Sedentary Behaviour Impairs Skeletal Muscle Repair Modulating the Inflammatory Response

Area of Science:

• Muscle physiology
• Inflammation research
• Regenerative medicine

Background:

• Sedentary behavior is prevalent and linked to various health issues.
• Skeletal muscle injury triggers complex inflammatory and repair processes.
• The impact of sedentary lifestyles on muscle healing remains incompletely understood.

Purpose of the Study:

• To investigate how sedentary behavior influences skeletal muscle repair and inflammation after injury.
• To compare the inflammatory and regenerative responses between sedentary and exercise groups.

Main Methods:

• Rats were assigned to sedentary (SED) or exercise (EX) groups for 8 weeks.
• Skeletal muscle injury was induced using cardiotoxin (CTX) in the tibial anterior muscle.
• Histological and immunohistochemical analyses assessed myotube formation, fibrosis, and immune cell infiltration (neutrophils, M1/M2 macrophages) at 1, 7, and 15 days post-injection.

Main Results:

• Sedentary rats exhibited increased neutrophils and M1 macrophages at 7 and 15 days post-injection compared to exercised rats.
• Exercised rats showed a higher M2 macrophage count on day 1 post-injection.
• Sedentary rats displayed reduced myotube percentage and significantly more fibrosis at 7 and 15 days post-injection.
• By day 15, sedentary muscle had only 54% normal fibers versus 90% in exercised muscle.

Conclusions:

• Sedentary behavior exacerbates and prolongs the pro-inflammatory M1 macrophage response after muscle injury.
• Exercise promotes a beneficial M2 macrophage response and accelerates skeletal muscle regeneration.
• Sedentary lifestyles significantly impair skeletal muscle repair processes, leading to delayed healing and increased fibrosis.