Objective and subjective methods for measuring physical activity and sedentary behaviour in older adults

Abstract

The studies presented in this thesis highlight important issues relating to the measurement ofnphysical activity (PA) and sedentary behaviour (SB) in older adults, especially relating to thentransfer of these methods to free-living environments.Study One examined cut-points for ActiGraph GT3X+ (AG) for estimating time spent in SB innolder adults in free-living environments. ActivPAL3t (AP) was used as the reference standard.nMovement patterns were measured in 41 older adults over seven consecutive days with both AGnand AP. The results suggested that different cut-points must be used in older adults. In the case ofnolder adults when using 1-minute epochs, for example, 25 counts/minute must be considered whennusing the AG vertical axis only, or 200 counts/minute when using the three axes of thenaccelerometer.Study Two assessed the reliability and validity of a single question about sitting time on weekendnand weekdays and a 24-hour recall (MARCA) for the last two days (n=41) that provides contextualninformation about use of time. The single question showed poor validity, but fair agreement fornclassifying individuals into tertiles. The MARCA showed good validity and moderate agreement forncategorising participants into tertiles of time spent in SB. It is important to highlight that bothninstruments showed more accurate estimates for groups than for individuals.nStudy Three assessed MET values of common daily activities in middle age and older adults innfree-living environments and compared these with MET values listed in the Compendium ofnPhysical Activities (CPA). Sixty participants completed a semi-structured protocol of sitting, lying,nself-paced walking and four self-selected activities in their residences. 20 different activities werenmeasured among the participants, observing a wide range of movement patterns. Measured METsnwere significantly different from values in the CPA for several activities (sitting, walking,nsweeping, trimming, and laundry). It was concluded that using values from the CPA in older adultsnmay result in overestimation of total daily energy expenditure, particularly when considering thatnmost of the day is spent in sedentary activities.Study Four assessed the validity of four different AG equations for predicting energy expendituren(EE) in older adults; and assessed agreement between physical activity levels obtained from thesenequations and from four sets of published AG equations, with those from indirect calorimetry. Thenequations (Freedson, Crouter (refined equation), and Santos-Lozano (vertical axis [VT] and vectormagnituden[VM])) were compared with measured EE. 40 participants completed the study and 16ndifferent activities were assessed. It was concluded that when selecting an equation to estimate totalndaily EE from accelerometer data, equations with more accurate estimates of sedentary behaviournmight be preferred. However, when the main interest is to estimate total time spent in differentnphysical activity levels, a method with higher agreement for categorising activities may benpreferred.ConclusionThe work contained in this thesis will help researchers to 1) implement more accurate tools in thensurveillance of PA and SB in larger studies, 2) better understand the strengths and limitations ofncurrent predictive methods when applying them in free-living environments, and 3) improveninterpretation and translation of energy expenditure measures in older adults.n