>>287673603
Unironically go read the /fit/ sticky. You're probably in general just not in good enough condition for those harder maps. Start lifting weights and supplementing cardio.
If you're willing to try a supplement take creatine before playing, it helps to give the energy needed for the more intense maps.
Finally, experiment with playstyles so you can be more efficient in your movements. Try to lead swings into eachother so you aren't wasting energy. If all else fails rely more on wrist motion, though I don't find that as fun personally.