HIIT (High-intensity interval training) workouts can be a great addition to a training regimen. These workouts are different than typical endurance training in that they instead incorporate short periods of intense anaerobic exercise with less intense recovery periods until you are too exhausted to continue. This is much different than typical endurance training where you are trying not to go anaerobic as you build aerobic strength for sustained efforts over long distances.
Even if training for endurance events, HIIT workouts are an important component for endurance events.
First, aerobic workouts are a necessary part of an endurance athletes training plan. But, the addition of anaerobic (HIIT) workouts help endurance athletes build speed through explosive training sessions building muscle strength and causes the development of joints to reduce injury.
Second, these workouts are relatively short, especially compared to most endurance workouts. A HIIT workout may be 10-20 minutes in length. But, the intensity should, and if done correctly, will, exhaust you. These are great to add in on days when time is limited.
Third, bursts of HIIT my be more effective to weight loss than longer less intense workouts. So, if you are trying drop some weight as part of your training (and, in addition to healthy eating habits), these workouts can be beneficial.
HIIT workouts are not done daily. Even if you do them regularly, there is no need to do them more than 3 days per week. But the timing will be dependent on your other training and racing goals.
So, incorporate HIIT workouts into your weekly schedule. They will be an important part of maximizing your progress.