Three Hypotheses of Muscle Soreness

There are three basic hypotheses that attempt to explain the nature of muscular soreness (Alter, 1996):

(i) The torn tissue hypothesis or connective tissue damage hypothesis; (ii) The metabolic accumulation hypothesis; and (iii) The localized spasm of motor units hypothesis.

Although analyzed separately, they can occur together, and there may be other causes.

Torn Tissue or Connective Tissue Damage. One explanation is the torn tissue hypothesis: soreness results from microscopic tearing of muscle fibers or connective tissues. More recently this has been expanded into the connective tissue damage hypothesis, which suggests soreness is due to irritation or damage of connective tissue — usually a result of exercise or training that uses eccentric contractions (the elongation or stretching of a muscle while it is contracting under resistance).

Metabolic Accumulation or Osmotic Pressure and Swelling. This hypothesis, developed by de Vries, is intended to explain delayed localized soreness. By this hypothesis, exercise above a minimal level causes decreased blood flow to the muscle, or ischemia, which in turn causes pain that results in a protective, reflex, tonic muscle contraction. The tonic contraction brings about more ischemia, and a vicious cycle is born.

Localized Spasm of Motor Units. The third basic hypothesis attributes soreness to localized spasm of motor units.

Hypothesis (i) has become the dominant, evidence-supported model — and current research extends it with a mechanism the source doesn't cover: the microtrauma triggers an inflammatory cascade (elevated creatine kinase, C-reactive protein, prostaglandins, cytokines like IL-6 and TNF-alpha) and sensitizes nociceptors, which produces the delayed pain. Hypotheses (ii) and (iii) are now considered largely superseded — lactic acid accumulation specifically has been explicitly refuted as a DOMS cause (see lactic-acid-system's own 2026 update). See verification_note in this module's frontmatter.

• Three hypotheses: (1) torn tissue / connective tissue damage; (2) metabolic accumulation (osmotic pressure & swelling); (3) localized spasm of motor units.
• They can occur together; other causes are possible.
• Connective tissue damage is usually linked to eccentric contractions.
• de Vries cycle: exercise → decreased blood flow (ischemia) → pain → reflex tonic contraction → more ischemia (vicious cycle).
• 2026 update: hypothesis (i), extended with an inflammatory-cascade mechanism (microtrauma → CK/CRP/cytokines → nociceptor sensitization), is now the dominant model. Hypotheses (ii) and (iii) are largely superseded; lactic acid as a DOMS cause has been explicitly refuted.

• muscle-soreness — acute vs. DOMS overview.
• eccentric-action — eccentric work tied to connective tissue damage.
• lactic-acid-system — metabolic by-products in the accumulation hypothesis.