Intervals are a key part of running training. Read on for the basics of what intervals are and why you would run them!
What are Intervals?
Running "intervals" refers to breaking a run into short fast sections, with some rest in between. The rest can be walking or slow running, usually for several minutes. They are usually run on a track, but can be done anywhere. The terms "intervals", "repeats", "track work", and "speed work" are often used interchangeably, although there are subtle differences. An example interval workout might be 8 x 800m with 400m jog recovery. This basically means run 800m (2 laps on a track) fairly hard (maybe 10K race pace), jog a slow lap, and then repeat this 8 times.
Why Run Intervals?
There are several main reasons why interval workouts are beneficial:
1) Intervals allow you to do a greater quantity of fast running. By breaking a run into sections with some rest in between, you can total more running at a faster pace than by just doing a continuous run. For example, a runner would normally be unable to maintain 5K race pace in practice for much more than a mile. However, this same runner could total 3 miles or more at race pace by running 1 lap (400m) at a time at race pace, with a couple minutes rest between each fast lap. Intervals essentially allow you to "work around fatigue" to get more high intensity running into your workout.
2) Intervals prepare your body to run faster on race day. To run fast in a race, you need to run fast in practice. For example, no matter how many miles someone runs at 10:00 mile pace, they will never be able to break 20 minutes for a 5K since they have never run close to this pace (6:27) before. Since your daily runs are usually much slower than race pace, intervals can help you by allowing you to run race pace or faster in practice. Running intervals faster than race pace helps race pace feel comfortable or even slow, the same way training at distances longer than the race helps the race distance feel short.
3) Intervals work different physiological systems than "normal" running. Related to the first two points, running intervals and other fast running has specific physiological benefits not adequately achieved by slower running. Most interval training is done at VO2 max pace or faster, with high heart rates. This helps build your ability the transport and use oxygen, as well as both reduce lactic acid buildup and be able run better when it occurs. Intervals help build the muscles required for running fast, since your form can change dramatically when you run faster. Your fast running form itself is also improved, resulting an better running efficiency.