I used to be a fairly competent badminton player and played in a few junior tournaments in Europe as a teenager. So I was fit, did my shuttle runs and sprints religiously along with weight training 3-5 times a week and then court training as many times.
Well, I thought I was fit until I played squash for the first time. Played the first game, went off the court, drunk nearly two liters of water and pretty much passed out. Utterly and totally fucked. Fitness levels to play this game professionally must be stratospheric.