Cardiorespiratory fitness in adolescents before and after the COVID-19 confinement: a prospective cohort study.

Long periods of free-movement restrictions may negatively affect cardiorespiratory fitness and health. The present study investigated changes after the COVID-19 confinement in maximal oxygen intake (VO2 max) levels in a sample of 89 Spanish school children aged 12 and 14 years at baseline (49.8% girls). The 20-m shuttle run test served to estimate VO2 max before and after the COVID-19 confinement. Paired t-tests estimated an overall difference of - 0.5 ml.kg-1.min-1 (SD 0.3) (p = 0.12), whereas the highest significant reductions were observed for girls aged 14 years (- 1.5 ml.kg-1.min-1 (SD 0.6) (p < 0.05)). Boys aged 14 years showed a slight increase (0.4 ml.kg-1.min-1 (SD 0.5) (p = 0.44)), whereas boys aged 12 years presented an important decrease (- 1.2 ml.kg-1.min-1 (SD 0.7) (p = 0.14)). Healthy Fitness Zone (HFZ) levels also experienced a decrease of - 3.4% as regards baseline levels over the examined period. All the examined subgroups showed lower levels in relation to a normal VO2 max rate development, although girls aged 14 and boys aged 12 years accounted for the highest part.Conclusion: The results indicate that COVID-19 confinement might delay the normal development of VO2 max in adolescents. Strategies to tackle this concerning decline are warranted. What is Known: • First study analyzing cardiorespiratory fitness levels in teenagers after COVID-19 confinement. What is New: • Important delay in maximal oxygen intake identified in a sample of Spanish teenagers. • These results should be considered to develop strategies of a more active lifestyle in teenagers during and after confinements.