Concentric Training

Concentric training is an exercise that improves the ability of a muscle to shorten in length so as to increase its ability to overcome an opposing force.

The purpose of concentric training is to improve the ability of a muscle to perform some specific action, such as raising a weight with one's arm.

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 calcium-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. 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 (180°) orientation to a right angle (90°).

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 IIA and 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 do 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, that is, 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, i.e., reducing the width of the sarcomere. Because of the way this action proceeds, it is sometimes referred to as the “sliding filament model.”

Perhaps the most familiar example of a concentric exercise is the biceps curl, in which a person lifts a weight (such as a dumbbell) using the strength of the upper arm (controlled by the biceps). Concentric training for this exercise consists in gradually increasing the weight (force; resistance) one can lift, from, say, 5 to 10 to 20 kg. Another concentric exercise used by powerlifters is the deadlift, in which a person picks up a barbell of some given weight starting with the barbell at rest on the floor. He or she raises the barbell to waist level while in a standing position. This exercise uses more than two dozen different muscles and muscle groups in the abdomen, back, legs, hips, and forearms. Some other examples of concentric exercises are:

Humans have used exercises and training to improve their strength 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 like 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 for strength training was the dumbbell in the 1700s. The dumbbell consisted of two 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 transformation of strength training from individual exercises using natural or simple synthetic materials to the use of sophisticated, specialized equipment began in the early 20th century with the invention of pulley systems, against which a person could improve his or her muscle strength. Today, individuals interested in concentric training and other strength-improvement exercises have a multitude of specialized equipment for use in very specific types of muscle training.

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 contact, although bones are unable to move. Isotonic exercise are exercises in which muscles contract and shorten (concentric exercise) or relax and lengthen (eccentric exercise).

Traditionally, athletes paid relatively little attention to the speed and pace at which they conducted an exercise. It was not unusual for an athlete to begin an exercise, move along briskly through the stage of the exercise, and then complete the workout. More recently, researchers have found that the speed and pace of an exercise can have significant effects on the final result produced by the exercise. Gain in muscle strength may, in fact, be significantly related to the time devoted to a single stage of an exercise; the rest period, if any, between the concentric and eccentric stages of the exercise; the time between repetitions; and the number of repetitions of the exercise.

The ranges in approach to concentric 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 ten seconds each. Most recently, an even slower protocol, called super slow resistance training, has been developed by Ken Hutchins, in which a complete concentric-eccentric cycle may take anywhere from 100 to 180 seconds. Variations of these three approaches have also been recommended and promoted by a number of trainers and sport medicine experts.

Concentric forces are used in virtually any type of exercise performed by any individual during recreational exercises or sporting events.

As with almost any exercise or sporting activity, a person should prepare for concentric 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 concentric 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, include sprains, strains, and tears. The type and degree of risk is associated with the type of exercise in which one is involved, along with an individual's own personal health status. For example, older individuals who have decided to initiate a program of concentric exercise (or any other type of exercise) should confer with their physicians to determine the type of exercise program that is appropriate for their own age, gender, and health status.

The effects of concentric training in and of itself, in comparison with eccentric 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 concentric training (by itself or in conjunction with other types of training) for any given situation. Some tentative conclusions can be drawn, however, such as:

See also Eccentric training ; Isometric training .