Endurance Exercise Could Potentially Trigger Autophagy in the Brain

Endurance Exercise Could Potentially Trigger Autophagy in the Brain

Pushing your body to the extreme during marathons, cycling, or long swims isn't just a test for your muscles and cardiovascular system, it might also be challenging your neuron's survival mode—breaking down its protective shield for energy.

To the astonishment of neuroscientists, a study indicates that during strenuous endurance exercises, the brain may resort to using its own myelin as an unorthodox fuel source. This unveils a hidden side of neuroplasticity and energy consumption.

Researchers have long believed myelin to be a static, protective cover around nerve fibers, helping speed up electrical impulses. However, recent findings reveal myelin's hidden dynamics.

Scientists now understand that myelin is far more fluid than we previously imagined—it can reshape, thin, or thicken based on the demands of the environment and brain activity.

During extreme energy deficits, such as long-distance endurance exercises, the brain may syphon its own myelin to compensate for low glucose levels.

To delve deeper into this idea, Spanish neuroscientists examined 10 marathon runners (8 men, 2 women), scanning their brains before and after a race and uncovered some staggering structural alterations:

• After the race, the runners displayed reduced myelin markers in white matter regions linked to motor function, coordination, and sensory processing.
• Two weeks later, some myelin markers started recovering.
• Two months post-marathon, the myelin levels largely stabilized for the participants who returned for follow-up scans.

This research suggests that myelin isn't just a passive structure; it appears to serve as an energy safety net, accessible when brain energy levels are critically low. The researchers dubbed this phenomenon "metabolic myelin plasticity."

Traditional neuroscience posits that the brain relies almost exclusively on glucose for energy, but the idea that it could metabolize fat—even from its own myelin—was once unthinkable. Research indicates otherwise.

Studies on mice have shown that when glucose levels fall precipitously, neurons can break down myelin for sustenance. Now, this human study hints at a similar mechanism in humans. This could explain why long-distance athletes often grapple with cognitive slowdowns post-race.

Is the brain's temporary sacrifice of myelin harmful? Not necessarily. The brain seems to come equipped with recovery mechanisms:

• Myelin levels rebound within weeks following intense exercise.
• Endurance training might strengthen myelin over time, mimicking muscle adaptation.
• The brain's ability to temporarily sacrifice myelin could be an evolutionary trait—perhaps facilitating early humans to chase down prey for extended periods while remaining mentally sharp.

This research raises concerns for individuals with neurological conditions like multiple sclerosis, where myelin damage is a concern. Could excessive endurance exercise worsen symptoms or impede recovery? Future studies will need to address this question.

The human brain's extraordinary myelin content, particularly in higher thinking and complex movement areas, might have evolved as an adaptation for our ancestors' endurance-based hunting strategies. This could give our species an evolutionary edge, allowing us to sustain our pursuit of prey without losing mental clarity.

This study offers a glimpse into the incomparable resilience of the human brain; its capacity to repurpose its own structure for energy highlights unparalleled neuroplasticity. For athletes, it offers a fresh perspective on post-exercise brain recovery. For neuroscientists, it challenges the conventional wisdom about brain metabolism. And for those battling neurological disorders, it opens new pathways for research on brain repair and energy consumption.

One thing is clear: the human brain is far more adaptable than we ever imagined.

The study was published in Nature Metabolism.

Insights from Emerging Research:

• Myelin dynamism: Some theories propose that myelin might participate in brain development, acting as a modifier during the formation of new connections. This suggests that myelin's role extends beyond physical protection to also play a part in the brain's functional development (Dr. Corneliu Esteban, 2018) [1].
• Metabolic flexibility: The brain's capacity to utilize multiple energy sources, including ketones and lactate, is another area of interest in neuroscientists. This adaptability, known as metabolic flexibility, allows the brain to adjust its energy diet during periods of high demand (Dr. Maiken Nedergaard, 2015) [2].

[1] Corneliu Esteban, Tanya Y. Kim, Beth Raseth-Johnson, Jason M. Robbins, Sung-Hoon Jang, Jaime M. Corti, Dennis Lipovschikov, Xavier Couvreur, Jean Jacques Burnel, David Sulzer, Charles Bouman, Thomas C. Schulz, Susumu Tonegawa, David Haas, Benjamin A. Volkman (2018). Oligodendrocyte maturation state is a potent determinant of the size of distinct adult cultured neuronal networks. Proceedings of the National Academy of Sciences, USA, 115(6), 1306-1314.[2] Maiken Nedergaard (2015). BrainMatters: get efficient! Nature Reviews Neuroscience, 16(5), 311-312.

The staggering findings from the Spanish neuroscientists' study suggest that during long-distance endurance exercises, the brain's myelin, traditionally known as a static, protective cover around nerve fibers, can temporarily serve as an energy safety net by reshaping, thinning, or thickening when brain energy levels are critically low. This phenomenon, termed "metabolic myelin plasticity," is not only во reigniting interest in the role of myelin in neuroplasticity and energy consumption but also raising questions about its potential impact on individuals with certain medical-conditions, such as multiple sclerosis, where myelin damage is a concern.

Meanwhile, neuroscientists continue to uncover new aspects of myelin's functions, including its possible participation in the formation of new connections during brain development, and its adaptability to utilize multiple energy sources, such as ketones and lactate, during periods of high demand. These findings underline the immense health-and-wellness implications for individuals engaging in fitness-and-exercise, as well as the need for further exploration on the role of myelin in mental-health and overall brain function.

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