Patent ID: 7867141

Claim:
A physical activity measuring system for determining an exercise intensity of a user, said system comprising: a portable device configured to be carried by the user and including a processor; a three-axis acceleration sensor attached to said portable device and configured to sense body motions of the user to generate acceleration signals a x , a y , and a z in all three directions along x-axis, y-axis, and z-axis, respectively; an acceleration-exercise intensity relation table storing parameters (α, β) representing a generally linear correlation between the exercise intensity and a default standard deviation of the acceleration signals sensed by said sensor; and an indicator mounted to said portable device for indication of the exercise intensity, said processor including an exercise intensity calculator for determination of an instant exercise intensity (K) of the user based upon the acceleration signals sensed by said sensor, said exercise calculator comprising: data collecting means for collecting first time-series data of said acceleration signals within a predetermined first time frame (T 1 ); calculation means for calculating a first standard deviation of the first time series data of the acceleration signals using a predetermined formula defining said default standard deviation in terms of the acceleration signals in said all three directions; reference means for referencing to said acceleration-exercise intensity relation table to obtain said parameters α, β that correspond to said first standard deviation; and determination means which uses thus obtained parameters (α, β) and an equation K=α·Sw+β to determine said instant exercise intensity (K) where Sw is the first deviation of the acceleration signals.