Soren Brage

Physical activity and clustered cardiovascular risk in children: a cross-sectional study (The European Youth Heart Study)

BACKGROUND Atherosclerosis develops from early childhood; physical activity could positively affect this process. This studys aim was to assess the associations of objectively measured physical activity with clustering of cardiovascular disease risk factors in children and derive guidelines on the basis of this analysis. METHODS We did a cross-sectional study of 1732 randomly selected 9-year-old and 15-year-old school children from Denmark, Estonia, and Portugal. Risk factors included in the composite risk factor score (mean of Z scores) were systolic blood pressure, triglyceride, total cholesterol/HDL ratio, insulin resistance, sum of four skinfolds, and aerobic fitness. Individuals with a risk score above 1 SD of the composite variable were defined as being at risk. Physical activity was assessed by accelerometry. FINDINGS Odds ratios for having clustered risk for ascending quintiles of physical activity (counts per min; cpm) were 3.29 (95% CI 1.96-5.52), 3.13 (1.87-5.25), 2.51 (1.47-4.26), and 2.03 (1.18-3.50), respectively, compared with the most active quintile. The first to the third quintile of physical activity had a raised risk in all analyses. The mean time spent above 2000 cpm in the fourth quintile was 116 min per day in 9-year-old and 88 min per day in 15-year-old children. INTERPRETATION Physical activity levels should be higher than the current international guidelines of at least 1 h per day of physical activity of at least moderate intensity to prevent clustering of cardiovascular disease risk factors.

TV viewing and physical activity are independently associated with metabolic risk in children: the European Youth Heart Study.

Background TV viewing has been linked to metabolic-risk factors in youth. However, it is unclear whether this association is independent of physical activity (PA) and obesity. Methods and Findings We did a population-based, cross-sectional study in 9- to 10-y-old and 15- to 16-y-old boys and girls from three regions in Europe (n = 1,921). We examined the independent associations between TV viewing, PA measured by accelerometry, and metabolic-risk factors (body fatness, blood pressure, fasting triglycerides, inverted high-density lipoprotein (HDL) cholesterol, glucose, and insulin levels). Clustered metabolic risk was expressed as a continuously distributed score calculated as the average of the standardized values of the six subcomponents. There was a positive association between TV viewing and adiposity (p = 0.021). However, after adjustment for PA, gender, age group, study location, sexual maturity, smoking status, birth weight, and parental socio-economic status, the association of TV viewing with clustered metabolic risk was no longer significant (p = 0.053). PA was independently and inversely associated with systolic and diastolic blood pressure, fasting glucose, insulin (all p < 0.01), and triglycerides (p = 0.02). PA was also significantly and inversely associated with the clustered risk score (p < 0.0001), independently of obesity and other confounding factors. Conclusions TV viewing and PA may be separate entities and differently associated with adiposity and metabolic risk. The association between TV viewing and clustered metabolic risk is mediated by adiposity, whereas PA is associated with individual and clustered metabolic-risk indicators independently of obesity. Thus, preventive action against metabolic risk in children may need to target TV viewing and PA separately.

Assessment of physical activity in youth

Despite much progress with physical activity assessment, the limitations concerning the accurate measurement of physical activity are often amplified in young people due to the cognitive, physiological, and biomechanical changes that occur during natural growth as well as a more intermittent pattern of habitual physical activity in youth compared with adults. This mini-review describes and compares methods to assess habitual physical activity in youth and discusses main issues regarding the use and interpretation of data collected with these techniques. Self-report instruments and movement sensing are currently the most frequently used methods for the assessment of physical activity in epidemiological research; others include heart rate monitoring and multisensor systems. Habitual energy expenditure can be estimated from these input measures with varying degree of uncertainty. Nonlinear modeling techniques, using accelerometry perhaps in combination with physiological parameters like heart rate or temperature, have the greatest potential for increasing the prediction accuracy of habitual physical activity energy expenditure. Although multisensor systems may be more accurate, this must be balanced against feasibility, a balance that shifts with technological and scientific advances and should be considered at the beginning of every new study.

Independent associations of physical activity and cardiorespiratory fitness with metabolic risk factors in children: the European youth heart study

Aims/hypothesisHigh levels of cardiorespiratory fitness (CRF) and physical activity (PA) are associated with a favourable metabolic risk profile. However, there has been no thorough exploration of the independent contributions of cardiorespiratory fitness and subcomponents of activity (total PA, time spent sedentary, and time spent in light, moderate and vigorous intensity PA) to metabolic risk factors in children and the relative importance of these factors.MethodsWe performed a population-based, cross-sectional study in 9- to 10- and 15- to 16-year-old boys and girls from three regions of Europe (n = 1709). We examined the independent associations of subcomponents of PA and CRF with metabolic risk factors (waist circumference, BP, fasting glucose, insulin, triacylglycerol and HDL-cholesterol levels). Clustered metabolic risk was expressed as a continuously distributed score calculated as the average of the standardised values of the six subcomponents.ResultsCRF (standardised β = −0.09, 95% CI −0.12, −0.06), total PA (standardised β = −0.08, 95% CI −0.10, −0.05) and all other subcomponents of PA were significantly associated with clustered metabolic risk. After excluding waist circumference from the summary score and further adjustment for waist circumference as a confounding factor, the magnitude of the association between CRF and clustered metabolic risk was attenuated (standardised β = −0.05, 95% CI −0.08, −0.02), whereas the association with total PA was unchanged (standardised β = −0.08 95% CI −0.10, −0.05).Conclusions/interpretationPA and CRF are separately and independently associated with individual and clustered metabolic risk factors in children. The association between CRF and clustered risk is partly mediated or confounded by adiposity, whereas the association between activity and clustered risk is independent of adiposity. Our results suggest that fitness and activity affect metabolic risk through different pathways.

Criterion-related validity of the last 7-day, short form of the International Physical Activity Questionnaire in Swedish adults

OBJECTIVE To examine the validity of the short, last 7-day, self-administered form of the International Physical Activity Questionnaire (IPAQ). DESIGN All subjects wore an accelerometer for seven consecutive days and completed the IPAQ questionnaire on the eighth day. Criterion validity was assessed by linear regression analysis and by modified Bland-Altman analysis. Specificity and sensitivity were calculated for classifying respondents according to the physical activity guidelines of the American College of Sports Medicine/Centers for Disease Control and Prevention. SETTING Workplaces in Uppsala, Sweden. SUBJECTS One hundred and eighty-five (87 males) participants, aged 20 to 69 years. RESULTS Total self-reported physical activity (PA) (MET-min day(-1)) was significantly correlated with average intensity of activity (counts min(-1)) from accelerometry (r = 0.34, P < 0.001). Gender, age, education and body mass index did not affect this relationship. Further, subcomponents of self-reported PA (time spent sitting, time in PA, time in moderate and vigorous activity (MVPA)) were significantly correlated with objectively measured PA (P < 0.05). Self-reported time in PA was significantly different from time measured by accelerometry (mean difference: -25.9 min day(-1); 95% limits of agreement: -172 to 120 min day(-1); P < 0.001). IPAQ identified 77% (specificity) of those who met the current PA guidelines of accumulating more than 30 min day(-1) in MVPA as determined by accelerometry, whereas only 45% (sensitivity) of those not meeting the guidelines were classified correctly. CONCLUSIONS Our results indicate that the short, last 7-days version of the IPAQ has acceptable criterion validity for use in Swedish adults. However, the IPAQ instrument significantly overestimated self-reported time spent in PA. The specificity to correctly classify people achieving current PA guidelines was acceptable, whereas the sensitivity was low.

Reexamination of validity and reliability of the CSA monitor in walking and running.

PURPOSE To evaluate the reliability and validity of the CSA (model 7164) accelerometer (MTI) in a wide walking-running speed range in laboratory and field. METHOD Twelve male subjects performed three treadmill walking/running sessions and one field trial with the same continuous protocol involving progressively increasing velocities at 5 min per interval from 3 to 6 km x h(-1) (walking) and 8 to 20 km x h(-1) (running). In the field trial, this protocol was terminated after 35 min (14 km.h(-1)), but the trial then extended with 5-km running at a freely chosen velocity. In both scenarios, two CSAs were mounted on each hip and the step frequency measured at each velocity. Oxygen uptake VO(2) x kg(-1) was measured on the last two treadmill sessions. Correlation analyses were performed for mean CSA output relationship with speed, VO(2) per kilogram, and step frequency. RESULTS In all trials, CSA output rose linearly (R2 = 0.92, P < 0.001) with increasing speed until 9 km.h-1 but remained at approximately 10000 counts.min-1 during running, thus underestimating VO(2) per kilogram at speeds > 9 km x h(-1). Estimation errors increased with speed from 11% (P < 0.01) at 10 km x h(-1) to 48% (P < 0.001) at 16 km x h(-1), when assuming a linear relationship. Freely chosen velocities in the field trial ranged from 10.9 to 16.3 km.h-1. No difference in the CSA-speed relationship was observed between the two scenarios. Differences in CSA output between subjects could partially be attributed to differences in step frequency (R = -0.34 (P = 0.02) for walking and R = -0.63 (P < 0.001) for running). CONCLUSION CSA output increases linearly with speed in the walking range but not in running, presumably due to relatively constant vertical acceleration in running. Between-subject reliability was related to step frequency because CSA data are filtered most at higher movement frequencies. Epidemiological CSA data should thus be interpreted with these limitations in mind.

A systematic review of reliability and objective criterion-related validity of physical activity questionnaires

Physical inactivity is one of the four leading risk factors for global mortality. Accurate measurement of physical activity (PA) and in particular by physical activity questionnaires (PAQs) remains a challenge. The aim of this paper is to provide an updated systematic review of the reliability and validity characteristics of existing and more recently developed PAQs and to quantitatively compare the performance between existing and newly developed PAQs.A literature search of electronic databases was performed for studies assessing reliability and validity data of PAQs using an objective criterion measurement of PA between January 1997 and December 2011. Articles meeting the inclusion criteria were screened and data were extracted to provide a systematic overview of measurement properties. Due to differences in reported outcomes and criterion methods a quantitative meta-analysis was not possible.In total, 31 studies testing 34 newly developed PAQs, and 65 studies examining 96 existing PAQs were included. Very few PAQs showed good results on both reliability and validity. Median reliability correlation coefficients were 0.62–0.71 for existing, and 0.74–0.76 for new PAQs. Median validity coefficients ranged from 0.30–0.39 for existing, and from 0.25–0.41 for new PAQs.Although the majority of PAQs appear to have acceptable reliability, the validity is moderate at best. Newly developed PAQs do not appear to perform substantially better than existing PAQs in terms of reliability and validity. Future PAQ studies should include measures of absolute validity and the error structure of the instrument.

Accelerometers and pedometers: methodology and clinical application.

Purpose of reviewThe relationship between physical activity and health varies considerably, partly due to the difficulty of assessing physical activity accurately. This review examines recent literature on the validation of movement sensors to assess habitual physical activity. Recommendations are given for the use of movement sensors during free-living conditions and methods of data analysis and interpretation are discussed. Recent findingsRecent progress in physical-activity research includes detailed comparative studies of different monitor brands. The move away from using linear-regression equations and the use of novel data-analysis strategies is increasing the accuracy with which energy expenditure can be estimated from accelerometry. New technologies, including the combination of accelerometry with the measurement of physiological parameters, have great potential for the increased accuracy of physical-activity assessment. SummaryAccelerometry is able to adequately assess physical activity and its association with health outcomes but currently methods have limited accuracy for the estimation of free-living energy expenditure. Pedometers provide an inexpensive overall measure of physical activity but are unable to assess intensity, frequency and duration of activity or to estimate energy expenditure. Interpretation of monitor output is best kept as close to the measurement domain as possible.

Methods of Measurement in epidemiology: Sedentary Behaviour

BACKGROUND Research examining sedentary behaviour as a potentially independent risk factor for chronic disease morbidity and mortality has expanded rapidly in recent years. METHODS We present a narrative overview of the sedentary behaviour measurement literature. Subjective and objective methods of measuring sedentary behaviour suitable for use in population-based research with children and adults are examined. The validity and reliability of each method is considered, gaps in the literature specific to each method identified and potential future directions discussed. RESULTS To date, subjective approaches to sedentary behaviour measurement, e.g. questionnaires, have focused predominantly on TV viewing or other screen-based behaviours. Typically, such measures demonstrate moderate reliability but slight to moderate validity. Accelerometry is increasingly being used for sedentary behaviour assessments; this approach overcomes some of the limitations of subjective methods, but detection of specific postures and postural changes by this method is somewhat limited. Instruments developed specifically for the assessment of body posture have demonstrated good reliability and validity in the limited research conducted to date. Miniaturization of monitoring devices, interoperability between measurement and communication technologies and advanced analytical approaches are potential avenues for future developments in this field. CONCLUSIONS High-quality measurement is essential in all elements of sedentary behaviour epidemiology, from determining associations with health outcomes to the development and evaluation of behaviour change interventions. Sedentary behaviour measurement remains relatively under-developed, although new instruments, both objective and subjective, show considerable promise and warrant further testing.

Low cardiorespiratory fitness is a strong predictor for clustering of cardiovascular disease risk factors in children independent of country, age and sex.

Background and design Few studies have investigated the association between maximal cardiorespiratory capacity (fitness) and the clustered cardiovascular disease (CVD) risk in children and youth from culturally diverse countries. This cross-sectional study examined the association between fitness and clustered CVD risk in children and adolescents from three European countries. Methods Participants were 2845 randomly selected school children aged 9 or 15 years from Portugal (n = 944), Denmark (n = 849) and Estonia (n = 1052). Cardiorespiratory fitness was determined during a maximal test on a cycle ergometer. CVD risk factors selected to assess the degree of clustering were the total cholesterol/high-density lipoprotein cholesterol ratio, plasma triglycerides, insulin resistance (homeostasis model assessment), sum of four skinfolds, and systolic blood pressure. Results There was a strong association between cardiorespiratory fitness and the clustering of CVD risk factors. The odds ratios for clustering in each quartile of fitness, using the quartile with the highest fitness as reference, were 13.0 [95% confidence interval (CI) 8.8-19.1]; 4.8 (95% CI 3.2-7.1) and 2.5 (95% CI 1.6-3.8), respectively, after adjusting for country, age, sex, socio-economic status, pubertal stage, family history of CVD and diabetes. In stratified analyses by age group, sex and country, similar strong patterns were observed. Conclusion Low cardiorespiratory fitness is strongly associated with the clustering of CVD risk factors in children independent of country, age and sex.