You take time out of your hard-working life to go out running, you take advantage of midday to swim lengths, you worry about being in shape and you do sport for love or for competition.
If you want your body to keep up this pace and also the pace of the aerobics instructor, pasta is a food that you should take very much into account in your diet.
This will provide you with the necessary carbohydrates to create energy reserves in your muscles so that fatigue takes longer to set in.