Automatic Identification of Physical Activity Type and Duration by Wearable Activity Trackers: A Validation Study.

BACKGROUND: Activity trackers are now ubiquitous in certain populations, with potential applications for health promotion and monitoring and chronic disease management. Understanding the accuracy of this technology is critical to the appropriate and productive use of wearables in health research. Although other peer-reviewed validations have examined other features (eg, steps and heart rate), no published studies to date have addressed the accuracy of automatic activity type detection and duration accuracy in wearable trackers. OBJECTIVE: The aim of this study was to examine the ability of 4 commercially available wearable activity trackers (Fitbits Flex 2, Fitbit Alta HR, Fitbit Charge 2, and Garmin Vívosmart HR), in a controlled setting, to correctly and automatically identify the type and duration of the physical activity being performed. METHODS: A total of 8 activity types, including walking and running (on both a treadmill and outdoors), a run embedded in walking bouts, elliptical use, outdoor biking, and pool lap swimming, were tested by 28 to 34 healthy adult participants (69 total participants who participated in some to all activity types). Actual activity type and duration were recorded by study personnel and compared with tracker data using descriptive statistics and mean absolute percent error (MAPE). RESULTS: The proportion of trials in which the activity type was correctly identified was 93% to 97% (depending on the tracker) for treadmill walking, 93% to 100% for treadmill running, 36% to 62% for treadmill running when preceded and followed by a walk, 97% to 100% for outdoor walking, 100% for outdoor running, 3% to 97% for using an elliptical, 44% to 97% for biking, and 87.5% for swimming. When activities were correctly identified, the MAPE of the detected duration versus the actual activity duration was between 7% and 7.9% for treadmill walking, 8.7% and 144.8% for treadmill running, 23.6% and 28.9% for treadmill running when preceded and followed by a walk, 4.9% and 11.8% for outdoor walking, 5.6% and 9.6% for outdoor running, 9.7% and 13% for using an elliptical, 9.5% and 17.7% for biking, and was 26.9% for swimming. CONCLUSIONS: In a controlled setting, wearable activity trackers provide accurate recognition of the type of some common physical activities, especially outdoor walking and running and walking on a treadmill. The accuracy of measurement of activity duration varied considerably by activity type and tracker model and was poor for complex sets of activity, such as a run embedded within 2 walking segments.

Multivariate Analyses and Classification of Inertial Sensor Data to Identify Aging Effects on the Timed-Up-and-Go Test.

Many tests can crudely quantify age-related mobility decrease but instrumented versions of mobility tests could increase their specificity and sensitivity. The Timed-up-and-Go (TUG) test includes several elements that people use in daily life. The test has different transition phases: rise from a chair, walk, 180° turn, walk back, turn, and sit-down on a chair. For this reason the TUG is an often used test to evaluate in a standardized way possible decline in balance and walking ability due to age and or pathology. Using inertial sensors, qualitative information about the performance of the sub-phases can provide more specific information about a decline in balance and walking ability. The first aim of our study was to identify variables extracted from the instrumented timed-up-and-go (iTUG) that most effectively distinguished performance differences across age (age 18-75). Second, we determined the discriminative ability of those identified variables to classify a younger (age 18-45) and older age group (age 46-75). From healthy adults (n = 59), trunk accelerations and angular velocities were recorded during iTUG performance. iTUG phases were detected with wavelet-analysis. Using a Partial Least Square (PLS) model, from the 72-iTUG variables calculated across phases, those that explained most of the covariance between variables and age were extracted. Subsequently, a PLS-discriminant analysis (DA) assessed classification power of the identified iTUG variables to discriminate the age groups. 27 variables, related to turning, walking and the stand-to-sit movement explained 71% of the variation in age. The PLS-DA with these 27 variables showed a sensitivity and specificity of 90% and 85%. Based on this model, the iTUG can accurately distinguish young and older adults. Such data can serve as a reference for pathological aging with respect to a widely used mobility test. Mobility tests like the TUG supplemented with smart technology could be used in clinical practice.

Clustering physical activity phenotypes using the ATLAS index on accelerometric data from an epidemiologic cohort study.

While many studies have identified associations of physical activity with both mortality and morbidity, the effects of different dose-patterns are still unclear. Employing the recently introduced ATLAS index, the aim of the research work for this paper was to investigate whether physical activity phenotypes can actually be extracted from a large-scale epidemiological accelerometer data set, and if these match the ones proposed. The ATLAS parameters were computed for 6386 data sets from the NHANES 2005-2006 cohort study, and x-Means clustering was performed on the results. Thus, four distinct clusters were identified, named: 'insufficiently active', 'irregularly active', 'busy bee' and 'physical worker/weekend warrior'. In conclusion, it is possible to identify different activity phenotypes using the ATLAS index. More research is necessary with regard to the regularity component and the relation of activity patterns and medical parameters in the groups identified.

Walking objectively measured: classifying accelerometer data with GPS and travel diaries.

PURPOSE: This study developed and tested an algorithm to classify accelerometer data as walking or nonwalking using either GPS or travel diary data within a large sample of adults under free-living conditions. METHODS: Participants wore an accelerometer and a GPS unit and concurrently completed a travel diary for seven consecutive days. Physical activity (PA) bouts were identified using accelerometry count sequences. PA bouts were then classified as walking or nonwalking based on a decision-tree algorithm consisting of seven classification scenarios. Algorithm reliability was examined relative to two independent analysts' classification of a 100-bout verification sample. The algorithm was then applied to the entire set of PA bouts. RESULTS: The 706 participants' (mean age = 51 yr, 62% female, 80% non-Hispanic white, 70% college graduate or higher) yielded 4702 person-days of data and had a total of 13,971 PA bouts. The algorithm showed a mean agreement of 95% with the independent analysts. It classified PA into 8170 walking bouts (58.5 %) and 5337 nonwalking bouts (38.2%); 464 bouts (3.3%) were not classified for lack of GPS and diary data. Nearly 70% of the walking bouts and 68% of the nonwalking bouts were classified using only the objective accelerometer and GPS data. Travel diary data helped classify 30% of all bouts with no GPS data. The mean ± SD duration of PA bouts classified as walking was 15.2 ± 12.9 min. On average, participants had 1.7 walking bouts and 25.4 total walking minutes per day. CONCLUSIONS: GPS and travel diary information can be helpful in classifying most accelerometer-derived PA bouts into walking or nonwalking behavior.

Objectively measured physical activity and body composition indices in Brazilian adolescents / Atividade física mensurada objetivamente e índices de composição corporal em adolescentes Brasileiros

The aim of the study was to explore the association between objectively measured physical activity and body composition indices in 13-year old adolescents living in country undergoing rapid nutritional transition. A population-based cross-sectional study nested within the 1993 Pelotas (Brazil) Birth Cohort was undertaken. A total of 457 boys and girls (80.5% of the target sample, 52.1% boys) participated in the study. Physical activity was measured by the Actigraph accelerometer for 5 consecutive days and expressed as total physical activity (i.e. average intensity, counts per minute) and time (min per day) spent at moderate and vigorous intensity activity. The outcomes investigated were sum of triceps and subscapular skinfolds, waist circumference, waist-to-hip ratio and waist-to-thigh ratio. After adjustment for sex, socioeconomic status, age, Tanner stage of sexual maturation, diet pattern, height, and birth weight, time (min/day) spent at vigorous intensity activity was inversely associated with waist circumference and sum of skinfolds. A one minute/day increase in vigorous intensity physical activity was associated, on average, with a reduction of 0.15cm in waist circumference (p=0.007) and 0.20mm in sum of skinfold thicknesses (p=0.02). These associations were stronger in boys than in girls. Total activity and time spent in moderate intensity physical activities were not associated with any of the outcomes in the adjusted analyses. Vigorous physical activity appears to have the strongest association with body composition. Preventive efforts aimed to decrease the obesity in adolescents may be more successful if they focus on vigorous intensity, instead of moderate intensity physical activities.

O objetivo deste estudo foi explorar a associação entre atividade física mensurada objetivamente e índices de composição corporal em adolescentes de 13 anos de idade residentes em um país sofrendo rápida transição nutricional. Um estudo transversal de base populacional aninhado a Coorte de Nascimentos de 1993 de Pelotas (Brasil) foi realizado. Um total de 457 meninos e meninas (80,5% da população alvo; 52,1% meninos) participaram do estudo. Atividade física foi mensurada pelo acelerômetro Actigraph por 5 dias consecutivos e expressa como atividade física total (intensidade média, counts por minuto) e tempo (min/dia) em atividades moderadas e vigorosas. Os desfechos investigados foram somatório de dobras triciptal e subescapular, circunferência da cintura, razão cintura-quadril e razão cintura-coxa. Após ajustes para sexo, nível econômico, idade, estágio de maturação sexual de Tanner, padrão de dieta, estatura e peso ao nascer, o tempo (min/dia) em atividades vigorosas foi inversamente associado à circunferência da cintura e somatório das dobras. O aumento de um minuto por dia no tempo em atividades vigorosas foi associado, em média, com uma redução de 0,15cm na circunferência da cintura (p=0,007) e 0,20mm no somatório das dobras (p=0,02). Estas associações foram mais fortes nos meninos comparado as meninas. Atividade física total e tempo em atividades moderadas não foram associados com nenhum dos desfechos na análise ajustada. Atividades vigorosas parecem ter a associação mais forte com composição corporal. Esforços preventivos que visem diminuir a obesidade em adolescentes podem ter mais sucesso se focarem em atividades vigorosas ao invés de atividades de intensidade moderada.