The two most common types of interval training for running are low intensity intervals and high intensity intervals. Both are good training methods, but they are for different types of running. While low intensity interval training for running is best for marathon runners and those runners preparing for very long distances, high intensity interval training for running is best for sprinters and those runners preparing for shorter runs. The best interval training will also depend on the athlete's fitness level and athletic goals. A middle ground between low and high intensity interval training for running may be the best option for some runners.
The best interval training for running will be custom-made for a specific runner. A racer may want to consider the race he or she is preparing for when designing his or her interval training program, but most runners will fit into either the low intensity category or the high intensity category. It is a wise idea for beginners to tailor the interval training for running programs, as such training is very strenuous and the body may not be prepared for it. Going into an interval training program cold may actually be counterproductive and lead to injury.
Low intensity interval training for running is the less strenuous of the two options, so beginners may want to start here. During this training, the runner will run faster than moderate pace for one to two miles (1.6 - 3.2 km), then rest at a slower pace for several minutes. The process is then repeated. The rest period allows the muscles of the legs to recover briefly, which allows the runner to run for longer durations. It also helps increase lactic acid threshold; as the body burns glycogen for energy, the lactic acid byproduct builds up in the muscles. Interval training helps the body learn to combat lactic acid build up, which can prevent or delay fatigue.
High intensity interval training involves running for shorter periods at a fast pace, then rest for several minutes at a slower pace. The rest periods in high intensity training is generally much shorter than that of low intensity training, and the runner will run at a much faster pace than he or she would during low intensity training. The general idea of high intensity training is to build fast twitch muscles that will help the runner sprint faster or maintain a faster speed for short distances. Athletes participating in team sports such as baseball or football would most likely benefit from high intensity training more than they would from low intensity training.