Introduction: Physical activity has been established as an important health behavior. Children who are proficient performers of gross motor skills typically are more physically active and less sedentary than children with poor gross motor skill proficiency (MSP). Though physical activity (PA) is a commonly researched correlate of gross MSP, it cannot fully explain a child's level of gross MSP. Little is known about genetic influences on MSP, but evidence suggests that the brain-derived neurotrophic factor (BDNF) val66met polymorphism is associated with delays in fine motor learning and retention and thus parallels may be drawn to gross MSP and the polymorphism. Physical activity (PA) is also an important factor in the secretion of BDNF. The purpose of this study was to examine the BDNF val66met polymorphism in terms of gross and fine MSP, PA, and sedentary time in children. Methods: Boys and girls (n = 105) between the ages of 9-10 years were recruited to participate. Demographic information (child birthdate, race, grade, and parent education) was obtained via parent survey. Height and weight were directly measured to determine body mass index (BMI). Saliva samples were collected and genotyped for the BDNF val66met polymorphism. Gross MSP was assessed using locomotor, object control, and total skill scores from The Test of Gross Motor Development-2 (TGMD-2) (Ulrich, 2000). Fine MSP was assessed using scores on the pegboard and star-copying tasks from the Bruininks-Oseretsky Test of Motor Proficiency-2 (BOT-2) (Bruininks & Bruininks, 2005), and scores on the Bubbles Burst iPad application. Participants wore an Actigraph GT3X accelerometer to assess PA and sedentary time. Results: Complete data were obtained from 82.9% (n = 87) of the sample. Sixty-four percent (n = 67) of participants were non-Met-carriers, 30% (n = 31) were Met-carriers, and 6% (n = 7) were Met-Met-carriers. Boys spent significantly less time sedentary (57.4% ± 6.3%) than girls (62.4% ± 7.0%), and greater percentages of time in moderate PA (5.1% ± 1.3%) than girls (3.5% ± 1.2%) and vigorous PA (3.0% ± 1.7%) than girls (1.7% ± 1.1%). Boys performed significantly better on the object control subtest (39.2 ± 5.1) than girls (32.1 ± 6.0), and boys also outperformed girls on the locomotor subtest (42.0 ± 2.9 versus 40.3 ± 4.5, respectively). Scores on the BOT-2 pegboard task and object control scores were weakly but significantly associated (r = .274, p ≤ .001). Object control scores and sex significantly predicted time spent in moderate-to-vigorous PA (MVPA), F(5, 81) = 9.470, p < .001, r = .607). A significant inverse association between object control scores and sedentary time was found F(5, 81) = 3.859, p < .005, R2 = .192. Discriminant function analyses explained about 27% of the variation in carrier status (Rc2 = 26.4) and indicated that sedentary time, MVPA, locomotor skills, and fine motor skills (pegboard and star-copying scores) significantly differentiated carrier status. Conclusions: Object control skills play an important role in the promotion of PA, particularly in girls. BDNF val66met polymorphism carrier status was influenced by MVPA and sedentary time, and to some extent, fine and gross MSP. Time spent in MVPA may override deficits associated with the polymorphism.
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