It's easy to mistake circuit training for interval training. You may hear people use the terms interchangeably. Also, circuit training for runners involves sets and repetition of sprints, jogs or both -- another reason why it's easy to confuse the two workout structures. But as we mentioned in the previous section, each has its own distinct purposes in a runner's toolkit, and one doesn't necessarily replace the other.
An easy way to distinguish the two is that in interval training, you do only one aerobic activity, such as running or cycling or swimming -- and none of the weight-training drills or body-weight exercises. If running to train for a race, an interval training workout breaks up your total race distance into segments or repetitions. You'll warm up first, then run each rep a little faster than your race pace. Advanced runners will recover between laps by jogging, whereas more novice runners will walk between laps. Typically, you'll add reps to each training session. Using interval training to condition for any event that's 10 kilometers (6 miles) or less, you'll wind up running approximately the length of your race when you add the total distance of all the reps you do in the session. For example, if you're a 5K runner, each time you do an interval workout session, all of your sets together that day generally add up to 5 kilometers (3 miles).
Interval training allows you to set and gauge your pace, because you predetermine the length of your laps and time them. Circuit training, as we saw earlier, focuses more on building strength, which is why you do sets of resistance exercises and weightlifting drills separated by jogging or running. One of the biggest complaints people make about interval training is that they can eventually become bored with it. On the other hand, circuit training offers unlimited variety, which is a surefire way to prevent a "blah" workout.
Although circuit training is popular among serious runners for off-season strength conditioning, interval training is the rigorous cardiovascular workout that you need to build aerobic stamina necessary for race day.
When you do speed work with interval training, it's suggested that you allow your body to rest for a day or two between sessions. With circuit training, you can do exercises targeting the lower body one day, then do drills focusing on the upper body the very next day, giving specific muscle groups 24 to 48 hours rest between workouts. If you do total body resistance circuit training, give yourself 48 hours between weight-training workouts. You can read more about interval training in How Interval Training Works.
Now that we know what circuit training is -- and what it's not -- read on to learn more about some of its pros and cons.