A wearable exercise and performance assessment system in which a harness adapted to be attached to the torso of a wearer. The harness comprises a mount for releasably mounting an electronics module housing at a predetermined location on the torso of the wearer. The electronics module housing comprises a plurality of motion sensors. A processor, e.g. within the housing, processes received sensor data signals and outputs a resulting feedback signal to a performance feedback device. The processor comprises a sensor signal receiver arranged to receive motion sensor data signals over time from the plurality of motion sensors and to log the received signals with a synchronised time signal. One or more of said received sensor data signals is processed to identify data features therein indicative of repeated movements by the wearer and to delineate each repetition thereof. The processor applies said repetition delineation to one or more further received motion sensor data signal in order determine a performance parameter for each individual repetition thereof.