Adaptive response in human skeletal muscle subjected to prolonged eccentric training

Area of Science:

• Exercise Physiology
• Muscle Adaptation
• Skeletal Muscle Biology

Background:

• Eccentric training involves muscle lengthening under load.
• Understanding peripheral adaptations to prolonged eccentric exercise is crucial for optimizing training protocols.
• Previous research has explored muscle hypertrophy and strength gains, but less is known about specific adaptations in eccentric work capacity.

Purpose of the Study:

• To investigate the peripheral adaptation processes in the vastus lateralis muscle from repeated eccentric training over an extended period.
• To assess changes in maximal dynamic concentric muscle strength and eccentric work capacity.
• To examine the effects of eccentric training on muscle fiber type distribution, glycogen content, and ultrastructure.

Main Methods:

• Eleven healthy males (24 +/- 4 years) underwent 8 weeks of eccentric training.
• Maximal dynamic concentric muscle strength and eccentric work capacity were measured.
• Muscle biopsies were analyzed for fiber type, glycogen depletion, and ultrastructural changes (mitochondria, Z-bands).

Main Results:

• Maximal dynamic concentric strength showed only slight improvement.
• Eccentric work capacity increased dramatically by 375%.
• Eccentric exercise post-training selectively depleted glycogen in type 2B fibers and increased type 2C fibers. Mitochondria volume density increased, while Z-band width remained unaffected.

Conclusions:

• Skeletal muscles functionally adapt to extreme tension demands imposed by prolonged eccentric training.
• Improved coordination and reorganization of the muscle fiber contractile apparatus are key mechanisms driving these adaptations.
• Eccentric training enhances muscle's ability to handle high-tension loads, indicated by increased work capacity and specific fiber adaptations.