Abstract: Objective: The aim of this study was to evaluate the validity of RT3 Triaxial accelerometer in the aspects of measuring different types of physical activity and verify the precision accuracy of energy expenditure prediction model in the RT3 software in order to develop more accurate energy expenditure prediction formula for Chinese. Methods: In the method of Indirect heat measurement, 14 males and 16 females completed 20 activities including 2mph walking, 3mph walking, 3mph 3% grade walking, 3mph 8% grade walking, 4mph brisk walking, 4mph 3% grade brisk walking, 5mph and 6mph running, slow and quick skipping, 10mph and 13mph bicycle riding, ascending stairs, descending stairs, cleaning table, washing clothes, mopping floor, playing table tennis, strength testing for upper limb and lower limb. Results: The R² between counts of vector magnitude, Vertical (V), medial–lateral (ML), anterior–posterior (AP) planes and METs were0.63、0.62、0.59,0.46, the results showed three axis could occur synchronous changes with physical activities. The R² between counts of vector magnitude counts , vertical counts and METs were almost same when measuring not only walking but also daily living activities. Conclusions: Using three-axis accelerometer is not considered much better than uniaxial acceleration sensor. RT3 itself consumption prediction model is not suitable for Chinese people .RT3 could sensitively measure flat walking, but couldn’t accurately detect walking on slope, ascending and descending stairs. Regression formulas according to walking and all activities in the research and Common activities regression formula have more accuracy in predicting energy consumption than foreign formulas; however the error is still inevitable.

Key words: RT3 Triaxial Accelerometer, Physical Activity, Validity