Endurance exercise does not modify nerve fibre morphology in the rat soleus nerve

Area of Science:

• Neuroscience
• Exercise Physiology
• Muscle Biology

Background:

• Nerve adaptations to exercise are crucial for understanding physical performance.
• Previous studies have yielded conflicting results regarding exercise-induced changes in nerve myelination and axon growth.

Purpose of the Study:

• To investigate the impact of a 13-week treadmill running program on axon and myelin sheath characteristics in the rat nerve to the soleus muscle (NSM).
• To assess the effects of exercise on the metabolic capacity of the soleus muscle by measuring key enzyme activities.

Main Methods:

• Young male Wistar rats were subjected to treadmill exercise (70 min/day, 6 days/week) or served as sedentary controls.
• Soleus muscle enzyme activities (phosphofructokinase and succinate dehydrogenase) were measured.
• Axon and myelin sheath cross-sectional areas of the NSM were quantified using electron microscopy and digital analysis.

Main Results:

• Exercise training significantly increased soleus muscle oxidative (SDH activity +68.2%) and anaerobic glycolytic (PFK activity +42.8%) capacities.
• No significant differences were observed in the total number of myelinated nerve fibers, axon size, myelin sheath size, or myelination degree in the NSM between exercised and control groups.

Conclusions:

• Treadmill exercise enhances soleus muscle metabolic functions without altering nerve fiber morphology in the NSM.
• Exercise intensity may be a critical factor influencing nerve adaptations, and findings on nerve fiber growth should not be generalized across all exercise protocols.