Method for determining an instant velocity of a user and for improving estimation of heart rate

The present disclosure concerns a method for determining an instant velocity of a user using a sensing device (1) destined to be worn on an arm of the user and comprising a motion sensor (2) for measuring and delivering an motion signal representative of the user's movements when the sensing device (1) is worn; the method comprising: measuring the motion signal; identifying when the user is performing a rhythmical activity and estimating a fundamental movement frequency of the user from the measured motion signal; identifying when the user is walking or running by calculating an activity level of the user using the measured motion signal and the fundamental movement frequency; when the user is walking or running, providing a relationship between the measured motion signal and corresponding motion features relating to a propulsive impulsion of a user's step; estimating a frequency of the user's step and a user-relative step length of the user using the motion feature; and determining a user-relative instants velocity by combining the estimated step frequency and the estimated step length; the instant velocity being determined from the user-relative instant velocity using a calibration factor from the user-relative instant velocity using a calibration factor.