Another way to develop conditioning and improve your speed and efficiency is to do interval training. If you do 12 x 100 on an interval, instead of a straight 1200, you usually swim each 100 faster because you get some rest. Also, you know when you start getting slower because you are watching the pace clock.

To get started, time yourself on a 500 or 800 swim and figure the average time per 100. Then add 15 seconds to that average per 100.  That is your interval. The interval includes your swim time and your rest time.  For instance, if you swim a 500 in 10:50, that's an average of 2:10 per 100. Your interval should start out at 2:25. To make it easier to read the clock, make your interval 2:30. That means you leave to swim a 100 every 2:30. If you swim the 100 in 2 minutes, you get 30 seconds rest. If you swim in 2:15, you get 15 seconds rest.

 

At your next workout, try swimming 10 x 100 on an interval of 2:30. See if you can hold a steady pace. When you find that you get at least 20 seconds rest per 100, decrease the interval to 2:20. Also, try increasing the number of 100s that you swim. This will add some variety to your workouts.