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

Presented to the Innovations in Rehabilitation Conference, February 16–17, 2007, Rotorua, New Zealand, and the World Confederation of Physical Therapy Congress, June 2–6, 2007, Vancouver, BC, Canada.
https://doi.org/10.1016/j.apmr.2007.07.039Get rights and content

Abstract

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.

Section snippets

Participants

A convenience sample of 25 patients with chronic stroke was recruited from the hospital stroke service and local newspaper advertising. This sample size was chosen to provide sufficient numbers for analysis based on previous sample sizes of between 10 and 16 in similar validation studies.11, 15 Participants were eligible for inclusion if they were at least 6 months poststroke, were aged between 30 and 80, had not had more than 2 falls in the previous 6 months, and had not had any lower-limb

Results

Twenty-five participants with a median age of 69 years (range, 42–79y) were enrolled in the study. There were 17 men and 8 women. Ten participants had right-sided paresis. The median score on the PF index of the SF-36 was 19 (range, 11–29). The median gait speed was 0.5m/s (range, 0.1–0.9m/s). All participants walked independently with a median score on the RMI of 14 (range, 10–15). Twenty-two participants reported independent walking outside over pavements (RMI item 9), and 20 participants

Discussion

In this study, we show that the SAM has good criterion validity for adults with stroke compared with 3-DGA and footswitches. This extends previous work with handheld counters.15 Our study also extends previous work by using different environments and conditions, which we selected for their relevance to community mobility.26 Therefore, a range of commonly encountered outdoor terrains was included such as uneven surfaces, concrete, grass, inclines, declines, and stairs. Because the SAM is

Conclusions

This study has shown that the SAM has criterion validity when used on the nonparetic limb to measure steps in both clinical and natural environments. However, more errors are apparent when the SAM is worn on the paretic limb while walking over a variety of terrains. Validation is recommended before the use of the SAM in patients with neurologic conditions affecting bilateral legs because there may be more error, particularly in outdoor environments.

Acknowledgments

We gratefully acknowledge the contributions of Pat Bennett and Alan Barber, MD, PhD, of the Auckland District Health Board for subject recruitment.

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  • Cited by (0)

    Supported by a Health Research Council Clinical Training Fellowship (grant no. 06/059).

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

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