Validation of the AX3 triaxial accelerometer in older functionally impaired people

Background: Studying physical activity (PA) trends in older populations and potential interventions for increasing PA is important, as PA is a factor in many age-related health outcomes such as chronic disease, premature mortality, physical function, and injuries from falls[1]. Objective measures of PA provide valuable information regarding the functional impact that ageing and chronic disease states may have on a patient’s life. Aims: The purpose of this study was to test the validity of the AX3 PA monitor in an older population, to investigate if the AX3 is a valid measure of distinct types or levels of activity in older people with a spectrum of mobility. Methods: Validity of the AX3 PA monitor was tested using the RT3 as a means of cross validating the AX3. Study participants wore both the AX3 and the RT3 accelerometers, positioned on their non-dominant side, while completing a series of standardised everyday activities. Results: Although overall correlation was high (r>0.8) between the RT3 and lower-limb mounted AX3 counts, the correlation between the two devices was much stronger for walking activity than for any of the non-walking activities. Discussion: Activity counts at all lower limb positions for the AX3 and RT3 were highly correlated. Correlation between wrist-mounted AX3 counts and lower limb AX3 counts was only moderate, and worsened when walking aids were in use. Conclusions: The results of this study indicate that the AX3 monitor is a valid tool, which might be used to objectively measure walking activity in older, functionally impaired adults; a welcome finding for this under-researched area.