Abstract
Few studies have investigated the effect of caffeine on exercise responses in children. No study has compared the effects of caffeine on exercise responses between children versus adults. PURPOSE Compare the effects of caffeine on physiological responses to exercise between young boys versus college age men. METHODS Twenty-six 7–9 year old boys and eighteen 18–25 year old men participated in a double-blind, double-crossover placebo study. Subjects received in random order twice each, either a placebo drink (cherry flavored Sprite®-PL) or drink plus anhydrous caffeine (5 mg/kg body mass, CAF). Following a 60-minute absorption period children rode at 25 W and then 50 W while men rode at 50 W and then 60% VO2 max for 8 minutes each on an electronically braked ergometer while heart rate (HR), oxygen consumption (VO2), and respiratory exchange ratio (RER) were monitored continuously, and blood pressure (BP) was measured every two minutes. RESULTS HR was significantly lower (p < 0.05) at 25 W (119±10 vs 126±9 bpm) and 50 W in boys (150±15 vs 157±13 bpm) in CAF vs. PL, respectively. In men HR was the same at both 50 W (107±17 vs. 106±16 bpm) and 60% VO2 max (146±8 vs. 146±10 bpm) in CAF vs. PL, respectively. Systolic BP(SBP) was higher at 25 W (132±12 vs 128±12 mmHg, p < 0.05) and 50 W in boys (147±14 vs 144±14 mmHg, p = 0.067) in CAF vs. PL, respectively. Diastolic BP (DBP) was higher at 25 W (71±8 vs 68±8 mmHg, p < 0.05) and 50 W in boys (73±9 vs 70±9 mmHg, p < 0.05) in CAF vs PL, respectively. Blood pressure in men was always higher in CAF vs. PL but never reached statistical significance. Specifically, SBP was similar at 50 W (161±16 vs 159±15 mmHg, p = 0.685) and 60% VO2 max (200±20 vs 198±21 mmHg, p = 0.245) in CAF vs. PL, respectively. Diastolic BP was similar at 50 W (79±11 vs 76±8 mmHg, p = 0.058) and 60% VO2 max (84±12 vs 83±8 mmHg, p = 0.559) in CAF vs. PL, respectively. Both VO2 and RER were the same at both 25 W and 50 W in boys, and 50 W and 60% VO2 max in men in CAF vs PL. CONCLUSIONS Caffeine (5 mg/kg) has a similar effect on metabolic responses to exercise in boys and men. The same dose causes a significant elevation in exercise BP and decrease in HR in boys while in men there was only a trend for a similar change in BP (although not significant) with no change in HR.
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