NOVELTY - The apparatus (116) has an input interface (100) e.g. message interface, for receiving heart activity data (110) of a person i.e. athlete. A processor (102) i.e. miniature electronic digital computer, determines a recovery heart rate change speed (114) during a recovery heart rate period (112) in the data, and determines a sympathetic activity state of sympathetic nervous system of the person based on the determined speed. The processor stores multiple predetermined sympathetic activity states, where each state is associated with a predetermined range of the speed.    USE - Apparatus i.e. polar electro design and manufacture heart rate monitor(RTM: personal heart rate monitor registering and evaluation equipment), for use with fitness equipment such as treadmill for determination of sympathetic activity i.e. muscle sympathetic nerve activity, of a sympathetic nervous system of a person i.e. athlete, for providing interval-type training such as fitness training or game such as football, soccer and/or ice-hockey. Can also be used for wrist-worn portable device, terminal of radio system such as mobile telephone, personal digital assistant (PDA) or personal computer such as desktop computer, laptop computer, palmtop computer and server computer.    ADVANTAGE - The processor determines the recovery heart rate change speed during the recovery heart rate period, and determines the sympathetic activity state of the sympathetic nervous system of the person based on the determined speed, thus enabling monitoring day-to-day sympathetic activity of elite athletes and enabling reducing training load.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for determination of sympathetic activity    (2) a computer program comprising computer executable instructions for causing an apparatus to perform a process of determination of sympathetic activity.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of an apparatus.    Input interface (100)    Processors (102, 108)    Heart activity data (110)    Recovery heart rate period (112)    Recovery heart rate change speed (114)    Apparatus (116)