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ORIGINAL RESEARCH ARTICLES

The Accuracy of Variously Positioned Pedometers for Lower-Limb Prosthesis Users

Guerra, Gary PhD; Smith, John D. PhD; Gomez, Paula CO, MS; Siriwatsopon, Juthamas BEd

Author Information
Journal of Prosthetics and Orthotics: October 2019 - Volume 31 - Issue 4 - p 257-261
doi: 10.1097/JPO.0000000000000264
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Abstract

Limb loss has the capacity to hamper an individual’s ability to live independently and participate in a variety of activities of daily living such as working and providing food and shelter for themselves and their family.1 A person with amputation who continues to live a sedentary lifestyle will most likely have an increase in health-related issues.2 A sedentary lifestyle increases the risk of developing cardiovascular disease and other chronic diseases such as obesity,3 which is a risk factor for type 2 diabetes.4 Unfortunately, persons with amputations have a higher risk for mortality from cardiovascular disease than their peers who do not have amputations,5 and to reduce the risks of developing cardiovascular disease, persons with amputations must maintain an active lifestyle.6 A recent review of literature provided strong evidence of the wide range of health benefits that physical activity offers.7 The benefits of physical activity are not solely preventive; in fact, an individual who lives a more active lifestyle can achieve increased physical function8 and a higher quality of life.9,10

With an increasing prevalence of metabolic diseases resulting from inactivity, the need to identify accurate physical activity monitors has become progressively more important.11 Questionnaires and surveys rely on an individual’s ability to recall activity but may not be accurate representations of daily physical activity,12 and the ability of questionnaires to give objective measures of activity is also debatable.13 Using objective activity monitors such as pedometers to measure activity of persons with amputation is preferred because self-report methods have been shown to be less accurate for measuring actual activity in this population.14 Pedometers are inexpensive, accurate, reliable, and provide important measures of ambulant activity such as step count and distance walked over short and longer durations.15 Newer pedometers use a piezoelectric sensor to measure steps and distance in the vertical plane,16,17 and have been regarded as valid tools for measuring physical activity.18 Moreover, measuring activity of individuals with amputation in both developed as well as resource-limited environments (RLEs) requires the use of an affordable, reliable, and robust activity monitor. Using an accurate and economical pedometer to measure prosthetic activity can give clinicians, researchers, funding agents, and persons with amputation important outcome measures on activity levels.19 Unfortunately, there is limited research in tracking activity of individuals with amputation. This may be as a result of the unavailability of economical and accurate tools to measure this activity. The recommended mounting location for pedometers is at the anterior midline of the hip, and in the past, wider abdominal circumferences have had an effect on pedometer accuracy.20 Currently, there are no data on the validity and reliability of the HJ-329 pedometer worn at different positions in individuals wearing a lower-limb prosthesis.

An ability to modify the suggested wearing position can increase potential use and acceptability of a pedometer, yet there is a limited amount of literature examining the accuracy of pedometers worn in nontraditional wearing positions such as the pocket or around the neck.21 Prosthesis wearers are just as susceptible to a sedentary lifestyle as able-bodied persons, and as such, persons with amputation and prosthetists should have access to affordable and accurate activity quantification devices. We sought out to explore the accuracy of pedometers in the population of persons with lower-limb amputation, which have been previously deemed accurate for able-bodied persons. The uniqueness of the artificial limb and ambulation characteristics of the wearer merited the need to explore the accuracy of the pedometers to properly measure activity in this population.

Our objective was to evaluate the accuracy of a new version of an activity monitor, the Omron HJ-329 (Omron Healthcare, Inc, Lake Forrest, IL), for lower-limb prosthetic wearers, as well as to investigate the accuracy of the wearable while worn at various locations. We chose to explore accuracy of placement of pedometers in various locations in an attempt to elucidate whether or not potential users and prosthetists could freely place the device at various points on the body or according to their preferences.

METHODS

PARTICIPANTS

All participants were recruited from the Laboratorio Gilete O&P clinic located in Bogota, Colombia. Interested individuals signed an approved institutional review board consent form. The study was reviewed and approved by the Loma Linda University Institutional Review Board. Individuals who volunteered for the study met the following inclusion criteria: individuals with lower-limb amputation with a healthy residual limb, between ages 18 to 65 years, and at least 6 months postamputation. They had a comfortable and functioning final prosthesis and were capable of walking unassisted without the use of a cane, walker, or other assistive device for 200 m. Individuals who were pregnant were excluded.

PROCEDURES

Participant height and weight with prosthesis and shoes on were collected using the SECA S-214 portable height rod (Hanover, MD, USA) and the DR400C digital body weight scale (Webb City, MO, USA). Demographics of study participants were collected as well. Before data collection, the Omron HJ-329 pedometer batteries were replaced with new batteries and fit to the investigator at the right and left hips. The investigator walked 100 steps while counting actual hand tallied counts to check for accuracy of all devices. If the device registered a margin of error of greater than 3% (3 steps of 100), which is the recommended maximum permissible rate of step miscount,22,23 the pedometer was not used. This procedure occurred until a properly functioning pedometer without the aforementioned error was confirmed. The same pedometers were used in the same locations for all participant data collection.

The participants were fit with a Velcro Walk4Life pedometer belt (Walk4Life Inc, Plainfield, IL, USA) on the waistline of the hip; an Omron HJ-329 piezoelectric pedometer was fit at the left and right hips, in left and right pockets, and around the neck using a neck strap. On level ground, a straight 100 m indoor path was marked using a measuring wheel, and an orange cone was placed at the end of the path that served as the turning point for participants. Once the pedometers were fit to the participant, the participant was asked to move to the starting line and the pedometers were reset to zero. The participant was then instructed to walk to the cone, turn around, and walk back to the start line at his/her normal self-selected pace, with no restriction or control of how fast or slow he/she walked. Pedometers have a tendency to provide less accurate measurements when participants ambulate at speeds below 3 mph.24 The participant height, weight, and stride length were input into the pedometer settings for each participant. The investigator counted each step using a hand tally counter (Model no.77; Lab Safety Supply Inc, Janesville, WI, USA), which served as the criterion measure of actual step counts. Upon completion of the walk, participants were instructed to cease motion while pedometer and hand tally counts were recorded.

STATISTICAL ANALYSIS

All statistical tests were performed using IBM SPSS Statistics Software for Windows (Chicago, IL, USA). Repeated-measures (RMs) analyses of variance (ANOVAs) were used to determine differences in pedometers and actual counts (ACs) obtained between amputation classification (affected and nonaffected side) while walking, with α set at 0.05. Mauchly’s test of sphericity was used to test for the equality of variances of the differences among amputation classification and step count, after which the Greenhouse-Geisser correction was used as the correct test of within-subjects effects. A single-measure intraclass correlation coefficient (ICC) from a two-way random effects ANOVA was used to assess the agreement between ACs and pedometer counts, with 0.90 or greater considered high agreement, 0.80 to 0.89 moderate agreement, and 0.79 or lower low agreement.25 Bland-Altman plots of actual counts compared with pedometer counts provided an indication of any overrepresentation or underrepresentation of steps as well as agreement between measures.26 If error scores were 0, this indicated no differences between actual steps taken and steps registered by the pedometer. Percentage error was calculated as ([steps detected by pedometer − AC]/AC) × 100 and reflected as absolute values.

RESULTS

Participant characteristics can be seen in Table 1. Our study sample saw more participants presenting with left affected limbs. The mean and SD values for the AC and pedometer counts are provided in Table 2. The Greenhouse-Geisser correction was used to determine the significance for walking (F2.59,22.0 = 0.651, P = 0.569) because the Mauchly’s test statistic was significant (P = 0.000). We found no significant interaction, so a main effect test was performed. There was no main effect of where the pedometer was worn (F2,17 = 0.262, P = 0.773), nor was there a main effect of step count (Pillai’s Trace = 0.297, F5,13 = 1.101, P = 0.406). This indicated no differences between any of the pedometers. Sidak post hoc tests also revealed no significant differences between pedometers worn on the affected and nonaffected sides, although pedometers worn on the nonaffected side tended to be slightly more accurate than those worn on the affected side. Agreement was low between actual counts and pocket right and pocket left pedometers. Wearing the pedometer on the hip had the highest agreement, which is consistent with previous literature.27 The greatest ICCs and lowest error were observed in the pedometers located at the right and left hip locations (Table 3).

T1
Table 1:
Characteristics of study participants
T2
Table 2:
Counts registered during a 200-m walk in prosthesis wearers
T3
Table 3:
Intraclass correlation coefficients between actual counts and pedometer counts while walking

Absolute percentage errors were greatest with the pedometer in the left pocket (6.8%; 95% confidence interval [CI], −1.8 to 15.5) and on the neck strap (6.7%; 95% CI, −0.69 to 14.1), followed by the right pocket (5.9%; 95% CI, −0.18 to 12.1]), right hip (2.6%; 95% CI, −0.78 to 5.9]), and left hip (2.2%; 95% CI, 0.22 to 4.28]). For the difference between the means, the Cohen’s d effect size values were as follows: actual count and neck strap (d = 0.40), actual count and right pocket (d = 0.35), actual count and left pocket (d = 0.30), actual count and right hip (d = 0.19), actual count and left hip (d = 0.00). The Bland-Altman plots demonstrated mean error among the pedometers, and the tighter limit of agreement visible with the left hip pedometer compared with the other pedometer locations (Figure 1).

F1
Figure 1:
Bland-Altman plots for pedometer and actual counts for each location.

DISCUSSION

We evaluated accuracy of a pedometer in lower-limb prosthesis users and examined accuracy when worn at different body locations. Previous literature identified 3% pedometer error as an acceptable error reading.22 The pedometers in the current study had a wide range of percentage errors. The least amount of error was seen in the pedometer located at the left hip (1.80%) followed by the right hip (2.35%), right pocket (5.79%), left pocket (7.05%), and the neck strap location (7.03%). Among individuals with unilateral amputations, no differences in metrics between affected and nonaffected limbs were observed. For our bilateral participants, the same nondifferences were observed.

Pairwise comparisons were explored, and while there were trends for greater accuracy when worn on the opposite side of the affected leg, there were still no significance differences. There were no significant differences between the various placement locations and actual counts. Findings in this study indicate that no matter where the pedometer is placed and what side is affected, persons with a lower-limb amputation using a prosthesis have the option to place the pedometer anywhere they like. Previous studies have found that placement of a pedometer can affect its accuracy28; however, those findings can be attributed to different pedometers and walking speeds. On the other hand, previous studies have suggested that pedometers can accurately record steps on various placement on the body, similar to the current study, but that speed can ultimately affect this accuracy.29 If the individual cannot wear the pedometer on one side, then they can wear it on the opposite side. In addition, they can wear the pedometer at any of the locations explored in this study if they choose to. Although the current study did not assess speed of the subjects while walking, we find that at their self-selected overground speed on a level surface, the HJ-113 accurately records steps on various body locations.

The cost of the pedometer we used is approximately $30 USD, the Fitbit (San Francisco, CA) costs approximately $75 USD but might not be appropriate as a clinical tool. Excellent but more expensive activity monitors, such as the Modus Health Step-Watch (Washington, DC, USA), offer a number of additional metrics for the prosthetist to use as an outcome measure tool.30 In all parts of the world, the ability to accurately track prosthesis wearers’ walking with an affordable device is essential. However, a potential advantage of consumer wrist-worn activity monitors is their ability to be worn on a user’s wrist, thereby removing the necessity of continually placing the monitor on and off the body. Pedometers are still most accurate when worn at the waist or pocket; future research should investigate compliance between wrist- and waist-worn activity monitors. A limitation of this current study is that data collection was conducted in a controlled indoor setting during a short 200-m trial with a small sample size. Future studies should examine both short-term activity and volume of activity monitoring via pedometers worn by persons with lower-limb amputation in a variety of terrains, as well as explore activity of persons with lower-limb amputation in free-living conditions and cadence and velocity metrics. Another limitation of our study was that the majority of our participants lost their limbs as a result of trauma, and our decision to not restrict amputation level recruitment is certainly a limitation, but one which could be mitigated through future work. Furthermore, although small, we did not exclude bilateral participants in our analysis because of a desire to include a sample representative of the study location. A suitable control group of able-bodied participants could also highlight the differences, if any, between the two populations. We did not assess reliability of hand tally counters and thereby assumed if there was error in recording steps with the hand tally, it would be evenly distributed due to the same person recording all subjects. The results of this study may not be generalizable to individuals who have lost their limbs due to other causes.

Activity monitors can provide a means to motivate and engage individuals to participate in physical activity.31 Pedometers and other wearables are becoming increasingly popular with able-bodied individuals in developed nations. The same should be true for prosthesis wearers in developing countries. It is reasonable to say that the Omron HJ-329 pedometer can be used to track basic ambulant activity with confidence in individuals with lower-limb amputations.

ACKNOWLEDGMENTS

We appreciate the efforts of Ms. Martha Rodriguez, PT, and Laboratorio Gilete for their assistance with the research investigation as well as Ms. Juthamas Siriwatsopon.

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Keywords:

prosthetics; outcome measures; activity monitor; pedometer

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