Interval training is alternating between higher and lower intensity exercise. Interval training allows you to train at a higher intensity for a greater time than a single, continuous high intensity bout. I believe that interval training is the most important workout for any runner, from absolute beginner through to elite. Interval training provides greater results in fitness for the time/effort than any other approach.
1 Types of interval training
- Aerobic Intervals. This is what many runners think of when they hear 'interval training'. These are often runs of 1-8 minutes at a high perceived effort, repeated so that the total mileage is around 3-6 miles. The longer intervals (5+ minutes) are often used with a recovery time of 1:1. The shorter intervals have disproportionally shorter recoveries (half the interval time or less). A measured distance is normally used, such as a track, but any reasonably flat surface you can mark with the distances works. (I use the local greenway, which is marked at quarter miles). Jack Daniel's refers to these as simply 'interval training' or 'I Pace intervals'.
- Anaerobic Intervals. The key distinction between aerobic and anaerobic intervals is the recovery. Aerobic intervals have a strictly controlled recovery period so that each interval starts with some aerobic stress remaining. Anaerobic intervals have full recovery, which is usually far longer than the interval itself. The interval is often two minutes or less in duration and run at a very high intensity. Jack Daniel's refers to these as 'Repetition Training' or 'R Pace intervals'.
- Beginners Run/Walk. Using a run/walk pattern for beginners is a great example of interval training. It allows a beginner to get in far more training time than a single, continuous run would do. For more details, read Starting to run
- Hill training is a type of interval training, usually doing high intensity uphill and recovering on the downhill. However, it can be better to do the high intensity downhill and recover uphill. For more details, read Delayed Onset Muscle Soreness
- Fartlek is a term given to running at different paces with no fixed structure. The word 'fartlek' comes from the Swedish for 'speed play'. Often a Fartlek session will involve choosing a visible landmark (next tree, top of the hill, etc) and a pace during the run. This can be done solo, or in a group, with each person taking turns to choose the landmark and the pace.
- Run/walk long runs can be used to build endurance. For established runners, this is more common in marathon and ultramarathon training than shorter distances.
- High Intensity Interval Training (HIIT). This training uses very high intensity running for very short periods, often with very short recoveries. This type of interval training produces some of the best results for the time allocated.
- Medium Intensity, High Volume intervals. This is the style of workout used by Emil Zatopek, AKA the "Czech Locomotive" who won several medals at the 1952 Olympics. Zatopek would run 100x 400m intervals at about 3 seconds slower than his 10K pace (72 seconds) with 200m recoveries. Yes, that is one hundred intervals, for about 25 miles at slightly slower than 10K pace.
2 Tangent - What about Tempo runs?
A tempo run is a continuous high intensity run lasting 20-40 minutes. Many training plans include both intervals and tempo training. So which is better? One study (http://www.pponline.co.uk/encyc/0437.htm) that compared interval and tempo training found that long intervals and tempo training produced similar results, but the interval training required only 2/3 the time of the tempo training. So for a given time commitment, interval training produces better results. My experiences is that interval training produces far better results for the effort than tempo training, mirroring this study.