Those pursuing better metabolic health might hear the term “metabolic conditioning” and wonder: Is this type of workout the key to optimal metabolism? Unsurprisingly, the answer is not as straightforward as marketing claims would have you believe.
Programs often defined as metabolic conditioning include CrossFit, Insanity, P90X, and the HIIT class at your local gym. These routines incorporate cardio and strength exercises performed at different intensities, with structured patterns of work and rest periods. The idea is to stress and strengthen specific energy pathways to fine-tune your body’s metabolic function. At the same time, you’re building stronger muscles, improving cardiovascular performance, and burning fat.
“Metabolic conditioning are workouts that attempt to preferentially use one energy system and then let that energy system recover, repeatedly, with the goal of increasing its capacity.” – Matthew Laye, PhD
What most get wrong about metabolic conditioning: It’s not limited to those high-intensity “MetCon” workout classes you see advertised. How you structure your workout affects how energy is created, how it is used, and how rapidly it is expended—and different structures offer different benefits for fitness and metabolic health. So what’s happening in your cells and metabolic pathways during different types of workouts? And how can you safely and effectively incorporate metabolic conditioning into your routine? Here’s what you need to know.
What Is Metabolic Conditioning?
Metabolic conditioning is any form of exercise that helps increase the storage and delivery of energy for physical activity, according to the American Council of Exercise (ACE). This includes high-intensity cardio, circuit training, steady state running, or walking.
“They are workouts that attempt to preferentially use one energy system and then let that energy system recover, repeatedly, with the goal of increasing its capacity,” says physiologist Matthew Laye, PhD, associate professor at the Idaho College of Osteopathic Medicine.
During any workout, our muscles contract with the help of ATP, the primary molecule for storing and transferring energy in cells. The more ATP supplied to working muscles, the longer those muscles can work.
Our body creates ATP in different ways. When you consume energy in the form of calories, your body converts those calories into ATP. But because the body can only store a minimal amount of ATP (80-100 grams) within the muscles, it needs to consistently produce ATP on a cellular level. It does that via three energy systems:
- The phosphagen system generates immediate energy by breaking down creatine phosphate, a molecule that can rapidly release high amounts of energy stored in the muscle cells; this kind of energy can fuel maximal effort, short-duration activities of about 7-10 seconds (think: an explosive weight lifting rep, or a short sprint).
- The glycolytic system comes into play when exercise continues for more than a few seconds up to a few minutes and rapidly produces ATP primarily from muscle glycogen and glucose stores to fuel slightly longer less intense efforts. This is the “intermediate” energy pathway. (Though it’s worth noting that the glycolytic system can be divided into the “fast” and “slow” systems. Here we’re describing the fast system; slow is associated with more oxygen use.)
- Finally, the oxidative (or aerobic) system is the “long-term” energy system. This uses oxygen to burn carbohydrates and fat to slowly produce ATP during longer-duration, lower-intensity activities.
In exercise, all three energy systems are engaged simultaneously, but one system typically provides the majority of the energy in a given moment, depending on the type of exercise you’re doing. For example, explosive, short-term activities such as weightlifting, all-out sprints, or high-intensity interval training (i.e., most of the activities popularly associated with “MetCon”) require immediate fuel from the phosphagen and glycolytic systems (with recovery time in between efforts so your body can quickly replenish energy stores—mainly for the phosphagen system). Structured patterns of high-intensity work challenge those immediate and intermediate energy pathways to rapidly provide your cells with adenosine triphosphate (ATP). With training, the body increases the amount PCr and glucose stored and the concentration of key enzymes in each of these pathways, increasing both the rate of ATP generation/resynthesis and the amount of ATP available to use. The net effect is more weight lifted, more HIIT intervals, more intensity.
On the other hand, steady-state exercise, which requires less overall ATP production (like running or cycling at an easy, consistent pace), primarily utilizes the oxidative system. This system cannot produce ATP as fast as the non-oxidative systems but can continue providing ATP for hours. Similar to the glycolytic systems, adaptations to aerobic exercise increase the fuel storage for the mitochondria and the enzyme concentrations to use those fuels. But steady-state exercise over time also increases the body’s ability to deliver oxygen to mitochondria via improved cardiac function (pumping of blood) and increased capillary density (pipes for blood) in muscle.
When it comes to metabolic conditioning, what system you’re using is less about the type of exercises you do and more about the intensity and duration of those exercises, says ACE. For example, very high-intensity exercise and more time resting (a ratio of 1:12 or 1:20, like sprinting for 10 seconds and resting for two minutes) targets your phosphagen system by allowing phosphocreatine to fully resynthesize, while doing slightly less intense exercise followed by more rest (a ratio of 1:3 or 1:5, such as lifting weights for one minute and resting for three minutes) will work the glycolytic system. Low-intensity exercise with less time resting (a ratio of 1:2, 1:1, or 2:1) will focus adaptations on your oxidative system.
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How Does Metabolic Conditioning Support Metabolic Health?
All exercise is beneficial for metabolic health in the long term. In fact, it positively affects us on a molecular level, indicating changes that may support long-term health, according to 2020 research published in the journal Circulation. By improving the capacity of energy pathways in the body, metabolic conditioning can positively affect your body composition and metabolism.
For starters, metabolic conditioning exercises (think: compound movements like squats and lunges that involve multiple joints and work multiple muscles or muscle groups simultaneously) are designed to be performed at a moderate to high intensity. Working at a higher intensity also increases your cardiovascular fitness, which improves your body’s ability to move oxygen and nutrients to your working muscles as well as remove metabolic waste, which allows you to keep performing that activity (and will eventually make that same effort feel easier as you get fitter).
And the harder you work, the higher the energy expenditure. That’s true during a workout and afterward, thanks to a phenomenon called excess post-exercise oxygen consumption, commonly known as the afterburn effect. The more intense your workout, the more energy it takes post-exercise to bring your body back to its resting state, research has shown. Circuit-style resistance training and high-intensity interval training showed significantly higher energy expenditure 14 hours post-exercise compared to the participants’ baseline metabolic rate, according to a 2021 study in International Journal of Exercise Science.
That afterburn effect is why metabolic conditioning can be such an excellent exercise method for weight loss, which relies partly on burning more calories than you consume. In particular, MetCon programs that combine cardio and strength training into one workout can help you lose fat—specifically the “bad” visceral fat more than subcutaneous fat—and gain muscle more quickly and more efficiently than if you were to do each style of exercise on its own, according to research published in PLOS One.
Both moderate- and high-intensity interval training (or HIIT), which fall under the umbrella of metabolic conditioning, can reduce body fat percentage, research in Obesity Reviews determined; and doing the kind of compound, total-body exercises a MetCon workout requires will make you stronger by building more muscle mass. And maintenance of muscle requires more calories than maintenance of fat. That’s because protein synthesis—the method by which muscles grow—is one of the most energy-consuming cellular processes, research has shown.
That extra muscle mass also increases glucose uptake capacity and improves insulin sensitivity, studies have shown. Better insulin sensitivity allows your cells to store blood glucose more effectively. Six weeks of an intensive CrossFit program (based on metabolic conditioning) improved blood sugar levels, reduced insulin resistance, and decreased the risk for heart disease in people with Type 2 diabetes, a 2018 study published in the journal Experimental Physiology found.
Who Should Try Metabolic Conditioning, and How Do You Do It Safely?
Because metabolic conditioning encompasses any type of physical activity, it’s endlessly customizable. That makes it a kind of training anyone can try simply by modifying the exercises to their fitness level. For instance, when it comes to strength training, you can start with bodyweight exercises and progress to weights. You should know how to do basic strength training exercises with proper form before adding weights or increasing the intensity. (If you’re new to any strength training, consider working with a personal trainer, and it’s generally a smart idea to check with your healthcare provider before starting any new exercise routine.)
Remember, metabolic conditioning revolves around structured patterns of work and rest periods. For example, high-intensity interval training is a type of metabolic conditioning, but not all metabolic conditioning is HIIT. Other kinds of MetCon include circuit training (typically five to seven exercises done with little to no rest in between, followed by a rest period), AMRAP workouts (where you complete as many repetitions of an exercise as possible during a set amount of time), and EMOM workouts (where you perform a certain number of reps of a different activity at the start of each minute and rest for the remainder of each minute) are also MetCon workouts.
If you want to create your own metabolic conditioning workout, rather than following a specific program, the most important thing is to create a structured pattern that focuses on the work-to-rest ratio. For example, you might choose a certain number of high-intensity exercises (think: burpees or kettlebell swings), perform each for 30 seconds followed by 60 seconds of rest, and then repeat the circuit. Don’t skimp on the rest periods: They’re just as important as the work periods because they allow your muscles to recover so you can adequately challenge them during the next effort. A general rule of thumb: The shorter the work time, the more intense the effort should be.
As you get stronger and fitter, you can play around with those ratios, making intense efforts longer and rest periods shorter or intense efforts even harder, with more extended rest periods for recovery. You can also add other variables, such as using heavier resistance or weights to increase the intensity, adding more repetitions or additional exercises to a circuit, or doing more sets during a training session to make workouts more challenging, ACE recommends. Change only one element at a time, so you don’t overload your body.
High-intensity MetCon workouts shouldn’t last more than 35 minutes (not including a warmup and cooldown), according to the National Exercise & Sports Trainers Association.
Nor should you do MetCon workouts exclusively. Because of their intensity, your body needs time to recover between workouts. Research published in the journal Frontiers in Physiology suggests that you should wait at least 24 hours between strength training sessions to see improvements. Complement your MetCon workouts with low-intensity, steady-state cardio and traditional strength training for a well-balanced program.
