Key Takeaways

  1. Doing cardio usually makes it harder to gain strength and muscle.
  2. You can minimize (or eliminate) the downsides of cardio by keeping your cardio workouts less than 30 to 45 minutes, focusing on low-impact exercise like cycling, and doing your cardio and strength training workouts on separate days.
  3. HIIT cardio can help you burn more calories in less time, but it can also interfere with strength and muscle gain by causing too much fatigue.

According to many gym goers, cardio and weightlifting are like oil and water.

They don’t mix well.

For instance, you’ve probably heard that cardio in any amount or intensity interferes with strength and muscle gain, but is it really that straightforward?

Others say that low-intensity steady state cardio (LISS) hurts your gains, but high intensity interval training (HIIT) doesn’t. Is that true?

Well, scientists at Victoria University in Melbourne probed these questions in a 2016 study titled “Endurance Training Intensity Does Not Mediate Inference to Maximal Lower-Body Strength Gain during Short-Term Concurrent Training.”

This study looked at “concurrent training,” which is the inclusion of both cardiovascular and resistance training in the same routine, and specifically at how it impacts strength and muscle gain.

Dr. Eric Helms has been studying concurrent training for most of his career as a published scientist, author, and bodybuilding coach, which is why I wanted to pick his brain on this study, and what it means for us fitness folk.

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Here’s his take…

(Rather listen to this interview instead? Click the play button below.)

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Mike Matthews: People combine lifting with cardio for various reasons, some being better than others. Then there’s the debate about whether you should do high intensity interval training versus more moderate or lower intensity cardio. Which is better for what and why?

Eric Helms: Great question. So yeah, this is a pretty cool study. We reviewed it again in that first issue of MASS we did. I think Greg wrote this one, if I recall correctly. It’s been a while now, we’re on like our last issue of the year, which is cool.

But anyway, this is a study by Fife and colleagues. Easier to pronounce that our German Volume Training study author. But it’s entitled, “Endurance Training Intensity Does Not Mediate Interference to Maximal Lower Body Strength Gain During Short Term Concurrent Training.” I’ll talk about why that title is important.

Back in around say a long time ago, we established that at the molecular level and kind of the … without getting too detailed, the adaptations that you make to get better at cardio are fundamentally different to some degree in certain areas than the adaptations you make to strength training.

Metabolically for strength training you’ve gotta be able to put out a high output of energy and not have any care about, quote/unquote “pacing.” You want it right now. If you have to do like a snatch. Those are specific adaptations that are gonna happen. However, with endurance training, you’re basically telling your body, “Hey, I need a constant stream of low energy output.” Those do quote/unquote, “interfere.” That’s where the term “the interference effect” came from.

Then there’s a meta-analysis back in 2012, which really kind of painted the picture, the broad brush strokes of the interference conversation. We saw from that that there was an inverse relationship, or rather a linear relationship that the amount of total volume of cardio you do is related to how much interference you experience. That makes sense. Obviously if you go walk your dog or if you become an endurance athlete, you would expect those two things to have different effects on your resistance training, right?

Mike: That’s systemic, right? It’s not like, “Oh, but running, yeah, it might just mess with my squats, but it won’t mess with my overhead press, right?”

Eric: Interestingly enough, that is something that is still getting teased out. The answer might be yes or no depending on the study you’re looking at.

Mike: What are your thoughts on…I know that’s kind of tangential, but I’m just curious. What are your thoughts based on what you’ve seen and what you know?

Eric: Well, I think it’s both. That’s because when…if you really want to drill down to the concurrent training hypothesis, there’s both an acute and a chronic hypothesis. There’s one that says, “Hey, this is a molecular level issue and therefore it’s not gonna be specific.” If you’re doing endurance training, which is largely whole body or at least it’s gonna have adaptations that affect a lot of your body. It’s gonna affect a lot of your lifts and vice versa.

Then there is the kind of the acute hypothesis, which is really simple that’s saying, “Hey, if you are tired from cardio, you’re going to be poor at lifting weights.” And they’re both true. If you think about it.

If you go to the gym and bust out a hard cardio session and try to do squats, it’s not gonna go well. Therefore the adaptations you get afterwards are not gonna be ideal. But there’s also some things happening at the level that we can’t really see that are at that molecular level where there are competing adaptations. So-

Mike: And that could be relevant even if you have your workouts separated, right? So even if you did your cardio on one day and did your lifting on the next day?

Eric: Well, yeah. I’d say if we want to jump to the punch here. There are a number of ways to kind of mitigate interference globally. The worst thing you can do is right before you lift, do cardio. Kind of when stepping down the hierarchy of the next best thing you could do would be to do weights and then cardio. Then at least you’re avoiding that acute fatigue going into your resistance training. That seems to be better than the latter.

But even better than that would be to do them at least six hours apart or on separate days. We have a fair amount of research now that would suggest that that’s kind of like the ideal succession of things to do. Then probably even one step better than that would be to minimize your cardio as much as you possibly can.

That’s an option for someone who is like a contest prep bodybuilder or a physique athlete or someone who has to diet for a weight class. Or someone who is just dieting, say, a model. Someone who’s dieting for a photo shoot. You can definitely get effective fat loss without using cardio.

Cardio can sometimes just make dieting a lot easier. So your food doesn’t have to totally tank. It might help you mobilize fat and just make the process a little bit better. But more or less a deficit is a deficit. So when it’s purely a fat loss goal, you can certainly minimize the amount of cardio you’re doing. I think that’s probably a good idea in most cases. Unless you just really enjoy it. That would improve adherence.

Mike: What are your thoughts on just getting to the goal faster? That’s been I guess the main thing that I’ve recommended to people is being in a deficit kind of sucks. That’s actually just been kind of my personal approach. But I tend to be, and we mentioned, that the last time around, I tend to be one of those more masochistic kind of people. That I don’t really care how I feel about things, it’s just what’s most effective.

So if I can lose fat faster without sacrificing muscle or feeling like a zombie, then I’m gonna do it, including cardio. If that means I can take my cut…if I can make it 25% faster and then get back to feeling good in my workouts and making progress, then I’m gonna do it. You know what I mean?

Eric: Well, yeah, I think that’s totally valid. The real question is if you can. I think that all depends on the dosage, right? So if you’re doing two to three cardio sessions a week and they’re not going over 30, 45 minutes, and they’re not on the same day or they’re separated from your training, it’s probably gonna cause a negligible amount of an issue.

Mike: That’s always how I’ve done it. More like 25, 30 minutes, a couple, two, three times a week. I personally have always preferred high intensity. I would do it on an upright bike. That’s just what I’ve always liked.

Eric: Yeah. So I think it all depends on how you’re gonna distribute it and how much you want to do. If someone is going with that same philosophy, but starts banging out post resistance training cardio every day and morning sessions, and is doing two-a-days, then I would think they’re would actually be a significant loss of muscle mass in that process. That might not be worth it.

Mike: Yeah.

Eric: You know, it-

Mike: I’ve never done that.

Eric: It also depends on your goals.

Mike: That sounds awful.

Eric: No, yeah. But it’s not uncommon. It depends on your goal too. If you were a bodybuilder, at the end of your diet or near the end of your diet, you’re gonna be getting on stage multiple times. Either once, maybe finishing, kind of eating up into your show. But you can’t really put fat back on and do well. So if you are kind of eating up into your show, it has to be very conservative. You’re dropping cardio off in a titrated manner, increasing food in a titrated manner.

But let’s say you’re a strength athlete. Well, shit, man, you might want to diet off five kilos in six weeks and do a fair amount of cardio and just have shitty training for five weeks. But then you’ve got a whole 12 week prep period where you’re increasing calories, decreasing cardio, and just making sure you don’t go over say two percent higher than your weight class.

Knowing that you could still make it with a mild water cut or a little shift from high fiber to low fiber foods right towards the end. That might be a better pay off versus kind of having a slow diet the whole time where your training just always slightly sucks.

So it does depend on the goal and what makes sense in a practical manner. But there are times when you’d probably want to minimize the amount of cardio you could do. There’s other times where you want to get away with as much as you can without causing a problem, like you were talking about.

There’s other times where you don’t care if you lose a little muscle briefly if your primary goal is just performance output and muscle’s just one component of that. Then maybe you could regain it once you actually finish the diet. Then have a solid block of good training.

Mike: Yeah, I’ve spoken with people. What’s fairly common is people training for marathons or half marathons and that’s really their focus for a bit. They just want to know what can they do in the gym to minimize the muscle loss? Ideally they would like to lose no muscle, but if they have to lose some, they’re okay with that. They just want to minimize the damage.

Eric: Yup. Well, what I’ve been getting at here is that there’s a bunch of different strategies out there to try to see if we can minimize the interference effect. The meta-analysis I was referring to before had a few strategies in there.

It suggested, hey, maybe cycling is a good way to go. The theory being there that you’re not doing a whole lot of eccentric actions, which is lengthening under contraction and what we do to brake. Very common in most movements, but cycling just kind of a constant push forward. So you’re removing some of the muscle damaging eccentric action. In addition, there’s no impact for cycling. So some of the joint stress won’t be there.

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There’s evidence showing that cycling, and you’d think other similar movements like an elliptical or maybe a rower, things with no impact and little to no eccentric, would also have a lesser effect on interference. Timing, like we already talked about. Those are the main strategies that have been looked at to minimize the interference effect.

Then also, the one that is in this present study we’re gonna discuss by Fife, is the intensity of the cardio itself. So there is the thought, the prevailing thought and the hypothesis that came out from that meta-analysis and other studies, that the issue is the difference in intensity between the cardio you’re doing and the resistance training. That if you were to do short bursts, say a 30 second or 45 second sprint followed by a recovery period, because that’s essentially the same metabolic work to rest ratio and intensity of resistance training. Therefore you would not have that molecular interference. That is probably true.

However, there is an issue with doing that. In that if you are gonna do HIIT, true HIIT where for that say 30 or 45 seconds, you can’t hold a conversation, you can’t do anything except breathe as hard as you can to actually complete it. We’re talking all out, 100% sprint on a bike, an elliptical, a rower, on flat ground, whatever. That is something that’s gonna have an increased recovery cost. Higher intensity means higher recovery.

I think we got on kind of this…we put HIIT on too much of a pedestal in the 2000s. Where we just focused on that one aspect that it shares all those metabolic traits with resistance training. And it was more time efficient for burning calories. So therefore it was the holy grail. Oh, and hey, cherry on top, there’s a little bit of an afterburn effect where you burn calories throughout the rest of the day. Nevermind that that’s only gonna be like 10, 20, 30, 40 calories, it’s still something. Therefore HIIT is the solution.

While all of those aspects are true, there is an afterburn effect, there shouldn’t be a molecular interference, and it is more time efficient, I think everyone has just really forgotten about the recovery cost of HIIT. This is probably the first study that really kind of highlights that.

In fact, in this study, they essentially found that sprint intervals on a bike, even cycling, were problematic compared to moderate intensity steady state. So they compared moderate intensity steady state cycling to HIIT sprints on a bike and they found that the sprinting actually decreased hypertrophy and strength more or had a larger interference effect, I should say, compared to moderate intensity.

This most likely comes down to not the molecular differences, but actually just the fatigue caused by it. Actually preventing you from training effectively and from recovering, so that you can get in the gym and do the work that’s really gonna help you gain strength and either retain muscle or gain muscle.

Little thing I always say when people are telling me that they want to do sprints on the ground for their cardio for contest prep because they’ve seen someone else do it, or they think it looks hardcore, it sounds fun. Is I go, “Well, look, you could make this argument that HIIT’s gonna help you retain more muscle, but it’s really hard to make that argument when you’re on crutches.” ‘Cause I’ve seen so many bodybuilders strain their hamstring or fully tear it because they’re trying to be sprinters.

Even sprinters don’t sprint max speed four to five times a week. They have a fully periodized program and they carefully integrate it with resistance training. So this trend of bodybuilders just getting out there and just hammering sprints without training specifically to be that kind of an athlete, has led to a lot of hamstring strains. This is some-

Mike: It just wrecks your legs. I mean I’ve done it when I was younger. I was like, “Yeah, I’ll try that for cardio.” That lasted about a week and I was like, “I think if I do this, I’ll probably never squat again, so I’m gonna stop doing this.”

Eric: Yeah, exactly. Essentially there was less strength gain, less muscle mass gain, and more signs of an interference effect really in the HIIT group. So it really kind of puts that nail in the coffin in my opinion of going, “Hey, we can’t just lose context and just look at the molecular differences.” You have to think about exercises having a recovery cost and how that’s gonna affect everything else.

Sure, overall you just want to limit your cardio. But if you have to do cardio or you want to do cardio, let’s say you’re doing Crossfit or something like that. You’re thinking about where to position it relative to your resistance training and how to sequence your training. Become a little more complicated and you do have to consider it versus just kind of applying this carte blanche, “I’m gonna just go hard and go short and that’ll be just better because it’s more like my lifting.”

Well, it’s like, “Well, you wouldn’t just double your lifting to lose fat, would you?” If you had four hard days of training and you needed to diet, you wouldn’t just go to four two-a-days of lifting weights and double your volume. You know that would be bad. But in many case you’re trying to do something similar by adding a ton of HIIT.

Mike: Interesting. Have your personal experiences working with people agreed with that? ‘Cause the reason why I ask is over the years, again, I myself have done what I would say is probably qualifies as HIIT. The high intensity intervals were hard. In terms of length, they were never longer than 60 seconds, probably more like 30 or 45 seconds. I’ve recommended it again for people that want to lose fat as quickly as possible.

Now to be fair, if we’re looking at it in the context of what weightlifting they were doing, the basic programs that I have out there for men and women are not tremendously difficult. They’re essentially push pull legs programs with some accessory work. None of your workouts are more than 45 or 60 minutes. So we’re looking at two kind of harder workouts per week and then anywhere from one to three not-so-hard workouts per week.

I myself in doing that and doing HIIT when I was cutting, I don’t know, I never had any signs of falling behind in recovery. Now to be fair, yeah, my lifts stagnated and I just kind of whatever took that in stride. Just working with a lot of people nobody comes, no individual case comes to mind where it was like, “Okay, this is clearly too much. You should just be walking instead.” Now of course you could make it too much, but what are your thoughts on that?

Eric: Well, it sounds like you’re already in the realm of reasonable when you start out with what you’re doing with your clients. So you’re not starting off with I’m gonna crush these people and then I have to walk it back. I oversold the differences in the kind of just my inflection in my voice and how I presented the results.

In this study, if you were to truly look at the statistics and go hard line what was the main outcome? The main outcome was that man, it didn’t seem like there was big difference between HIIT and moderate intensity steady state. There was a slight difference in favoring the moderate intensity steady state for hypertrophy and maybe the interference effect a little bit. But overall, it looked like, hey, HIIT didn’t beat out moderate intensity steady state. Counter to what we’ve…the dogma we’ve believed. That’s probably the safest bet to make from this study.

So let me just kind of walk back the extremity with which I presented these findings. I think basically people should feel a little more safe doing steady state cardio and knowing that probably on a…if you look at time mastered or number of sessions per week, it’s probably not gonna be that much worse or that much better to do HIIT or MISS [moderate intensity steady state] or vice versa.

Mike: I guess then the context of why you’re doing it matters too. You mentioned that. But are you doing it… ’cause again, I really only do…I mean, that’s not true actually. These days I do yeah, I’d say moderate intensity biking just ’cause I like to do cardio. But I would do HIIT when I’m cutting and otherwise I just wouldn’t be doing it.

But for those people out there that are doing cardio for longer periods of time for whatever reason, that’s also a different circumstance than someone who’s like, “Look, I want to lose a lot of fat over the next 10 to 12 weeks and I want to feel good. If that means sacrificing some potential progress in my weight lifting, then I’m fine with that.” That’s just a different context.

Eric: Yeah. If the trade off is worth the speed, that’s totally fine. I think that’s exactly what you have to do is look at, “All right, what are my goals? Then how soon do I want them? Is that reasonable in the first place? Then what level of sacrifice do I not care about?”

You look at the study and you go, “Right, so the HIIT group didn’t gain as much lean body mass.” It was a small amount. “But maybe if I add HIIT to my training and moderate intensity steady state, sure, maybe I won’t gain or retain quite as much muscle mass. But if I get leaner faster and I can maintain that and then go into a bulking phase, maybe that will be…it won’t even matter six months from now.”

I think that’s a fair perspective. But really, people just need to be informed going into what they’re doing. If you are starting a diet and you come into it and you’re thinking that you have to do HIIT because that’s gonna be better for maintenance of strength and hypertrophy, this study tells you that strength will be roughly the same. In terms of hypertrophy, it might actually be slightly worse than doing less fatiguing cardio.

If you’re afraid of MISS because you’ve heard of the interference effect and you think, “Well, wow. That’s the intensity zone that’s gonna interfere the most with your training.” Well, it depends on the dosage. It may cause actually slightly more problems to really beat yourself up.

So think about the modality of training you’re doing. If you’re doing cycling or elliptical and you’re keeping it to say one to three sessions per week and the HIIT sessions are brief and you’re auto-regulating it. Or you’re mixing the two, you’re probably gonna be fine.

In my personal practice, I typically don’t have people do more than one, two, three cardio sessions per week. Certainly not more than one or two, maybe three HIIT sessions. I am trying to make sure that it’s low impact, low eccentric action, and that it’s separated from resistance training if possible. If I have to, after.

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I think from what I’ve seen is that the benefits are worth the trade offs in those cases. If you can moderate it and if you want to have effective fat loss or faster fat loss. Or if you just need that extra edge to really get quite lean, if that’s your goal, in a reasonable time frame. And you want to have a decent amount of calories to play with to eat. Then yeah, those are all reasonable applications of cardio.

I think the big take home from this study is just that HIIT is not the holy grail. If taken too far, it might be slightly worse than a lower intensity.

Mike: Absolutely. Where would you like to see this research go from here? What’s the next question that you would like to see answered?

Eric: Yeah. I would like to see some practical comparisons of different types of configurations combining them. ‘Cause I think what you rarely see, research always pits one thing versus another. It goes is HIIT better than MISS? Or vice versa? Or is heavy load training better than light load training?

But rarely do we have studies of hey, is a combined heavy and light load training program set up in an intelligent way compared to something that’s just high reps or just low reps, better? Or is all HIIT or all low intensity steady state better? But what if we combine them?

So I would love to see someone have a mix of different cardio intensities and see if that was a bit better. Try to figure out, okay, based on prior research and what we think makes sense logically, what’s the most HIIT we would give somebody? Okay, maybe one to two sessions, then we’ll do the rest from MISS.

And compare that to an all MISS group or an all HIIT group and see if perhaps that one in the middle can maybe lose fat faster without actually losing any more muscle mass and be better than both. I think that’s possible. So I’d love to see a study set up in that manner.

Mike: Maybe you’ll be the one doing it.

Eric: Maybe.

Mike: Okay, great, Eric. Well, this was…I’m sorry, Dr. Helms, PHD. This was very enlightening. I’m excited to do the next one when the time comes.

Eric: Sounds good. I look forward to it.

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What’s your take on combining cardio and weightlifting? Have anything else to share? Let me know in the comments below!