Eccentric exercise per se does not affect muscle damage biomarkers: early and late phase adaptations

Area of Science:

• Exercise Physiology
• Muscle Biology
• Sports Science

Background:

• Acute high-intensity eccentric exercise in untrained individuals often leads to muscle damage biomarkers.
• The relationship between eccentric exercise and muscle damage requires further elucidation.

Purpose of the Study:

• To determine if a causal link exists between eccentric exercise and muscle damage.
• To investigate the role of muscle unaccustomedness in exercise-induced muscle damage.

Main Methods:

• Twenty-four men were divided into concentric-only or eccentric-only isokinetic resistance training groups for 10 weeks.
• Muscle function (range of motion, soreness, peak torque) and damage biomarkers (creatine kinase, C-reactive protein) were assessed.
• Assessments were conducted pre- and post-exercise sessions, with specific follow-ups at 1-3 and 5 days.

Main Results:

• Eccentric exercise initially caused more muscle damage than concentric exercise, but this effect diminished with repeated sessions.
• After 10 weeks of training, neither protocol induced significant muscle damage biomarkers.
• Strength gains were comparable between groups and specific to the exercise mode.

Conclusions:

• Eccentric exercise itself does not inherently cause muscle damage; unaccustomedness is the primary trigger.
• Exercise-induced muscle damage is not a prerequisite for achieving strength increases.
• Adaptation to eccentric exercise reduces subsequent muscle damage responses.