Abstract: A method for determining a value of a performance indicator for a periodic movement performed by a human or an animal. The method includes receiving (210) time series data from an inertial sensor used for sensing the periodic movement, partitioning (220) the received time series data into periods of the movement, and transforming (230) the time series data of each period into a data representation of a defined size. The method further includes classifying (240) each period into a movement class, and determining (250) a value of a performance indicator for at least one period of the movement, based on the data representation and on the movement class of the at least one period.