The HBT intervention consists of fortnightly scheduled phone calls to patients over the 6-month course of the study. A nurse-tutor collects information on: disease status, pain, disability, prodromal symptoms of exacerbation, number of home exercise sessions performed, and use of non-steroidal anti-inflammatory drugs. In consultation with the physiatrist, the nurse gives advice on solutions for persistent pain and any symptoms of exacerbation. The patient is always encouraged to perform regularly the physical activity and the exercises prescribed. The physiatrist is involved as a second-opinion consultant.