Pedometers


Step counting has been in use since the mid-1900s, and it remains relevant in health research today, largely because of the somewhat universal understanding of what a step is and the prevalence of walking.39


Pedometers are among the longest-standing


device-based measures of physical behavior and are a relatively basic technology.39 The simplest pedometers use a lever arm in a housing worn at the waist; when the lever arm moves beyond a specified threshold, a step is counted.39


However,


the spring-lever arm mechanisms are affected by slow walking and external factors such as obesity and pedometer tilt can cause underestimation of steps. In contrast, newer pedometers with accelerometer mechanisms are less susceptible to tilting and other factors.40


A 2018 study evaluated several pedometers and research-grade


step counters under free-living conditions. The StepWatch, a research-grade step counter worn on the ankle, achieved the highest criterion validity and counted between 95.3% and 102.8% of hand-counted steps over the course of a day. Generally, most waist-worn devices undercounted steps (by 20%–30%) and most wrist-worn devices overcounted steps (by 20%–30%) compared to hand-counted steps over the course of a day, although this was dependent on the settings used for the most advanced devices.41


If used in a healthy adult population with a typical


movement profile, a validated pedometer is an inexpensive and easy-to-use tool for quickly capturing stepping behavior or to jump-start behavior change for a physical behavior promotion, such as a couch to 5K program.42,43


Heart Rate Monitors


Most device-based measures use a single sensor—an accelerometer—to capture movement. Although these movement data can be translated to intensity and energy, devices using an accelerometer have limited utility for certain types of activities; for example, a device placed on the hip or wrist of a cyclist will not record much movement, yet the cyclist’s activity intensity may be high. Independently, heart rate sensors provide a physiological signal that can robustly capture intensity and be used to estimate energy expenditure. Heart rate monitors straddle the line between research-grade and consumer-grade devices, as some devices, such as a Holter monitor, capture raw electrocardiogram data that are suitable for clinical and research purposes. More commonly in free-living situations, a chest strap with a transmitter, such as the Polar H10, can be used to measure the electrical activity in the heart and record the number of beats per minute. This information can be transmitted to a paired smartphone application or to exercise equipment, such as stationary bikes and treadmills in gyms and group fitness classes. A more recent advancement in free-living heart rate measurement is pho-


toplethysmography (PPG), which captures heart rate by measuring the volumetric changes in blood circulation using an infrared light source and a photodetector placed against the skin.44


PPG sensors are often a feature of multimodal, wrist-


worn, consumer-grade wearables and are used to measure heart rate and estimate heart rate variability. Though PPG sensors are noninvasive, they do have some limitations; for instance, they require consistent skin contact and can be sensitive to motion artifact (voluntary or involuntary movement of the sensor that comes about due to shaking with movement of the body) during activity, especially at higher intensities.45


Overall, PPG provides a reasonable estimate of free-living


heart rate trends in most individuals, especially with the newest-model consumer- grade devices. A 2020 systematic review and meta-analysis found that the use of heart rate data coupled with accelerometer sensor data yielded better energy expenditure estimates than using accelerometer sensor data alone.46


Guidelines CHAPTER 8: Physical Activity Assessment 123


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