Hang in there! you can't start off at 40 mins right off the bat. like Bizi, i've heard 20 sustained is the threshold for an aerobic workout though - have not heard 40 - that may include the warm up and cool down.

but anyway, you start at what you can do and no more. otherwise it is unhealthy! say, 5 mins, and if you can't do five you do, three, or just one. then you gradually find you hold out for longer. for some of us it takes more time to build up than others, don't let anybody tell you how much you 'should' be building up, or that you aren't doing enough. the important thing - but also the most difficult - is to just keep on doing it regularly. at least three times a week is recommended.

if you do that, you will get better and better. guaranteed.

~ waves ~ who has developed a temporary allergy to the scale