60-s Epochs Research Articles

Accelerometer-assessed physical activity and sedentary time among colon cancer survivors: associations with psychological health outcomes.

The purpose of this study was to determine associations of objectively assessed moderate-to-vigorous intensity physical activity (MVPA) and sedentary time with psychological health outcomes including depression symptoms, anxiety symptoms, and overall satisfaction with life in colon cancer survivors. Colon cancer survivors (N = 180) from Alberta, Canada (n = 91), and Western Australia (n = 89) completed a mailed survey that assessed depression symptom severity, state anxiety, and satisfaction with life (SWL). Sedentary time and MVPA were assessed using the Actigraph(®) GT3X+ accelerometer (60-s epochs) via a 7-day monitoring protocol. MVPA and sedentary time were corrected for wear time and then examined as quartiles (Q). Multivariate analysis of variance was used to examine associations of MVPA and sedentary time with psychological health. There was a significant association between psychological health outcomes and objectively assessed MVPA [Wilks' λ = 0.886, F(3382.2) = 2.156, p = 0.024] that suggested a small and significant association between MVPA and SWL (p = 0.032). A significant multivariate analysis of variance (MANOVA) [Wilks' λ = 0.945, F(3159) = 3.1, p = 0.028] suggested participants meeting guidelines reported significantly fewer anxiety symptoms (M(diff) = -1.23, p = 0.027) and higher perceptions of SWL (M(diff) = 3.0, p = 0.008). No significant associations emerged for sedentary time [Wilks' λ = 0.956, F(9382.3) = 0.788, p = 0.628]. Contrary to previously published research using self-reports, objectively assessed MVPA and sedentary time were not associated with depression symptoms. Objectively assessed MVPA was associated with SWL and anxiety outcomes in colon cancer survivors. Colon cancer survivors should continue to engage in regular and sustained MVPA for the accrual of psychological health benefits.

Agreement between accelerometer-assessed and self-reported physical activity and sedentary time in colon cancer survivors

Research conducted on the general population indicates self-reported measures of physical activity and sedentary behaviour are inaccurate when compared with objective measures; however, it is not clear if this also applies to cancer survivors. In this study, we compared accelerometer-based and self-reported measures of moderate- to vigorous-intensity physical activity (MVPA) and sedentary time among colon cancer survivors. A total of 176 colon cancer survivors, recruited from the Western Australia and Alberta cancer registries, wore an Actigraph GT3X+ accelerometer for 7 days and completed self-reported questions about recent MVPA (Godin Leisure-Time Exercise Questionnaire) and usual sedentary time (Marshall Domain-Specific Sitting Questionnaire). Accelerometer data were processed using 60-s epochs and summarized using Freedson's cut points. Spearman's rho and intraclass correlation coefficients (ICCs) were used to assess correlation and agreement for daily MVPA and sedentary time estimates from the two methods. Total mean minutes per day spent in MVPA was 12 min based on accelerometer data and 26 min based on self-reported data (P Difference < 0.01). Correlation between the methods was fair (rho = 0.51); however, agreement was poor (ICC = 0.33). Mean daily time spent sedentary was similar in both methods (∼8.5 h); however, both correlation and agreement were poor (rho = 0.19, ICC = 0.16). We found fair correlation but poor agreement between the self-reported and accelerometer-based assessments of MVPA used in this study. For sedentary time, both correlation and agreement between the two methods were poor. Studies of colon cancer survivors using these self-report measures are likely to have a considerable amount of exposure misclassification.

Isoflurane and ketamine anesthesia have different effects on ventilatory pattern variability in rats

We hypothesize that isoflurane and ketamine impact ventilatory pattern variability (VPV) differently. Adult Sprague-Dawley rats were recorded in a whole-body plethysmograph before, during and after deep anesthesia. VPV was quantified from 60-s epochs using a complementary set of analytic techniques that included constructing surrogate data sets that preserved the linear structure but disrupted nonlinear deterministic properties of the original data. Even though isoflurane decreased and ketamine increased respiratory rate, VPV as quantified by the coefficient of variation decreased for both anesthetics. Further, mutual information increased and sample entropy decreased and the nonlinear complexity index (NLCI) increased during anesthesia despite qualitative differences in the shape and period of the waveform. Surprisingly mutual information and sample entropy did not change in the surrogate sets constructed from isoflurane data, but in those constructed from ketamine data, mutual information increased and sample entropy decreased significantly in the surrogate segments constructed from anesthetized relative to unanesthetized epochs. These data suggest that separate mechanisms modulate linear and nonlinear variability of breathing.

Accuracy of a New Time-Resolved Step Counter in Children

Most pedometers record cumulative steps, limiting ability to assess level of physical activity or nonwear periods. The SportBrain iStep X1 has potential to overcome this limitation by recording and storing step count data in 60-s epochs. We evaluated accuracy of this instrument in children and the duration of consecutive zero step count minutes that indicated nonwear time periods. Seventeen children walked or ran on a treadmill at 2, 3, 4 and 5 miles/hour and walked around a track while wearing the SportBrain and Digiwalker SW-701 pedometer. We compared percent error in step counts for each pedometers relative to observer counts. A subsample wore a SportBrain pedometer during up to 5 days of usual activity. The SportBrain pedometer performed with acceptable accuracy at all evaluated treadmill speeds and during self-paced walking, recording steps within an average of 4% of observed step counts. It outperformed the Digiwalker, especially at slower speeds and in overweight children. During normal wear only 1% of zero count periods were more than 60 min. We conclude that the SportBrain iStep X1 pedometer provides a valid measure of step counts in short averaging times useful for assessing patterns of physical activity in population studies and periods of nonwear.

OP16 How is Objectively Measured Physical Activity Associated with Falls and fear of Falling in Older Community Dwelling Men?

BackgroundFalls are a major cause of disability in older age and fear of falling (FOF) may limit physical activity. Associations between falls, fear of falling and objectively measured physical activity...

Comparison of Epoch and Uniaxial Versus Triaxial Accelerometers in the Measurement of Physical Activity in Preschool Children: A Validation Study

The objectives of this study were to explore whether triaxial is more accurate than uniaxial accelerometry and whether shorter sampling periods (epochs) are more accurate than longer epochs. Physical activity data from uniaxial and triaxial (RT3) devices were collected in 1-s epochs from 31 preschool children (15 males, 16 females, 4.4 ± 0.8 yrs) who were videoed while they engaged in 1-hr of free-play. Video data were coded using the Children's Activity Rating Scale (CARS). A significant difference (p < .001) in the number of minutes classified as moderate to vigorous physical activity (MVPA) was found between the RT3 and the CARS (p < .002) using the cut point of relaxed walk. No significant difference was found between the GT1M and the CARS or between the RT3 and the CARS using the cut point for light jog. Shorter epochs resulted in significantly greater overestimation of MVPA, with the bias increasing from 0.7 mins at 15-s to 3.2 mins at 60-s epochs for the GT1M and 0 mins to 1.7 mins for the RT3. Results suggest that there was no advantage of a triaxial accelerometer over a uniaxial model. Shorter epochs result in significantly higher number of minutes of MVPA with smaller bias relative to direct observation.

Moderate and vigorous physical activity intensity cut-points for the Actical accelerometer

Accelerometry is increasingly used as a physical activity surveillance device that can quantify the amount of time spent moving at a range of intensities. This study proposes physical activity intensity cut-points for the Actical accelerometer. Thirty-eight volunteers completed a multi-stage treadmill protocol at 3, 5, and 8 km · h−1 (2, 3.3, and 8 METs) while wearing Actical accelerometers initialized to collect data in 60-s epochs. Using a decision boundary analytical approach, moderate and vigorous physical activity intensity cut-points were derived for the Actical accelerometer. In adults (n = 26), the cut-point for moderate physical activity intensity occurred at 1535 counts per minute and the vigorous cut-point occurred at 3960 counts per minute. In children (n = 12), the cut-point for moderate physical activity intensity occurred at 1600 counts per minute and the vigorous cut-point occurred at 4760 counts per minute. Improved classification of physical activity intensity using the decision boundary cut-points was observed compared with using mean values for each protocol stage. The cut-points derived are recommended for use in adults. The cut-points derived for children confirm the findings of previous studies.

Epoch Length and Its Effect on Physical Activity Intensity

Researchers have begun to investigate the issue of epoch length on children's physical activity using small sample sizes, and to date, no studies have been conducted in adolescents. The purpose of this study was to investigate the effect of different epoch lengths (5, 15, 30, and 60 s) on derived levels of physical activity in both a child and an adolescent sample. Three hundred and eleven children age 7-11 yr and 234 adolescents age 12-16 yr were asked to wear an accelerometer during waking hours for 7 d. The epoch was set at 5 s, and when data were downloaded, the activity counts were then reintegrated into 15-, 30-, and 60-s epochs. A significant epoch effect was seen for time spent in vigorous physical activity, light physical activity, and rest in the child and adolescent samples and moderate-to-vigorous and moderate physical activities in the child sample only. The Bland-Altman analysis showed reasonable agreement on moderate-to-vigorous, moderate, vigorous, and light physical activities and rest between 5- and 15-, 5- and 30-, and 30- and 60-s epochs in the child sample and between 5- and 15-, 5- and 30-, and 15- and 30-s epochs in the adolescent sample. A short epoch is strongly recommended for child and adolescent samples to obtain a "real" picture of young people's physical activity behavior and to prevent accumulation of counts reflecting the average activity level when longer epochs are used. Activity prevalence studies using epoch lengths of 5 and 60 s in a child or an adolescent sample should not be compared nor should 15- and 60- and 30- and 60-s epochs in an adolescent sample.

Assessment of EEG dynamical complexity in Alzheimer’s disease using multiscale entropy

Multiscale entropy (MSE) is a recently proposed entropy-based index of physiological complexity, evaluating signals at multiple temporal scales. To test this method as an aid to elucidating the pathophysiology of Alzheimer's disease (AD), we examined MSE in resting state EEG activity in comparison with traditional EEG analysis. We recorded EEG in medication-free 15 presenile AD patients and 18 age- and sex-matched healthy control (HC) subjects. MSE was calculated for continuous 60-s epochs for each group, concurrently with power analysis. The MSE results from smaller and larger scales were associated with higher and lower frequencies of relative power, respectively. Group analysis demonstrated that the AD group had less complexity at smaller scales in more frontal areas, consistent with previous findings. In contrast, higher complexity at larger scales was observed across brain areas in AD group and this higher complexity was significantly correlated with cognitive decline. MSE measures identified an abnormal complexity profile across different temporal scales and their relation to the severity of AD. These findings indicate that entropy-based analytic methods with applied at temporal scales may serve as a complementary approach for characterizing and understanding abnormal cortical dynamics in AD.

Assessing Physical Activity In Girls Using Accelerometry - 60s Versus 10s Sampling Intervals

Children exhibit physical activity patterns mainly comprised of sporadic and intermittent bouts, each lasting under 15s in duration. Despite this fact, most studies utilize a 60s accelerometry sampling interval to objectively quantify physical activity in youths. This relatively long sampling interval may underestimate children's true physical activity behaviour. PURPOSE: To assess the difference in intensity, duration and number of continuous bouts of physical activity in children and adolescents when using accelerometry intervals of 60s vs. 10s. METHODS: A total of 106 girls and adolescents (mean = 13.0 ± 2.6 yrs old) wore ActiGraph GT1M accelerometers for all waking hours (except while bathing, swimming, etc.) over seven days. Accelerometers were set at 10s epochs and the raw data was subsequently re-integrated into 60s epochs. From data of both epoch lengths, daily bouts of moderate (MPA; 3-5.9 METs), vigorous (VPA; 6-8.9 METs) and very vigorous (VVPA; ≥9 METs) activities were quantified using a Visual Basic data reduction program. The number of continuous 5 min, 10 min and 20 min bouts at each intensity was also calculated. RESULTS: There was no difference in total MPA minutes between the 10s and 60s analysis. Total VPA, and VVPA were 80.4%, and 61.5% greater in the 10s sampling than in the 60s integrated sampling, respectively (p<0.01). When examining continuous bouts of activity, the 10s analysis generally resulted in more continuous bouts compared with the 60s analysis, especially when examining 5 min bouts of MPA (19.1%), 20 min bouts of VPA (14.6%), and of VVPA (0.9%)(p<0.01). CONCLUSION: The commonly used 60s accelerometry sampling interval underestimates the amount of physical activity that children and adolescents engage in, especially at the higher intensity levels. Thus, a sampling interval of 10s or less is warranted to better assess physical activity levels of different intensities in children and adolescents.

Epoch Length and Accelerometer Outputs in Children

To determine the effects of epoch length and activity count cutpoints on ActiGraph (AG; ActiGraph Health Services, Pensacola, FL) accelerometer estimates of time in moderate-to-vigorous physical activity (MVPA) in fifth-grade children monitored during physical education (PE) compared with a direct observation (DO) criterion standard. A sample of 32 fifth-grade males and females (mean age = 10.3 +/- 0.5 yr) wore an AG attached at the waist for a 30-min PE class. Participants were concurrently videotaped, and the Computerized System for Observing Fitness Instruction Time (C-SOFIT) was used to create a DO measure of MVPA time (DO_MVPA). AG data were collected in 5-s epochs then integrated into 10-, 15-, 20-, 30-, and 60-s epochs. AG activity counts were converted into time (in s) in MVPA using validated (and epoch-adjusted) children's activity count cutpoints established by Treuth et al. (AG_T), Mattocks et al. (AG_M), and Freedson et al. (AG_F). All AG_T and AG_M epoch detected significantly lower time in MVPA than DO_MVPA. The percentage of DO_MVPA detected by AG_T and AG_M epochs ranged from 46% to 61% and from 26% to 47%, respectively. All AG_F epochs yielded similar (i.e., nonsignificant) mean estimates of MVPA versus DO_MVPA, with modest increases in root mean squared error (RMSE) with increasing epoch length. The percentage of DO_MVPA detected by AG_F epochs ranged from 93% to 100%. All AG_F epoch lengths provide comparable mean estimates to DO-detected MVPA time in fifth-grade children during PE. To minimize error among individual estimates, shorter epoch lengths should be used, with 5-s epochs yielding the lowest RMSE in the current study. Considerations of both epoch length and activity count cutpoint are important to improved detection of intermittent bouts of MVPA among fifth-grade children.

Experimental Design and the Relative Sensitivity of BOLD and Perfusion fMRI

This paper compares the statistical power of BOLD and arterial spin labeling perfusion fMRI for a variety of experimental designs within and across subjects. Based on theory and simulations, we predict that perfusion data are composed of independent observations in time under the null hypothesis, in contrast to BOLD data, which possess marked autocorrelation. We also present a method (sinc subtraction) of generating perfusion data from its raw source signal that minimizes the presence of oxygen-sensitive signal changes and can be used with any experimental design. Empirically, we demonstrate the absence of autocorrelation in perfusion noise, examine the shape of the hemodynamic response function for BOLD and perfusion, and obtain a measure of signal to noise for each method. This information is then used to generate a model of relative sensitivity of the BOLD and perfusion methods for within-subject experimental designs of varying temporal frequency. It is determined that perfusion fMRI provides superior sensitivity for within-subject experimental designs that concentrate their power at or below ∼0.009 Hz (corresponding to a “blocked” experimental design of 60-s epochs). Additionally, evidence is presented that across-subject hypothesis tests may be more sensitive when conducted using perfusion imaging, despite the better within-subject signal to noise obtained in some cases with BOLD.