Validity and Comparability of a Wrist-Worn Accelerometer in Children

Area of Science:

• Pediatric Exercise Science
• Biomedical Engineering
• Physical Activity Measurement

Background:

• Wrist-worn accelerometers offer a practical alternative to hip-worn devices for long-term physical activity monitoring.
• Assessing physical activity in children is crucial for understanding health behaviors and outcomes.

Purpose of the Study:

• To validate the Actiwatch (wrist-worn) for estimating energy expenditure in children.
• To establish cut-off values for classifying light, moderate, and vigorous physical activity.
• To compare the Actiwatch with the Actigraph (hip-worn) and assess the Actiwatch's reliability.

Main Methods:

• Indirect calorimetry served as the criterion measure for validity assessment.
• Receiver Operating Characteristic (ROC) analyses were used to determine activity intensity cut-off values.
• Simultaneous wear of Actiwatch and Actigraph during free-living conditions assessed comparability; reliability was tested using a mechanical shaker.

Main Results:

• A significant correlation (0.80) was found between accelerometer output and energy expenditure.
• Cut-off values for 1.5, 3, and 6 METs were identified as 80, 262, and 406 counts per 15 seconds, respectively.
• Energy expenditure estimates showed significant differences between Actiwatch and Actigraph; Actiwatch demonstrated low intra- and inter-instrument variation (0.72%–8.4%).

Conclusions:

• The wrist-worn Actiwatch is a valid and reliable instrument for estimating energy expenditure and physical activity intensity in children aged 8–10 years.
• Established cut-off values facilitate accurate classification of physical activity intensity using the Actiwatch in pediatric populations.