273 Pediatric Exercise Science, 2008, 20, 273-284 © 2008 Human Kinetics, Inc. Lubans and Morgan are with the School of Education, University of Newcastle, Callaghan Campus, NSW 2308, Australia. Callister is with the School of Biomedical Sciences, University of Newcastle, Callaghan Campus, NSW 2308, Australia. Collins is with the School of Health Sciences, University of Newcastle, Callaghan Campus, NSW 2308, Australia. The Relationship Between Pedometer Step Counts and Estimated VO 2 Max as Determined by a Submaximal Fitness Test in Adolescents David R. Lubans, Philip J. Morgan, Robin Callister, and Clare E. Collins The purpose of this study was to examine the relationship between pedometer step counts and estimated VO 2 max as determined by a submaximal exercise test. Par- ticipants (N = 115; 65 girls, 50 boys) wore pedometers for five days and completed the Queen’s College Step Test (QCST). Based on these results participants were classified as HIGH, MOD, or LOW cardiorespiratory fitness. Boys accumulated more steps per day (p < .05) than girls (12,766 ± 4,923 versus 10,887 ± 2,656). The relationship between estimated VO 2 max and mean steps/day was moderate (r = .34, p < .01). Participants classified as having HIGH fitness levels accumulated more steps/day than LOW-fit adolescents (p < .05). The results from this study suggest that estimated VO 2 max as determined by a submaximal exercise test is moderately associated with mean steps/day in adolescents. Participation in regular physical activity is associated with a variety of positive health outcomes for young people (41). Higher levels of physical activity during youth are associated with good mental health (31), improved self-esteem (12) and an improved profile for a number of health risk behaviors (32). While many of the physiological benefits of physical activity are difficult to establish in youth (9), a physically active lifestyle during this period is associated with a reduced risk for numerous lifestyle diseases, including type II diabetes and cardiovascular disease (4,48,34). In addition to these benefits, researchers have hypothesized that physi- cal activity levels in youth influence cardiorespiratory fitness. However, studies examining this relationship have produced equivocal results (37,5). A number of possible explanations have been offered to account for the poor associations found between cardiorespiratory fitness and physical activity among youth. First, cardiorespiratory fitness has a strong genetic component (7) and adap- tive responses to training will vary between individuals (3). Second, the activity patterns of youth are sporadic (50) and it has been suggested that few children and