Step Activity Monitor: Increased Accuracy in Quantifying Ambulatory Activity

Abstract

Summary: This study compares the accuracy of a two-dimensional accelerometer worn on the ankle (a step activity monitor) with that of an electronic, digital pedometer worn on the belt line. Twcnty-nine human subjects were evaluated while they briskly walked 400 M, slowly walked 10 M. and ascended and dcsccndcd a flight 01 stairs. The step activity monitor had less error in all activities; its mean absolute error was 0.54%, whereas that of the pedometer was 2.82%. The difference was more pronounced in obese subjects (body mass index greater than 30), with an overall mean absolute error of 0.48% for the step activity monitor and 6.12% for the pedometer (ncal-ly 13 times that of the step activity monitor). For subjects with a body mass index less than 30, the step activity monitor had an overall error of 0.56% and the pedometer had an overall error of 1.56% (less than 3 times that of the step activity monitor). The absolute error of the pedometer was positively correlated with body mass index (r = 0.792, p < 0.0001) and weight (r = 0.753, p < 0.0001), whereas the error of the step activity monitor was not significantly correlated with either. Neither device was significantly biased by age, gcndcr, or the presence of a lower-extremity joint prosthesis. The accuracy and additional capabilities, including a real-time mcmory record of activity, of the step activity monitor make it well suited for objectively quantifying ambulatory activity, especially for obese subjects.Wear is the removal of material that occurs as a result of relative motion between load-bearing surfaces. in vivo polyethylene wear rates vary widely, but they have traditionally been measured with a denominator of time (S-8,lO-12,15.17,24,25,31.32). Wear is a function of use, not of time. In laboratory testing, wear rates are reported as a function of thc number of loading cycles (9,lO). A similar clinical measure of joint use that is convenient and reproducible would be valuable in assessing the use of a prosthetic joint.A variety of methods have been used to quantify activity, including questionnaires and activity rating scales (1,20.27,33), indirect calorimetry (4.21), heartrate monitoring (14,lfi). and several typcs of pedometers and accelerometers (2,4,14,(18)(19)(20)(21)(22)(23)(25)(26)(27)29). A pedometer has been used to quantify thc ambulatory activity of selected joint-replacement patients (25) and to analyze functional outcomes (3,26). Because the pedometer senses and records pelvic oscillations, certain movements of the lower extremity, which can cause wear of a prosthetic joint. may not be recorded. Furthermore, use of a pedometer is limited to subjects with relatively normal body habitus and gait. The pe-

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“…Future versions of the IDEEA 1 system will be able to address this topic. The average number of steps taken per day by the patients in our study (6078 ± 3806) represents a 22% increase over averages reported previously (4988 steps per day in 111 patients) [36,52,53,63]. Although this increase is substantial, it does fall within the wide range of activity (395-17,718 steps per day) that has been described in the same studies.…”

Walking performance in people with diabetic neuropathy: benefits and threats

“…Step activity monitors (SAMs) (Prosthetics Research Study, Seattle, WA, USA) were used to record the performance of daily walking activity [19]. The SAM is a reliable and valid tool for the measurement and recording of walking activity [20].…”

Reliability of Ambulatory Walking Activity in Patients With Hematologic Malignancies

“…[21] However, the major limitations of many pedometers are their accuracy and reliability [21,22] because they are worn at the waist and thus are sensitive to vertical movement. Therefore, the response may be affected by position, mode of the pedometer attachment, movement style, and walking speed of the individual being monitored.…”

“…Self-report measures of walking activity have been reported to be imprecise compared with objective measures. [19,20] Relatively new techniques allowing unobtrusive long-term activity monitoring with the use of pedometers and microprocessor-based accelerometer recorders may provide a clearer view of how much an individual actually walks in his/her own surroundings.[21] However, the major limitations of many pedometers are their accuracy and reliability [21,22] because they are worn at the waist and thus are sensitive to vertical movement. Therefore, the response may be affected by position, mode of the pedometer attachment, movement style, and walking speed of the individual being monitored.…”

“…[21,22] Microprocessor-based accelerometers are developed to overcome the limitations of waist-attached devices because settings can be adapted according to height, cadence, and the walking style of the subject. [22] The accuracy of these devices has consistently been reported to be above 98%. [23] Most studies of the test-retest reliability of walking activity have reported only relative reliability, such as the ICCs (varying from 0.84 to 0.97).…”