Acute muscle soreness is the pain felt in muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

s during and immediately after strenuous physical exercise

Physical exercise

Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons including strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance, as well as for the purpose of...

. The pain appears within a minute of contracting the muscle and disappears within two or three minutes or up to several hours after relaxing it.

The following causes have been proposed for acute muscle soreness:

• Accumulation of chemical end products of exercise in muscle cells, such as H⁺
  Hydron (chemistry)
  In chemistry, a hydron is the general name for a cationic form of atomic hydrogen : most commonly a "proton". However, hydron includes cations of hydrogen regardless of their isotopic composition: thus it refers collectively to protons , deuterons , and tritons...
  
  
• Tissue edema
  Edema
  Edema or oedema ; both words from the Greek , oídēma "swelling"), formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling...
  
   caused by the shifting of blood plasma
  Blood plasma
  Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
  
   into the muscle tissue during contraction
• Muscle fatigue (the muscle tires and cannot contract any more)

Acute muscle soreness is one form of exercise-induced muscle damage, the other being delayed onset muscle soreness

Delayed onset muscle soreness

Delayed onset muscle soreness , also called muscle fever, is the pain and stiffness felt in muscles several hours to days after unaccustomed or strenuous exercise. The soreness is felt most strongly 24 to 72 hours after the exercise. It is caused by eccentric exercise...

, which appears between 24 and 72 hours after exercise.