Actigraph-defined moderate-to-vigorous physical activity cut-off points among children: statistical and biobehavioural relevance.

AIM: To compare Actigraph-defined moderate-to-vigorous physical activity (MVPA) cutpoints among children, combining statistical and biobehavioural analyses. METHODS: One hundred and thirteen children aged 10.0 +/- 0.8 years wore accelerometer for three days. The time they spent in MVPA was estimated using 10 thresholds ranged from 3000 to 3900 cpm. A statistical construct including 45 Bland and Altman pairwise analyses was used to compare the 10 estimates of MVPA. A regression was performed to develop an equation relating mean differences to the between-cutpoint gaps. RESULTS: Mean differences in the MVPA estimates ranged from 1.6 to 12.8 min as a function of increment. Raw estimates of MVPA decreased according to an arithmetic sequence with a common difference of 200 cpm. This difference translates into a drop of 12% in MVPA and a misclassification of up to 5% of children. Mean differences (Y) could be predicted from increments (X) using: Y= 0.02 X (R(2)= 0.99, SEE = 0.72, p < 0.0001). CONCLUSION: When a lack of agreement should be assumed as the between-cutpoint gap exceeds 200 cpm, statistical differences may occur earlier at 90 cpm. Yet, the current equation makes it possible to compare and adjust results from studies/interventions using diverse cutpoints for MVPA among children.

Diagnostic quality of Actigraph-based physical activity cut-offs for children: what overweight/obesity references can tell?

BACKGROUND: There is conflicting literature about Actigraph-based cut-off points (CoP) that define the lower limit of moderate-to-vigorous physical activity (MVPA) among children. The aim of the present study was to compare the diagnostic quality of Actigraph-based CoP relative to different body mass index (BMI) classification systems of the weight status of children. METHODS: One hundred and thirteen children aged 8-11 years recruited from three randomly selected elementary schools wore the Actigraph, model 7164 (Actigraph Manufacturing Technology) for 3 days. Five CoP, expressed in counts per minute (c.p.m.; CoP 1000 CoP 2000, CoP 3000, CoP 3200, and CoP 3600) were used to compute their MVPA. The area under the receiver operating characteristic curves (AUC) together with specific indices allowed assessment of the performance of these CoP in reference to overweight/obesity status as defined using BMI-based criteria from the International Obesity Task Force (IOTF), French References (FR) and World Health Organization (WHO) standards. RESULTS: Overweight/obesity frequency ranged from 30% to 42%, with no sex-related difference. All AUC (range, 0.623-0.660) were significantly higher than 0.500 except from those of CoP 1000 and 2000 using the IOTF criteria (0.602 +/- 0.058 and 0.601 +/- 0.057, respectively) and the FR (0.608 +/- 0.060 for CoP 1000). Furthermore, with the WHO standards, all the CoP provided non-significant AUC (range, 0.566-0.597). According to the IOTF and the FR criteria, respectively, CoP 3600 had the highest probability of correct decision (0.62 and 0.68), the lowest misclassification errors (0.38 and 0.32), the highest validity coefficient (0.21 and 0.29), and the highest expected maximum utility (59 and 83). CONCLUSION: When children are classified using BMI-based criteria, the threshold of 3600 c.p.m. should be more appropriate in discriminating non-overweight from overweight/obese.

Relationship Between the MTI Accelerometer (Actigraph) Counts and Running Speed During Continuous and Intermittent Exercise.

This study was designed to investigate the relationship between Actigraph counts and running speed; and to describe differences due to accelerometer position on the body and due to exercise modality. Eleven physical education students (age, 25.1 ± 3.7 years; height, 1.73 ± 0.10 m; body mass, 70.8 ± 10.8 kg) completed two exhaustive exercise tests (continuous and intermittent), with MTI accelerometers mounted both at the hip and ankle. Exercise consisted of running for 3-min at incremental speeds until volitional exhaustion. During both exercise tests, the relationship between the ActiGraph outputs worn at the hip and speed was linear in the range 1.1 - 3.3 m·s(-1) (r(2) = 0.94 and 0.95, p < 0.01 for continuous and intermittent exercise respectively). A coefficient of determination of r(2) = 0.97 (p < 0.01) was found with ankle wearing from walking, jogging and running at high speeds. There was a body placement effect at all absolute speeds (p < 0.01); but no exercise effect on accelerometer counts and no interaction between placement and exercise (p> 0.05). The ActiGraph seems to be a reliable tool for estimating a wide range of activity or exercise intensities. An ActiGraph worn at the ankle may be more appropriate to reflect normal human movement. Key PointsActigraph counts are not influenced by the type of activity.The levelling off of Actigraph output depends mainly on its location on the body, and does not reflect a lack of sensivity at higher speeds.The ActiGraph can be an alternative tool to estimate activity intensity in various conditions.

Comparison of the diagnostic quality of body mass index, waist circumference and waist-to-height ratio in screening skinfold-determined obesity among children.

This study compared the diagnostic quality of the body mass index (BMI), waist circumference (WC), and waist-to-height ratio (WHtR) in screening obesity among children, according to gender and maturation. A sample of 65 boys and 57 girls aged from 6.8 to 11.8 years underwent anthropometry and total percentages of body fat (%TBF)--the reference criterion--were obtained by skinfolds. Diagnostic quality was derived from the area under the ROC curve (AUC), sensitivity, specificity, accuracy, and Youden index (YI). In general, AUC ranged 0.80-1.00, with relatively higher values for WC in boys and late maturers. In the aforementioned subgroups, WC and WHtR were more sensitive than BMI. Furthermore, WC was more consistent in terms of the balance between sensitivity and specificity than BMI or WHtR, across gender and maturational status. The YI ranged 0.59-0.92 and 0.58-0.85 according to gender and maturational status, respectively. Higher values of YI were obtained with WC in boys and late maturers. BMI displayed better accuracy values (86.8-95.2%) among boys and early maturers. WHtR was least useful in classifying children's obesity status. Waist circumference exhibits an overall better performance, among boys and late maturers. Paediatricians should systematically add WC to clinical and epidemiological measurements.

Physical activity and sedentary lifestyle in children as time-limited functions: usefulness of the principal component analysis method.

This study was designed to examine the hourly variation in and the interplay between physical activity and sedentary behavior (SB) in order to highlight key time periods for physical activity interventions for children. Data for physical activity and SB obtained with ActiGraph in 56 boys and 47 girls aged from 8 to 11 years. These data were divided into sixty minute-time samples for moderate-to-vigorous physical activity (MVPA) and SB, and analyzed using a principal component analysis (PCA) and correlation statistics. The PCA provides 10 factors which account for 80.4% of the inertia. Only two of these factors did not display competition between MVPA and SB. Contrary to some reports, a coefficient of correlation of -.68 (p < 10(-4)) was found between daily time spent at MVPA and SB. Some salient traits of children's behaviors were shown through PCA. The results suggested that efficacy of interventions targeting the morning hours (07:00 AM-11:59 AM) and the afternoon period (02:00 PM-05:59 PM) warrants attention.

Moderate-to-vigorous physical activity among children: discrepancies in accelerometry-based cut-off points.

OBJECTIVE: To highlight the discrepancies in accelerometry cut-off points of moderate-to-vigorous physical activity (MVPA) according to the definitions of Puyau et al. (MVPA(P)) and Trost et al. (MVPA(T)). RESEARCH METHODS AND PROCEDURES: Forty-five children from 8 to 11 years old were monitored with the ActiGraph (ActiGraph, LLC, Fort Walton Beach, FL) for 3 consecutive days. Daily time spent at MVPA obtained with MVPA(P) was compared with that obtained with MVPA(T) using variability, regression, and agreement statistics. Data were then discussed with regard to physical activity recommendations. RESULTS: The mean daily time spent at MVPA(P) (28 +/- 18 minutes) was significantly lower (p < 10(-4)) than that spent at MVPA(T) (141 +/- 39 minutes). The coefficient of determination between the two definitions was low (R(2) = 0.49 +/- 0.71). There was a lack of agreement between the two definitions, with a mean error or bias of 113 min/d. Thirty-four point eight percent and 100% of children underwent 30-minute MVPA/d with MVPA(P) and MVPA(T) definitions, respectively. DISCUSSION: Comparability between studies devoted to describing children's physical activity or to assessing interventions may lack consistency according to the definition, with a real risk of misclassification.