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  • Author: Per Wollmer x
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Magnus Dencker, Tina Tanha, Per Wollmer, Magnus K. Karlsson, Lars Bo Andersen and Ola Thorsson

Background:

Limited data exist of tracking and changes in accelerometer-measured physical activity in children.

Methods:

Physical activity was assessed by accelerometers for 4 days in 167 children (boys, n = 90; girls n = 77) age 9.8 ± 0.6 years. Follow-up measurement was made 2.0 ± 0.1 yrs later (range 1.9−2.1 yrs). General physical activity (GPA) was defined as mean count/minute. Minutes of inactivity; light, moderate, and vigorous physical activity (LMVPA); moderate and vigorous physical activity (MVPA); and vigorous physical activity (VPA) per day were calculated both as absolute values and as percentage of total registration time.

Results:

Spearman rank order correlation indicated low tracking of MVPA and VPA in girls (r = .25−0.33, P < .05), and low-moderate tracking of GPA, inactivity, LMVPA, MVPA and VPA in boys (r = .23−0.40, P < .05). Time in inactivity increased at follow-up by 5%−14%. Most of the assessed physical activity variables were decreased at follow-up by 6% to 30%.

Conclusions:

Physical activity tracks at a low-moderate degree from age 10−12 years, which confirm previous investigations that have used self-report assessments. The low-moderate tracking of physical activity variables indicate that those who were most active initially remained most active. Increasing inactive behavior was observed and that several other physical activity variables were decreased at follow-up.

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Daniel Arvidsson, Elias Johannesson, Lars Bo Andersen, Magnus Karlsson, Per Wollmer, Ola Thorsson and Magnus Dencker

Background: Nerve growth factor (NGF) and brain-derived neural factor (BDNF) are important for brain function and detectable in the blood. This study explored the longitudinal associations of physical activity and body fat with serum NGF and BDNF in children. Methods: Two waves of measurements were performed 2 years apart in 8- to 11-year-old children, including physical activity using the ActiGraph model 7164, body composition by dual-energy X-ray absorptiometry, and serum NGF and BDNF determined by multiplex immunoassay. The first wave included 248 children. Full information maximum likelihood estimation with robust standard errors was applied in structural equation modeling. Results: Vigorous physical activity showed a direct positive longitudinal relationship with NGF (standardized coefficient β = 0.30, P = .01) but not with BDNF (β = 0.04, P = .84). At the same time, body fat percentage was positively related to both NGF (β = 0.59, P < .001) and BDNF (β = 0.17, P = .04). There was an indication of an indirect relationship of vigorous physical activity with NGF (product of unstandardized coefficient β = −0.18, P = .02) and BDNF (β = −0.07, P = .05) through the negative relationship with body fat percentage (β = −0.36, P < .001). Conclusions: Vigorous physical activity is directly related to serum NGF and indirectly through the level of body fat. The relationships with serum BDNF are more complex.