Does Cardio Kill Your Gains? The Interference Effect Explained

Does cardio kill your gains? For most lifters, no, not in any way that matters. Older research from the 1980s found a real interference effect between endurance and resistance training, but larger, more recent reviews have found that concurrent training does not meaningfully reduce maximal strength or overall muscle growth for most people, especially when the two types of training are spaced apart.

The one place a real, if small, effect still shows up is explosive power, and even that is manageable with basic scheduling. Here is what the research actually supports.

What is the interference effect?

It is the idea that training for endurance and strength at the same time interferes with the adaptations you would get from either one alone, first documented by exercise physiologist Robert Hickson in a 1980 study that found concurrent training blunted strength gains compared to strength training by itself. That study became the foundation for decades of lifters avoiding cardio out of fear it would sabotage their muscle.

The problem is that Hickson's original study used a small sample and a specific, demanding training setup that does not resemble how most people actually combine cardio and lifting today.

Does cardio actually kill your gains?

Not meaningfully, based on the newer, larger body of research. A comprehensive 2022 review by Schumann and colleagues, analyzing 43 studies, found that concurrent aerobic and resistance training did not meaningfully reduce gains in maximal strength or overall muscle hypertrophy. The main exception was explosive strength and power output, which showed a modest negative effect, particularly when cardio and lifting were done in the same session with less than about a 3-hour gap between them.

That is a meaningfully different picture than the "cardio kills gains" framing that is still common. The interference effect is real in a narrow sense, mainly power and explosiveness, but the broad fear that any cardio will blunt muscle growth or basic strength is not well supported by the current evidence.

Does it matter if you're a beginner or an advanced lifter?

Somewhat. Research suggests the interference effect is minimal to nonexistent for untrained beginners adding cardio to a new lifting program, likely because beginners have so much room to adapt that competing demands rarely become the limiting factor. The picture is a little more mixed for advanced, already well-trained lifters, and a 2024 systematic review found the interference effect on strength was small in men and essentially absent in women, though more research is still needed to fully understand why that difference shows up.

If you're new to lifting, this is one less thing to worry about. If you have been training seriously for years and are chasing very specific strength or power goals, that is where paying closer attention to scheduling and cardio volume matters more.

How should you schedule cardio and lifting to avoid interference?

Separate them by a few hours if both happen on the same day, and if you truly cannot separate them, lift first. Strength and power work depend more heavily on being fresh and neuromuscularly primed than most steady-state cardio does, so doing your hardest lifting first protects the training that is most sensitive to fatigue. Training cardio and lifting on entirely different days sidesteps the issue altogether, which is a natural fit if you're already spreading training across the week the way we cover in how many days a week you should work out.

How much cardio is too much when you're trying to build muscle?

There is no single number that applies to everyone, but a moderate amount, a few sessions a week at a manageable duration and intensity, is unlikely to meaningfully hurt muscle growth as long as your eating and recovery keep pace. The real risk shows up at the extremes: stacking high volumes of endurance training on top of a full lifting program without adjusting food intake or sleep, where the limiting factor becomes total recovery capacity rather than any biochemical interference between the two training types. That is the same recovery math behind what is a deload week and signs of overtraining, both worth a look if you are trying to do a lot of both.

The part that is easy to lose track of once you're combining training types is whether your lifting numbers are actually holding up over time. Ori builds your training plan around real progressive overload and adjusts it based on what you log, so if a stretch of added cardio is starting to eat into your lifting performance, it shows up in your numbers instead of staying a guess.

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FAQ

Does cardio actually kill your gains? Not meaningfully for most people. Older research from the 1980s found a real interference effect, but larger, more recent reviews covering dozens of studies found concurrent training did not meaningfully reduce maximal strength or overall muscle growth, particularly when cardio and lifting sessions are spaced apart.

What is the interference effect? It is the theory that combining endurance training and resistance training in the same program blunts the strength and muscle gains you would get from lifting alone, originally documented by researcher Robert Hickson in 1980. Later research has shown the effect is smaller and more situational than that original study suggested.

Does the interference effect matter more for beginners or advanced lifters? Research suggests untrained beginners show little to no interference effect on strength gains from adding cardio. The picture is more mixed for advanced, already well-trained lifters, though the difference is still generally small when sessions are separated.

How should you schedule cardio and lifting to avoid interference? Separate the two by at least a few hours if you are training both in a day, and lift first if you have to do both in one session, since lifting depends more on fresh neuromuscular output than most cardio does. Training on different days entirely avoids the question altogether.

How much cardio is too much if you're trying to build muscle? There is no single universal number, but a moderate amount, a few sessions a week at a manageable duration and intensity, is unlikely to meaningfully hurt muscle growth as long as you are still eating and recovering enough. Very high volumes of endurance training on top of a full lifting program is where competing recovery demands become the bigger concern.