Rhonda: Does high-intensity interval training affect bone mass or bone density? Do you know?

Dr. Gibala: This is where, you know, it goes, like, to this point, you know, I've encouraged us to think about mode-specific when we're making some of these comparisons. I think that's where it depends, right? And so we know that more higher impact events or activities, certainly when we're young, tend to, you know, lay down more bone.

And so, you know, if we're talking high-intensity cycling versus high-intensity running, those things are very different, right? Are you running on concrete? Are you running outside in beautiful trails? All of those things matter. You know, the flip side to that is if we talk about injury risk, people say, well, I can't do high-intensity training, I'm gonna increase my risk for injury.

Well, you know, I'm someone with classic left knee osteoarthritis. I just tore a meniscus in my right knee playing hockey, so I'm gonna have osteoarthritis in that knee soon. I can engage in very vigorous interval training on the bike. I can't, and I don't run anymore. So, you know, HIIT training on the bike, no problem. Any sort of running outside is excruciating for me.

Rhonda: So joint problems in general, people can, do you think people can engage in cycling?

Dr. Gibala: I do, yes. And, you know, we know certainly, and again, like I'm not an expert in this area, but, you know, talking to experts and just trying to read and stay abreast of the literature, you know, we know that people who have joint injuries, certainly meniscal injuries or osteoarthritis, one of the best things that you can do is remain active.

And it's obviously frustrating advice for many people because they're like, I want to be active, but it hurts when I'm active. And so moving towards less weight bearing activities that allow you to be active around the joint and maybe, you know, help with the tissues around the joint, but aren't impactful forces.

So cycling is a fantastic exercise for individuals with osteoarthritis, because you can still engage in fairly vigorous activity without hurting or damaging, you know, specifically your knees in this case.

Rhonda: Yeah, that's great. I know there's quite a few people that are under the misconception that they cannot do any type of high intensity interval training because they have joint issues.

Dr. Gibala: They don't want to do box jumps, right? But-

Rhonda: Yeah, I mean, jumping rope, which may actually be great for the bones. I mean, it's impactful and you can do, certainly do high intensity intervals with a jumping rope as well. What about, so there's, we talk about like some of this, you know, we're talking about some of these like misconceptions, I guess.

And you kind of touched on this a little bit when we were talking about maybe, you know, people that shouldn't engage in high intensity interval training, like the people with AFib or angina, what was it? That heart problem.

The fact that doing high intensity interval training could cause AFib or coronary calcification, or just even like elite athletes in general, like at the high level, you can see they have a higher tendency for AFib and coronary calcification, but in the same breath, they also have a lower risk of, you know, cardiovascular related mortality. Is there a way to reconcile those things?

Dr. Gibala: So again, not expert, but my read of this, including, you know, there's some really good reviews that have come out recently. And again, we could drop those in the show notes to direct people to reading on this, but the, you know, the old Latin phrase, the poison is in the dose, right?

There's definitely evidence that individuals who over a lifetime engage in very high intensity, very high volume exercise may be at greater risk for some of these issues that you just referred to, heart issues. To my read and my understanding, while there's theories out there, a definitive cause and effect or mechanistic basis hasn't been definitively established.

And the other is, it's been pointed out that those days, like while clearly that risk is there and you see examples of this, it doesn't fit or doesn't line up with the longevity data, which is still that, you know, lifetime runners will still have, you know, a few more years of life compared to others. So I think it's an issue that still really needs to be resolved.

And probably the safest advice would be, you know, extreme exercise may carry some consequences, right? Whether it's the U-shape or the the J-shaped curve, there is something to that. And if you're on, you know, this is, for the vast majority of people, this isn't an issue, but, you know, if you are that extreme exerciser, you just need to be mindful of the fact that that may carry some increased cardiovascular risk.

Rhonda: Yeah. So one more oddball question before my last one, which is, what are your thoughts on this, like hypoxic training, like, have you heard of, like, the mouth taping during, like, a HIIT or?

Dr. Gibala: So my sense would, yes, I've definitely heard of it. You know, clearly when you move to more intensive exercise, the vast majority of your ventilation is through your mouth.

So it's really hard to engage in vigorous exercise when you're restricting either nasal breathing or mouth breathing. You're gonna compromise your performance. It may feel really hard, you know, because you're inducing this added stress. Whether it's beneficial, I'm not convinced of that. I, you know, I think the data around blood flow restricted training is much more interesting, and there's some really, really interesting work coming out of that.

You know, you can make the case that maybe you're gonna see some changes in respiratory or diaphragm muscle or that, but getting back to the idea of what limits VO2 max, it's generally not a pulmonary limitation. It's a heart limitation. And so strategies that are really trying to additionally stress the pulmonary system.

So, you know, if people wanna try it, fine. I don't think there's tremendous evidence that that's gonna potentiate training responses. Rhonda: What's the interesting thing about blood flow restriction? Is it...

Dr. Gibala: Well, you know, like I think, you know, as a therapist, so I'm aware of some ongoing work, I guess that's about it. And, you know, this isn't our work, but I'm aware of some work looking at blood flow restriction exercise and training in very, very high level endurance athletes showing some interesting changes in performance related metrics or some measures. And yeah, so like I say, that work is ongoing. The hard thing with these is it's, you can't truly blind someone to blood flow restricted training, right? Like many of these interventions that we've talked about, it's tough to have a true control who's completely blinded to the intervention that can influence some things. But, you know, the idea of blood flow restricted training, allowing individuals getting back to joint issues, maybe working at a lower absolute force or workload, but still seeing the metabolic stresses induced with blood flow restricted training, you know, there's some interesting work there, I think.