Measuring energy costs of leisure activity in adolescents using a CO2 breath test

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Abstract
To determine whether a 13C-bicarbonate, isotope dilution technique could be used to estimate relative changes in energy expenditure of leisure activities of short duration, we studied eight adolescents who performed the following activities: watching television (120 min); playing a stringed instrument (60 min plus 60 min of sitting); and walking plus rest during two approximately isocaloric sessions (slow walk at 40% of peak ˙VO2 for 43 min plus 77 min of sitting; fast walk at 73% of peak ˙VO2 for 22 min plus 98 min of sitting). The rate of appearance of CO2(RaCO2) was determined from the ratio of the oral dose of13 C-bicarbonate and the isotopic enrichment of breath CO2. The net rates of excretion of CO2 (˙VCO2) and oxygen consumption were measured. ˙VCO2 and RaCO2 were correlated (r = 0.93;P 2