Eccentric exercise-induced muscle damage impairs muscle glycogen repletion

Area of Science:

• Exercise Physiology
• Muscle Biology
• Sports Science

Background:

• Eccentric exercise, characterized by muscle lengthening under tension, is known to induce muscle damage.
• Recovery of muscle function and energy stores after eccentric exercise is crucial for adaptation and performance.

Purpose of the Study:

• To investigate the time course of muscle ultrastructural damage and glycogen replenishment following a single bout of eccentric exercise in untrained young males.
• To compare glycogen utilization patterns between eccentric and concentric exercise at similar metabolic intensities.

Main Methods:

• Five healthy, untrained young males performed 45 minutes of eccentric cycling exercise.
• Muscle biopsies of the vastus lateralis were analyzed for intracellular damage and glycogen content immediately after and 10 days post-exercise.
• Subjects consumed a eucaloric, meat-free diet and remained sedentary outside of exercise.

Main Results:

• Immediately post-exercise, muscle samples exhibited myofibrillar tearing and edema.
• Ten days after exercise, myofibrillar necrosis and inflammatory cell infiltration were observed, with no signs of regeneration.
• Muscle glycogen was significantly utilized during exercise (33 mmol/kg) and remained depleted in both Type I and Type II fibers 10 days later.
• Glycogen use in Type II fibers was notably high compared to concentric exercise at similar intensities.

Conclusions:

• Eccentric exercise induced substantial and persistent muscle damage, exceeding 10 days for recovery.
• Prolonged muscle glycogen depletion may be linked to the observed ultrastructural alterations and delayed recovery.
• Untrained individuals may require extended recovery periods after eccentric exercise to restore muscle integrity and carbohydrate reserves.