Rebekah Steele

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.

Targeting sedentary time or moderate- and vigorous-intensity activity: independent relations with adiposity in a population-based sample of 10-y-old British children

BACKGROUND It is unclear whether subcomponents of physical activity (PA) are associated with adiposity independent of time spent while sedentary. OBJECTIVE The objective was to examine associations between objectively measured PA and its subcomponents [ie, time spent at light-intensity PA, moderate-intensity PA (MPA), vigorous-intensity PA (VPA), and moderate-plus-vigorous-intensity PA (MVPA)], independent of sedentary time, and self-reported leisure screen time (television and electronic game use) with indexes of adiposity in a population-based sample of British children. DESIGN A cross-sectional study was conducted in 1862 UK children aged 9-10 y. PA and sedentary activity were measured by accelerometry, and indicators of adiposity were waist circumference, body mass index (BMI), and fat mass index calculated from bioimpedance measurements. Screen time was assessed by self-report. We examined the associations between PA subcomponents and adiposity by multilevel linear models adjusted for birth weight, maternal BMI, energy intake, and sleep duration. RESULTS Objectively measured sedentary time was positively associated with waist circumference (P = 0.04) and fat mass index (P = 0.05), independent of age and sex. However, this association was attenuated after adjustment for MVPA and other covariates. VPA (all P < 0.0001), combined MVPA (all P < 0.01), and total activity (counts/min) (all P < 0.001) were all inversely associated with each of the adiposity indexes, independent of sedentary time and other important covariates. Associations were weaker for MPA: P = 0.05, 0.87, and 0.1 for waist circumference, BMI, and fat mass index, respectively. CONCLUSIONS Time spent in VPA appears to be more strongly associated with adiposity than sedentary time. Interventions may therefore need to incorporate higher intensity-based activities to curb the growing obesity epidemic.

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.

An investigation of patterns of children's sedentary and vigorous physical activity throughout the week

BackgroundParticipation in higher intensity activity (i.e. vigorous physical activity [VPA]) appears more consistently associated with lower adiposity, unfortunately little is known about the nature and patterns of VPA participation in children.ObjectiveTo examine the volume and patterns of vigorous and sedentary activity during different segments of the week (weekend, school-based and out-of-school). We also investigated differences by sex, socioeconomic status (SES) and weight status.DesignA cross-sectional study including 1568 UK children aged 9-10 years.Outcome measuresSedentary activity (mins), total activity (counts/min) and VPA (mins) were measured by accelerometry. Using a series of 2 level mixed effects linear regression models we tested differences across the segmented week (school time [0900-1500] vs. out-of-school time [0700-0900 & 1500-2100]; and weekday vs. weekend); all models were adjusted for sex, weight status (gender- and age-specific body mass index [BMI] cut points), SES, age and accelerometer registered wear time.ResultsBoys and girls accumulated higher VPA out-of-school compared to during school (boys mean ± SD 16.9 ± 9.6 vs 12.6 ± 5.8; girls, 13.1 ± 7.7 vs 8.2 ± 4.0, both p < 0.001); but there were no differences for weekday v weekend VPA (p > 0.05). Less time was spent sedentary on weekdays compared to weekends (p < 0.001). Although boys were more physically active and girls accumulated more sedentary time, the overall pattern in which their physical activity intensity varied across the various day segments was similar when stratified by weight status and SES; and large volumes of sedentary time were observed each hour across the day.ConclusionsThe promotion of VPA during the weekend may hold the greatest promise for increasing VPA. Interventions aimed at increasing physical activity in 9-10 year old children should aim to target all children independent of sex, SES or weight status.

Occupational physical activity across occupational categories

This study investigated the amount of physical activity that occurs during normal working hours, highlighting the occupational differences in physical activity by occupational category. Data were collected by means of a self-administered questionnaire (Tecumseh Occupational Physical Activity Questionnaire [TOQ]), which measures past year Occupational Physical Activity (OPA) and by a motion-sensing device (Yamax DigiWalker Pedometer SW - 700). Ninety male and female participants aged 18-62 years participated in the study. Participants were stratified by occupational category according to the Australian Standard Classification of Occupations (ASCO), which was then condensed into professional, white-collar and blue-collar workers. The results showed significant (p < .05) increases in OPA from the professional category (least active) through to the blue-collar workers (most active) in terms of walking activity. Mean daily step counts were 2,835, 3,616 and 8,757 for professional, white-collar and blue-collar respectively. Occupational Physical Activity Scores and Work Activity Units (WAU) in MET - min x wk(-1) from the TOQ showed similar patterns, with blue collar reporting significantly (p < .05) more past year OPA than their white-collar and professional workers. Significant correlations were also shown between the pedometer (step-count data) and the TOQ (r = .38 - .74, p < .01).

Obesity is associated with altered lung function independently of physical activity and fitness.

Measures of obesity, especially central adiposity, have been associated with reduced lung function. However, previous studies may have been affected by confounding by physical activity and fitness. This study aimed to examine the relationship among body fatness, fat distribution, and lung function, adjusted for physical activity energy expenditure (PAEE) and aerobic fitness (VO2max), in a cohort of British white adults with a family history of type 2 diabetes. A total of 320 adults (mean age 40.4 ± 6.0 years) attended for anthropometric and VO2max testing, and had ambulatory heart rate monitoring for 4 days to determine PAEE. Spirometry was used to measure forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC). The tests were repeated 12 months later, and a cross‐sectional analysis using linear regression with repeated measures was performed. Measures of obesity (BMI, waist circumference (WC), fat mass (FM), body fat percentage (BF%)) were associated with lower lung function in men and women (P < 0.01), while waist‐to‐hip ratio (WHR) was associated with lower lung function in men only (P < 0.001). Associations remained after adjusting for age, smoking status, height, PAEE, and VO2max. The estimated difference in mean FEV1 and FVC per unit increase in the exposure measures were consistently stronger in men compared to women (P for interaction <0.001). Obesity is inversely associated with lung function in adults, but central fat distribution appears to have a stronger relationship with respiratory mechanics in men than in women. These associations were independent of the degree of physical activity and aerobic fitness in this cohort.

Breakfast consumption and physical activity in British adolescents

Studies show an inverse relationship between breakfast frequency and weight gain. This may reflect poor eating habits generally and associated low physical activity (PA) or direct impacts of breakfast on mechanisms leading to lethargy and reduced PA. The relationship between breakfast frequency and PA is inconclusive. We aimed to determine whether breakfast frequency is associated with PA levels in British adolescents independent of body composition and socio-economic status (SES). Habitual breakfast frequency (self-report questionnaire) was assessed in 877 adolescents (43% male, age 14·5 (SD 0·5) years old). PA was measured over 5 d (accelerometry, average counts/ min; cpm). Associations between daily PA and breakfast frequency were assessed using linear regression adjusted for body fat percentage and SES. Effect modification by sex and associations with PA during the morning (06.00-12.00 hours) were explored. For boys, there were no significant associations between breakfast frequency and PA. For girls, less frequent breakfast consumption was significantly associated with lower PA (cpm) during the morning (occasional v. frequent b - 6·1 (95% CI - 11·1, -1·1), P = 0·017) when adjusted for body fat percentage and SES. There were no associations between PA and breakfast consumption over the whole day; however, for girls, less frequent breakfast consumption may be associated with lower PA levels during the morning, suggesting that breakfast consumption should perhaps be taken into consideration when aiming to promote PA in adolescent girls.

Physical Activity Awareness of British Adolescents.

OBJECTIVES To assess adolescent physical activity (PA) awareness and to investigate associations with biologic and psychosocial factors. DESIGN Cross-sectional study from November 1, 2005, through July 31, 2007 (the ROOTS study). SETTING Population-based sample recruited from Cambridgeshire and Suffolk schools (United Kingdom). PARTICIPANTS Of 799 participants, 43.6% were male. The mean (SD) age was 14.5 (0.5) years. MAIN EXPOSURES Self-rated PA perception, self-reported psychosocial factors, and measured anthropometry. MAIN OUTCOME MEASURES We measured PA with accelerometry for 5 days. Inactive was defined as less than 60 minutes per day of moderate and vigorous PA (MVPA) measured by accelerometry. Associations between awareness (agreement between self-rated and accelerometry-measured active/inactive) and potential correlates were investigated using multinomial logistic regression. RESULTS Approximately 70.1% of adolescents were inactive (81.2% of girls and 55.8% of boys; odds ratio [OR], 3.41; 95% confidence interval [CI], 2.41-4.82). There were 52.6% of all girls (64.8% of inactive girls) and 33.6% of all boys (60.3% of inactive boys) who inaccurately rated themselves as active (overestimators). Compared with girls accurately describing themselves as inactive (28.6%), girl overestimators had lower fat mass (OR, 0.84; 95% CI, 0.70-0.99), higher socioeconomic status (high vs low OR, 2.38; 95% CI, 1.07-5.32), more parent support (OR, 1.57; 95% CI, 1.12-2.22), and better family relationships (OR, 0.25; 95% CI, 0.09- 0.67). Among boys accurately describing themselves as inactive (22.1%), overestimators had lower fat mass (OR, 0.86; 95% CI, 0.77-0.96) and reported more peer support (OR, 1.75; 95% CI, 1.32-2.30) and less teasing (OR, 0.75; 95% CI, 0.61-0.92). CONCLUSIONS A substantial number of adolescents believe themselves to be more physically active than they really are. They may be unaware of potential health risks and unlikely to participate in PA promotion programs. Increasing information of PA health benefits beyond weight control might encourage behavior change.

A Comparison of Face-to-Face or Internet-Delivered Physical Activity Intervention on Targeted Determinants

This article describes the equivalency testing results of a 12-week behavior change program on targeted determinates of physical activity (PA) and self-reported health status. Participants (n = 192) were randomized to face-to-face, combined Internet and face-to-face, and Internet-only groups. Equivalency testing was used to examine differences and statistical equivalency across groups for all outcome measures (social support, self-efficacy, perceived health status, and motivational readiness for PA). Participants were assessed at baseline, postintervention, and 2 and 5 months postintervention. Motivational readiness for PA increased across all groups. The face-to-face and combined groups showed changes in social support; however, they were not statistically different and were equivalent. There were no changes in self-efficacy or physical health status. Overall face-to-face and the Internet delivery modes show similar results. If Internet-based programs can be shown to be as effective as face-to-face, they may in turn be a more efficient and cost-effective delivery method.

Examination of program exposure across intervention delivery modes: face-to-face versus internet

BackgroundThere has been increasing interest in the ability of the internet to produce behaviour change. The focus of this study was to describe program exposure across three intervention groups from a randomised trial (RT) comparing traditional face-to-face, internet-mediated (combined internet plus face-to-face), and internet-only program delivery.MethodsBaseline and immediately post-intervention survey data, and exposure rates from participants that commenced the RT were included (n = 192). Exposure was defined as either face-to-face attendance, website usage, or a combination of both for the internet-mediated group. Characteristics of participants who were exposed to at least 75% of the program material were explored. Descriptive analysis and logistical regression were used to examine differences between groups for program exposure.ResultsAll groups showed decrease in program exposure over time. Differences were also observed (χ2 = 10.37, p < 0.05), between intervention groups. The internet-mediated (OR = 2.4, 95% CI 1.13–5.1) and internet-only (OR = 2.96, 95% CI 1.38–6.3) groups were more likely to have been exposed to at least 75% of the program compared to the face-to-face group. Participants with high physical activity self-efficacy were 1.82 (95% CI 1.15–2.88) times more likely to have been exposed to 75% of the program, and those allocated to the face-to-face group were less likely to have attended 75% of the face-to-face sessions if they were classified as obese (OR = 0.21 95% CI 0.04–0.96).ConclusionThese results suggest that the internet groups were as effective as the face-to-face delivery mode in engaging participants in the program material. However, different delivery methods may be more useful to different sub-populations. It is important to explore which target groups that internet-based programs are best suited, in order to increase their impact.