Does Cardio Kill Your Gains? What the Latest Research Actually Shows
5 min read
For decades, lifters have been warned about the "interference effect."
The basic idea is simple: resistance training tells the body to become bigger and stronger, while endurance training creates a different set of adaptations. Combine the two, and the cardio may interfere with the results you are trying to get from lifting.
That concern has some legitimate scientific history behind it. But it has also been simplified into a much broader gym rule:
If you want to build muscle, don't do too much cardio.
A large 2026 umbrella review published in Sports Medicine gives us an updated look at whether that warning is actually justified.
The short answer is reassuring.
For most recreationally trained adults, combining cardio and resistance training does not appear to meaningfully compromise muscle growth, strength, or power.
But that does not mean programming no longer matters.
What Is the Interference Effect?
The interference effect refers to the possibility that endurance training may reduce some of the adaptations produced by resistance training when both are performed concurrently.
There are plausible reasons this could happen.
Resistance and endurance exercise create different physiological demands. High volumes of endurance training also create additional fatigue, consume recovery resources, and place more stress on the muscles being trained.
If someone repeatedly performs demanding endurance work on already-fatigued legs, it is reasonable to wonder whether their squat performance, recovery, and eventual strength or muscle gains could suffer.
The mistake is assuming that because interference can occur, any meaningful amount of cardio automatically interferes with lifting.
That is not what the broader research shows.
A 2026 Review Looked at 144 Studies
The new umbrella review is particularly useful because the researchers did not analyze a single training study. They evaluated 17 previous meta-analyses encompassing 144 individual studies and 1,492 healthy participants.
The outcomes included aerobic capacity, muscle strength, power, and hypertrophy.
When concurrent training was compared with resistance training alone, the combined approach produced greater improvements in aerobic capacity—as we would expect.
More importantly, strength, power, and muscle growth were comparable between concurrent training and resistance training alone.
In other words, adding endurance exercise generally improved cardiovascular fitness without producing a detectable overall penalty to the major resistance-training adaptations examined in the review.
That is difficult to reconcile with the idea that cardio inherently "kills your gains."
That Does Not Mean You Can Do Unlimited Cardio
This is where the research requires some interpretation.
An average result across many studies does not mean every possible combination of lifting and endurance training will produce identical results.
There is an obvious difference between adding a few moderate cardiovascular sessions to a four-day resistance-training program and simultaneously trying to maximize bodybuilding progress while preparing for a marathon.
Training creates stress. The body has a finite ability to recover from it.
As endurance volume and intensity increase, so do the potential demands on recovery. This becomes especially relevant when the cardio heavily involves the same muscles you are trying to develop through resistance training.
A hard running session followed by heavy lower-body training is a different recovery problem than an easy cycling or walking session performed on another day.
The practical question therefore should not be:
"Can I do cardio while trying to build muscle?"
For most people, the answer is clearly yes.
The better question is:
"How much cardio can I perform while still recovering from and progressing in the training that matters most to my goals?"
Does the Order of Cardio and Lifting Matter?
The 2026 review also examined training sequence.
Overall, the researchers did not find a significant effect showing that one sequence was universally superior. However, the results suggested that performing resistance training before endurance training may favor strength and possibly hypertrophy when both are performed together.
That makes practical sense when strength or muscle growth is the priority.
If you perform a demanding cardiovascular session immediately before lifting, you may begin your resistance training with more fatigue and less ability to produce force. Even if that does not create a long-term interference effect by itself, consistently reducing the quality of your most important training is probably not an ideal strategy.
When possible, putting the highest-priority training first is a reasonable rule.
And when cardio and resistance training can be separated into different sessions—or different days—the immediate fatigue from one session becomes easier to manage.
The Type of Cardio Matters Too
Not all cardio creates the same training stress.
Walking, moderate cycling, incline treadmill work, running, intervals, and sprinting may all improve cardiovascular fitness, but they differ considerably in muscular fatigue, impact, intensity, and recovery demands.
This is one reason low-intensity cardiovascular work can fit particularly well alongside hypertrophy and strength training. It can improve aerobic fitness and increase energy expenditure without necessarily creating large amounts of additional muscular fatigue.
Higher-intensity work can also have a place, but it needs to be treated as training rather than free exercise that carries no recovery cost.
We recently discussed another side of this in What Can a 91-Year-Old World-Record Sprinter Teach Us About Aging?. Sprinting can provide adaptations that slower cardiovascular work does not, but those benefits come with very different physical demands.
The appropriate cardio prescription therefore depends on what the rest of the training program is trying to accomplish.
What About Advanced Lifters?
There is an important limitation to the new review.
The authors specifically noted that evidence in highly trained and elite athletes remains limited.
That matters because the closer someone gets to their physiological potential, the more relevant small differences in training and recovery may become.
A relatively new lifter can often improve multiple physical qualities simultaneously. An advanced athlete attempting to maximize a specific adaptation has less room for error and may need to manage competing training demands more carefully.
This is consistent with a principle we discussed in Are You Actually Advanced? What Changes After 5–10 Years of Training: training decisions become increasingly consequential as adaptation becomes harder to produce.
So the 2026 findings should not be interpreted as proof that an elite bodybuilder can add unlimited endurance work without consequences.
They are much more reassuring for the person who wants to be muscular, strong, and cardiovascularly fit at the same time.
You Probably Do Not Need to Choose Between Muscle and Cardiovascular Fitness
The old interference-effect discussion often creates a false choice.
You can prioritize muscle and strength without deliberately neglecting cardiovascular fitness.
For most adults, that would be a strange tradeoff to make.
A well-designed program can include resistance training as the primary stimulus for strength and hypertrophy while also including enough cardiovascular work to develop aerobic fitness and support long-term health.
The important part is managing the total training dose.
If lifting performance is consistently declining, soreness never resolves, lower-body sessions are suffering, or progression has stalled after adding substantial endurance work, the cardio prescription may need to change.
But avoiding cardio entirely because of a theoretical interference effect is not supported by the current evidence.
Cardio does not automatically kill your gains. Poorly managed training can.
That distinction is much more useful.
It also reflects the approach behind The Foundation: resistance training, cardiovascular fitness, recovery, and progression should be programmed as parts of the same system rather than treated as competing goals.
References
Held S, Wolf L, Rappelt L, Bloch W, Donath L, Micke F, Geisler S, Isenmann E. Maximizing Adaptations in Concurrent Training: An Umbrella Review of Meta-analyses. Sports Medicine. 2026;56(6):1489-1512. doi:10.1007/s40279-026-02401-y.
About the Author
AFT Fitness Coaching develops structured, evidence-based training systems for adults who want to build muscle, improve body composition, and train with greater confidence. The Arcos Program combines proven training principles with long-term progression, giving members a clear plan instead of another random workout.