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Cardiorespiratory Fitness Is Strongly Related to the Metabolic Syndrome in Adolescents

Response to Janssen and Cramp

¹ College of Nursing & Healthcare Innovation, Arizona State University, Phoenix, Arizona
² College of Health Sciences, University of Texas at El Paso, El Paso, Texas
³ Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California

Address correspondence to Gabriel Q. Shaibi, PhD, PT, College of Nursing & Healthcare Innovation, 500 N. 3rd St., Phoenix, AZ 85004. E-mail: gabriel.shaibi{at}asu.edu

The recent report by Janseen and Cramp (1), describing the independent associations between cardiorespiratory fitness (CRF) and the metabolic syndrome in adolescents participating in the National Health and Nutrition Examination Survey 1999–2002, addresses a critical issue related to fitness and chronic disease risk in youth. However, the authors’ findings and interpretation should be received with caution. First, the authors suggest that CRF is an objective measure of physical activity largely determined by recent activity habits. In youth, associations between fitness and activity are weak at best (2), and, while these associations may increase during adolescence, the proposal that CRF is primarily a function of recent physical activity patterns is largely unsubstantiated. In fact, data from the Heritage Family Study (3) suggest that a large proportion of the variance in CRF may be explained by genetic factors.

Second, the authors concluded that CRF is an independent predictor of the metabolic syndrome phenotype; however, they neglected to enter a measure of adiposity into their regression models. We have previously demonstrated that once adiposity is adjusted for, CRF is not a significant determinant of the metabolic syndrome in youth (4). Given that the measure of CRF in the National Health and Nutrition Examination Survey dataset is weight dependent, fitness in heavier youth will be lower because these youth have to perform more work during a similar exercise protocol and, hence, will exhibit higher heart rates at a lower treadmill grade. Furthermore, if CRF is expressed as a ratio relative to total body mass, i.e., milliliters per kilogram per minute, discrepancies will be even more pronounced as a function of having a larger denominator in the fitness expression. As a result, youth in the lowest fitness category may simply be heavier and not necessarily exhibit impairments in their circulatory and respiratory systems that deprives working tissues of oxygen. Therefore, the authors’ findings may simply indicate that heavier youth are more likely to exhibit the metabolic syndrome, as previously shown by Cook et al. (5), rather than illustrating an independent association between fitness and the metabolic syndrome.

References

1. Janssen I, Cramp WC: Cardiorespiratory fitness is strongly related to the metabolic syndrome in adolescents. Diabetes Care 30: 2143–2144, 2007[Free Full Text]
   
2. Morrow JR, Freedson PS: Relationship between habitual physical activity and aerobic fitness in adolescents. Ped Exer Science 6: 315–329, 1994
   
3. Bouchard C, Daw EW, Rice T, Perusse L, Gagnon J, Province MA, Leon AS, Rao DC, Skinner JS, Wilmore JH: Familial resemblance for VO2max in the sedentary state: the HERITAGE family study. Med Sci Sports Exerc 30: 252–258, 1998
   
4. Shaibi GQ, Cruz ML, Ball GD, Weigensberg MJ, Kobaissi HA, Salem GJ, Goran MI: Cardiovascular fitness and the metabolic syndrome in overweight latino youths. Med Sci Sports Exerc 37: 922–928, 2005
   
5. Cook S, Weitzman M, Auinger P, Nguyen M, Dietz WH: Prevalence of a metabolic syndrome phenotype in adolescents: findings from the third National Health and Nutrition Examination Survey, 1988–1994. Arch Pediatr Adolesc Med 157: 821–827, 2003[Abstract/Free Full Text]
   

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				I. Janssen and W. Cramp Cardiorespiratory Fitness Is Strongly Related to the Metabolic Syndrome in Adolescents: Response to Shaibi, Cruz, and Goran Diabetes Care, February 1, 2008; 31(2): e9 - e9. [Full Text] [PDF]

This Article Extract Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Google Scholar Articles by Shaibi, G. Q. Articles by Goran, M. I. PubMed PubMed Citation Articles by Shaibi, G. Q. Articles by Goran, M. I. Social Bookmarking                What's this?