ActiGraph GT1M Research Articles

Sedentary Time and Screen-Based Sedentary Behaviors of Children With a Chronic Disease

The objectives of this study were to (i) assess sedentary time and prevalence of screen-based sedentary behaviors of children with a chronic disease and (ii) compare sedentary time and prevalence of screen-based sedentary behaviors to age- and sex-matched healthy controls. Sixty-five children (aged 6-18 years) with a chronic disease participated: survivors of a brain tumor, hemophilia, type 1 diabetes mellitus, juvenile idiopathic arthritis, cystic fibrosis, and Crohn's disease. Twenty-nine of these participants were compared with age- and sex-matched healthy controls. Sedentary time was measured objectively by an ActiGraph GT1M or GT3× accelerometer worn for 7 consecutive days and defined as less than 100 counts per min. A questionnaire was used to assess screen-based sedentary behaviors. Children with a chronic disease engaged in an average of 10.2 ± 1.4 hr of sedentary time per day, which comprised 76.5 ± 7.1% of average daily monitoring time. There were no differences between children with a chronic disease and controls in sedentary time (adjusted for wear time, p = .06) or in the prevalence of TV watching, and computer or video game usage for varying durations (p = .78, p = .39 and, p = .32 respectively). Children with a chronic disease, though relatively healthy, accumulate high levels of sedentary time, similar to those of their healthy peers.

The relationship of moderate-to-vigorous physical activity to cognitive processing in adolescents: findings from the ALSPAC birth cohort.

The aim of this study was to assess the relations of daily moderate-to-vigorous physical activity (MVPA) to cognitive functions in 15-year-old adolescents from the Avon Longitudinal Study of Parents and Children while controlling for aerobic fitness. A sub-sample of 667 adolescents (M(age) = 15.4 ± 0.16 years; 55% females) who provided valid data on variables of interest, were used in the analyses. MVPA was objectively assessed using an Actigraph GT1M accelerometer and aerobic fitness was expressed as physical work capacity at the heart rate of 170 beats per minute from a cycle ergometer test. A computerized stop-signal task was used to measure mean reaction time (RT) and standard deviation of RT, as indicators of cognitive processing speed and variability during an attention and inhibitory control task. MVPA was not significantly related to cognitive processing speed or variability of cognitive performance in hierarchical linear regression models. In simple regression models, aerobic fitness was negatively related to mean RT on the simple go condition. Our results suggest that aerobic fitness, but not MVPA, was associated with cognitive processing speed under less cognitively demanding task conditions. The results thus indicate a potential global effect of aerobic fitness on cognitive functions in adolescents but this may differ depending on the specific task characteristics.

Responsiveness to Change of Self-Report and Device-Based Physical Activity Measures in the Living Well With Diabetes Trial.

This study evaluated the responsiveness to change in physical activity of 2 self-report measures and an accelerometer in the context of a weight loss intervention trial. 302 participants (aged 20 to 75 years) with type 2 diabetes were randomized into telephone counseling (n = 151) or usual care (n = 151) groups. Physical activity (minutes/week) was assessed at baseline and 6-months using the Active Australia Survey (AAS), the United States National Health Interview Survey (USNHIS) walking for exercise items, and accelerometer (Actigraph GT1M; ≥1952 counts/minute). Responsiveness to change was calculated as responsiveness index (RI), Cohen's d (postscores) and Cohen's d (change-scores). All instruments showed significant improvement in the intervention group (P < .001) and no significant change for usual care (P > .05). Accelerometer consistently ranked as the most responsive instrument while the least responsive was the USHNIS (responsiveness index) or AAS (Cohen's d). RIs for AAS, USNHIS and accelerometer did not differ significantly and were, respectively: 0.45 (95% CI: 0.26-0.65); 0.38 (95% CI: 0.20-0.56); and, 0.49 (95% CI: 0.23-0.74). Accelerometer tended to have the highest responsiveness but differences were small and not statistically significant. Consideration of factors, such as validity, feasibility and cost, in addition to responsiveness, is important for instrument selection in future trials.

Objectively measured physical activity in European children: the IDEFICS study.

To provide sex- and age-specific percentile values for levels of physical activity (PA) and sedentary time of European children aged 2.0-10.9 years from eight European countries (Sweden, Germany, Hungary, Italy, Cyprus, Spain, Belgium and Estonia). Free-living PA and sedentary time were objectively assessed using ActiGraph GT1M or ActiTrainer activity monitors in all children who had at least 3 days' worth of valid accelerometer data, with at least 8 h of valid recording time each day. The General Additive Model for Location Scale and Shape was used for calculating percentile curves. Reference values for PA and sedentary time in the European children according to sex and age are displayed using smoothed percentile curves for 7684 children (3842 boys and 3842 girls). The figures show similar trends in boys and girls. The percentage of children complying with recommendations regarding moderate-to-vigorous physical activity (MVPA) is also presented and varied considerably between sexes and country. For example, the percentage of study participants who were physically active (as assessed by MVPA) for 60 or more minutes per day ranged from 2.0% (Cyprus) to 14.7% (Sweden) in girls and from 9.5% (Italy) to 34.1% (Belgium) in boys. This study provides the most up-to-date sex- and age-specific reference data on PA in young children in Europe. The percentage compliance to MVPA recommendations for these European children varied considerably between sexes and country and was generally low. These results may have important implications for public health policy and PA counselling.

Comparison of three generations of ActiGraph activity monitors under free-living conditions: do they provide comparable assessments of overall physical activity in 9-year old children?

BackgroundA recent review concludes that the agreement of data across ActiGraph accelerometer models for children and youth still is uncertain. The aim of this study was to evaluate the agreement of three generations of ActiGraph accelerometers in children in a free-living condition.MethodsSixteen 9-year-olds wore the ActiGraph AM7164, GT1M and GT3X+ simultaneously for three consecutive days. We compared mean counts per minute (mcpm) and time spent at different intensities from the three generations of monitors, and the agreement of outputs were evaluated by intra-class correlation coefficients (ICC) and Bland-Altman plots.ResultsThe ICC for mcpm was 0.985 (95% CI = 0.898, 0.996). We found a relative difference of 11.6% and 9.8% between the AM7164 and the GT1M and AM7164 and the GT3X+, respectively. The relative difference between mcpm assessed by the GT1M and GT3X+ was 1.7%. The inter-generation differences varied in magnitude and direction across intensity levels, with the largest difference found in the highest intensities.ConclusionWe found that the ActiGraph model AM7164 yields higher outputs of mean physical activity intensity (mcpm) than the models GT1M and GT3X+ in children in free-living conditions. The generations GT1M and GT3X+ provided comparable outputs. The differences between the old and the newer monitors were more complex when investigating time spent at different intensities. Comparisons of data assessed by the AM7164 with data assessed by newer generations ActiGraphs should be done with caution.

Incidental and Planned Exercise Questionnaire for seniors: validity and responsiveness.

This study assessed the criterion validity and responsiveness of the Incidental and Planned Exercise Questionnaire (IPEQ) specifically developed for aging research. The sample comprised 315 community-dwelling inactive older adults (mean age = 73.2 yr) who participated in a trial investigating the effect of a walking program on falls. At baseline, a subsample (n = 177) also wore an accelerometer (ActiGraph GT1M) for 7 d, and 126 of those had four valid days or more of accelerometer data. Validity coefficients (Spearman ρ) were calculated between accelerometer counts per minute, average steps per day, average moderate- to vigorous-intensity physical activity (MVPA) using two cut points (760 and 1041 counts per minute), and IPEQ-MVPA (the sum of physical activity hours per week derived from nine IPEQ items excluding the indoor chores question). Responsiveness was the mean IPEQ change in the intervention group divided by the SD of the mean change in control group. The correlation coefficients between IPEQ-MVPA and counts per minute per day and steps per day were 0.33 and 0.31, respectively. The coefficients with accelerometer MVPA at low and medium cut points were 0.29 and 0.33, respectively, and 0.26 and 0.35 for walking. The Bland-Altman plot showed increased errors with higher values of IPEQ-MVPA. IPEQ incidental physical activity questions and IPEQ as a whole were significantly correlated with accelerometer light intensity (100-760 counts per minute, ρ = 0.29 and 0.23). The 12-month responsiveness of total IPEQ was 0.30 and 0.44 for the "planned walking" item. IPEQ provides a practical and valid measure of MVPA in surveillance and intervention studies. Incidental activities are mostly of a light-intensity nature, and their low ambulatory component may explain the lower correlation between IPEQ as a whole and accelerometer measures.

G-25 Thematic Poster - Cardiovascular Responses to Resistance Exercise

Post-menopausal women exhibit lower bone mineral density (BMD) and current health guidelines highlight the potential importance of reducing sedentary behavior (SB) to mitigate bone loss in this segment of the female population. PURPOSE: To determine if bone health status at the femoral neck (FN) and lumbar spine (LS) can be predicted from objectively-measured SB and physical activity data in 50 community-dwelling, post-menopausal women. METHODS: Waist-mounted ActiGraph GT1M or GT3X devices were used to quantify levels of sedentary [< 100 counts per minute (cpm)], light (100-1040 cpm), and moderate- to vigorous-intensity (>1040 cpm) behavior during a consecutive, 7-day period. Daily sedentary time (DST) was operationally defined as the total amount of time each day during which SB occurred for a minimum of 10 minutes and the number of breaks in DST was designated at the total number of instances each day (based on a 1-min epoch) in which time blocks of 100 or more cpm were adjacent to time blocks containing less than 100 cpm. Accelerometry data were expressed relative to non-wear time and a minimum 4 days of at least 10 hours of daily wear time were required for accelerometer data to be considered valid for each participant. A probability estimate of meeting health-related guidelines for physical activity participation (30 min·d-1 for at least 5 d·wk-1) was also computed and bone health status (normal vs. osteopenia/osteoporosis) of FN and LS was derived from T scores generated using dual energy x-ray absorptiometry. RESULTS: After controlling for potential confounding factors (body mass and calcium and vitamin D supplement use), binomial logistic regression analysis indicated that reduced daily sedentary time and a great number of breaks in daily sedentary time were significant predictors of osteopenia/osteoporosis at the FN (Wald (1, N = 44) = 4.72, p = .030 and Wald (1, N = 44) = 4.17, p = .041, respectively, but not at the LS Wald (1, N = 44) = 0.15, p = .697 and Wald (1, N = 44) = 0.14, p = .704, respectively. Moreover, the degree of adherence to health-related PA guidelines was not a significant predictor of bone health status at the FN or LS. CONCLUSION: Our findings suggest that more frequent interruptions in sedentary behavior may exert a positive impact on bone health in post-menopausal females. Study received no funding.

The association between physical activity and reduced body fat lessens with age — Results from a cross-sectional study in community-dwelling older adults

IntroductionThe aim of this study was to describe the relationship between accelerometer-determined physical activity (PA) and adiposity in community-dwelling older adults. In addition, we were interested in comparing the extent of correlation between questionnaire and accelerometer determined PA. Methods636 community-dwelling older adults (66±7years) were studied. Adiposity was measured using dual-energy X-ray absorptiometry and BMI was calculated. We measured minutes/day spent in sedentary, light, moderate and vigorous intensity activity using both questionnaires and Actigraph GT1M accelerometers. ResultsParticipants spent a median of 583(IQR 522–646), 225(176–271), 27(12–45) and 0(0–0) minutes in sedentary, light, moderate and vigorous activities respectively. There was a non linear dose–response inverse relationship between activity intensity and adiposity. After adjusting for age, sex and other levels of PA, for every 10minute increase in activity, total body fat decreased by 169g(95% CI 61–277), 905g(632–1178), and 2208g(759–3657) for light, moderate and vigorous activities respectively. There was an interaction between age and activity; as age increased, the magnitude of the effects of light and moderate activities on adiposity decreased. Sedentary minutes were not associated with adiposity after adjusting for time spent at other PA intensities. Questionnaire measures of PA were weakly correlated with body fat measures when compared to accelerometer determined PA. ConclusionBoth the amount and intensity of PA, but not sedentary time, have an independent dose–response association with adiposity. The association is much stronger using objective assessment compared to questionnaire. The magnitude of these associations decrease with age suggesting that physical activity programmes may need to be modified with increasing age.

Accelerometer-determined physical activity and self-reported health in a population of older adults (65–85 years): a cross-sectional study

BackgroundThe link between physical activity (PA) and prevention of disease, maintenance of independence, and improved quality of life in older adults is supported by strong evidence. However, there is a lack of data on population levels in this regard, where PA level has been measured objectively. The main aims were therefore to assess the level of accelerometer-determined PA and to examine its associations with self-reported health in a population of Norwegian older adults (65–85 years).MethodsThis was a part of a national multicenter study. Participants for the initial study were randomly selected from the national population registry, and the current study included those of the initial sample aged 65–85 years. The ActiGraph GT1M accelerometer was used to measure PA for seven consecutive days. A questionnaire was used to register self-reported health. Univariate analysis of variance with Bonferroni adjustments were used for comparisons between multiple groups.ResultsA total of 560 participants had valid activity registrations. Mean age (SD) was 71.8 (5.6) years for women (n = 282) and 71.7 (5.2) years for men (n = 278). Overall PA level (cpm) differed considerably between the age groups where the oldest (80–85 y) displayed a 50% lower activity level compared to the youngest (65–70 y). No sex differences were observed in overall PA within each age group. Significantly more men spent time being sedentary (65–69 and 70–74 years) and achieved more minutes of moderate to vigorous PA (MVPA) (75–79 years) compared to women. Significantly more women (except for the oldest), spent more minutes of low-intensity PA compared to men. PA differed across levels of self-reported health and a 51% higher overall PA level was registered in those, with “very good health” compared to those with “poor/very poor health”.ConclusionNorwegian older adults PA levels differed by age. Overall, the elderly spent 66% of their time being sedentary and only 3% in MVPA. Twenty one percent of the participants fulfilled the current Norwegian PA recommendations. Overall PA levels were associated with self-reported health.

Combined influence of epoch length, cut-point and bout duration on accelerometry-derived physical activity

BackgroundIt is difficult to compare accelerometer-derived estimates of moderate-to-vigorous physical activity (MVPA) between studies due to differences in data processing procedures. We aimed to evaluate the effects of accelerometer processing options on total and bout-accumulated time spent in MVPA in adults.Methods267 participants from the ProActive Trial provided 1236 days of valid physical activity (PA) data, collected using a 5-s epoch with ActiGraph GT1M accelerometers. We integrated data over 5-s to 60-s epoch lengths (EL) and applied two-level mixed effects regression models to MVPA time, defined using 1500 to 2500 counts/minute (cpm) cut-points (CP) and bout durations (BD) from 1 to 15 min.ResultsTotal MVPA time was lower on longer EL and higher CP (47 vs 26 min/day and 26 vs 5 min/day on 1500 vs 2500 cpm on 5-s and 60-s epoch, respectively); this could be approximated as MVPA = exp[2.197 + 0.279*log(CP) + 6.120*log(EL) - 0.869*log(CP)*log(EL)] with an 800 min/day wear-time. In contrast, EL was positively associated with time spent in bout-accumulated MVPA; the approximating equation being MVPA = exp[54.679 - 6.268*log(CP) + 6.387*log(EL) - 10.000*log(BD) - 0.162*log(EL)*log(BD) - 0.626*log(CP)*log(EL) + 1.033*log(CP)*log(BD)]. BD and CP were inversely associated with MVPA, with higher values attenuating the influence of EL.ConclusionsEL, CP and BD interact to influence estimates of accelerometer-determined MVPA. In general, higher CP and longer BD result in lower MVPA but the direction of association for EL depends on BD. Reporting scaling coefficients for these key parameters across their frequently used ranges would facilitate comparisons of population-level accelerometry estimates of MVPA.

Associations between objectively assessed and self-reported sedentary time with mental health in adults: an analysis of data from the Health Survey for England

ObjectiveThere is increasing interest in the association between sedentary behaviour and mental health, although most studies have relied solely on self-reported measures, thus making results prone to various biases. The...

Office Workers' Objectively Measured Sedentary Behavior and Physical Activity During and Outside Working Hours

To examine objectively determined sedentary behavior and physical activity (PA) during and outside working hours in full-time office workers. A total of 170 participants wore an ActiGraph GT1M accelerometer for 7 days. Time spent sedentary (<100 counts/min), in light-intensity PA (100 to 1951 counts/min), and moderate-to-vigorous PA (≥1952 counts/min) was calculated for workdays (including working hours and nonworking hours) and nonworkdays. Participants accumulated significantly higher levels of sedentary behavior (68% vs 60%) and lower levels of light-intensity activity (28% vs 36%) on workdays in comparison with nonworkdays. Up to 71% of working hours were spent sedentary. Individuals who were most sedentary at work were also more sedentary outside work. Those who are most sedentary at work do not compensate by increasing their PA or reducing their sedentary time outside work. Occupational interventions should address workplace and leisure-time sedentary behavior.

Physical activity maintenance in the transition to adolescence: a longitudinal study of the roles of sport and lifestyle activities in British youth.

BackgroundPromoting physical activity in youth is important for health, but existing physical activity interventions have had limited success. We aimed to inform intervention design by i) describing drop-out, continuation and uptake of specific activities over the transition to adolescence; and ii) examining Variety (number of different activities/week) and Frequency (number of activity session/week) of activity participation and their associations with changes in objectively measured physical activity from childhood to adolescence.MethodsAt age 10.2±0.3 and 14.2±0.3 years, 319 children in the SPEEDY study (46% boys) wore GT1M Actigraph accelerometers for 7 days and provided self-reported participation (never, once, 2 to 3 times or four or more times, over the last 7 days) in 23 leisure-time activities. Associations of change in moderate-to-vigorous intensity PA (MVPA) (≥2000 counts/minute) and change in total physical activity (TPA) (average accelerometer counts/minute) with exposure variables Z-score transformed (change in) Variety and Frequency were examined using multilevel linear regression, clustered by school, in simple and adjusted models.ResultsThe number of children ever reporting a specific activity ranged from 30 (‘Hockey’) to 279 (‘Running or jogging’). Some activities were susceptible to drop-out (e.g. ‘Skipping’) but others were commonly continued or taken up (e.g. ‘Household chores’). Overall, Variety and Frequency declined (mean±SD ΔVariety −3.1±4.4 activities/week; ΔFrequency −7.2±12.0 session/week). ΔMVPA and ΔTPA were not associated with Variety or Frequency at baseline, nor with ΔVariety or ΔFrequency (p>0.29 in all models).ConclusionsPopularity of specific activities as well as drop-out, continuation and uptake should be considered in future intervention development. Activities that are commonly continued or taken up may be more valuable to encourage in interventions than those with low participation or high drop-out. We did not find evidence to support the idea that Variety and Frequency may be key elements to include in future interventions.

Influência do número de dias e de horas válidas de uso do acelerômetro na estimativa do nível de atividade física em pré-escolares de Recife, Pernambuco, Brasil

A few studies have proposed the number of hours/day and the number of days of monitoring that should be completed to obtain good quality accelerometry data for preschool children. The aim of this study was to analyze how the estimates of physical activity levels and sample profiles (demographic and anthropometric data) vary according the use of different criteria to define valid monitoring periods. Children (n=180) aged three to five years were randomly selected among participants from a longitudinal study performed in Recife, Brazil. Children wore a GT1M Actigraph accelerometer on the right waist during a period of seven days, including the weekend days, using 15 s epochs. A total of 176 children were included in the study (52.8% boys; mean age of 4.3 years [s=0.8]). Using the criterion of 10+ hours/day of wearing time to define a valid monitoring day, 67.0% (n=118) and 36.9% (n=65) of the children showed 3+ and 5+ valid days, respectively. When the criterion of 5+ hours/day was used, the time spent in moderate activity was approximately 10 minutes shorter than when the criterion of 10+ hours/day was used. The criterion of 10+ hours/day for defining a valid monitoring day leads to a sample size reduction and the criterion of 5+ hours/day underestimates the moderate activity level.

Quality Control Methods in Accelerometer Data Processing: Identifying Extreme Counts

BackgroundAccelerometers are designed to measure plausible human activity, however extremely high count values (EHCV) have been recorded in large-scale studies. Using population data, we develop methodological principles for establishing an EHCV threshold, propose a threshold to define EHCV in the ActiGraph GT1M, determine occurrences of EHCV in a large-scale study, identify device-specific error values, and investigate the influence of varying EHCV thresholds on daily vigorous PA (VPA).MethodsWe estimated quantiles to analyse the distribution of all accelerometer positive count values obtained from 9005 seven-year old children participating in the UK Millennium Cohort Study. A threshold to identify EHCV was derived by differentiating the quantile function. Data were screened for device-specific error count values and EHCV, and a sensitivity analysis conducted to compare daily VPA estimates using three approaches to accounting for EHCV.ResultsUsing our proposed threshold of ≥ 11,715 counts/minute to identify EHCV, we found that only 0.7% of all non-zero counts measured in MCS children were EHCV; in 99.7% of these children, EHCV comprised < 1% of total non-zero counts. Only 11 MCS children (0.12% of sample) returned accelerometers that contained negative counts; out of 237 such values, 211 counts were equal to −32,768 in one child. The medians of daily minutes spent in VPA obtained without excluding EHCV, and when using a higher threshold (≥19,442 counts/minute) were, respectively, 6.2% and 4.6% higher than when using our threshold (6.5 minutes; p<0.0001).ConclusionsQuality control processes should be undertaken during accelerometer fieldwork and prior to analysing data to identify monitors recording error values and EHCV. The proposed threshold will improve the validity of VPA estimates in children’s studies using the ActiGraph GT1M by ensuring only plausible data are analysed. These methods can be applied to define appropriate EHCV thresholds for different accelerometer models.

Validity and reliability of two brief physical activity questionnaires among Spanish-speaking individuals of Mexican descent.

BackgroundMexican Americans are the largest minority group in the US and suffer disproportionate rates of diseases related to the lack of physical activity (PA). Since many of these Mexican Americans are Spanish-speaking, it is important to validate a Spanish language physical activity assessment tool that can be used in epidemiology as well as clinical practice. This study explored the utility of two Spanish translated physical activity questionnaires, the Stanford Brief Activity Survey (SBAS) and the Rapid Assessment of Physical Activity (RAPA), for use among Spanish-speaking Mexican Americans.MethodsThirty-four participants (13 M, 21 F; 37.6 ± 9.5 y) completed each of the two PA surveys twice, one week apart. During that week 31 participants also wore an ActiGraph GT1M accelerometer for 7 days to objectively measure PA. Minutes of moderate and vigorous PA (MVPA) were determined from the accelerometer data using Freedson and Matthews cut points.ResultsValidity, determined by Spearman correlation coefficients between questionnaire scores and minutes of ActiGraph measured MVPA were 0.38 and 0.45 for the SBAS and RAPA, respectively. Test-retest reliability was 0.61 for the SBAS and 0.65 for the RAPA. Sensitivity and specificity were 0.60 and 0.47 for the SBAS, and 0.73 and 0.75 for the RAPA. Participants who were classified as meeting the 2008 National Physical Activity Guidelines by the RAPA engaged in significantly (p < 0.05) more minutes of MVPA than those who were not, while there were no significant differences in minutes of MVPA classified by the SBAS.ConclusionsThe SBAS and the RAPA are both reasonably valid measures for quickly assessing PA and determining compliance to the PA guidelines in Spanish-speaking Mexican Americans. Although the two questionnaires had comparable reliability, the RAPA was better able to distinguish between those who met and did not meet National PA Guidelines.

Comparison of Self-reported versus Accelerometer-Measured Physical Activity

The International Physical Activity Questionnaire (IPAQ) is one of the most widely used questionnaires to assess physical activity (PA). Validation studies for the IPAQ have been executed, but still there is a need for studies comparing absolute values between IPAQ and accelerometer in large population studies. To compare PA and sedentary time from the self-administered, short version of the IPAQ with data from ActiGraph accelerometer in a large national sample. A total of 1751 adults (19-84 yr) wore an accelerometer (ActiGraph GT1M) for seven consecutive days and completed the IPAQ-Short Form. Sedentary time, total PA, and time spent in moderate to vigorous activity were compared in relation to sex, age, and education. Men and women reported, on average, 131 min·d (SE = 4 min·d) less sedentary time compared with the accelerometer measurements. The difference between self-reported and measured sedentary time and vigorous-intensity PA was greatest among men with a lower education level and for men 65 yr and older. Although men reported 47% more moderate to vigorous physical activity (MVPA) compared with women, there were no differences between sexes in accelerometer-determined MVPA. Accelerometer-determined moderate PA was reduced from 110 to 42 min·d (62%) when analyzed in blocks of 10 min (P < 0.0001) compared with 1-min blocks. The main correlation coefficients between self-reported variables and accelerometer measures of physical activity were between 0.20 and 0.46. The participants report through IPAQ-Short Form more vigorous PA and less sedentary time compared with the accelerometer. The difference between self-reported and accelerometer-measured MVPA increased with higher activity and intensity levels. Associations between the methods were affected by sex, age, and education, but not body mass index.

Who children spend time with after school: associations with objectively recorded indoor and outdoor physical activity

BackgroundUnderstanding how the determinants of behaviour vary by context may support the design of interventions aiming to increase physical activity. Such factors include independent mobility, time outdoors and the availability of other children. At present little is known about who children spend their time with after school, how this relates to time spent indoors or outdoors and activity in these locations. This study aimed to quantify who children spend their time with when indoors or outdoors and associations with moderate to vigorous physical activity (MVPA).MethodsParticipants were 427 children aged 10–11 from Bristol, UK. Physical activity was recorded using an accelerometer (Actigraph GT1M) and matched to Global Positioning System receiver (Garmin Foretrex 201) data to differentiate indoor and outdoor location. Children self-reported who they spent time with after school until bed-time using a diary. Each 10 second epoch was coded as indoors or outdoors and for ‘who with’ (alone, friend, brother/sister, mum/dad, other grown-up) creating 10 possible physical activity contexts. Time spent and MVPA were summarised for each context. Associations between time spent in the different contexts and MVPA were examined using multiple linear regression adjusting for daylight, age, deprivation and standardised body mass index.ResultsDuring the after school period, children were most often with their mum/dad or alone, especially when indoors. When outdoors more time was spent with friends (girls: 32.1%; boys: 28.6%) than other people or alone. Regression analyses suggested hours outdoors with friends were positively associated with minutes of MVPA for girls (beta-coefficient [95% CI]: 17.4 [4.47, 30.24]) and boys (17.53 [2.76, 32.31]). Being outdoors with brother/sister was associated with MVPA for girls (21.2 [14.17, 28.25]) but not boys. Weaker associations were observed for time indoors with friends (girls: 4.61 [1.37, 7.85]; boys: (7.42 [2.99, 11.85]) and other adults (girls: 5.33 [2.95, 7.71]; boys: (4.44 [1.98, 6.90]). Time spent alone was not associated with MVPA regardless of gender or indoor/outdoor location.ConclusionsTime spent outdoors with other children is an important source of MVPA after school. Interventions to increase physical activity may benefit from fostering friendship groups and limiting the time children spend alone.

The freedom to explore: examining the influence of independent mobility on weekday, weekend and after-school physical activity behaviour in children living in urban and inner-suburban neighbourhoods of varying socioeconomic status

BackgroundChildren’s independent mobility (CIM) is critical to healthy development in childhood. The physical layout and social characteristics of neighbourhoods can impact opportunities for CIM. While global evidence is mounting on CIM, to the authors’ knowledge, Canadian data on CIM and related health outcomes (i.e., physical activity (PA) behaviour) are missing. The purpose of this study was to examine if CIM is related to multiple characteristics of accelerometry-measured PA behaviour (total PA, light PA, moderate-to-vigorous PA, time spent sedentary) and whether associations between CIM and PA behaviour systematically vary by place of residence, stratifying by gender and type of day/period (weekdays, after-school, weekend).MethodsParticipants were recruited through Project BEAT (Built Environment and Active Transport; http://www.beat.utoronto.ca). Children (n = 856) were stratified into four neighbourhood classifications based on the period of neighbourhood development (urban built environment (BE) (old BE) versus inner-suburban BE (new BE)) and socioeconomic status (SES; low SES and high SES). Physical activity was measured via accelerometry (ActiGraph GT1M). CIM was assessed via parental report and two categories were created (low CIM, n = 332; high CIM, n = 524). A series of two-factor ANOVAs were used to determine gender-specific differences in PA for weekdays, weekend days and the after-school period, according to level of CIM, across four neighbourhood classifications.ResultsChildren who were granted at least some independent mobility (high CIM) had more positive PA profiles across the school week, during the after-school period, and over the weekend; they were also less sedentary. The influence of CIM on PA behaviour was particularly salient during the after-school period. Associations of CIM with PA varied by gender, and also by neighbourhood classification. CIM seemed to matter more in urban neighbourhoods for boys and suburban neighbourhoods for girls.ConclusionOur findings highlight the importance of independent mobility to multiple characteristics of children’s PA behaviour across the week. Furthermore, they emphasize that independent mobility-activity relationships need to be considered by gender and the type of neighbourhood independent mobility is offered in. Future work will focus on developing a predictive model of CIM that could be used to inform decision-making around alleviating barriers to CIM.

Differences in fat loss in response to physical activity among severely obese men and women

Direct measurement of physical activity may be critical to revealing its relationship with the change in fat mass over time. The aim of this study was to determine the relationship between accelerometer-determined change in physical activity and change in fat mass in severely obese men and women. A total of 49 severely obese men (n = 12) and women (n = 37) (mean age 42.8 years (standard deviation (SD) 9.6); mean body mass index 42.0 kg/m2 (SD 5.9) participated in a 1-year lifestyle intervention with 4 measurements of physical activity (Actigraph GT1M accelerometer), energy intake (180-item food frequency questionnaire), and body composition. Associations were determined using linear regression analyses. In the total group change in both duration and intensity of physical activity were independently related to change in fat mass (partial r = -0.38 to -0.31, p = 0.001-0.007) after adjustment for baseline body weight, gender and change in energy intake. A gender-specific effect of change in physical activity duration was found for change in fat mass (p for change in physical activity duration*gender < 0.001), where the association was significant in men (partial r = -0.53, p < 0.001), but not in women (partial r = -0.17, p = 0.149). Increased intensity of physical activity was associated with loss of fat mass in severely obese men and women, whereas physical activity duration was associated with fat mass loss in men.