Distance runners and sprinters often practice intervals on tracks. When doing intervals on a track we would use distance to specify our rest and recovery periods. For someone who is into long distance intervals, I would recommend running 400 meters(one time around)and walking 400 meters. After three weeks of training i would then progress to jogging the lap for active recovery as opposed to walking. Do this workout for 30 minutes, and on a day that you are not strength training.

With swimming intervals I reccomend doing 20 reps of 50 yard swims. here is how i prescribe recovery in this fitness activity. Create a challenge and give yourself a time to complete each 50 yard swim. For example if you can do 50 yards in 45 seconds then make your recovery time 45 seconds. Continue this process for 30 minutes.