Magnus Dencker

Health-related aspects of objectively measured daily physical activity in children

It is well established that physical inactivity in adults is associated with increased mortality and morbidity. Whether daily physical activity level is related to risk factors for cardiovascular disease (CVD) in children has been debated. Furthermore, objective data on the habitual daily physical activity in children have at large been scarce in the literature. The main reason for this is the fact that daily physical activity is very difficult to measure in children. In recent years, a new device, the accelerometer, has emerged as a frequently used instrument for the measurement of daily physical activity. This review summarizes recently published studies that have used accelerometers to measure daily physical activity in children and related activity data to known risk factors for CVD.

Daily physical activity related to aerobic fitness and body fat in an urban sample of children.

This study evaluates associations between objectively measured daily physical activity vs aerobic fitness and body fat in children aged 8–11 years. A cross‐sectional study of 225 children aged 7.9–11.1 years was performed. Abdominal fat mass (AFM) and total body fat (TBF) were quantified by dual‐energy x‐ray absorptiometry. TBF was calculated as percentage of total body mass (BF%). Body fat distribution was calculated as AFM/TBF. Aerobic fitness was measured by indirect calorimetry during a maximal cycle ergometer exercise test. Daily physical activity was assessed by accelerometers for 4 days and daily accumulation of moderate‐to‐vigorous and vigorous activity was calculated. Significant relationships (P<0.05) existed for vigorous activity vs ln BF% (r=−0.40), ln AFM (r=−0.35), TBF/AFM (r=−0.22) and aerobic fitness (r=0.38), whereas moderate‐to‐vigorous activity displayed weaker relationships (−0.22, −0.18, −0.12 NS, and 0.25). Multiple regression analyses with inclusion of possible confounders concluded that vigorous activity was independently related to aerobic fitness and ln BF% or ln AFM. Moderate‐to‐vigorous activity was only independently related to aerobic fitness. In this population, low daily accumulation of vigorous activity was, already in children aged 8–11 years, associated with more body fat and lower aerobic fitness. A similar relation was not found for daily accumulation of moderate‐to‐vigorous activity.

Reference values for respiratory system impedance by using impulse oscillometry in children aged 2-11 years.

The forced oscillation technique makes it possible to evaluate the mechanical properties of the respiratory system with a minimum of cooperation. The method is therefore especially useful in children. Impulse oscillometry (IOS) is a commercially available version of this technique. There is, as yet, limited information on reference values for IOS in children. The aim of this study was to extend the reference values for IOS variables and to study their correlation with height, weight and age in healthy children. A sample (n = 360) of children (age 2·1–11·1 years) was measured by using impulse oscillometry (IOS; Jaeger, Würzburg, Germany). The sample was based on children attending kindergarten in Finland and children attending primary school in Sweden. Measurements of respiratory resistance (Rrs) and reactance (Xrs) at 5, 10, 15 and 20 Hz, total respiratory impedance (Zrs) and the resonance frequency (Fr) were made. All variables were related to body height. Most of them were also weakly related to weight. Reference equations for children (height 90–160 cm) are presented.

BMI and objectively measured body fat and body fat distribution in prepubertal children

Background  Body Mass Index (BMI) is often used as a surrogate estimate of body fat in epidemiological studies. This study explores the association between BMI, body fat and body fat distribution assessed by Dual‐Energy X‐Ray Absorptiometry (DXA) in younger children.

Prediction of fat-free body mass from bioelectrical impedance among 9-to 11-year-old Swedish children

Aim:  Predictive equations for estimating body composition from bioelectrical impedance analysis (BIA) among Scandinavian children are lacking. In the present study, equations for estimation of fat‐free body mass (FFM) and lean tissue mass (LTM) were developed and cross‐validated from BIA using dual‐energy X‐ray absorptiometry (DXA) as the reference measurement of body composition.

Effects of a three-year intervention: the Copenhagen School Child Intervention Study.

INTRODUCTION This study assessed short-term and long-term effects of a 3-yr controlled school-based physical activity (PA) intervention on fatness, cardiorespiratory fitness (VO(2peak)) and CVD risk factors in children. METHODS The study involved 18 schools (10 intervention and 8 controls) and included a follow-up 4 yr after the end of intervention. The analyses included 696, 6- to 7-yr-old children at baseline, 612 postintervention (age 9.5 yr) and 441 at follow-up (age 13.4 yr). The intervention consisted of a doubling of the amount of physical education (PE; from 90 to 180 min·wk(-1)), training of PE teachers, and upgrading of PE and playing facilities. Anthropometrics and systolic blood pressure (SBP) were measured. VO(2peak) was directly measured, and PA was assessed using accelerometry. Fasting blood samples were analyzed for CVD risk factors. A composite risk score was computed from z-scores of SBP, triglycerides, total cholesterol-to-HDL cholesterol ratio, homeostatic model assessment (HOMA score), skinfolds, and inverse VO(2peak). RESULTS The HOMA score of the intervention group boys had a smaller increase from baseline to postintervention compared with control boys (P = 0.004). From baseline to follow-up intervention group boys had a smaller increase in SBP compared with control boys (P = 0.010). There were no other significant differences between groups. CONCLUSIONS This 3-yr school-based PA intervention caused positive changes in SBP and HOMA score in boys but not in girls, and no effects were seen in PA, VO(2peak), fatness, and the other measured CVD risk factors. Our results indicate that a doubling of PE and providing training and equipment may not be sufficient to induce major improvements in CVD risk factors in a normal population.

Accelerometer-measured daily physical activity related to aerobic fitness in children and adolescents

Abstract Maximum oxygen uptake ([Vdot]O2PEAK) is generally considered to be the best single marker for aerobic fitness. While a positive relationship between daily physical activity and aerobic fitness has been established in adults, the relationship appears less clear in children and adolescents. The purpose of this paper is to summarise recently published data on the relationship between daily physical activity, as measured by accelerometers, and [Vdot]O2PEAK in children and adolescents. A PubMed search was performed on 29 October 2010 to identify relevant articles. Studies were considered relevant if they included measurement of daily physical activity by accelerometry and related to a [Vdot]O2PEAK either measured directly at a maximal exercise test or estimated from maximal power output. A total of nine studies were identified, with a total number of 6116 children and adolescents investigated. Most studies reported a low-to-moderate relationship (r = 0.10–0.45) between objectively measured daily physical activity and [Vdot]O2PEAK. No conclusive evidence exists that physical activity of higher intensities are more closely related to [Vdot]O2PEAK, than lower intensities.

A 2-year school-based exercise programme in pre-pubertal boys induces skeletal benefits in lumbar spine.

Aim: The aim of this study was to evaluate if a general school‐based exercise intervention programme in pre‐pubertal boys would render site‐specific benefits in bone mineral accrual and gain in femoral neck structure.

A Six-Year Exercise Program Improves Skeletal Traits without Affecting Fracture Risk - a Prospective Controlled Study in 2621 Children.

Most pediatric exercise intervention studies that evaluate the effect on skeletal traits include volunteers and follow bone mass for less than 3 years. We present a population‐based 6‐year controlled exercise intervention study in children with bone structure and incident fractures as endpoints. Fractures were registered in 417 girls and 500 boys in the intervention group (3969 person‐years) and 835 girls and 869 boys in the control group (8245 person‐years), all aged 6 to 9 years at study start, during the 6‐year study period. Children in the intervention group had 40 minutes daily school physical education (PE) and the control group 60 minutes per week. In a subcohort with 78 girls and 111 boys in the intervention group and 52 girls and 54 boys in the control group, bone mineral density (BMD; g/cm2) and bone area (mm2) were measured repeatedly by dual‐energy X‐ray absorptiometry (DXA). Peripheral quantitative computed tomography (pQCT) measured bone mass and bone structure at follow‐up. There were 21.7 low and moderate energy‐related fractures per 1000 person‐years in the intervention group and 19.3 fractures in the control group, leading to a rate ratio (RR) of 1.12 (0.85, 1.46). Girls in the intervention group, compared with girls in the control group, had 0.009 g/cm2 (0.003, 0.015) larger gain annually in spine BMD, 0.07 g (0.014, 0.123) larger gain in femoral neck bone mineral content (BMC), and 4.1 mm2 (0.5, 7.8) larger gain in femoral neck area, and at follow‐up 24.1 g (7.6, 40.6) higher tibial cortical BMC (g) and 23.9 mm2 (5.27, 42.6) larger tibial cross‐sectional area. Boys with daily PE had 0.006 g/cm2 (0.002, 0.010) larger gain annually in spine BMD than control boys but at follow‐up no higher pQCT values than boys in the control group. Daily PE for 6 years in at study start 6‐ to 9‐year‐olds improves bone mass and bone size in girls and bone mass in boys, without affecting the fracture risk.

Lack of physical activity in young children is related to higher composite risk factor score for cardiovascular disease

Aim:  This study evaluates whether accelerometer‐measured physical activity is related to higher composite risk factor scores for cardiovascular disease (CVD) in children.