Episode #358 :July 2025 Research Review (A New Twist On Supersets, CrossFit Injuries, and Too Much Cardio?)

21:37I think that because a lot of the folks that I work with

21:40Dr. Austin Baraki:do have a super variable situation, whether they're working in healthcare, They're maybe flipping to days and nights and various other sorts of things. But if I do have somebody who is, you know, training towards a competition and they're, you know, in a resource-rich environment, as you describe it, I have certainly used the more fixed approach, whether cut off by RPE or kind of, you know, with other explicit programming parameters, but to get this amount of work done kind of however you can. So I think we're aligned on that, I think.

22:12Dr. Jordan Feigenbaum:Yeah, two different approaches, even though they're similar, quite different as far as how it plays out. All right. Second study. This is titled Understanding Sports Injury Risks in CrossFit, a prospective cohort study on athletic demographics, training profiles, injury history and psychological factors. This is published in the Scandinavian Journal of Medicine and Science and Sports, July 2025 edition by Nadiri et al. Linked the paper in the show notes below. All right. So let's give a little background here on CrossFit. People have accused us of being like CrossFit sympathizers. We're like pro-CrossFit.

22:45Dr. Jordan Feigenbaum:And I don't know that either of us would identify that way. Like, oh, we love CrossFit. I think both of us, we're like CrossFit agnostic. We're like, it's fine if you like it.

22:56Dr. Austin Baraki:Yeah, I mean, I think, sure. I think probably we both lean maybe a little bit more in favor than like absolutely neutral. Because I think if we were completely neutral, then we'd be holding it up, say, in one hand. And then, you know, saying that people who claim that gardening is their preferred form of physical activity and holding those up almost equally. And I don't think that either of us would do that. There is some, you know, legitimate benefit towards exposure to some of the skills or the intensities or the social aspect, the community, various other sorts of things that I think, even though neither of us currently choose to participate in that particular form because we enjoy doing other things.

23:35Dr. Austin Baraki:I think it's more beneficial than neutral, broadly speaking, for people who do choose to participate in it.

23:42Dr. Jordan Feigenbaum:Yeah. I just think if you're comparing it to a bodybuilding-focused program, powerlifting, or a general strength conditioning program, it's all about the same. It's just preferences at that point. But people, broadly speaking, especially those who interface with us, and I don't know if it's just because our selection bias is strength-focused individuals and they have a little little bit maybe more knowledge or at least perceived knowledge into training. They're like, well, it's injurious. The risk factor for injury is super high with CrossFit, and these workouts are dumb. And I'm like, okay. At that point, yeah, maybe we are more sympathizers in that case.

24:15Dr. Jordan Feigenbaum:And this is not unique to just people in the strength-focused field. So 15 years ago, Mike Boyle, one of these veteran coaches who's been around forever and ever, said that high rep Olympic weightlifting is dangerous. Be careful with CrossFit. Alan Cosgrove, another longtime coach, said that CrossFit's program is all over the place and that there are more effective and safer choices. And there have other been positions taken against CrossFit from the ACSM and the NSCA. And all of this is to say that a lot of people and national organizations with large platforms have been suggesting that CrossFit is dangerous for a long time.

24:49Dr. Jordan Feigenbaum:But is this based in evidence or is it just vibes? You look at the actual data on this, CrossFit's injury rate is very similar to what is seen in other type of resistance training. It's about two to four injuries per thousand participation hours. Nearly all published injury rates for CrossFit are in this window. So when people are like, CrossFit is uniquely injurious, and I'm like, you got receipts for that, or is it just vibes? And if it's just vibes, that's fine. But when countered with this information, do you think that people should update their priors and be like, Well, I feel that if it's done in a particular way in a particular population, that it is more injurious.

25:23Dr. Jordan Feigenbaum:The risk is higher. I'm like, well, that's fine as long as it hasn't been tested and shown to be. How would you want to investigate that? Because if there is a study that shows exactly how you would set it up and it's different, then would you update your position?

25:36Dr. Austin Baraki:Yeah, that's the important question up front is like I think about this all the time in some of the discussions that we find ourselves getting into, being curious. sometimes I actually go through the exercise of asking the person. Sometimes I don't because it is apparent from the way they're speaking of, is there any type of evidence or what type of evidence would you need in order to change your mind on this? I think that a lot of the times when we make a claim or stake a position on something, if we were asked that, we could basically describe what we would need to see in order for us to say, oh, guess I was wrong on that, right?

26:10Dr. Austin Baraki:when you're engaging with somebody on any topic, if you were to ask them that or consider actually asking them, what type of evidence, propose a hypothetical study that if it came out in a certain way would change your mind on this. And then what do you know? Maybe that study exists. Then the expectation is that, hey, maybe we ought to update things or caveat things. It doesn't mean that we're attacking your existence, attacking you as a person, but rather it's like, if this is our shared epistemology, our shared reality, then we ought to agree on kind of like what standards we're looking for.

26:43Dr. Austin Baraki:Whereas if there's no, there's nothing, you know, there, then you're unlikely to make much progress in the discussion.

26:50Dr. Jordan Feigenbaum:Yeah, agreed. The only two things that kind of stand out to me on the, with the existing evidence base, which I talked about in podcast episode 274, the science of injury risk in CrossFit, the two things that do stand out to me that are potentially unique to CrossFit. One is the risk of rhabdomyolysis. And I don't know if there's some sort of selection bias or like reporting bias when it comes to like, look, these people were performing this type of workout and they had rhabdo. It does certainly seem like there have been more reported cases of rhabdomyolysis from CrossFit than from like powerlifting training, for example, or bodybuilding training.

27:23Dr. Jordan Feigenbaum:And whether that's due to the nature of the exercise or how it's completed, you know, meaning like there's a competitive environment or the environments are hotter than usual or whatever, or just the highly motivated population. I think all of those things are reasonable to suggest. So maybe a higher risk of rhabdomyolysis, I'd feel okay with speculating there. And also like individuals who are new to exercise, if they jump right into CrossFit, I do think there is a sort of window of vulnerability there in that they're relatively untrained and they're kind of tossed into this relatively high workload, competitive environment, and there might be an increased risk right there.

27:59Dr. Jordan Feigenbaum:Although again, that's mostly speculative. There are only like two prospective studies that have kind of shown that and it's not great data. So I'm more like on the fence about that than I am the rhabdo. But overall, I'm like, eh, CrossFit probably has the same injury risk overall as other types of training.

28:12Dr. Austin Baraki:Does that seem like a reasonable position to you? Seems a very reasonable position based on the data we have at this time in this very nebulous world of sports and training related injury. There you go. Yeah, right. So one interesting tidbit that this study is adding

28:26Dr. Jordan Feigenbaum:to the sort of body of evidence is that there's this emerging role of maybe like psychological influence on injury risk. So personality traits such as like perfectionism, a strong athletic identity, poor self-control, an obsessive type of character trait. These can lead to poor decision-making in training wherein people like won't take weight off the bar or they'll add weight to the bar. For example, these are just two examples. And so like perfectionism is defined as this character trait relating to the pursuit of flawlessness and excessively high performance standards. Somebody has an athletic identity.

28:59Dr. Jordan Feigenbaum:That's the degree to which they define themselves through their role as a quote-unquote athlete. Self-control is the ability to manage thoughts, emotions, and behavior in the context of training recovery, particularly if it's going poorly, for example. So this study aimed to look at the injury risk in CrossFitters with a specific emphasis on these psychological factors. So the study, There's 348 CrossFit athletes in Iran who had been doing CrossFit for at least one year, three times a week, and they had no injuries prior to enrollment in the study. They did a number of assessments. So they took this self-control inventory.

29:34Dr. Jordan Feigenbaum:The test is called a brief self-control scale. It asks questions like, I focus daily on my long-term goals, and people would rate, do they agree with this or not agree on a scale of one to five? They assessed obsession and passion for exercise with the passion for exercise scale. Did not know that that existed before this. They were asking questions like, I interpret threats as positive opportunities. They assessed athletic identity, which was evaluated via the athletic identity measurement scale. Great names. Great names here. They assessed perfectionism and more. On top of that, so they did that at the beginning of the study.

30:11Dr. Jordan Feigenbaum:and then participants were surveyed twice per week via WhatsApp, Instagram, DMs, etc. to check for injuries using a standardized questionnaire. Now with this questionnaire and with the study design, they defined sports injury as any musculoskeletal complaint experienced by an athlete resulting from training or competition regardless of the need for medical treatment or time lost from training activities where time lost means they had to modify the training that they were doing or could not participate in an unrestricted way. All reported injuries were apparently verified via a physical therapist or ortho specialist, either in person or over the phone, which I thought was interesting.

30:51Dr. Jordan Feigenbaum:It wasn't clear to me that a PT, they got a hopped on a call or whatever, or saw the person in real life and they were like, actually, this isn't an injury. So I'd be curious to know if there was some sort of like, we actually reported hundreds of injuries, but only 70 of them were real.

31:06Dr. Austin Baraki:Yeah, the rest got reassurance that they were just sore in an expected fashion or something like that. I mean, that's one scenario I could potentially envision, but I don't know. If these people have already been participating across it for at least a year, you would expect them to have insight into that type of thing. Totally.

31:20Dr. Jordan Feigenbaum:So it was about a nine-month follow-up. 53 of the participants withdrew, so 295 subjects remained. The 76 individuals reported a total of 94 injuries, so about 25 % had an injury over the nine-month follow-up period. The rates were similar between men and women. The actual injury rate was 2.04 injuries per 1 ,000 participation hours, right in that two to four injuries per 1 ,000 hours window that we talked about earlier. The shoulder was the most common location for injuries. And the second most common was low back, about 18 % for each. And people say, well, yeah, see, CrossFit, the injuries are highest in the shoulder and then the low back and the knees were third.

32:00Dr. Jordan Feigenbaum:I'm like, yeah, these are the most common locations for humans to have injury. period so like not particularly surprising yeah matching base rate that we see in lots of other

32:10Dr. Austin Baraki:areas in sports there are some unique kind of i would say sports with unique demands on particular areas of the body where you would expect a different pattern right certain injuries that you only see in certain sports really for example but by and large when you when when you look at things very broadly speaking yeah shoulder back knees extremely extremely common yeah most of

32:28Dr. Jordan Feigenbaum:these injuries were mild that's important to note requiring little to no time away from full unrestricted training. Most of them didn't require medical attention. Most did not have severe pain, stuff like that. So again, most self-limiting, which kind of jives with the existing data on this, that the injuries from resistance training, majority of them are not catastrophic. They resolve on their own within a week or two and don't require medical attention. The risk factors that they identified, now these were major risk factors. So having like significant impact on the likelihood that somebody developed an injury.

32:57Dr. Jordan Feigenbaum:Well, increase in the number of sessions, an increase in the duration of sessions both of those things contribute to total workload training load that the person was exposed to just exposure yeah yep exactly a history of previous injury um that would be an interesting question to ask your residents just off the off the dome but hey what's the uh biggest predictor for someone suffering an injury during exercise they'd be like oh it's got to be like orthopedic something but nope history of injury and they'd

33:24Dr. Austin Baraki:be like oh i should have thought about that yeah because it's such a common type of risk factor for lots of other conditions where the most common reason to have it is that you've had it before. Not surprising. Yeah, exactly.

33:33Dr. Jordan Feigenbaum:Or family history or whatever. Yeah. And then interestingly, from a psychological perspective, the sort of self-control had a big impact on risk, whereas the people with higher ratings of self-control had significantly reduced risk of injury.

33:49Dr. Austin Baraki:Obsessive... This kind of, that self-control variable, I conceptualize that as like having Dr. Miles on your shoulder, asking you the should you versus could you question before we do go to take that set.

34:00Dr. Jordan Feigenbaum:It's Dr. Miles on the good side saying, hey, should you do this? And then I'm on the other side, send it. That's right. Obsessive passion, those sort of character traits, increased risk. But yeah, things that might contrast to people's assumptions, gender, age, BMI, coaching, or supervision, none of these predicted injury risks. So I think a lot of people when it comes to CrossFit are like, oh, there's the coaching. The coaching is the problem. And if someone's talking about maybe the programming and it's like suitability for a wide swath of the individuals, okay. Like I'm fine with that insofar as it pertains to like workload, total workload.

34:37Dr. Jordan Feigenbaum:But the actual like supervision thing was kind of suggested against in this data set. Perfectionism and athletic identity did not have strong predictive power, which kind of violates the assumption but also just an interesting thing. That's why you have a hypothesis and you go test it. I'd want to see this tested a number of other times before I completely wrote off those character traits because I do think there's probably something there, but not in this data set. And I'm fine. I'm willing to accept that. So my interpretation here, first and foremost, the injury risk in CrossFit is similar to other types of exercise, whether it's powerlifting-based training, bodybuilding-based training, things of that nature.

35:12Dr. Jordan Feigenbaum:I don't think that CrossFit – I don't think it's reasonable to say that CrossFit has a higher-than-normal injury risk compared to these other activities. The second point is that most of the injury risk is secondary to increased exposure, whether that's the number of sessions, the duration of sessions. As your training load goes up, you get exposed to more and more and more. Yeah, that likely increases risk of injury, but that's not unique to CrossFit. That's similar across the board. It's just total training load and then opportunities, I guess, for more injuries past a certain point. And again, to point out the third thing here, that the history of injury, that is probably the biggest predictor here.

35:48Dr. Jordan Feigenbaum:The prior injury predicted a nearly four times increased risk of sustaining a new injury. And so can't really do anything about that. Not modifiable, you know, but at the same time, just something to have in the back of your head. My only criticism here, you know, I like that it was prospective. So they like set the criteria and went forward with it, which I think is more useful because retrospective, you know, recall of injuries and other factors. is that there's some squish there for sure. My biggest criticism and maybe my only real one here is that the injury definition is kind of stupid. Oh, any musculoskeletal complaint and it did not like compromise, necessarily compromise your training ability, didn't require like a medical evaluation or whatever.

36:35Dr. Jordan Feigenbaum:That includes like DOMS, like delayed onset muscle soreness. Or what if you had like severe quad pain, 10 out of 10 quad pain, but it lasted for 10 seconds. Is that, that's an injury?

36:45Dr. Austin Baraki:Yeah, it seems like the definition here is set up to be more sensitive than specific, I guess, if we're going to use some biostatistical terms that they were aiming to just catch everything they possibly could and then maybe use this PT ortho consult to try to, you know, as a screening kind of confirmatory test sequence to try to weed out the ones that were, you know, caught initially, but quote unquote fake or what we would deem as not true injuries. and hopefully to improve the specificity from there, which if that was in fact what happened, where they did essentially a super broad swath of screening to catch everything they could and then kind of filter that through some degree of expertise, which we can say, is that enough?

37:28Dr. Austin Baraki:Were they actually experts in this kind of definitional approach? That feels kind of reasonable to me compared with the opposite way around, where you only have injuries defined very rigidly in a particular way to where it's like, anybody who matches this definition, it's like, yes, you can absolutely say they were injured, but it's like, it's only if you had pain that kept you out of competition for six weeks or something like that. It's like, well, there's some in between there. So I think that there's a debate to be had around this because it is a very nebulous topic. Unfortunately, you got to set your definition somewhere.

38:01Dr. Austin Baraki:I do like the concept, whether this is exactly how they did it in the study or whether I just came up with it on the fly of almost like a screening confirmatory approach would seem to give you some more confidence in the stats on the back end.

38:15Dr. Jordan Feigenbaum:Yeah.

38:15Dr. Austin Baraki:If they did that, I retract my complaint, and then I'm going to give them a pat on the back. Yeah, right.

38:20Dr. Jordan Feigenbaum:But if they did not do that, then it seems to me that if anything, this injury rate, 2.04 injuries per thousand participation hours in this cohort is artificially high. If they did not actually like, oh, this is not an injury. We're taking this off the books. So in that case, CrossFit's injury rate looks even better, which is much to the chagrin of people who want to hate on CrossFit. So yeah, while higher training load tends to beget more gains, the people need to be able to tolerate it. If someone's new to CrossFit, they should probably cap the intensity and build, meaning that they shouldn't just, hey, go dark, max out on your effort here.

38:58Dr. Jordan Feigenbaum:The results, the additional results that somebody may get from that sort of intensity are just really not worth the risk. And so if I had any sort of modification to how CrossFit is commonly practiced, although again, huge variation across the different gyms, different coaches, different programming, I would say, look, your first six weeks of CrossFit, none of the efforts that you do should be maximal. And I just made up six weeks, and this is more speculative because I would want to see that study to feel confident about it. But overall, I think CrossFit is a fine way to meet or exceed the exercise guidelines, physical activity targets.

39:29Dr. Jordan Feigenbaum:I do not think that the data supports the idea that CrossFit is uniquely dangerous, not even close. Yeah, there are risks and benefits to everything, even exercise, but the risks of exercise, including injury, tend to be massively outweighed by the benefits, even if that exercise is CrossFit.

39:43Dr. Austin Baraki:Well said. I think that we've said it this way before, but you need to prepare for what you're trying to do. You need to be prepared for the thing that you're about to attempt if it's something that's going on in the gym. the total amount of exposure that you have to it that total kind of area under the curve you can't avoid that there's some cumulative risk that goes along with that but the cumulative benefits out outweigh those cumulative risks in almost every scenario of exercise and even with all of those factors as optimally lined up as they can be sometimes it still happens yeah and that's part of that's part of the game right that's that's it to be like that there you go All right.

40:27Dr. Jordan Feigenbaum:Right after this message from our sponsors, we'll be back with the third and final paper on the July 2025 research review. This podcast is brought to you by ButcherBox. One thing I try to stay consistent with is keeping enough protein in the house so I don't end up ordering takeout a few times a week. That sounds simple, but between work and everything else, the grocery store trip is usually the first thing that gets cut. ButcherBox fixed that for me. They deliver grass-fed beef, organic chicken, wild-caught seafood, and more, all sourced to the standards they are transparent about. Every box is customizable, so you pick the cuts and the proteins that fit how you actually cook and what you're actually going to eat.

41:02Dr. Jordan Feigenbaum:It's like having a butcher on call who already did the sourcing homework for you. And let me just tell you, the quality is legit. I've been grilling a lot lately. It's summer here in San Diego, and the meat has been excellent. It tastes great. It shows up right to my door, exactly what I want, and I don't have to think about it. I don't have to make a trip. That's the whole point. It's an easy button for your food. Now, whether you're grilling on the weekend, meal prepping for the week, or just trying to get a real dinner on the table on a Tuesday, you've already got something good in the freezer ready to go.

41:29Dr. Jordan Feigenbaum:Go to butcherbox.com slash barbell to get$20 off your first box, plus your choice of free ground beef for life, or free chicken thighs, or top sirloins in every box for a year, with free shipping always. That's butcherbox.com slash barbell, B-A-R-B-E-L-L. Be sure to use our link so they know that we sent you. This podcast is brought to you by Factor. The last few months have been a real time crunch for me. I've been finishing the book, Signal, and between that, training, and everything else I've been doing, cooking has been a real challenge. And Factor has been the thing keeping my nutrition from going by the wayside.

42:01Dr. Jordan Feigenbaum:Having meals ready to go that I can heat up in two minutes and actually feel good about eating has made a real difference on the days where I just don't have those 30 minutes to stand in the kitchen, especially when it's late at night. Factor meals are chef-crafted and dietician-designed. They're ready to eat with no prep and no cleanup. They have over 100 menu items rotating every week, including new options like salmon burgers, shredded pork, and collard greens. Plus add-ons like protein shakes and pumpkin cheesecake. Over 175 banned ingredients, so the stuff that you probably don't want in your food isn't going to be there either.

42:31Dr. Jordan Feigenbaum:I use Factor and I bet you could benefit from it too. Especially if your schedule gets tight, food is usually the first thing that slips. This keeps that from happening. Head over to factormeals.com slash BBM50off and use code BBM50off to get 50 % off and one free breakfast item per box for a year. while supplies last until October 31st, 2026. That's code BBM50OFF at factormeals.com. Again, BBM50OFF at factormeals.com. See the website for more details. This podcast is brought to you by Quince. End of summer is when I start thinking about what I actually want in my closet for the next few months.

43:04Dr. Jordan Feigenbaum:You know, not a full overhaul, just swapping out the stuff that's worn out and filling in some gaps. And that's what keeps bringing me back to Quince. They do everyday staples really well. Their organic cotton teas are soft and hold up wash after wash. Their cashmere sweaters are legitimately good for the price point and they transition straight into fall. If you need pants, their premium denim and tailored chinos start at just$60 and the fit and fabric are on par with brands charging three or four times that. Ask me how I know. Now everything at Quince is priced 50 to 80 % less than similar brands because they work directly with the factories and skip the middlemen.

43:37Dr. Jordan Feigenbaum:You are paying for the materials and the construction, not a logo or marketing campaign. Now one of my go-tos this summer has been their organic cotton mesh stitched sweater polos. I have it almost every color and it's one of those pieces where you look put together but you're actually comfortable, which is why these are going to stay in my rotation for the fall. And Quince goes way beyond just clothing. They've got premium bedding, bath essentials, cookware, travel gear. It's one of those brands where you buy one thing and end up recommending it to everyone. Both Lee and I have their sheets and they're great.

44:03Dr. Jordan Feigenbaum:So upgrade your every day. Download the Quince app for app exclusive offers or go to quince.com slash BBM. Get free shipping on your order and 365-day returns. Now available in Canada and the UK too. That's QUINCE.com slash BBM. All right, we're back here on the Barbell Medicine Podcast. This is our third and final paper, the 2025 July Research Review. This is an interesting paper. It just came out in the journal Circulation. It's titled Ventricular Arrhythmia and Cardiac Fibrosis in Endurance Experienced Athletes. This was with a research group out of the UK. Been getting a lot of airplay on Twitter, for example.

44:42Dr. Jordan Feigenbaum:So let's give you guys a little background. We're going to talk about hearts and endurance training and specifically like risk of sudden cardiac arrest. Now, sudden cardiac arrest is defined as the abrupt cessation of cardiac activity, so your heart beating, so that the victim becomes unresponsive with no normal breathing and no signs of circulation. Now, sudden cardiac death can result, it's the abrupt and unexpected death occurring within an hour of the onset of sudden cardiac arrest. Now, post-mortem studies in athletes who have suffered sudden cardiac death indicate left ventricular fibrosis as one of the strongest predictors, mainly because it is thought that this left ventricular fibrosis can cause what's known as a ventricular arrhythmia.

45:25Dr. Jordan Feigenbaum:This is believed to be the main mechanism of sudden cardiac death in athletes. although the annual incidence of sudden cardiac death during sport varies between studies, it's reported to be up to 6.8 per 100 ,000 athletes in certain cohorts. And this varies by age, sports, and the level of training. So for example, it's much lower in middle-aged recreational athletes at 1.2 per 100 ,000 person years. So it does change, tends to be higher in triathletes who have a much higher workload and it tends to go up the older that the individuals are. And it is predominantly in men, not in women. We talked about this on our podcast, episode 208, which is also linked in the show notes.

46:09Dr. Jordan Feigenbaum:So just to recapitulate, we're talking about the risk of endurance athletes, maybe having some fibrosis. So a little scar in their heart that could lead to an arrhythmia that could cause sudden cardiac arrest, which could lead to sudden cardiac death. That's really what we're talking about. So let's talk about this myocardial fibrosis, this cardiac scar. Myocardial fibrosis is characterized by a collagen infiltration into the muscular layer of the heart, typically due to lack of oxygen, such as during a heart attack, could also be from inflammation, so like myocarditis after an infection, or as the result of chronic exposure to high blood pressure, forcing the heart to pump against a higher pressure circuit.

46:51Dr. Jordan Feigenbaum:There are other causes as well as different types of fibrosis, but that's the gist. Basically, it's scar tissue laid down in the muscular layer of the heart due to some sort of injury. Now, the presence and magnitude of myocardial fibrosis can be determined via microscopic analysis of cardiac muscle obtained by postmortem biopsy. If you take a little chunk of it, look at it under a microscope. Or you can do a cardiac MRI and analyze this as well. Now, it should be noted that the type of fibrosis, it has a specific signature. So like after a heart attack, there's a specific pattern of fibrosis as well as a specific region that is traditionally affected.

47:27Dr. Jordan Feigenbaum:And this is much different than what's seen in athletes. And if you're a cardiologist listening to this, you're well aware. And I don't want to bore the audience by going into subendocardial. No, I don't want to talk about all that. But just you need to know that based on cardiac MRI, we can see specific areas and specific types of fibrosis based on the cause of that fibrosis. generally speaking though in healthy individuals without a history of heart disease there's little to no sign of myocardial fibrosis on mri however the general population is not 100 healthy and in the largest study of non-athletes to date the presence of myocardial fibrosis is somewhere between seven to twenty percent a systematic review of endurance athletes which in total included 509 athletes who had undergone cardiac mri showed that the overall prevalence of myocardial fibrosis was 5.9%.

48:19Dr. Jordan Feigenbaum:Now, importantly, in that systematic review, we're not just looking at older endurance athletes, not just elite level endurance athletes, not just endurance athletes who have been training 10, 15, 20 hours plus a week, but basically anyone who identifies as an endurance athlete, they got lumped into this study. And so the rate where they found some sort of myocardial fibrosis on MRI was 5.9%. We talked about this on another podcast, excess exercise, talk about athlete's heart, this and some more detail. That's episode 215, linked in the show notes below. With all that background out of the way, this study aimed to determine whether myocardial fibrosis in asymptomatic veteran endurance athletes was prospectively associated with the incidence of ventricular arrhythmia.

49:03Dr. Jordan Feigenbaum:Before we get into the study design and the results, Austin, I would prefer if you could summarize this like, hey, look, myocardial fibrosis, why is this important? Ventricular arrhythmia, why is that important? Why are we even studying this in the first place?

49:16Dr. Austin Baraki:Yeah. So having scar laid down in the heart muscle, as you mentioned, can happen for a lot of reasons in the same way that if you see a scar on a person, on their face, on their skin, it could have gotten there through a number of different mechanisms of injury. It could happen from a cut. It could happen from a fight. It could happen from a burn. It could, you know, all sorts of things that could happen to a person to lead them to develop a scar. it could happen from an autoimmune disease attacking their own body from all sorts of different things and similar concepts apply when it comes to scar being laid down in the heart muscle itself there are various mechanisms of injury by which it can get there and so if you in a kind of cross-sectional fashion just take a group of people and you look at their hearts and you're very likely to find at least some people who have some evidence of scarring in their heart you don't know exactly unless they have active issues you don't know when that happened in their life or necessarily what it came from.

50:10Dr. Austin Baraki:But you can try to, you know, compare and contrast different populations, folks who are not terribly healthy with folks who are very healthy with folks who are maybe more strength athletes, power athletes, ultra endurance athletes, people who've been doing it for not very long versus very long periods of time. And you might be able to tease out different patterns or, you know, how often these people are found to have some of these things. And so there has been this concern that ultra, you know, endurance, or very high intensity and very high duration efforts for very long periods of time, decades at a time, for example, may increase the risk of developing some of this.

50:47Dr. Austin Baraki:By what exact mechanism? You know, I don't think that that's the purpose of this study, nor is it super well articulated at this point. But if there is scar in the heart, by whatever mechanism it got there, it can interfere with how electricity travels through it. Electricity benefits from having a nice, clear electrical wiring system to go through. And so when there's scar in the way, it can cause very erratic conduction of electricity and abnormal heart rhythms that can be potentially lethal. Yeah.

51:13Dr. Jordan Feigenbaum:So effectively, what you would want to find out is how many people in this endurance cohort have a scar? And of those individuals who have a scar, well, how many of them have some sort of arrhythmia? Like if you're going to study them for a long period of time. So like not only do they have the scar, but is the scar maybe predictive of having one of these arrhythmias because zero out of 10 would not want. So in this particular study, they took 106 male cyclists or triathletes aged over 50 who had been doing greater than 10 hours of exercise per week for more than 15 years and had been regularly competing at local, national, or international level competitions.

51:52Dr. Jordan Feigenbaum:The average amount of training they were doing was like 11 to 12 hours per week for more than 20 years, and they competed in somewhere between 250 to 300 competitions over their lifespan. They had a comparator group of 27 age-matched non-athletic controls who basically also did the same sort of test and the same sort of follow-up period. They had to be exercising less than three hours per week. Now, all of the individuals in both the endurance athlete group and the non-athlete group, none of them were symptomatic. They couldn't have heart disease, They couldn't have a history of arrhythmias. They couldn't have a history of high blood pressure.

52:28Dr. Jordan Feigenbaum:These are all exclusion criteria. All of these folks underwent baseline physical exams and medical history, not only for what sort of medical conditions and medications that they take, but also lifestyle history. They all got a cardiac MRI, and they all had an implantable loop recorder placed. Now, this is a minor surgery. It's a small device placed just under the skin to record the heart's activity. Just imagine your smartwatch on steroids because it's really close to the heart. really fancy heart rate monitor. Of note, only six of them had them removed before the end of the study. So interesting.

53:01Dr. Jordan Feigenbaum:They also had an exercise stress test, which was monitoring for some sort of arrhythmia while they were exercising at maximum full tilt boogie. And they had about a two-year follow-up year. So the results of the study. Of the 106 athletes, endurance athletes, who had been training about 11 to 12 hours per week for over 20 years and competing a ton, And 50 of them had some myocardial fibrosis on cardiac MRI. And there were 56 who had no evidence of myocardial fibrosis. All of them who did have the fibrosis, who did have this cardiac scar, the specific signature was non-ischemic, meaning it wasn't the same as a heart attack.

53:38Dr. Jordan Feigenbaum:There was no evidence of heart attack or myocardial infarction in any of the athletes. The only difference between the group of athletes who did have the scar and those who didn't was that they were slightly older. about 61 years old in those with the scar versus 57 years old in the ones who didn't have a scar. The athletes had a significantly greater prevalence of the scar, this myocardial fibrosis, than the healthy non-athletes. So 50, again, out of the 106 athletes that were studied compared to only three out of the 27 controls. There were no significant differences on MRI in any parameter between those with and without the fibrosis.

54:17Dr. Jordan Feigenbaum:So whether you want to talk about like the different diameters, a different functionality that the cardiac MRI measures, so no real differences between those with and without the scar. There was no evidence of issues with blood flow to the heart during exercise stress test in any athlete, regardless of whether or not they had fibrosis or not. But the real interesting thing here was that three out of the 106 athletes who did have a myocardial fibrosis had sustained ventricular tachycardia, and an additional 20 had non-sustained ventricular tachycardia. Austin, what is sustained ventricular tachycardia, non-sustained?

54:54Dr. Jordan Feigenbaum:What the heck? What are we talking about here? Yeah.

54:57Dr. Austin Baraki:To give a simple explanation, normally the electrical signaling through the heart starts at the top called the atria and goes down into the ventricles and it gets conducted along kind of the expected highway of electrical conduction. Nice, smooth, fast, efficient, and it leads to the heart pumping kind of synchronously and efficiently. When that electrical signal generates from a spot outside of that normal path, meaning it originates in the ventricles, we call that usually a ventricular contraction. So sometimes your heart might be humming along doing its normal thing, and then you get a little early heartbeat.

55:32Dr. Austin Baraki:And when we look at it on an EKG, it looks a little bit funky and bizarre because the electricity is coming from someplace else. And so that's called a PVC or a premature ventricular contraction. When those ventricular contractions, meaning beats that were kind of triggered by electricity originating from a spot other than where it's supposed to come from, and then it happens again and again and again, particularly quickly, we call that ventricular tachycardia. That can happen for just a couple beats and then it stops on its own. That's actually relatively more common. I see that a lot of the time on my hospitalized patients because we're actively monitoring them.

56:06Dr. Austin Baraki:And so we tend to catch more things when they happen, even if the patient has no symptoms, and they will say they had a few beats of non-sustained ventricular tachycardia. So then we might ask a couple questions about potential causes or contributors to that. But ultimately, it's not something that's an emergency in most of these folks outside of particular contexts. Whereas if instead that ventricular tachycardia sustains, meaning it goes on and on and on without stopping on its own, that's potentially dangerous and is not a rhythm that you can stay in long term compared with other rhythms like being in sinus rhythm or even having atrial fibrillation you can live with, be in that rhythm for a long time and not die.

56:46Dr. Austin Baraki:But you can't be in VT for a very long time or indefinitely and be okay. So that's something we would try to get you out of and address the underlying causes and contributors for because it's an example of one of these potentially lethal cardiac rhythms that we do not like to see, particularly when it is sustained. Yeah.

57:02Dr. Jordan Feigenbaum:So to summarize, you don't want VT, whether it's sustained or non-sustained. Non-sustained is a little bit more benign, right? You're like, okay, I'll ask some questions. Whereas sustained, you're like, you might need an implantable cardiac defibrillator, for example. And actually one of the people who had this got an implantable cardiac defibrillator. But of the 106 athletes, 23 total had some form of ventricular tachycardia. Three of them were sustained, 20 of them were non-sustained, and more of those who had any type of this ventricular tachycardia had that scar, that myocardial fibrosis. 18 out of the 23 versus only 5 didn't have any of this fibrosis.

57:38Dr. Jordan Feigenbaum:So if you were just interpreting things to now based on what I've said, you're like, look, the scar thing, it doesn't seem like I want that. And if anything, it seems to increase the risk of ventricular tachycardia or those with the scar for some other reason may have a higher risk of ventricular tachycardia for some other reason that happens to co-occur perhaps with this scar. So my interpretation of all of this, first thing I want to point out, all of these folks were asymptomatic. Nobody had like chest pain. Nobody had shortness of breath. Nobody was like, wow, well, now that you identified this, I have been feeling a little funky.

58:11They were all feeling relatively normal.

58:14Dr. Jordan Feigenbaum:the presence of that scar non-ischemic myocardial fibrosis was significantly higher in athletes than a control group of age-matched non-athletes four times greater was the risk so at the beginning of this i said well look some proportion of the population has a scar uh typically not this non-ischemic pattern because there's either some underlying heart disease or something else we don't really know exactly but it seemed to be that non-athletes tended to have a higher level of this Whereas this study, this particular group of athletes, it actually looks to be much higher than age-matched control.

58:50Dr. Jordan Feigenbaum:So that's kind of interesting. It suggests that there may be a higher prevalence of fibrosis in athletes, particularly older individuals, and particularly those doing a lot of training, 11 to 12 hours per week for many, many years. And that's definitely a different subpopulation of athletes than it's been looked at before. And I think it's mostly due to age and how long these people have been doing the training for. That seems like a reasonable conclusion. However, I don't know that having that scar is really driving the arrhythmia. Theoretically, the fibrosis could be a marker of some sort of underlying cardiomyopathic process.

59:26Dr. Jordan Feigenbaum:Something else could have been happening that wasn't really assessed in this particular study. We don't know. Another question is like, okay, well, look, if it is due to exercise, you just train less, would that fix the scar? Because existing evidence to date suggests that that doesn't really modify the scar in some sort of salutary way. So unclear there. And I guess despite the relatively high prevalence of this scar, this myocardial fibrosis, you know, and some of them having the ventricular arrhythmia, most of these endurance athletes aren't dropping dead during training. And in fact, when you look at like major adverse cardiac events in endurance athletes, whether it's heart attack, stroke, or whatever, it's much lower than their age match controls in the general population.

1:00:10Dr. Jordan Feigenbaum:population. But that all being said, we could focus on that, perseverate, end the podcast, go off into the sunset, feel good about telling people like, look, man, don't worry about it. There's still no condition that I know of where having a scar in the heart is good. You would prefer not to have it. I just don't know the significance of it based on this study alone. One thought I had, I did some digging and went down a rabbit hole. What if there's like some sort of genetic interaction in this population wherein some sort of genetic polymorphism or, you know, a number of them, a polygenic sort of change.

1:00:44Dr. Jordan Feigenbaum:What if it like allows people to respond better to endurance training so they select that path, right? But it also leads to a small subset of them having this, they develop a scar. There is an example of this. Most endurance athletes, for example, have this sort of preserved or really enhanced cardiac function. Their heart pumps out more blood because they're trained. A small subset actually has a reduced ejection fraction, so the amount of blood that they pump out per heartbeat. There's like a differential type of remodeling of the heart, even though they can sustain endurance activity at a high level.

1:01:22Dr. Jordan Feigenbaum:It's unclear if that's risky, but that is a subset of endurance athletes, and you're like, huh, is this some sort of genetic thing? and that there seems to be some genetic traits that are genetic polymorphisms that are associated with that sort of adaptation.

1:01:34Dr. Austin Baraki:Yeah, I wouldn't be surprised actually if that ends up being true to some extent. I mean, this is a similar cascade that we see in a lot of other health conditions. So to give an example, like fatty liver disease is extremely prevalent worldwide. Huge swaths of the population have it. Only a small subset go on from having regular old fatty liver disease to having steatohepatitis. Only a small subset of those people end up going on to have cirrhosis. Only a small subset of those people end up going on to have liver cancer. Only a small subset of those people end up actually dying from their liver cancer.

1:02:08Dr. Austin Baraki:And so, you know, we could apply that to lots of other conditions as well. And so here you might have a large group of people who are being exposed to this thing of, you know, relatively high intensity and ultra long duration activity across the lifespan, a not insignificant swath of them end up developing some of this cardiac fibrosis. Some of those percentages were definitely higher than I think most would expect. But of those percentages, only a smaller fraction end up having maybe some sort of cardiac conduction abnormality, for example, electrical abnormalities on the EKG. And then only a small subset of those actually end up having true arrhythmias, be it sustained or non-sustained.

1:02:48Dr. Austin Baraki:and then only a small subset of those arrhythmias lead to sudden cardiac death, for example. And so I think, you know, as far as an explanation of why or how there might be this big discrepancy between how prevalent the fibrosis is and how, you know, uncommon the actual sudden cardiac death is, that follows a similar pattern to a lot of things. What proportion of smokers end up developing chronic lung disease? What proportion of those end up getting lung cancer? What proportion of those end up dying of lung cancer? It gets smaller and smaller and smaller. That's the way a lot of these things work.

1:03:18Dr. Austin Baraki:And so I agree with you. There's not a condition I can think of where scarring is good. You'd prefer to not have it. And I feel probably a little bit more, I lean more in favor that the scar is likely contributory to the electrical issues that we're seeing here and probably plays at least some part, if not a large part of the higher risk of sudden cardiac death in that population compared to healthy age match controls. And so I think ultimately it's like, what do you do with this information? Well, again, people who are training that much for that long, most of them are doing it for performance-oriented goals, competitive goals.

1:03:58Dr. Austin Baraki:Most of them are not necessarily doing it to that level because they think that that is the best or the only way towards health and longevity. Some of them might be under that illusion that they might think that I need to do, you know, ultra marathons all the time to be maximally healthy and have maximized longevity, which I don't think either of us would subscribe to that idea as that being necessary or even ideal. And so, yeah, I think that if we're making general health-oriented exercise recommendations, I think that this is a risk to be aware of. I think it applies to a very small set of the population.

1:04:33Dr. Austin Baraki:And so if I'm talking to somebody who's worried about this, I'm like, well, why do you train the way you do? What are your goals? You have to like, well, I want to go and win the triple Ironman this year or something. It's like, yeah, well, there's a lot of risks to doing that. And this is potentially one of them. There's maybe some things that we might be able to do to mitigate some of that risk as far as getting as good of control as we can of other cardiovascular risk factors, trying to ensure your health is as good as it can be in all the other areas, recognizing that, hey sudden cardiac death is fortunately uncommon but maybe you're a little higher risk of that doing this than you know somebody who is doing general health and fitness exercise and not training towards this thing and a lot of those folks would say yeah i'm fine with that because i love this and this is what i want to do you can't you know mitigate every risk in all circumstances

1:05:17Dr. Jordan Feigenbaum:unfortunately no and still be efficacious yeah sure yeah uh the authors i listened to an interview with the authors and they said, quote, there is no part of our message that is about doing less sport or even telling people to train less. Their whole point of this was like, well, look, this is a risk factor. We don't know that the individuals who develop this, if they would like avoid it, they might've avoided developing the scar if they trained less, or if now they change their training to train less, if the scar would resolve or if their risk of, you know, VTAC would otherwise, you know, resolve.

1:05:53Dr. Jordan Feigenbaum:The real message that they wanted to get across was like, look, if you got a patient who, you know, is an endurance athlete and particularly an older individual with long training history or whatever, you're probably going to do an EKG on them for some sort of health screening, particularly if they have a report of like, look, I feel like maybe some premature contracture, something feels funky, you're gonna do an EKG. If you find PVCs on there or whatever, it's probably not enough to just ask them a few questions and then just write it off, particularly in this population where they're training a lot, the risk of having this myocardial fibrosis may be higher.

1:06:25Dr. Jordan Feigenbaum:And so at that point, you may decide to get a cardiac MRI just to say, well, look, do you got a scar? Do you got the fibrosis or not? And if they do, maybe you do a stress test to see, like, can you induce some of this sustained ventricular arrhythmia? Because if so, that would be a significantly increased risk of sudden cardiac arrest and subsequently sudden cardiac death. Still small, small risk, but non-zero. And so I just don't know that I would tell somebody who's like, look, I want to live as long as possible. I want to be as healthy as possible. I want to be as fit as possible. Should I stop training at like five hours of conditioning per week instead of taking it up to 10?

1:07:02Dr. Jordan Feigenbaum:I'm like, I don't think I can say that because I know that as you improve your VO2 max and more activity, like these things tend to promote health more than this risk. But if they ever said, you know, I feel a little interesting thing in my chest, I'd be like, oh, well, cool. Let's address that because that seems reasonable to me. Yeah.

1:07:19Dr. Austin Baraki:I think I'm on a similar train of thought, you know, to the question of like, is any of this reversible if they're to modify their training? I wouldn't expect it to be. I don't expect to see reversibility of like myocardial fibrosis or scarring in these types of situations, but rather more so in like a prospective advisory way. If somebody is asking me for advice on training specifically for longevity, my advice to them is not going to be, hey, instead of just like working towards meeting or exceeding the physical activity guidelines, instead, I think that you should be aiming to do like ultra marathons multiple times a year.

1:07:50Dr. Austin Baraki:Like that's not the way that I would necessarily advise somebody towards a health and longevity oriented goal. But even that advice is not just because it's like, oh, I'm just mortified that you're going to experience sudden cardiac death by doing that. It's just that the potential benefits of getting up to that level are not necessarily worth it to most people. and there is some signal of risk here to where you could probably have a more favorable life if you didn't necessarily reach that far. Totally. Yeah, I think that's reasonable.

1:08:18Dr. Jordan Feigenbaum:So I don't know that I would tell anybody to do less conditioning, but I do think that monitoring and assessing the people who maybe have something strange going on, reasonable.

1:08:31Dr. Austin Baraki:Yeah, me too. Yeah, advising people to do less. This is just applicable to such a tiny segment of the population who are actually training up to this level that I'm not terribly concerned with it.

1:08:40Dr. Jordan Feigenbaum:If you're training 10 hours plus a week for just conditioning, I'm not talking you out of that. Like, you know what I'm saying? Like, what could I say? They're like, well, you know, you got this risk. And they're like, well, how big is the risk? I'm like, I don't know. They're like, okay, cool. I've got to get a new doctor. Anyway, all right. Well, that is a wrap here on our July 2025 research review. Thank you so much for listening. Thanks to Dr. Austin Brockie for sharing his expertise with us. Before you guys go anywhere, please leave us a five-star rating and a review. It really helps drive traffic to our podcast so we can keep bringing you the latest nuance in health and fitness.

1:09:14Dr. Jordan Feigenbaum:From everyone here at Barbell Medicine, I'm Dr. Jordan Feigenbaum. We'll catch you next week and every week right here on the Barbell Medicine Podcast.