Physical therapy (also known as physiotherapy) is an allied health profession concerned with the assessment, diagnosis, and treatment of disease and disability through physical means. It is based upon principles of medical science, and is generally held to be within the sphere of conventional (rather than alternative) medicine. Physiotherapy is practiced by physiotherapists (also known as physical therapists, e.g. in the United States), though aspects may also be practiced under supervised delegation by physiotherapy assistants or other health professionals.