Rhonda: While it's tempting to think of exercise in terms of calories burned, we know the role is much more nuanced. Exercise plays multiple roles: it aids in muscle building, enhances insulin sensitivity, promotes better sleep, and even manipulates the homeostat of our appetite, influencing our hunger and satiety cues. We can generally think of nutrition as the main regulator of body mass, with exercise playing a supporting role.

But a burning question remains: Can we really boost our metabolism post-workout? This effect, sometimes called the 'afterburn effect,' does have some scientific basis, according to recent podcast guest Dr. Martin Gibala. In scientific terms, it's known as EPOC or Excess Post-Exercise Oxygen Consumption.

Let's hear what he had to say about this phenomenon.

What about body composition, weight loss? Obviously, diet is an important component in those equations, but can people use high intensity interval training to help lose fat? Also even help, you know, there's their increase the muscle also, you know, is there a role for high intensity interval training in?

Dr. Gibala: So, you're right in that, you know, and I tell my students is this is hardly novel that, you know, we control body mass mainly through nutrition, but we control fitness through exercise and physical activity. And so, clearly exercise generally and high intensity exercise can play a role, a supportive role in terms of weight management, body composition changes.

We've shown in some of our six and 12 week studies that you can change, you can have measurable changes in body composition such that there's a slight loss of fat mass, fat percentage, or a slight increase in lean mass with high intensity interval training. But it tends to be relatively subtle and how it compares with continuous exercise.

Again, I think the biggest thing is there's probably a time saving aspect there. And so, you can do less total exercise or certainly have a lower time commitment with more vigorous intensity exercise and burn the same number of calories. There is something to the idea of personal trainers talk about the afterburn effect, this idea of a heightened rate of metabolism and recovery.

We've measured it. You know, you look on the internet and you'll see these massive differences in afterburn, right, where HIIT is way up here and moderate is way down here. It's certainly nothing to that magnitude. And, but there is a difference, but it tends to be relatively small and it dissipates relatively quickly.

But those small differences can add up over time. And so, you know, people will say, well, how can high intensity be effective or how can certainly sprint type training be effective at this because you don't burn more many calories during the efforts. Well, you do burn a greater rate of calories in recovery and those two things can play off.

But again, I think right now the best data is like a lot of things we've talked about, you might get away with some time savings or a smaller total dose of exercise and still get to the same place with more vigorous activity.