The invention relates to apparatus to be worn at or adjacent to the knee joint of a person to detect the impact effect of forces applied to the knee joint and, as a result of the detection, and typically analysis of information relating to the person wearing the apparatus, feedback information is provided to the person, in one embodiment during the time when the apparatus is being worn, so as to provide timely feedback to the person wearing the apparatus of the impact on the PF joint. The person wearing the apparatus or monitoring the same can use the feedback whilst the apparatus is being worn, in order to allow the person to change their movement or stop their movement with immediate effect and thereby prevent or minimise the risk of the injury occurring.
