Effects of caffeine on physiological responses to exercise in young boys and girls

To describe the influence of caffeine on physiological responses to exercise in young children and determine whether sex differences in these responses exist. Twenty-six healthy 7- to 9-yr-old boys and 26 healthy 7- to 9-yr-old girls volunteered to participate in a double-blind, randomized, double crossover study design. Each child randomly received both the placebo (PL) and caffeinated (5 mg x kg(-1)) drink (CAF) twice each on four separate days. Following a 1-h wash-in period and resting measures, each child rode a cycle ergometer at 25 and then 50 W for 8 min each, while HR, blood pressure (BP), and oxygen consumption (VO2) were measured. HR (bpm) was significantly (P < 0.05) lower at rest and at 25 and 50 W in CAF versus PL in both boys and girls. Diastolic BP (mm Hg) was significantly (P