When you exercise, your metabolism increases. This can cause an increase in the amount of calories that can be burned even when you are done with your workout. For the rest of the day, following your workout, your body will continue to burn calories even if you are not being physically active.
If you are trying to work on how fast you can swim, develop the flexibility in your ankle. Your ankles will act as propeller or flippers to propel you forward. If you can build up the strength in your ankles, you will be able to move your feet faster and in a better motion.