Why Do We Get Tired During Long Exercise?
Carbohydrate Ingestion on Exercise Metabolism and Physical Performance
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists have long believed that running out of muscle sugar (glycogen) makes us tired during long exercise. But this review of over 100 years of research shows that's not the main problem. Instead, low blood sugar (hypoglycemia) is what really makes us stop exercising. When blood sugar drops too low, the brain stops us to protect itself from damage. Taking carbohydrates during exercise prevents this low blood sugar and helps us exercise longer.
Surprising Findings
Muscle glycogen depletion does NOT cause fatigue on its own
For 50+ years, athletes and coaches have believed that running out of muscle glycogen causes 'the wall.' This review shows that's not the case - the brain stops exercise to protect itself from low blood sugar, not because muscles are out of fuel.
Practical Takeaways
Focus on maintaining blood sugar during exercise rather than just loading glycogen beforehand
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists have long believed that running out of muscle sugar (glycogen) makes us tired during long exercise. But this review of over 100 years of research shows that's not the main problem. Instead, low blood sugar (hypoglycemia) is what really makes us stop exercising. When blood sugar drops too low, the brain stops us to protect itself from damage. Taking carbohydrates during exercise prevents this low blood sugar and helps us exercise longer.
Surprising Findings
Muscle glycogen depletion does NOT cause fatigue on its own
For 50+ years, athletes and coaches have believed that running out of muscle glycogen causes 'the wall.' This review shows that's not the case - the brain stops exercise to protect itself from low blood sugar, not because muscles are out of fuel.
Practical Takeaways
Focus on maintaining blood sugar during exercise rather than just loading glycogen beforehand
Publication
Journal
Endocrine Reviews
Year
2026
Authors
Timothy Noakes, Philip J. Prins, Alex Buga, Dominic P. D’Agostino, Jeffrey S Volek, Andrew P Koutnik