Association between age at onset of independent walking and objectively measured sedentary behavior is mediated by moderate-to-vigorous physical activity in primary school children

Objective Age at onset of walking has been shown as an early predictor of physical activity in infants and children. However, little is known about whether age at onset of walking may predict sedentary behavior (SB). The aim of the present study was to examine the association between the timing of onset of walking and objectively measured SB, and whether this association is mediated by moderate-to-vigorous physical activity (MVPA) in children. Methods The subjects were 388 elementary school children aged 6-12 years. Current weight and height data were collected. Birth weight and the age in months the child first walked independently were reported based on the parents' recall. Children's SB and physical activity were objectively measured using a triaxial accelerometer (Active style Pro HJA-350IT, OMRON). The following summary outcome variables were derived from accelerometer data: Time (min/day) spent in SB (<= 1.5 metabolic equivalents [METs]) and MVPA (>= 3.0 METs). Results The mean +/- SD time (min/day) spent in sedentary was 376 +/- 62 and MVPA was 67.6 +/- 20.8. Multiple linear regression analyses revealed that a later age at independent walking was associated with increased time spent in SB (beta = 0.15, P < 0.001) and decreased time spent in MVPA (beta = -0. 18, P < 0.001) after adjusting for gender, birth weight, current age, body weight, schools, and time spent wearing the accelerometer. When MVPA was introduced as a covariate in the model predicting SB, the association between the age at independent walking and time spent in SB was completely attenuated (beta = 0.04, P = 0.215), while MVPA was significantly associated with SB (beta = -0.61, P < 0.001). Conclusions Our results indicate that infants who walked at a later age spent more time in SB in childhood, and this association is mediated by MVPA. Appropriate interventions which focus on increasing MVPA and thereby reducing SB may be beneficial in infants who demonstrate a later age at onset of independent walking.