For total EE , correlation coefficients were statistically significantly lower in uniaxial compared to multisensor devices .
For active EE , correlations were slightly but not significantly lower in uniaxial compared to triaxial and multisensor devices .
The high level of heterogeneity in the validation studies is only partly explained by the type of activity monitor and the activity monitor outcome .
Triaxial and multisensor devices tend to be more valid monitors .
The assessment of physical activity in healthy population s and in those with chronic diseases is challenging .
The aim of this systematic review was to identify whether available activity monitors ( AM ) have been appropriately vali date d for use in assessing physical activity in these groups .
Improving energy expenditure estimation by using a triaxial accelerometer.
In our study of 125 subjects ( 53 men and 72 women ) for two 24-h periods , we vali date d energy expenditure ( EE ) , estimated by a triaxial accelerometer ( Tritrac-R3D ) , by using a whole-room indirect calorimeter  under close-to-normal living conditions . The estimated EE was correlated with the measured total EE for the 2 days ( r = 0 . 925 and r = 0.855 ; P < 0.001 ) and in minute-by-minute EE ( P < 0.01 ) . Resting EE formulated by the Tritrac was found to be similar to the measured values [ st and ard errors of estimation ( SEE ) = 0.112 W/kg ; P = 0.822 ] . The Tritrac significantly underestimated total EE , EE for physical activities , EE of sedentary and light-intensity activities , and EE for exercise such as stepping ( all P < 0.001 ) . We developed a linear and a nonlinear model to predict EE by using the acceleration components from the Tritrac . Predicted EE was significantly improved with both models in estimating total EE , total EE for physical activities , EE in low-intensity activities , minute-by-minute averaged relative difference , and minute-by-minute SEE ( all P < 0 . 05 ) . Furthermore , with our generalized models and by using subjects ' physical characteristics and body acceleration , EE can be estimated with higher accuracy ( averaged SEE = 0.418 W/kg ) than with the Tritrac model
For total EE , correlation coefficients were statistically significantly lower in uniaxial compared to multisensor devices .
For active EE , correlations were slightly but not significantly lower in uniaxial compared to triaxial and multisensor devices .
The high level of heterogeneity in the validation studies is only partly explained by the type of activity monitor and the activity monitor outcome .
Triaxial and multisensor devices tend to be more valid monitors .
The assessment of physical activity in healthy population s and in those with chronic diseases is challenging .
The aim of this systematic review was to identify whether available activity monitors ( AM ) have been appropriately vali date d for use in assessing physical activity in these groups .