According to training theory, eccentric contraction is one of the 3 possible forms of muscle work, along with isometrics and concentrics. It plays an important role in movement sequences in everyday life and in sports.
What is eccentric contraction?
Eccentric muscle work is characterized by lengthening a muscle while simultaneously contracting it. Eccentric muscle work is characterized by a muscle being lengthened with simultaneous contraction. The attachment points of the tendons to the involved bones 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, 2 protein filaments in the sarcomeres are responsible for controlling this process, actin and myosin. The actin filaments are attached to the outer boundaries of the units, while the intervening myosin is attached to them with heads. During a contraction, the myosin heads flip over, striving 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 forces acting from outside. In an eccentric contraction, the myosin heads hold the tension but give way, allowing the actin filaments to slide back outward and the sarcomere to lengthen. As it lengthens, more and more connections are forced to break away. Eventually, only a few myosin heads remain to maintain contact and apply all the force. As a result, the mechanical load during eccentric contraction is very high in the individual functional subunits and in the muscle as a whole.
Function and task
Eccentric contractions and the associated muscle work have an important function in many movement sequences that involve 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 stresses 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 that activate the muscles that work against gravity. In standing, for example, these are the knee extensors, and in supporting, the triceps on the upper arm. The objective pursued by the central nervous system is fall prevention and protection from injury. The knee extensors, predominantly the quadriceps femoris muscle, are eccentrically engaged during squats, preventing us from collapsing. The same mechanism takes effect when setting down loads that have previously been lifted with the arms. The elbow flexors, the biceps brachii muscle and the brachialis muscle, play an important role in this process.
brachialis muscle. Such strains often occur 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 with controlled eccentric muscle work. Eccentric muscle work is also an important factor in sports and especially in strength training. In many sports, sudden and controlled deceleration movements are a very significant performance factor, especially when an opponent is involved. Good strength values in the eccentric range give athletes an advantage 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 of not only achieving an increase in strength in the sense of hypertrophy, but also improving the function of the muscle. In the context of rehabilitation after injury or illness, eccentric strength training is also an important component. While concentric training primarily optimizes blood flow and the metabolic function of the muscle, eccentric strength training leads more quickly to an improvement in stability and safety. This is especially true in the case of diseases and injuries that affect leg function.
Diseases and ailments
All types of contractions, and therefore strength development, can be affected by various diseases and injuries.However, the eccentric component, unlike the concentric, is affected even with short-term inactivity. Injuries in the muscle such as strains, muscle fiber tears and complete muscle tears hurt during all contractions. During eccentric inactivities, the intensity of pain is usually much higher than during the other types of contractions due to the greater mechanical stress. During prolonged inactivity, deterioration of the muscle’s metabolic status plays an important role in addition to the pain problem. A typical symptom of a mechanical problem in the muscle is the increase in pain after exercise. Diseases and injuries that result in complete or incomplete paralysis of individual muscles or muscle chains rapidly lead to muscle deterioration and consequent loss of strength. These mechanisms include, for example, spinal cord injuries resulting in paraplegia or peripheral nerve lesions resulting in flaccid paresis of the supplied muscles. Eccentric contraction is affected by such processes more rapidly and more frequently than the other forms of contraction. This is particularly evident in paraplegics who have little or no leg function. Often, affected people are able to stand or walk a few steps with assistive devices. They lock their knees in hyperextension and thus achieve a certain stability via the joints, without active muscles. As soon as this knee position is resolved towards flexion, the leg axis can no longer be slowed down and held when gravity is applied. The same applies to diseases that lead to systemic muscle loss, such as the group of muscular dystrophies and amyotrophic lateral sclerosis. These diseases progress inexorably. During this process, eccentric functions are affected first, isometric and concentric contractions are possible for longer. This has immediate consequences for everyday activities such as walking and standing. Other loads and movements that are not as affected by gravity are longer feasible.
