REVIEW ARTICLE
Step Counting: A Review of Measurement Considerations
and Health-Related Applications
David R. Bassett Jr.
1
•
Lindsay P. Toth
1
•
Samuel R. LaMunion
1
•
Scott E. Crouter
1
Published online: 22 December 2016
The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract Step counting has long been used as a method of
measuring distance. Starting in the mid-1900s, researchers
became interested in using steps per day to quantify
ambulatory physical activity. This line of research gained
momentum after 1995, with the introduction of reasonably
accurate spring-levered pedometers with digital displays.
Since 2010, the use of accelerometer-based ‘‘activity
trackers’’ by private citizens has skyrocketed. Steps have
several advantages as a metric for assessing physical
activity: they are intuitive, easy to measure, objective, and
they represent a fundamental unit of human ambulatory
activity. However, since they measure a human behavior,
they have inherent biological variability; this means that
measurements must be made over 3–7 days to attain valid
and reliable estimates. There are many different kinds of
step counters, designed to be worn on various sites on the
body; all of these devices have strengths and limitations. In
cross-sectional studies, strong associations between steps
per day and health variables have been documented. Cur-
rently, at least eight prospective, longitudinal studies using
accelerometers are being conducted that may help to
establish dose–response relationships between steps/day
and health outcomes. Longitudinal interventions using step
counters have shown that they can help inactive individuals
to increase by 2500 steps per day. Step counting is useful
for surveillance, and studies have been conducted in a
number of countries around the world. Future challenges
include the need to establish testing protocols and accuracy
standards, and to decide upon the best placement sites.
These challenges should be addressed in order to achieve
harmonization between studies, and to accurately quantify
dose–response relationships.
Key Points
Steps are a fundamental unit of human locomotion,
and thus are a preferred metric for quantifying
physical activity.
In cross-sectional studies, strong associations
between steps per day and health variables have been
documented.
Many step-counting devices are available for both
consumer and research use, but the need for industry
standardization is acknowledged and must be
addressed in order to harmonize data.
1 Introduction and Usage
Step counters are devices worn on the body that measure
steps and/or distance traveled. The original purpose of
these devices was to measure distance traveled, when
walking was the most common mode of transportation. As
early as 1960, researchers have been interested in using
step counters to assess physical activity [1]. In the 1990s,
the use of step counters to measure physical activity and
study relationships between physical activity and health
began in earnest [2]. Since 2011, interest in step counting
& David R. Bassett Jr.
dbassett@utk.edu
1
Department of Kinesiology, Recreation and Sport Studies,
University of Tennessee, Knoxville, 1914 Andy Holt Ave.,
Knoxville, TN 37996, USA
123
Sports Med (2017) 47:1303–1315
DOI 10.1007/s40279-016-0663-1
has exploded within the general population, as people have
become fascinated with tracking their levels of physical
activity. This is part of a larger movement known as ‘‘the
quantified self’’ [3] in which people are seeking to gain
knowledge through numbers, and using technology to
acquire data on aspects of a person’s daily life in terms of
physiological variables, environmental exposures, and
psychological mood states.
In recent years, the popularity of activity trackers that
count steps has grown substantially. A single company,
Fitbit, has experienced exponential growth, and sold 21.4
million devices worldwide in 2015 [4] (Table 1). Using the
search terms ‘‘pedometer’’ and ‘‘activity tracker,’’ Amazon
and Walmart listed 181 and 139 different devices,
respectively, on their websites (13 July 2016). These
activity trackers may provide estimates of steps, calories,
distance traveled, time in activity, and ‘‘wear time.’’ While
consumer interest has increased in recent years, there is a
problem in that the accuracy of these devices is not regu-
lated by any government agency or scientific body to
ensure that they are giving valid information. To fill this
void, the Consumer Technology Association (CTA)
formed a Health and Fitness Technology Division in 2010.
In 2016, they hosted a Medical Advisory Summit to bring
together key players in the technology and medical fields,
for the purpose of having a forum to develop standards for
wearable devices to track physical activity. The CTA is
attempting to develop best-practice testing protocols and
voluntary standards that companies can meet in order to
achieve data quality (i.e., performance benchmarks).
2 History of Step Counting
Step counting began as a method of estimating distance.
Thus, it is a logical extension of other measurement
methods based on the human body, including the inch (i.e.,
width of thumb), the hand (i.e., width of the palm), the foot
(i.e., length of the foot), the cubit (i.e., distance from elbow
to fingertip), and the fathom (i.e., distance between
fingertips with arms outstretched). The word mile comes
from the Latin phrase milia passuum, meaning ‘‘one
thousand paces.’’ The Roman mile was approximately
1000 paces (or 2000 steps) of a full-grown adult [5].
Leonardo da Vinci is credited with inventing the first
mechanical step counter. It was worn at the waist, with a
long lever arm that was tied to the thigh. When the thigh
moved back and forth in walking, the gears were rotated,
causing steps to be counted [6].
Thomas Jefferson commissioned a step counter made by
one of the best watch-makers in Paris. It was worn in a vest
pocket, and had a lever arm which was tied to a string that
passed through a hole in the bottom of the vest pocket. The
other end of the string was tied to a strap below the knee,
and walking caused it to pull on a lever arm attached to
gears. He used his pedometer to measure out the distance to
Paris landmarks in steps. Jefferson noted an English mile
would require 2066.5 steps, while the brisk walk of winter
reduced it to 1735 steps [7]. He sent a pedometer to James
Madison in 1788 along with a detailed one-page letter of
instructions [8].
In 1777, Abraham-Louis Perrelet, a Swiss-born watch-
maker invented a self-winding mechanism for pocket
watches that used an oscillating weight inside the watch
that moved up-and-down during walking. In 1780 he
invented a self-contained pedometer that also used a
spring-suspended lever arm to count steps [9]. In 1820,
Abraham-Louis Breget designed a mechanical pedometer/
stopwatch for Alexandre I, Tsar of Russia, for use in
measuring the distance and pace of his marching armies
[10].
The Yamasa company in Tokyo, Japan (internationally
known as Yamax) designed a manpo-kei (10,000 steps
meter) in 1965 [11]. The 10,000 steps per day slogan
originated in Japan around 1965, shortly after the Tokyo
Olympics. This was believed to be the amount of physical
activity that would be sufficient to decrease the risk of
coronary heart disease. The Yamasa company continually
refined their step counter, adding a mechanism to prevent
double-counting of steps in 1987 [11]. Around 1990,
Yamasa introduced the Digi-walker (DW-500) containing a
hair-spring suspended lever arm, an electronic event
counter, and a digital display [12].
Since 1996, quantifying steps has become an accepted
method of assessing physical activity in scientific research.
One pedometer (Yamax DW-500) was found to be more
accurate and reliable than others [12]. A few years later,
this step counter was used to validate questions about
walking distance on physical activity questionnaires [13].
At about this time, other researchers began using
pedometers for population surveillance [14] and walking
interventions [15].
Table 1 Number of Fitbit devices sold worldwide from 2010 to
2015. From Statista [4]
Year No. of devices sold per year (in thousands)
2010 58
2011 208
2012 1279
2013 4476
2014 10,904
2015 21,355
1304 D. R. Bassett Jr. et al.
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3 Types of Step Counters
There are many different types of step counters. They fall
into five general categories, based on where they are worn
on the body, and the internal mechanism (spring-suspended
lever arm vs. accelerometer) used to record steps. In this
section, we review the mechanisms, accuracy, and sources
of error for the various types of step counters.
3.1 Waist-Worn, Spring-Levered
The traditional step counter was designed to be worn at the
waist, attached to the belt or waistband. The most basic
type uses a mechanical internal mechanism. In walking or
running, the vertical accelerations of the body cause the
horizontal, spring-suspended lever-arm to move up and
down with each step. The movement of the lever arm opens
and closes an electrical circuit, causing an electronic
counting device to register steps. In the case of the Yamax
pedometer, every movement of the trunk that exceeds the
vertical acceleration threshold of 0.35 g is considered a
step [16]. Whenever the threshold is exceeded, it results in
an event being recorded.
The main sources of error for this class of devices are
slow walking speeds and obesity, which both result in
underestimation of steps. Studies have demonstrated that
most waist-mounted pedometers are very accurate at
speeds of 3.0 mph (80.4 m/min) and above, but their
accuracy declines at slower speeds. At 2.0 mph (54 m/
min) they may capture 75% of steps, and at 1.0 mph they
hardly register steps at all. Thus, waist-mounted
pedometers are notoriously inaccurate in older adults in
assisted-care settings, who walk with a slow, shuffling gait
[17]. Double-counting of steps is a common problem in
inexpensive pedometers, if care is not taken to prevent it.
Spring-levered pedometers have diminished accuracy in
obese individuals. According to Crouter et al. [18], this is
because when they are tilted away from the vertical axis
their sensitivity is diminished, causing them to undercount
steps.
3.2 Waist-Worn, Accelerometer
More recent waist-mounted step counters use an internal
mechanism consisting of a piezoelectric or piezo-resistive
accelerometer (typically tri-axial). In walking or running,
there is a sinusoidal pattern of acceleration with both
positive and negative accelerations being recorded during
various phases of the ambulatory cycle. With this type of
step counter, the number of zero crossings or peaks of the
vertical acceleration of the body versus time curve is used
to determine the number of steps. The Omron HJ-720, the
New Lifestyles NL-2000, the Fitbit One, and the Fitbit Zip
are examples of this type of pedometer.
Waist-worn accelerometer-based step counters are gen-
erally more accurate than spring-levered pedometers. Two
such devices (New Lifestyles NL-2000 and Omron HJ-
720) are not impacted by obesity or tilt angle [18, 19].
However, these devices still show a tendency for dimin-
ished accuracy at slow walking speeds.
3.3 Pocket
Some activity trackers can be worn in the pants pocket,
including the Omron HJ-720, Phillips DirectLife, Fitbit
Zip, and Misfit Shine. Similar to the waist-worn devices,
these monitors have triaxial accelerometers that detect
accelerations of the body during walking and running.
Major sources of error are basically similar to those of
waist-worn, accelerometer-based devices. Also, in the case
of the Omron, steps taken in brief walking bouts go
undetected because of the presence of a 4-s filter [20].
3.4 Thigh
The activPAL monitor is designed to be taped to the thigh.
This device uses a uni-axial accelerometer which responds
to gravitational acceleration as well as the accelerations
resulting from leg movements. The accelerations that occur
during walking and running are used to count steps. Data
are stored in memory, time-stamped, and can later be
downloaded to a computer for subsequent recall.
The activPAL is useful as a tracking device only, since it
has no data display for providing biofeedback to partici-
pants. It accurately counts steps down to 1.5 mph (40.2 m/
min) [21] and only underestimates steps by 3.5% at 1.0
mph (26.8 m/min) [22].
3.5 Ankle
The most accurate step counter for walking is the Step-
Watch 3 device, worn on the ankle [23, 24]. It contains an
analog accelerometer (not a micro-electrical mechanical
system or MEMS accelerometer) that samples a 120 Hz
data stream of acceleration. The StepWatch is able to
detect several signature movements involved in stepping,
ensuring that it has high sensitivity and specificity for
recording steps.
The StepWatch is accurate to within 1–2% of actual
steps, even at very slow walking speeds, and even in
individuals who are obese [25]. In addition, Hickey et al.
[26] have shown that this device is even accurate for
housework activities like dusting, filing, and cleaning.
However, the StepWatch will record extra steps if the user
performs bicycling, heel tapping, or leg swinging [24]. In
Step Counting 1305
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addition, the StepWatch undercounts steps in running,
when programmed with the default settings [26].
3.6 Foot
Shoe-mounted step counters are designed so that contact of
the heel with the ground causes a step to be recorded. Some
fit on the shoe laces. Another type has a pressure trans-
ducer, circuitry and rechargeable battery are placed into the
heel of a normal shoe and can detect when the heel is in
contact with the ground [27]. This shoe-mounted device is
consistent with defining a step as any time the foot is lifted
up off the ground and put back down again. This latter type
was tested in patients with chronic health failure and
healthy age-matched volunteers, and found to be more
accurate than body-worn step counters. The sources of
error with foot step counters have not been investigated,
but they most likely exhibit the same errors as ankle step
counters.
3.7 Wrist
Recently, wrist-worn activity trackers have been designed
that measure steps (e.g., Nike Fuelband, Jawbone UP,
Garmin VivoFit, Fitbit Flex, Fitbit Surge, Fitbit Charge,
Misfit Shine, Polar A360, Polar Loop, etc.). At first glance,
it may seem illogical to place a device on the wrist in order
to assess steps taken by the feet. However, a study by Chen
et al. [28] reported that three wrist devices (Fitbit flex,
Garmin Vivofit, and Jawbone Up) were quite accurate
(absolute percent error for steps = 1.5–9.6%) during
treadmill walking and running at 54–134 m/min. Smart-
watches such as the Apple Watch, Samsung Gear S2, and
Pebble Watch are also reported to have acceptable validity
and reliability, at least for measuring steps during over-
ground walking [29]. Their accuracy for counting steps
during activities of daily life has not been studied.
Wrist step counters do not count steps when the wrist is
stationary. For example, they do not record steps taken
when pushing a stroller [28], or holding onto treadmill
hand rails. Furthermore, wrist-worn step counters record
invalid steps when folding laundry [28], or gesturing while
talking. These sources of error are troubling to physical
activity researchers who are focused on obtaining accurate
step counts.
The US National Health and Nutrition Examination
Survey, or NHANES (2008–2014) used an Actigraph
GT3X? worn on the non-dominant wrist. The previous
deployment of the Actigraph 7164 in NHANES
(2003–2006) had used the waist location. The wrist
placement site and a waterproof case increased wear times,
and had the added benefit of providing a valid assessment
of sleep duration and quality [30]. Unfortunately, the step
detection algorithm developed for the waist does not seem
to work for the wrist location. Tudor-Locke et al. [31]
examined the accuracy of the wrist and waist attachment
sites for the ActiGraph GT3X?. Compared to directly
observed steps, the waist site performed better than the
wrist site at most treadmill speeds, regardless of the
bandpass filter. However, in the free-living environment
the wrist recorded more steps than the waist, likely due to
extraneous arm movements. In the free-living environment,
the waist-worn ActiGraph measured 6743 ± 2398 (default
filter) and 13,029 ± 3734 (low-frequency extension) steps
per day. The wrist ActiGraph measured 9301 ± 2887
(default filter) and 15,493 ± 3958 (low-frequency exten-
sion) steps per day. ActiGraph is working to improve their
step counting algorithm for the wrist (John Schneider,
ActiGraph L.L.C., personal communication, 6/23/2016).
In summary, there are various ways of defining and
measuring a step. When researchers seek to determine the
accuracy of a device for step counting, it is important to
select a criterion measure that is consistent with both of
these. For many purposes, visual observation and hand-
tally of steps by a trained investigator can serve as a valid
criterion.
4 Why Count Steps?
Tryon [32] has noted that steps are a fundamental unit of
human locomotion, and thus are a preferred metric for
quantifying physical activity. Measurement of steps has a
number of other advantages:
• Steps are intuitive, and readily understandable to the
layperson
• Steps can be measured easily and accurately
• Steps are objective
• Steps can be used to place people into less active and
more active categories
• Steps/day has strong associations with physical
health variables
• Steps are motivational, and they facilitate behavior
change
• Steps have the potential to be useful in translating
scientific results into public health messages.
5 Classification of Steps per Day
Pedometers can be used as an overall index of how active a
person is. Tudor-Locke and Bassett [33] proposed a clas-
sification scheme for categorizing adults based on their
daily steps (Table 2). These categories were developed by
taking descriptive data on steps per day, and thinking of
1306 D. R. Bassett Jr. et al.
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terms that characterized groups based on perceptions of
their activity levels. With recent studies showing that
individuals who take more steps per day have more
favorable cardiometabolic risk profiles, in the future it may
be possible to develop criterion-referenced standards for
steps per day and assign terms that refer to disease risk.
Steps differ from other units of measurement. The sci-
entific community has adopted le Syste`me International
d’Unite´s (SI units) in an attempt to reduce confusion in
scientific writing. SI units provide a consistent system to
express scientific data on physical quantities (centimeters,
grams, seconds, etc.), to facilitate the exchange of infor-
mation. However, steps are a behavior rather than an object
or event. Thus, the step is an ‘‘anthropometric’’ unit of
measurement, they cannot be quantified by absolute units
like meters or kilojoule.
The steps that a person takes vary according to his/her
height, age, and fitness level. The length of a walking step,
at a self-selected pace, is roughly proportional to a person’s
height (i.e., approximately 42% of height) [34]. The
amount of energy expended per step is roughly propor-
tional to a person’s body weight (cal/kg/step) [34],
although it is also dependent upon speed of locomotion and
whether one is walking or running (Fig. 1). Finally, the
intensity of steps can vary with one’s level of aerobic fit-
ness. Frail, elderly individuals tend to take slower, shorter
steps while younger, more athletic individuals often take
running steps. This is consistent with differences in phys-
ical work capacity and aerobic fitness across the age span.
6 What is a Step?
Merriam-Webster defines a step as ‘‘a movement made by
lifting your foot and putting it down in a different place’’
[35]. (Marching in place could also be considered stepping,
though it does not fit this definition.) Researchers working
in the field of human gait and rehabilitation sometimes
broaden this definition of a step to include a prosthetic
device that takes the place of a foot. So, a step can be
defined as any time the foot or prosthetic device is lifted off
the ground and put back down again, in the process of
ambulating.
The Oxford dictionary defines a step as ‘‘an act or
movement of putting one leg in front of the other in
walking or running’’ [36]. Note that this definition implies
that a step needs to be part of a sequence of similar events
that make up a continuous walking or running bout. Some
researchers believe that a minimum walking bout requires
that several steps be taken [37].
Some researchers define a step as an event that occurs
when the foot or prosthetic device is unweighted, moved to
a new location, and then re-weighted, in the load path of
the body (Michael Orendurff, personal communication, 4
March 2012). This definition acknowledges that frail,
elderly individuals often take ‘‘shuffling’’ steps in which
the foot is not lifted all the way off the ground, but rather
moved forward while maintaining contact with the ground.
Even in healthy people, certain activities (e.g., waltz,
tango, and tennis) may involve ‘‘sliding’’ the foot from one
location to another. According to the first two definitions
discussed, shuffling and sliding events would not be clas-
sified as steps.
Some ankle-mounted accelerometers detect forward
accelerations of the foot during the swing phase. This
measurement method is consistent with defining a step as
any time the foot is moved ahead of the opposite foot into a
position to accept weight transfer from the other limb (i.e.,
the ‘‘load path’’) and then put down again. Interestingly,
people with Parkinson’s disease may advance the lower
limb while it is still bearing 1–5% of body weight, but this is
considered a step as long as the opposite limb bears greater
than 50% of body weight. By this definition, one foot would
be in stance phase and the other would be in swing phase,
even if the swing limb is dragging across the floor.
It is interesting to consider all the different kinds of
steps humans take. There are forward steps, backward
steps, side-to-side steps, diagonal steps, puttering steps,
walking steps, and running steps. Subtle movements to
Table 2 Steps-per-day categories and classification system of Tudor-
Locke and Bassett [33]
Steps per day Classification
\5000 Sedentary lifestyle
5000–7499 Physically inactive
7500–9999 Moderately active
C10,000 Physically active
C12,500 Very active
Fig. 1 Relationship between locomotive speeds and rates of caloric
expenditure. Reproduced from Hatano et al. [34] with permission
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