Dr. Gibala: My sense is when it comes to higher intensity, especially short duration work, the traditional way of thinking when we think of perceived effort, it's just... It doesn't fit as well, right? Like classic Borg RPE scales are, you know, based on six to 20 because that generally correlated with, you know, young fit individuals who had a resting heart rate of 60 and a maximum heart rate of 200.

That's where that rating scale comes in. And so, you know, the more intense, especially if it's continuous exercise, the higher the heart rate, the higher the perceived effort. But we just see such a disconnect between ratings of perceived effort and heart rate. I'll give you a very specific example. We've done a study looking at that 10 by one protocol.

So these are 10 one minute efforts at objectively measured maximal heart rates of 85 to 90% of maximum in older individuals, 63 years on average, obese with type two diabetes. On a 10 point rating scale, they started out as a five. They eventually got to about an eight. And so the average RPE was about a seven out of 10, even though these people were doing very high power outputs at very high percentages of their maximal heart rate.

So it's just a striking example. In our initial sprint studies, the one minute sprint studies, three 20 second efforts, our first ones we were saying, go as hard as you can sprint from danger pace. And we, and in those we were using a 20 point scale, they'd come back 14, 15 out of 20. Because now if we ask them to continue that sprint pace for a minute, I'm sure we got to 20.

But since they're so short, so yeah, to your point, it's exactly right. Perceived effort. I don't want to say it goes out the window, but it maybe needs a rethink when we're referring to these very short, very hard intermittent type efforts.

Rhonda: So where do you think, let's say someone new to HIIT, where, like, would a good place to start be more of these like shorter, like intervals?

Dr. Gibala: It's a really good question. And this is where, you know, we haven't really talked health risk and all that, I'm sure we'll get into it. But like, a standard thing that we'll just tell people is get out of your comfort zone. So wherever your starting point is, your own perceived starting point, make yourself a little bit more uncomfortable than usual for a short period and then back off.

And so, you know, I use this analogy all the time. If your only exercise is walking around the block and you want to get into intervals, it's literally for the next two light posts, I'm going to pick up the pace a little bit and then I'm going to back off. So I feel a little bit more out of breath. I can feel I'm breathing a little bit more.

I can't talk to my partner like I generally can on our moderate walks. It can be as simple as that. Just get out of your comfort zone. If you're someone who's already dialed in on the bike and you got a smartwatch and all of that, it's like, hey, get your heart rate up longer or go longer and try and keep your heart rate there, you know, or rather than 20 seconds, you're going to go for three minutes as hard as you can.

You're not going to be liking me, I know, the next time you're going to do that. But it's going to be a very different challenge for you, right? And this is where I think that the more empowering term, interval training, it's okay because it doesn't matter if you're magically getting to some 80% level or whatever the experts tell you you should be at.

It's just start with the alternating pattern and then build from there. Start to dial it in maybe a little bit more and get more discerning. But as a starting point, just get out of your comfort zone and back off and repeat that a few times.

Rhonda: This kind of reminds me of the, was it the interval walkers versus the walkers?

Dr. Gibala: Absolutely, yes. You know, excellent data and these are, you know, relatively small but well-controlled randomized controlled trials looking at interval walking versus continuous steady state walking, including in individuals with type 2 diabetes, three, four-month interventions where individuals were randomly assigned to an interval walking group, continuous walking or a control group, the interval and continuous walkers matched for total exercise volume, total exercise intensity.

So you can imagine the continuous walkers, I think their average heart rate was around 65% of maximum. The interval walkers got that up to 70 and then down to 60. So we're just talking gentle hills and valleys. After four months, the interval walkers, greater improvement in cardiorespiratory fitness, greater reduction in or greater change in body composition, greater loss of fat, and most importantly in individuals with type 2 diabetes, greater reduction in 24-hour blood sugar measured using continuous glucose monitoring.

So it's not to say that continuous walking is bad. I think it's just a little bit of evidence that adding some intervals or varying the pace even slightly, we're not talking sprint training, may provide some greater benefit.