Pro- and macroglycogenolysis in skeletal muscle during maximal treadmill exercise

Area of Science:

• Exercise Physiology
• Skeletal Muscle Metabolism
• Biochemistry

Background:

• Skeletal muscle glycogen serves as a primary energy source during exercise.
• The distinct roles and degradation patterns of proglycogen and macroglycogen during intense exercise remain incompletely understood.
• Understanding glycogen dynamics is crucial for optimizing athletic performance and recovery.

Purpose of the Study:

• To investigate the degradation patterns of proglycogen and macroglycogen in equine skeletal muscle during maximal intensity exercise.
• To determine the relative contribution of proglycogen and macroglycogen to glycogenolysis during strenuous physical exertion.
• To explore the initial phases of glycogen resynthesis post-exercise.

Main Methods:

• Ten Standardbred trotters underwent a maximal treadmill exercise test to exhaustion.
• Muscle biopsies were collected at rest, immediately after exercise, and 15 minutes post-exercise.
• Analysis included measurements of muscle ATP, creatine phosphate, lactate, free glucose, proglycogen, and macroglycogen concentrations.

Main Results:

• Maximal exercise induced significant anaerobic metabolism, evidenced by decreased ATP and creatine phosphate, and increased lactate.
• Both proglycogen and macroglycogen showed significant degradation during exercise, indicating equal contribution to glycogenolysis.
• Muscle free glucose increased post-exercise, with a further rise observed at 15 minutes, and proglycogen levels showed a trend towards recovery.

Conclusions:

• Proglycogen and macroglycogen are equally utilized during intense exercise in skeletal muscle.
• Glycogen resynthesis likely commences in the proglycogen pool shortly after the cessation of strenuous activity.
• These findings provide insights into the dynamic regulation of glycogen metabolism under high-energy demand conditions.