Waking Movement Research Articles

Twenty-four hour physical activity, sedentary behaviour and sleep profiles in adults living with rheumatoid arthritis: a cross-sectional latent class analysis

BackgroundRheumatoid Arthritis (RA), an autoimmune systemic inflammatory disease, affects more than 17 million people globally. People with RA have higher risk of premature mortality; often experience chronic fatigue, pain and disrupted sleep; and are less physically active and more sedentary than healthy counterparts. It remains unclear how people with RA may balance sleep and awake movement activities over 24-hours, or how differences in 24-hour behaviours may be associated with determinants of health, or alignment with published activity guidelines.MethodsCross-sectional exploration of objective measures of 24-hour sleep-wake activities in 203 people with RA. Latent Class Analysis (LCA) derived classes from time, by tertile, in six sleep-awake activities over 24 h. Comparisons of model fit statistics, class separation and interpretability defined best fit for number of classes. Variations in sleep-awake behaviour across classes and association of profile allocation with determinants of health, quality metrics for sleep, sitting and walking and alignment with published guidelines were explored. Multinomial logistic regression identified factors associated with likelihood of profile allocation.ResultsLCA identified 2 to 6 classes and a 4-class model was determined as best fit for 24-hour sleep-awake behaviour profiles. One profile (26%) presented with more balanced 24-hour sleep, sitting and walking behaviours. The other three profiles demonstrated progressively less balanced 24-hour behaviours including: having low (< 7 h), high (> 8 h), or recommended (7–8 h) sleep duration in respective combination with high sitting (> 10 h), limited walking (< 3 h) or both when awake. Age, existing sitting and walking habit strength and fatigue were associated with likelihood of belonging to different profiles. More balanced 24-hour behaviour was aligned with better quality metrics for sleep, sitting and walking and published guidelines.DiscussionFor people living with RA it is important to understand the ‘whole person’ and their ‘whole day’ to define who may benefit from support to modify 24-hour sleep-awake behaviours and which behaviours to modify. Supports should be informed by an understanding of personal or health-related factors that could act as barriers or facilitators for behavioural change, including exploring existing habitual sitting and walking behaviours.Trial registrationsClinicalTrials.gov ID: NCT02554474 (2015-09-16) and ClinicalTrials.gov ID: NCT03404245 (2018-01-11)

Intervention effects on children’s movement behaviour accumulation as a result of the Transform-Us! school- and home-based cluster randomised controlled trial

BackgroundIt is unknown if and how children’s movement behaviour accumulation patterns change as a result of physical activity and/or sedentary behaviour interventions. It is important to establish the effectiveness of interventions targeting changes in such accumulation patterns. This study aimed to investigate the effect of the Transform-Us! school- and home-based intervention program on children’s movement behaviour accumulation patterns, focusing on sporadic accumulation versus time in bouts.MethodsBaseline and post-intervention (18 months) accelerometer data from the Transform-Us! 2 × 2 factorial design cluster randomised controlled trial was used (Melbourne, 2010–2012; analytical sample n = 267; aged 8–9 years). Linear mixed models were fitted to examine effects of three different interventions (targeting increases in physical activity [PA-I], reductions in sedentary time [SB-I], or both [PA + SB-I]) compared to a usual practice (control) group on post-intervention movement behaviour accumulation compositions with eight components, including sporadic time and bouts of sedentary time, and light-, moderate- and vigorous-intensity physical activity.ResultsIntervention effects on distribution of time in the post-intervention waking movement behaviour accumulation composition (adjusted for baseline composition) were small and not significant. However, visual inspection of the change in compositions over time revealed that only groups with a sedentary behaviour intervention component (SB-I and PA + SB-I) reduced time in sedentary bouts, compared to the overall sample compositional mean. In addition, the SB-I group was the only group with an increase in vigorous-intensity physical activity. The combined intervention group (PA + SB-I) was characterized by the largest proportional increase in MPA bouts. The usual practice group was characterized by the largest proportional increases in both sporadic and bouts of sedentary time.ConclusionsThis study showed some early evidence to suggest that the “break up your sitting” message may result in greater impact than the “move more” message. Future research, including larger sample sizes, should investigate if this type of messaging is indeed more effective in changing movement behaviours and ultimately child health.Trial registrationInternational Standard Randomized Controlled Trial Number ISRCTN83725066; Australian New Zealand Clinical Trials Registry Number ACTRN12609000715279.

0085 SleepInceptionNet: A Deep Learning Algorithm for Real-Time Sleep Stages Scoring Using Single-channel EEG

Abstract Introduction Most of the current automatic polysomnography sleep staging methods use multi-signal data and require a sequence of preceding and following epochs to score the stage of a specific epoch, which may not be desirable for analysis in real-time and/or in free-living conditions. We developed a deep learning-based sleep staging algorithm, namely SleepInceptionNet, that is designed to score each epoch using only single-channel electroencephalogram (EEG) data within that specific epoch. Methods Polysomnography data of 883 participants (937,975 thirty-second epochs) in the Multi-Ethnic Study of Atherosclerosis (MESA) obtained from the National Sleep Research Resource (NSRR) were randomly divided into a separate training/validation set of 194 participants and a test set of 689 participants. Each 30-second raw central EEG channel signal was transformed to time-frequency domain images using continuous wavelet transform method. Sleep stage in each epoch was obtained using SleepInceptionNet, in which the InceptionV3 convolutional neural network structure was trained and tuned on the time-frequency images of the training set to classify each epoch into one of the five stages of Wake, N1, N2, N3, or rapid eye movement (REM) sleep. Results Compared to the ground truth manually scored polysomnography sleep stages, SleepInceptionNet achieved an overall kappa agreement of 0.690 and overall weighted accuracy of 0.897. The model showed accuracy (mean±SD across the test set participants) of 0.940±0.067 in detecting Wake, 0.883±0.047 in detecting N1, 0.845±0.055 in detecting N2, 0.939±0.038 in detecting N3, and 0.930±0.038 in detecting REM epochs, in reference to manually scored polysomnography. Conclusion SleepInceptionNet showed a high agreement with manually scored polysomnography in epoch-by-epoch classification of sleep stages. This study demonstrates the viability of real-time, accurate sleep staging using a single-channel EEG, which could have a variety of applications such as delivery of on-demand interventions during specific sleep stages in free-living conditions. Support (If Any) MESA Sleep Ancillary study was funded by NIH-NHLBI Association of Sleep Disorders with Cardiovascular Health Across Ethnic Groups (RO1 HL098433). MESA is supported by NHLBI (HHSN268201500003I, N01-HC-95159, N01-HC-95160, N01-HC-95161, N01-HC-95162, N01-HC-95163, N01-HC-95164, N01- HC-95165, N01-HC-95166, N01-HC-95167, N01-HC-95168, and N01-HC-95169) and NCATS (UL1-TR-000040, UL1-TR-001079, and UL1-TR-001420). NSRR was supported by NHLBI (R24 HL114473, 75N92019R002).

Correlations Between Wake Phenomena and Fatigue Loads Within Large Wind Farms: A Large-Eddy Simulation Study

This work proposes a methodology aiming at simulating the whole wind farm behavior, from the wake phenomena to the wind turbine fatigue loads, in a both accurate and efficient way and for a large range of operating conditions. This approach is based on Large Eddy Simulation (LES), coupled to an Actuator Disk (AD) approach. In order to recover pertinent fatigue loads with that wind turbine model, the blade trajectories are replicated through the disk and the AD aerodynamic forces are interpolated onto these “virtual blades” at each time step. The wake centerline is also tracked in the whole wind farm, in order to highlight the correlations between the wake phenomena and the wind turbine fatigue damage. The described methodology is deployed in simulations of the Horns Rev wind farm for several wind directions. The time-averaged power production is first compared to measurements and other LES results, with a very good agreement for large wind sectors. We then investigate the fatigue loads for several machines inside the wind farm and wind directions. We clearly show the link between the upstream wake movement and the resulting high and low frequency oscillations of the root bending moments and of the yaw and tilt moments, and therefore on the resulting fatigue equivalent loads. This study demonstrates the capacity of the numerical tool to accurately capture the wind farm flow and the rotor behaviors, as well as the correlations between the wake phenomena and the resulting fatigue loads.

Striatal mechanism of the restless legs syndrome.

Brain iron deficiency has been reported to be associated with the restless legs syndrome (RLS). However, 30%-50% of RLS patients do not respond to iron therapy, indicating that mechanisms other than brain iron deficiency may also participate in this disease. The striatum is known to be involved in the modulation of motor activity. We speculated that dysfunction of the striatum may induce RLS. Two groups, wild-type (WT) and iron-deficient (ID) rats were used. Each group was divided into two subgroups, control and N-methyl-d-aspartate striatal-lesioned. After baseline recording, striatal-lesioned wild-type (WT-STL) and striatal-lesioned iron-deficient (ID-STL) rats were given pramipexole and thioperamide injections. Iron-deficient and ID-STL rats were then given a standard rodent diet for 4 weeks, and their sleep and motor activity were recorded. WT-STL rats showed periodic leg movements (PLM) in wake, an increase in PLM in slow wave sleep (SWS), a decrease in rapid-eye-movement sleep, and a decrease in the daily average duration of episodes in SWS. The sleep-wake pattern and motor activity did not differ between ID and ID-STL rats. Thioperamide or pramipexole injection decreased PLM in sleep and in wake in WT-STL rats and ID-STL rats. Unlike ID rats, whose motor hyperactivity can be reversed by iron replacement, PLM in wake and in sleep in ID-STL rats were not fully corrected by iron treatment. Lesions of the striatum generate RLS-like activity in rats. Dysfunction of the striatum may be responsible for failure to respond to iron treatment in some human RLS patients.

Dynamic wake tracking using a cost-effective LiDAR and Kalman filtering: Design, simulation and full-scale validation

Wind turbines in a wind farm typically operate in the wake of other turbines, inevitably leading to a power loss and enhanced structural degradation of turbines downstream. Knowledge of the wake characteristics such as position and magnitude is valuable for optimising wind farm operations. An expensive multi-beam scanning Light Detection And Ranging system (LiDAR) can easily track and characterise the wake; however, this task is non-trivial for a cost-effective LiDAR with solely a few fixed laser beams. Therefore, this paper presents a dynamic wake tracking algorithm well-suited for a cost-effective LiDAR. The proposed algorithm estimates the lateral and vertical wake-centre positions by exploiting the wake meandering dynamics and Kalman filtering. Numerical simulation results showed that the wake tracking performance by the proposed method was remarkably successful in the low turbulent wind field, and robust to any changes in the vertical mean wind shear. Similarly, in full-scale validation, the proposed algorithm using a fixed beam LiDAR demonstrated its reliable wake tracking capability that surprisingly was as good as traditional methods based on a multi-beam scanning LiDAR. Thus, the proposed algorithm presents a cost-effective alternative to track the wake movement, which is particularly valuable for numerous applications, for example, closed-loop wake steering control.

Self-Generated Whisker Movements Drive State-Dependent Sensory Input to Developing Barrel Cortex

Cortical development is an activity-dependent process [1-3]. Regarding the role of activity in the developing somatosensory cortex, one persistent debate concerns the importance of sensory feedback from self-generated movements. Specifically, recent studies claim that cortical activity is generated intrinsically, independent of movement [3, 4]. However, other studies claim that behavioral state moderates the relationship between movement and cortical activity [5-7]. Thus, perhaps inattention to behavioral state leads to failures to detect movement-driven activity [8]. Here, we resolve this issue by associating local field activity (i.e., spindle bursts) and unit activity in the barrel cortex of 5-day-old rats with whisker movements during wake and myoclonic twitches of the whiskers during active (REM) sleep. Barrel activity increased significantly within 500ms of whisker movements, especially after twitches. Also, higher-amplitude movements were more likely to trigger barrel activity; when we controlled for movement amplitude, barrel activity was again greater after a twitch than a wake movement. We then inverted the analysis to assess the likelihood that increases in barrel activity were preceded within 500ms by whisker movements: at least 55% of barrel activity was attributable to sensoryfeedback from whisker movements. Finally, when periods with and without movement were compared, 70%-75% of barrel activity was movement related. These results confirm the importance of sensory feedbackfrom movements in driving activity in sensorimotor cortex and underscore the necessity of monitoring sleep-wake states to ensure accurate assessments of the contributions of the sensory periphery to activity in developing somatosensory cortex.

The research of the effectiveness of the ice cover destruction by the resonance method from the pair motion of the load

In the work, the efficiency of study of the ice cover by the resonant method from the pair movement of the load is experimentally investigated. Studies were conducted in the experimental ice tank. At the initial stage of the study, a series of experiments was conducted to determine the effect of the mass of the load on the parameters of flexural-gravity waves generated in model ice. Further, the effect of the distance between the load models during their pair wake movement was studied. Study have shown that, depending on the distance between the models, either an increase or a decrease in the effectiveness of ice cover destruction was observed by flexural-gravity waves, which is associated with the interference phenomenon — an increase and decrease in the resulting amplitude of two coherent wave systems generated from the motion of the models. In general, it can be concluded that, to increase the efficiency of the resonant method of breaking the ice, flexural-gravity waves can be used as repeated passes of a single load across the ice cover, as well as pair movement.

Behavioral states modulate sensory processing in early development.

Sleep-wake states modulate cortical activity in adults. In infants, however, such modulation is less clear; indeed, early cortical activity comprises bursts of neural activity driven predominantly by peripheral sensory input. Consequently, in many studies of sensory development in rodents, sensory processing has been carefully investigated, but the modulatory role of behavioral state has typically been ignored. In the developing visual and somatosensory systems, it is now known that sleep and wake states modulate sensory processing. Further, in both systems, the nature of this modulation shifts rapidly during the second postnatal week, with subcortical nuclei changing how they gate sensory inputs. The interactions among sleep and wake movements, sensory processing, and development are dynamic and complex. Now that established methods exist to record neural activity in unanesthetized infant animals, we can provide a more comprehensive understanding of how infant sleep-wake states interact with sensory-driven responses to promote developmental plasticity.

A numerical study of correlations between wake meandering and loads within a wind farm

This paper aims at the better understanding of the correlations between rotor loads and the wake meandering inside a wind farm. The flow rotor dynamics are simulated by means of Large Eddy Simulations coupled to Actuator Disk models. The wake meandering is captured through a centerline tracking, itself based on the available power in the flow. Two turbulence intensities are investigated, TIs = 6% and 10%. Results show that the yawing moment is very well correlated to the wake movement, even for wind turbines located deeper into the the wind farm. Correlations can also be found between the wake oscillation and the root bending moments. Wake signatures can also be identified from the amplitude of the high-frequency oscillations of the root bending moments; however, the correlation is sometimes less visible, and deviations can be correlated to wind events or wake decay.

An Influence Analysis Method of Wake Turbulence in V-open Runway Operation Mode

In the design of large airports in China, Beijing Daxing international airport and Chengdu Tianfu international airport have adopted V-open runways. However, there is a relative lack of operational regulations for the V-open runway at home and abroad, it is of great significance to study the mutual influence of wake of aircrafts running parallel runway and V-open runway at the same time. The formation process, change period and movement characteristics of aircraft wake are systematically studied, and the wake movement model affected by the anisotropic wind speed is established. Taking the east one and the north one runways of Chengdu Tianfu international airport as an example, the influence of the wake on each other is analyzed by using the wake movement model. The specific values of the coverage of wake dangerous area under different conditions are obtained. Calculation results show that when the runway east one and the runway west one takes independent parallel instrument approach mode, the track offset angle of go-around aircraft from the runway east one is greater than 20.3°, its wake will affect aircraft departing from runway north one.

Developmental 'Awakening' of Primary Motor Cortex to the Sensory Consequences of Movement

Before primary motor cortex (M1) develops its motor functions, it behaves like a somatosensory area. Here, by recording from neurons in the forelimb representation of M1 in postnatal day (P) 8-12 rats, we demonstrate a rapid change in the types of movements that trigger sensory responses. At P8-10, M1 neurons respond overwhelmingly to sleep-related twitches of the forelimb, but the same neurons do not respond to forelimb movements when the animal is awake. Then, only two days later, M1 neurons suddenly respond to feedback from wake movements; this transition results from a change in sensory gating by the external cuneate nucleus. Also, at P12, the onset of local cortical inhibition leads to fewer M1 neurons responding to twitches; pharmacological disinhibition unmasks the more robust twitch responsiveness observed at P8. Thus, M1 initially establishes a somatosensory framework that lays a foundation for later-emerging motor control and plasticity.

Motor hyperactivity of the iron-deficient rat - an animal model of restless legs syndrome.

BackgroundAbnormal striatal dopamine transmission has been hypothesized to cause restless legs syndrome. Dopaminergic drugs are commonly used to treat restless legs syndrome. However, they cause adverse effects with long‐term use. An animal model would allow the systematic testing of potential therapeutic drugs. A high prevalence of restless legs syndrome has been reported in iron‐deficient anemic patients. We hypothesized that the iron‐deficient animal would exhibit signs similar to those in restless legs syndrome patients.MethodsAfter baseline polysomnographic recordings, iron‐deficient rats received pramipexole injection. Then, iron‐deficient rats were fed a standard rodent diet, and polysomnographic recording were performed for 2 days each week for 4 weeks.ResultsIron‐deficient rats have low hematocrit levels and show signs of restless legs syndrome: sleep fragmentation and periodic leg movements in wake and in slow‐wave sleep. Iron‐deficient rats had a positive response to pramipexole treatment. After the iron‐deficient rats were fed the standard rodent diet, hematocrit returned to normal levels, and sleep quality improved, with increased average duration of wake and slow‐wave sleep episodes. Periodic leg movements decreased during both waking and sleep. Hematocrit levels positively correlated with the average duration of episodes in wake and in slow‐wave sleep and negatively correlated with periodic leg movements in wake and in sleep. Western blot analysis showed that striatal dopamine transporter levels were higher in iron‐deficient rats.ConclusionsThe iron‐deficient rat is a useful animal model of iron‐deficient anemic restless legs syndrome. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society

Electrophysiological Evidence for Alternative Motor Networks in REM Sleep Behavior Disorder.

This study provides evidence that nocturnal movements during REM sleep in Parkinson's disease (PD) patients are not processed by the same corticobasal ganglia network as movements in the waking state. This implicates the existence of an alternative motor network that does not depend directly on the availability of l-Dopa in the basal ganglia. These findings further indicate that some PD patients are able to perform movements in the dopamine depleted state, possibly by bypassing the pathological basal ganglia network. The existence and direct activation of such alternative motor networks might finally have potential therapeutic effects for PD patients.

Gating of reafference in the external cuneate nucleus during self-generated movements in wake but not sleep.

Nervous systems distinguish between self- and other-generated movements by monitoring discrepancies between planned and performed actions. To do so, corollary discharges are conveyed to sensory areas and gate expected reafference. Such gating is observed in neonatal rats during wake-related movements. In contrast, twitches, which are self-generated movements produced during active (or REM) sleep, differ from wake movements in that they reliably trigger robust neural activity. Accordingly, we hypothesized that the gating actions of corollary discharge are absent during twitching. Here, we identify the external cuneate nucleus (ECN), which processes sensory input from the forelimbs, as a site of movement-dependent sensory gating during wake. Whereas pharmacological disinhibition of the ECN unmasked wake-related reafference, twitch-related reafference was unaffected. This is the first demonstration of a neural comparator that is differentially engaged depending on the kind of movement produced. This mechanism explains how twitches, although self-generated, trigger abundant reafferent activation of sensorimotor circuits in the developing brain.

Lurasidone Suppresses Rapid Eye Movement Sleep and Improves Sleep Quality in Rats

Patients with psychiatric disorders, including schizophrenia and bipolar disorder, are reported to suffer from sleep disorders. To investigate the effects of lurasidone on sleep architecture in rats using sleep electroencephalography. Seven adult male rats were used in this study. A pair of electrode wires was implanted in the dura of each rat and electromyograms were recorded from their dorsal neck muscles. Drugs were administered at the start of the lights-on period, and electroencephalograms (EEG)were recorded for 6 hours in individual soundproof boxes. The course of sleep in rats has been classified into 3 stages: WAKE, non-REM (NREM) sleep and rapid eye movement (REM) sleep. Total NREM duration, REM duration, and latencies to the initial REM and NREM were calculated. In addition, the number and mean duration of bouts in every 2-hour period were calculated in each stage. EEG power in each of the following frequency bands during NREM sleep was quantified: delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (12-30 Hz) and gamma (30-80 Hz). Lurasidone shortened REM sleep duration and prolonged the mean duration of one bout in WAKE and NREM sleep. Quantitative frequency analyses during NREM sleep revealed that lurasidone increases slow waves and decreases fast waves. The serotonin 5-HT 1A receptor partial agonist, tandospirone, and selective serotonin 5-HT 7 receptor antagonist, SB-258741, also exhibited REM-inhibitory effects similar to those of lurasidone. These results suggest that lurasidone ameliorates sleep disorders associated with psychosis through, at least partly, serotonin 5-HT 1A and serotonin 5-HT 7 receptors.

Developing Sensorimotor Systems in Our Sleep

Every animal must learn how to use its limbs within the developmental context of an ever-changing body. Typically, investigations of sensorimotor development focus on waking movements. Here, I consider another class of behavior: twitching movements that occur exclusively during active (REM) sleep. Twitches are particularly abundant in early infancy, when critical sensorimotor networks are established. In light of behavioral, electrophysiological, neurophysiological, and computational investigations of this unique behavior, twitches may prove critical for the development and maintenance of the sensorimotor system, as well as its repair after injury or disease.

Myoclonic Twitching and Sleep-Dependent Plasticity in the Developing Sensorimotor System

As bodies grow and change throughout early development and across the lifespan, animals must develop, refine, and maintain accurate sensorimotor maps. Here we review evidence that myoclonic twitches-brief and discrete contractions of the muscles, occurring exclusively during REM (or active) sleep, that result in jerks of the limbs-help animals map their ever-changing bodies by activating skeletal muscles to produce corresponding sensory feedback, or reafference. First, we highlight the spatiotemporal characteristics of twitches. Second, we review findings in infant rats regarding the multitude of brain areas that are activated by twitches during sleep. Third, we discuss evidence demonstrating that the sensorimotor processing of twitches is different from that of wake movements; this state-related difference in sensorimotor processing provides perhaps the strongest evidence yet that twitches are uniquely suited to drive certain aspects of sensorimotor development. Finally, we suggest that twitching may help inform our understanding of neurodevelopmental disorders, perhaps even providing opportunities for their early detection and treatment.

J2320103 慣性センサを用いた歩行姿勢判定に関する研究 : 足首のセンサを用いた簡易な歩行姿勢判定アルゴリズム

We have studied the walking posture diagnosis using inertial measurement units. We acquired the acceleration data of a waking model and a general subject attached inertial sensors to their ankles, creating the algorithm judging angels of the upper body and the leg opening from the analysis of the waking movement features.

Utility of Actiwatch Sleep Monitor to Assess Waking Movement Behavior in Older Women

Wrist-worn accelerometer devices measure sleep in free-living settings. Few studies, however, have investigated whether these devices can also measure waking movement behavior (e.g., total movement volume, physical activity). The purpose of this study was to investigate the ability of a wrist-worn Actiwatch 2 sleep monitor to rank total movement volume and physical activity levels compared with a waist-worn ActiGraph GT1M accelerometer and self-reported leisure time physical activity, respectively. In addition, we compared temporally matched activity measured via the ActiGraph GT1M and Actiwatch 2 over the study week. A subset of women from the Healthy Women Study (n = 145; age, 73.3 ± 1.7 yr) wore an Actiwatch 2 on their nondominant wrist and an ActiGraph GT1M on their dominant hip for seven consecutive days. Participants recorded their leisure time physical activity in a 7-d diary and completed the past year version of the Modifiable Activity Questionnaire. Analyses were conducted for all wake periods and separately for active periods when both devices were worn. Spearman rank-order correlation coefficients for total movement volume between the Actiwatch 2 and ActiGraph GT1M were significant for wake periods (r = 0.47, P < 0.001) and, to a lesser extent, for active periods (r = 0.26, P < 0.01). However, the Actiwatch 2 did not rank participant's physical activity levels similarly to self-reported leisure time physical activity estimates (κ ≤ 0.05, P > 0.05). Multilevel model analyses comparing temporally matched activity measured via the ActiGraph GT1M and Actiwatch 2 suggest that the two devices yielded similar levels of activity during wake periods (B = 0.90; SE, 0.008; P < 0.001) and during active periods (B = 0.81; SE, 0.01; P < 0.001). A wrist-worn Actiwatch 2 may be useful for ranking total movement volume and for assessing the pattern of activity over a day in older women. However, our data do not support using a wrist-worn Actiwatch 2 device for measuring physical activity.