Failure of caffeine to affect substrate utilization during prolonged running

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Abstract
Nine sub-3-h male marathoners performed 3 45-min monitored treadmill runs at .apprx. 75% of .ovrhdot.VO2 max [maximal O2 uptake] during a 2-wk period. The men were assigned in a random, double-blind fashion following the control run to receive either 350 ml of decaffeinated coffee or 350 ml of decaffeinated coffee with 400 mg of caffeine added 1 h before the second run with crossover to the other beverage for the 3rd run. Venous blood was analyzed for free fatty acids, triglycerides, glucose and lactic acid before beverage consumption and before and after each run. .ovrhdot.VO2, .ovrhdot.VCO2, respiratory exchange ratio (R) ventilation (.ovrhdot.VE), and perceived exertion were measured at 15, 30 and 45 min of each run. Of the blood parameters, free fatty acid and lactic acid concentration increased following caffeine ingestion. There was no difference in .ovrhdot.VO2, .ovrhdot.VCO2, or R between the 3 runs. Perceived exertion showed a significant decrease (P < 0.05) at each time point in caffeine added and decaffeinated compared to control. Triglycerides, glucose and lactic acid increased similarly in all 3 runs. In these well-trained marathoners, although plasma free fatty acids were elevated significantly prior to exercise after caffeine ingestion, there was no indirect evidence of altered substrate utilization during subsequent treadmill running.