Published online June 1, 2005
PEDIATRICS Vol. 115 No. 6 June 2005, pp. e690-e696 (doi:10.1542/peds.2004-1543)

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ELECTRONIC ARTICLE

Influence of Excess Adiposity on Exercise Fitness and Performance in Overweight Children and Adolescents

Anne-Caroline Norman, MS-IV^*,, Bart Drinkard, MSPT, CCS, Jennifer R. McDuffie, PhD, RD^*, Samareh Ghorbani, BS^*, Lisa B. Yanoff, MD^* and Jack A. Yanovski, MD, PhD^*

^* Unit on Growth and Obesity, Developmental Endocrinology Branch, National Institute on Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland
Duke University School of Medicine, Durham, North Carolina
Rehabilitation Medicine Department, Clinical Center, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland

Objective. Relatively little is known about how excess body mass affects adolescents' capacity to perform sustained exercise. We hypothesized that most of the difficulty that severely overweight adolescents have with sustained exercise occurs because the metabolic costs of moving excess mass result in use of a high proportion of their total oxygen reserve.

Methods. We compared results from a maximal cycle ergometry fitness test in 129 severely overweight adolescents who had BMIs of 41.5 ± 9.7 kg/m² and ages of 14.5 ± 1.8 years (range: 12.1–17.8 years) and 34 nonoverweight adolescents who had BMIs of 20.1 ± 2.9 kg/m² and ages of 14.5 ± 1.5 years (range: 12.0–18.1 years). Oxygen uptake (O₂) was compared at 3 times: during a 4-minute period of unloaded cycling (ULO₂), at the lactate threshold estimated by gas exchange (LTO₂), and at maximal exertion (O₂ max). Heart rate was obtained at rest and at O₂ max. Participants also completed a 12-minute walk/run performance test to obtain distance traveled (D12) and heart rate.

Results. Absolute LTO₂ and O₂ max and LTO₂ as a percentage of O₂ max were not different in overweight and nonoverweight adolescents during the cycle test. However, absolute ULO₂ was significantly greater in overweight adolescents: ULO₂ accounted for 35 ± 8% of O₂ max (and 63 ± 15% of LTO₂) in overweight adolescents but only 20 ± 5% of O₂ max (and 39 ± 12% of LTO₂) in nonoverweight adolescents. Resting heart rate before initiating the cycle test was significantly greater in overweight than nonoverweight adolescents (94 ± 14 vs 82 ± 15 beats per minute). However, maximal heart rate during the cycle test was significantly lower in overweight adolescents (186 ± 13 vs 196 ± 11 beats per minute). During the walk/run test, mean D12 was significantly shorter for overweight than for nonoverweight adolescents (1983 ± 323 vs 1159 ± 194 m). D12 was negatively related to BMI SDS (r = –0.81) and to ULO₂ (r = –0.98).

Discussion. Overweight and nonoverweight adolescents had similar absolute O₂ at the lactate threshold and at maximal exertion, suggesting that overweight adolescents are more limited by the increased cardiorespiratory effort required to move their larger body mass through space than by cardiorespiratory deconditioning. The higher percentage of oxygen consumed during submaximal exercise indicates that overweight adolescents are burdened by the metabolic cost of their excess mass. Their greater oxygen demand during an unloaded task predicted poorer performance during sustained exercise. Exercise prescriptions for overweight adolescents should account for the limited exercise tolerance imposed by excess body mass, focusing on activities that keep demands below lactate threshold so that exercise can be sustained.

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Key Words: obesity • anaerobic threshold • exercise test • body composition • oxygen uptake • physical fitness • running • walking

Abbreviations: O₂ max, maximum oxygen uptake • SDS, SD score • ULO₂, unloaded oxygen uptake • LTO₂, oxygen uptake at the lactate threshold • O₂ max, oxygen uptake at maximal exertion • HRR, heart rate reserve • RPE, rating of perceived exertion • bpm, beats per minute • D12, distance achieved at 12 minutes during walk/run test • ANCOVA, analysis of covariance

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Accepted Dec 20, 2004.

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