While this 30-minute workout was designed for beginner swimmers, you can adjust the duration and intensity to match your level. Keep a kickboard at the end of your lane to use during the warm up. Adjust the intensity of each phase of your workout according to the outline below. The intensity scale runs from 1 (easiest) to 10 (hardest). As you move from phase to phase, remember to vary your strokes, using freestyle, backstroke, breaststroke and, if you can, butterfly. Take a 30 to 60 second rest between each phase if you need. The warm up: Go for a 100-yard (4 pool lengths) swim using a stroke of your choice at an intensity of 4 to 5, then a 50-yard swim using scissor kicks with a kickboard at an intensity of 5 to 6. The workout: 25-yard swim at an intensity of 4; 25-yard swim at an intensity of 6 25-yard swim at an intensity of 6; 25-yard swim at an intensity of 4 50-yard swim at an intensity of 4 50-yard swim at an intensity of 6 Repeat these four intervals. The cool down: Swim 100 yards at an intensity of 4.