A media-playback device for playing back media content for a user performing a repetitive-motion activity, the media-playback device comprising: a content output device that operates to output media content; a cadence-acquiring device comprising a movement-determining device and a cadence-determination engine configured to determine a cadence based on movement data captured by the movement-determining device; a phase-delay calibration engine configured to determine a delay associated with the time required to detect an action point within the repetitive-motion activity of the user and the time required to output a beat of the identified media content item corresponding to the detected action point for at least one cadence value, wherein the determining of the delay comprises using a cadence-phase data table stored in a memory device in the media-playback device, wherein the cadence-phase delay data table stores respective values that represent the phase delay at corresponding cadence values; a cadence-based media content selection engine configured to identify a media content item based on the cadence determined by the cadence-acquiring device, wherein the media content item comprises music with a tempo that corresponds to the cadence; and a phase-aligned media playback engine configured to: identify the action point within the repetitive-motion activity based on the movement data; align (262; 380) the identified media content item to the repetitive-motion activity based on the determined delay; and cause the media-output device to output the aligned media content item so that the beat of the media content item is outputted to reach the user coincidentally with the action point. a content output device that operates to output media content; a cadence-acquiring device comprising a movement-determining device and a cadence-determination engine configured to determine a cadence based on movement data captured by the movement-determining device; a phase-delay calibration engine configured to determine a delay associated with the time required to detect an action point within the repetitive-motion activity of the user and the time required to output a beat of the identified media content item corresponding to the detected action point for at least one cadence value, wherein the determining of the delay comprises using a cadence-phase data table stored in a memory device in the media-playback device, wherein the cadence-phase delay data table stores respective values that represent the phase delay at corresponding cadence values; a cadence-based media content selection engine configured to identify a media content item based on the cadence determined by the cadence-acquiring device, wherein the media content item comprises music with a tempo that corresponds to the cadence; and a phase-aligned media playback engine configured to: identify the action point within the repetitive-motion activity based on the movement data; align (262; 380) the identified media content item to the repetitive-motion activity based on the determined delay; and cause the media-output device to output the aligned media content item so that the beat of the media content item is outputted to reach the user coincidentally with the action point. identify the action point within the repetitive-motion activity based on the movement data; align (262; 380) the identified media content item to the repetitive-motion activity based on the determined delay; and cause the media-output device to output the aligned media content item so that the beat of the media content item is outputted to reach the user coincidentally with the action point.