An apparatus comprises: memory configured to store a user-specific calibration metric, at least one processing core, configured to determine an activity type identifier of an activity a user is engaged in, and to determine a user-specific intensity level of the activity, wherein determining the user-specific intensity level is based at least partly on the identifier of the activity type, the user-specific calibration metric and data obtained from a kinematic sensor, and to obtain the user-specific calibration metric by performing a calibration procedure. The calibration procedure preferably includes obtaining heart rate data and may comprise mapping a set of kinematic data to user specific intensity levels.
