When in a concentric exercise, shortening of a muscle occurs as the myosin and actin cross bridges repeatedly attach and detach to draw the actin across the myosin — creating force. Each cross-bridge attachment and detachment cycle is powered by the splitting of one molecule of adenosine triphosphate (ATP). Examples of such exercises include kicking a ball or lifting a weight. In controlled release reversals of such concentric motions, the eccentric movement stretches the muscle with opposing force that is stronger than the muscle force. When myofilaments of the muscle fiber are stretched in such eccentric contractions there can be reduced numbers of detachments of cross bridge myosin and actin links. With more cross bridges remaining attached there is greater force production in the muscle. Examples of activities involving eccentric muscle contraction include walking down a hill or resisting the force of gravity while lowering a heavy object. Eccentric actions place a stretch on the sarcomeres to the point where the myofilaments may experience strain, otherwise known as exercise induced delayed onset muscle soreness (DOMS). One area of research that has much promise in relation to DOMS and eccentric exercise is the repeated-bout effect (RBE). To help prevent or lessen DOMS from eccentric exercise, or to facilitate recovery from it, the exerciser would eccentrically stimulate the muscle then repeat at weekly intervals to build up strength and allow the strain (in response to a given force level) to reduce over time. Muscle injury Eccentric contractions are a frequent cause of muscle injury when engaging in unaccustomed exercise. But a single bout of such eccentric exercise leads to adaptation which will make the muscle less vulnerable to injury on subsequent performance of the eccentric exercise. Findings Several key findings have been researched regarding the benefits of eccentric training: Eccentric training creates greater force owing to the "decreased rate of cross-bridge muscle detachments." Patients and athletes will have more muscle force for bigger weights when eccentric training. Eccentric contractions use less energy and actually absorb energy that will be used as heat or elastic recoil for the next movement. Increased DOMS leads to more tenderness in eccentric, rather than pure pain or tendon swelling amongst patients. Repeated-bout Effect markedly reduces DOMS. "Completing bouts of eccentric training and then repeating the workout 1 week (or more) later will result in less DOMS after the second workout." Older individuals are less vulnerable to injury