracts, it does not always shorten. For instance, holding a heavy object like a dumbbell in the same position or holding a sleeping child in your arms produces muscle tension without any change in muscle length.
Muscles can undergo three types of contractions: shortening, no length change (isometric), and lengthening. The force–velocity relationship explains how the speed of a muscle's length change is related to the amount of force that it generates. As the shortening velocity increases, the force decreases hyperbolically until it reaches zero at the maximum velocity. Conversely, when a muscle is stretched, the force increases above the isometric maximum, reaching an absolute maximum.
Concentric contraction occurs when muscle tension is sufficient to overcome the load, causing the muscle to shorten as it contracts. This happens during activities such as bicep curls or standing up from a squatting position. Eccentric contraction, on the other hand, acts as a braking force to protect joints from damage. It occurs when the muscle works to decelerate a joint at the end of a movement, such as during downhill walking.
Adaptive shortening is a physiological process where muscles and connective tissues shorten or become "tight" over time due to being chronically held in shortened positions. This is commonly observed in individuals who sit for extended periods or engage in repetitive postural positions, such as athletes performing thousands of similar movements. Adaptive shortening can lead to symptoms like pain, reduced range of motion, and stiffness in the hips, hamstrings, and hip flexors.
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Adaptive shortening of muscles
Muscle contraction is the activation of tension-generating sites within muscle cells. However, muscle tension can be produced without a change in muscle length, such as when holding something heavy in the same position. For instance, holding a sleeping child in your arms or holding a dumbbell at the same height.
When a muscle shortens, it means it is contracting. In concentric contraction, muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. This occurs when the force generated by the muscle exceeds the load opposing its contraction. During a concentric contraction, a muscle is stimulated to contract according to the sliding filament theory.
The symptoms of adaptive shortening include pain, specifically low back pain or hip pain, and a reduced range of motion around the hips. Adaptive shortening may also manifest as a feeling of stiffness around the hips, hamstrings, and hip flexors. This condition can be reversed through specific exercises and stretches, although it may be challenging to diagnose until the muscle has already shortened significantly.
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Concentric contractions
However, concentric contractions can lead to wear and tear on your joints, increasing the risk of injury and overuse. They can also cause delayed-onset muscle soreness. Combining eccentric and concentric contractions produces greater results in strength training, as it increases muscle strength and mass.
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Eccentric contractions
Muscle contraction and shortening are not synonymous. Muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position.
Eccentric training involves using the target muscles to control weight as it moves in a downward motion. This type of training can help build muscle, improve athletic performance, and reduce the risk of injury. An example of an eccentric contraction is the action of lowering a dumbbell back down from a lift during a biceps curl—as long as the dumbbell is lowered slowly, rather than being allowed to drop.
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Muscle length and tension
Muscles can undergo three different types of contractions: isotonic, concentric, and eccentric. Isotonic contractions are further divided into concentric and eccentric contractions. Concentric contractions occur when muscle tension is sufficient to overcome the load, and the muscle contracts and shortens. This type of contraction is observed during activities such as a biceps curl or standing from a squatting position. Eccentric contractions occur when the muscle works to decelerate a joint at the end of a movement, acting as a braking force to protect the joints from damage. This type of contraction can be observed during downhill walking or while lowering something heavy.
The force-velocity relationship describes the speed at which a muscle changes its length relative to the amount of force it generates. As the shortening velocity increases, the force decreases hyperbolically until it reaches zero at the maximum velocity. Conversely, when a muscle is stretched, the force increases above the isometric maximum until it reaches an absolute maximum. This property is essential for the active damping of joints, where opposing muscles simultaneously work to return the joint to equilibrium.
The length-tension relationship describes the strength of an isometric contraction relative to the length of the muscle. Muscles generate the greatest active tension when they are close to their ideal length, often their resting length. When a muscle is stretched or shortened beyond this ideal length, the maximum active tension generated decreases. This decrease is minimal for small deviations but becomes more significant as the length deviates further from the ideal.
Adaptive shortening is a physiological process where muscles and connective tissues shorten or become "tight" over time due to being chronically held in shortened positions. This is commonly observed in individuals who sit for extended periods or engage in repetitive postural positions, such as athletes performing thousands of similar movements. Adaptive shortening can lead to symptoms such as pain, reduced range of motion, and stiffness in the hips, hamstrings, and hip flexors.
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Frequently asked questions
Muscle shortening is a part of the muscle contraction process. It occurs when there is sufficient muscle tension to overcome the load, causing the muscle to contract and shorten.
Muscle shortening and muscle contraction are not synonymous. Muscle contraction refers to the increase in tension or force, which may or may not result in a change in muscle length. Muscle shortening specifically refers to the decrease in muscle length.
There are three main types of muscle contractions: isometric, isotonic, and isokinetic. Isometric contractions involve changes in muscle tension without changes in length. Isotonic contractions involve changes in muscle length without changes in tension. Isokinetic contractions involve changes in both muscle length and tension.
Muscle shortening occurs when the muscle fibres contract and generate tension, resulting in a decrease in muscle length. This can happen during activities such as lifting a heavy object or performing a bicep curl.
Muscle shortening can have both positive and negative effects. It can help generate force and facilitate movements, but excessive or prolonged muscle shortening can lead to muscle tightness, reduced range of motion, and pain, a condition known as adaptive shortening.
