If you've ever read through the class descriptions at your local gym and scratched your head, you're not alone. From HIIT (high-intensity interval training) to LISS (low-impact steady-state cardio) to EMOM (every minute on the minute), there seems to be an alias for every type of workout out there. One buzzy workout everyone is talking about is MetCon-codename for metabolic conditioning. What is metabolic conditioning, exactly? We tapped Holly Rilinger, Nike master trainer, to give us the low-down on this popular form of exercise.

What is metabolic conditioning?

Simply put, metabolic conditioning is any form of exercise that increases the efficiency of any of the body's three energy systems (phosphagen, glycolytic, and oxidative - more on them later), Rilinger explains. These workouts can be tailored to specific goals and an individual's fitness level, whether that's being able to lift heavier or sprint faster.

Many athletes use metabolic conditioning to enhance their sports performance, but it's also a great way to rev up your metabolism and lose weight. How so? As a modality of HIIT, metabolic conditioning allows you to work out in high-intensity intervals, maximising your kilojoule burn in a short amount of time. The intensity helps reset your metabolism to a higher rate during your workout, so it takes hours for your body to cool down again. The result is what's known as EPOC (excess post-exercise oxygen consumption), which is just a fancy way of saying that your body will continue to burn kilojoules long after you've finished your workout.

Tell me more about these three metabolic energy systems.

Again, your body's three energy systems are phosphagen, glycolytic, and oxidative. The phosphagen system supplies immediate energy to your body with a chemical called ATP (adenosine triphosphate), which is essentially energy that is converted from food. Your phosphagen system kicks in when you do quick, high-intensity exercises that fire up your fast-twitch muscle fibers, like Olympic lifts and sprints, but unlike other energy systems, it tires out fast.

Once your phosphagen system tuckers out, your glycolytic system kicks in. "It supplies ATP for activities, such as heavy weight lifting and longer sub-maximal sprints that last up to a few minutes in duration," Rilinger says.

Then, there's the oxidative system (also known as aerobic), which is basically the engine for endurance activities, like running a marathon or doing a triathlon. But it's important to note that all three energy systems don't work independently of each other. "No one system is every doing all the work. In fact, they're all working at any given moment - some are just doing more of the work that the others," Rilinger says.

How can I make metabolic conditioning part of my workout?

Focused athlete doing push-ups on kettlebells in gym

Designing the perfect metabolic conditioning workout for you depends on your fitness goals because the energy system you're conditioning relies on work-to-rest ratios, aka the amount of time you're exercising versus the amount of time you're recovering.

"Different ratios of work-to-rest periods call upon different energy systems and cause specific adaptations. It's important that the work-to-rest ratios are adjusted to fit the specific athletic or health-related goal," Rilinger explains.

That said, here are some other things to keep in mind as you design your own MetCon workout:

Determine your fitness level.

We recommend working with a certified personal trainer to help determine your fitness level to avoid injury and address existing health conditions that might prevent you from doing certain exercises. Some people like to use heart rate as a means of determining their fitness level. Here's how to calculate your target heart rate zone:

  1. Subtract your age from 220. This number will give you your maximum heart rate-this means you're working at a max effort.
  2. Calculate your resting heart rate by counting your heart beats per minute when you're not doing anything, like lying in bed.
  3. Determine your heart rate reserve by subtracting your resting heart rate from your max heart rate.
  4. Multiply your heart rate reserve by 0.7 and then add your resting heart rate to this number.
  5. Multiply your heart rate reserve by 0.85 and then add your resting heart rate to this number.

The numbers you have is the range of your heart rate training zone for vigorous intensity exercise, so while you're working out, your heart rate should be between these two numbers.

Choose the best work-to-rest ratio for your fitness goal.

As a general rule, Rilinger says lower work-to-rest ratios, such as 1:10, are ideal for developing power, while higher ratios, like 1:1 and 1:3, are best for improving endurance. Your phosphagen system works best with a 1:12 work-to-rest ratio. For example, sprinting on a bike for 10 seconds and recovering for two full minutes. With your glycolytic system, Rilinger says the ideal work-to-rest ratio is 1:2. "For instance, doing five kettlebell exercises and working for 20 seconds and resting for 40 seconds each," she says. Finally, for the oxidative system, the best ratio is 4:1. Try doing five dumbbell exercises consecutively for 30 seconds each and then resting for 30 seconds.

Select the exercises for your workouts.

Once you've determined your fitness level and the work-to-rest ratio that works best for your goals, it's time to choose the exercises. Select five moves that target a variety of muscle groups and perform them in succession, resting at the end of the round. Tailor the exercises so that they will help you improve your skill level and endurance.

"While there are a variety of ways to structure a workout, to get the most out of your MetCon workout, use total-body exercises with moderate loads that still allow you to use proper form," Rilinger recommends. "Remember it's important that you allow enough time to recover between sets, say two to three minutes." If you repeat the exercise bout sooner, you run the risk of lowering the intensity and turning the workout into an aerobic session.

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