1e-runner,
I did my max test today - it hurt! I've got a friend who is a sports scientist and she got me in the lab to do a test on the treadmill. Basically it starts at walking pace and goes up 1kph per min until you can't take any more...she also measured VO2max too so that meant I had to wear an ox mask. You could probably replicate the HR max test in a gym easily enough, though if you really give it some you might come off the back of the treaddie - there was a lovely mattress waiting for me "just in case".