A method (500) for determining running phases of a user (U) on a treadmill. The treadmill 100 comprises a base extending along a longitudinal axis. The base comprising: a first rotating element and a second rotating element adapted to rotate about respective rotational axes transversal to the longitudinal axis of the base； a physical exercise surface operatively connected to the first rotating element and to the second rotating element； an electric motor operatively associated with at least one of said first rotating element and second rotating element, the electric motor being configured to make the first rotating element and the second rotating element rotate, also driving the physical exercise surface into rotation； a data processing unit operatively connected to the electric motor, the data processing unit being configured to control said electric motor. The method (500) comprising steps of: - (a) determining (501), by the data processing unit, a magnitude variable over time correlated to the interaction of the user with the physical exercise surface while performing the physical activity, the magnitude variable over time having a substantially periodic trend； - (b) determining (502), by the data processing unit, respective time instants of at least two points among a plurality of points of the periodic trend of the magnitude variable over time, the respective time instants of each point of said plurality of points being representative of the instants of the interaction of the user with the physical exercise surface of the treadmill while running； - (c) determining (503), by the data processing unit, at least one running phase of the user on the physical exercise surface of the treadmill as a function of the respective time instants of said at least two points determined from the plurality of points of the periodic trend of the magnitude variable over time.
