A method for monitoring a person performing a physical exercise based on a sequence of image frames showing the person's exercise activity is described. The method comprises the steps of extracting, based on the sequence of image frames, for each image frame a set of body key points using a neural network, the set of body key points being indicative of the person's posture in the image frame, and deriving, based on a subset of the body key points in each image frame, at least one characteristic parameter indicating the progression of the person's movement. The method further comprises detecting a start loop condition by evaluating the time progression of at least one of the characteristic parameters, said start loop condition indicating a transition from a start posture of the person to the person's movement when performing the physical exercise.
