Fully proportional actigraphy: A new instrument

The relevance of activity measurement is reviewed. Technical information regarding a new, small, lightweight, fully proportional accelerometer-based activity monitor suited for a wide range of wrist, waist, and ankle activity measurements over extended time periods in free-ranging persons is presented. Calibration data demonstrating within- and between-device reliability and validity are presented. Field trial data are presented showing that wrist and waist actigraphs can predict kilocalories of energy expended. The issue of how activity monitors should be validated is discussed. Instrument reliability is distinguished from clinical repeatability. Recommendations are provided to assist investigators with instrument selection.