Pedometers

Pedometers provide data on steps taken, and therefore, only really measure walking/running activity. They do not capture activities such as cycling, swimming, or weight lifting, nor do they capture the added energy requirement from walking on an incline or the decreased energy requirement associated with running down-hill. In the caloric sense, it is therefore not possible to assess intensity, frequency or duration of activity from pedometer data; however if these are defined in the ambulatory movement-only domain, a pedometer that stores step frequency information in high resolution (“time-series pedometer”) provides an estimate of those dimensions of activity. In contrast, a pedometer which only stores total number of steps (“simple pedometer”) can only assess volume. The dimensions of physical activity assessed by the two main types of pedometers are described in Table P.3.1.

One systematic review reported median correlation (relative validity) of r =0.86 for assessing total volume of physical activity when compared to different accelerometers (specifically uniaxial accelerometers), depending on the specific instruments used, monitoring frame and conditions implemented, and the manner in which the outputs are expressed [20].

Dimension	Possible to assess?
	Simple pedometer	Time series pedometer
Duration		✔
Intensity		✔
Frequency		✔
Volume	✔	✔
Total physical activity energy expenditure
Type
Timing of bouts of activity (i.e. pattern of activity)		✔
Domain
Contextual information (e.g. location)
Posture
Sedentary behaviour		✔

Pedometers are low-cost motion sensors which respond to oscillations in the acceleration of the body segment (hip, thigh, wrist, etc) during gait cycles [22], providing output in number of steps during the given time frame (e.g., minute, hourly, daily, weekly).

Pedometer mechanisms

There are wide variations between pedometer instruments and this is typically reflected in their cost. The variation in cost and accuracy is related to the different internal mechanisms used to measure steps. There are at least four different mechanisms [3, 14]:

• Spring-suspended lever arm with metal-on-metal contact
• Magnetic reed proximity switch and horizontal beam
• Piezo-electric crystal or MEMS, i.e. an accelerometer-based system
• Global positioning system (GPS) receiver

Some smartphone applications derive steps from the inbuilt accelerometer (famously used to orientate the screen in portrait or landscape) and/or global positioning system (GPS) receiver data; the former is based on a specific interpretation of the acceleration signal and the latter may be derived by dividing distance travelled by stride length [11].

Pedometer instruments

A pedometer instrument consists of one of the above mechanisms packaged alongside other features, which can include:

• Memory for storage of total steps (i.e. volume) or in high resolution time-series
• Visual displays
• Attachment clips and belts
• Input buttons/screens (for inputting data such as stride length)
• Connectors/ports for charging and uploading data to a computer
• Computer chips for on-board processing and estimation of other variables such as distance or calories

Although many pedometers are designed and marketed for the specific purpose of measuring steps, other devices can also be classified as pedometers as they perform the same functions. For example, some devices sold as ‘accelerometers’ also provide a measure of steps, and as mentioned above smartphone applications are available which make use of in-built accelerometers as well as the more advanced storage, computing, and visual display options that this platform offers. Algorithms have been developed for measuring steps using raw tri-axial accelerometry data at ankle, thigh and waist locations across a range of gait velocities in a laboratory [7].

The accuracy of instruments for measuring steps varies (see section 9 for instrument specific details). A review of modern consumer-wearable activity trackers reported high relative validity for counting steps and lower validity for estimating energy expenditure and sleep [6].

Another study demonstrated that measures of steps were most accurate on level surfaces (≤1% for some devices), but less so during stair use. When estimates of distance were derived from steps, these were typically within 5% of true values, but during stair use error was at least 45% across devices [8]. Accuracy of step count and distance was higher at slow walking speed, as previously reported [3], but no differences were observed between moderate and fast walking speeds [8].

Sampling frequency

The frequency with which steps can be recorded (sampling frequency or time resolution) varies according to the sophistication of the device. Some pedometers are only able to store the accumulated total, making it necessary for participants to log step counts in a dairy on a regular basis (e.g. at the end of each day, or before and after a walking/running trip to work to measure steps during that trip). This reporting task and the fact that actual wear time may not be captured are potential sources of bias and lost data.

Newer models (time-series pedometers) have a large data storage capacity, ranging from daily to sub-minute level (time-series) recording, which is preferable for research purposes; for time-series data with high ( < 60-sec) resolution, inferences can be drawn on other activity domains (intensity, frequency, duration, timing), as well as wear/non-wear probability.

Wear location

Pedometers have been commonly worn on a belt around the waist or on a wrist band. However, as pedometers have become smaller and more often incorporated into other devices, wear locations have evolved, for example, some devices can be kept in pockets (e.g. smartphones) or worn at chest, thigh or ankle locations.

A study investigating the comparison of chest-, hip- and wrist-worn measured step counts vs manual counting across a range of walking and running speeds showed a higher agreement of chest and hip placement when compared to wrist [4].

Typical gait velocity should be considered for wear location of different devices. More sensitive pedometers (e.g. based on piezoelectric or MEMS-based acceleration measurement) have been recommended in individuals who naturally ambulate at a slower pace e.g. the elderly [10]. Measurement of steps at slow gait velocities is reportedly more accurate at the ankle than at hip, wrist or chest [9, 12].

Comparison of pedometers over fixed distances or at a variety of treadmill speeds is not reflective of their performance in free-living conditions. [15].

Smartphone pedometer applications

Smartphone applications which mimic traditional pedometer instruments are increasingly popular. Use of smartphones for physical activity assessment is appealing due to increasingly high ownership levels and limited increase in burden for participant, as well as being cost effective and convenient for researchers. They may also be beneficial for self-monitoring and behaviour change.

There is a plethora of available applications using smartphone technologies such as accelerometers and/or GPS receivers to estimate steps, and are designed to perform this task regardless of what phone (and therefore sensors) is being used and whether the phone is carried in bag/purse, armband, hand or pocket. Those that have undergone validity testing have performed relatively poorly when compared to observation of steps and measurement using a dedicated pedometer [11] Analyses found large error across a range of laboratory and free-living testing, including walking, running, stair use and driving. This was typified by the performance in a 20-step test as shown in Figure D.3.2 [11].

Walking is one of the most common forms of physical activity and pedometers readily measure an important aspect of this activity. Investigators should consider the type of activities the studied population are likely to engage in. If it is predominantly walking then a pedometer may be suitable.

The typically low cost of pedometers makes them feasible for large-scale studies (i.e. >1000 subjects), and this economic feasibility means that pedometers may also be considered for surveillance. They can be used to:

• Distinguish between individuals who vary based on steps per day
• Measure changes in walking activity in interventions aiming to increase walking
• Conduct comparisons of different populations with respect to walking
• Compare time trends of walking activity (if data at different time points is available)
• For the public, pedometers are an easy way to see if one is meeting step recommendations
• For use as a motivational tool to increase walking as part of an intervention

Pedometers are useful in clinical and community-wide intervention seeking to increase activity and have been successfully used as an incentive to increase activity through walking. The ‘Rockhampton 10,000 steps a day’ (Queensland, Australia) and the Colorado (Denver, USA) ‘On the Move’ programs have led to state/country wide programs to increase activity. Bravata et al. [1] systematically reviewed the use of pedometers as an intervention tool to improve physical activity levels. The results suggested that the use of a pedometer is associated with significant increases in physical activity.

Distance walked during a given time period has been estimated from number of steps by multiplication of average (assumed) stride length. The accuracy of this estimate depends upon several factors, such as accuracy and variability of the stride length parameter. Some pedometer models allow for a low level of individual calibration; the participant walks a set distance and count the number of strides taken, from which average stride length is calculated and entered into the device. Pedometer step recording accuracy is influenced by body size and speed of locomotion so should be used with caution in populations of vastly different ages and heights [16].

Pedometers are most accurate for assessing steps, less accurate for assessing total distance, and even less accurate for assessing energy expenditure [3, 6]. Therefore, as most pedometers only provide a total (daily) step count, other inferences drawn from this measurement such as distance travelled or energy expenditure will likely be associated with large uncertainty [2].

Activity level classification

The following classification of overall physical activity based on steps has been suggested by Tudor-Locke [17]:

• Under 5000 steps/day – “sedentary lifestyle”
• 5,000-7,499 steps/day is typical of daily activity excluding sports/exercise and might be considered “inactive”
• 7,500-9,999 likely includes some exercise or walking (and/or a job that requires more walking) and might be considered “somewhat active”
• 10,000 steps/day indicates the point that should be used to classify individuals as – active
• > 12,500 steps/day should be classified as “highly active”

Various recommendations have been published for healthy children, all greater than 10,000 steps per day which is a commonly cited step target for adults. For example, boys who accumulated 13,000 steps.d-1 and girls who accumulated 12,000 steps.d-1 were found to engage in sufficient moderate physical activity to meet recommendations for 60 minutes of moderate activity per day as measured by accelerometer [13].

An overview of the characteristics of pedometer methods is outlined in Table P.3.2.

Strengths

• Quality models provide a valid and reliable measure of steps taken
• Time-series models provide information on activity patterns
• Can be used as a motivational tool

Limitations

• Behaviour may alter in response to readings if step counts are visible
• Some individuals, particularly children may tamper with the monitor if it has buttons
• Can register ‘false’ activity with movement such as travelling on the train or in a car
• It is not possible to assess intensity, frequency or duration of activity from simple pedometer data
• Not an accurate method for the assessment of energy expenditure
• Some pedometer protocols are reliant on the user logging their own step readings on a daily basis, and are therefore susceptible to recall and social desirability biases in these cases

Consideration	Comment
Number of participants	Small to large
Relative cost	Low
Participant burden	Low
Researcher burden of data collection	Low
Researcher burden of data analysis	Medium*
Risk of reactivity bias	Yes
Risk of recall bias	Yes*
Risk of social desirability bias	Yes*
Risk of observer bias	No
Participant literacy required	No
Cognitively demanding	No

Considerations relating to the use of pedometers for assessing physical activity are summarised by population in Table P.3.3.

Population	Comment
Pregnancy	Pregnancy may cause the pedometer to be set at an angle and reduce its capacity to detect vertical acceleration.
Infancy and lactation	Not suitable.
Toddlers and young children	May rely on another person to log values at end of day. If still at age of being carried, may be the carrier’s steps rather than the infants.
Adolescents	Visual feedback may not only alter behaviour but result in shaking monitor to add counts. May also result in competition between individuals.
Adults
Older Adults	May be less accurate for those with slower walking speed. May have difficulty remembering to put in on/off after sleep or showers may be increased.
Ethnic groups
Other	In obese subjects the increased abdominal adiposity may cause the pedometer to be set at an angle and reduce its capacity to detect vertical acceleration. Differences between the ability of pedometer devices to accurately detect steps are related to waist circumference [12]Not useful for measuring activity in people who are unable to walk.

• Decisions should be made at the outset on the number of days, and which days to be monitored
• Weekend and weekdays may be required for a habitual estimate of walking activity
• Pedometers can be returned either face-to-face or via post
• For smaller studies it may be possible for the researcher to collect pedometers
• Incentives can be offered to enhance compliance and improve the return rate
• The choice of pedometer should be made carefully after considering the literature as well as recent technological advances
• An open display can influence behaviour and cause reactivity, which may be a problem for some studies
• If reactivity is suspected, data from day one can be compared with subsequent days

• Pedometers
• Written instructions for wearing
• Logs to record daily steps depending on pedometer storage capacity (ideally time put on in morning and when monitor was removed should also be indicated)
• Instructions for returning the pedometers - this may require stamped addressed envelopes

A method specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open in a new page.