StepWatch Activity Monitor Research Articles

Commentary on “Walking Stride Rate Patterns in Children and Youth”

“How should I apply this information?” This study used a unique way of analyzing stride rate data collected for children with cerebral palsy (CP) Gross Motor Function Classification System (GMFCS) levels I–III, children with distal arthrogryposis (AR), and youth who were typically developing (TD) over a 7-day period. The authors used data collected with the StepWatch Activity Monitor (SW). Trajectory curves were developed to represent the average number of minutes per day spent at each stride rate, from inactivity (0 strides/minute) to peak stride rate, for each group. They then compared the amount of inactivity, peak stride rates, and variability in stride rates across the 3 groups of children. Children with AR and CP had significantly increased periods of inactivity compared with the TD group. This suggests that these youth participate less in age-appropriate physical activities than TD peers. Less variability in walking speed with lower peak stride rates was found in the children with CP compared with the TD group. This was specifically evident in children classified as GMFCS levels II and III who may require orthoses and assistive devices for mobility. Variability is an important component of motor development, and variable walking speed is necessary for full participation in daily activities. Treatment interventions should, therefore, address increasing variability in gait speed for children with CP and AR. As these children age, orthotics and assistive devices should be reevaluated to ensure that they allow for maximum activity level and versatile speed of movement. Finally, SW measures the child's actual performance of the functional activity of walking in their natural environment over the course of the day. This is different from other outcome measures and may be useful if the goal of intervention is to increase a child's ability to keep up with peers in a school setting, or when preparing a child for participation in a recreation/sports program. “What should I be mindful about in applying this information?” The reader needs to remember that subjects were from a convenience sample and most were Caucasian. Although the authors analyzed stride rate patterns in a large number of youth who were TD, comparisons were made to smaller groups of children with CP and AR. Data were collected on children between the ages of 6 and 15 years; however, comparisons between the TD and CP groups were for children between 10 and 13 years. The reader also needs to be mindful about the use of secondary analysis of different data sets that may pose a problem of consistency in data collection. There are also many confounding variables; that is, environmental factors, body size, physical condition/fitness, etc, that were not monitored or explained that may affect the child's activity level. Strengths of the study include (1) nearly equal boys and girls in each age group, (2) clear method of determining noncompliance, (3) data averaged for 5 days within a 7-day period including 1 week-end day, (4) accuracy of the device demonstrated by comparing it to a manual count, and (5) a transformation method used to normalize data. Overall, an adequate picture of children's walking stride rate patterns is demonstrated for wide age range of both boys and girls. Donna Redman-Bentley, PT, PhD Western University of Health Sciences, Pomona, California Mary Wardell, PT, DPT, MS, PCS Long Beach Memorial Miller Children's Hospital, Long Beach, California

Validation of the StepWatch Device for Measurement of Free-Living Ambulatory Activity in Patients With Chronic Obstructive Pulmonary Disease

This study examined the validity of the StepWatch activity monitor and the optimal number of monitoring days in patients with chronic obstructive pulmonary disease (COPD). StepWatch activity data were obtained from databases of two studies: one of patients with COPD who participated in a trial of two exercise persistence interventions (n = 17) and a second, cross-sectional study of activity in chronically healthy older adults (n = 60). Independent t tests, Pearson's correlations, and Bland-Altman plots were used to examine the activity data (total steps, activity intensity, and distribution of activity). Results indicated that patients with COPD registered 50% fewer total steps and had lower levels of walking intensity compared with chronically healthy older adults. Activity parameters had moderate-to-high correlations with disease severity, peak cycle workload, and physical functioning. More monitoring days were associated with greater measurement precision. This study provides preliminary evidence to support the validity of the StepWatch device for measuring free-living ambulatory physical activity in COPD.

Reliability of daily step activity monitoring in adults with incomplete spinal cord injury

We determined the number of days of step activity monitoring required to establish stable measures of walking activity in adults with incomplete spinal cord injury (iSCI). Eleven individuals with iSCI (mean age 49 +/- 14 years) wore a StepWatch Activity Monitor during waking hours for 7 consecutive days. We used generalizability theory to identify sources of variance in daily step counts and determine the minimum number of days necessary to obtain a reliability coefficient (G-coefficient) greater than or equal to 0.80. Average daily step activity (DSA) was 1,281 +/- 1,594 steps. Participants and days accounted for 70.9% and 1.3% of total variance in DSA, respectively, while unidentifiable error accounted for 27.8% of the total variance in DSA. A minimum of 2 days was required to achieve a G-coefficient greater than or equal to 0.80. An acceptably stable measure of walking activity in adults with iSCI can be obtained by averaging step count values from any 2-day period in a week. Results from this investigation should be useful in evaluating the effect of activity-based programs designed to enhance locomotor function in persons with iSCI.

LEARN 2 MOVE 7-12 years: a randomized controlled trial on the effects of a physical activity stimulation program in children with cerebral palsy

BackgroundRegular participation in physical activities is important for all children to stay fit and healthy. Children with cerebral palsy have reduced levels of physical activity, compared to typically developing children. The aim of the LEARN 2 MOVE 7-12 study is to improve physical activity by means of a physical activity stimulation program, consisting of a lifestyle intervention and a fitness training program.Methods/DesignThis study will be a 6-month single-blinded randomized controlled trial with a 6-month follow up. Fifty children with spastic cerebral palsy, aged 7 to 12 years, with Gross Motor Function Classification System levels I-III, will be recruited in pediatric physiotherapy practices and special schools for children with disabilities. The children will be randomly assigned to either the intervention group or control group. The children in the control group will continue with their regular pediatric physiotherapy, and the children in the intervention group will participate in a 6-month physical activity stimulation program. The physical activity stimulation program consists of a 6-month lifestyle intervention, in combination with a 4-month fitness training program. The lifestyle intervention includes counseling the child and the parents to adopt an active lifestyle through Motivational Interviewing, and home-based physiotherapy to practise mobility-related activities in the daily situation. Data will be collected just before the start of the intervention (T0), after the 4-month fitness training program (T4), after the 6-month lifestyle intervention (T6), and after six months of follow-up (T12). Primary outcomes are physical activity, measured with the StepWatch Activity Monitor and with self-reports. Secondary outcomes are fitness, capacity of mobility, social participation and health-related quality of life. A random coefficient analysis will be performed to determine differences in treatment effect between the control group and the intervention group, with primary outcomes and secondary outcomes as the dependent variables.DiscussionThis is the first study that investigates the effect of a combined lifestyle intervention and fitness training on physical activity. Temporary effects of the fitness training are expected to be maintained by changes to an active lifestyle in daily life and in the home situation.Trial registrationThis study is registered in the Dutch Trial Register as NTR2099.

Test-Retest Reliability of the StepWatch Activity Monitor Outputs in Healthy Adults

Activity Monitors give an objective measure of usual walking performance. This study aimed to examine the test-retest reliability of the StepWatch Activity Monitor outputs (mean steps/day; peak activity index; sustained activity indices of 1, 5, 20, 30, 60 minutes; steps at high, medium, and low stepping rates). Thirty healthy adults age 18 to 49 years wore the StepWatch for 2 3-day periods at least 1 week apart. The intraclass correlation coefficients of the StepWatch outputs ranged from 0.44 to 0.91 over 3 days. The coefficient of variation ranged from 3.0% to 51.3% over the monitoring periods, with higher variation shown for shorter monitoring periods. The most reliable 5 outputs had 95% limits of agreement between 3-day periods that were less than 40%. These were mean steps/day ( ± 39.1%), highest step rate in 1 ( ± 17.3%) and 5 ( ± 37.4%) minutes, peak activity index ( ± 25.6%), and percentage of inactive time ( ± 9.52%). Mean steps/day, highest step rate in 1 and 5 minutes, peak activity index, and percentage of inactive time have good test-retest reliability over a 3-day monitoring period, with lower reliability shown by the other StepWatch outputs. Monitoring over 1 or 2 days is less reliable.

Single-Case Study: Traditional Thermoplastic AFO Versus Adjustable Dynamic Response™—A Crossover Single-Case Study

Past studies have suggested that ankle-foot orthoses (AFOs) improve walking; however, it is unclear what biomechanical designs are most effective. This 10-week trial investigated the effects of a traditional thermoplastic style AFO compared with an Adjustable Dynamic Response™ (ADR™) AFO in a single-case subject. The subject was a 74-year-old man affected by postpolio syndrome with a prior history of AFO use. Patient usage and activity levels were measured with a StepWatch™ Activity Monitor, gait characteristics were measured with a GAITRite® System, and patient satisfaction was measured with a standardized AFO satisfaction questionnaire. The subject wore the traditional AFO for the first 5 weeks of the trial and the ADR™ AFO for the remaining 5 weeks of the trial. Weeks 1 and 5 were considered washout periods, and data were not collected for these weeks with the StepWatch Activity Monitor. Patient usage and activity levels were improved in the ADR™ AFO over the traditional AFO showing an average of 6,606 steps per day in the ADR™ AFO compared with 4,504 steps per day in the traditional AFO. The subject also spent more time engaged in moderate to high activity levels, versus low activity levels, in the ADR™ AFO compared with the traditional AFO. Gait characteristics, such as increased velocity and increased step length, were improved in both AFOs compared with no AFO at all with slightly higher improvements in the ADR™ AFO over the traditional AFO. The AFO satisfaction questionnaire suggested a higher level of patient satisfaction in the ADR™ AFO over the traditional AFO.

Step activity monitoring in lumbar stenosis patients undergoing decompressive surgery

Symptomatic degenerative central lumbar spinal stenosis (LSS) is a frequent indication for decompressive spinal surgery, to reduce spinal claudication. No data are as yet available on the effect of surgery on the level of activity measured with objective long-term monitoring. The aim of this prospective, controlled study was to objectively quantify the level of activity in central LSS patients before and after surgery, using a continuous measurement device. The objective data were correlated with subjective clinical results and the radiographic degree of stenosis. Forty-seven patients with central LSS and typical spinal claudication scheduled for surgery were included. The level of activity (number of gait cycles) was quantified for 7 consecutive days using the StepWatch Activity Monitor (SAM). Visual analogue scales (VAS) for back and leg pain, Oswestry disability index and Roland-Morris score were used to assess the patients' clinical status. The patients were investigated before surgery and 3 and 12 months after surgery. In addition, the radiographic extent of central LSS was measured digitally on preoperative magnetic resonance imaging or computed tomography. The following results were found preoperatively: 3,578 gait cycles/day, VAS for back pain 5.7 and for leg pain 6.5. Three months after surgery, the patients showed improvement: 4,145 gait cycles/day, VAS for back pain 4.0 and for leg pain 3.0. Twelve months after surgery, the improvement continued: 4,335 gait cycles/day, VAS for back pain 4.1 and for leg pain 3.3. The clinical results and SAM results showed significant improvement when preoperative data were compared with data 3 and 12 months after surgery. The results 12 months after surgery did not differ significantly from those 3 months after surgery. The level of activity correlated significantly with the degree of leg pain. The mean cross-sectional area of the spinal canal at the central LSS was 94 mm(2). The radiographic results did not correlate either with objective SAM results or with clinical outcome parameters. In conclusion, this study is the first to present objective data on continuous activity monitoring/measurements in patients with central LSS. The SAM could be an adequate tool for performing these measurements in spine patients. Except for leg pain, the objective SAM results did not correlate with the clinical results or with the radiographic extent of central LSS.

Circuit-Based Rehabilitation Improves Gait Endurance but Not Usual Walking Activity in Chronic Stroke: A Randomized Controlled Trial

Mudge S, Barber PA, Stott NS. Circuit-based rehabilitation improves gait endurance but not usual walking activity in chronic stroke: a randomized controlled trial. Objective To determine whether circuit-based rehabilitation would increase the amount and rate that individuals with stroke walk in their usual environments. Design Single-blind randomized controlled trial. Setting Rehabilitation clinic. Participants Sixty participants with a residual gait deficit at least 6 months after stroke originally enrolled in the study. Two withdrew in the initial phase, leaving 58 participants (median age, 71.5y; range, 39.0–89.0y) who were randomized to the 2 intervention groups. Interventions The exercise group had 12 sessions of clinic-based rehabilitation delivered in a circuit class designed to improve walking. The control group received a comparable duration of group social and educational classes. Main Outcome Measures Usual walking performance was assessed using the StepWatch Activity Monitor. Clinical tests were gait speed (timed 10-meter walk) and endurance (six-minute walk test [6MWT]), confidence (Activities-Based Confidence Scale), self-reported mobility (Rivermead Mobility Index [RMI]), and self-reported physical activity (Physical Activity and Disability Scale). Results Intention-to-treat analysis revealed that the exercise group showed a significantly greater distance for the 6MWT than the control group immediately after the intervention ( P=.030) but that this effect was not retained 3 months later. There were no changes in the StepWatch measures of usual walking performance for either group. The exercise and control groups had significantly different gait speed ( P=.038) and scores on the RMI ( P=.025) at the 3-month follow-up. These differences represented a greater decline in the control group compared with the exercise group for both outcome measures. Conclusions Circuit-based rehabilitation leads to improvements in gait endurance but does not change the amount or rate of walking performance in usual environments. Clinical gains made by the exercise group were lost 3 months later. Future studies should consider whether rehabilitation needs to occur in usual environments to improve walking performance.

Validity and Reproducibility of Motion Sensors in Youth

To review recently published studies on the reproducibility, validity, and feasibility of motion sensors used to assess physical activity in healthy children and adolescents (2-18 yr). On October 2004, a systematic literature search in PubMed, EMBASE, and PsycINFO was performed. This search has been updated on October 2007. In this update, the clinimetric quality of three pedometers (Digi-Walker, Walk4Life, and Sun TrekLINQ) and nine accelerometers (ActiGraph, BioTrainer, StepWatch Activity Monitor, Actiwatch, Actical, Tritrac-R3D, RT3, ActivTracer, and Mini-Motionlogger) has been evaluated and compared using a checklist. Thirty-two recently published clinimetric studies have been reviewed. All 12 motion sensors have been validated in youth in one or more studies. There is strong evidence for moderate validity of the StepWatch in children and adolescents (4-18 yr) and moderate to good validity of the ActiGraph in preschool children and young children (2-8 yr). There is less evidence for the reproducibility and feasibility of the 12 motion sensors. Strong evidence exists for good reproducibility of the ActiGraph in preschool children (2-4 yr). Compared to the review performed in 2004, there is increased evidence for the clinimetric quality of pedometers and accelerometers in youth. Most motion sensors seem reproducible, valid, and feasible in assessing physical activity in youth.

Timed Walking Tests Correlate With Daily Step Activity In Persons With Stroke

Mudge S, Stott NS. Timed walking tests correlate with daily step activity in persons with stroke. Objectives To examine the relationship among 4 clinical measures of walking ability and the outputs of the StepWatch Activity Monitor in participants with stroke. Design Correlational study. Setting Clinic and participants' usual environments. Participants Fifty participants more than 6 months after stroke were recruited. All participants were able to walk independently, but with some residual difficulty. Interventions Not applicable. Main Outcome Measures Rivermead Mobility Index (RMI), Rivermead Motor Assessment (RMA), six-minute walk test (6MWT), ten-meter walk test (10MWT), StepWatch outputs (based on daily step counts and stepping rates). Results The correlations between the RMA and all StepWatch outputs were low ( ρ=0.36–0.48; P<.05), as were most for the RMI (ρ=0.31–0.52; P<.05). The 10MWT and 6MWT had moderate to high correlations (ρ=0.51–0.73; P<.01) with most StepWatch outputs. Multiple regression showed that the 6MWT was the only significant predictor for most StepWatch outputs, accounting for between 38% and 54% of the variance. Age and the RMI were further significant predictors of 1 and 2 outputs, respectively. Conclusions The 6MWT has the strongest relationship with the StepWatch outputs and may be a better test than the 10MWT to predict usual walking performance. However, it should be remembered that the 6MWT explains only half the variability in usual walking performance. Thus, activity monitoring captures aspects of walking performance not captured by other clinical tests and should be considered as an additional outcome measure in stroke rehabilitation.

How humans walk: Bout duration, steps per bout, and rest duration

Much is known about human walking, but it is not known how walking is used during typical activities. Since improving walking ability is a key goal in many surgical, pharmacological, and physiotherapeutic interventions, understanding typical community mobility demands regarding the length of walking bouts, the number of sequential steps frequently performed, and the duration of common nonwalking (rest) behavior seems prudent. This study documents the gait of daily living in 10 nondisabled employed adults to define walking bout duration, sequential step counts, and length of rest periods over a 2-week period. Subjects wore a StepWatch Activity Monitor (OrthoCare Innovations; Mountlake Terrace, Washington) that counted steps in each 10-second time window. Custom code summed sequential steps, periods of walking behavior (bouts), and periods without steps (rest). Sixty percent of all walking bouts lasted just 30 seconds or less; a 2-minute walking bout was just 1 percent of total walking bouts. Forty percent of all walking bouts were less than 12 steps in a row, and 75 percent of all walking bouts were less than 40 steps in a row. Rest periods were predominantly very short, with half of all rests periods lasting 20 seconds or less. The community mobility demand for nondisabled employed adults appears to involve frequent short-duration walking behavior with low numbers of sequential steps strung together and many short-duration nonwalking (rest) behaviors.

Test—retest reliability of the StepWatch Activity Monitor outputs in individuals with chronic stroke

Objective: To examine the test—retest reliability of the StepWatch Activity Monitor outputs over two periods, a week apart, in participants with stroke. Design: Test—retest reliability study over monitoring periods of one, two and three days. Setting: Participant's usual environment. Participants: Forty participants more than six months post stroke. Main measures: StepWatch outputs: total step count, number of steps at high medium and low stepping rates, sustained activity indices, peak activity index. Results: The intraclass correlation coefficients were high for all StepWatch outputs and all monitoring periods but were highest for the three-day monitoring period (0.930—0.989) and lowest for the one-day monitoring period (0.830—0.950). The coefficient of variation ranged from 6.7% to 48.7% over the monitoring periods, with higher variation shown for shorter monitoring periods. The most reliable four outputs had 95% limits of agreement between three-day periods that were less than 40%. These were total step count (±37.8%), highest step rate in 1 minute (±23.0%), highest step rate in 5 minutes (±38.6%) and peak activity index (±29.8%). The highest step rate in 1 minute was the only StepWatch output that had 95% limits of agreement less than 40% for the two-day (±31.2%) and one-day (±36.7%) monitoring periods. Conclusions: Total step count, highest step rate in 1 minute, highest step rate in 5 minutes and peak activity index have good test—retest reliability over a three-day monitoring period, with lower reliability shown by the other StepWatch outputs. In general, monitoring over one or two days is less reliable.

Gait Speed and Step-Count Monitor Accuracy in Community-Dwelling Older Adults

Accurate assessment of physical activity (PA) is necessary to identify the sedentary older individual who is in need of activity intervention. Activity monitors are quite popular, although it has been suggested that they are less accurate at slow gait speeds. To examine the accuracy of the three activity monitors in older individuals who walk at various gait speeds. Participants were 34 community-dwelling older men and women (mean age 79.2) who were asked to simultaneously wear three activity monitors: the Yamax DigiWalker (DW) pedometer (hip), the Actigraph (AG) accelerometer (hip), and the StepWatch activity monitor (SAM) (ankle). Monitor accuracy was evaluated against observed steps taken during a 100-step walking test. Percent error of the monitors was calculated as [(monitor steps - observed steps)/observed steps] x 100. Participants were categorized into three groups (< 0.80, 0.80-1.0, > 1.0 m x s(-1)) according to gait speed, which was determined by a timed 4-m walk. Overall, the DW and AG failed to detect 16% and 7% of observed steps, respectively, and the SAM overestimated by 5.5%. When stratified by gait speed, all three monitors faired well at the gait speeds > 1.0 m x s(-1). For gait speeds between 0.80 and 1.0 m x s(-1), the SAM overestimated steps by 6.6%, and the AG and DW underestimated steps by 5.7% and 12.7%, respectively. However, at gait speeds < 0.80 m x s(-1), the AG and DW performed poorly, underestimating steps by 19.1% and 31.2%, whereas the SAM performed better, having overestimated steps by 6.5%. All three objective activity monitors performed well at moderate and higher walking speeds, but at decreased gait speeds, the SAM seemed to be the most accurate.

Criterion Validity of the StepWatch Activity Monitor as a Measure of Walking Activity in Patients After Stroke

Mudge S, Stott NS, Walt SE. Criterion validity of the StepWatch Activity Monitor as a measure of walking activity in patients after stroke. Objectives To test the validity of the StepWatch Activity Monitor (SAM) in subjects with stroke against 2 criterion standards, 3-dimensional gait analysis (3-DGA) and footswitches in a variety of indoor and outdoor walking conditions, including different speeds and different terrains, and to test the accuracy of the SAM when worn on the paretic limb. Design Criterion standard validation study. Setting Gait laboratory and outside course. Participants Twenty-five participants with physical disability after stroke. Interventions Not applicable. Main Outcome Measures The total step count measured simultaneously by SAM and either 3-DGA or footswitches for both paretic and nonparetic limbs. Results The total step count measured by the SAM and 3-DGA was highly correlated (nonparetic limb, r=.959; paretic limb, r=.896). The 95% limits of agreement (LOA) (derived from Bland-Altman analysis) between the SAM and 3-DGA were within ±10 steps for SAMs worn on either the nonparetic or paretic limb. The total step count measured simultaneously by the SAM and footswitches was also highly correlated for each limb (nonparetic, r=.999; paretic, r=.963). The 95% LOA between the SAM and footswitches were ±9 steps on the nonparetic limb but higher at ±57 steps on the paretic limb. Further analysis showed that the measurement differences occurred during the outdoor component of the combined walk. The 95% LOA between footswitches on both limbs were not more than ±9 steps for walking, suggesting that the error was accounted for by the SAM on the paretic limb, which both over- and underread the total step count in the outdoor walking conditions. Conclusions Criterion validity of the SAM to measure steps in both clinical and natural environments has been established when used on the nonparetic limb. However, more errors are apparent when the SAM is worn on the paretic limb while walking over a variety of outdoor terrains. Validation is recommended before use in patients with neurologic conditions affecting bilateral legs because there may be more error, particularly in outdoor activities.

Feasibility of a walking workstation to increase daily walking

Objective:The number of calories expended in the workplace has declined significantly in the past 75 years. A walking workstation that allows workers to walk while they work has the potential...

Use of the StepWatch Activity Monitor for Characterization of Normal Activity Levels of Children

Clinical and research measures for walking activity measure capacity and performance. Existing tools such as 3-dimensional gait analysis and validated gross motor instruments examine capacity but do not measure performance. We defined normal activity levels for 20 children ages 5-7 and 9-11 years using the StepWatch Activity Monitor (SAM). Average daily step counts varied widely by age and sex (mean 7604 +/- 2485), but the percent time spent at high, medium, and low levels of activity was very consistent regardless of age or sex of the child.

Accuracy Of Three Commonly Used Activity Monitors In Community Dwelling Older Adults

Adequate physical activity levels are a key health concern in older individuals. Accurate assessment of physical activity (PA) is necessary in order to identify the sedentary older individual that is in need of intervention. PURPOSE To determine the accuracy of the three objective activity monitors in a group of community dwelling older adults and to explore whether gait speed effects the accuracy of these monitors. METHODS Subjects included 21 community dwelling men and women (mean age 75.9 ± 4.5 years) from suburban Pittsburgh, Pennsylvania. Participants were asked to wear a combination of three activity monitors: the Yamax DigiWalker (DW) pedometer (hip), the ActiGraph (AG) accelerometer (hip), and the StepWatch Activity Monitor (SAM) (ankle). Monitor accuracy was evaluated against observed steps taken during a 100 step walking test. Gait speed was determined with a timed 6 meter walk at the participant's self-selected walking speed. Participants were categorized into three groups based on gait speed (<0.80, 0.80–1.0, > 1.0 m/s). Percent error was calculated as [(monitor steps - observed steps)/observed steps] × 100. RESULTS Preliminary results from 20 participants indicate the DW and AG failed to detect 9.9% and 3.7% of observed steps, respectively and SAM overestimated by 8.2%. Stratified by gait speed, participants with the slowest gait speed (n=3), the DW and AG underestimated by 20.3% and 19.3%, respectively. The SAM overestimated by 10.7%. For those in the middle gait speed category (n=12), the DW and AG again underestimated by 5.5% and 1.7%, respectively. The SAM overestimated by 7.7%. For those with the fastest gait speed (n=5), the DW underestimated by 15%. The AG and SAM overestimated by 0.4% and 8.0%, respectively. Spearman Rank Order Correlation Coefficients indicated a positive association between gait speed and percent error for all three monitors. The AG was the only monitor whose percent error was significantly related to gait speed (rho = 0.47, p = 0.03). CONCLUSIONS When examining the group as a whole, the three activity monitors appear to accurately assess observed steps during a 100 step test. Upon further inspection, in older adults walking slowly, two of the monitors failed to detect 20% of the steps taken. For accurate assessment of PA in older adults, gait speed should be considered. Supported by: University of Pittsburgh, Dept. of Epidemiology Small Grants Fund

Accuracy Of Three Commonly Used Activity Monitors In Community Dwelling Older Adults

Adequate physical activity levels are a key health concern in older individuals. Accurate assessment of physical activity (PA) is necessary in order to identify the sedentary older individual that is in need of intervention. PURPOSE To determine the accuracy of the three objective activity monitors in a group of community dwelling older adults and to explore whether gait speed effects the accuracy of these monitors. METHODS Subjects included 21 community dwelling men and women (mean age 75.9 ± 4.5 years) from suburban Pittsburgh, Pennsylvania. Participants were asked to wear a combination of three activity monitors: the Yamax DigiWalker (DW) pedometer (hip), the ActiGraph (AG) accelerometer (hip), and the StepWatch Activity Monitor (SAM) (ankle). Monitor accuracy was evaluated against observed steps taken during a 100 step walking test. Gait speed was determined with a timed 6 meter walk at the participant's self-selected walking speed. Participants were categorized into three groups based on gait speed (<0.80, 0.80–1.0, > 1.0 m/s). Percent error was calculated as [(monitor steps - observed steps)/observed steps] × 100. RESULTS Preliminary results from 20 participants indicate the DW and AG failed to detect 9.9% and 3.7% of observed steps, respectively and SAM overestimated by 8.2%. Stratified by gait speed, participants with the slowest gait speed (n=3), the DW and AG underestimated by 20.3% and 19.3%, respectively. The SAM overestimated by 10.7%. For those in the middle gait speed category (n=12), the DW and AG again underestimated by 5.5% and 1.7%, respectively. The SAM overestimated by 7.7%. For those with the fastest gait speed (n=5), the DW underestimated by 15%. The AG and SAM overestimated by 0.4% and 8.0%, respectively. Spearman Rank Order Correlation Coefficients indicated a positive association between gait speed and percent error for all three monitors. The AG was the only monitor whose percent error was significantly related to gait speed (rho = 0.47, p = 0.03). CONCLUSIONS When examining the group as a whole, the three activity monitors appear to accurately assess observed steps during a 100 step test. Upon further inspection, in older adults walking slowly, two of the monitors failed to detect 20% of the steps taken. For accurate assessment of PA in older adults, gait speed should be considered. Supported by: University of Pittsburgh, Dept. of Epidemiology Small Grants Fund

Utility of a step activity monitor for the measurement of daily ambulatory activity in children

McDonald CM, Widman L, Abresch RT, Walsh SA, Walsh DD. Utility of a step activity monitor for the measurement of daily ambulatory activity in children. Arch Phys Med Rehabil 2005;86:793–801. Objectives To evaluate the reliability and validity of the StepWatch Activity Monitor (SAM) as a reliable and valid measurement tool for assessing ambulatory activity in able-bodied children and to assess the ambulatory activity of able-bodied children. Design Descriptive study. Setting General community. Participants Ninety-seven able-bodied children, aged 6 to 20 years. Interventions Not applicable. Main outcome measures Anthropometric parameters, calibration of a step activity monitor to ensure accuracy, and 3 days of simultaneous heart rate and step activity monitoring. Results The SAM had an accuracy of 99.87% compared with the observer-counted steps and was shown to be valid and reliable when compared with heart rate monitoring. The subjects in all age groups (6–10y, 11–15y, 16–20y) spent most of their active time at low step rate but took the fewest steps at this rate. Although the least amount of time was spent at high step rate, it accounted for the most steps. The 6- to 10-year-old group took more total steps per day than any of the other groups. Boys spent significantly more time at high step rate than girls in all age groups (mean for boys, 66±4min/d; girls, 47±4 min/d). Conclusions The SAM is an accurate, valid, and useful tool for measuring continuous, time-based step activity during real-world community activity for children and adolescents.

Use of step activity monitoring for continuous physical activity assessment in boys with Duchenne muscular dystrophy

McDonald CM, Widman LM, Walsh DD, Walsh SA, Abresch RT. Use of step activity monitoring for continuous physical activity assessment in boys with Duchenne muscular dystrophy. Arch Phys Med Rehabil 2005;86:802–8. Objectives To evaluate the StepWatch Activity Monitor (SAM) as a quantitative measure of community ambulation, to investigate activity patterns and heart rate of ambulatory boys with Duchenne muscular dystrophy (DMD), and to correlate the step activity with measures of body composition and strength. Design Case-control study. Setting General community and laboratory. Participants Sixteen ambulatory boys with DMD and 20 male controls (age range, 5–13y). Interventions Not applicable. Main outcome measures Laboratory determinations of body composition, knee extension strength, and minute-by-minute step rate and heart rate during 3 days of community activity. Results During the 3 days of activity, DMD subjects, when compared with controls, (1) had significantly more inactive minutes (1096±90min/d vs 1028±85min/d), (2) took significantly fewer steps and spent fewer minutes at moderate (66±31min/d vs 94±30min/d) and high step rates (43±30min/d vs 72±38min/d), (3) had higher resting heart rate (110±12 beats/min vs 94±7 beats/min) and lower increase in heart rate with increased step rate, and (4) had lower maximum heart rates (164±24 beats/min vs 208±16 beats/min). Percentage of body fat and knee extension strength correlated with total step activity in the DMD group but not in the control group. Conclusions Step-rate monitoring with the SAM provides useful outcome measures with which to evaluate the activity of ambulatory boys with DMD. Their heart rate did not increase with activity to the same degree as observed in the control group.