ASSESSMENT OF ENERGY-EXPENDITURE FOR PHYSICAL-ACTIVITY USING A TRIAXIAL ACCELEROMETER

A triaxial accelerometer was used to evaluate the relationship between energy expenditure due to physical activity (EE(act)) and body accele ration during different types of activity. In a laboratory experiment, 11 male subjects performed sedentary activities and walked on a motor driven treadmill (3-7 km.h(-1)). EE(act) was calculated from total en ergy expenditure (EE(tot)), as measured by indirect calorimetry, and s leeping metabolic rate (SMR): EE(act) = EE(tot) - SMR. Body accelerati ons were measured with a triaxial accelerometer at the low back. Speci al attention was paid to the analysis of unidirectional and three-dire ctional accelerometer output. During sedentary activities a linear rel ationship between EE(act) and the sum of the integrals of the absolute Value of accelerometer output from all three measurement directions ( IAA(tot)) was found (r = 0.82, P < 0.001, S-y,S-x = 0.22 W.kg(-1)). Du ring walking EE(act) was highly correlated with the integral of absolu te accelerometer output in antero-posterior direction (IAA(x); r = 0.9 6, P < 0.001, S-y,S-x = 0.53 W.kg(-1)). When all examined activities w ere included in a regression analysis, a strong Linear relationship be tween EE(act) and IAA(tot) was found (r = 0.95, P < 0.001, S-y,S-x = 0 .70 W.kg(-1)). Using this relationship, EE(act) during sedentary activ ities as well as EE(act) during walking could be estimated with an acc uracy of about 15%. Although sedentary activities and walking represen t a large part of normal daily physical activity, the validity and use fulness of the triaxial accelerometer-measuring IAA(tot)-to predict EE (act) in daily life must be studied under free-living conditions.