A postural bio-feedback device worn by subjects for 4-10 hours a day for 6 days spread across 6 weeks for the sub acute low back pain group and for 8 days spread across 10 weeks for the chronic group. The device records movement and muscle activity data relating to the lower back. Bio-feedback is delivered to the subject as an audible tone, visual cue or vibration and aims to prompt the subject to alter their posture or position in line with recommendations given by the treating practitioner. Four small sensors are adhered to the lower back and send data wirelessly to a data logger carried in the pocket by the subject (the size of a small mobile phone).