1. An apparatus for an interval exercise performable by a person, the interval exercise including at least two training intervals, each including a work phase and a recovery phase, the apparatus comprising: a processing device to process a first exercise parameter data characterizing an exertion level of the interval exercise; a detector to detect a work phase of a training interval from the first exercise parameter data; a detector to detect a value of the first exercise parameter from the exercise parameter data at the end of the work phase; and a determiner to determine a threshold level of a physiological parameter, measured from the person and characterizing the person's recovery level in a recovery phase, based on the value of the first exercise parameter at the end of the work phase.