Reallocating time spent in physical activity intensities: Longitudinal associations with physical fitness (DADOS...

Firstly, to investigate the longitudinal associations between accelerometer-derived physical activity (PA) intensities and physical fitness (PF) at 24-month follow-up in adolescents. Secondly, to examine how substituting time spent in low or moderate PA intensities with vigorous PA at baseline was related to PF at 24-month follow-up.

Longitudinal observational study METHOD: The DADOS (Deporte, ADOlescencia y Salud) study is a 3-year longitudinal research project carried out between years 2015-2017. The analyses included 189 adolescents (91girls) aged 13.9±0.3 years at baseline. PA was assessed by a wrist-worn GENEActiv triaxial accelerometer and expressed as minutes/day of light, moderate and vigorous PA. Cardiorespiratory, musculoskeletal and motor fitness were assessed by field tests and a global fitness z-score was calculated as the mean of the z-scores values of each fitness test. Association between PA intensities and PF were determined using linear regression. Isotemporal analyses estimating the association of reallocating PA intensities with PF were performed.

Baseline vigorous PA was positively associated with cardiorespiratory fitness and global fitness score at follow-up in boys (β=0.234;p=0.002, β=0.340;p<0.001) and girls (β=0.184;p=0.043, β=0.213;p=0.004). In boys, baseline vigorous PA was also positively associated with musculoskeletal and motor fitness (β=0.139;p=0.035, β=0.195;p=0.021). The substitution of 10min/day of light PA or moderate PA with 10min/day of vigorous PA at baseline was positively associated with all PF components and global fitness score in boys (p<0.001), and with global fitness score girls (p<0.05).

These findings highlight the need of promoting vigorous PA due to its specific influence on adolescent's PF.