Just when you think you’ve nailed down the names of all the different exercises in your new workout program (and are ready to give it a whirl), it calls for a circuit here, throws in a bit of interval training there, and wait, a super… huh? What dimension did you just step into, you wonder.

We’ve all been there. Understanding fitness lingo basically feels like hearing French or Klingon for the first time. Still, there are certain terms within the fitness lexicon that can be hard for even gym veterans to differentiate, such as circuits, intervals, and supersets. When you see them in action, they don’t seem that different. Each describes an intense way to work out, and all can help you get fitter. But there are ways to bring out the best of their hidden powers under particular circumstances.

Let’s go over the basics of each.

1. Circuits

If you’ve ever done a group strength-training or boot camp-style class, you’ve done some circuit-style training. A circuit is composed of as little as four to as many as 10 different movements. Because these often involve dumbbells or a barbell, they tend to be considered strength movements, says fitness coach JC Deen of JCD Fitness. Cardio machines are rarely involved.The overarching goal is to complete every exercise in quick succession with the best form possible. You can determine how you want to do that: Either do the entire circuit a set number of times (or rounds), or complete as many rounds as you can in, say, 20 minutes. It doesn’t sound very long, but just imagine fluidly moving between full-body exercises, such as push-ups, mountain climbers, planks, lunges, and more, without pause. We’re sweating just thinking about it.The individual exercises themselves can also be based on a set amount of work (number of reps) or performed for a particular time. If done for time, you decide on the work and rest periods. For example, you might perform an exercise for 30 seconds nonstop before catching your breath for a glorious 10 to 30 seconds. Then you move onto the next exercise in the circuit for another 30 seconds of work, and repeat.

2. Intervals

Intervals describe the general type of training that involves repeated bouts of moderate-to-high effort intermixed with rest periods. With intervals, it’s really all about the work-to-rest ratio. We say “ratio” because your work duration can vary.For example, in one style of interval training, Tabata, you’ll perform 20 seconds of all-out effort, followed by 10 seconds of rest (that’s a 2:1 work-to-rest ratio). But you could also sprint for 60 seconds, rest for two minutes, and repeat (a 1:2 work-to-rest ratio). And if you’re new to intervals, you may want to start with a less-structured style, like fartlek training (try saying that without giggling). In this style, you’ll run quickly until you’re tired, slow to a jog to recover, then pick up the pace again.But perhaps the most well-known style is high-intensity interval training. HIIT is the in vogue thing to do if you want to supersize your workout efforts. Studies suggest that sprint-based workouts with intermittent rest periods are highly effective for improving fitness and eliciting cardiovascular benefits similar to a longer slog.Hormonal and inflammatory responses to different types of sprint interval training. Meckel Y, Nemet D, Bar-Sela S. Journal of strength and conditioning research / National Strength & Conditioning Association, 2011, Dec.;25(8):1533-4287. Sounds sweet, right? The kicker is that the “high-intensity” in its name isn’t just there for dramatic flair.“In this instance, intensity is referring to effort of force production, not effort of sustained endurance,” says Will Levy, head trainer at Melbourne Strength & Conditioning.In other words, to really cash in on HIIT, you need to be ready to feel downright uncomfortable when you crank out near 100 percent effort for a length of time. “There may be times when as little as 3 or 4 seconds is called for, and 20 seconds would probably be the upper limit, as it is virtually impossible to sustain true 100 percent intensity for any longer than that for even high-level athletes,” Levy says.And that’s where HIIT-ers can go wrong. It’s not about the duration of your high, but the high in your intensity.Satellite cell pool enhancement in rat plantaris muscle by endurance training depends on intensity rather than duration. Kurosaka M, Naito H, Ogura Y. Acta physiologica (Oxford, England), 2011, Dec.;205(1):1748-1716. If you’re not completely breathless by the end of your interval, you could have done more. The work-to-rest ratio varies depending on your goal, but the important thing, as Levy says, is that you actually rest during the rest periods—not jog, pedal, or move slower. Actually stop and rest.

3. Supersets

Supersets are included in many strength training programs to add more total work (also known as volume). In a superset, you complete all the prescribed reps of two exercises back-to-back before a period of rest. Ideally, you would choose an appropriate weight that you can sustain throughout every superset—not so heavy that your muscles are immediately fatigued, but not so light that you can sneak a look at your Instagram feed.When picking the exercises to superset, the common practice is to combine movements that target opposing muscle groups (e.g., a chest exercise followed by a back exercise).If you’re wondering, you can tack on one more exercise to turn it into a leveled-up superset called a tri-set, or giant set, which follows similar guidelines. In general, supersets are really helpful for moving through workouts with a greater number of exercises more quickly.

How to Put Them to Use

They all sound swell, but their true strengths lie in how you use them and what your goal is. In terms of keeping things interesting, circuits offer the largest variety of exercises for your workout, whereas intervals repeat the same exercise at a high effort. Supersets are kept at two exercises, but it’s not unusual to incorporate several supersets into a single workout.

“Circuit training, intervals, and supersets all burn glycogen [the body’s stored form of carbohydrates], and they’re all energy-intensive, so they can all contribute to helping a person burn fat if their diet is in order,” Deen says. In reality, there are no ironclad rules around how to carry out or incorporate the trio into your exercise regimen.

Here are some general guidelines.

1. Circuits are ideal as an addition to an existing fitness program.

Of the three training types covered here, circuit training is the most “well-rounded” for covering your fitness bases in a more efficient manner—especially if you’re crunched for time. Circuits are generally less effective for building strength on their own since the aspects that make circuits effective—well-roundedness and expediency—aren’t ideal for aspiring Hulk-sters.Deen likes adding them at the end of the week for his clients who are more focused on fat loss. “Depending on one’s goals, they’re generally most useful as a final circuit, or a “finisher,” after a more structured strength training has been performed,” Levy says.

2. Intervals are ideal for weight loss and improving athletic performance.

In spite of the skewed ratio of work-to-rest periods during interval training, its reported effects on your metabolism and your body’s ability to better mobilize fat stores make it a popular addition to a weight-loss program.Effect of exercise intensity, duration and mode on post-exercise oxygen consumption. Børsheim E, Bahr R. Sports medicine (Auckland, N.Z.), 2004, Mar.;33(14):0112-1642. Two weeks of high-intensity aerobic interval training increases the capacity for fat oxidation during exercise in women. Talanian JL, Galloway SD, Heigenhauser GJ. Journal of applied physiology (Bethesda, Md. : 1985), 2006, Dec.;102(4):8750-7587. “I generally use intervals for cardio needs on a weight-loss program, yet rarely on a muscle-gain protocol,” Deen says. One thing to remember is that although HIIT workouts temporarily boost the number of calories burned, it’s less than what most people think—not enough to warrant a celebratory post-gym cheeseburger.All forms of interval training are great for whipping your cardiovascular system into shape and increasing your ability to withstand higher intensities for longer stretches, but according to Levy, HIIT is most useful for getting faster, stronger, and more explosive.Uniqueness of interval and continuous training at the same maintained exercise intensity. Gorostiaga EM, Walter CB, Foster C. European journal of applied physiology and occupational physiology, 1992, Jan.;63(2):0301-5548. Lastly, it’s not recommended that you do HIIT daily. Rest at least 48 hours between HIIT sessions, and for most, two to three sessions a week will be all you need to see results.

3. Supersets are ideal for building muscle.

Supersets can be perfect for building either muscular endurance or muscular strength. In plain English, muscular endurance describes how long your muscles can keep up with a certain amount of work before they’re exhausted. When it comes to muscular strength, the 1RM max test is kind of a gold standard: Using all of your strength, how much weight can you lift and fatigue your muscles in one repetition? Supersets are a popular way to boost muscular endurance, which in turn allows you to do more work at higher intensities and gradually prod your muscles to grow (win-win!). Those looking to increase muscular strength can still use supersets with a higher weight, less repetitions, and longer rest periods.

The Takeaway

The common thread among these training techniques is that they’re designed to kick your butt by keeping your heart rate elevated. There’s no universal right or wrong way to utilize them. Their emphasis on reduced rest periods between sets and a higher intensity can help you achieve a variety of goals—as long as you’ve got the right nutrition and resting periods to support them.