Answered from cited sources · retrieved September 20, 2026
why do muscles get sore after exercise
Muscle soreness after exercise is caused by microscopic tears in muscle fibers and the resulting inflammation as the body repairs and strengthens the tissue.
Muscle soreness after exercise, known as delayed onset muscle soreness (DOMS), is primarily caused by microscopic tears in muscle fibers and the subsequent inflammatory response that occurs during the body's repair process [1][3][5]. This soreness typically peaks 24 to 72 hours after intense or unaccustomed physical activity, particularly exercises involving eccentric contractions, where muscles lengthen while under tension [1][2][5]. Contrary to popular belief, lactic acid buildup is not the cause of this soreness, as it clears from the body within an hour after exercise [5]. Instead, the pain is associated with the body's natural process of repairing and strengthening muscle tissue [1][5].
- Role of Eccentric Exercise. DOMS is most commonly triggered by eccentric exercises, which involve lengthening a muscle while it is under tension, such as the lowering phase of a bicep curl or running downhill.
- Lactic Acid Myth. Lactic acid is a byproduct of anaerobic energy production that clears from the body within an hour of exercise and is not responsible for the soreness felt days later.
- Muscle Repair and Growth. The soreness is a normal part of the body's repair process, where muscle fibers are rebuilt stronger than they were before the exercise.
- Emerging Theories. Some researchers are investigating newer theories, such as neural microdamage to proprioceptive terminals, to better explain the complex mechanisms behind DOMS.
Sources
- Delayed Onset Muscle Soreness (DOMS)my.clevelandclinic.org · published December 19, 2025
- Pathophysiology of Exercise-Induced Muscle Damage and Its Structural, Functional, Metabolic, and Clinical Consequences - PMCpmc.ncbi.nlm.nih.gov · published July 16, 2020
- DOMS: Causes, recovery, and preventionmedicalnewstoday.com · published October 21, 2022
- Muscle tenderness from exercise: mechanisms? - PMC - NIHpmc.ncbi.nlm.nih.gov
- Is Lactic Acid Really What Causes Sore Muscles After ...houstonmethodist.org · published October 19, 2021
- Delayed Onset Muscle Soreness and Critical Neural Microdamage-Derived Neuroinflammationmdpi.com · published August 30, 2022
- Delayed-Onset Muscle Soreness Begins with a Transient Neural Switchmdpi.com
- Pathophysiology of Acute Exercise-Induced Muscular Injury: Clinical Implicationspmc.ncbi.nlm.nih.gov
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