Ulrich, if its made for a 40 you should be ok, provided you're not wearing a Michelin man style gambeson- that is, an overstuffed one. Mind you, it is most likely the weight of it that is giving you trouble...keep at it, keep handling it- you might even make a workout of it, putting it on, taking it off- do that ten times and see how you feel. Then you can add 'reps' to that. It is a lot harder than lifting hand weights because it'll flop and fold over if you're not paying attention, but it makes for a good workout nonetheless. You will get the hang of it eventually, no pun intended.