Associations of Monitor-Independent Movement Summary and Health-Related Fitness With Gross Motor Skills in Young Children

The purpose of this study was to determine the associations of device-based assessments of physical activity (PA) and health-related fitness (HRF) with gross motor skills (GMS) in preschool-aged children. Participants were 3- to 5-year-old children (N = 316; 49.6% female) who participated in the 2012 National Youth Fitness Survey. GMS was assessed using the gross motor quotient calculated from the Test for Gross Motor Development—Second Edition. PA was assessed using wrist-worn ActiGraph GT3X accelerometers with raw triaxial acceleration data summarized using monitor-independent movement summary units (MIMS). Analyzed metrics included average MIMS per day and peak 30-min MIMS. HRF assessment consisted of a plank score and a sum of skinfold assessment. Weighted hierarchical regressions tested the associations between PA, HRF, and GMS variables with a secondary weighted mediation analysis that examined whether HRF mediated the association between PA and GMS. Peak 30-min MIMS significantly correlated with GMS (b = 0.17, p = .005). Plank scores had the strongest correlation with GMS (b = 0.23, p = .004), and weighted mediation analyses revealed that plank scores partially mediated the association between peak 30-min MIMS and GMS (indirect effect = 0.03, p = .01, 23.1% mediation). Peak 30-min MIMS significantly associated with GMS in preschool children, an association partially mediated by core muscular endurance.