Fast-twitch muscles are larger and denser than slow-twitch muscles and can generate more force and power with quicker response times. They’re the ones used during anaerobic workouts like HIIT, heavy lifting, and plyometrics. “The larger and denser your muscles are, the more ATP required, which means a higher level of calorie burn,” says Proniewych.
Doing workouts that require your body to produce energy without oxygen (anaerobically) as opposed to with oxygen (aerobically) means creates a bigger oxygen deficit in your system that’ll it’ll need to repay during recovery. Plus, anaerobic exercises rely primarily on fast-twitch muscles.
HIIT has the trifecta when it comes to EPOC igniters: 1. It’s high intensity. 2. It’s anaerobic. 3. It utilizes fast-twitch muscles. Boom! To get the most afterburn, “make sure it’s an exercise that you can push your body as hard as it will allow,” says Wehrman.
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More research needs to be done in regards to the length of time EPOC effects the body. Some studies say it lasts only 15 minutes, while others have determined that increased oxygen consumption can happen for several hours. What does ring true is that how many calories you burn post-workout depends is different for everybody and that the real benefit of EPOC is the collective impact of this elevated caloric burn overtime. “People should understand that EPOC is determinant on various factors. Adaptation response will work differently for people and specific fitness levels,” says Abby Rivas, EP-C at High Performance Physical Therapy. So, making sure your workouts are varied, consistent, and progressively challenging are all key to keeping your EPOC effect optimized.
Endurance running, swimming, and cycling, are all great workouts, but they won’t boost your metabolic rate as much as HIIT or resistance training. “Steady-state exercises that are a constant level of intensity for longer periods of time tend to have much lower EPOC effect, which means less calorie burn,” explains Poniewych. This is because the energy you’re expending is being produced using oxygen, meaning it doesn’t need much, if any, extra oxygen to replenish ATP post-workout — it’s doing it in real-time.
