Macro partitioning
Ingestion of 9 mg/kg caffeine before prolonged exercise at ~80% VO2max significantly increases time to exhaustion and reduces early-phase muscle glycogenolysis by approximately 55% during the first 15 minutes of exercise.
Take 9 mg of caffeine per kg of body weight about an hour before a long, intense workout (like a long run or bike ride at 80% of your max effort). This dose has been shown to significantly extend how long you can exercise by sparing muscle glycogen in the first 15 minutes, allowing you to cycle longer before exhaustion. Be aware that a small number of people may experience stomach discomfort at this high dose.
The subjects cycled significantly longer during the Caf trial (96.2 +/- 8.8 min) than in the Pl trial (75.8 +/- 4.8 min). Net glycogenolysis during the initial 15 min of cycling was reduced in the Caf vs. Pl trial (4.7 +/- 1.5 vs. 10.6 +/- 1.3 mmol l-1 kg dry muscle-1 min-1; P < 0.05).
Why this rating
Randomized, double-blind (single-blind in text, but controlled), crossover design with direct muscle biopsies, though sample size is small (n=8).
Source
Caffeine ingestion and muscle metabolism during prolonged exercise in humans
Lawrence L. Spriet et al. · American Journal of Physiology-Endocrinology and Metabolism · 1992
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