What is Interval Training?
The time for a particular swim repetition is called the interval. Another way to think of it is the "go again" time. When you finish a swim, the balance is rest or recovery time before you start another swim. This "work followed by rest" training method makes for better improvement in performance than straight training without structured rest. You should try to gradually decrease both the swim and the rest times.
Example: Do 6 x 50 yards (two lengths in a 25 yard pool) freestyle on 1:10 (One minute and 10 seconds)
Start successive 50 yard swims when each one minute and 10 second period has elapsed. SO if you started out on a 50 swim when the clock read "60 seconds", your next 50 swim would begin on the "10", then on the "20" , then on the "30", etc. Your interval should give you about 15 seconds of rest before you start again, so you need to know about how much time you require for both. Time your swims and your rest, add that together, then see if you can do multiple swims on that total time, or interval. Remember it includes SWIM AND REST!
To be most efficient, keep going from one swim set to another with only the amount of rest the interval allows. Use your intervals as tools to improve endurance and speed. The clock is a splendid helper in telling you how well you are swimming and measuring your fitness level.