They're not the same thing, but they can be. Here's what you need to know about circuit training and interval training.
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In a modern fitness world where words like HIIT, EMOM, and AMRAP are thrown around as often as dumbbells, it can be dizzying to navigate the terminology of your workout routine. One common mix-up that it's time to get straight: the difference between circuit training and interval training.
No, they are not the same thing, and, yes, you should know the difference. Master these two types of workouts, and your fitness (and gym vocab) will be better because of it.
What Is Circuit Training?
Circuit training is when you alternate between several exercises (usually five to 10) that target different muscle groups, according to Pete McCall, a certified personal trainer and spokesperson for the American Council on Exercise, and creator of the All About Fitness podcast. For example, you might move from a lower-body exercise to an upper-body exercise to a core exercise, then another lower-body move, upper-body move, and core move before repeating the circuit. (See: How to Build the Perfect Circuit Routine)
"The whole idea of circuit training is to work different muscles all at the same time with a minimum amount of rest," says McCall. "Because you alternate which body part you're targeting, one muscle group rests while the other is working."
For example, since your legs get to rest during pull-ups and your arms get to rest during squats, you can nix any rest time between exercises—making for a more effective workout that not only builds strength but also keeps your heart thumping and revs your metabolism too, says McCall. (And that's just one of the many benefits of circuit training.)
"Because you're moving from exercise to exercise with very little rest, circuit training produces a pretty significant cardiorespiratory response," he says. Which means, yes, you can totally count it as cardio.
If you use heavy enough weights, you'll work to the point of fatigue (where you just can't do another rep): "That means you're improving muscular strength and can enhance muscle definition," says McCall. (Here's the difference between muscular strength and muscular endurance.)
Once you get comfortable with that idea, expand your movement selection beyond body part: "Now, we're starting to look at training movement patterns instead of muscles. That means focus on pushing, pulling, lunging, squatting, and hip hinging movements instead of just upper body or lower body," says McCall.
What Is Interval Training?
Interval training, on the other hand, is when you alternate periods of moderate- to high-intensity work with periods of either active or passive rest, says McCall. Unlike circuit training, interval training has less to do with what you're doing and, instead, is mostly about the intensity of what you're doing.
For example, you could do interval training with one movement (like kettlebell swings), several movements (like burpees, squat jumps, and plyo lunges), or with a strictly cardio exercise (like running or rowing). All that matters is that you're working (hard!) for a certain period of time and resting for a certain period of time.
You've probably heard that high-intensity interval training (HIIT) specifically has insane health benefits, and it's totally true: "You burn more calories in a relatively shorter period of time," says McCall. "It allows you to work at a higher intensity, but since you have periods of rest, it reduces overall stress on the tissue, relieves your nervous system, and allows your energy stores to build up again."
Can Your Workout Be *Both* Circuit and Interval Training?
Yep! Think back to the last boot camp–style workout class you did. There's a good chance you were rotating through a selection of moves that each hit different a muscle group (à la circuit training) but also had a specific work/rest ratio (à la interval training). In this case, it totally counts as both, says McCall.
It's also possible to do circuit training and interval training in the same workout but not at the same time. For example, you could do a warm-up, work through a circuit of strength moves, and then finish off with a HIIT workout on the air bike.
How to Optimize Your Circuit and Interval Training
Now that you know what circuit training and interval training actually are, it's time to make them work for you.
When you're putting together your own circuit or interval training workouts, be careful with your exercise selection: "You don't want to use the body part too many times or do too many repetitive movements," says McCall. "With anything, if you do too much of the same exercise, it could result in an overuse injury."
And for interval training specifically, choose strategically between active and passive rest: If you're doing a particularly difficult move (kettlebell swings or burpees, for example) you'll probably need to gulp some water and catch your breath during the rest interval. Doing a less-intense move during your work intervals (like bodyweight squats)? Try an active recovery move like a plank, says McCall.
The most important thing to keep in mind? You don't want to do too much of either: "If you do too much high-intensity training it could cause overtraining, which can cause adrenal fatigue and disrupt the hormone balance in your body," says McCall. (See: 7 Signs You Seriously Need a Rest Day)
"A good week would be maybe two days of circuit training at a relatively moderate intensity, and two or three days of interval training at a moderate to high intensity," he says. "I wouldn't do HIIT more than three or four times a week, because, with HIIT, you have to be doing the recovery on the back-end. Remember: You want to train smarter, not harder." (Here's more on how to design the perfect week of workouts.)