causal
Analysis v1
Strong Support
When you exercise for a long time (over 2-3 hours), it's actually having low blood sugar that makes you feel tired and stop exercising—not your muscles running out of stored energy.
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Evidence from Studies
Supporting (1)
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Community contributions welcome
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Carbohydrate Ingestion on Exercise Metabolism and Physical Performance
Narrative Review
2026 Mar 11This study reviewed over 160 studies and found strong evidence that low blood sugar (hypoglycemia) during exercise, not running out of muscle sugar (glycogen), is what really makes people stop exercising. When athletes take carbohydrates during exercise, it keeps blood sugar up and they can keep going even if their muscles are low on glycogen.
Contradicting (0)
0
Community contributions welcome
No contradicting evidence found
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.