Kirsten Corder

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.

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.

Physical activity, cardiorespiratory fitness, and the metabolic syndrome in youth

The metabolic syndrome is defined as the coexistence of multiple cardiovascular and diabetes risk factors, the prevalence of which has increased dramatically in adult populations in the last decades. More recently, the same cluster of metabolic risk factors has also been recognized in children and adolescents. Epidemiological evidence suggests that high levels of cardiorespiratory fitness (CRF) and physical activity are associated with a favorable metabolic risk profile in adults. However, in youth the role of these factors is less clear. Therefore, the purpose of this mini-review is to examine the recent evidence between objectively measured habitual physical activity and CRF with clustered metabolic risk in youth. In general, it appears that both physical activity and CRF are separately and independently associated with metabolic risk factors in youth, possibly through different causal pathways. Further research is necessary to quantify how much physical activity is needed to prevent the metabolic syndrome and the diseases with which it is associated. Public health approaches that encourage increased physical activity and reduce sedentary behaviors may prove useful in reducing the population burden associated with metabolic risk.

Determinants of Change in Physical Activity in Children and Adolescents: A Systematic Review

Context Data are available on correlates of physical activity in children and adolescents, less is known about the determinants of change. This review aims to systematically review the published evidence regarding determinants of change in physical activity in children and adolescents. Evidence acquisition Prospective quantitative studies investigating change in physical activity in children and adolescents aged 4–18 years were identified from seven databases (to November 2010): PubMed, SCOPUS, PsycINFO, Ovid MEDLINE, SPORTDdiscus, Embase, and Web of Knowledge. Study inclusion, quality assessment, and data extraction were independently validated by two researchers. Semi-quantitative results were stratified by age (4–9 years, 10–13 years, and 14–18 years). Evidence synthesis Of the 46 studies that were included, 31 used self-reported physical activity; average methodologic quality was 3.2 (SD=1.2), scored 0–5. Of 62 potential determinants identified, 30 were studied more than three times and 14 reported consistent findings (66% of the reported associations were in the same direction). For children aged 4–9 years, girls reported larger declines than boys. Among those aged 10–13 years, higher levels of previous physical activity and self-efficacy resulted in smaller declines. Among adolescents (aged 14–18 years), higher perceived behavioral control, support for physical activity, and self-efficacy were associated with smaller declines in physical activity. Conclusions Few of the variables studied were consistently associated with changes in physical activity, although some were similar to those identified in cross-sectional studies. The heterogeneity in study samples, exposure and outcome variables, and the reliance on self-reported physical activity limit conclusions and highlight the need for further research to inform development and targeting of interventions.

Is it possible to assess free-living physical activity and energy expenditure in young people by self-report?

BACKGROUND It is unclear whether it is possible to accurately estimate physical activity energy expenditure (PAEE) by self-report in youth. OBJECTIVE We assessed the validity and reliability of 4 self-reports to assess PAEE and time spent at moderate and vigorous intensity physical activity (MVPA) over the previous week in British young people between 4 and 17 y of age. DESIGN PAEE and MVPA were derived from the Childrens Physical Activity Questionnaire, Youth Physical Activity Questionnaire, and Swedish Adolescent Physical Activity Questionnaire; a lifestyle score indicative of habitual activity was derived from the Child Heart and Health Study in England Questionnaire. These data were compared with criterion methods, PAEE, and MVPA derived from simultaneous measurements by doubly labeled water and accelerometry in 3 age groups: 4-5 y (n = 27), 12-13 y (n = 25), and 16-17 y (n = 24). Validity was assessed by using Spearman correlations and the Bland-Altman method, and reliability was assessed by using intraclass correlation coefficients. RESULTS The strength of association between questionnaire and criterion methods varied (r = 0.09 to r = 0.46). Some questionnaires were able to accurately assess group-level PAEE and MVPA for some age groups, but the error was large for individual-level estimates throughout. Reliability of the Youth Physical Activity Questionnaire and Child Heart and Health Study in England Questionnaire was good (intraclass correlation coefficient: 0.64-0.92). CONCLUSIONS Absolute PAEE and MVPA estimated from these self-reports were not valid on an individual level in young people, although some questionnaires appeared to rank individuals accurately. Age (the outcome of interest) and whether individual or group-level estimates are necessary will influence the best choice of self-report method when assessing physical activity in youth.

Comparison of two Actigraph models for assessing free-living physical activity in Indian adolescents

Abstract This aim of this study was to compare the new Actigraph (GT1M) with the widely used Model 7164. Seven days of free-living physical activity were measured simultaneously using both the Model 7164 and GT1M in 30 Indian adolescents (mean age 15.8 years, s = 0.6). The GT1M was on average 9% lower per epoch than model 7164, thus a correction factor of 0.91 is suggested for comparison between the two monitors. The differences between monitors increased in magnitude with intensity of activity (P < 0.001) but remained randomly distributed (r = 0.01, P = 0.96). No significant difference was observed between monitors for time spent in moderate (P = 0.31) and vigorous (P = 0.34) physical activity when using the same epoch length. The Model 7164 classified less time as sedentary (P < 0.001) and more time as light-intensity activity (P < 0.001) than the GT1M. In conclusion, data from the GT1M can be compared with historical data using average counts per minute with a correction factor, and the two models might be comparable for assessing time spent in moderate to vigorous physical activity in children when using the same epoch length.

Perception versus reality: awareness of physical activity levels of British children.

BACKGROUND Interventions to increase childrens physical activity have had limited success. One reason may be that children and their parents overestimate childrens levels of physical activity, although there is a small amount of data on this topic. PURPOSE This study aims to assess awareness of physical activity levels among British school children aged 9-10 years and their parents. METHODS Physical activity was measured using an accelerometer in a cross-sectional study of 1892 children (44% male; M age=10.3 years, SD=0.3) from 92 Norfolk schools (Sport, Physical Activity and Eating Behavior: Environmental Determinants in Young People [SPEEDY] study). Data were collected between April and July 2007 and analyzed in 2008. Inactive was defined as <60 minutes/day of moderate and vigorous physical activity. Agreement between physical activity perception (child- and parent-rated) and objective physical activity was assessed. Associations between biological (height, weight, fat mass index); parental (support, BMI, physical activity); and peer factors (support, objective physical activity) and child and parental physical activity awareness were studied using multinomial logistic regression. RESULTS In all, 39% of girls and 18% of boys were inactive. A total of 80% of parents of inactive children wrongly thought that their child was sufficiently active. In all, 40% of inactive children overestimated their physical activity level. Compared to parents who accurately described their children as inactive, parents who overestimated were more likely to have girls (p=0.005), to have a child with a lower fat mass index (p<0.001), or to report more parental and peer support (p=0.014 and p<0.001, respectively). CONCLUSIONS Most parents of inactive children wrongly consider their children to be sufficiently active; parents of children with a lower fat mass index appear to assume that their children are adequately active. Increasing awareness regarding health benefits of physical activity beyond weight control might help reverse misperceptions of physical activity levels and encourage behavior change.

Change in objectively measured physical activity during the transition to adolescence

Background Physical activity (PA) declines during adolescence but change in different PA intensities across population subgroups is rarely explored. We describe change in sedentary (SED) time, light (LPA), moderate (MPA) and vigorous PA (VPA) assessed at three time points over 4 years. Methods Accelerometer-assessed PA (min) was obtained at baseline (N=2064), 1 and 4 years later among British children (baseline mean±SD 10.2±0.3-year-old; 42.5% male). Change in SED (<100 counts/min (cpm)), LPA (101–1999 cpm), MPA (2000–3999 cpm) and VPA (≥4000 cpm) was studied using three-level (age, individual and school) mixed-effects linear regression including participants with data at ≥2 time points (N=990). Differences in change by sex, home location and weight status were explored with interactions for SED, LPA and moderate and vigorous PA (MVPA). Results SED increased by 10.6 (95% CI 9.1 to 12.2) min/day/year. MPA and VPA decreased by 1.4 (1.0 to 1.8) and 1.5 (1.1 to 1.8) min/day/year, respectively. VPA decreased more than MPA as a percentage of the baseline value. MVPA declined more steeply among boys (3.9 (3.0 to 4.8)) versus girls (2.0 (1.2 to 2.7) min/day/year) despite lower MVPA among girls at all ages; rural (4.4 (3.5 to 5.2)) versus urban individuals (1.3 (0.4 to 2.3) min/day/year) and on weekends (6.7 (5.2 to 8.1)) versus weekdays (2.8 (1.9 to 3.7) min/day/year). MVPA was consistently lower among overweight/obese individuals (−17.5 (−3.9 to −2.5) min/day/year). Conclusions PA decreases and is replaced by SED during early adolescence in British youth. Results indicate the urgency of PA promotion among all adolescents but especially girls and in rural areas. Increasing VPA and targeting PA promotion during weekends appear important.

Differences in physical activity and sedentary time in relation to weight in 8-9 year old children.

BackgroundThe health benefits of physical activity for children are well established. Although objective measures of physical activity are increasingly used there is still a lack of adequate data on physical activity in children. Sex differences in physical activity have been consistently demonstrated and lower levels of physical activity in obese than non-obese children have been shown. However, differences across the whole weight spectrum have not been examined in detail. The aim of this study was to assess associations between physical activity and sedentary time across the weight spectrum in children, and to determine whether the associations differed by sex.MethodsParticipants in the current study were 176 boys and 169 girls aged 8–9 years old taking part in a longitudinal study of associations between eating behaviours, physical activity and weight gain during childhood. Height, weight and waist circumference were measured, and physical activity data were collected using an Actigraph model GT1M worn for 5 consecutive days. Associations between sex, weight and physical activity were analysed using linear regression models.ResultsBoys had higher total activity (mean difference = 119, p < 0.001) and more minutes of moderate and vigorous physical activity (MVPA) (mean difference = 25, p < 0.001) than girls. A higher percentage of boys (72%) than girls (30%) met current physical activity guidelines of 60 minutes MVPA per day. In boys, weight status significantly predicted total activity (p = 0.001) and MVPA (p = 0.001) but there were no significant associations in girls. There was no significant difference in time spent sedentary between boys and girls, and weight status did not predict sedentary time.ConclusionIn boys, physical activity was progressively lower across the weight spectrum, but in girls physical activity was consistently low across all weight categories. Intervention is required prior to 8 years old to prevent weight-related declines in physical activity in boys and further research is required to determine at what age, if ever, weight related differences in physical activity are apparent in girls.

Changes in Children's Physical Activity Over 12 Months: Longitudinal Results From the SPEEDY Study

OBJECTIVE: We measured physical activity changes among 10-year-old British children over 12 months and assessed biological and demographic determinants. METHODS: Physical activity was measured with accelerometers (counts per minute) over ≥3 days at baseline and 1 year later in a prospective study of 844 children (41.6% male; mean ± SD baseline age: 10.2 ± 0.3 years) from 92 schools. Meeting physical activity recommendations was defined as ≥60 minutes/day at ≥2000 counts per minute. Biological (height, weight, and fat percentage) and demographic factors (gender, rural/urban home location, and socioeconomic status) were assessed at baseline. Associations between physical activity changes and multiple factors were studied. RESULTS: Physical activity decreased over 1 year (baseline: 665.7 ± 209.8 counts per minute; follow-up: 623.2 ± 179.2 counts per minute; P < .001), with 70.4% of children meeting physical activity recommendations at the baseline evaluation and 65.8% at the follow-up evaluation (P < .001). The decrease occurred mainly on weekends (−47.2 ± 395.8 counts per minute; P = .002), with no significant change on weekdays (8.0 ± 201.6 counts per minute; P = .20). Girls (P < .001), participants with greater body fat percentage (P = .001), and participants of higher socioeconomic status (P = .008) were more likely to exhibit physical activity decreases. CONCLUSIONS: Physical activity decreased over 1 year among children in primary school, predominantly during the weekend. Because these children were relatively active at baseline, prevention of physical activity decreases in childhood, particularly among girls and on weekends, may be a suitable health promotion target.