Maria Hildebrand

Age group comparability of raw accelerometer output from wrist- and hip-worn monitors.

PURPOSE The study aims were to compare raw triaxial accelerometer output from ActiGraph GT3X+ (AG) and GENEActiv (GA) placed on the hip and the wrist and to develop regression equations for estimating energy expenditure. METHODS Thirty children (7-11 yr) and 30 adults (18-65 yr) completed eight activities (ranging from lying to running) while wearing one AG and one GA on the hip and the wrist. Oxygen consumption (V˙O2) was measured with indirect calorimetry. Analysis involved the use of ANOVA to examine the effect of activity, brand, and placement on the acceleration values, intraclass correlation coefficient to evaluate the agreement between the two brands and placements, and linear regression to establish intensity thresholds. RESULTS A significant difference in acceleration values between the hip and the wrist placement was found (P < 0.001). The output from the wrist placement was, in general, higher compared with that from the hip. There was no main effect of monitor brand in adults (P < 0.12) and children (P < 0.73), and the intraclass correlation coefficient showed a strong agreement (0.96-0.99). However, a three-way interaction and systematic error between the brands was found in children. Acceleration from both brands and placements showed a strong correlation with V˙O2. The intensity classification accuracy of the developed thresholds for both brands and placements was, in general, higher for adults compared with that for children and was greater for sedentary/light (93%-97%), and vigorous activities (68%-92%) than that for moderate activities (33%-59%). CONCLUSIONS Accelerometer outputs from AG and GA seem comparable when attached to the same body location in adults, whereas inconsistent differences are apparent between the two brands and placements in children, hence limiting the comparability between brands in this age group.

Physical activity, sedentary time and adiposity during the first two decades of life

High amounts of time spent sedentary and low levels of physical activity have been implicated in the process of excessive adiposity gains in youth. The aim of this review is to discuss the role of physical activity, sedentary time and behaviour (i.e. television (TV)-viewing) in relation to adiposity during the first two decades of life with a specific focus on whether the association between sedentary time, and behaviour and adiposity is independent of physical activity. We identified nine cohort studies (three prospective) whether sedentary time was associated with adiposity independent of physical activity. Eight of these studies suggested that sedentary time was unrelated to adiposity when physical activity was taken into account. Results from studies (n 8) examining the independent association between TV-viewing and adiposity independent of physical activity were mixed. Those that observed a positive association between TV-viewing and adiposity independent of physical activity discussed that the association may be due to residual confounding. A few additional studies have also challenged the general notion that low levels of physical activity leads to fatness and suggested that higher baseline fatness may be predictive of a decline in physical activity. It appears unlikely that higher levels of sedentary time are associated with or predictive of, higher levels of adiposity when physical activity is controlled for in youth. Specific sedentary behaviours such as TV-viewing may be associated with adiposity independent of physical activity but the results may be explained by residual confounding.

Validity of the ActiGraph GT1M during walking and cycling.

Abstract The ActiGraph activity monitors have developed and newer versions of the ActiGraph accelerometers (GT1M, GT3X and GT3X +) are now available, including changes in hardware and software compared to the old version (AM7164). This is problematic as most of the validation and calibration work includes the AM7164. The aims of the study were to validate the ActiGraph GT1M during level and graded walking and to assess the potential underestimation of physical activity during cycling. Data were obtained from 20 participants during treadmill walking and ergometer cycling. Energy expenditure was measured via indirect calorimetry and used as the criterion method. Activity counts were highly correlated with energy expenditure during level walking (R2 = 0.82) and graded walking at 5% and 8% (R2 = 0.82 and R2 = 0.67, respectively). There was no linear relationship between activity counts and energy expenditure during cycling. The average activity counts for all data points during cycling was 1,157 counts per minute (CPM) (SD = 974), and mean energy expenditure was 5.0 metabolic equivalents. The GT1M is a valid tool for assessing walking across a wide range of speeds and gradients. However, there is no relationship between activity counts and energy expenditure during cycling and physical activity is underestimated by ≈73% during cycling compared to walking.

Association between birth weight and objectively measured sedentary time is mediated by central adiposity: data in 10,793 youth from the International Children’s Accelerometry Database

Background: Birth weight is an early correlate of disease later in life, and animal studies suggest that low birth weight is associated with reduced activity and increased sedentary time. Whether birth weight predicts later sedentary time in humans is uncertain. Objectives: We examined the relation between birth weight and sedentary time in youth and examined whether this association was mediated by central adiposity. Design: We used pooled cross-sectional data from 8 observational studies conducted between 1997 and 2007 that consisted of 10,793 youth (boys: 47%) aged 6–18 y from the International Children’s Accelerometry Database. Birth weight was measured in hospitals or maternally reported, sedentary time was assessed by using accelerometry (<100 counts/min), and abdominal adiposity (waist circumference) was measured according to WHO procedures. A mediation analysis with bootstrapping was used to analyze data. Results: The mean (±SD) time spent sedentary was 370 ± 91 min/d. Birth weight was positively associated with sedentary time (B = 4.04, P = 0.006) and waist circumference (B = 1.59, P < 0.001), whereas waist circumference was positively associated with sedentary time (B = 0.82, P < 0.001). Results of the mediation analysis showed a significant indirect effect of birth weight on sedentary time through waist circumference (B: 1.30; 95% bias-corrected CI: 0.94, 1.72), and when waist circumference was controlled for, the effect of birth weight on sedentary time was attenuated by 32% (B = 2.74, P = 0.06). Conclusion: The association between birth weight and sedentary time appears partially mediated by central adiposity, suggesting that both birth weight and abdominal adiposity may be correlates of sedentary time in youth.

Evaluation of raw acceleration sedentary thresholds in children and adults.

The aim was to develop sedentary (sitting/lying) thresholds from hip and wrist worn raw tri‐axial acceleration data from the ActiGraph and GENEActiv, and to examine the agreement between free‐living time spent below these thresholds with sedentary time estimated by the activPAL. Sixty children and adults wore an ActiGraph and GENEActiv on the hip and wrist while performing six structured activities, before wearing the monitors, in addition to an activPAL, for 24 h. Receiver operating characteristic (ROC) curves were used to determine sedentary thresholds based on activities in the laboratory. Agreement between developed sedentary thresholds during free‐living and activPAL were assessed by Bland‐Altman plots and by calculating sensitivity and specificity. Using laboratory data and ROC‐curves showed similar classification accuracy for wrist and hip thresholds (Area under the curve = 0.84–0.92). Greatest sensitivity (97–98%) and specificity (74–78%) were observed for the wrist thresholds, with no large differences between brands. During free‐living, Bland‐Altman plots showed large mean individual biases and 95% limits of agreement compared with activPAL, with smallest difference for the ActiGraph wrist threshold in children (+30 min, P = 0.3). Sensitivity and specificity for the developed thresholds during free‐living were low for both age groups and for wrist (Sensitivity, 68–88%, Specificity, 46–59%) and hip placements (Sensitivity, 89–97%, Specificity, 26–34%). Laboratory derived sedentary thresholds generally overestimate free‐living sedentary time compared with activPAL. Wrist thresholds appear to perform better than hip thresholds for estimating free‐living sedentary time in children and adults relative to activPAL, however, specificity for all the developed thresholds are low.

Are Birth Weight, Early Growth, and Motor Development Determinants of Physical Activity in Children and Youth? A Systematic Review and Meta-Analysis

UNLABELLED The purpose of this systematic review was to explore whether birth weight, early growth and motor development act as determinants of physical activity in children and youth. METHODS We performed a systematic literature search on the possible early life determinants. A meta-analysis was performed on the association between birthweight and objectively measured physical activity. RESULTS We identified 9 studies examining birth weight, in which none of the studies with objectively measured physical activity observed an association between birth weight and physical activity. The meta-analysis confirmed this result (b=-3.08, 95% CI -10.20, 4.04). The 3 studies examining early growth and physical activity in youth differ in methodology and the results are inconsistent. Two studies suggest an association between earlier motor development and physical activity and sport participation in youth. This was not confirmed in a third study. CONCLUSION Our meta-analysis suggests that birth weight is not an important determinant of physical activity in youth. Available data does not allow firm conclusions whether early growth and motor development act as determinants of physical activity in youth.