Eccentric training involves voluntary muscular movements that result in overall lengthening of a muscle in response to an external resistance or force placed on that muscle.
The purpose of eccentric training is to improve the strength of a muscle or group of muscles, increasing the amount of resistance that muscles are able to overcome in activities such as lifting, throwing, running, or jumping.
Anyone who is interested in muscle strengthening—whether for athletic competitions, to improve personal ability, or to improve overall fitness—can benefit from eccentric training. Males and females of all ages and ethnic backgrounds belong in this category. Eccentric training has also been shown to be helpful in dealing with a number of physical ailments, including anterior cruciate ligament (ACL) damage, sarcopenia (loss of muscle tissue as a result of aging), muscle tendon injuries, osteopenia (an early stage of osteoporosis), tendinosis, and chronic patellar tendonitis.
Muscle cells are very long structures that consist of bundles of myofibrils, long cylindrical structures that are batched together to make a muscle cell. Myofibrils, in turn, consist of two types of protein called myosin and actin. A single myofibril is subdivided into numerous units called sarcomeres, each of which consists of a number of matched myosin and actin units. At rest, actin and myosin are prevented from contacting each other by two other proteins: tropomyosin and the Ca++ binding protein troponin.
Groups of muscle cells are attached at each end to adjacent bones by means of tendons, which mediate any movement that occurs between muscles and bones. Muscle contraction begins when a signal from the nervous system activates a sequence of chemical changes within the muscle cells. This sequence of chemical changes causes the muscle cell to shorten, pulling on the tendons at both ends of the muscle cell. The shortening of muscle cells produced by this action is known as a concentric action. Displacement of the tendons, in turn, causes a reorientation of the position of bones attached to the tendons. For example, shortening of the biceps muscle causes a reorientation of elbow bones in such a way as to change the bones from a largely straight angle (180%) orientation to a right angle (90%) orientation.
At the termination of the original neural signal to the muscle, the muscle begins to relax. The relaxation and lengthening of a muscle is known as an eccentric action. An eccentric action can occur in one of two ways. First, the muscle can relax and lengthen almost immediately. For example, a person who has just completed the lift of a dumbbell during a biceps curl can, at that point, simply drop the dumbbell. Second, the muscle can relax and lengthen more slowly over a period of time, under the control of messages from the central nervous system. In the biceps-curl example, the dumbbell is not dropped immediately, but the arm is slowly restored to its original position. Both concentric and eccentric actions are under the voluntary control of the central nervous system. A person can choose the amount of force exerted on a resistance and the rate at which the force is applied. The presumption behind eccentric training is that this conscious control over a muscle results in hypertrophy of the muscle—that is, an increase in the mass of the cells that make up the muscle. The greater control one exerts over eccentric muscular action, the greater the strength of that muscle.
The structure and function of muscle fibers varies somewhat depending on the anatomical location. One kind of muscle fiber is known as a Type I fiber. It responds relatively slowly to nerve messages, produces relatively low force, and is relatively resistant to fatigue. Type I fibers are sometimes referred to as “slow-twitch” fibers because of their low rate of operation. Type I fibers are used primarily for aerobic exercises. Type II fibers are subdivided into Type IIA and Type IIB fibers, both of which respond more rapidly to neural messages, produce greater forces, and are less resistant to fatigue than are Type I fibers. Because they respond more quickly than Type I fibers, Type II fibers are sometimes called “fast-twitch” fibers. Type IIA fibers are used primarily for long term aerobic exercise, while Type IIB are used mostly for short-term anaerobic exercise.
The purpose of exercise is to increase the efficiency with which muscle cells function, or the amount of resistance they are able to overcome. In theory, this objective can be accomplished in one of two ways: by increasing the number of muscle cells present in the body (hyperplasia) or by increasing the size of individual muscle cells (hypertrophy). In fact, exercise achieves only the latter of these two objectives. Only a limited variety of muscle types in the body are capable of undergoing hyperplasia, and they are not the muscles used in exercise or sporting activities.
The process of muscle contraction begins when the body sends a nerve message from the central nervous system to one end of a muscle cell. That nerve message initiates a complex series of chemical reactions that activates a sequence of changes in the myosin and actin components of a myofibril. In that process, a myosin molecule essentially “grabs onto” an adjacent actin molecule and pulls it forward by one unit, much as a ratchet gear moves an adjacent gear by one unit. Each time this process is repeated, the actin molecule moves one unit further, reducing the total length of the myosin/actin combination (the width of the sarcomere). Because of the way this action proceeds, it is sometimes referred to as the “sliding filament model.”
The efficiency with which a muscle cell operates is determined by how well myosin units are able to grab onto and move actin units compared to the force against which they operate. The muscle cells in one individual's body, for example, may be able to slide actin units well enough to counteract a 10-kilogram force; that is, the muscle may be able to pick up a 10-kilogram weight. By contrast, the muscle cells in a second person's body may be able to counteract a 12-kilogram force; that is, pick up a 12-kilogram weight. The purpose of a concentric exercise is to increase the mass of one's muscle cells to extend its ability to overcome greater and greater counteracting forces, such as being able to pick up a 12-kilogram weight rather than a 10-kilogram weight.
Humans have used various forms of concentric training for millennia. Perhaps the earliest mention of formal strength training dates to about 3600 BCE in China, during a period in which rulers required their subjects to participate in regular exercises. Tomb art from ancient Egypt clearly shows men performing strength exercises by lifting bags of sand and throwing heavy objects. Literature throughout the ages refers to exercise and training activities in which participants used readily available objects, such as stones and ropes, to perform strength exercises. One of the earliest devices constructed synthetically for strength training was the dumbbell in the 1700s. The dumbbell consisted of two bell clappers joined to each other by a metal rod, similar to the modern device of the same name. (The name arose from the fact that the clappers could no longer make a noise, so they were “dumb bells.”)
The earliest research on eccentric actions is usually traced to the studies of German physiologist Adolf Fick in the early 1880s. Fick noticed that a muscle in the process of lengthening (eccentric action) could produce a greater force than when the same muscle was shortening (concentric action). Health and fitness experts saw almost no application of Fick's discovery until 70 years later, when a classic study on eccentric action was reported by three researchers at University College, London: B. C. Abbott, Brenda Bigland, and J. M. Ritchie. The researchers devised a simple and ingenuous experiment to compare concentric and eccentric actions. They joined two bicycles to each other and placed riders on each of the bicycles. While one rider attempted to peddle forward (a concentric action), the second rider attempted to prevent movement of the bicycles by braking on his/her cycle (an eccentric action). Researchers found that the rider exerting an eccentric action (braking) had to use much less force to maintain equilibrium than did the rider exerting a concentric action (trying to move forward). Trainers suddenly became aware of the potential of developing eccentric strength in improving a person's overall muscular strength. At almost the same time, Danish physiologist Erling Asmussen suggested a new term to describe this type of muscular action: excentric action (“away from the center”), which he contrasted with concentric action (“toward the center”). The somewhat more illustrative term excentric was eventually changed to its proper form of eccentric.
Most exercises can be classified into one of two general categories: isometric and isotonic. Isometric exercises are those in which muscles contract, but bones do not move. An example of an isometric exercise is pushing against an unmovable object, such as a wall, which causes the muscles to contract, although bones are unable to move. Isotonic exercises are exercises in which muscles contract and shorten (concentric exercise) or relax and lengthen (eccentric exercise).
The format in which an eccentric exercise takes place depends to a large extent on the overall objective of the exercise. Research indicates that the effectiveness of improving muscle strength for a particular physical activity (such as running or playing tennis) depends on exercising the specific muscles that will be used in the activity.
The ranges in concentric and eccentric training are reflected in historical approaches known as high intensity training (HIT), slow resistance training (SRT), and super slow resistance training (SSRT). HIT was invented in the 1970s by Arthur Jones, founder of the Nautilus health and fitness program. Jones recommended exercise programs that are brief, infrequent, and intense—programs in which muscle systems are brought nearly to the point of failure and then relaxed, with the goal of reaching maximum growth and efficiency. An alternative training program, SRT, was developed in the 1980s by American physiologist Vincent “Ben” Bocchicchio. The SRT protocol calls for slow concentric and eccentric phases of 10 seconds each. Most recently, an even slower protocol called super slow resistance training has been developed by Ken Hutchins. In SSRT, a complete concentric-eccentric cycle may take anywhere from 100 to 180 seconds. Variations of these three approaches have been recommended and promoted by a number of trainers and sports medicine experts.
As with almost any exercise or sporting activity, a person should prepare for eccentric exercising with warm-up and stretching exercises to prepare the body for the stress that will be placed on muscles during the exercise itself.
One common risk associated with eccentric exercise is muscle soreness. As efforts are made to increase muscular size and strength, overtraining can result in pain and soreness that are not life-threatening, but that may require a reassessment of the schedule used for a particular type of exercise. Overtraining can also result in a variety of muscular, tendon, and bone problems, including sprains, strains, and tears. The type and degree of risk is associated with the type of exercise, along with an individual's own personal health status. For example, older individuals who have decided to initiate a program of eccentric exercise (or any other type of exercise) should confer with their physicians to determine the type of exercise program that is appropriate for their age, gender, and health status.
The effects of eccentric training in and of itself, in comparison with concentric training, and in comparison with isometric training have been studied extensively for a variety of sports and in association with a number of body parts. The variety of research designs makes it difficult to provide any simplistic generalizations about the effectiveness of eccentric training for any given situation. One attempt to summarize research findings about eccentric training, however, was provided by American bodybuilder Aaron Bubbico and exercise scientist Len Kravitz in 2010. Among their findings were the following:
See also Muscle toning .
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National Strength and Conditioning Association, 1885 Bob Johnson Dr., Colorado Springs, CO, 80906, (719) 632-6722, (800) 815-6826, Fax: (719) 632-6367, nsca@ nsca.com, https://www.nsca.com .
National Athletic Trainers' Association, 1620 Valwood Pkwy., Ste. 115, Carrollton, TX, 75006, (214) 637-6282, http://www.nata.org .
David E. Newton, AB, MA, EdD