Longitudinal associations of meeting the WHO physical activity guidelines and physical fitness, from preschool to childhood.

There is a well-established relationship between physical activity (PA) and physical fitness in children, being the latter an important marker for present and future health; however, there is still insufficient knowledge for the transition from the preschool age to early childhood. Therefore, this study in Swedish children aimed to investigate the estimated effect of meeting the aerobic component of the PA guidelines at 4 and/or 9 years of age on physical fitness measured at 9 years of age. PA was assessed using a wrist-worn ActiGraph accelerometer and identical data processing in 217 healthy children in Sweden (114 boys and 103 girls). Physical fitness test included cardiorespiratory (20 m shuttle run test), motor (4 × 10 m shuttle run), and muscular fitness (hand grip strength and long jump). A linear mixed model was run, investigating the interaction between meeting the PA guidelines and time (either 4 or 9 years of age) and each fitness component (at 4 and 9). Interactions by sex were also checked. Meeting the PA guidelines consistently (at 4 and 9 years) was significantly associated to better performance in physical fitness parameters for motor fitness (-0.76 s, p < 0.001) and lower body muscular fitness (+4.6 cm; p < 0.001) at 9 years. There was an interaction between meeting the PA guidelines and time point, for cardiorespiratory fitness (+4.58 laps; p < 0.001). This study shows that meeting the PA guidelines at 4 and 9 years of age is associated to higher physical fitness at 9 years of age.

Interpretation of associations between the accelerometry physical activity spectrum and cardiometabolic health and locomotor skills in two cohorts of children using raw, normalized, log-transformed, or compositional data.

It is discussed whether associations between accelerometer-derived physical activity intensities and outcomes should be analysed as absolute or relative data. The aim of the present study was to compare interpretation of association patterns of spectrum physical activity descriptions with outcome using raw, normalized, log-transformed, or compositional data. We used two datasets including 1) 841 schoolchildren and a cardiometabolic health outcome and 2) 1081 preschool children and a locomotor skill outcome. Accelerometry (ActiGraph GT3X+) data were described using multiple variables across the intensity spectrum. We varied the binning of variables to examine sensitivity of the compositional analyses to changes in the distribution centre. We used multivariate pattern analysis for all analyses and interpretations of data. Analyses of absolute (i.e., non-compositional) data showed weak associations for lower intensities and strongest associations with cardiometabolic health and locomotor skills for vigorous intensities. The same association patterns were partly observed for the compositional data, but association patterns were in some cases conflicting. The binning of variables had a major influence on associations for compositional data, but not for absolute data, meaning that conclusions depend on the operationalization of compositional data. These differences challenge and confuse interpretation of association patterns derived from the different approaches.