As far as I know there is no legal maximum on the number of treatments, there is however legislation relating to injury obtained at work etc.
I have trained with the No Hands Massage company up to Advanced Practitioner, and I am now a trainer for Injury Prevention massage in the Midlands.
Massage is a great treatment to be able to provide, its just such a shame that it causes a lot of therapists serious injury and or pain. Fortunately there is now help and training available!
Safe massage work requires an understanding of good and appropriate posture for massage, techniques and strokes that avoid stress and strain on the body, and ways of massaging that offer powerful strokes for the client without knackering the therapist.
How many of you do warm up exercises and stretches before spending a day massaging? How many marathon runners warm up before their days run?
If this is something you are interested in please check out the website linked in my signature, drop me a PM or come along to Beauty UK where Jen Longmore (director of IPM) is doing a talk about this very subject and I'll be there as the demo bunny body and to answer questions.
Mat xx
PS: Just to add I regularly have 5 massage clients a day without a problem, some days I've more.