Soreness in the muscle during exercise is known as ‘muscle failure’, and occurs when metabolic waste and other compounds build up in the muscle cell and hinder the ability of the muscle to contract.
Muscle failure generally goes away quite quickly.…
Prolonged muscle soreness is called ‘Delayed Onset Muscle Soreness’, or DOMS. It is caused by similar mechanisms as above, but is more delayed in its clearance. This is the soreness that somebody would feel after a hard run or a brutal leg session leaving them unable to walk up stairs the next day.
Lactic Acid is commonly thought to induce muscle failure or soreness, but has not been shown to be the causative factor. It is highly correlated though, as lactic acid is produced when the muscle is sore; however it is more of a fuel source than an actual cause of soreness.
Non-steroidal Anti-inflammatory agents like Aspirin or Ibuprofen can reduce future DOMS when taken at around the time of exercise.
Some light exercise, or moving the affected joints and muscles, can also alleviate DOMS. This may be due to merely moving the affected muscles.
Proper pre-workout nutrition can also play a role in preventing DOMS, as BCAA supplementation has been shown to be beneficial (this can be consumed through whey protein or protein-containing foods or as a supplement on its own).