Vector Magnitude Counts Research Articles

Physical activity cut-points for older adults using the Zio XT onboard accelerometer

IntroductionThe Zio® XT continuous ambulatory electrocardiographic monitor (Zio) contains an accelerometer that can help quantify an individual’s physical activity in the free-living environment.Purpose(1) To estimate activity cut-points to estimate daily time spent performing very light, light, or moderate to vigorous physical activity (VLIPA, LIPA, MVPA) for the Zio accelerometer. (2) To describe how Zio’s 24-h wear protocol affects estimates of daily MVPA relative to a waist-worn accelerometer’s waking-wear protocol.MethodsThree hundred eighty one participants from the Atherosclerosis Risk in Communities (ARIC) study wore a waist-mounted ActiGraph GT3X (except while sleeping or water-based activities) and a Zio (24-h) simultaneously for three to seven days. For each person-minute, physical activity was summarized as the Mean Amplitude Deviation (MAD) for the Zio and Vector Magnitude Counts (VMC) for the GT3X. Cut points previously used in ARIC were mapped from GT3X VMC to Zio MAD using a conditional two-sample quantile–quantile approach.ResultsEvenson VMC cut-points for the GT3X (VLIPA≥76, LIPA≥903, MVPA≥2075 counts/min) were mapped to MAD for Zio (9.04, 28.2, and 58.1 mili-g). Daily hours spent in each intensity category were each strongly correlated (ICC > 0.7) between summaries produced by Zio and GT3X when restricting estimates to overlapping wear time. Zio and GT3X-estimated MVPA had high agreement (ICC = 0.77) when using device-specific wear time, but Zio measured one hour more of daily LIPA and VLIPA (95% CI = 0.83, 1.07 hrs/day).ConclusionsWe recommend the use of our cut-points for clinical research with Zio accelerometry in populations of older adults.

Comparison of Sleep and Physical Activity Metrics From Wrist-Worn ActiGraph wGT3X-BT and GT9X Accelerometers During Free-Living in Adults

Background: ActiGraph accelerometers can monitor sleep and physical activity (PA) during free-living, but there is a need to confirm agreement in outcomes between different models. Methods: Sleep and PA metrics from two ActiGraphs were compared after participants (N = 30) wore a GT9X and wGT3X-BT on their nondominant wrist for 7 days during free-living. PA metrics including total steps, counts, average acceleration—Euclidean Norm Minus One (ENMO) and Mean Amplitude Deviation, intensity gradient, the minimum acceleration value of the most active 10 and 30 min (M10, M30), time spent in activity intensities from vector magnitude (VM) counts, and ENMO cut points and sleep metrics (sleep period time window, sleep duration, sleep onset, and waking time) were compared. Results: Excellent agreement was evident for average acceleration-Mean Amplitude Deviation, counts, total steps, M10, and light PA (VM counts) with good agreement evident from the remaining PA metrics apart from moderate–vigorous PA (VM counts) which demonstrated moderate agreement. Mean bias for all PA metrics were low, as were the limits of agreement for the intensity gradient, average acceleration-Mean Amplitude Deviation, and inactive time (ENMO and VM counts). The limits of agreement for all other PA metrics were >10%. Excellent agreement, low mean bias, and narrow limits of agreement were evident for all sleep metrics. All sleep and PA metrics demonstrated equivalence (equivalence zone of ≤10%) apart from moderate–vigorous PA (ENMO) which needed an equivalence zone of 16%. Conclusions: Equivalent estimates of almost all PA and sleep metrics are provided from the GT9X and wGT3X-BT worn on the nondominant wrist.

Actigraphy methodology in the Kids Mod PAH trial: Physical activity as a functional endpoint in pediatric clinical trials.

Pulmonary vasodilator treatment can improve hemodynamics, right ventricular function, symptoms, and survival in pediatric pulmonary hypertension (PH). However, clinical trial data are lacking due to many constraints. One major limitation is the lack of relevant trial endpoints reflective of hemodynamics or functional status in patients in whom standard exercise testing is impractical, unreliable, or not reproducible. The Kids Mod PAH trial (Mono- vs. Duo Therapy for Pediatric Pulmonary Arterial Hypertension) is an ongoing multicenter, Phase III, randomized, open-label, pragmatic trial to compare the safety and efficacy of first-line combination therapy (sildenafil and bosentan) to first-line monotherapy (sildenafil alone) in 100 pediatric patients with PH across North America. Investigators will measure participants' physical activity with a research-grade, wrist-worn actigraphy device at multiple time points as an exploratory secondary outcome. Vector magnitude counts per minute and activity intensity will be compared between the treatment arms. By directly and noninvasively measuring physical activity in the ambulatory setting, we aim to identify a novel, simple, inexpensive, and highly reproducible approach for quantitative assessment of exercise tolerance in pediatric PH. These data will increase the field's understanding of the effect of pulmonary vasodilator treatment on daily activity - a quantitative measure of functional status and wellbeing in pediatric PH and a potential primary outcome for future clinical trials in children with cardiopulmonary disorders.

Physical activity and cognitive function: moment-to-moment and day-to-day associations

BackgroundThe beneficial effect of acute physical exercise on cognitive performance has been studied in laboratory settings and in long-term longitudinal studies. Less is known about these associations in everyday environment and on a momentary timeframe. This study investigated momentary and daily associations between physical activity and cognitive functioning in the context of everyday life.MethodsMiddle-aged adults (n = 291, aged 40–70) were asked to wear accelerometers and complete ecological momentary assessments for eight consecutive days. Processing speed and visual memory were assessed three times per day and self-rated evaluations of daily cognition (memory, thinking, and sharpness of mind) were collected each night. The number of minutes spent above the active threshold (active time) and the maximum vector magnitude counts (the highest intensity obtained) before each cognitive test and at a daily level were used as predictors of momentary cognitive performance and nightly subjective cognition. Analyses were done with multilevel linear models. The models were adjusted for temporal and contextual factors, age, sex, education, and race/ethnicity.ResultsWhen participants had a more active time or higher intensity than their average level within the 20 or 60 minutes prior to the cognitive test, they performed better on the processing speed task. On days when participants had more active time than their average day, they rated their memory in the evening better. Physical activity was not associated with visual memory or self-rated thinking and sharpness of mind.ConclusionsThis study provides novel evidence that outside of laboratory settings, even small increases in physical activity boost daily processing speed abilities and self-rated memory. The finding of temporary beneficial effects is consistent with long-term longitudinal research on the cognitive benefits of physical activity.

Association of Parkinson’s disease status with accelerometer-derived physical activity and sedentary behavior in older women: The Women’s Health Study (WHS)

Evidence suggests that individuals diagnosed with Parkinson’s Disease (PD) spend less time in moderate-to-vigorous intensity physical activity (MVPA) compared to those without PD. However, prior studies primarily included men and did not consider movement across the entire intensity spectrum. To address these gaps, the association of PD status with total volume physical activity and time spent in sedentary, low light-intensity physical activity (LLPA), high light-intensity physical activity (HLPA), and MVPA among older women was examined. This is a cross-sectional analysis of 17,466 ambulatory women enrolled in the Women’s Health Study (WHS) with a median (IQR) age of 70 (67–75) years who were asked to wear an accelerometer for 7 days from 2011 to 2015 for the ancillary study. Reported PD status was assessed via annual mail-in questionnaires prior to device wear. Compared to those without PD (n = 16,661), PD (n = 80) was associated with 98,400 fewer vector magnitude (VM) counts per day and with spending an average of 23.2 more minutes per day sedentary and 10.5 more minutes per day in LLPA. Further, PD was associated with spending 6.4 and 27.3 fewer minutes per day in HLPA and MVPA, respectively, compared to women without PD. PD in women is associated with more daily sedentary time and less time spent in health-enhancing physical activity. Prevention strategies to promote physical activity should be emphasized to enhance health and limit progression of disability in women living with PD.

Measurement of Physical Activity by Actigraphy in Infants and Young Children with Pulmonary Arterial Hypertension

To evaluate the feasibility, tolerability, and adherence with wearable actigraphy devices among infants and children with pulmonary arterial hypertension (PAH). This multicenter, prospective, observational study included children ages 0-6years with and without PAH. Participants wore the ActiGraph wGT3X-BT on the hip and FitBit Inspire on the wrist during waking hours for 14days. Steps, vector magnitude counts per minute, activity intensity, heart rate, and heart rate variability were compared between groups. Forty-seven participants (18 PAH, 29 control) were enrolled from 10 North American sites. PAH patients were mostly functional class II (n=16, 89%) and treated with oral medications at the time of enrollment. The number of wear days was not significantly different between the groups (ActiGraph: 10 [95% CI: 5.5, 12.2] in PAH vs 8 [4, 12] in control, P=.20; FitBit 13 [10, 13.8] in PAH vs 12 [8, 14] in control, P=.87). Complete data were obtained in 81% of eligible ActiGraph participants and 72% of FitBit participants. PAH participants demonstrated fewer steps, lower vector magnitude counts per minute, more sedentary activity, and less intense physical activity at all levels compared with control participants. No statistically significant differences in heart rate variability were demonstrated between the 2 groups. Measurement of physical activity and other end points using wearable actigraphy devices was feasible in young children with PAH. Larger studies should determine associations between physical activity and disease severity in young patients with PAH to identify relevant end points for pediatric clinical trials.

Convergent Validity Between Epoch-Based activPAL and ActiGraph Methods for Measuring Moderate to Vigorous Physical Activity in Youth and Adults

Purpose: We investigated convergent validity of commonly used ActiGraph scoring methods with various activPAL scoring methods in youth and adults. Methods: Youth and adults wore an ActiGraph and activPAL simultaneously for 1–3 days. We compared moderate to vigorous physical activity (MVPA) estimates from the ActiGraph Evenson 15-s (youth) and Freedson 60-s (adult) cut-point scoring methods and four activPAL scoring methods based on metabolic equivalents (METs), step counts, vertical axis counts, and vector magnitude counts. All activPAL methods were applied to 15-s epochs for youth and 60-s epochs for adults, and the METs method was also applied to 1-s epochs. Epoch-level agreement was examined with classification tests (sensitivity, positive predictive value, and F1) using the ActiGraph methods as the referent. Day-level agreement was examined using tests of mean error, mean absolute error, and Spearman correlations. Results: Relative to ActiGraph methods, which indicated a mean MVPA of 41 min/day for youth and 24 min/day for adults, the activPAL METs method applied to 15-s epochs in youth and 60-s epochs in adults yielded the most comparable estimates of MVPA. Daily MVPA estimated from all other activPAL scoring methods generally had poor agreement with ActiGraph methods in youth and adults. Conclusion: When using the same epoch lengths between monitors, MVPA estimation via the activPAL METs scoring method appears to have good comparability to ActiGraph cut points at the group-level and moderate comparability at the individual-level in youth and adults. When using this scoring method, the activPAL appears to be appropriate for measuring daily minutes of MVPA in youth and adults.

Calibrating Physical Activity and Sedentary Behavior for Hip-Worn Accelerometry in Older Women With Two Epoch Lengths: The Women's Health Initiative Objective Physical Activity and Cardiovascular Health Calibration Study.

The purpose of this study was to develop 60-second epoch accelerometer intensity cutpoints for vertical axis count and vector magnitude (VM) output from hip-worn tri-axial accelerometers among women 60-91 years. We also compared these cutpoints against cutpoints derived by multiplying 15-second epoch cutpoints by four. Two hundred apparently healthy women wore an ActiGraph GT3X+ accelerometer on their hip while performing a variety of laboratory-based activities that were sedentary (watching television, assembling a puzzle), low light (washing/drying dishes), high light (laundry, dust mopping), or MVPA (400-meter walk) intensity. Oxygen uptake was measured using an Oxycon™ portable calorimeter. Sedentary behavior and physical activity intensity cutpoints for vertical axis and VM counts were derived for 60-second epochs from receiver operating characteristic (ROC) and by multiplying the 15-second cutpoints by four); both were compared to oxygen uptake. The median age was 74.5 years (interquartile range 70-83). The 60-second epoch cutpoints for vertical counts were 0 sedentary, 1-73 low light, 74-578 high light, and >=579 MVPA. The 60-second epoch cutpoints for VM were 0-88 sedentary, 89-663 low light, 664-1730 high light, and >=1731 MVPA. For both sets of cutpoints, the ROC approach yielded more accurate estimates than the multiplication approach. The derived 60-second epoch cutpoints for vertical counts and VM can be applied to epidemiologic studies to define sedentary behavior and physical activity intensities in older adult populations.

The Relationship Between Physical Activity and Limited Range of Motion in the Older Bedridden Patients.

The purpose of this study is to examine the association between physical activity and contracture in older patients confined to bed in long-term care (LTC) facilities. Patients wore ActiGraph GT3X+ for 8 hours on their wrists, and vector magnitude (VM) counts were obtained as the amount of activity. The passive range of motion (ROM) of joints was measured. The severity of ROM restriction classified, as the tertile value of the reference ROM of each joint, was scored 1-3 points. Spearman's rank correlation coefficients (Rs) were used to measure the association between the VM counts per day and ROM restrictions. The sample comprised 128 patients with a mean (SD) age of 84.8 (8.8) years. The mean (SD) of VM was 84574.6 (115195.2) per day. ROM restriction was observed in most joints and movement directions. ROMs in all joints and movement directions, except wrist flexion and hip abduction, were significantly correlated with VM. Furthermore, the VM and ROM severity scores showed a significant negative correlation (Rs = -0.582, p < .0001). A significant correlation between the physical activity and ROM restrictions indicates that a decrease in the amount of physical activity could be one of the causes of contracture.

Accelerometer-measured physical activity and postmenopausal breast cancer incidence in the Women's Health Accelerometry Collaboration.

Few studies have examined accelerometer-measured physical activity and incident breast cancer (BC). Thus, this study examined associations between accelerometer-measured vector magnitude counts per 15 seconds (VM/15s) and average daily minutes of light physical activity (LPA), moderate-to-vigorous PA (MVPA), and total PA (TPA) and BC risk among women in the Women's Health Accelerometry Collaboration (WHAC). The WHAC comprised 21,089 postmenopausal women (15,375 from the Women's Health Study [WHS]; 5714 from the Women's Health Initiative Objective Physical Activity and Cardiovascular Health Study [OPACH]). Women wore an ActiGraph GT3X+on the hip for ≥4days and were followed for 7.4 average years to identify physician-adjudicated in situ (n=94) or invasive (n=546) BCs. Multivariable stratified Cox regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for tertiles of physical activity measures in association with incident BC overall and by cohort. Effect measure modification wasexaminedby age, race/ethnicity, and body mass index (BMI). In covariate-adjusted models, the highest (vs. lowest) tertiles of VM/15s, TPA, LPA, and MVPA were associated with BC HRs of 0.80 (95% CI, 0.64-0.99), 0.84 (95% CI,0.69-1.02), 0.89 (95% CI,0.73-1.08), and 0.81 (95% CI,0.64-1.01), respectively. Further adjustment for BMI or physical function attenuated these associations. Associations were more pronounced among OPACH than WHS women for VM/15s, MVPA, and TPA; younger than older women for MVPA; and women with BMI ≥30 than <30kg/m2 for LPA. Greater levels of accelerometer-assessed PA were associated with lower BC risk. Associations varied by age and obesity and were not independent of BMI or physical function.

Methodological heterogeneity biases physical activity metrics derived from the Actigraph GT3X in multiple sclerosis: A rapid review and comparative study.

Physical activity (PA) is reduced in persons with multiple sclerosis (MS), though it is known to aid in symptom and fatigue management. Methods for measuring PA are diverse and the impact of this heterogeneity on study outcomes is unclear. We aimed to clarify this impact by comparing common methods for deriving PA metrics in MS populations. First, a rapid review of existing literature identified methods for calculating PA in studies which used the Actigraph GT3X in populations with MS. We then compared methods in a prospective study on 42 persons with MS [EDSS 4.5 (3.5-6)] during a voluntary course of inpatient neurorehabilitation. Mixed-effects linear regression identified methodological factors which influenced PA measurements. Non-parametric hypothesis tests, correlations, and agreement statistics assessed overall and pairwise differences between methods. In the rapid review, searches identified 421 unique records. Sixty-nine records representing 51 eligible studies exhibited substantial heterogeneity in methodology and reporting practices. In a subsequent comparative study, multiple methods for deriving six PA metrics (step count, activity counts, total time in PA, sedentary time, time in light PA, time in moderate to vigorous PA), were identified and directly compared. All metrics were sensitive to methodological factors such as the selected preprocessing filter, data source (vertical vs. vector magnitude counts), and cutpoint. Additionally, sedentary time was sensitive to wear time definitions. Pairwise correlation and agreement between methods varied from weak (minimum correlation: 0.15, minimum agreement: 0.03) to perfect (maximum correlation: 1.00, maximum agreement: 1.00). Methodological factors biased both point estimates of PA and correlations between PA and clinical assessments. Methodological heterogeneity of existing literature is high, and this heterogeneity may confound studies which use the Actigraph GT3X. Step counts were highly sensitive to the filter used to process raw accelerometer data. Sedentary time was particularly sensitive to methodology, and we recommend using total time in PA instead. Several, though not all, methods for deriving light PA and moderate to vigorous PA yielded nearly identical results. PA metrics based on vertical axis counts tended to outperform those based on vector magnitude counts. Additional research is needed to establish the relative validity of existing methods.

Impact of ActiGraph sampling rate on free-living physical activity measurement in youth

ActiGraph sampling frequencies of more than 30 Hz may result in overestimation of activity counts in both children and adults, but research on free-living individuals has not included the range of sampling frequencies used by researchers. Objective. We compared count- and raw-acceleration-based metrics from free-living children and adolescents across a range of sampling frequencies. Approach. Participants (n = 445; 10–15 years of age) wore an ActiGraph accelerometer for at least one 10 h day. Vector magnitude counts, mean amplitude deviation, monitor-independent movement summary units, and activity intensity classified using six methods (four cut-points, two-regression model, and artificial neural network) were compared between 30 Hz and 60, 80, 90, and 100 Hz sampling frequencies using mean absolute differences, correlations, and equivalence testing. Main results. All outcomes were statistically equivalent, and correlation coefficients were ≥0.970. Absolute differences were largest for the 30 versus 80 and 30 versus 100 Hz count comparisons. For comparisons of 30 with 60, 80, 90, or 100 Hz, mean (and maximum) absolute differences in minutes of moderate-to-vigorous physical activity per day ranged from 0.1 to 0.3 (0.4 to 1.5), 0.3 to 1.3 (1.6 to 8.6), 0.1 to 0.3 (1.1 to 2.5), and 0.3 to 2.5 (1.6 to 14.3) across the six classification methods. Significance. Acceleration-based outcomes are comparable across the full range of sampling rates and therefore recommended for future research. If using counts, we recommend a multiple of 30 Hz because using a 100 Hz sampling rate resulted in large maximum individual differences and epoch-level differences, and increasing differences with activity level.

Use of bilateral wrist-worn accelerometers to characterize upper limb activity time, intensity and asymmetry of use in physically demanding and sedentary working task

In the present study, we employed wearable accelerometers to characterize the patterns of mono- and bilateral activity of upper limbs (UL) in 46 individuals of a metalworking company (machine tool, fabrication and administrative departments) who were monitored for 4 h of their shift. UL accelerations were processed to calculate minutes of use and vector magnitude counts for both limbs plus several parameters (i.e. magnitude ratio, mono- and bilateral-arm use index) useful for characterizing the existence of asymmetries. The results show that machine tool operators exhibited marked asymmetry of use in favor of their dominant limb and were characterized by the lowest values of mono- and bilateral-arm use index, which indicate a superior use of the dominant limb in movements involving the use of a single or both limbs. Such evidences suggest that the use of wrist-worn accelerometers may provide essential information for assessing the risk of work-related UL disorders.

Performance Of The Wrist-worn Actigraph GT3X+ In Measuring Physical Activity In Older Women

The ActiGraph GT3X+ (ActiGraph LLC, Pensacola, FL) has been worn on the wrist in studies with the purpose of measuring sleep. However, its performance in assessing physical activity (PA) when worn on the wrist remains unclear. PURPOSE: This study examined the performance of the wrist-worn GT3X+ accelerometer in measuring energy expenditure of PA (PAEE) and classifying PA intensity in a healthy, non-obese population of older women. METHODS: Women [n = 89, age = 65.6 (4.3)] wore the GT3X+ and the SenseWear Armband Mini monitor (SWAM, BodyMedia Inc. Pittsburgh, PA) concurrently for 2 weeks when then doubly labeled water method (DLW) was used to determine total daily energy expenditure (EE). Indirect calorimetry was performed on the last day of the 2 weeks to determine resting EE. Manufacturer-provided software was used to process GT3X+ (2 equations were selected) and SWAM data. Bivariate correlations, Intra Class Correlations, and Bland-Altman plots were performed to evaluate agreement between the GT3X+ and criterion measures for time spent in sedentary, light and moderate-to-vigorous PA (determined by SWAM) and PAEE (determined by SWAM and by DLW and resting EE). An epoch-by-epoch (EBE) analysis was performed to evaluate discrepancy and agreement of PA intensity classification between the GT3X+ and the SWAM. RESULTS: For PAEE, the GT3X+ showed a moderate correlation with criterion measures (r = 0.413 and 0.400 with the SWAM and r = 0.564 and 0.501 with DLW and resting EE), but Bland-Altman plots showed large variability. When estimating time spent in PA intensity, the GT3X+ underestimated sedentary time and overestimated PA intensity when compared to the SWAM. During the EBE analysis, the GT3X+ misclassified light intensity PA as moderate-to-vigorous PA 72% of the time. However, vector magnitude counts per minute (CPM) showed a strong correlation with criterion measures (r = 0.68 and 0.625 for SWAM and DLW and resting EE respectively). CONCLUSIONS: The currently available PAEE estimation equations from the manufacturer-provided software do not allow us to accurately measure PAEE or PA intensity with the wrist-worn GT3X+ in a population of older women. A high correlation of CPM from the GT3X+ with criterion measures indicates that the problem may lie in the available equations and cut points, not in the device itself.

The impact of ActiGraph’s low-frequency extension filter on measurement of children’s physical activity

ABSTRACT This study examines differences in accelerometer-based measurements of children’s movement with and without applying ActiGraph’s low-frequency extension (LFE) filter. Thirty children wore ActiGraph GT9X devices during structured physical activity (PA) periods. Raw accelerometry data for each activity period were processed with and without the LFE filter applied. For each activity period, paired t-tests were used to compare vector magnitude counts and minutes spent in moderate-to-vigorous physical activity (MVPA) with and without the LFE filter applied. Repeated measures MANOVA models were used for compositional data analysis of the percentage of time spent in sedentary behaviour and light, moderate, and vigorous PA with and without the LFE filter applied. Applying the LFE filter significantly increased vector magnitude counts and estimated minutes spent in MVPA for all activity periods when compared to the normal filter. For brisk walking, the LFE filter had a significant impact on the composition of time spent in sedentary behaviour and PA intensities. Children’s activity data processed with the LFE filter may not be compatible with cut-points for activity levels developed with the normal filter, and caution should be taken when comparing children’s activity levels or movement data between studies that do and do not use the LFE filter.

Comparison of Child and Adolescent Physical Activity Levels From Open-Source Versus ActiGraph Counts

ActiGraph counts are commonly used for characterizing physical activity intensity and energy expenditure and are among the most well-studied accelerometer metrics. Researchers have recently replicated the counts processing method using a mechanical setup, now allowing users to generate counts from raw acceleration data. Purpose: The purpose of this study was to compare ActiGraph-generated counts to open-source counts and assess the impact on free-living physical activity levels derived from cut points, machine learning, and two-regression models. Methods: Children (n = 488, 13.0 ± 1.1 years of age) wore an ActiGraph wGT3X-BT on their right hip for 7 days during waking hours. ActiGraph counts and counts generated from raw acceleration data were compared at the epoch-level and as overall means. Seven methods were used to classify overall and epoch-level activity intensity. Outcomes were compared using weighted kappa, correlations, mean absolute deviation, and two one-sided equivalence testing. Results: All outcomes were statistically equivalent between ActiGraph and open-source counts; weighted kappa was ≥.971 and epoch-level correlations were ≥.992, indicating very high agreement. Bland–Altman plots indicated differences increased with activity intensity, but overall differences between ActiGraph and open-source counts were minimal (e.g., epoch-level mean absolute difference of 23.9 vector magnitude counts per minute). Regardless of classification model, average differences translated to 1.4–2.6 min/day for moderate- to vigorous-intensity physical activity. Conclusion: Open-source counts may be used to enhance comparability of future studies, streamline data analysis, and enable researchers to use existing developed models with alternative accelerometer brands. Future studies should verify the performance of open-source counts for other outcomes, like sleep.

Accelerometer-based estimation of oxygen uptake in adults with Down syndrome: vector magnitude vs. vertical axis.

Triaxial accelerometer output [vector magnitude (VM) counts] may better estimate physical activity intensity as reflected in the rate of oxygen uptake (V̇O2 ) than the traditional vertical axis (VA) counts in adults with Down syndrome (DS). This study examined the accuracy of VM vs. VA counts in estimating V̇O2 in adults with and without DS across different physical activities and sedentary behaviours. Sixteen adults with DS (10 men and 6 women; 31±15years) and 19 adults without DS (10 men and 9 women; 24±5years) performed 12 tasks. V̇O2 was measured by portable spirometer (K4b2 , Cosmed) and VM and VA with an accelerometer (wGT3X-BT, Actigraph). Vector magnitude and VA were significant predictors of V̇O2 in adults with DS (P<0.001; R2 =0.74 and 0.65, respectively) and adults without DS (P<0.001; P<0.001; R2 =0.75 and 0.61, respectively). Absolute error of prediction was significantly smaller for VM than VA for sitting, playing app, drawing, sweeping, standing and basketball (P≤0.005), but smaller for VA than VM for walking at 0.8m·s-1 (P=0.005). Bland-Altman plots for adults with and without DS indicated narrower limits of agreement for VM than VA (-5.57 to 5.57 and -6.44 to 6.44mL·kg-1 ·min-1 ; -6.21 to 6.17 and -7.75 to 7.74mL·kg-1 ·min-1 , respectively). Vector magnitude and VA are significant predictors of V̇O2 in adults with and without DS, yet VM more accurately estimated V̇O2 than VA for most tasks. Development of accelerometer-based prediction of physical activity levels in adults with and without DS may improve by utilising VM counts.

Associations Between Actigraphy-Assessed Health Behaviors and Cognitive Performance in Older Adults

Lifestyle behaviors are important determinants of healthy brain aging. Research has not fully explored how sleep quality and physical activity may differentially influence specific domains of cognitive function. The present study aimed to estimate the relative influence of sleep quality and physical activity on cognitive performance in three domains in a sample of older adults. Older adults (ages 60-89, M = 74.74) without cognitive impairment (N= 160) wore an accelerometer for 7 days in a free-living environment. We used average vector magnitude counts per minute to measure total physical activity (TPA), and average wake after sleep onset (WASO) to measure sleep quality. We created cognitive composite scores (executive function, attention, and verbal memory) from neuropsychological data using confirmatory factor analysis. We regressed cognitive scores onto TPA and WASO with age and education entered as covariates. Higher amounts of physical activity and better sleep quality were associated with better executive function (R2 = 20.3%, F (4, 155) = 11.12, p < .001). Neither physical activity nor sleep quality was associated with verbal memory or attention. Results suggest that more physical activity and improved ability to stay asleep may benefit executive function, but not other cognitive domains. Future studies should clarify the interaction and mechanisms of action between health behaviors and cognitive performance in older adults.

Dispersion of daily physical activity behaviors in school-age children: A novel approach to measure patterns of physical activity.

The objectives of this paper are (1) to examine patterns of physical activity (PA) and sedentary behavior; (2) to describe development of a method to quantify movement dispersion; and (3) to determine the relationship between variables of movement (i.e., volume, intensity, and dispersion), volume of sedentary behavior, and estimated cardiorespiratory capacity in school-aged children. A secondary analysis of an existing data set with raw accelerometer data identified PA patterns of movement dispersion in school-aged children. Bar graphs visually depicted each participant's daily vector magnitude counts. The research team developed a dispersion variable-movement dispersion-and formula to provide a new quantification of daily PA patterns. Total movement dispersion represents both intensity and distribution of movement, whereas pure movement dispersion refers to the distribution of movement during the wear time, independent of intensity. Kendall's tau examined the relationship between several variables: body mass index percentile, average minutes of sedentary behavior, average minutes of light PA, average minutes of moderate-vigorous PA (MVPA), derived VO2 max, total movement dispersion, and pure movement dispersion. Three participants' activity graphs were presented as examples: (1) active, (2) inactive, and (3) mixed. The more active participant had the highest values for pure and total movement dispersion. The inactive participant had much lower pure and total movement dispersion values compared to the active participant. The mixed participant had high average minutes of MVPA yet lower pure and total movement dispersion values. Total movement dispersion had a significant correlation with average minutes of light PA (r = .406, p = .016) and average minutes of MVPA (r = .686, p < .001). Pure movement dispersion was significantly correlated with average minutes of light PA (r = .448, p = .008) and average minutes of MVPA (r = .599, p < .001). Average minutes of sedentary behavior (SB) were not significantly correlated with total (r = .041, p = .806) or pure movement dispersion (r = .165, p = .326). Movement dispersion may provide another tool to advance knowledge of PA, potentially leading to improved health outcomes. Raw accelerometer data, such as that gathered at the elementary school in this study, offer opportunities to identify school-aged children at risk for obesity, SB, and lack of PA.

The Relationship of Physical Activity Level With Arterial Stiffness, Cerebral Blood Flow, and Cognitive Function in Young Adults

PURPOSE: This study aimed to investigate the relationship of physical activity level with arterial stiffness, cerebral blood flow, and cognitive function in young adults.METHODS: Forty-six young adults participated in this cross-sectional study. Physical activity levels were assessed for seven consecutive days using accelerometers. To assess arterial stiffness, the carotid–femoral artery pulse wave velocity (cfPWV) and augmentation index (AIx) were measured. Cognitive function was assessed using the Stroop Color-Word test, and cerebral blood flow was evaluated using near-infrared spectroscopy devices during the cognitive function test.RESULTS: AIx was inversely associated with axis-1 counts, vector magnitude counts, moderate-intensity physical activity (MPA) time, and moderate-to-vigorous intensity physical activity (MVPA) time (r≤-0.31, p≤.04). The AIx adjusted to the heart rate of 75 beats per minute was inversely correlated with axis-1 counts, vector magnitude counts, step counts, MPA time, and MVPA time (r≤-0.33, p≤.03). There was no relationship between cfPWV and physical activity level parameters (r≤0.10, p≥.51). The difference between oxygenated and deoxygenated hemoglobin levels was positively related to axis-1 counts, step counts, MPA time, and MVPA time (r≥0.31, p≤.04). Regarding cognitive function, the response time for the presented words was negatively associated with step counts (r=-0.42, p&lt;.01) and MPA time (r=-0.29, p=.048), and response time on the presented words with matched color was negatively related to step counts (r=-0.31, p=.04).CONCLUSIONS: More physically active adults are more likely to have lower arterial stiffness, increased brain oxygenation, and better cognitive function, even if they are young and healthy.