Interval training routines are designed to vary the intensity of a workout with alternating segments of easy, moderate and hard exertion.  Set your timex ironman interval timers, and alerts will notify when you need to change the pace.  A classic beginner interval workout is the run/walk.  for example, after warming up, start your interval timer and run for 1 minute.  When you hear an alert, walk for 3 minutes.  At the next alert, repeat the series again.  Interval training has been shown to improve speed and endurance more effectively than traditional steady-state workouts.