I had some physio during my pregnancy, this involved manipulating my back and legs and teaching me exercises to try & help me strengthen my back so that it wouldn’t hurt so much.
Physiotherapists usually take a degree course (see http://www.nhscareers.nhs.uk/details/Default.aspx?Id=337 from the NHS careers website), which includes both theory and practice elements. Biology would provide a good background to a job in physiotherapy.
My wife is a doctor in occupational health (deals with people’s health probs related to their work), and has lots of patients with bad backs. She often ‘refers’ them to the physiotherapists so they can be taught special exercises to help strengthen their backs.
I’d say “Study hard!” as it’s competitive to get into Physiotherapy degree courses – the NHS Careers site Sarah linked says “Three A levels at grade A-C (one should be a biological science)”, and I’ve heard that the offers are usually ABB or BBB. The degree includes a lot of anatomy and physiology, and stuff about diseases, as well as teaching practical skills. More details e.g. here.