Uniaxial Accelerometer Research Articles

Validation and Comparison of 3 Accelerometers for Measuring Physical Activity Intensity During Nonlocomotive Activities and Locomotive Movements

The current study evaluated the validity of 3 commercially-available accelerometers to assess metabolic equivalent values (METs) during 12 activities. Thirty-three men and thirty-two women were enrolled in this study. The subjects performed 5 nonlocomotive activities and 7 locomotive movements. The Douglas bag method was used to gather expired air. The subjects also wore 3 hip accelerometers, a Lifecorder uniaxial accelerometer (LC), and 2 triaxial accelerometers (ActivTracer, AT; Actimarker, AM). For nonlocomotive activities, the LC largely underestimated METs for all activities (20.3%-55.6%) except for desk work. The AT overestimated METs for desk work (11.3%) and hanging clothes (11.7%), but underestimated for vacuuming (2.3%). The AM underestimated METs for all nonlocomotive activities (8.0%-19.4%) except for hanging clothes (overestimated by 16.7%). The AT and AM errors were significant, but much smaller than the LC errors (23.2% for desk work and -22.3 to -55.6% for the other activities). For locomotive movements, the 3 accelerometers significantly underestimated METs for all activities except for climbing down stairs. We conclude that there were significant differences for most activities in 3 accelerometers. However, the AT, which uses separate equations for nonlocomotive and locomotive activities, was more accurate for nonlocomotive activities than the LC.

Comparison of variations between percentage of body fat, body mass index and daily physical activity among young Japanese and Thai female students

BackgroundIn our series of investigations concerning the causes of seasonal change in fat accumulation in young university students, we could not find any contribution of seasonal variation in the ratio of carbohydrate and fat metabolism to that of body fat percentage in Japanese and Thai participants. After our previous study, we examined the effect of daily physical activity on body fat percentage to look for the major causes of seasonal change in fat accumulation in young university students.FindingsIn this study, we measured participants’ (young Japanese and Thai university students) daily physical activity by a uniaxial accelerometer in addition to the measurements of body fat percentage and body mass index by a bioelectrical impedance meter. We found that there was significant and moderate negative correlation between body fat percentage and daily step counts among Japanese but not Thai participants. We observed significant, moderate and positive correlations between the percentage of body fat and body mass index among Japanese and Thai participants.ConclusionsDaily physical activity plays an important role in the seasonal variation of body fat percentage of Japanese female students. Our present study also confirmed the importance of daily physical activity for controlling body mass index and for the prevention of obesity.

Activity levels after pulmonary rehabilitation – what really happens?

ObjectivesTo assess the changes in physical activity in subjects with chronic obstructive pulmonary disease over 6months after pulmonary rehabilitation. DesignProspective, observational study. Activity was measured over 2-day periods at the end of rehabilitation, and repeated every 6weeks for 6months using the ActivPAL uni-axial accelerometer. These results were compared with the shuttle walking test (SWT) and the St. George's Respiratory Disease Questionnaire (SGRDQ). SettingUK community hospital. ParticipantsAdults completing a community rehabilitation programme. Main outcome measureTime spent standing and mobilising (‘uptime’). ResultsOf 34 subjects recruited, 28 completed the 6-month study period (mean age 69years, mean forced expiratory volume in 1second 1.3l). Participants wore the monitor for 13.8 to 14.2hours/day. At baseline (post-rehabilitation), participants spent 1.7 [standard deviation (SD) 1.3]hours/day walking and 3.5 (SD 2.6)hours/day standing. Taking the group as a whole, mean uptime decreased marginally by 13.6minutes after 24weeks compared with baseline, with significant individual variability. In all but one subject who showed decreased activity, this was apparent after 6weeks. There were no significant changes in the mean SWT or SGRDQ. Significant associations between total uptime and the SWT were found, but coefficients were weak. It was not possible to predict individual responses from baseline data. ConclusionThe accelerometer provides useful supplementary data in patients completing rehabilitation programmes, and the results reveal wide variation. The weak associations between activity data and the SWT suggest that monitors provide additional information. More work is required to determine the factors associated with early deterioration in activity in order to design appropriate interventions.

Age-Related Differences in Actual and Perceived Levels of Physical Activity in Adolescent Girls

Age-related differences in actual and perceived physical activity were investigated in a sample of adolescent girls, also considering the relationship between physical activity and motor abilities. Self-reported physical activity was measured in 11-year-old (n=66) and 13-year-old (n=52) girls by means of the physical activity questionnaire-children form, and actual levels of activity were assessed by means of the Lifecorder uniaxial accelerometer. The Sit-and-Reach Test was employed to estimate flexibility, while lower limb strength was measured by squat jump and counter-movement jump tests. Weight and height were measured, and sex-specific age-related body mass index cutoff points were used to identify overweight and obesity. Findings showed a drop in objective vigorous physical activity in older girls, which was also reflected in the physical activity questionnaire. Contrary to expectations, no association was found between motor abilities and measured physical activity. Results highlight the need to understand the reasons why girls progressively reduce their involvement in physical activity as they get older, so as to plan interventions aimed at preventing this decline.

Comparative Validity of Accelerometer-Based Measures of Physical Activity for People With Multiple Sclerosis

Coote S, O'Dwyer C. Comparative validity of accelerometer-based measures of physical activity for people with multiple sclerosis. ObjectiveTo estimate the criterion validity of accelerometer-based devices as measures of steps and energy expenditure in healthy controls and people with multiple sclerosis (MS) with varying disability levels during everyday activities. DesignCross-sectional study. SettingUniversity research room. ParticipantsPeople with MS who used at most a stick to walk outdoors (MS-A; n=19), people with MS who used bilateral support for gait (MS-B; n=11), and healthy controls (n=15). InterventionsParticipants completed 85 minutes of 9 scripted everyday activities. Main Outcome MeasuresEstimates of metabolic equivalent thresholds (METs) and kilocalories from a portable metabolic system, and steps counted from video of the activities. Step and MET estimates from an integrative accelerometer and from a uniaxial accelerometer, and kilocalorie estimates from the integrative accelerometer. ResultsThe uniaxial accelerometer had >30% error for steps for all groups. MET estimates had an intraclass correlation coefficient (ICC) <0.2 for all groups. For the integrative accelerometer, step estimates for controls had an ICC of .69 and <1% error. The step estimates for MS-A and MS-B groups had >20% error. The MET estimates had an ICC of .50 to .65 and 6% to 15% error. Kilocalorie estimates had 2.9% error for controls, 8.16% for MS-A, and 2.56% for MS-B groups. ICCs were all >.67, and mean differences from criterion were <20kcal. ConclusionsThe agreement between steps and MET estimates from both devices and the criterion was poor, particularly for people with MS. Only the step and MET estimates for the control group for the integrative accelerometer were not significantly different from the criterion. Kilocalorie estimates from the integrative accelerometer using the proprietary algorithms of the device provide the most valid estimate of physical activity during activities of daily living for people with a range of walking disabilities resulting from MS.

Estimation of Resistance Exercise Energy Expenditure Using Triaxial Accelerometry

Recently, it was demonstrated that a uniaxial accelerometer worn at the hip could estimate resistance exercise energy expenditure. As resistance exercise takes place in more than 1 plane, the use of a triaxial accelerometer may be more effective in estimating resistance exercise energy expenditure. The aims of this study were to estimate the energy cost of resistance exercise using triaxial accelerometry and to determine the optimal location for wearing triaxial accelerometers during resistance exercise. Thirty subjects (15 men and 15 women; age = 21.7 ± 1.0 years) performed a resistance exercise protocol consisting of 2 sets of 8 exercises (10RM loads). During the resistance exercise protocol, subjects wore triaxial accelerometers on the wrist, waist, and ankle; a heart rate monitor; and a portable metabolic system. Net energy expenditure was significantly correlated with vertical (r = 0.67, p < 0.001), horizontal (r = 0.43, p = 0.02), third axis (r = 0.36, p = 0.048), and sum of 3 axes (r = 0.50, p = 0.005) counts at the waist, and horizontal counts at the wrist (r = -0.40, p = 0.03). Regression analysis using fat-free mass, sex, and the sum of accelerometer counts at the waist as variables was used to develop an equation that explained 73% of the variance of resistance exercise energy expenditure. A triaxial accelerometer worn at the waist can be used to estimate resistance exercise energy expenditure but appears to offer no benefit over uniaxial accelerometry. The use of accelerometers in estimating resistance exercise energy expenditure may prove useful for individuals and athletes who participate in resistance training and are focused on maintaining a tightly regulated energy balance.

Comparing Different Accelerometer Cut-Points for Sedentary Time in Children

Actigraph accelerometers are hypothesized to be valid measurements for assessing children's sedentary time. However, there is considerable variation in accelerometer cut-points used. Therefore, we compared the most common accelerometer sedentary cut-points of children performing sedentary behaviors. Actigraph Actitrainer uniaxial accelerometers were used to measure children's activity intensity (29 children, 5-11 years old) during different activities, namely playing computer games, nonelectronic sedentary games, watching television and playing outdoors. A structured protocol was the criterion for assessing the validity of four common cut-points (100, 300, 800, 1100 counts/minute). The median counts during all sedentary behaviors were below the lowest comparison cut-point of 100 cpm. The 75th percentile values for the sedentary behaviors were always below the cut-point of 300 cpm. Our results suggest that the cut-point of <100 cpm is the most appropriate.

Reliability of accelerometric measurement of physical activity in older adults-the benefit of using the trimmed sum.

There is general consensus that physical activity is important for preserving functional capacities of older adults and positively influencing quality of life. While accelerometry is widely accepted and applied to assess physical activity in studies, several problems with this method remain (e.g., low retest reliability, measurement errors). The aim of this study was to test the intra-instrumental retest reliability of a wrist-worn accelerometer in a 3-day measurement of physical activity in older adults and to compare different estimators. A sample of 123 older adults (76.5 ± 5.1 years, 59 % female) wore a uniaxial accelerometer continuously for 1 week. The data were split into two repeated measurement values (week set) of 3 days each. The sum, the 80–99th quantiles and the 80–99th trimmed sums were built for each week set. Retest reliability was assessed for each estimator and graphically demonstrated by Bland–Altman plots. The intraclass correlation of the retest reliability ranged from 0.22 to 0.91. Retest reliability increases when a more robust estimator than the overall sum is used. Therefore, the trimmed sum can be recommended as a conservative estimate of the physical activity level of older adults.

Prediction of Energy Expenditure From Wrist Accelerometry in People With and Without Down Syndrome

This study examined the relationship between energy expenditure and wrist accelerometer output during walking in persons with and without Down syndrome (DS). Energy expenditure in metabolic equivalent units (METs) and activity-count rate were respectively measured with portable spirometry and a uniaxial wrist accelerometer in 17 persons with DS (age: 24.7±6.9 years; 9 women) and 21 persons without DS (age: 26.3±5.2 years; 12 women) during six over-ground walking trials. Combined groups regression showed that the relationship between METs and activity-count rate differed between groups (p<.001). Separate models for each group included activity-count rate and squared activity-count rate as significant predictors of METs (p≤.005). Prediction of METs appeared accurate based on Bland-Altman plots and the lack of between-group difference in mean absolute prediction error (DS: 17.07%; Non-DS: 18.74%). Although persons with DS show altered METs to activity-count rate relationship during walking, prediction of their energy expenditure from wrist accelerometry appears feasible.

Comparative Interinstrument Reliability of Uniaxial and Triaxial Accelerometers in Free-Living Conditions

The aim of this study was to measure the inter-instrument reliability of the ActiGraph and RT3 accelerometers in free-living conditions. 15 healthy adults wore eight ActiGraph accelerometers and five RT3 accelerometers fastened to their back with an elastic belt and adjustable buckle in free-living conditions. For both accelerometers, the inter-instrument coefficient of variation (CV) decreased with increasing physical activity intensity. The inter-instrument CV of the ActiGraph (3% to 10.5%) was significantly lower than that of the RT3 (12.6% to 35.5%; p < 0.05). This finding demonstrates that the ActiGraph has higher inter-instrument reliability than the RT3. For both accelerometers, the inter-instrument reliability was higher for moderate and vigorous physical activity, the two intensities recommended for public health purposes. Studies using these devices can be compared with a low risk of misclassification of participants who meet the recommendation to perform moderate to vigorous physical activity.

Comparison of uniaxial and triaxial accelerometry in the assessment of physical activity among adolescents under free-living conditions: the HELENA study

BackgroundDifferent types of devices are available and the choice about which to use depends on various factors: cost, physical characteristics, performance, and the validity and intra- and interinstrument reliability. Given the large number of studies that have used uniaxial or triaxial devices, it is of interest to know whether the different devices give similar information about PA levels and patterns. The aim of this study was to compare physical activity (PA) levels and patterns obtained simultaneously by triaxial accelerometry and uniaxial accelerometry in adolescents in free-living conditions.MethodsSixty-two participants, aged 13-16 years, were recruited in this ancillary study, which is a part of the Healthy Lifestyle in Europe by Nutrition in Adolescence (HELENA). All participants wore a uniaxial accelerometer (ActiGraph GT1M®, Pensacola, FL) and a triaxial accelerometer (RT3®, Stayhealthy, Monrovia, CA) simultaneously for 7 days. The patterns were calculated by converting accelerometer data output as a percentage of time spent at sedentary, light, moderate, and vigorous PA per day. Analysis of output data from the two accelerometers were assessed by two different tests: Equivalence Test and Bland & Altman method.ResultsThe concordance correlation coefficient between the data from the triaxial accelerometer and uniaxial accelerometer at each intensity level was superior to 0.95. The ANOVA test showed a significant difference for the first three lower intensities while no significant difference was found for vigorous intensity. The difference between data obtained with the triaxial accelerometer and the uniaxial monitor never exceeded 2.1% and decreased as PA level increased. The Bland & Altman method showed good agreement between data obtained between the both accelerometers (p < 0.05).ConclusionsUniaxial and triaxial accelerometers do not differ in their measurement of PA in population studies, and either could be used in such studies.

Cardiorespiratory fitness, weight status and objectively measured sedentary behaviour and physical activity in rural and urban Portuguese adolescents

Relationships among weight status (body mass index [BMI]), cardiorespiratory fitness (CRF) and objective measures of sedentary behaviour and physical activity (PA) were considered in a cross-sectional sample of Portuguese adolescents. The sample included 362 youth aged 13-16 years (165 males, 197 females) from urban and rural regions of the Portuguese midlands. CRF was assessed with the 20-m shuttle-run test. An uniaxial accelerometer was used to obtain five consecutive days of activity behaviours including time being sedentary. Pearson correlations and logistic regression analysis were used to examine relationships among variables. Rural adolescents were less active than their urban peers over the weekend. Both rural and urban youth with higher levels of CRF had a lower relative risk of being overweight/obese. The observations indicate important associations between weight status and CRF in both rural and urban Portuguese adolescents. In addition, place of residence has an important impact on weight status of this sample of adolescents.

Influence of Cut-Points on Patterns of Accelerometry-Measured Free-Living Physical Activity in Rural and Urban Black South African Women

We describe the effect of 2 different accelerometer cut-points on physical activity (PA) patterns in rural and urban black South African women. Hip-mounted uni-axial accelerometers were worn for 6 to 7 days by rural (n = 272) and urban (n = 16) participants. Twenty-hour (4 AM to 12 AM) PA counts (cts) and volumes (min·day⁻¹) were extracted: sedentary (SED, <100 cts·min⁻¹), light (100-759 cts·min⁻¹), moderate-1 (MOD1, 760-1951 cts·min⁻¹), moderate-2 to vigorous (MOD2VG, ≥1952 cts·min⁻¹), and bouts ≥10 min for ≥760 cts·min⁻¹ (MOD1VGbt) and ≥1952 cts·min⁻¹ (MOD2VGbt). Valid data were obtained from 263 rural women and 16 urban women. Total counts and average counts were higher (+80,399 cts·day⁻¹, +98 cts·min⁻¹.day⁻¹) (P < .01), SED lower (-61 min·day⁻¹, P = .0042), MOD1 higher (+65 min·day⁻¹, P < .0001), and MOD1VGbt higher (+19 min·day⁻¹, P = .0179) in rural women compared with urban women. Estimated adherence (≥30 min·day⁻¹ for 5 days·wk⁻¹) was 1.4-fold higher in rural women than urban women for MOD-1VGbt, but 3.3-fold higher in urban women than rural women for MOD2VGbt. Rural women accumulate greater amounts of PA than urban women within a particular count band. Depending on which moderate PA cut-point was used to estimate PA public health adherence, rural women could be classified as less physically active than urban women.

Evaluation of the Indian Migration Study Physical Activity Questionnaire (IMS-PAQ): a cross-sectional study

BackgroundSocio-cultural differences for country-specific activities are rarely addressed in physical activity questionnaires. We examined the reliability and validity of the Indian Migration Study Physical Activity Questionnaire (IMS-PAQ) in urban and rural groups in India.MethodsA sub-sample of IMS participants (n = 479) was used to examine short term (≤1 month [n = 158]) and long term (> 1 month [n = 321]) IMS-PAQ reliability for levels of total, sedentary, light and moderate/vigorous activity (MVPA) intensity using intraclass correlation (ICC) and kappa coefficients (k). Criterion validity (n = 157) was examined by comparing the IMS-PAQ to a uniaxial accelerometer (ACC) worn ≥4 days, via Spearman's rank correlations (ρ) and k, using Bland-Altman plots to check for systematic bias. Construct validity (n = 7,000) was established using linear regression, comparing IMS-PAQ against theoretical constructs associated with physical activity (PA): BMI [kg/m2], percent body fat and pulse rate.ResultsIMS-PAQ reliability ranged from ICC 0.42-0.88 and k = 0.37-0.61 (≤1 month) and ICC 0.26 to 0.62; kappa 0.17 to 0.45 (> 1 month). Criterion validity was ρ = 0.18-0.48; k = 0.08-0.34. Light activity was underestimated and MVPA consistently and substantially overestimated for the IMS-PAQ vs. the accelerometer. Criterion validity was moderate for total activity and MVPA. Reliability and validity were comparable for urban and rural participants but lower in women than men. Increasing time spent in total activity or MVPA, and decreasing time in sedentary activity were associated with decreasing BMI, percent body fat and pulse rate, thereby demonstrating construct validity.ConclusionIMS-PAQ reliability and validity is similar to comparable self-reported instruments. It is an appropriate tool for ranking PA of individuals in India. Some refinements may be required for sedentary populations and women in India.

Validation of Uniaxial and Triaxial Accelerometers for the Assessment of Physical Activity in Preschool Children

Given the unique physical activity (PA) patterns of preschoolers, wearable electronic devices for quantitative assessment of physical activity require validation in this population. Study objective was to validate uniaxial and triaxial accelerometers in preschoolers. Room calorimetry was performed over 3 hours in 64 preschoolers, wearing Actical, Actiheart, and RT3 accelerometers during play, slow, moderate, and fast translocation. Based on activity energy expenditure (AEE) and accelerometer counts, optimal thresholds for PA levels were determined by piecewise linear regression and discrimination boundary analysis. Established HR cutoffs in preschoolers for sedentary/light, light/moderate and moderate/vigorous levels were used to define AEE (0.015, 0.054, 0.076 kcal·kg-1·min-1) and PA ratio (PAR; 1.6, 2.9, 3.6) thresholds, and accelerometer thresholds. True positive predictive rates were 77%, 75%, and 76% for sedentary; 63%, 61%, and 65% for light; 34%, 52%, and 49% for moderate; 46%, 46%, and 49% for vigorous levels. Due to low positive predictive rates, we combined moderate and vigorous PA. Classification accuracy was improved overall and for the combined moderate-to-vigorous PA level (69%, 82%, 79%) for Actical, Actiheart, and RT3, respectively. Uniaxial and triaxial accelerometers are acceptable devices with similar classification accuracy for sedentary, light, and moderate-to-vigorous levels of PA in preschoolers.

Assessment of objectively measured physical activity levels in individuals with intellectual disabilities with and without Down's syndrome.

ObjectiveTo investigate, using accelerometers, the levels of physical activity being undertaken by individuals with intellectual disabilities with and without Down's syndrome.MethodsOne hundred and fifty two individuals with intellectual disabilities aged 12–70 years from East and South-East England. Physical activity levels in counts per minute (counts/min), steps per day (steps/day), and minutes of sedentary, light, moderate, vigorous, and moderate to vigorous physical activity (MVPA) measured with a uni-axial accelerometer (Actigraph GT1M) for seven days.ResultsNo individuals with intellectual disabilities met current physical activity recommendations. Males were more active than females. There was a trend for physical activity to decline and sedentary behaviour to increase with age, and for those with more severe levels of intellectual disability to be more sedentary and less physically active, however any relationship was not significant when adjusted for confounding variables. Participants with Down's syndrome engaged in significantly less physical activity than those with intellectual disabilities without Down's syndrome and levels of activity declined significantly with age.ConclusionsIndividuals with intellectual disabilities, especially those with Down's syndrome may be at risk of developing diseases associated with physical inactivity. There is a need for well-designed, accessible, preventive health promotion strategies and interventions designed to raise the levels of physical activity for individuals with intellectual disabilities. We propose that there are physiological reasons why individuals with Down's syndrome have particularly low levels of physical activity that also decline markedly with age.

Investigation of restoration effects on the dynamic characteristics of the Hagia Sophia bell-tower by ambient vibration test

Ambient vibration test is preferred to condition assessment of historical structures due to the fact that this method does not create any negative effect on the measured structures. The method enables to observe the changes in the dynamic characteristics of structures by making measurements for different cases such as damaged, restored, etc. Many historical structures have been restored nowadays because of increasing concern to these structures in the modern societies. The study presents the natural frequencies, mode shapes and modal damping ratios of the bell-tower of Hagia Sophia Church in Trabzon, Turkey, which was restored one year ago by Local Office of Cultural Ministry of Turkey. The masonry bell-tower is about 23.5m high and dates back to the XIII century. Full-scale ambient vibration tests were performed for pre-restored and restored cases under environmental and randomly generated impact loads. In the measurement, totally nine uni-axial seismic accelerometers were used to collect responses of the tower in the orthogonal directions. The measurement is carried out on the three different levels of the tower by using a reference point. Two commonly used methods which are Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) are used to identify the modal parameters of the tower. The first five natural frequencies and their corresponding modal damping ratios are attained by selecting each mode on the power spectral density functions. Also, the bending and torsional modes of the tower are extracted from these spectra. The effects of the restoration are evaluated by comparing the dynamic characteristics of the tower for pre-restored and restored cases.

Validity of a brief self-report instrument for assessing compliance with physical activity guidelines amongst adolescents

ObjectivesTo examine the validity of a brief self-report questionnaire for assessing physical activity, and compliance and non-compliance with moderate-to-vigorous physical activity (MVPA) recommendations in Australian adolescents against accelerometry. DesignCross-sectional study. MethodsMVPA of 203 adolescents (124 females, 79 males) aged 15–17 years was objectively assessed for 8 consecutive days using uni-axial accelerometers and calculated using age-specific cut-points. Adolescents self-reported the number of days (0–7) they were physically active for a total of at least 60min/day (1) over the past 7 days and (2) over a typical week. Compliance with physical activity recommendations was defined as (1) 5 and (2) 7 days of self-reported MVPA (of at least 60min/day), and (3) ≥60min MVPA per average day, and (4) >60min MVPA on every day according to accelerometry. Spearman's Rho correlations analysed the association between accelerometry-derived MVPA/day and self-reported MVPA days/week for the whole sample, sex and weight status. Percent agreement determined the proportion of adolescents correctly identified as not meeting physical activity recommendations (specificity) or as meeting physical activity recommendations (sensitivity) according to the self-report questionnaire. ResultsModerate to large correlations were found between the self-report and accelerometer data (0.2–0.51) across population subgroups. The percent agreement between the self-report and accelerometry data was good for specificity; however, the sensitivity was low, potentially due to poor compliance with recommendations. ConclusionsCompared to accelerometry, the brief MVPA self-report questionnaire appears to have acceptable validity for measuring non-compliance with physical activity recommendations in 15–17 year old adolescents.

Identification of Children's Activity Type with Accelerometer-Based Neural Networks

The study's purpose was to identify children's physical activity type using artificial neural network (ANN) models based on uniaxial or triaxial accelerometer data from the hip or the ankle. Fifty-eight children (31 boys and 27 girls, age range = 9-12 yr) performed the following activities in a field setting: sitting, standing, walking, running, rope skipping, playing soccer, and cycling. All children wore uniaxial and triaxial ActiGraph accelerometers on both the hip and the ankle. Four ANN models were developed using the following accelerometer signal characteristics: 10th, 25th, 75th, and 90th percentiles; absolute deviation; coefficient of variability; and lag-one autocorrelation. The accuracy of the models was evaluated by leave-one-subject-out cross-validation. The models based on hip accelerometer data correctly classified the activities 72% and 77% of the time using uniaxial and triaxial accelerometer data, respectively, whereas the models based on ankle accelerometer data achieved a percentage of 57% and 68%. The hip models were better able to correctly classify the activities walking, rope skipping, and running, whereas the ankle models performed better when classifying sitting. The models based on triaxial accelerometer data produced a better classification of the activities standing, running, rope skipping, playing soccer, and cycling than its uniaxial counterparts. Applying ANN models to processing accelerometer data from children is promising for classifying common physical activities. The highest percentage of correctly classified activities was achieved when using triaxial accelerometer data from the hip.

Examining physical activity and inactivity in 9–12 years old children

Information about children's daily physical activity in Eastern-Europe is essential because of the increasing prevalence in overweight and obesity. Sixty-three children (age=11.16 ± 1.10 years; 33 boys and 30 girls) from two public elementary schools had their physical activity objectively measured using uni-axial accelerometer every 5 seconds for five consecutive days (3 weekdays, 2 weekend days). After data cleaning, 10 children were excluded from database. There were no significant differences in boys' and girls' BMI (17.6 ± 2.2 vs. 17.1 ± 2.4) and BF% (18.0 ± 5.2 vs. 19.4 ± 5.0). Children engaged in more sedentary, light, moderate, and vigorous physical activity and had higher counts per minute during weekdays compared to weekend days. There were no sex differences in moderate to vigorous physical activity (87.6 ± 22.4 vs. 93.5 ± 20.6 min and 53.6 ± 21.3 vs. 59.4 ± 22.0 min) during weekday and weekend days. Data indicated that 96% of the girls and 92% of the boys met the international physical activity guideline for children of 60 minutes of MVPA, on weekdays.