Aims: 

Physical activity is known to be associated with many beneficial health effects, but understanding this association has been insufficient due to lack of objective measurements. Motion sensors can measure accurately the amount and intensity of physical activity. The aim of the present study was to assess the association of the number and intensity of step-related impacts with oxygen consumption.

Methods: 

Resting metabolic rate was measured in ten healthy young men with a portable indirect calorimeter. The subjects walked and ran on treadmill at velocities of 3, 6 and 9 km/h and oxygen consumption was measured. The subjects wore on their waist an accelerometer that recorded the number and magnitude of impacts. Oxygen consumption was converted to metabolic units (MET). Effect of velocity on MET was evaluated by one-way analysis-of-variance, and of number of impacts per minute, mean acceleration, and combined function of impacts and acceleration by linear regression analysis.

Results: 

MET differed significantly between velocity levels (Mean MET: 2.4, 4.7, 9.0 for 3, 6 and 9 km/h, respectively). Number of impacts, mean acceleration, and combined impacts and acceleration correlated positively with MET value (regression coefficients 0.021, 4.57, and 0.018; and R^2's 0.53, 0.87, and 0.92; respectively).

Conclusions: 

The quadratic association between MET values and speed is caused by the change of walking to running after 6 km/h. Combination of accelerometer-based number and magnitude of impacts is highly associated with energy expenditure in METs, showing that this method is applicable in metabolic studies.