LE MASURIER, G. C., and C. TUDOR-LOCKE. Comparison of Pedometer and Accelerometer Accuracy under Controlled Conditions. Med. Sci. Sports Exerc., Vol. 35, No. 5, pp. 867–871, 2003.
Purpose: The purpose of this investigation was to compare the concurrent accuracy of the CSA accelerometer and the Yamax pedometer under two conditions: 1) on a treadmill at five different speeds and 2) riding in a motorized vehicle on paved roads.
Methods: In study 1, motion sensor performance was evaluated against actual steps taken during 5-min bouts at five different treadmill walking speeds (54, 67, 80, 94, and 107 m·min−1). In study 2, performance was evaluated during a roundtrip (drive 1 and drive 2) motor vehicle travel on paved roads (total distance traveled was 32.6 km or 20.4 miles). Any steps detected during motor vehicle travel were considered error.
Results: In study 1, the Yamax pedometer detected significantly (P < 0.05) fewer steps than actually taken at the slowest treadmill speed (54 m·min−1). Further, the pedometer detected fewer steps than the accelerometer at this speed (75.4% vs 98.9%, P < 0.05). There were no differences between instruments compared with actual steps taken at all other walking speeds. In study 2, the CSA detected approximately 17-fold more erroneous steps than the pedometer (approximately 250 vs 15 steps for the total distance traveled, P < 0.05).
Conclusions: The magnitude of the error (for either instrument) is not likely an important threat to the assessment of free-living ambulatory populations but may be a problem for pedometers when monitoring frail older adults with slow gaits. On the other hand, CSA accelerometers erroneously detect more nonsteps than the Yamax pedometer under typical motor vehicle traveling conditions. This threat to validity is likely only problematic when using the accelerometer to assess physical activity in sedentary individuals who travel extensively by motor vehicle.
Accurate measures of physical activity (PA) are required by researchers interested in describing and evaluating the relationship between PA and important health outcomes (e.g., obesity, hypertension, and glucose tolerance). Advances in technology have generated an increased interest in objective monitoring of PA using body-worn sensors (e.g., accelerometers and pedometers). Recently published journal supplements have reflected this evolution of PA measurement (7,8), and a new PA assessment textbook prominently features chapters on both accelerometry and pedometry (17). A simple search of PubMed using the key words “accelerometer” and “physical activity” elicits 130 studies published between 1990 and 2002. A similar search substituting the term “pedometer” elicits 37 studies. Despite the evidence of increasing utilization of motion sensors for research and practice purposes, the process of objective monitoring is still in its infancy and the threat of measurement bias has not been extensively evaluated. Continued study is necessary to increase our understanding and interpretation of objectively monitored PA.
Pedometers are the least expensive ($10–30 per unit) and most user-friendly (14) of the two motion sensors and therefore are seen as more practical (inexpensive and feasible) for surveillance, screening, program evaluation and intervention through personal feedback (1,4,18,19). The brand that has received the most scientific attention has been the Yamax (Yamax Corporation, Tokyo, Japan) pedometers, perhaps because of an initial brand comparison study that concluded that these instruments were the most accurate of those assessed at the time (2). Since that time, Yamax pedometers have shown strong relationships (r = 0.80–0.90) under laboratory conditions with more expensive accelerometers including CSA model 7164 (MTI Health Services, Fort Walton Beach, FL) (3). Under controlled field conditions, the Yamax pedometer correlated with Tritrac (R3D, Professional Products, Reining Int., Madison, WI) and CSA accelerometers at r = 0.84–0.93 (6). The accumulated evidence indicates that the output of pedometers is highly representative of that produced by accelerometers (13).
In both these studies (6,13), pedometer-determined steps taken were compared with accelerometer-determined activity counts, an output representative of steps taken combined with velocity of movement. A dual-mode CSA accelerometer model 7164-version 2.2 is now available that collects both activity count data and the number of cycles in the signal, which manufacturers claim are representative of the simpler output: steps taken. A recent study examined steps taken as measured by the dual-mode accelerometer and the Yamax pedometer in free-living individuals and determined that, although the correlation between the two instruments was indeed strong (r = 0.86), the accelerometer detected 1,800+ more steps per day than the pedometer (11). This is similar to the difference detected between an ankle-borne accelerometer (Step Activity Monitor, SAM, Prosthetic Research Study, Seattle, WA) and a Sportline pedometer (Campbell, CA) under free-living conditions (10). We hypothesized that the discrepancy between the two instruments was likely due to differences in sensitivity thresholds set to detect vertical accelerations. The CSA accelerometer requires a force ≥ 0.30 g to register and record a movement; the corresponding value for the Yamax pedometer is ≥ 0.35 g (11). We would therefore expect that some of the discrepancy might be explained by a greater ability of the accelerometer to detect lower forces typical of slower walking speeds. Previous research has shown that the Yamax pedometer underestimates the number of steps taken at slower walking speeds (indicative of lower forces) (2,5). On the other hand, a lower sensitivity threshold may result in the accelerometer erroneously detecting more nonstep movements as steps taken, for example, simple agitation experienced while riding in a motorized vehicle. Therefore, the purpose of this investigation was to compare the concurrent accuracy of the dual-mode CSA accelerometer and the Yamax pedometer to actual steps taken observed under two conditions: 1) on a treadmill at five different speeds and, 2) riding in a motorized vehicle.