Extracellular matrix disruption and pain after eccentric muscle action

Area of Science:

• Exercise Physiology
• Muscle Biology
• Cellular Biology

Background:

• Eccentric muscle actions, involving muscle lengthening under load, can cause delayed-onset muscle soreness (DOMS).
• The precise cellular mechanisms triggering DOMS remain incompletely understood.

Purpose of the Study:

• To investigate the temporal relationship between muscle damage indicators, pain perception, and cellular changes following eccentric exercise.
• To elucidate the cellular events contributing to delayed muscle soreness.

Main Methods:

• Maximal resisted lengthening of elbow flexor muscles was performed in a single bout.
• Measurements included elbow joint position, pain perception, and muscle biopsy analysis at various time points post-exercise.
• Biopsies were analyzed for mast cell degranulation, extracellular matrix integrity, and plasma constituent presence.

Main Results:

• A decrease in resting muscle length was observed immediately post-exercise, persisting for 48 hours.
• Significant muscle soreness was reported at 48 hours post-exercise.
• Muscle biopsies revealed mast cell degranulation, myofiber-extracellular matrix separation, and increased extracellular plasma constituents at 48 hours.

Conclusions:

• Myofiber disruption allows intracellular proteins to leak out and extracellular components to enter, leading to swelling.
• Disruption of the extracellular matrix initiates an inflammatory response, including mast cell degranulation.
• Delayed muscle soreness after eccentric exercise is likely caused by inflammation resulting from extracellular matrix disruption.