Muscle damage and repeated bout effect induced by enhanced eccentric squats

Area of Science:

• Exercise Physiology
• Sports Science
• Muscle Adaptation

Background:

• Previous research on muscle damage and the repeated bout effect focused on eccentric-only exercise.
• The study investigates muscle damage and adaptation following enhanced eccentric squat exercise using a flywheel device.

Purpose of the Study:

• To evaluate muscle damage markers after enhanced eccentric squat exercise.
• To assess the repeated bout effect of this exercise protocol.
• To determine if flywheel-enhanced eccentric exercise induces muscle protection.

Main Methods:

• Thirteen healthy males performed 100 enhanced eccentric squat repetitions using a flywheel device.
• Muscle damage was assessed via creatine kinase (CK) levels, quadriceps isometric peak torque, and muscle soreness.
• Measurements were taken at baseline, immediately post-exercise, and daily up to 96 hours, with a repeat protocol after 4 weeks.

Main Results:

• The first exercise bout significantly increased CK and soreness, and decreased isometric peak torque up to 96 hours.
• Following the second bout (4 weeks later), CK showed no significant increase, and torque/soreness returned to baseline levels faster.
• All muscle damage markers were significantly lower after the second bout compared to the first.

Conclusions:

• Enhanced eccentric exercise induces muscle damage symptoms lasting up to 96 hours.
• A four-week interval between exercise bouts leads to significant muscle protection (repeated bout effect).
• Flywheel-enhanced eccentric exercise, even when not eccentric-only, confers protective adaptations.