Described herein is a computer processing system 100 including a processing unit 106. The processing unit is configured to access activity data relating to a user's movements during a session. The processing unit processes said activity data to identify one or more wave start points 206 and one or more wave end points 210； and estimate one or more waves 202 caught by the user during the session, each wave being defined by a wave start point and a corresponding wave end point.
