8.9: Considerations for Measurement of Physical Activity in Youth

An important consideration when evaluating youth physical activity behaviors and subsequent interventions is in how physical activity is measured. Self-report tools that rely on recall or memory are limited by our ability to accurately recall our behaviors. Self-report tools that are completed in real-time (e.g., logs, diaries) often create a high amount of burden on the participant to continually track their activities. For children, self-report measures often rely on parents serving as a proxy and reporting activity levels for their child. These reports are limited to the time which the parent spent with their child and parent perceptions of the child’s activity level while they were apart (e.g., at school, sport practices, after-school programs). Children tend to be more sporadic in their physical activity than adults are. If you have ever observed children, especially young children, playing on a playground or in a park, this quickly becomes apparent. A child may play for a few minutes on the swings before sprinting to the slide to play with a friend, take a break to play in the sandbox and then join a stop-and-go game of soccer. These short bursts of activity are harder to record or recall.

In recent years, devices have been designed that can capture physical activity, including pedometers and accelerometers. Pedometers measure step count and are a cheap and easy way to capture the volume of physical activity performed by an individual. Accelerometers, on the other hand, measure the amount of acceleration, and can therefore capture intensity. When accelerometer data is processed, it can identify not only the volume of physical activity performed by a participant, but also the intensity and the length of specific bouts of exercise. Accelerometer software from device manufacturers produce data referred to as “counts” with more counts per minute indicating higher intensities of physical activity. There have been many studies done to determine appropriate cut points to separate sedentary, light, moderate, and vigorous activity based on counts per minute. However, rather than arriving at a consensus, this has resulted in a multitude of different sets of cut points that researchers must choose from. To do so, the setting, age of participants, and activities included in development and validation of those cut points should be considered.