If you’ve heard of metabolic conditioning — or metcon — it’s probably in the context of a class that offers circuit training as a way to build strength, muscle, and cardiovascular conditioning at the same time.
But in truth, metabolic conditioning covers different approaches to building cardiovascular fitness, including low-intensity, steady-state (or LISS) workouts, high-intensity interval training (or HIIT), and the Tabata Protocol, an especially fiendish approach to HIIT that can leave even elite athletes in a puddle.
Here’s a primer on how they all work.
What Is Metabolic Conditioning?
Metabolic conditioning is a broad term for what is usually called “cardio,” or cardiovascular training — a form of exercise that focuses primarily on improving the health and performance of your heart and lungs, and your ability to perform large amounts of work in a short amount of time.
Why are there so many different forms of cardio conditioning?
If you paid attention in biology class, you may remember that your body has not one, but three major ways of supplying energy to your working muscles: the oxidative, the glycolytic, and the phosphagen pathways, or energy systems.
All three systems are in near-constant operation at all times, but different types of activities cause your body to favor one over the others:
The oxidative, or aerobic system is the slowest, but longest-lasting of the three energetic pathways.
Fundamentally, we are aerobic creatures, so this system is always running in the background (even now as you read these words!) regardless of the activity you choose.
You can emphasize the oxidative system with slow- to medium-intensity activities like walking, hiking, medium-intensity cycling, or other forms of LISS, but it’s also very active during strength training workouts as you recover between sets.
On a 1-to-10 effort scale — 10 being the highest — oxidative workouts rank about a six or a seven.
The glycolytic system is a faster, and more exhaustible pathway, most active when you perform medium-high to high-intensity activities: sprints lasting 30-90 seconds, lap-swimming of 20-50 meters, high-intensity strength-training circuits, or other forms of HIIT.
Effort level is about eight or nine out of 10.
Finally, the phosphagen system is the fastest and most powerful energetic pathway, and the soonest to burn out.
It’s emphasized when you perform all-out efforts lasting about ten seconds or less: a 50-meter dash, a 10-second shuttle run, a high-jump, a long-jump, or any other one-and-done athletic activity.
Effort level is 10 out of 10: as fast and as hard as you can go.
A well-rounded conditioning program encompasses at least some work on all three energy systems.
How to Work Your Different Metabolic Pathways
Those workouts can encompass a wide array of different activities, from standard forms of cardio training to jumps, throws, explosive movements, and strength-training exercises.
The only constraint is that the moves you choose place significant demands on your heart and lungs (so bodyweight squats work better than dumbbell curls) and that you can perform the movement safely, even when you’re fatigued (so bear crawls work better than heavy deadlifts).
Trainers and coaches typically describe met-con workouts with work-to-rest ratios: The longer and easier the work period, and the shorter the rest period, the more your body favors the oxidative system.
The shorter and harder the work period, and the longer the rest period, the more your body emphasizes the phosphagen end of the spectrum.
Somewhere in between are workouts that emphasize the glycolytic pathway.
A workout consisting of 10 minutes of work at a 70% effort, followed by one minute of rest, performed three times (3 x 10:00 : 1:00 @70%) would be a classic “oxidative” workout, good for building long-duration endurance.
A workout consisting of 60 seconds of work at 85% effort, followed by two minutes of rest, performed 6 times (6 x 1:00 : 2:00 @85%) would be a “glycolytic” workout, good for building short-duration endurance.
Finally, a workout consisting of 10 seconds of work at 100% effort, followed by three minutes of rest, performed 10 times (10 x :10 : 3:00 @100%) would be a “phosphagen” workout, good for building “burst” speed and power.
These are loose guidelines. Again: None of the energy systems works in isolation, and different people respond differently to each type of workout.
For an average person, a marathon-distance run is primarily oxidative; for an elite runner pushing for a personal record, however, the same run would likely lean heavily on the glycolytic pathway.
For most people, a walk around the block is a low-level oxidative activity.
But if you’re very heavy or have been sedentary or bedridden for a long time, a walk like that might quickly become glycolytic.
The different types of workouts also place very different demands on your ability to recover.
You can perform oxidative (LISS) workouts several times a week with no ill effects, but glycolytic (HIIT) and phosphagen system workouts place greater demands on your body.
Most trainers recommend sticking to no more than two HIIT workouts per week, with a few days of complete recovery — or other types of workouts — between those bouts.
Metabolic conditioning doesn’t really train your metabolism to run faster.
By forcing your body to run on different energy systems, however, these workouts improve your metabolic flexibility — your capacity to work at varying levels of intensity and your capacity to switch between them quickly and easily.
While you can perform any type of metcon workouts using a single, cardio-type exercise like sprinting, swimming, or jumping rope, you can work your cardiovascular system just as effectively — and, arguably more — with a variety of different movements performed in a circuit with little rest between them.
This is what most people think of when they hear the term “met-con.”
There are classic met-con workouts that fitness enthusiasts talk about, and sometimes compete in, but it’s easy enough to create your own, based on what you like and the equipment you have available.
1. Choose a series of basic, compound exercises for various large muscle groups.
These moves could include:
free-weight exercises, like dumbbell overhead presses
bodyweight movements, like air squats
jump variations, like skater jumps or box jumps
throws, like medicine-ball overhead throws, or rotational throws
cardio moves, like jumping rope, rowing, shadow boxing, or sprinting.
Don’t include high-skill moves (like barbell snatches, cleans, or deadlifts) or isolation moves (like dumbbell curls or lateral raises), or any move you can’t perform safely when fatigued.
2. Arrange the moves in an order that makes sense: alternating between exercises that focus on the upper and the lower body, or moves that you perform on a mat and those you perform standing, or between cardio-type moves and strength-focused ones, or place them on a scale from lowest to highest intensity.
3. Finally, structure the workout using either time parameters (say, 45 seconds at each station) or with reps (20 reps per move, for example).
Choose how long you’ll rest between circuits (10 seconds, 20 seconds, 30 seconds —usually ideally pretty short). Then choose a total number of circuits you’ll perform.
This work/rest schedule is what makes met-con workouts both flexible and challenging.
The more reps you perform per move, and the faster you move between exercises, the harder the workout.
Metcon Workout Examples
Some specialized approaches to met-con circuits include:
EMOM or “every minute on the minute”
In this system, choose a move or a circuit of different moves, and perform a set number of reps of each move at the top of each minute that elapses during your workout.
Let’s say your moves are the kettlebell swing, the bodyweight squat, and the pushup.
Choose a number of reps for each move that’s challenging but not exhausting — a 70% effort.
Let’s say for you that’s ten swings, fifteen squats, and eight on-the-knees pushups.
Set up your gear — kettlebell, mat, towel, water — so you can easily reach everything you need.
Place a clock with a secondhand or a digital clock where you can see it.
Start the timer and perform ten swings. Then put the kettlebell down and rest of the remainder of that minute.
When the next minute begins, perform 15 bodyweight squats.
Then repeat the process with eight on-the-knees pushups.
Rest for the rest of the minute, and repeat the whole sequence a total of seven times for a fun and challenging 21-minute workout.
The exercises, rep numbers, and time frame are all up to you — just choose exercises you can perform with perfect form, using a resistance level you can handle but still challenges you.
Some advantages of EMOM:
You can adjust your intensity level at any time.
If you try the circuit and it’s too easy or too hard, you can adjust the reps up or down accordingly.
You’re also motivated to complete the reps quickly — the slower you work, the more you cut into your rest period.
It’s also easy to track your progress.
If you completed all the assigned reps in all seven rounds of the above workout, up the intensity by adding a rep or two to each set next time.
AMRAP or “as many rounds as possible”
With this approach, you set a timer for a set period — say, 20 minutes.
Using the example above, you’d perform as many rounds of ten reps of swings, 15 squats, and eight pushups in that time frame, resting only as needed.
The clock stays running the whole time — even when you rest.
It’s brutal — but remember you can rest any time — even mid-set — and move at your own pace.
As with EMOM workouts, you can track your progress fairly easily with AMRAPS — just note how many round (or portions of rounds) you completed and try to beat it next time.
A second variation of this approach to AMRAP is “as many reps as possible,” in which you perform each exercise for a set time frame (say, 30 seconds), and attempt to get as many good-form reps in that time frame as you can.
How is metabolic conditioning different from HIIT?
HIIT, or high-intensity interval training, is a form of metcon in which you stick to one exercise for the entire session: hill sprints, burpees, sled pushes, Airdyne sprints, stair sprints.
Again, you’ll work with a set distance, number of reps, or a time constraint — say 300 yards (for a sprint), 20 reps (for burpees), 45 seconds (for an Airdyne sprint).
After each sprint, you rest for a set time (usually 2-4 times the duration of your work set), and repeat, attempting to go as fast or faster (or, alternatively, further) with each successive set.
How is metabolic conditioning different from Tabata?
The Tabata Protocol is an unusual method in which your work period — always 20 seconds — is double your rest period.
That means you are unable to recover fully between work intervals.
In the classic Tabata protocol, you sprint (or row, or cycle, or lift) all-out — at 100% of your maximum effort — for 20 seconds.
Then you rest for 10 seconds, and repeat the cycle a total of six or eight times — four minutes total.
Try it once, working at your max effort for those 20-second blocks, and you’ll be shocked at how long four minutes can seem.
The original study of this method (performed in Japan in 1996) exhausted a group of elite speed skaters in just four minutes.
Why You Shouldn’t Do High-Intensity Metcons Too Often
At their hardest, met-con workouts can work like a strong cup of coffee, perking you up and keeping you alert for hours at a time.
They’re fast, they’re effective, and they’re fun, too. So you might be tempted to do them even as often as five days a week or more.
Don’t do it: As beneficial as hard met-con workouts can be, they can also burn you out and eventually cause injury.
You’re pushing your muscles and cardiovascular system into the red zone over and over. Sooner or later, you’ll (at best) stall — or (at worst) get injured.
Two bouts of this type of workout per week is plenty.
High-intensity met-cons can also make you stiff and sore, so spend a little extra time after your workout on recovery techniques, like deep breathing, foam rolling, yoga, and static stretching.
These moves will relieve tension, flush the metabolites out of your muscle, and help you downshift after all that uber-intense thrashing around.