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00005768-200909000-0001900005768_2009_41_1827_kang_response_9article< 29_0_2_0 >Medicine & Science in Sports & Exercise©2009The American College of Sports MedicineVolume 41(9)September 2009p 1827RESPONSE[SPECIAL COMMUNICATIONS: Response]Kang, Minsoo; Holbrook, Elizabeth A.; Barreira, Tiago V.Department of Health and Human Performance, Middle Tennessee State University, Murfreesboro, TNDear Editor-in-Chief:In their recent letter, Jehn et al. (6) questioned our conclusions regarding measurement validity and reliability of the Omron HJ-151 and HJ-720ITC pedometers (5) and implied that our conclusions could not be extended to low-intensity ambulatory activity or for chronically ill populations. We agree that researchers cannot make generalizations across populations or conditions from a single piece of validity evidence. As a measurement tool is validated, its accuracy (or lack thereof) is specific to the population and parameters for which the device was originally assessed (7). Therefore, the use of the tool cannot be generalized to situations in which the environmental conditions, walking speeds, mounting positions, and populations are different from the context of the validation process. Our study was conducted among college students with a normal gait pattern. Considering that validity is context specific, the results of our study should not be generalized to other populations or conditions.Similarly, the concept of context specificity also extends to the physical activity monitors themselves. For this reason, although Jehn et al. (6) provide evidence that spring-levered pedometers may not be accurate at slow speeds, we caution the authors in comparing the validity of physical activity monitors for recording ambulatory activity at slow speeds among monitors with vastly different internal mechanisms. Moreover, previous authors have shown the superiority of piezoelectric pedometers when compared with spring-levered models (2,4) and that piezoelectric pedometers are fairly accurate at speeds as slow as 54 m·min−1 (2,3).In our study of college students, walking speeds were selected objectively from the compendium of physical activities (1) to illustrate walking at 2.0 mph ("slow"), 3.0 mph ("moderate"), and 4.0 mph ("very brisk"). The scripted protocol was used to allow natural variations in our participants' perceptions of "slow," "moderate," and "very brisk" speeds to be observed, enabling the pedometer to be assessed across a wide range of speeds (from 1.5 to 5.9 mph). In our study, the average speeds corresponding to "slow" and "moderate" were even slower than those elicited by older individuals (age = 71.9 ± 5.7 yr) at "slow" (3.1 mph) and "normal" (3.5 mph) walking speeds (4). Both models recorded steps with less than 3% absolute error, illustrating a high degree of accuracy among the tested intensities. Moreover, the incorporation of self-selected walking trials enabled validity and reliability evidence to be established for both pedometers at each participant's freely chosen walking speed, providing a "real-life" representation of the accuracy of these devices.In regard to the concept of context specificity, perhaps Shepard (8) described the process of establishing validity evidence best, as "being a never-ending process" (1993, p. 407). We agree with the authors that the Omron pedometers may not be appropriate for clinical populations with abnormal gait characteristics. We encourage such research to be performed because the unique possibility of the Omron pedometers to be mounted at various body positions may make these pedometers more attractive to special populations.Minsoo KangElizabeth A. HolbrookTiago V. BarreiraDepartment of Health and Human PerformanceMiddle Tennessee State UniversityMurfreesboro, TNREFERENCES1. Ainsworth BE, Haskell WL, Whitt MC, et al. Compendium of physical activities: update of activity codes and MET intensities. Med Sci Sports Exerc. 2000;32(9 suppl):S498-516. [Context Link]2. Crouter SE, Schneider PL, Bassett DR Jr. Spring-levered versus piezo-electric pedometer accuracy in overweight and obese adults. Med Sci Sports Exerc. 2005;37(10):1673-9. [CrossRef] [Full Text] [Medline Link] [Context Link]3. Crouter SE, Schneider PL, Karabulut M, Bassett DR Jr. Validity of 10 electronic pedometers for measuring steps, distance, and energy cost. Med Sci Sports Exerc. 2003;35(8):1455-60. [CrossRef] [Full Text] [Medline Link] [Context Link]4. Grant PM, Dall PM, Mitchell SL, Granat MH. Activity-monitor accuracy in measuring step number and cadence in community-dwelling older adults. J Aging Phys Act. 2008;16(2):201-14. [Medline Link] [Context Link]5. Holbrook EA, Barreira TV, Kang M. Validity and reliability of Omron pedometers for prescribed and self-paced walking. Med Sci Sports Exerc. 2009;41(3):670-4. [Context Link]6. Jehn ML, Schmidt-Trucksass A, Halle M. Validity and reliability of Omron pedometers at slow walking speeds. Med Sci Sports Exerc. 2009;41(9):1826. [CrossRef] [Full Text] [Medline Link] [Context Link]7. Rowe DA, Mahar MT. Validity. In: Wood TM, Zhu W, editors. Measurement Theory and Practice in Kinesiology. Champaign (IL): Human Kinetics; 2006, pp. 9-26. [Context Link]8. Shepard LA. Evaluating test validity. Rev Res Edu. 1993;19:405-50. 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