Does the Cardio ‘Interference Effect’ Really Slow Your Gains?

Cardio and strength training are both important to your fitness, a fact that I have always known but currently am unable to shut up about. I am mainly a strength training person (a weightlifter, to be specific), and for a long time I thought that lifting a lot was enough. But when I added more cardio to my routine, I saw my lifting improve. Cardio is good for you, who knew.

But there’s a popular misunderstanding about combining these two areas of fitness. The cardio “interference effect,” an educated gym bro might tell you, is scientific proof that cardio will kill your gains. Therefore, the less cardio you do, the more muscle you’ll pack on.

This isn’t true, although there are a few grains of truth that have led to this belief. Let’s walk through them and see where they really apply.

Time management is important

Any time you spend doing cardio is time that you’re not under a barbell, squatting. In that sense, the more cardio you do, the less time you have for lifting.

Runners have a similar reason for avoiding strength training: They’d rather spend an hour out on the road than an hour in a stuffy gym. That doesn’t change the fact that runners really do need to do strength training, and lifters need to give their hearts and lungs a chance to work, too.

How to solve this problem: Plan better. If you go to the gym on Monday, Wednesday, and Friday, you’ve probably got some time on Tuesday and Thursday you could use to hop on an exercise bike or do a cardio dance video or go for a hike. (If walking is strenuous enough, it counts.)

Even if you don’t have time for a full cardio workout, you can probably find a few minutes each day for a mini workout or a quick HIIT session (ideally real HIIT, not the fake stuff, but anything is better than nothing).

You need to eat enough for both

If you’re gaining muscle, you may be trying to help the process along by eating enough food to gain weight. Some lifters may be afraid of cardio because it burns calories, making it harder to gain weight.

The solution to this one is simple: Just make sure to eat enough. The total amount of calories you take in should be appropriately balanced against the total amount you burn between your everyday moving-around and your deliberate exercise. If your weight is going in the wrong direction, adjust your food or your exercise to get back on track.

Cardio may interfere with gains, but only at extremes

The grain of truth in this myth is that there have been studies in which people who train for both strength and cardio have less strength gains than people who only train for strength. You can find a rundown of some of them here.

But the case isn’t closed there. There are also studies that show untrained people improving their strength in spite of cardio, and that show cycling may not interfere as much as running, if at all. And if you aren’t extremely specialised in your sport, the interference effect may not matter at all.

The effect is also fairly small even where it does exist: Cardio doesn’t stop anyone from gaining muscle, it just presents a possible tradeoff. So even if the interference effect is true and even if it applies to you personally, it’s still not killing your gains — just, at worst, bruising them slightly.

We can also take a common-sense approach here. On the one hand, nobody has been an elite marathoner and an elite powerlifter at the same time. You need totally different body types and training schedules for those goals anyway.

On the other, there are plenty of athletes who combine impressive strength with incredible endurance. Watch the Crossfit Games if you don’t believe me. It’s possible that the world’s top Crossfitters could be a little bit stronger if they didn’t also have to do bike sprints, or that they could run faster if they didn’t also have to lift. But their training has clearly allowed them to become good at both.

Cardio is good for lifting, actually

So maybe there’s a small interference effect, or maybe there isn’t. You might be tempted to err on the side of caution and simply not do any cardio and focus solely on weight training, but that’s not a risk-free decision. Let’s talk about what you’re leaving on the table if you completely neglect your cardio: Work capacity.

Training cardio (or “conditioning,” if you want a more lifter-friendly word) will make your heart bigger and stronger, and will increase the size and amount of your blood vessels. It makes your body better at getting oxygen and nutrients to your muscles, and flushing metabolic waste products out of your muscles. Those are all things that help you recover more quickly between sets of an exercise.

Ever since I, personally, added more cardio to my life, I’ve noticed that I can do a ton more work in the gym. I used to have to sit down for five minutes between sets of heavy squats; if I was working up to a big deadlift I might wait even more. If my program called for triples on clean and jerks, my lungs would be burning as much as my muscles by the time I finished. Which all makes sense, since heavy lifts are taxing on your whole body.

But now I run a few times a week, and I make a point of doing my accessory workouts (the lighter lifts, like curls) with as little rest time as possible. I also work some conditioning stuff into my routine, like sandbag carries and kettlebell swings. These moves give my heart and lungs a workout similar to what they’d get from an interval cardio session.

And now I breeze through my workouts. Three minutes is plenty between squat sets. I can set up a circuit of presses, curls, and rows, and get through it with barely any rest at all. The result is that my workouts are shorter than before. Twenty-rep sets are challenging rather than impossible. If I have to do two lifts soon after each other in competition, I don’t have to worry that I might not be ready for the second. And, importantly, since my workouts are easier, I can use that same amount of time to do more work. I am certain that I’m gaining strength and muscle more effectively now than I was when I had to take those long rests. So give a little cardio a try — it might help you too.