Eccentric exercise

Muscles produce force in three main ways: concentric, in which the muscle shortens as it produces force; isometric, in which it holds steady with almost no change in length; and eccentric (lengthening), in which the muscle produces force while lengthening. Eccentric exercise refers to the third of these forms.

The lowering phase of a push-up, the downward phase of a squat, and slowly lowering a dumbbell are all eccentric. In everyday life, muscles also lengthen to support the body when we walk downstairs, sit down in a chair, or land while running. An easy way to think of this is as a brake that controls your speed as gravity pulls your body downward.

The same muscle can produce more force eccentrically than its maximum concentric force. So even with the same weight, the slow lowering phase places a greater stimulus on the muscles and tendons. This is why using the eccentric phase separately has become an established approach in rehabilitation and training.

The name can be confusing: despite the word “contraction,” the muscle actually gets longer during the eccentric phase. This is because it slowly lengthens while maintaining force against gravity or a load. When you lift a dumbbell, the biceps brachii shortens to produce force; when you slowly lower it again, the same muscle lengthens while maintaining force. This “lowering” phase is eccentric.

There are several names for this same phase. “Eccentric training,” “negative training,” and “slow-lowering exercise” all emphasize this phase. Heel drops, in which you slowly lower your heels, are a typical example.

The eccentric phase uses relatively little energy. This means that producing the same force tends to cause less breathlessness and a smaller rise in heart rate. However, the mechanical load on the muscles and tendons is high, so people unaccustomed to it may experience lingering muscle soreness.

Eccentric contraction is well known as the form of exercise that produces the most pronounced delayed onset muscle soreness. As muscles produce force while lengthening, microscopic damage occurs in the muscle fibers and connective tissue. Inflammation and nerve sensitization then follow during recovery, showing up as soreness about a day later. Characteristically, it starts around 12–24 hours after exercise rather than immediately afterward, and is most severe between 24–72 hours.

The degree of soreness depends on how familiar the stimulus is. It is more pronounced with exercise you have not done for a long time or movements you are trying for the first time, and repeating the same exercise greatly reduces soreness the next time. This is called the repeated bout effect. It is easy to assume that lactate causes muscle soreness, but the eccentric phase actually produces less lactate, so the soreness is explained as arising from other causes (Lactate).

Tendon rehabilitation is where eccentric exercise has attracted the most attention. Chronic tendinopathy is understood as a disruption in the process by which a tendon adapts to load. The foundation of rehabilitation is therefore to gradually reintroduce tolerable loads, helping the tendon adapt to new loading.

A study by Alfredson et al. (1998) helped bring eccentric exercise to prominence in this context. Fifteen people with chronic Achilles tendinopathy performed slow heel-lowering exercises for 12 weeks (180 repetitions a day), and the authors reported that all participants returned to their pre-injury level of activity. This heel-drop protocol subsequently became the most widely used exercise in rehabilitation for midportion Achilles tendinopathy.

Follow-up studies have reported similar improvements with isotonic approaches involving slow movements with heavy weights. As a result, current rehabilitation practice emphasizes both the eccentric phase itself and the principle of gradually applying sufficient load.

Tendon rehabilitation often follows a framework that progressively increases the demands of loading. It starts with isometric exercise (holding), moves on to isotonic exercise (lifting and lowering), and finally progresses to energy storage and release (springing movements, plyometrics). The eccentric phase often appears in the middle stage. It is commonly introduced once some load can be tolerated, rather than early on when pain is severe. Moving to the next stage after the tendon has adapted to the stimulus at each stage can help avoid sudden spikes in load.

The principle by which all resistance stimuli, including eccentric exercise, drive tissue adaptation is called mechanotransduction. Cells detect mechanical load and convert it into chemical signals, leading to the production of proteins such as collagen and the remodeling of tissue. This applies not only to muscles but also to tendons, cartilage, and bones.

However, adaptation rates differ between tissues. Muscles adapt relatively quickly, while tendons, ligaments, and bones follow more slowly. Even if you feel that your strength has already improved, your tendons may still be preparing, so it is better to increase load at the pace of the slowest-adapting tissue (Load-capacity relationship, Load management).

Within the eccentric phase, the lengthened phase refers specifically to the position reached after lowering to a point where the muscle is substantially lengthened under load. Examples include the bottom of a deep squat or the point where your arm is nearly straight as you slowly lower a dumbbell.

Slowly lowering into this range while producing force also provides a stimulus similar to stretching. A body of research therefore suggests that strength training through a wide range of motion alone may also improve flexibility (Stretch tolerance theory). This perspective suggests that a well-designed strength exercise can address both goals, rather than treating strength training and stretching as separate activities.

Training muscles that are frequently injured during running, such as the hamstrings, has also drawn attention to methods that require force production in a lengthened position. The explanation is that this may help prepare the muscles to produce force in the position they encounter as the leg reaches forward during running.

• Lower slowly. On stairs or during squats, simply taking 3–4 seconds to lower yourself, more slowly than you rise, can provide an eccentric stimulus.
• Start light. Unfamiliar eccentric exercise can cause pronounced soreness the next day. Start with fewer repetitions and lighter weights, then increase gradually.
• Check how your body responds the next day. If soreness is greater than usual, try adjusting by reducing the load a little in your next session.
• Try heel drops at the edge of a step. Stand with only the balls of your feet supported on the edge of a step, then slowly lower your heels. Hold the handrail to keep your balance steady.
• If your Achilles tendon hurts, work with a professional. When a tendon is painful, a safer approach is to proceed with a number of repetitions and pain limits tailored to you.

“Eccentric” refers to a “type” of contraction. It is not the name of an exercise program, and it differs from other seemingly similar concepts as follows.

• Concentric contraction is the phase in which the force produced by the muscle exceeds the external resistance, causing the muscle to shorten. It is the opposite phase paired with eccentric contraction.
• Isometric exercise involves producing force with almost no change in joint angle or muscle length. In progressive loading, it is often placed in an early stage before eccentric exercise.
• Isotonic exercise involves moving a joint while lifting a constant weight. It includes both concentric and eccentric phases.
• Muscle strain is not a type of exercise but an injury involving a tear in muscle fibers or the area where muscle and tendon meet. It is discussed alongside eccentric exercise because it often occurs during the eccentric phase.