To the Editor -
Mitre et al in the January 2009 issue of Pediatrics provides very
direct guidance to practitioners (1). Mitre et al state that
"Commercially available pedometers are inaccurate for children, especially
in the overweight or obese group. They are poor tools for monitoring
physical activity and require caution in their use." This strong
conclusion is not adequately supported by this and other relevant research
and thus may lead clinicians to reject a practical and inexpensive tool
for physical activity measurement.
Mitre et al describes accuracy of two pedometers in normal and
overweight children at treadmill speeds ranging from 0.5 -2.0 mph and
during a brief walk (230 m) at a self selected pace. Average errors
between pedometer detected steps and observer counted steps were high,
ranging from 60% to over 90% during treadmill walking and from 21-36% at a
self selected pace. Certainly, as the authors have described, we would
expect that many pedometers would exhibit reduced accuracy in step
counting at slower walking speeds (2). However, many pedometers have
displayed high accuracy of step outputs (+/- 1%) when evaluated at >=
3.0 mph (2). The conclusion primarily determined by slow walking may
improperly steer pediatric researchers and practitioners away from
consideration of the pedometer as a low cost objective measure of physical
activity in children.
Mitre et al mistakenly report that they tested a piezoelectric
pedometer, in fact the Omron HJ-105 pedometer used in the study is not a
piezoelectric pedometer, but rather is a hair spring-suspended lever arm
pedometer (2). Not surprisingly, Mitre et al obtained similar results for
the Omron HJ-105 and the Yamax SW-200, a coiled spring-suspended lever arm
pedometer. This is an important clarification because commercial
piezoelectric pedometers have demonstrated an ability to accurately detect
steps at slower walking speeds and at a larger degree of tilt from
vertical placement resulting from increased abdominal adiposity (3).
Omron Healthcare (Kyoto, Japan) does manufacture several piezoelectric
pedometers including models HJ-112, 150, 151, and 720ITC. Piezoelectric
pedometers are also available from several other manufacturers including
the New Lifestyles (Lees Summit, Missouri) NL-1000 and NL-2000, and the
Yamax (Tokyo, Japan) PW-611. Collectively, these devices range in cost
from $13 to $65.
Miter et al fail to cite two important studies that reported accuracy
of both spring-suspended lever arm and piezoelectric pedometer models in
children compared to a directly observed steps criterion. Duncan et al.
assessed 85 children ages 5-7 and 9-11 years during treadmill walking at
1.6, 2.5, and 3.4 mph (4). Results were similar between pedometer models
with a mean percent error of approximately 20%, 5%, and < 1% at the
above walking speeds, respectively. A larger study by Nakae et al.
assessed 394 children in 1st-6th grade during self-selected slow, normal,
and fast walking speeds on a 50 m outdoor course (5). Results for the
spring-lever arm pedometer exhibited substantial error (ranging from
approximately 10-50%) across self-selected speeds and across nearly all
age groups. However, the piezoelectric pedometers evaluated exhibited
much lower error (approximately 3%) at self-selected normal speed and
error range from approximately 3-20% at slow speeds across all age groups.
These two studies demonstrate that the piezoelectric pedometers evaluated
can provide an accurate measure of steps taken among children between the
ages of 5 and 11 years at normal walking speeds.
As Mitre et al noted (1), most spring-suspended lever arm pedometers
are purposefully manufactured with a force sensitivity threshold for step
detection designed to avoid counting fidgeting and other non-ambulatory
movements as steps. This design decision leads to relatively lower
accuracy at slower walking speeds. Some pedometers have lower sensitivity
thresholds to allow detection of slower or shuffling steps. These devices
try to avoid over counting steps by using step filtering algorithms to
determine if patterns of step accumulation appear ambulatory in nature,
and remove detected movements that are classified as non-ambulatory (6).
In summary, when considering a pedometer as a measure of physical
activity in children, it is important to recognize both the strengths and
limitations of the device. If a researcher or clinician requires a
device that can detect and record all bodily motion regardless of speed,
it is likely that a pedometer is not an appropriate instrument. However,
if interested in a general measure of steps taken at normal walking or
running speeds, current evidence suggests that a piezoelectric pedometer
can provide accurate outputs across a wide age range of children.
Although some physical activity related research questions may require
greater instrument accuracy or the ability to detect steps at even the
slowest walking speeds, it is likely that pedometers are appropriate for
many research and evaluation efforts concerning children's physical
activity.
James McClain, PhD, MPH
Cancer Prevention Fellow
Applied Research Program
Division of Cancer Control and Population Sciences
National Cancer Institute
Bethesda, Maryland
REFERENCES
1. Mitre N., Lanningham-Foster L., Foster R., Levine J. A. Pedometer
accuracy for children: can we recommend them for our obese population?
Pediatrics. 2009;123(1):e127-131.
2. Crouter S. E., Schneider P. L., Karabulut M., Bassett D. R., Jr.
Validity of 10 electronic pedometers for measuring steps, distance, and
energy cost. Med Sci Sports Exerc. 2003;35(8):1455-1460.
3. Crouter S. E., Schneider P. L., Bassett D. R., Jr. Spring-levered
versus piezo-electric pedometer accuracy in overweight and obese adults.
Med Sci Sports Exerc. 2005;37(10):1673-1679.
4. Duncan J. S., Schofield G., Duncan E. K., Hinckson E. A. Effects
of age, walking speed, and body composition on pedometer accuracy in
children. Res Q Exerc Sport. 2007;78(5):420-428.
5. Nakae S., Oshima Y., Ishii K. Accuracy of spring-levered and piezo
-electric pedometers in primary school Japanese children. J Physiol
Anthropol. 2008;27(5):233-239.
6. McClain J. J., Sisson S. B., Washington T. L., Craig C. L., Tudor-
Locke C. Comparison of Kenz Lifecorder EX and ActiGraph accelerometers in
10-yr-old children. Med Sci Sports Exerc. 2007;39(4):630-638.
Conflict of Interest:
None declared
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