Think about how you feel on the treadmill versus during a high-intensity interval workout: You probably feel like you could maintain that steady-state for a pretty solid amount of time without wheezing, while just one round of HIIT leaves you gasping for breath.
That difference is important to understand, because it’s how you can tell aerobic vs. anaerobic workouts apart. Your body creates energy in two basic ways: anaerobically (without oxygen) and aerobically (with oxygen), and each of those methods will affect your body differently. Understanding that process can help you burn calories and fat — plus increase your overall strength, power and endurance.
What’s an anaerobic workout?
Any activity performed at a high enough intensity that your body can’t provide the necessary energy to complete it with oxygen intake alone is considered anaerobic. “Anaerobic workouts primarily utilise fast twitch muscle fibres that can function only for a short amount of time without the help of additional inhaled oxygen,” explains Lesley Bell, a personal trainer and brain health coach.
READ MORE: Is It Better To Do Cardio Before Or After Weight Training?
Without oxygen, the body uses adenosine triphosphate (ATP) and glucose in the muscle cells for energy. But that process can’t be sustained more than 90 to 120 seconds of high-intensity exercise because your muscles have produced a significant amount of lactic acid in that time; after that, “your body must begin to utilise inhaled oxygen in order to break down glucose and fatty acids” to continue to produce energy, says Bell, and that’s when your aerobic energy system takes over (more on that in a minute).
“Anaerobic is done at a high intensity and usually using multiple intervals,” says Andy Coggan, a fitness director. If you’ve ever done a HIIT workout, that’s anaerobic exercise. Plyometrics, sprinting and weight lifting are all considered anaerobic — you’re going all out with 100-percent effort, but you can only sustain that effort for a short period of time. “Most sports involve anaerobic bursts followed by periods of rest,” too, he adds.
What’s an aerobic workout?
If the word “aerobics” makes you think of women dancing in Spandex, you’re on the right track — those low-intensity classes are designed to keep your heart rate up for an extended period of time.
“Aerobic exercise is anything where oxygen intake is sufficient enough to provide the energy necessary to sustain that exercise without tapping into alternative energy sources,” says Coggan. These workouts primarily utilise slow-twitch muscle fibres and the glucose and fatty acids the anaerobic system has already produced for fuel, which can sustain activity for extended periods of time, adds Bell.
Any lower- to moderate-intensity exercise is considered aerobic. Think about steady-state exercise like walking, running, cycling or even dancing. You’re not going to be gasping for breath during these workouts, because your body is continuously consuming enough oxygen for you to power through.
Why are aerobic and anaerobic workouts important?
Obviously, these styles of training are pretty different. And they’re both equally important in a well-rounded fitness regimen.
Aerobic exercise triggers fat burning, because you still have oxygen in your muscle tissue. It also “improves the cardiovascular system by strengthening the heart and potentially increasing the maximal amount of oxygen the body can utilise (AKA your VO2 max),” says Bell, which can improve your endurance.
On the other hand, anaerobic exercise — like HIIT — has been shown to burn more total calories in a shorter amount of time. You’ll also build stronger joints and bones due to the increased impact on your body.
To picture how these training methods affect your body, think about the bodies of elite athletes: A typical cross-country runner or marathoner follows a highly aerobic training programme, whereas a Cross Fitter is someone who prioritises an anaerobic programme.
But you can’t just do cardio or just do weights if you want to get fitter or stronger—even if you have a specific goal in one of those areas.