Physical activity patterns using accelerometry in the National Weight Control Registry

The National Weight Control Registry (NWCR) was established in 1993 to examine characteristics of successful weight‐loss maintainers. This group consistently self‐reports high levels of physical activity. The aims of this study were to obtain objective assessments of physical activity in NWCR subjects and compare this to physical activity in both normal‐weight and overweight controls. Individuals from the NWCR (n = 26) were compared to a never obese normal‐weight control group matched to the NWCR group's current BMI (n = 30), and an overweight control group matched to the NWCR group's self‐reported pre‐weight‐loss BMI (n = 34). Objective assessment of physical activity was obtained for a 1‐week period using a triaxial accelerometer. Bouts of moderate‐to‐vigorous physical activity (MVPA) ≥10 min in duration, as well as nonbout MVPA (bouts of MVPA 1–9 min in duration) were summed and characterized. NWCR subjects spent significantly (P = 0.004) more time per day in sustained bouts of MVPA than overweight controls (41.5 ± 35.1 min/day vs. 19.2 ± 18.6 min/day) and marginally (P = 0.080) more than normal controls (25.8 ± 23.4). There were no significant differences between the three groups in the amount of nonbout MVPA. These results provide further evidence that physical activity is important for long‐term maintenance of weight loss and suggest that sustained volitional activity (i.e., ≥10 min in duration) may play an important role. Interventions targeting increases in structured exercise may be needed to improve long‐term weight‐loss maintenance.     

Pre‐ to Postoperative Physical Activity Changes in Bariatric Surgery Patients: Self Report vs. Objective Measures

Bariatric surgery patients report significant pre‐ to postoperative increases in physical activity (PA). However, it is unclear whether objective measures would corroborate these changes. The present study compared self‐reported and accelerometer‐based estimates of changes in moderate‐to‐vigorous intensity PA (MVPA) from pre‐ (pre‐op) to 6 months postsurgery (post‐op). Twenty bariatric surgery (65% laparoscopic‐adjustable gastric banding, 35% gastric bypass) patients (46.2 ± 9.8 years, 88% female, pre‐op BMI = 50.8 ± 9.7 kg/m²) wore RT3 accelerometers as an objective measure of MVPA and completed the Paffenbarger Physical Activity Questionnaire (PPAQ) as a subjective measure before and 6 months after bariatric surgery. Time (min/week) spent in MVPA was calculated for the PPAQ and RT3 (≥1‐min and ≥10‐min bouts) at pre‐op and post‐op. Self‐reported MVPA increased fivefold from pre‐op to post‐op (44.6 ± 80.8 to 212.3 ± 212.4 min/week; P < 0.005). By contrast, the RT3 showed nonsignificant decreases in MVPA for both ≥1‐min (186.0 ± 169.0 to 151.2 ± 118.3 min/week) and ≥10‐min (41.3 ± 109.3 to 39.8 ± 71.3 min/week) bouts. At pre‐op, the percentage of participants who accumulated ≥150‐min/week of MVPA in bouts ≥10‐min according to the PPAQ and RT3 was identical (10%). However, at post‐op, 55% of participants reported compliance with the recommendation compared to 5% based on RT3 measurement (P = 0.002). Objectively‐measured changes in MVPA from pre‐op to 6 months post‐op appear to be much smaller than self‐reported changes. Further research involving larger samples is needed to confirm these findings and to determine whether self‐report and objective PA measures are differentially associated with surgical weight loss outcomes.     

Contribution of the After-School Period to Children’s Daily Participation in Physical Activity and Sedentary Behaviours

ObjectivesChildren’s after-school physical activity (PA) and sedentary behaviours (SB) are not well understood, despite the potential this period holds for intervention. This study aimed to describe children’s after-school physical activity and sedentary behaviours; establish the contribution this makes to daily participation and to achieving physical activity and sedentary behaviours guidelines; and to determine the association between after-school moderate- to vigorous-intensity physical activity (MVPA), screen-based sedentary behaviours and achieving the physical activity and sedentary behaviour guidelines.MethodsChildren (n = 406, mean age 8.1 years, 58% girls) wore an ActiGraph GT3X accelerometer. The percentage of time and minutes spent sedentary (SED), in light- physical activity (LPA) and MVPA between the end-of-school and 6pm (weekdays) was calculated. Parents (n = 318, 40 years, 89% female) proxy-reported their child’s after-school participation in screen-based sedentary behaviours. The contribution that after-school SED, LPA, MVPA, and screen-based sedentary behaviours made to daily levels, and that after-school MVPA and screen-based sedentary behaviours made to achieving the physical activity/sedentary behaviour guidelines was calculated. Regression analysis determined the association between after-school MVPA and screen-based sedentary behaviours and achieving the physical activity/sedentary behaviours guidelines.ResultsChildren spent 54% of the after-school period SED, and this accounted for 21% of children’s daily SED levels. Boys spent a greater percentage of time in MVPA than girls (14.9% vs. 13.6%; p<0.05), but this made a smaller contribution to their daily levels (27.6% vs 29.8%; p<0.05). After school, boys and girls respectively performed 18.8 minutes and 16.7 minutes of MVPA, which is 31.4% and 27.8% of the MVPA (p<0.05) required to achieve the physical activity guidelines. Children spent 96 minutes in screen-based sedentary behaviours, contributing to 84% of their daily screen-based sedentary behaviours and 80% of the sedentary behaviour guidelines. After-school MVPA was positively associated with achieving the physical activity guidelines (OR: 1.31, 95%CI 1.18, 1.44, p<0.05), and after-school screen-based sedentary behaviours were negatively associated with achieving the sedentary behaviours guidelines (OR: 0.97, 95%CI: 0.96, 0.97, p<0.05).ConclusionsThe after-school period plays a critical role in the accumulation of children’s physical activity and sedentary behaviours. Small changes to after-school behaviours can have large impacts on children’s daily behaviours levels and likelihood of meeting the recommended levels of physical activity and sedentary behaviour. Therefore interventions should target reducing after-school sedentary behaviours and increasing physical activity.     

Association of physical activity intensity and bout length with mortality: An observational study of 79,503 UK Biobank participants

BackgroundSpending more time active (and less sedentary) is associated with health benefits such as improved cardiovascular health and lower risk of all-cause mortality. It is unclear whether these associations differ depending on whether time spent sedentary or in moderate-vigorous physical activity (MVPA) is accumulated in long or short bouts. In this study, we used a novel method that accounts for substitution (i.e., more time in MVPA means less time sleeping, in light activity or sedentary) to examine whether length of sedentary and MVPA bouts associates with all-cause mortality.Methods and findingsWe used data on 79,503 adult participants from the population-based UK Biobank cohort, which recruited participants between 2006 and 2010 (mean age at accelerometer wear 62.1 years [SD = 7.9], 54.5% women; mean length of follow-up 5.1 years [SD = 0.73]). We derived (1) the total time participants spent in activity categories—sleep, sedentary, light activity, and MVPA—on average per day; (2) time spent in sedentary bouts of short (1 to 15 minutes), medium (16 to 40 minutes), and long (41+ minutes) duration; and (3) MVPA bouts of very short (1 to 9 minutes), short (10 to 15 minutes), medium (16 to 40 minutes), and long (41+ minutes) duration. We used Cox proportion hazards regression to estimate the association of spending 10 minutes more average daily time in one activity or bout length category, coupled with 10 minutes less time in another, with all-cause mortality. Those spending more time in MVPA had lower mortality risk, irrespective of whether this replaced time spent sleeping, sedentary, or in light activity, and these associations were of similar magnitude (e.g., hazard ratio [HR] 0.96 [95% CI: 0.94, 0.97; P < 0.001] per 10 minutes more MVPA, coupled with 10 minutes less light activity per day). Those spending more time sedentary had higher mortality risk if this replaced light activity (HR 1.02 [95% CI: 1.01, 1.02; P < 0.001] per 10 minutes more sedentary time, with 10 minutes less light activity per day) and an even higher risk if this replaced MVPA (HR 1.06 [95% CI: 1.05, 1.08; P < 0.001] per 10 minutes more sedentary time, with 10 minutes less MVPA per day). We found little evidence that mortality risk differed depending on the length of sedentary or MVPA bouts. Key limitations of our study are potential residual confounding, the limited length of follow-up, and use of a select sample of the United Kingdom population.ConclusionsWe have shown that time spent in MVPA was associated with lower mortality, irrespective of whether it replaced time spent sleeping, sedentary, or in light activity. Time spent sedentary was associated with higher mortality risk, particularly if it replaced MVPA. This emphasises the specific importance of MVPA. Our findings suggest that the impact of MVPA does not differ depending on whether it is obtained from several short bouts or fewer longer bouts, supporting the recent removal of the requirement that MVPA should be accumulated in bouts of 10 minutes or more from the UK and the United States policy. Further studies are needed to investigate causality and explore health outcomes beyond mortality.

Louise Millard and co-workers study associations between bouts of moderate-to-vigorous physical activity and mortality.     

Comparison of Self-Reported and Accelerometer-Assessed Physical Activity in Older Women

Background

Self-reported physical activity measures continue to be validated against accelerometers; however, the absence of standardized, accelerometer moderate-to-vigorous physical activity (MVPA) definitions has made comparisons across studies difficult. Furthermore, recent accelerometer models assess accelerations in three axes, instead of only the vertical axis, but validation studies have yet to take incorporate triaxial data.

Methods

Participants (n = 10 115) from the Women’s Health Study wore a hip-worn accelerometer (ActiGraph GT3X+) for seven days during waking hours (2011–2014). Women then completed a physical activity questionnaire. We compared self-reported with accelerometer-assessed MVPA, using four established cutpoints for MVPA: three using only vertical axis data (760, 1041 and 1952 counts per minute (cpm)) and one using triaxial data (2690 cpm).

Results

According to self-reported physical activity, 66.6% of women met the US federal physical activity guidelines, engaging in ≥150 minutes per week of MVPA. The percent of women who met guidelines varied widely depending on the accelerometer MVPA definition (760 cpm: 50.0%, 1041 cpm: 33.0%, 1952 cpm: 13.4%, and 2690 cpm: 19.3%).

Conclusions

Triaxial count data do not substantially reduce the difference between self-reported and accelerometer-assessed MVPA.     

Moderate‐To‐vigorous physical activity is associated with decreases in body mass index from ages 9 to 15 years

Objective:

The purpose of this study is to determine whether time spent in objectively measured physical activity is associated with change in body mass index (BMI) from ages 9 to 15.

Design and Methods:

The participants were enrolled in the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (n = 938). At ages 9, 11, 12, and 15 the time spent in moderate‐to‐vigorous physical activity (MVPA) was objectively measured, and BMI was calculated (kg/m²). Longitudinal quantile regression was used to analyze the data. The 10th, 25th, 50th, 75th, and 90th BMI percentiles were modeled as the dependent variables with age and MVPA (h/day) modeled as predictors. Adjustment was also made for gender, race, sleep, healthy eating score, maternal education, and sedentary behavior.

Results:

A negative association between MVPA and change in BMI was observed at the 90th BMI percentile (?3.57, 95% CI ?5.15 to ?1.99 kg/m² per hour of MVPA). The negative association between time spent in MVPA and change in BMI was progressively weaker toward the 10th BMI percentile (?0.27, 95% CI ?0.62 to 0.07 kg/m² per hour of MVPA). The associations remained similar after adjusting for the covariates, and when the analyses were stratified by gender.

Conclusion:

Time spent in MVPA was negatively associated with change in BMI from age 9 to 15. The association was strongest at the upper tail of the BMI distribution, and increasing time spent in MVPA could help reduce the prevalence of childhood obesity.

     

Girls' perception of neighborhood factors on physical activity, sedentary behavior, and BMI

Objective: The purpose of this study was to examine the association of perceived physical neighborhood factors with physical activity, sedentary behavior, and BMI among adolescent girls. Research Methods and Procedures: Sixth grade girls (n = 1554) completed a questionnaire on neighborhood factors (e.g., safety, esthetics, access to physical activity resources). The dependent variables included non‐school metabolic equivalent weighted moderate to vigorous physical activity (MW‐MVPA) and non‐school sedentary behavior, both measured using accelerometry, and BMI. Results: The following neighborhood factors were associated with lower BMI: seeing walkers and bikers on neighborhood streets, not having a lot of crime in the neighborhood, seeing other children playing outdoors, having bicycle or walking trails in the neighborhood, and access to physical activity facilities. The absolute contribution for the average girl for each of these neighborhood factors was relatively small, with none of these factors exceeding 0.8 kg/m² BMI units. The following neighborhood factors were associated with higher MW‐MVPA: having well‐lit streets at night, having a lot of traffic in the neighborhood, having bicycle or walking trails in the neighborhood, and access to physical activity facilities. Girls with ≥9 places to go for physical activity had 14.0% higher non‐school MW‐MVPA than girls with ≤4 places. Discussion: This study identified several neighborhood factors associated with non‐school MW‐MVPA and BMI, but none of the factors explored were associated with non‐school sedentary behavior. Of all of the neighborhood factors we examined, reporting more physically active destinations contributed the largest absolute amount to the average girl's non‐school MW‐MVPA, according to this cross‐sectional study.     

Physical activity levels of normal-weight and overweight girls and boys during primary school recess

Objective: This study aimed to compare moderate‐to‐vigorous physical activity (MVPA) and vigorous physical activity (VPA) in normal‐weight and overweight boys and girls during school recess. Research Methods and Procedures: Four hundred twenty children, age 6 to 10 years, were randomly selected from 25 schools in England. Three hundred seventy‐seven children completed the study. BMI was calculated from height and weight measurements, and heart rate reserve thresholds of 50% and 75% reflected children's engagement in MVPA and VPA, respectively. Results: There was a significant main effect for sex and a significant interaction between BMI category and sex for the percent of recess time spent in MVPA and VPA. Normal‐weight girls were the least active group, compared with overweight boys and girls who were equally active. Fifty‐one boys and 24 girls of normal weight achieved the 40% threshold; of these, 30 boys and 10 girls exceeded 50% of recess time in MVPA. Eighteen overweight boys and 22 overweight girls exceeded the 40% threshold, whereas 8 boys and 8 girls exceeded the 50% threshold. Discussion: Overweight boys were significantly less active than their normal‐weight male counterparts; this difference did not hold true for girls. Even though nearly double the number of normal‐weight children achieved the 40% of MVPA during recess compared with overweight children, physical activity promotion in school playgrounds needs to be targeted not only at overweight but at other health parameters, as 40 overweight children met the 40% MVPA target proposed for recess.     

Treadmill desks: A 1‐year prospective trial

Objective: Sedentariness is associated with weight gain and obesity. A treadmill desk is the combination of a standing desk and a treadmill that allow employees to work while walking at low speed. Design and Methods: The hypothesis was that a 1‐year intervention with treadmill desks is associated with an increase in employee daily physical activity (summation of all activity per minute) and a decrease in daily sedentary time (zero activity). Employees (n = 36; 25 women, 11 men) with sedentary jobs (87 ± 27 kg, BMI 29 ± 7 kg/m², n = 10 Lean BMI < 25 kg/m², n = 15 Overweight 25 < BMI < 30 kg/m², n = 11 Obese BMI > 30 kg/m²) volunteered to have their traditional desk replaced with a treadmill desk to promote physical activity for 1 year. Results: Daily physical activity (using accelerometers), work performance, body composition, and blood variables were measured at Baseline and 6 and 12 months after the treadmill desk intervention. Subjects who used the treadmill desk increased daily physical activity from baseline 3,353 ± 1,802 activity units (AU)/day to, at 6 months, 4,460 ± 2,376 AU/day (P < 0.001), and at 12 months, 4,205 ± 2,238 AU/day (P < 0.001). Access to the treadmill desks was associated with significant decreases in daily sedentary time (zero activity) from at baseline 1,020 ± 75 min/day to, at 6 months, 929 ± 84 min/day (P < 0.001), and at 12 months, 978 ± 95 min/day (P < 0.001). For the whole group, weight loss averaged 1.4 ± 3.3 kg (P < 0.05). Weight loss for obese subjects was 2.3 ± 3.5 kg (P < 0.03). Access to the treadmill desks was associated with increased daily physical activity compared to traditional chair‐based desks; their deployment was not associated with altered performance. For the 36 participants, fat mass did not change significantly, however, those who lost weight (n = 22) lost 3.4 ± 5.4 kg (P < 0.001) of fat mass. Weight loss was greatest in people with obesity. Conclusions: Access to treadmill desks may improve the health of office workers without affecting work performance.     

The comparison of a technology-based system and an in-person behavioral weight loss intervention

The purpose of this study was to compare a technology‐based system, an in‐person behavioral weight loss intervention, and a combination of both over a 6‐month period in overweight adults. Fifty‐one subjects (age: 44.2 ± 8.7 years, BMI: 33.7 ± 3.6 kg/m²) participated in a 6‐month behavioral weight loss program and were randomized to one of three groups: standard behavioral weight loss (SBWL), SBWL plus technology‐based system (SBWL+TECH), or technology‐based system only (TECH). All groups reduced caloric intake and progressively increased moderate intensity physical activity. SBWL and SBWL+TECH attended weekly meetings. SBWL+TECH also received a TECH that included an energy monitoring armband and website to monitor energy intake and expenditure. TECH used the technology system and received monthly telephone calls. Body weight and physical activity were assessed at 0 and 6 months. Retention at 6 months was significantly different (P = 0.005) between groups (SBWL: 53%, SBWL+TECH: 100%, and TECH: 77%). Intent‐to‐treat (ITT) analysis revealed significant weight losses at 6 months in SBWL+TECH (?8.8 ± 5.0 kg, ?8.7 ± 4.7%), SBWL (?3.7 ± 5.7 kg, ?4.1 ± 6.3%), and TECH (?5.8 ± 6.6 kg, ?6.3 ± 7.1%) (P < 0.001). Self‐report physical activity increased significantly in SBWL (473.9 ± 800.7 kcal/week), SBWL+TECH (713.9 ± 1,278.8 kcal/week), and TECH (1,066.2 ± 1,371 kcal/week) (P < 0.001), with no differences between groups (P = 0.25). The TECH used in conjunction with monthly telephone calls, produced similar, if not greater weight losses and changes in physical activity than the standard in‐person behavioral program at 6 months. The use of this technology may provide an effective short‐term clinical alternative to standard in‐person behavioral weight loss interventions, with the longer term effects warranting investigation.     

Identification and validity of accelerometer cut-points for toddlers

The purpose of this study was to derive ActiGraph cut-points for sedentary (SED), light-intensity physical activity (LPA), and moderate-to-vigorous physical activity (MVPA) in toddlers and evaluate their validity in an independent sample. The predictive validity of established preschool cut-points were also evaluated and compared. Twenty-two toddlers (mean age = 2.1 years ± 0.4 years) wore an ActiGraph accelerometer during a videotaped 20-min play period. Videos were subsequently coded for physical activity (PA) intensity using the modified Children's Activity Rating Scale (CARS). Receiver operating characteristic (ROC) curve analyses were conducted to determine cut-points. Predictive validity was assessed in an independent sample of 18 toddlers (mean age = 2.3 ± 0.4 years). From the ROC curve analyses, the 15-s count ranges corresponding to SED, LPA, and MVPA were 0-48, 49-418, and >418 counts/15 s, respectively. Classification accuracy was fair for the SED threshold (ROC-AUC = 0.74, 95% confidence interval = 0.71-0.76) and excellent for MVPA threshold (ROC-AUC = 0.90, 95% confidence interval = 0.88-0.92). In the cross-validation sample, the toddler cut-point and established preschool cut-points significantly overestimated time spent in SED and underestimated time in spent in LPA. For MVPA, mean differences between observed and predicted values for the toddler and Pate cut-points were not significantly different from zero. In summary, the ActiGraph accelerometer can provide useful group-level estimates of MVPA in toddlers. The results support the use of the Pate cut-point of 420 counts/15 s for MVPA.     

Prior Exercise Increases Dietary Oleate,but Not Palmitate Oxidation

Objective: Higher levels of physical activity have been associated with body weight maintenance, but previous work in our laboratory suggests that this is not purely related to energy balance. We hypothesize that this may be related to the partitioning of dietary fat between oxidation and storage. Research Methods and Procedures: Healthy women (age 24 ± 1 years, BMI = 21.2 ± 0.4 kg/m²) were recruited to participate in rest (n = 10) or exercise sessions of light (n = 11), moderate (n = 10), and heavy (n = 7) exercise. All exercises (1250 kJ above rest) were performed on a stationary cycle inside of a whole‐body calorimeter. [1‐¹³C]oleate and [d₃₁]palmitate were given in a liquid meal 30 minutes post‐exercise. An additional study was done with identical exercise sessions, but with administration of an oral dose of [1‐¹³C]acetate and [d₃]acetate 30 minutes post‐exercise to determine label sequestration. Results: Cumulative oxidation of [1‐¹³C]oleate was significantly greater after light (45 ± 3%), moderate (54 ± 4%), and heavy (51 ± 4%) exercise than that with rest (33 ± 3%) (p = 0.0008). Cumulative oxidation of [d₃₁]palmitate did not differ among trials (12 ± 2%, 14 ± 1%, 17 ± 2%, and 14 ± 2% for rest, light, moderate, and heavy, respectively; p = 0.30). Discussion: Exercise standardized for energy expenditure increases monounsaturated fat oxidation more than saturated fat oxidation and that the increase occurs regardless of intensity. Recommendations for physical activity for the purposes of weight control may be specific for dietary fat composition.     

Validation and calibration of an accelerometer in preschool children

Objective: Obesity rates in young children are increasing, and decreased physical activity is likely to be a major contributor to this trend. Studies of physical activity in young children are limited by the lack of valid and acceptable measures. The purpose of this study was to calibrate and validate the ActiGraph accelerometer for use with 3‐ to 5‐year‐old children. Research Methods and Procedures: Thirty preschool children wore an ActiGraph accelerometer (ActiGraph, Fort Walton Beach, FL) and a Cosmed portable metabolic system (Cosmed, Rome, Italy) during a period of rest and while performing three structured physical activities in a laboratory setting. Expired respiratory gases were collected, and oxygen consumption was measured on a breath‐by‐breath basis. Accelerometer data were collected at 15‐second intervals. For cross‐validation, the same children wore the same instruments while participating in unstructured indoor and outdoor activities for 20 minutes each at their preschool. Results: In calibrating the accelerometer, the correlation between V?o ₂ (ml/kg per min) and counts was r = 0.82 across all activities. The only significant variable in the prediction equation was accelerometer counts (R² = 0.90, standard error of the estimate = 4.70). In the cross‐validation, the intraclass correlation coefficient between measured and predicted V?o ₂ was R = 0.57 and the Spearman correlation coefficient was R = 0.66 (p < 0.001). Cut‐off points for moderate‐ and vigorous‐intensity physical activity were identified at 420 counts/15 s (V?o ₂ = 20 mL/kg per min) and 842 counts/15 s (V?o ₂ = 30 mL/kg per min), respectively. When these cutpoints were applied to the cross‐validation data, percentage agreement, kappa, and modified kappa for moderate activity were 0.69, 0.36, and 0.38, respectively. For vigorous activity, the same measures were 0.81, 0.13, and 0.62. Discussion: Accelerometer counts were highly correlated with V?o ₂ in young children. Accelerometers can be appropriately used as a measure of physical activity in this population.     

Do More Active Children Sleep More? A Repeated Cross-Sectional Analysis Using Accelerometry

Aim

To determine whether levels of daytime physical activity are associated with sleep duration and night waking in children assessed using accelerometry, and if these associations change over time.

Methods

24-hour accelerometry data were obtained from 234 children at 3, 5 and 7 years of age for at least 5 days at each time. Sleep duration was estimated using the Sadeh algorithm. Time spent in sedentary, light and moderate-vigorous (MVPA) activity was established using published cut-points. Appropriate statistical techniques were utilised to account for the closed nature of the data (24-hour periods).

Results

Time spent asleep was related more to sedentary or light activity and not to MVPA. The most active (95^th percentile) children spent 55–84 fewer minutes asleep and 16–19 more minutes awake at night compared to the least active (5^th percentile) children. Children with later bedtimes slept less at night (30–40 minutes) and undertook more sedentary (10–15 minutes) but also more light (18–23 minutes) activity during the day. However, no differences in MVPA were apparent according to bedtime. Children slept slightly less on weekend nights (11 minutes) compared with week-nights, but only at 3 years of age. Most relationships were broadly similar at 3, 5 and 7 years of age.

Conclusion

Children who are more physically active during the day have shorter total sleep time and are more awake at night than less active children. The protective effect of sleep on obesity does not appear to be mediated by increased physical activity.     

Correlates of reported and recorded time spent in physical activity in working adults: results from the commuting and health in cambridge study

Background

The correlates of physical activity in adults are relatively well studied. However, many studies use self-reported (‘reported’) measures of activity and we know little about the possible differences between the correlates of reported and objective (‘recorded’) measures of physical activity. We compared the correlates of reported and recorded time spent in moderate-to-vigorous physical activity (MVPA) in a sample of working adults.

Methods

In 2009, participants in the Commuting and Health in Cambridge study completed questionnaires assessing individual, socio-demographic, health and contextual characteristics. Recorded time spent in MVPA over seven days was ascertained using accelerometers and reported time spent in MVPA was assessed using the Recent Physical Activity Questionnaire (RPAQ). Correlates of MVPA were investigated using sex-specific linear regression models.

Results

486 participants (70% women) provided both reported and recorded physical activity data. 89% recorded at least 30 minutes of MVPA per day. In men, none of the potential explanatory variables were associated with both reported and recorded time spent in MVPA. In women, of all the potential explanatory variables only that of having a standing or manual occupation was associated with both reported (+42 min/day; 95% CI 16.4 to 68.4, p = 0.001) and recorded (+9 min/day; 95% CI: 3.5 to 15.7, p = 0.002) time spent in MVPA.

Discussion

The use of an objective measure of physical activity may influence the correlates which are observed. Researchers may wish to consider using and analysing recorded and reported measures in combination to gain a more complete view of the correlates of physical activity.     

Moderate Intense Physical Activity Depends on Selected Metabolic Equivalent of Task (MET) Cut-Off and Type of Data Analysis

Background

Accelerometry data are frequently analyzed without considering whether moderate-to-vigorous physical activities (MVPA) were performed in bouts of >10 minutes as defined in most physical activity guidelines. We aimed i) to quantify MVPA by using different commonly-applied physical activity guidelines, ii) to investigate the effect of bouts versus non-bouts analysis, and iii) to propose and validate a MVPA non-bouts cut-point to classify (in-) active subjects.

Methods

Healthy subjects (n=110;62±6yrs) and patients with Chronic Obstructive Pulmonary Disease (COPD) (n=113;62±5yrs) wore an activity monitor for 7 days. Three Metabolic Equivalent of Task (MET) cut-offs and one individual target (50% VO₂ reserve) were used to define MVPA. First, all minutes of MVPA were summed up (NON-BOUTS). Secondly, only minutes performed in bouts of >10 minutes continuous activity were counted (BOUTS). Receiver operating characteristic (ROC) curve analyses were used to propose and (cross-) validate new MVPA non-bout cut-points based on the criterion of 30 minutes MVPA per day (BOUTS). Likelihood ratios (sensitivity/[1-specificity]) were used to express the association between the proposed MVPA non-bout target and the MVPA bout target of 30 min*day^-1.

Results

MVPA was variable across physical activity guidelines with lowest values for age-specific cut-offs. Selecting a METs cut-point corresponding to 50% VO₂ reserve revealed no differences in MVPA between groups. MVPA’s analyzed in BOUTS in healthy subjects were 2 to 4 fold lower than NON-BOUTS analyses and this was even 3 to 12 fold lower in COPD. The MVPA non-bouts cut-point of 80 min*day^-1 using a 3 METs MVPA threshold delivered positive likelihood ratios of 5.1[1.5-19.6] (healthy subjects) and 2.3[1.6-3.3] (COPD).

Conclusion

MVPA varies upon the selected physical activity guideline/targets and bouts versus non-bouts analysis. Accelerometry measured MVPA non-bouts target of 80 min*day^-1, using a 3 METs MVPA threshold, is associated to the commonly-used MVPA bout target of 30 min*day^-1.     

Objectively measured sedentary behavior,physical activity,and plasma lipids in overweight and obese children

Objective:

This study examines the associations between objectively measured sedentary behavior, light physical activity (LPA), and moderate‐to‐vigorous physical activity (MVPA), and plasma lipids in overweight and obese children.

Design and Methods:

Cross‐sectional analyses were conducted among 126 children aged 5.5‐9.9 years. Sedentary behavior, LPA, and MVPA were assessed using accelerometry. Fasting blood samples were analyzed for plasma lipids (high‐density lipoprotein cholesterol [HDL‐C], low‐density lipoprotein cholesterol [LDL‐C], total cholesterol [TC], and triglycerides [TG]).

Results:

MVPA was not related to plasma lipids (P > 0.05). Independent of age, sex, energy intake, and waist circumference z‐score, sedentary behavior and LPA were associated with HDL‐C (β = ?0.23, 95% CI ?0.42 to ?0.04, P = 0.020; β = 0.20, 95% CI 0.14 to 0.39, P = 0.036, respectively). The strength of the associations remained after additionally adjusting for MVPA (sedentary behavior: β = ?0.22, 95% CI ?0.44 to 0.006, P = 0.056; LPA: β = 0.19, 95% CI ?0.005 to 0.38, P = 0.056, respectively).

Conclusion:

Substituting at least LPA for sedentary time may contribute to the development of healthy HDL‐C levels among overweight and obese children, independent of their adiposity. Comprehensive prevention and treatment strategies to improve plasma HDL‐C among overweight and obese children should target reductions in total sedentary time and promote the benefits of LPA, in addition to promoting healthy levels of adiposity, healthy dietary behaviors, and MVPA.

     

Low Plasma Leptin Concentration and Low Rates of Fat Oxidation in Weight‐Stable Post‐Obese Subjects

Objective: A low resting metabolic rate for a given body size and composition, a low rate of fat oxidation, low levels of physical activity, and low plasma leptin concentrations are all risk factors for body weight gain. The aim of the present investigation was to compare resting metabolic rate (RMR), respiratory quotient (RQ), levels of physical activity, and plasma leptin concentrations in eight post‐obese adults (2 males and 6 females; 48.9 ± 12.2 years; body mass index [BMI]: 24.5 ± 1.0 kg/m²; body fat 33 ± 5%; mean ± SD) who lost 27.1 ± 21.3 kg (16 to 79 kg) and had maintained this weight loss for ≥2 months (2 to 9 months) to eight age‐ and BMI‐matched control never‐obese subjects (1 male and 7 females; 49.1 ± 5.2 years; BMI 24.4 ± 1.0 kg/m²; body fat 33 ± 7%). Research Methods and Procedures: Following 3 days of weight maintenance diet (50% carbohydrate and 30% fat), RMR and RQ were measured after a 10‐hour fast using indirect calorimetry and plasma leptin concentrations were measured using radioimmunoassay. Levels of physical activity were estimated using an accelerometer over a 48‐hour period in free living conditions. Results: After adjustment for fat mass and fat‐free mass, post‐obese subjects had, compared with controls, similar levels of physical activity (4185 ± 205 vs. 4295 ± 204 counts) and similar RMR (1383 ± 268 vs. 1430 ± 104 kcal/day) but higher RQ (0.86 ± 0.04 vs. 0.81 ± 0.03, p < 0.05). Leptin concentration correlated positively with percent body fat (r = 0.57, p < 0.05) and, after adjusting for fat mass and fat‐free mass, was lower in post‐obese than in control subjects (4.5 ± 2.1 vs. 11.6 ± 7.9 ng/mL, p < 0.05). Discussion: The low fat oxidation and low plasma leptin concentrations observed in post‐obese individuals may, in part, explain their propensity to relapse.     

Physical Activity,Sedentary Time and Physical Capability in Early Old Age: British Birth Cohort Study

PurposeTo investigate the associations of time spent sedentary, in moderate-to-vigorous-intensity physical activity (MVPA) and physical activity energy expenditure (PAEE) with physical capability measures at age 60-64 years.MethodsTime spent sedentary and in MVPA and, PAEE were assessed using individually calibrated combined heart rate and movement sensing among 1727 participants from the MRC National Survey of Health and Development in England, Scotland and Wales as part of a detailed clinical assessment undertaken in 2006-2010. Multivariable linear regression models were used to examine the cross-sectional associations between standardised measures of each of these behavioural variables with grip strength, chair rise and timed up-&-go (TUG) speed and standing balance time.ResultsGreater time spent in MVPA was associated with higher levels of physical capability; adjusted mean differences in each capability measure per 1standard deviation increase in MVPA time were: grip strength (0.477 kg, 95% confidence interval (CI): 0.015 to 0.939), chair rise speed (0.429 stands/min, 95% CI: 0.093 to 0.764), standing balance time (0.028 s, 95% CI: 0.003 to 0.053) and TUG speed (0.019 m/s, 95% CI: 0.011 to 0.026). In contrast, time spent sedentary was associated with lower grip strength (-0.540 kg, 95% CI: -1.013 to -0.066) and TUG speed (-0.011 m/s, 95% CI: -0.019 to -0.004). Associations for PAEE were similar to those for MVPA.ConclusionHigher levels of MVPA and overall physical activity (PAEE) are associated with greater levels of physical capability whereas time spent sedentary is associated with lower levels of capability. Future intervention studies in older adults should focus on both the promotion of physical activity and reduction in time spent sedentary.     

Validation of the TracmorD Triaxial Accelerometer to Assess Physical Activity in Preschool Children

Objectives: To assess validity evidence of Tracmor_D to determine energy used for physical activity in 3‐4‐year‐old children. Design and Methods: Participants were randomly selected from GECKO Drenthe cohort (n = 30, age 3.4 ± 0.3 years). Total energy expenditure (TEE) was measured using the doubly labeled water method. Sleeping metabolic rate (SMR) was measured by indirect calorimetry (Deltatrac). TEE and SMR were used to calculate physical activity level (PAL) and activity energy expenditure (AEE). Physical activity was monitored using a DirectLife triaxial accelerometer, Tracmor_D with activity counts per minute (ACM) and activity counts per day (ACD) as outcome measures. Results: The best predictor for PAL was ACM with gender and weight, the best predictor for AEE was ACM alone (backward regression, R² = 0.50, P = 0.010 and R² = 0.31, P = 0.011, respectively). With ACD, the prediction model for PAL included ACD, height, gender, and sleep duration (R² = 0.48, P = 0.033), the prediction model for AEE included ACD, gender and sleep duration (R² = 0.39, P = 0.042). The accelerometer was worn for 5 days, but 3 days did not give a different estimated PAL. Conclusion: Tracmor_D provides moderate‐to‐strong validity evidence that supports its use to evaluate energy used for physical activity in 3‐4‐year‐old children.