Changes in calpain activity, muscle structure, and function after eccentric exercise.

Area of Science:

• Exercise Physiology
• Muscle Biology
• Biochemistry

Background:

• Eccentric exercise, characterized by muscle lengthening under tension, can induce significant muscle damage.
• Understanding the molecular mechanisms underlying muscle damage and recovery is crucial for optimizing training and rehabilitation.

Purpose of the Study:

• To investigate the impact of high-force eccentric exercise on muscle function, structure, and calpain activity.
• To elucidate the relationship between muscle damage, force production, and calpain's role in the repair process.

Main Methods:

• Healthy males performed maximal voluntary eccentric actions targeting knee extensors.
• Muscle force-generating capacity was assessed pre- and post-exercise.
• Muscle biopsies were analyzed for myofibrillar structure, extracellular matrix proteins, and calpain activity at various time points.

Main Results:

• A significant reduction in peak torque (47%) was observed, persisting for at least 4 days.
• Myofibrillar disruptions were evident in 36% of muscle fibers, correlating with force reduction.
• Calpain activity increased threefold post-exercise, though not directly correlated with the extent of myofibrillar damage.

Conclusions:

• Myofibrillar disruptions are the primary driver of prolonged force deficits following eccentric exercise.
• Calpain activity increases post-exercise, suggesting a role in both muscle damage and subsequent repair processes.