1. A portable apparatus comprising: a first interface configured to input speed data of a user or location data of the user from a positioning unit utilizing external reference points; a second interface configured to input motion data of the user from a self-contained activity determining unit; and a processing unit configured to determine, if the first interface only inputs the location data, speed data from the location data, select filtering characteristics based on the motion data, filter the speed data with the selected filtering characteristics, and determine physiological data of the user using the filtered speed data.