Effects of placement and orientation of body-fixed accelerometers on the assessment of energy expenditure during walking

This study investigates the influence of accelerometer placement and orientation on the integral of the modulus of body acceleration (IMA). Further, the assessment of the energy expenditure for physical activity (FEact) during a common daily activity, with and without correction for the gravitational component of accelerometer output, is also addressed. IMA was determined from the measured accelerometer output at the lower back to compare realistic and simulated IMA values. As walking is almost completely restricted to the sagittal plane, a two-dimensional approach was used and accelerometer outputs were simulated/measured in the body-fixed antero-posterior (sagittal) and vertical directions. Both simulated and measured IMA values were compared with FEact determined from indirect calorimetry.