User:Sandstein/Drafts/Muscle soreness

Delayed onset muscle soreness (DOMS), also called muscle fever, is the pain and stiffness felt in muscles about 24 to 72 hours after unaccustomed and/or strenuous exercise. It is a symptom of muscle damage caused by eccentric exercise. After such exercise, the muscle adapts rapidly to prevent muscle damage, and thereby DOMS, in repeated bouts.

Characteristics
DOMS is perceived as a dull, aching pain in the affected muscle, often combined with tenderness and stiffness. The pain is felt only when the muscle is stretched, contracted or put under pressure, not when it is at rest.

Although there is variance among exercises and individuals, DOMS usually increases in intensity in the first 24 hours after exercise, peaks from 24 to 72 hours, then subsides and disappears after about five to seven days after exercise.

Cause
DOMS is caused by eccentric exercise, that is, exercise consisting of eccentric (lengthening) contractions. Isometric (static) exercise causes much less DOMS, and concentric (shortening) exercise causes none.

Mechanism
DOMS was first described in 1902 by Theodore Hough, who concluded that this kind of soreness is "fundamentally the result of ruptures within the muscle". This is still considered broadly valid, although DOMS does not appear to involve the rupture of whole muscle fibers. What has been observed to accompany DOMS are ultrastructural disruptions of myofilaments, especially at the Z-disc, as well as damage to the muscle's connective tissue. That tissue damage may relate most directly to DOMS, as it may increase the mechanical sensitivity of the muscle nociceptors, or pain receptors, and cause pain with stretching and palpitation. The delayed onset of the soreness may occur because the inflammatory response process that sensitizes the nociceptors takes some time. However, the relationship between damage, inflammation and DOMS is not yet completely understood.

Two other theories that have been advanced to explain DOMS, muscle spasms and the presence of lactic acid in the muscle, are now considered unlikely to be correct, since there is evidence to refute them. In particular, lactic acid is removed from the muscle within an hour of intense exercise, and can't therefore cause the DOMS which normally begins about a day later.

Relation to other effects
Although DOMS is a symptom associated with muscle damage, its magnitude does not necessarily reflect the magnitude of muscle damage.

DOMS is one of the temporary changes caused in muscles by unaccustomed eccentric exercise. Other such changes include decreased muscle strength, reduced range of motion and muscle swelling. It has been shown, however, that these changes develop independently in time from one another and that therefore DOMS is not the cause of the reduction in muscle function.<ref name="Nosaka 66" /

Warning sign?
DOMS might conceivably serve as a warning to reduce muscle activity so as to prevent further injury. However, further activity temporarily alleviates the soreness, even though it causes more pain initially. Continued use of the sore muscle also has no adverse effect on recovery from DOMS and does not exacerbate muscle damage. It is therefore unlikely that DOMS is in fact a warning sign not to use the affected muscle.

Repeated-bout effect
After performing an unaccustomed eccentric exercise and exhibiting severe DOMS, the muscle rapidly adapts to attenuate further damage from the same exercise. This is called the "repeated-bout effect".

As a result of this effect, not only is DOMS attenuated, but other indicators of muscle damage, such as swelling, reduced strength and reduced range of motion, are also faster recovered from. The effect is mostly, but not wholly, specific to the exercised muscle: experiments have shown that some of the protective effect is also conferred on other muscles.

The magnitude of the effect is subject to many variations, depending for instance on the time between bouts, the number and length of eccentric contractions and the exercise mode. It also varies between people and between indicators of muscle damage. Generally, though, the protective effect lasts for at least several weeks. It seems to gradually decrease as time between bouts increases, and is undetectable after about one year.

The first bout does not need to be as intense as the subsequent bouts in order to confer at least some protection against DOMS. For instance, eccentric exercise performed at 40% of maximal strength has been shown to confer a protection of 20 to 60% from muscle damage incurred by a 100% strength exercise two to three weeks later. Also, the repeated-bout effect appears even after a relatively small number of contractions, possibly as few as two. In one study, a first bout of 10, 20 or 50 contractions provided equal protection for a second bout of 50 contractions three weeks later.

The reason for the protective effect is not yet understood. A number of possible mechanisms, which may complement one another, have been proposed. These include neural adaptations (improved use and control of the muscle by the nervous system), mechanical adaptations (increased muscle stiffness or muscle support tissue) and cellular adaptations (adaptation to inflammatory response and increased protein synthesis, among others).

Prevention
DOMS can be attenuated or prevented by gradually increasing the intensity of a new exercise program, thereby taking advantage of the repeated-bout effect.

DOMS can theoretically be avoided by limiting exercise to concentric and isometric contractions (although eccentric contractions in some muscles may be unavoidable, especially when muscles are fatigued). Limiting the length of eccentric muscle extensions during exercise (which may also not be practical depending on the mode of exercise) may also afford some protection against DOMS. A study comparing arm muscle training at different starting lengths found that training at the short length reduced muscle damage indicators by about 50% compared to the long length, but this effect was not found in leg muscles.

Stretching before and after exercise has been suggested as a way of reducing delayed onset muscle soreness, as have warming up before exercise, cooling down afterwards, and gently warming the area. However, there is also evidence that the effect of stretching on muscle soreness is negligible, and overstretching can itself cause DOMS.

Treatment
DOMS disappears by itself after about 72 hours. If treatment is desired, any measure that increases blood flow to the muscle, such as low-intensity work, massage, hot baths or a sauna visit may help somewhat.

Counterintuitively, continued exercise may temporarily suppress DOMS. Exercise increases pain thresholds and pain tolerance. This effect, called exercise-induced analgesia, is known to occur in endurance training (running, cycling, swimming), but little is known about whether it also occurs in resistance training. There are claims in the literature that exercising sore muscles appears to be the best way to reduce the soreness, but this has not yet been systematically investigated.