American Journal of Preventive Medicine
Aerobic fitness standardsDevelopment of Youth Aerobic-Capacity Standards Using Receiver Operating Characteristic Curves
Introduction
Aerobic capacity, also referred to as cardiorespiratory or cardiovascular fitness, is considered to be the most important dimension of health-related fitness. Numerous studies have documented the importance of an adequate aerobic capacity for good health in adults,1, 2, 3 and the evidence appears equally compelling in children and adolescents. Aerobic capacity in youth is associated with cardiovascular disease risk factors,4, 5, 6 and prospective studies have demonstrated that aerobic capacity tracks reasonably well from childhood/adolescence into adulthood.7 Declines in aerobic capacity from childhood to adolescence are also associated with an increased risk of overweight and metabolic syndrome in adults.8, 9, 10 Recent reports have indicated that approximately one third of U.S. adolescents possess inadequate levels of aerobic capacity.11, 12 Collectively, these studies provide strong evidence to support the importance of focused efforts to monitor and promote aerobic capacity in youth.
Youth fitness testing is a common part of most physical education programs, and aerobic capacity is perhaps the most commonly assessed component. Field tests of aerobic capacity (e.g., 1-mile run) are typically administered by physical education teachers with the goal of providing personalized information to children and/or parents. A unique advantage of the FITNESSGRAM® program is that fitness levels are evaluated using criterion-referenced standards that indicate how much fitness is needed for good health.13 The standards were established initially using a metabolic model to account for developmental changes and then modified by expert opinion.14 Later, these standards were linked to health by extrapolating adult standards backwards to values appropriate for youth.15 The standards have been well supported, and recent studies have demonstrated that they have good utility for detecting health risks.16 However, it is important to evaluate new approaches to improve the accuracy and clinical utility of youth fitness standards.
A challenge in setting criterion-referenced standards in youth is the need to link fitness to clinical health outcomes. Although morbidity and mortality are commonly used in adults, these are not appropriate indicators for establishing risk in youth. The availability of nationally representative data on aerobic capacity and clinical risk in the National Health and Nutrition Examination Survey (NHANES) provides the opportunity to develop standards that reflect potential health risk in youth. In this paper, new criterion-referenced standards are developed for aerobic capacity based on receiver operating characteristic (ROC) curves, an established procedure for establishing clinical thresholds.17 Although recent studies have used a similar methodology,16, 18 the present study also utilizes recently developed LMS (L=skewness, M=median, and S=coefficient of variation) growth curves19 to better characterize the developmental changes in aerobic capacity during adolescence.
Section snippets
Subjects
Data for the present study were obtained from the NHANES (1999–2000 and 2001–2002), conducted by the National Center for Health Statistics (NCHS), CDC. The NHANES is designed to assess the health and nutritional status of adults and children in the U.S. through interviews and direct physical examinations. For this project, a combination of data was used: aerobic-capacity data, anthropometric data, and metabolic examination data of children aged 12–18 years across two cross-sectional waves of
Results
The descriptive statistics for the sample population are summarized in Table 1. The average VO2max values (mL/kg/min) for the sample ranged from 39.1 to 41.1 in girls and from 43.5 to 49.4 in boys. However, there were no appreciable age-related trends evident in the cross-sectional analyses. The prevalence of individual risk factors varied between boys and girls, but the prevalence of metabolic syndrome (based on the present calculations) was 6.3% (1.2%) in boys and 5.9% (1.6%) in girls.
The
Discussion
This study describes the diagnostic characteristics of newly developed aerobic-capacity standards that could be used in school and sport programs or clinical settings to evaluate adolescents' level of aerobic capacity. The generally high AUC values and high Se/Sp values demonstrate that the aerobic-capacity thresholds have good utility for discriminating youth who may have metabolic syndrome.
The newly developed thresholds follow the same age-related patterns as the previous FITNESSGRAM
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