Purpose: To determine how factors are related to change in cardiorespiratory fitness (CRF) across time in middle school girls followed through high school.
Methods: Adolescent girls (N = 274, 59% African American, baseline age = 13.6 +/- 0.6 yr) performed a submaximal fitness test (PWC170) in 8th, 9th, and 12th grades. Height, weight, sports participation, and physical activity were also measured. Moderate-to-vigorous physical activity (MVPA) and vigorous physical activity (VPA) were determined by the number of blocks reported on the 3-Day Physical Activity Recall (3DPAR). Individual differences and developmental change in CRF were assessed simultaneously by calculating individual growth curves for each participant, using growth curve modeling.
Results: Both weight-relative and absolute CRF increased from 8th to 9th grade and decreased from 9th to 12th grade. On average, girls lost 0.16 kg.m.min.kg.yr in weight-relative PWC170 scores (P < 0.01) and gained 10.3 kg.m.min.yr in absolute PWC170 scores. Girls reporting two or more blocks of MVPA or one or more blocks of VPA at baseline showed an average increase in PWC170 scores of 0.40-0.52 kg.m.min.kg.yr (weight relative) and 22-28 kg.m.min.yr (absolute) in CRF. In weight-relative models, girls with higher BMI showed lower CRF (approximately 0.37 g.m.min.kg.yr), but this was not shown in absolute models. In absolute models, white girls (approximately 40 kg.m.min.yr) and sport participants (approximately 28 kg.m.min.yr) showed an increase in CRF over time.
Conclusion: Although there were fluctuations in PWC170 scores across time, average scores decreased during 4 yr. Physical activity was related to change in CRF over time; BMI, race, and sport participation were also important factors related to change over time in CRF (depending on expression of CRF-weight-relative vs absolute). Subsequent research should focus on explaining the complex longitudinal interactions between CRF, physical activity, race, BMI, and sports participation.