PATRICK L. SCHNEIDER, SCOTT E. CROUTER, and DAVID R. BASSETT, JR. Pedometer Measures of Free-Living Physical Activity: Comparison of 13 Models. Med. Sci. Sports Exerc., Vol. 36, No. 2, pp. 331–335, 2004.
Purpose: The purpose of this study was to compare the step values of multiple brands of pedometers over a 24-h period. The following 13 electronic pedometers were assessed in the study: Accusplit Alliance 1510 (AC), Freestyle Pacer Pro (FR), Colorado on the Move (CO), Kenz Lifecorder (KZ), New-Lifestyles NL-2000 (NL), Omron HJ-105 (OM), Oregon Scientific PE316CA (OR), Sportline 330 (SL330) and 345 (SL345), Walk4Life LS 2525 (WL), Yamax Skeletone EM-180 (SK), Yamax Digi-Walker SW-200 (YX200), and the Yamax Digi-Walker SW-701 (YX701).
Methods: Ten males (39.5 ± 16.6 yr, mean ± SD) and 10 females (43.3 ± 16.6 yr) ranging in BMI from 19.8 to 35.4 kg·m−2 wore two pedometers for a 24-h period. The criterion pedometer (YX200) was worn on the left side of the body, and a comparison pedometer was worn on the right. Steps counted by each device were recorded at the end of the day for each of the thirteen pedometers.
Results: Subjects took an average of 9244 steps·d−1. The KZ, YX200, NL, YX701, and SL330 yielded mean values that were not significantly different from the criterion. The FR, AC, SK, CO, and SL345 significantly underestimated steps (P < 0.05) and the WL, OM, and OR significantly overestimated steps (P < 0.05) when compared with the criterion. In addition, some pedometers underestimated by 25% whereas others overestimated by 45%.
Conclusion: The KZ, YX200, NL, and YX701 appear to be suitable for most research purposes. Given the potential for pedometers in physical activity research, it is necessary that there be consistency across studies in the measurement of “steps per day.”
The objective quantification of physical activity is a challenge to those involved in research and practice. Traditionally, physical activity has been assessed using questionnaires, but there are limitations in subjects’ recall ability, especially for ubiquitous, light-, or moderate-intensity activities (8). Thus, there has been interest in using objective monitors to record physical activity.
Pedometers are a type of motion sensor that are low-cost, unobtrusive, accurate (1,4,11), and their output (steps or distance) is easily comprehendible. Pedometers are typically worn on the belt or waistband and respond to vertical accelerations of the hip during gait cycles. They provide data on steps and some models estimate distance traveled and energy expenditure. Although pedometers measure ambulatory activity, they do not capture all types of physical activity (swimming, weight lifting, bicycling, etc.). Nevertheless, walking is one of the most common forms of activity and is readily captured by a pedometer. These devices are becoming increasingly popular in physical activity research on clinical interventions, community-wide interventions, surveillance, and international comparisons. A recent PubMed search revealed that the number of studies using pedometers nearly doubled (32 vs 60) from 1993–1997 to 1998–2002.
Pedometers have several practical applications. They can be used to: 1) distinguish between individuals who vary based on steps per day, 2) measure increases in physical activity with interventions, 3) conduct cross-study comparisons of different populations, and 4) compare time trends in physical activity. In addition, members of the general public are interested in using pedometers to determine whether they are meeting step recommendations. However, if the differences in steps between pedometer brands are large and a variety of brands are being used, then it becomes impossible to use pedometers for these purposes.
Pedometer models differ in regard to cost ($10–$200) and internal mechanisms. There are at least three basic types of mechanisms, including the spring-suspended lever arm with metal-on-metal contact, a magnetic reed proximity switch, and an accelerometer type (4,11). The first mechanism uses a spring-suspended horizontal lever that moves up and down in response to the hip’s vertical accelerations. This movement opens and closes an electrical circuit; the lever arm makes an electrical contact (metal-on-metal contact), and a step is registered. The second type of mechanism is a magnetic reed proximity switch. This type also uses a spring-suspended horizontal lever arm; however, with this mechanism, a magnet is attached to the lever arm, and it is the magnetic field that causes two overlapping pieces of metal encased in a glass cylinder (magnetic reed proximity switch) to touch, resulting in a step being counted. The third type uses an accelerometer-type mechanism consisting of a horizontal beam and a piezo-electric crystal. The walking motion generates a sinusoidal curve when vertical acceleration is plotted against time. This mechanism uses zero crossings of the acceleration vs time curve to detect steps.
A second issue is sensitivity, which is related to the internal mechanism, and is a function of the vertical acceleration “threshold” needed to trigger a step. Previous studies (1,4,11) have shown that these differences may translate into variations in accuracy among pedometer models. Some models have been shown to be accurate over a fixed distance (1,11) or at a variety of treadmill speeds (1,4) compared with direct observation of steps. However, no study has compared pedometer models under free-living conditions over 24 h. This is an important issue because pedometer output is often reported as “steps per day.”
One of the difficulties in assessing pedometer accuracy under free-living conditions is the lack of a “gold standard.” Although pedometer accuracy can be assessed by counting steps in controlled laboratory experiments, it is not be feasible to assess pedometer accuracy in this manner over 24 h. Therefore, it was decided to use a single pedometer (Yamax SW-200) as the criterion. In controlled laboratory settings, the Yamax SW series pedometers have consistently been shown to be among the most accurate (4,11). In addition, the Yamax pedometer is commonly used in applied research (7,9,13,16). The purpose of this study was to compare the step values of multiple brands of pedometers over the course of a 24-h period.
Department of Health and Exercise Science, University of Tennessee, Knoxville, TN
Address for correspondence: Patrick L. Schneider, Department of Health and Exercise Science, The University of Tennessee, 1914 Andy Holt Avenue, Knoxville, TN 37996; E-mail: firstname.lastname@example.org.
Submitted for publication July 2003.
Accepted for publication October 2003.