What Causes Muscle Soreness?

DOMS (delayed onset muscle soreness) describes the muscle pain, muscle soreness or muscle stiffness that occurs in the day or two after exercise. This muscle soreness is most frequently felt when you begin a new exercise program, change your exercise routine, or significantly increase the duration or intensity of your exercise routine.
Delayed onset muscle soreness is a normal response to exertion and is part of an adaptation process that leads to greater stamina and strength as the muscles recover and grow.

The delayed muscle soreness of DOMS is generally at its worst within the first 2 days following a new, intense activity and slowly subsides over the next few days.

What Causes Muscle Soreness After Exercise?
Delayed onset muscle soreness is thought to be a result of microscopic tearing of the muscle fibers. The amount of soreness depends on how hard and how long you exercise and what type of exercise you do. Any movement you aren't used to can lead to DOMS, but eccentric muscle contractions cause the most soreness.

Examples of eccentric muscle contractions include going down stairs, running downhill, lowering weights and the downward motion of squats and push-ups. In addition to small muscle tears there can be associated swelling in a muscle which may contribute to soreness and cause temporary weight gain.

Active recovery is a great way to treat DOMS an speed up recovery. Active recovery includes walking, hiking, biking, or other activities. Be sure to do these activities at easy to moderate levels when treating DOMS. Easy to moderate activity will help blood flow to the areas of soreness which helps the soreness subside. Drinking plenty of water is also recommended.