Eccentric contraction

The eccentric contraction According to training theory, it is one of the 3 possible forms of muscle work alongside isometry and concentric. It plays an important role in movement sequences in everyday life and in sports.

What is the eccentric contraction?

Eccentric muscle work is characterized by elongating a muscle while contracting it. The points of attachment of the tendons to the bones involved move away from each other under active control.

The smallest functional units in the muscle fibers, the sarcomeres, are pulled apart by external forces during this process. At the molecular level, two protein filaments in the sarcomeres are responsible for controlling this process, actin and myosin. The actin threads are attached to the perimeter of the units, while the intervening myosin is attached to them with heads. When contracting, the myosin heads tip over, trying to pull the actin toward the center of the sarcomere. Whether a movement occurs, and if so, which one, is decided on the one hand by the impulse programs in the brain and on the other hand by the external forces.

With an eccentric contraction, the myosin heads hold the tension, but give way, allowing the actin filaments to slide outward again and the sarcomere to lengthen. As the extension increases, more and more connections are forced to break. In the end there are only a few myosin heads left to keep in contact and have to muster all the strength. As a result, the mechanical stress during the eccentric contraction in the individual functional subunits and in the muscles as a whole is very high.

Function & task

Eccentric contractions and the associated muscle work have an important function in many motion sequences that are associated with high mechanical stress, whether in everyday life, at work or in sports. They are there to regulate the controlled yielding in joints against gravity or other external forces.

The loads caused by gravity are regulated by automated control processes in the central nervous system. The action of gravity unconsciously triggers series of impulses from the brain and spinal cord, which activate the muscles that work against gravity. When standing, for example, these are the knee extensors, when supporting the triceps on the upper arm. The goal pursued by the central nervous system is to prevent falls and protect against injury.

The knee extensors, mainly the quadriceps femoris muscle, are turned on eccentrically during squats and thus prevent us from collapsing. The same mechanism works when lowering loads that were previously lifted with the arms. The flexors of the elbow, the biceps brachii and the Brachialis muscle. Such loads often arise during transport work, for example when workers unload loads and stack them on a pallet. First, the loads are brought to the body with concentric contractions and finally put down again with controlled eccentric muscle work.

Eccentric muscle work is also an important factor in sport and especially in strength training. In many sports, sudden and controlled braking movements are a very important performance factor, especially when an opponent is involved. Good strength values ​​in the eccentric area give athletes advantages in competition and reduce the risk of injury.

In strength training, eccentric loads are used specifically to improve the mechanical properties in the muscle. This has the advantage that not only an increase in strength in the sense of hypertrophy is achieved, but also the function of the muscle is improved.

Training eccentric strength is also an important component in rehabilitation after injuries or illnesses. While concentric training mainly optimizes blood circulation and the metabolic status of the muscles, training eccentric leads more quickly to an improvement in stability and safety. This is especially true for illnesses and injuries that impair leg functions.

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Illnesses & ailments

All types of contractions and thus the development of strength can be impaired by various diseases and injuries. In contrast to the concentric components, however, the eccentric component is affected by short-term inactivity.

Injuries in the muscle such as strains, torn muscle fibers, and complete torn muscles hurt with all contractions. During eccentric loads, the pain intensity is usually significantly higher than with the other forms of contraction due to the greater mechanical load. In the case of long periods of inactivity, in addition to the pain problem, the deterioration in the metabolism of the muscle also plays an important role. A typical symptom of a mechanical problem in the muscle is the increase in pain after exercise.

Illnesses and injuries that result in complete or incomplete paralysis of individual muscles or muscle chains quickly lead to muscle breakdown and thus to a decrease in strength. These mechanisms include, for example, spinal cord injuries with paraplegia or peripheral nerve lesions with flaccid paresis of the supplied muscles.

The eccentric contraction is affected by such processes faster and more frequently than the other forms of contraction. This is particularly evident in paraplegics who have little or no leg function. The affected people are often able to stand with aids or to take a few steps. They lock the knees in hyperextension and thus achieve a certain stability via the joints without active muscles. As soon as this knee position is released in the direction of flexion, the leg axis can no longer be braked and held under the influence of gravity.

The same applies to diseases that lead to systemic muscle breakdown, such as the group of muscular dystrophies and amyotrophic lateral sclerosis. These diseases progress inexorably. During this process, the eccentric functions are affected first, isometric and concentric contractions are longer possible. This has direct consequences for everyday activities such as walking and standing. Other loads and movements that are not so much influenced by gravity can be carried out longer.