A dynamic muscle contraction causes joint movement and excursion of a body segment as the muscle contracts and shortens (concentric contraction) or lengthens under tension (eccentric contraction). The term concentric exercise refers to a form of dynamic muscle loading where tension in a muscle develops and physical shortening of the muscle occurs as an external force (resistance) is overcome, as when lifting a weight. In contrast, eccentric exercise involves dynamic loading of a muscle beyond its force-producing capacity, causing physical lengthening of the muscle as it attempts to control the load, as when lowering a weight.

During concentric and eccentric exercise, resistance can be applied in several ways: (1) constant resistance, such as body weight, a free weight, or a simple weight-pulley system; (2) a weight machine that provides variable resistance; or (3) an isokinetic device that controls the velocity of limb movement.

Although the term isotonic (meaning equal tension) has been used for many years to describe a resisted, dynamic muscle contraction, application of this terminology is incorrect. In fact, when a body segment moves through its available range, the tension that the muscle is capable of generating varies through the range as the muscle shortens or lengthens. This is due to the changing length-tension relationship of the muscle and the changing torque of the load. Therefore, in this textbook “isotonic” is not used to describe dynamic resistance exercise.

Rationale for Use of Concentric and Eccentric Exercise

Both concentric and eccentric exercise have distinct value in rehabilitation and conditioning programs. Concentric muscle contractions accelerate body segments, whereas eccentric contractions decelerate body segments (e.g., during sudden changes of direction or momentum). Eccentric contractions also act as a source of shock absorption during high-impact activities.

A combination of concentric and eccentric muscle action is evident in countless tasks of daily life, such as walking up and down inclines, ascending and descending stairs, rising from a chair and sitting back down, or picking up or setting down an object. Hence, it is advisable to incorporate a variety of concentric and eccentric resistance exercises in a rehabilitation progression for patients with impaired muscle performance to improve muscle strength, power, or endurance and to meet necessary functional demands.

Eccentric training, in particular, is thought to be an essential component of a rehabilitation or conditioning program to reduce the risk of musculoskeletal injury or reinjury during activities that involve high-intensity deceleration and quick changes of direction. Although chronic muscle-tendon disorders are commonly associated with activities that involve repetitive, eccentric muscle contractions, the progressive use of eccentric resistance training is advocated during the advanced stage of rehabilitaion, and its efficacy is supported by evidence.

Regimens of exercise that emphasize eccentric loading, such as plyometric training (stretch-shortening drills) or fast-velocity, eccentric isokinetic training, are often used to prepare a patient for high-demand sports or work-related activities. In addition, high-intensity, eccentric exercise is thought to improve physical performance, especially sport-related performance.

Characteristics and Effects of Concentric and Eccentric Exercise

Exercise load. A maximum concentric contraction produces less force than a maximum eccentric contraction under the same conditions In other words, greater loads can be lowered than lifted. This difference in the magnitude of loads that can be controlled by concentric versus eccentric muscle contractions may be associated with the contributions of the contractile and noncontractile components of muscle. When a load is lowered, the force exerted by the load is controlled not only by the active, contractile components of muscle but also by the connective tissue in and around the muscle. In contrast, when a weight is lifted, only the contractile components of the muscle lift the load.

With a concentric contraction, greater numbers of motor units must be recruited to control the same load compared to an eccentric contraction, suggesting that concentric exercise has less mechanical efficiency than eccentric exercise. Consequently, it requires more effort by a patient to control the same load during concentric exercise than during eccentric exercise. As a result, maximum resistance during the concentric phase of an exercise does not provide a maximum load during the eccentric phase. Although not practical, for maximum resistance during the eccentric phase, an additional load must be applied.

Although greater loads can be used for eccentric training than for concentric training, the relative adaptive gains in eccentric and concentric strength appear to be similar at the conclusion of an concentric or eccentric exercise program. It has been suggested that the higher incidence of delayed-onset muscle soreness associated with high-intensity eccentric exercise may influence the outcome of these two modes of training.

Given that eccentric exercise requires recruitment of fewer motor units to control a load than concentric exercise, when a muscle is very weak—less than a fair (3/5) muscle grade—active eccentric muscle contractions against no external resistance (other than gravity) can be used to generate active muscle contractions and develop a beginning level of strength and neuromuscular control. In other words, in the presence of substantial muscle weakness, it may be easier to control lowering a limb against gravity than lifting the limb.

There is greater stress on the cardiovascular system (i.e., increased heart rate and arterial blood pressure) during eccentric exercise than during concentric exercise, possibly because greater loads can be used for eccentric training. This underscores the need for rhythmic breathing during high-intensity exercise.

Velocity of exercise. The velocity at which concentric or eccentric exercises are performed directly affects the force-generating capacity of the neuromuscular unit. At slow velocities with a maximum load, an eccentric contraction generates greater tension than a concentric contraction. At slow velocities, therefore, a greater load (weight) can be lowered (with control) than lifted. As the velocity of exercise increases, concentric contraction tension rapidly and consistently decreases, whereas eccentric contraction forces increase slightly but then rapidly reach a plateau under maximum load conditions

A common error made by some weightlifters during high-intensity resistance training is to assume that if a weight is lifted quickly (concentric contraction) and lowered slowly (eccentric contraction), the slow eccentric contraction generates greater tension. In fact, if the load is constant, less tension is generated during the eccentric phase. The only way to develop greater tension is to increase the weight of the applied load during the eccentric phase of each exercise cycle. This usually requires assistance from an exercise partner to help lift the load during each concentric contraction. This is a highly intense form of exercise and should be undertaken only by healthy individuals training for high-demand sports or weightlifting competition. This technique is not appropriate for individuals recovering from musculoskeletal injuries.

Energy expenditure. Eccentric exercise consumes less oxygen and energy stores than concentric exercise against similar loads. Therefore, the use of eccentric activities such as downhill running may improve muscular endurance more efficiently than similar concentric activities because muscle fatigue occurs less quickly with eccentric exercise.

Mode specificity. Opinions and results of studies vary on whether the effects of training with concentric and eccentric contractions in the exercised muscle group are mode-specific. Although there is substantial evidence to support specificity of training, there is also some evidence to suggest that training in one mode leads to strength gains, though less significant, in the other mode. Because transfer of training is quite limited, selection of exercises that simulate the functional movements needed by a patient is a prudent choice.

Cross-training effect. Concentric and eccentric training has been shown to cause a cross-training effect, that is, a slight increase in strength in the same muscle group of the opposite, unexercised extremity. This effect, sometimes referred to as cross-exercise, also occurs with high-intensity exercise that involves a combination of concentric and eccentric contractions (lifting and lowering a weight). This effect in the unexercised muscle group may be caused by repeated contractions of the unexercised extremity in an attempt to stabilize the body during high-effort exercise. Although cross-training is an interesting phenomenon, there is no evidence to suggest that a cross-training effect has a positive impact on a patient’s functional capabilities.

Exercise-induced muscle soreness. Repeated and rapidly progressed eccentric muscle contractions against resistance are associated with a significantly higher incidence and severity of delayed-onset muscle soreness (DOMS) than resisted concentric exercise.Why DOMS occurs more readily with eccentric exercise is speculative, possibly the result of greater damage to muscle and connective tissue when heavy loads are controlled and lowered. It should be noted that there is at least limited evidence to suggest that if the intensity and volume of concentric and eccentric exercise are equal, there is no significant difference in the degree of DOMS after exercise.

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