Effects of Different Doses of Caffeine on Exercise Responses in Young Children

Abstract

This study investigated the effects of three different doses of caffeine on physiological responses to exercise in young children. Forty healthy children (20 boys and 20 girls) volunteered for a random, double-blind, counterbalanced study where they received either placebo (PL), 1 mg.kg(-1) (CAF-1), 3 mg.kg(-1) (CAF-3), or 5 mg.kg(-1) (CAF-5) caffeine, 60 min prior to preexercise measures, followed by cycle ergometer exercise at 25 W and then 60% VO2peak. During this time, heart rate (HR), oxygen consumption (VO2), and respiratory exchange ratio (RER) were measured continuously, while blood pressure (BP) was measured every 2 min. There were no significant gender x treatment interactions, and so the boys' and girls' data were combined. At preexercise, CAF-5 SBP and DBP were significantly (P < 0.05) higher than PL. Both CAF-1 and CAF-3 DBP were also significantly (P < 0.05) higher versus PL at preexercise. There were no treatment effects for exercise BP. At rest and during both exercise intensities, HR was significantly (P < 0.05) lower in CAF-3 (approximately 5 bpm) and CAF-5 (approximately 6 bpm) versus PL. There were no significant effects of CAF on metabolism (VO2 or RER) except for a lower RER in CAF-1 versus CAF-5 at 60% VO2peak. Low, mild, and moderate (1, 3, and 5 mg.kg(-1)) doses of caffeine have no effect on substrate use as reflected by RER. Further, caffeine intake resulted in an increase in BP and decrease in HR at preexercise and a slight decrease in HR with CAF-3 and CAF-5 versus PL during exercise.