Validating measures of free-living physical activity in overweight and obese subjects using an accelerometer.

BACKGROUND: Free-living physical activity can be assessed with an accelerometer to estimate energy expenditure but its validity in overweight and obese subjects remains unknown. OBJECTIVE: Here, we validated published prediction equations derived in a lean population with the TracmorD accelerometer (DirectLife, Philips Consumer Lifestyle) in a population of overweight and obese. We also explored possible improvements of new equations specifically developed in overweight and obese subjects. DESIGN: Subjects were 11 men and 25 women (age: 41±7 years; body mass index: 31.0±2.5 kg m(-2)). Physical activity was monitored under free-living conditions with TracmorD, whereas total energy expenditure was measured simultaneously with doubly-labeled water. Physical activity level (PAL) and activity energy expenditure (AEE) were calculated from total energy expenditure and sleeping metabolic rate. RESULTS: The published prediction equation explained 47% of the variance of the measured PAL (P<0.001). PAL estimates were unbiased (errors (bias±95% confidence interval): -0.02±0.28). Measured and predicted AEE/body weight were highly correlated (r(2)=58%, P<0.001); however, the prediction model showed a significant bias of 8 kJ kg(-1) per day or 17.4% of the average AEE/body weight. The new prediction equation of AEE/body weight developed in the obese group showed no bias. CONCLUSIONS: In conclusion, equations derived with the TracmorD allow valid assessment of PAL and AEE/body weight in overweight and obese subjects. There is evidence that estimates of AEE/body weight could be affected by gender. Equations specifically developed in overweight and obese can improve the accuracy of predictions of AEE/body weight.

Sleep duration and body-weight development during puberty in a Dutch children cohort.

BACKGROUND: Short sleep duration is associated with obesity during childhood and adulthood. OBJECTIVE: The objective of our study was to investigate the relationship between sleep duration and body mass index (BMI) from Tanner stages 1 to 5 in a Dutch children cohort. DESIGN: In 98 children, anthropometric measurements and leptin concentrations were measured from age 7 to 16 years; body composition, physical activity (Baecke questionnaire), hours television viewing and self-reported sleep duration were measured yearly from age 12 to 16 years. Moreover, the polymorphisms of the FTO gene (rs9939609) and parental BMI's were determined. RESULTS: At Tanner stages 1-5 sex differences were observed in height, body weight, waist circumference, fat mass per squared meter height and leptin concentrations per kg fat mass. Inverse relationships were observed between the change in BMI (kg m(-2)) and the change in hours of sleep per night (h) from Tanner stages 1 to 4 (r=-0.68, P<0.001), from Tanner stages 2 to 5 (r=-0.35, P<0.05) and from Tanner stages 1 to 5 (r=-0.33, P<0.05). Univariate analysis of variance showed that with progressive Tanner stages, BMI increases and sleep duration decreases in an interrelated way independent of possible confounders (R(2)=0.38, P<0.02). CONCLUSION: Changes in BMI during puberty were inversely related to changes in sleep duration, independent of possible confounders.

The relationship between leptin, gonadotropic hormones, and body composition during puberty in a Dutch children cohort.

OBJECTIVE: To investigate the relationship between leptin concentrations, gonadotropic hormone concentrations, and body composition during puberty in a Dutch children cohort. DESIGN: In a cohort of 98 children, we determined anthropometric measurements, body composition, and concentrations of leptin, FSH, and LH. RESULTS: Sex differences were observed from Tanner stage 1 onwards in weight, body fat percentage, and leptin/fat mass ratio. In boys and girls, the relationship between leptin concentrations and FM was weaker at Tanner stage 2 (R(2)=0.33 and R(2)=0.39; P<0.001), 3 (R(2)=0.27 and R(2)=0.36; P<0.002), and 4 (R(2)=0.21 and R(2)=0.28; P<0.03) than at Tanner stage 1 (R(2)=0.51 and R(2)=0.67; P<0.001) and 5 (R(2)=0.46 and R(2)=0.78; P<0.01). In girls, a peak in leptin concentrations (8.5+/-6.0 ng/ml) preceded a peak in LH and FSH concentrations (15.1+/-3.5 and 5.0+/-4.5 IU/l). A lead/lag relationship was observed of leptin at Tanner stage 1 to LH and FSH at Tanner stage 2 (R(2)=0.12, P<0.05 and R(2)=0.18, P<0.05). In boys, there was no peak in leptin, LH, and FSH; additionally, leptin at Tanner stage 3 was related FSH at Tanner stage 4 (R(2)=0.17, P<0.04). CONCLUSION: In boys and girls during puberty, factors independent of fat mass become (transiently) more important in the regulation of plasma leptin concentrations. Moreover, in girls, leptin is suggested to act as a permissive factor for the onset of puberty, while, in boys, leptin has a different timing and possibly different function.