Activity Monitoring in Prosthetic Users: Psychometric Properties of Motio StepWatch™
Self-reported activities of lower limb prosthetic users and Patient-Reported Outcome Measures (PROMs) have limited reliability and objectiveness, which has led to an increasing interest in accurate real-world activity monitoring. For prosthetic users, monitoring activity levels can be important for several reasons, including evaluating the effectiveness of their prosthetic device, assessing progress during rehabilitation, and promoting physical activity for overall health and well-being [1–3].
Measuring physical and level of activity in lower limb prosthetic users is crucial for monitoring progress and assessing the effectiveness of rehabilitation interventions.
We would like to highlight, among the myriad of options available, five categories of outcome measures used to evaluate the level of activity in lower limb prosthetic users: step count-based measures, gait characterization, type of activity/environmental barriers, community categories and others, such as frequent donning and doffing or heart rate [4-5].
Step count-based measures have become the most common outcome measures used to describe the level of activity for lower limb prosthetic users [2,4–6]. These measures provide clinicians with a quantitative and objective method to track patients' progress.
Studies have reported numerous variables related to step count, including the number of steps taken per day, week, or month, as well as intensity [7,8], continuous walking distance or periods [9,10], and maximal number of consecutive steps taken [11]. Other outcome measures related to a person's fitness level or intensity of activity were also calculated based on the step count during an activity data collection, such as cadence in steps per minute [12], frequency or time in a specific intensity interval, and time spent in inactivity [13,14].
According to previous studies by Stepien et al[2] and Godfrey et al[15], a large number of participants who used lower limb prostheses inaccurately reported their levels of low, medium, and high activity compared to objective assessments of their activity, and there was no apparent tendency towards over- or underreporting. To obtain more reliable data that directly indicates the usual level of activity or potential of a patient, conducting blind tests have the advantage of obtaining the most precise depiction of a patient's functional level, without the patient's awareness of being tested influencing the final outcome [17]. These tests record the daily activity of a patient under real-life conditions, where standard tests such as the 6 Minute Walk Test and the Timed-Up-Go can be performed during the day, without the patient realizing it or trying to optimize their performance.
Various devices have been tested in lower limb prosthetic users to measure activity levels. Activity monitors with integrated accelerometers, such as the StepWatch, have been found to be highly accurate and reliable for this purpose. Additionally, simpler pedometers have also been used, but they may not provide as detailed information as activity monitors.
Psychometric Properties of Motio StepWatch™
Motio's hardware is built upon the clinically approved and FDA-listed Modus Health StepWatch 4. The device is highly accurate in counting steps and detecting walking patterns and has been used in over 500 peer-reviewed journal articles and in more than 30 patient conditions [16]. In fact, when compared with other activity monitors or step counters, it reports higher accuracy (Figure 1).
Figure 1: Accuracy of different step counters in patients with impaired walking, from [17]
One of the key advantages of Motio Stepwatch is its ability to monitor patients with impaired gait accurately. The device has an accurate step detection for all walking styles and a resolution of steps per second, providing different metrics based on step count, such as steps per day, active minutes of a day, percentage of time spent in low/medium/high activity, peak stride velocity, and average and median cadence.
In several studies, excellent test-retest reliability has been found for the StepWatch in older adult populations, including those who are non-impaired, impaired, and those using a cane. For instance, one study published in the Prosthetics and Orthotics International SAGE Journals evaluated the test-retest reliability of the StepWatch 4 (compared with FitBit One) in individuals with transtibial amputations. The study found excellent agreement between repeated measurements of step count, with an ICC of 0.97-0.99, indicating excellent test-retest reliability [18].
Other studies conducted in 2018 [18,19] evaluated the StepWatch 4's concurrent validity in individuals with lower limb amputations. The researchers found a significant correlation between the StepWatch, the 10-meter walk test, and the Activity-Specific Balance Confidence Scale, indicating that the StepWatch is a valid measure of physical activity in these populations. The researchers also discovered that a 1-point rise in the Prosthetic Evaluation Questionnaire and Houghton Scale of Prosthetic Use led to increases in daily step counts of 172 and 1532, respectively [20].
As technology advances, there is a growing need to assess the chosen outcome measures and to what extent they represent real-world situations. Overall, step count-based measures and blind structured tests are promising tools for clinicians to monitor and assess the physical activity of lower limb prosthetic users. With the availability of accurate and reliable devices such as Motio StepWatch, clinicians can obtain valuable data to optimize the rehabilitation process and improve the patient's quality of life.
References
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