That depends on your goals. If the only reason you exercise is to be healthy in a long term, then a short workout a few times a week is enough. If you want to

That depends on your goals. If the only reason you exercise is to be healthy in a long term, then a short workout a few times a week is enough. If you want to be stronger/better at sports X/run marathons etc then no, aerobic classes are not enough. It's not even aiming for 'elite athlete', just aiming to be fit (you won't be fit in my definition if you only do 3x40min of aerobic classes a week).