Dose Response of Cardiorespiratory Fitness Interventions in Adolescents

Abstract

PURPOSE: The decline of cardiovascular fitness (CRF) in adolescents has become a major concern. Efforts have been to improve adolescents’ CRF through exercise interventions, but the dose response of the interventions has not been summarized. This study was to determine the exercise dose response needed for increasing CRF in adolescents (12-19 yr. old). METHODS: Google scholar, Web of Science, PsycINFO, Scopus, SPORTDiscus, and Cochrane databases were searched. In addition, the listed studies’ methodological quality was assessed. The standardized mean differences and 95 % confidence intervals (95 % CIs) were calculated as the effect size measures (ES). RESULTS: The search yielded 50 studies, a total of 15 studies were included in the review. Most of the included studies employed a randomized control trial study design (12/15, 67%). Samples sizes ranged from 20 to 60. Intervention length ranged from 6-60 weeks. The major indicator of CRF was VO2max, measured by laps (20-m shuttle run) or minutes (1-mile run). Aerobic exercise was utilized in most of the interventions (73%), followed by resistance training (20%), and a combination of aerobic and resistance training (6.7%). Interventions with intensity of “>60% maximal heart rate (HRmax)” were found statistically significant for improving CRF (ES =0.87, 95% CI 0.23 to 1.11, p=0.04). Frequency of “3 times weekly” was found to be statistically significant for improving CRF (ES =1.07, 95% CI 0.37 to 1.77, p=0.003). Duration of an intervention that was “10-15 weeks” yielded statistically significance in improving CRF (ES =1.02, 95% CI 0.27 to 1.27, p=0.002). The effects of CRF interventions were moderate to significant (ES = 0.59, 95 % CI 0.55-0.88), with high heterogeneity (I 2 = 94 %). There was no sex difference (p=0.07) in terms of the interventions. CONCLUSIONS: Exercise interventions achieving at least 60% of HRmax, meeting 3 times weekly for 10-15 weeks seem to have a positive effect on CRF among adolescents, but there is a high heterogeneity among those studies.