Validity of an Accelerometer-Based Activity Monitor System for Measuring Physical Activity in Frail Older Adults

This study aimed to investigate the validity of the accelerometer-based DynaPort system to detect physical activity in frail, older subjects. Eighteen home-dwelling subjects (Groningen Frailty Indicator [GFI] score ≥ 4, ≥ 75 years) were included. Activities in their home environment were simultaneously observed by two researchers and measured with the DynaPort system during six consecutive hours. Primary outcome measures were the sensitivity and specificity of the DynaPort for locomotion (90% considered as sufficient agreement). Other outcome measures were overall agreement, and sensitivity and specificity for other activities. Sensitivity and specificity for locomotion were 83.3% and 100.0%, respectively. Overall agreement was 74.6%. Sensitivity was sufficient for sitting (94.4%), but not for lying and standing (59.2% and 69.6%, respectively). Specificity was sufficient for lying and standing (100.0% and 93.3%, respectively), but not for sitting (80.7%). In conclusion, the DynaPort system is not a valid method for assessing physical activity in frail, older subjects.