Physical Activity Levels During School Recess in a Nationally Representative Sample of 10- to 11-Year-Olds.

PURPOSE: School recess provides a valuable opportunity for children's daily moderate- to vigorous-intensity physical activity (MVPA). This study aimed to quantify MVPA during school recess in a representative sample of Scottish children and examine whether recess MVPA varied by gender, socioeconomic status, season, urban/rural residency, and recess length. METHOD: Five-day accelerometry MVPA data were analyzed from 773 children (53.9% girls, 46.1% boys, 10- to 11-y-olds) from 471 schools. Binary logistic regression explored associations between meeting/not meeting the recommendation to spend 40% of recess time in MVPA and the aforementioned risk factors. Descriptive recess data were also analyzed. RESULTS: Participants spent an average of 3.2 minutes (SD 2.1) in MVPA during recess. Girls engaged in 2.5 minutes (SD 1.7) of MVPA compared with 4.0 minutes (SD 2.2) for boys. Only 6% of children met the recess MVPA recommendation. The odds of girls (odds ratio 0.09; 95% confidence interval, 0.04-0.25) meeting the recommendation was lower (P < .001) compared with boys. No statistically significant differences were observed in meeting the recommendation for the other risk factors. CONCLUSION: Levels of MVPA during school recess are very low in Scottish children, and interventions aimed at increasing MVPA during recess are needed.

Concurrent screen use and cross-sectional association with lifestyle behaviours and psychosocial health in adolescent females.

AIM: To describe concurrent screen use and any relationships with lifestyle behaviours and psychosocial health. METHODS: Participants wore an accelerometer for seven days to calculate physical activity sleep and sedentary time. Screen ownership and use and psychosocial variables were self-reported. Body mass index (BMI) was measured. Relationships were explored using mixed models accounting for school clustering and confounders. RESULTS: In 816 adolescent females (age: 12.8 SD 0.8 years; 20.4% non-white European) use of ≥2 screens concurrently was: 59% after school, 65% in evenings, 36% in bed and 68% at weekends. Compared to no screens those using: ≥1 screens at weekends had lower physical activity; ≥2 screens at the weekend or one/two screen at bed had lower weekend moderate-to-vigorous physical activity; one screen in the evening had lower moderate-to-vigorous physical activity in the after-school and evening period; ≥1 screens after school had higher BMI; and ≥3 screens at the weekend had higher weekend sedentary time. Compared to no screens those using: 1-3 after-school screens had shorter weekday sleep; ≥1 screens after-school had lower time in bed. CONCLUSION: Screen use is linked to lower physical activity, higher BMI and less sleep. These results can inform screen use guidelines.

The reimagination of school-based physical activity research in the COVID-19 era.

Deirdre Harrington and Michelle O'Reilly discuss the article "Effectiveness and cost-effectiveness of the GoActive intervention to increase physical activity among UK adolescents: A cluster randomised controlled trial" by Kirsten Corder and colleagues.

Maturational timing, physical self-perceptions and physical activity in UK adolescent females: investigation of a mediated effects model.

BACKGROUND: Advanced (early) biological maturation may be a risk factor for inactivity among adolescent girls. AIM: To test the mediational effects of body attractiveness and physical self-worth on the relationship between biological maturity and accelerometer assessed moderate-to-vigorous physical activity (MVPA) in a large multi-ethnic sample of girls from the Midlands area in the UK (11-14 years). SUBJECTS AND METHODS: Biological maturity (predicting age at peak height velocity (APHV)); self-perceptions of body attractiveness, physical self-worth, and minutes spent in MVPA were assessed in 1062 females aged 11-14 years. RESULTS: Structural equation modelling using maximum likelihood estimation and boot- strapping procedures supported the hypothesised model. Later maturation predicted higher perceptions of body attractiveness (ß = 0.25, p < .001) which, in turn, predicted higher perceptions of physical self-worth (ß = 0.91, p < .001) and, significantly higher MVPA (ß = 0.22, p < .001). Examination of the bootstrap-generated bias-corrected confidence intervals suggested that perceptions of body attractiveness and physical self-worth partially mediated a positive association between predicted APHV and MVPA (ß = 0.05, p < .001). CONCLUSIONS: Greater biological maturity (i.e. early maturity) in adolescent girls is associated with less involvement in MVPA and appears to be partly explained by lower perceptions of body attractiveness and physical self-worth. Physical activity interventions should consider girls' perceptions of their pubertal related physiological changes during adolescence, particularly among early maturing girls.

Process evaluation of the school-based Girls Active programme.

BACKGROUND: Girls Active is a physical activity programme, delivered in UK secondary schools, with the aim of increasing moderate-to-vigorous physical activity (MVPA) in girls aged 11-14 years. This study presents the process evaluation as part of a 14-month cluster randomised controlled trial designed to evaluate the effectiveness of the Girls Active programme and which showed no difference in the primary outcome (MVPA at 14 months) between intervention and control arms. METHODS: Quantitative and qualitative data were collected from intervention schools over the course of the 14 month trial. Feedback forms and attendance records were completed at the end of all teacher and peer leader training and review days. At 7- and 14-months, semi-structured interviews were conducted with the lead Girls Active teacher in all intervention schools (n = 10) and staff from the intervention provider (n = 4) and hub school (n = 1). At 14 months, separate focus groups with peer leaders (n = 8 schools), girls who participated in the evaluation component of the trial (n = 8 schools), and a sample of boys (n = 6 schools) were conducted. All participants in the intervention schools were asked to complete an exit survey at 14 months. Teachers (intervention and control) completed a school environment questionnaire at baseline, 7- and 14-months. RESULTS: The Girls Active programme, i.e., the training and resources, appeared to be well received by teachers and pupils. Factors that may have contributed to the lack of effectiveness include: some initial uncertainty by teachers as to what to do following the initial training, a predominant focus on support activities (e.g., gathering opinions) rather than actual physical activity provision, and school-level constraints that impeded implementation. CONCLUSIONS: Girls Active and what it was trying to achieve was valued by schools. The programme could be improved by providing greater guidance to teachers throughout, the setting of timelines, and providing formal training to peer leaders. TRIAL REGISTRATION: ISRCTN, ISRCTN10688342 . Registered 12 January 2015.

Effectiveness of the 'Girls Active' school-based physical activity programme: A cluster randomised controlled trial.

BACKGROUND: Globally, adolescent girls' physical activity (PA) levels are low. The 'Girls Active' secondary school-based programme, developed by the Youth Sport Trust, aims to increase PA in adolescent girls. This paper explores the effectiveness of the 'Girls Active' school-based PA programme. METHODS: A random sample of girls aged 11-14 from 20 secondary schools (Midlands, UK) participated in a two-arm cluster randomised controlled trial. Ten schools received Girls Active and 10 continued with usual practice. Measurements were taken at baseline, seven- and 14-month follow-up. PRIMARY OUTCOME: wrist-worn accelerometer measured moderate- to vigorous-intensity PA (MVPA). SECONDARY OUTCOMES: overall PA, light PA, sedentary time, body composition, and psychosocial outcomes. Generalised estimating equations, adjusted for school cluster and potential confounders, were used and A priori subgroup analysis was undertaken. Micro-costing and cost-consequence analyses were conducted using bespoke collection methods on programme delivery information. Outcomes for the cost-consequence analysis were health related quality of life measured by the Child Health Utility-9D and service use. RESULTS: Overall, 1752 pupils participated, 1211 (69.1%) provided valid 14-month accelerometer data. No difference in MVPA (mins/day; 95% confidence intervals) was found at 14 months (1.7; -0.8 to 4.3), there was at seven months (2.4; 0.1 to 4.7). Subgroup analyses showed significant intervention effects on 14-month in larger schools (3.9; 1.39 to 6.09) and in White Europeans (3.1; 0.60 to 6.02) and in early maturers (5.1; 1.69 to 8.48) at seven months. The control group did better in smaller schools at 14-months (-4.38; -7.34 to -1.41). Significant group differences were found in 14-month identified motivation (-0.09; -0.18 to -0.01) and at seven months in: overall PA (1.39 mg/day; 0.1 to 2.2), after-school sedentary time (-4.7; -8.9 to -0.6), whole day (5.7; 1.0 to 10.5) and school day (4.5; 0.25 to 8.75) light PA, self-esteem. Small, statistically significant, differences in some psychosocial variables favoured control schools. Micro-costing demonstrated that delivering the programme resulted in a range of time and financial costs at each school. Cost-consequence analysis demonstrated no effect of the programme for health related quality of life or service use. CONCLUSIONS: Compared with usual practice, 'Girls Active' did not affect 14-month MVPA. TRIAL REGISTRATION: ISRCTN10688342.

Minimum Wear Duration for the activPAL Professional Activity Monitor in Adolescent Females.

OBJECTIVES: This study aims to determine the minimum number of days of monitoring required to reliably predict sitting/lying time, standing time, light intensity physical activity (LIPA), moderate-to-vigorous intensity physical activity (MVPA) and steps in adolescent females. METHOD: 195 adolescent females (mean age = 15.7 years; SD = 0.9) participated in the study. Participants wore the activPAL activity monitor for a seven day protocol. The amount of time spent sitting/lying, standing, in LIPA and in MVPA and the number of steps per day were quantified. Spearman-Brown Prophecy formulae were used to predict the number of days of data required to achieve an intraclass correlation coefficient of both 0.7 and 0.8. RESULTS: For the percentage of the waking day spent sitting/lying, standing, in LIPA and in MVPA, a minimum of 9 days of accelerometer recording is required to achieve a reliability of ≥ 0.7, while a minimum of 15 days is required to achieve a reliability of ≥ 0.8. For steps, a minimum of 12 days of recording is required to achieve a reliability of ≥ 0.7, with 21 days to achieve a reliability of ≥ 0.8. CONCLUSION: Future research in adolescent females should collect a minimum of 9 days of accelerometer data to reliably estimate sitting/lying time, standing time, LIPA and MVPA, while 12 days is required to reliably estimate steps.

Uncovering physiological mechanisms for health disparities in type 2 diabetes.

Type 2 diabetes (T2D) prevalence in the United States is significantly higher in African Americans vs Whites. Yet, the physiological mechanisms contributing to this health disparity have been poorly described. To design effective strategies to reduce this disparity, there is a need to determine whether racial differences in diabetes prevalence are attributable to modifiable or non-modifiable factors. This review synthesizes and critically evaluates the potential physiological and genetic mechanisms that may contribute to the higher susceptibility of African Americans to T2D. These mechanisms include: 1) obesity and fat distribution; 2) metabolic flexibility; 3) muscle physiology; 4) energy expenditure and fitness; and 5) genetics. We focus on the clinical significance of findings and limitations of the recent literature.

Moderate-to-vigorous intensity physical activity during school hours in a representative sample of 10-11-year-olds in Scotland.

OBJECTIVES: Growing concern about children and adolescent physical inactivity has made the promotion of physical activity a public health priority. International recommendations suggest children should accumulate at least 30 min of moderate-to-vigorous physical activity (MVPA) during school hours. This study assessed levels of objectively-measured MVPA in a large nationally representative sample of Scottish children aged 10-11. Risk factors for not meeting the school-hours MVPA recommendation were examined. DESIGN: Cross-sectional. METHODS: Mean time spent in MVPA during school hours across five weekdays was measured using Actigraph accelerometry (May 2015-May 2016). Binary logistic regression, presented as odds ratio (O.R.) and confidence intervals (C.I.), explored associations between meeting/not meeting the recommendation by sex, socioeconomic status (SES), season, and urban/rural residence in 2022. RESULTS: Valid data were obtained from 773 children (53.9% girls, 46.1% boys) from 471 schools. Mean daily school-hours MVPA was 29 (SD 11) minutes; 42.7% of children reached the recommendation. The odds of girls (O.R. 0.43; C.I. 0.32, 0.57) meeting the recommendation was significantly lower (p < 0.001) compared to boys. Children living in rural areas had higher odds (O.R. 1.49; C.I. 1.04, 2.15) of meeting the recommendation compared with those in urban areas (p = 0.032). No significant differences in meeting the recommendation by SES (p = 0.700). The overall trend for season was significant (p < 0.001), with lower odds of meeting the recommendation in winter compared to summer. CONCLUSIONS: Most Scottish children aged 10-11 did not meet the 30 minute MVPA recommendation. Interventions to increase MVPA during school hours are essential to promote public health.

Association between Chronotype and Physical Behaviours in Adolescent Girls.

The aim of this study was to (1) describe accelerometer-assessed physical behaviours by chronotype, and (2) examine the association between chronotype and accelerometer-assessed physical behaviours in a cohort of adolescent girls. Chronotype (single question) and physical behaviours (GENEActiv accelerometer on the non-dominant wrist) were assessed in 965 adolescent girls (13.9 ± 0.8 years). Linear mixed-effects models examined the relationships among chronotype and physical behaviours (time in bed, total sleep time, sleep efficiency, sedentary time, overall, light and moderate-to-vigorous physical activity) on weekdays and weekend days. Over the 24 h day, participants spent 46% sedentary, 20% in light activity, 3% in moderate-to-vigorous physical activity, and 31% in 'time in bed'. Seventy percent of participants identified as 'evening' chronotypes. Compared to evening chronotypes, morning chronotypes engaged in less sedentary time (10 min/day) and had higher overall physical activity (1.3 mg/day, ~30 min of slow walking) on weekdays. Most girls identified as evening chronotypes with a large proportion of their day spent sedentary and a small amount in physical activities which may be exacerbated in evening chronotypes on weekdays. The results maybe be important for programmes aiming to promote physical activity in adolescent girls.

A steps/minute value for moderate intensity physical activity in adolescent females.

The number of steps/minute (i.e., cadence) that equates to moderate intensity in adolescents is not known. To that end, 31 adolescent females walked on a treadmill at 5 different speeds while wearing an ActivPAL accelerometer and oxygen uptake was recorded by indirect calorimetry. The relationship between metabolic equivalents (METs) and cadence was explored using 3 different analytical approaches. Cadence was a significant predictor of METs (r = .70; p < .001). Moderate intensity (3 METs) corresponded to 94 or 114 steps/minute based on the mixed model and ROC analysis, respectively. These two values, and a practical value of 100 steps/minute, were cross-validated on an independent sample of 33 adolescent females during over-ground walking at 3 speeds. The sensitivity and specificity of each value correctly identifying 3 METs were 98.5% and 87.2% for 94 steps/minute, 72.9% and 98.8 for 114 steps/minute and 96.5% and 95.7% for 100 steps/minute. Compromising on a single cadence of 100 steps/minute would be a practical value that approximates moderate intensity in adolescent females and can be used for physical activity interpretation and promotion.

Changes in commuting behaviours in response to the COVID-19 pandemic in the UK.

BACKGROUND: The UK Government restrictions on non-essential work in response to the coronavirus disease 2019 (COVID-19) pandemic forced millions of working aged-adults into an unplanned lifestyle change. We present data on changes in commuting behaviour in response to COVID-19 and describe the facilitators and barriers to switching commuting behaviours, with a specific focus on cycling and walking. METHODS: An online survey queried individuals' transport mode to/from work before and when becoming aware of COVID-19, when restrictions were in place and the transport mode they may use once restrictions are lifted. Free-form text responses were collected on why they may switch to a sustainable commute mode in the future and what would help/allow them to achieve this. Quantitative and qualitative data on those who commuted by car (single occupant) and public transport (bus/rail/park & ride) were analysed and presented separately. RESULTS: Overall, 725 car and public transport commuters responded; 72.4% were car commuters and 27.6% were public transport commuters before COVID-19. Of the car commuters, 81.9% may continue travelling by car once restrictions are lifted while 3.6% and 6.5% might change to walking and cycling, respectively. Of the public transport commuters, 49.0% might switch modes. From the free-form text responses three themes were identified: (a) perceived behavioural control towards cycling and walking (infrastructure and safety of roads, distance, weather) (b) key motivators to encourage a switch to cycling and walking (provision to support cycling, personal and environmental benefits); (c) the demands of current lifestyle (job requirements, family and lifestyle commitments). CONCLUSION: These UK data show how the COVID-19 pandemic has been an "external shock" causing some individuals to reassess their commuting mode. This provides an opportunity for theory-based behaviour change interventions tackling motivations, barriers and beliefs towards changing commute mode.

Cross-sectional analysis of levels and patterns of objectively measured sedentary time in adolescent females.

BACKGROUND: Adolescent females have been highlighted as a particularly sedentary population and the possible negative effects of a sedentary lifestyle are being uncovered. However, much of the past sedentary research is based on self-report or uses indirect methods to quantity sedentary time. Total time spent sedentary and the possible intricate sedentary patterns of adolescent females have not been described using objective and direct measure of body inclination. The objectives of this article are to examine the sedentary levels and patterns of a group of adolescent females using the ActivPAL™ and to highlight possible differences in sedentary levels and patterns across the week and within the school day. A full methodological description of how the data was analyzed is also presented. METHODS: One hundred and eleven adolescent females, age 15-18 yrs, were recruited from urban and rural areas in the Republic of Ireland. Participants wore an ActivPAL physical activity monitor for a 7.5 day period. The ActivPAL directly reports total time spent sitting/lying every 15 seconds and accumulation (frequency and duration) of sedentary activity was examined using a customized MATLAB(®) computer software programme. RESULTS: While no significant difference was found in the total time spent sitting/lying over the full 24 hour day between weekday and weekend day (18.8 vs. 18.9 hours; p = .911), significantly more sedentary bouts of 1 to 5 minutes and 21 to 40 minutes in duration were accumulated on weekdays compared to weekend days (p < .001). The mean length of each sedentary bout was also longer (9.8 vs. 8.8 minutes; p < .001). When school hours (9 am-3 pm) and after school hours (4 pm-10 pm) were compared, there was no difference in total time spent sedentary (3.9 hours; p = .796) but the pattern of accumulation of the sedentary time differed. There were a greater number of bouts of > 20 minutes duration during school hours than after school hours (4.7 vs. 3.5 bouts; p < .001) while after school time consisted of shorter bouts < 20 minutes. CONCLUSIONS: School is highlighted as a particularly sedentary setting for adolescent females. Interventions to decrease sedentary time at school and the use of wearable devices which distinguish posture should be encouraged when examining sedentary patterns and behaviors in this population.

Validation of MET estimates and step measurement using the ActivPAL physical activity logger.

The purpose of this study was to determine the validity of the metabolic equivalent (MET) equation and step rate function of the ActivPAL™ physical activity logger in a group of females. Using a standard treadmill protocol, 62 females aged 15-25 years walked on a treadmill at speeds between 3.2 and 7.0 km · h(-1) while wearing an ActivPAL. Oxygen consumption was measured using expired gas analysis at each speed and METs for each speed were estimated based on each participant's own resting metabolic rate. A sub-set of 18 participants also wore an Actigraph. Results showed that the in-built equation in the ActivPAL significantly underestimated (P < 0.001) METs under treadmill conditions at higher intensities. The ActivPAL equation is based on step rate yet the relationship between counts and measured METs (r = 0.76; P < 0.001) is stronger than that between steps and measured METs (r = 0.59; P < 0.001). Both the ActivPAL and Actigraph step functions showed no significant difference (P > 0.05) to video recorded step rate except at the slowest walking speed where the Actigraph significantly underestimated steps (P < 0.05). The development of a new equation based on the counts-METs relationship that includes a variety of speeds and activities would be useful. The ActivPAL step function performs better than the Actigraph at the slowest walking speed under treadmill conditions.

Development of an Interactive Lifestyle Programme for Adolescents at Risk of Developing Type 2 Diabetes: PRE-STARt.

BACKGROUND: Type 2 diabetes (T2D) is increasing in young people. Reporting on the processes used when developing prevention interventions is needed. We present the development of a family-based interactive lifestyle intervention for adolescents with risk factors for T2D in the future. METHOD: A multidisciplinary team in the UK site led the intervention development process with sites in Portugal, Greece, Germany and Spain. Potential programme topics and underpinning theory were gathered from literature and stakeholders. A theoretical framework based on self-efficacy theory and the COM-B (capability, opportunity, motivation, behaviour) model was developed. Sessions and supporting resources were developed and refined via two iterative cycles of session and resource piloting, feedback, reflection and refinement. Decision on delivery and content were made by stakeholders (young people, teachers, parents, paediatricians) and all sites. Materials were translated to local languages. Site-specific adaptations to the language, content and supporting resources were made. RESULTS: The "PRE-STARt" programme is eight 90-min interactive sessions with supporting curriculum and resources. Iterative development work provided valuable feedback on programme content and delivery. CONCLUSION: Reporting on the intervention development process, which includes stakeholder input, could yield a flexible approach for use in this emerging 'at risk' groups and their families.

Enhancing the value of accelerometer-assessed physical activity: meaningful visual comparisons of data-driven translational accelerometer metrics.

The lack of consensus on meaningful and interpretable physical activity outcomes from accelerometer data hampers comparison across studies. Cut-point analyses are simple to apply and easy to interpret but can lead to results that are not comparable. We propose that the optimal accelerometer metrics for data analysis are not the same as the optimal metrics for translation. Ideally, analytical metrics are precise continuous variables that cover the intensity spectrum, while translational metrics facilitate meaningful, public-health messages and can be described in terms of activities (e.g. brisk walking) or intensity (e.g. moderate-to-vigorous physical activity). Two analytical metrics that capture the volume and intensity of the 24-h activity profile are average acceleration (volume) and intensity gradient (intensity distribution). These allow investigation of independent, additive and interactive associations of volume and intensity of activity with health; however, they are not immediately interpretable. The MX metrics, the acceleration above which the most active X minutes are accumulated, are translational metrics that can be interpreted in terms of indicative activities. Using a range of MX metrics illustrates the intensity gradient and average acceleration (i.e. 24-h activity profile). The M120, M60, M30, M15 and M5 illustrate the most active accumulated minutes of the day, the M1/3DAY the most active accumulated 8 h of the day. We demonstrate how radar plots of MX metrics can be used to interpret and translate results from between- and within-group comparisons, provide information on meeting guidelines, assess individual activity profiles relative to percentiles and compare activity profiles between domains and/or time periods.

Micro-costing and a cost-consequence analysis of the 'Girls Active' programme: A cluster randomised controlled trial.

Physical inactivity has been identified as a leading risk factor for premature mortality globally, and adolescents, in particular, have low physical activity levels. Schools have been identified as a setting to tackle physical inactivity. Economic evidence of school-based physical activity programmes is limited, and the costs of these programmes are not always collected in full. This paper describes a micro-costing and cost-consequence analysis of the 'Girls Active' secondary school-based programme as part of a cluster randomised controlled trial (RCT). Micro-costing and cost-consequence analyses were conducted using bespoke cost diaries and questionnaires to collect programme delivery information. Outcomes for the cost-consequence analysis included health-related quality of life measured by the Child Health Utility-9D (CHU-9D), primary care General Practitioner (GP) and school-based (school nurse and school counsellor) service use as part of a cluster RCT of the 'Girls Active' programme. Overall, 1,752 secondary pupils were recruited and a complete case sample of 997 participants (Intervention n = 570, Control n = 427) was used for the cost-consequence analysis. The micro-costing analysis demonstrated that, depending upon how the programme was delivered, 'Girls Active' costs ranged from £1,054 (£2 per pupil, per school year) to £3,489 (£7 per pupil, per school year). The least costly option was to absorb 'Girls Active' strictly within curriculum hours. The analysis demonstrated no effect for the programme for the three main outcomes of interest (health-related quality of life, physical activity and service use).Micro-costing analyses demonstrated the costs of delivering the 'Girls Active' programme, addressing a gap in the United Kingdom (UK) literature regarding economic evidence from school-based physical activity programmes. This paper provides recommendations for those gathering cost and service use data in school settings to supplement validated and objective measures, furthering economic research in this field. Trial registration: -ISRCTN, ISRCTN10688342.

A data-driven, meaningful, easy to interpret, standardised accelerometer outcome variable for global surveillance.

OBJECTIVES: Our aim is to demonstrate how a data-driven accelerometer metric, the acceleration above which a person's most active minutes are accumulated, can (a) quantify the prevalence of meeting current physical activity guidelines for global surveillance and (b) moving forward, could inform accelerometer-driven physical activity guidelines. Unlike cut-point methods, the metric is population-independent (e.g. age) and potentially comparable across datasets. DESIGN: Cross-sectional, secondary data analysis. METHODS: Analyses were carried out on five datasets using wrist-worn accelerometers: children (N=145), adolescent girls (N=1669), office workers (N=114), pre- (N=1218) and post- (N=1316) menopausal women, and adults with type 2 diabetes (N=475). Open-source software (GGIR) was used to generate the magnitude of acceleration above which a person's most active 60, 30 and 2min are accumulated: M60ACC; M30ACC and M2ACC, respectively. RESULTS: The proportion of participants with M60ACC (children) and M30ACC (adults) values higher than accelerations representative of brisk walking (i.e., moderate-to-vigorous physical activity) ranged from 17 to 68% in children and 15 to 81% in adults, tending to decline with age. The proportion of pre-and post-menopausal women with M2ACC values meeting thresholds for bone health ranged from 6 to 13%. CONCLUSIONS: These metrics can be used for global surveillance of physical activity, including assessing prevalence of meeting current physical activity guidelines. As accelerometer and corresponding health data accumulate it will be possible to interpret the metrics relative to age- and sex- specific norms and derive evidence-based physical activity guidelines directly from accelerometer data for use in future global surveillance. This is where the potential advantages of these metrics lie.

Beyond Cut Points: Accelerometer Metrics that Capture the Physical Activity Profile.

PURPOSE: Commonly used physical activity metrics tell us little about the intensity distribution across the activity profile. The purpose of this paper is to introduce a metric, the intensity gradient, which can be used in combination with average acceleration (overall activity level) to fully describe the activity profile. METHODS: A total of 1669 adolescent girls (sample 1) and 295 adults with type 2 diabetes (sample 2) wore a GENEActiv accelerometer on their nondominant wrist for up to 7 d. Body mass index and percent body fat were assessed in both samples and physical function (grip strength, Short Physical Performance Battery, and sit-to-stand repetitions) in sample 2. Physical activity metrics were as follows: average acceleration (AccelAV); the intensity gradient (IntensityGRAD from the log-log regression line: 25-mg intensity bins [x]/time accumulated in each bin [y]); total moderate-to-vigorous physical activity (MVPA); and bouted MVPA (sample 2 only). RESULTS: Correlations between AccelAV and IntensityGRAD (r = 0.39-0.51) were similar to correlations between AccelAV and bouted MVPA (r = 0.48) and substantially lower than between AccelAV and total MVPA (r ≥ 0.93). IntensityGRAD was negatively associated with body fatness in sample 1 (P < 0.05) and positively associated with physical function in sample 2 (P < 0.05); associations were independent of AccelAV and potential covariates. By contrast, MVPA was not independently associated with body fatness or physical function. CONCLUSION: AccelAV and IntensityGRAD provide a complementary description of a person's activity profile, each explaining unique variance, and independently associated with body fatness and/or physical function. Both metrics are appropriate for reporting as standardized measures and suitable for comparison across studies using raw acceleration accelerometers. Concurrent use will facilitate investigation of the relative importance of intensity and volume of activity for a given outcome.

Compliance of Adolescent Girls to Repeated Deployments of Wrist-Worn Accelerometers.

PURPOSE: This study aimed to determine the cross-sectional and cumulative compliance of adolescent girls to accelerometer wear at three deployment points and to identify variables associated with compliance. METHODS: Girls from 20 secondary schools were recruited: 10 schools were participating in the "Girls Active" intervention and 10 were control schools. Physical activity was measured using the GENEActiv accelerometer worn on the nondominant wrist 24 h·d for up to 7 d at baseline, 7 months, and 14 months. Demographic and anthropometric characteristics were recorded. RESULTS: Seven valid days (≥16 h) of accelerometer wear was obtained from 83%, 77%, and 68% of girls at baseline (n = 1734), 7 months (n = 1381), and 14 months (n = 1326), respectively. Sixty-eight percent provided 7 valid days for both baseline and 7 months, 59% for baseline and 14 months, and 52% for all three deployment points. Estimates of physical activity level from 3 d of measurement could be considered equivalent to a 7-d measure (i.e., they fell within a ±5% equivalence zone). Cross sectionally, 3 valid days was obtained from at least 91% of girls; cumulatively, this was obtained from ≥88% of girls across any two deployment points and 84% of girls across all three deployment points. When controlling for clustering at school level and other potential predictors, physical activity level, being South Asian, being in the intervention group, and prior compliance were positively associated with monitor wear. CONCLUSIONS: Compliance reduced across deployment points, with the reduction increasing as the deployment points got further apart. High prior compliance and high physical activity level were associated with the most additional wear time.