At my dojo we do this often. We usely do this after a good cardio work out so our legs and arms are all ready mush. But this is how we do it, we go through katas as a class up to where you know, and once you know more you continue doing the kata you did last while the higher kyus go on. It gets really hard the more katas you know. It is really fun on test day when you do cardio and then put through the paces of techniques and then you grapple, then spare and to top it all off you do katas on request that means you do katas in the order the sensei wants them. It can be very hard, so you really got to dig deep and breath, its all about breathing, but it is still hard.