Purpose: To describe the influence of caffeine on physiological responses to exercise in young children and determine whether sex differences in these responses exist.
Methods: 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·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 (V̇O2) were measured.
Results: 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 ≤ 0.05) higher at rest, 25 W in both boys and girls, and at 50 W in boys, in CAF versus PL. Systolic BP (mm Hg) was significantly (P ≤ 0.05) higher at rest in both boys and girls, at 25 W in boys, and at 50 W in girls. During exercise, V̇O2 (L·min−1 or mL·kg−1·min−1) and RER were not different in CAF versus PL in either boys or girls.
Conclusions: A moderate dose of caffeine (5 mg·kg−1) does not affect metabolism (V̇O2 or RER) in young children at low-moderate intensities of exercise. However, CAF causes a significantly lower HR (bpm) and higher BP (mm Hg) in both young boys and girls.