In recent years，sedentary behavior has been defined as behaviors resulting in less than 1.5 Metabolic equivalents（METs）of energy expenditure in adults．It has become clear that extended periods of sedentary behavior contribute to several diseases．To date，energy expenditure during sedentary behavior in young children has not been clarified．No established methods exist for measuring energy expenditure during sedentary behavior in young children，and its impacts on children’s bodies are not clear．This study was performed to clarify energy expenditure associated with sedentary behavior in young children using a breath gas mass spectrometer and to create an equation to predict energy expenditure during sedentary behavior using a 9-axis sensor．Energy expenditure in children aged 5–6 years was measured using the breath-by-breath method and 9-axis sensors on the right and left wrists，and the back．The information in three axes was obtained from the accelerometer，gyro sensor，and magnetic sensor，each included in the 9-axis sensor．Energy expenditure revealed by the expiratory gas analyzer indicated that the Oxygen uptake per body weight（VO2/W） value 6.65±2.95 ml/min/kg．A prediction equation was developed VO2/W=3.128+ 1.567× Ln[Magnetometer(back)] that provides estimates that correlate better than the others（r = 0.301）with data obtained with our measuring method using a back mounted magnetic sensor．
