Acute muscle soreness

Acute muscle soreness (AMS) is the pain felt in muscles during and immediately, up to 24 hours, after strenuous physical exercise. The pain appears within a minute of contracting the muscle and it will disappear 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 lactic acid and H+
  • Muscle fatigue (the muscle tires and cannot contract any more)

There are no modern effective treatments for AMS.

Cause

Muscle soreness can stem from strain on the sarcomere, the muscle's functional unit.[1] Due to the mechanism of activation of the unit by the nerves, which accumulates calcium that further degrades sarcomeres. This degradation initiates the body inflammatory response, and has to be supported by surrounding connective tissues. The inflammatory cells and cytokines stimulates the pain receptors that causes the acute pain associated with AMS. Repair of the sarcomere and the surround connective tissue leads to delayed onset muscle soreness, which peaks between 24 and 72 hours after exercise.

Another causes of AMS would be from cramps during or after workout, which has been theorized to have been caused by two pathways:

Dehydration

Dehydration theory states that extracellular fluid (ECF) compartment becomes contracted due to the excessive sweating, causing the volume to decrease to the point until the muscles are contracted until the fluids can re-inhabit the vacuum.[2] Excessive sweating can also cause the electrolyte imbalance theory, which is sweating disturbs the body's balance of electrolyte, which results in exciting motor neurons and spontaneous discharge.

The feeling of soreness can also be attributed to the lack contraction from the muscle, which can lead to overexertion of the muscle. The decrease in contraction has been theorized to have been caused by the high level of concentrations of proton created by glycolysis.[3] Excess in protons displaces calcium ions which is used within the fibers in activating the sarcomere, resulting in a reduced contractile force.

Electrolyte imbalance

When exercising, lactic acid becomes lactate and H+ through glycolysis. With more lactic consumed during the process, there will be a higher H+ concentration, thus lowering the blood’s pH level. This low pH level will affect the energy production process through the inhibition of phosphofructokinase. Phosphofructokinase is a key enzyme in glycolytic process, which produces energy. With a pH of 6.4, there will be no glycolysis process existed, thus no energy will be produced. Higher concentration of H+ will also cause the loss of contractile force through the misplacement of calcium in muscle fiber, the misplacement of calcium in muscle fiber will disturb the formation of actin-myosin cross-bridge.[4]

Treatments

There are conflicting research in terms of treatments of muscle soreness.

Stretching and muscle soreness

Stretching immediately before or after a workout does provide little help, but is not significant enough to be considered as a preventative measure.[5]

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References
  1. Nelson, Nicole L.; Churilla, James R. (August 2016). "A narrative review of exercise-associated muscle cramps: Factors that contribute to neuromuscular fatigue and management implications: Exercise-Associated Muscle Cramps". Muscle & Nerve. 54 (2): 177–185. doi:10.1002/mus.25176. PMID 27159592.
  2. Layzer, Robert B. (November 1994). "The origin of muscle fasciculations and cramps". Muscle & Nerve. 17 (11): 1243–1249. doi:10.1002/mus.880171102. ISSN 0148-639X. PMID 7935546.
  3. Layzer, Robert B. (November 1994). "The origin of muscle fasciculations and cramps". Muscle & Nerve. 17 (11): 1243–1249. doi:10.1002/mus.880171102. ISSN 0148-639X. PMID 7935546.
  4. Myers, Jonathan; Ashley, Euan (1997-03-01). "Dangerous Curves: A Perspective on Exercise, Lactate, and the Anaerobic Threshold". Chest. 111 (3): 787–795. doi:10.1378/chest.111.3.787. ISSN 0012-3692. PMID 9118720.
  5. Herbert, Rob D; Gabriel, Michael (2002-08-31). "Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review". BMJ. 325 (7362): 468. doi:10.1136/bmj.325.7362.468. ISSN 0959-8138. PMC 119442. PMID 12202327.
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