Active Voice: Activity Trackers to Promote and Monitor Physical Activity in Research — Is It Too Good to Be True?
By Jessica McNeil, Ph.D., FACSM, CSEP-CEP

Jessica McNeil, Ph.D., FACSM, CSEP-CEP
Commercially available activity trackers have become increasingly popular for use as intervention and assessment tools in health promotion and chronic disease prevention research. As an intervention tool, these devices offer prompt and automated feedback on sedentary time and physical activity (PA) participation directly to the consumer. Research teams and fitness professionals can also use these devices and some of their features (e.g., heart rate monitoring) to educate and prescribe PA of various intensities to study participants or clients, allowing the exercise prescription to be personalized. As an assessment tool, these devices allow the research team to monitor PA participation more accurately within a home-based setting throughout an entire intervention, instead of relying on self-reported diaries or “snap shots” of activity monitoring pre- and post-intervention.

Each device collects raw data from various sensors (e.g., accelerometer, gyroscope) that are converted into meaningful metrics for the consumer (e.g., current heart rate, daily step count). The sensors installed into each device are similar. However, the algorithms used by each company/brand to interpret the raw data are often proprietary and unknown to the user. Although commercially available activity trackers have the potential for scalable use in research and PA promotion initiatives, this industry is constantly changing as brands/devices enter or leave the market. Therefore, it can be challenging for researchers to identify and test devices that can replace or complement existing accelerometry instruments like the ActiGraph used in research protocols

In our study, as published in the May 2019 issue of MSSE, we assessed the effects of prescribing 300 minutes per week of lower intensity PA (40-59 percent of heart rate reserve) or 150 minutes per week of higher intensity PA (60-80 percent of heart rate reserve) for 12 weeks using wearable activity trackers. Subjects were 45 breast cancer survivors, randomly assigned to one of the two PA interventions or to a no-PA control group. Various fitness and health-related outcomes were assessed at baseline and following completion of the interventions. We also assessed adherence to the PA prescription in both intervention groups using data from the wearable activity trackers.

Although adherence in the higher-intensity PA group was high (166 minutes or 2.8 hours per week), it was considerably higher in the lower-intensity PA group (more than 900 minutes or 15 hours per week). These results may suggest that the lower intensity PA prescription was too easy and/or effortless for these participants. These results also highlight the potentially large discrepancies between commonly used PA prescriptions and the actual PA accumulated through habitual ambulatory activities completed routinely throughout the day. Indeed, it is possible that a person who reports low levels of planned PA (less than 150 minutes per week) may also accumulate high amounts of ambulatory activity throughout the day (e.g., grocery shopping, gardening, running across the street to catch a bus). Therefore, we recommend for future trials aiming to modify PA participation that investigators consider implications of baseline ambulatory activity to be incorporated into planned interventions. It is also recommended that future epidemiologic research use accelerometers to provide detailed information on total PA (including ambulatory and structured), as well as sedentary time to complement current PA guidelines.

Jessica McNeil, Ph.D., FACSM, CSEP-CEP, is an exercise physiologist and postdoctoral fellow in the Department of Cancer Epidemiology and Prevention Research at Alberta Health Services in Calgary, Canada. Her postdoctoral work included the development of an exercise trial that compared a lower versus higher intensity physical activity prescription using commercially available activity trackers in breast cancer survivors. Dr. McNeil and her colleagues authored a research article presenting the results from this trial. Their article appears in the May 2019 issue of MSSE.