The evidence-led answer
NST verdict
Mostly no. Across the research, adding cardio to a lifting programme does not compromise muscle growth or maximal strength on average. A large pooled analysis of 43 studies found essentially no effect on either. Where a small interference does show up is specific. Explosive strength and power take a modest hit, especially when cardio and lifting are crammed into the same session. The effect at the muscle fibre level is slightly negative and worse with running than cycling. And in men doing high volumes of both, lower body strength gains can be blunted. None of that is a reason to skip cardio. If you want both, separate the sessions or put at least a few hours between them, lift first when they share a session, and lean towards cycling or incline walking rather than hard running near leg days. And cardio is worth doing regardless, for your heart, your fitness and your recovery capacity, which lifting alone will not give you.
Does cardio actually reduce muscle growth?
For most people, no. An updated pooled analysis of 43 studies compared people who did aerobic training alongside the same strength programme with people who did the strength programme alone. There was no significant difference in muscle growth, an effect of minus 0.01, which is nothing, and this held whether the cardio was cycling or running, however often it was done, and regardless of age or training experience. The visible muscle you build is not meaningfully reduced by also doing cardio. A separate review looked deeper, at the muscle fibre level, and did find a small negative effect on fibre size overall, driven mainly by running rather than cycling for slow twitch fibres. Both can be true: the size you can see is not meaningfully reduced, while there is a small fibre level signal that is worst with running.
Does it affect strength?
Maximal strength, how much you can lift for one rep, is also essentially unaffected on average, an effect of minus 0.06 that is not significant. Two qualifications. Explosive strength and power, jumps, fast lifts, rate of force development, do take a modest hit, an effect of minus 0.28, and more so when the cardio and the lifting are done in the same session rather than separated by a few hours. And in men specifically, a separate pooled analysis found that doing high volumes of both blunted lower body strength gains, an effect of minus 0.43; the same was not seen in women.
When does interference actually happen?
The interference effect is real but conditional. It shows up most when the endurance dose is high. An older pooled analysis linked greater endurance frequency and duration to bigger drops in size, strength and power, and small recreational amounts of cardio do not meaningfully cost muscle. It shows up more with running than cycling: at the muscle fibre level, the negative effect on slow twitch fibres was clear when the cardio was running but not cycling, probably because running involves more eccentric loading and muscle damage in the legs. And it shows up when the sessions are stacked: doing hard cardio right before or after lifting is the worst case for the power and same session effects.
How to do both without a trade off
Separate the sessions, and different days is ideal; if not, leave at least a few hours between them. Lift first when they share a session: doing resistance before endurance preserved lower body dynamic strength better than the reverse order, by about 6.9%. Choose the modality: if leg size or strength is the priority, favour cycling, incline walking or rowing over hard running, especially in the day or two around leg training. And keep the endurance dose sensible if muscle and strength are your main goals, two to three moderate sessions a week rather than daily long runs.
Why cardio is worth doing anyway
The "cardio kills gains" fear talks people out of something genuinely valuable. Aerobic training improves cardiorespiratory fitness and cardiovascular health, raises your work capacity and your ability to recover between hard sets, and helps manage body fat, none of which lifting on its own delivers. For all but competitive strength and power athletes, the small, avoidable trade off is a poor reason to give that up.
What this means in practice
If you lift and also want general fitness, do roughly two to three moderate cardio sessions a week. Put them on non lifting days where you can, or separate them from lifting by several hours. When cardio and lifting share a session, lift first. Favour cycling, rowing or incline walking over hard running in the day or two around leg training. Done this way, cardio has no meaningful cost to your muscle or your maximal strength, and it buys you fitness and health that lifting alone will not. Only if you compete in a strength or power sport and are in a peaking phase should you actively cut cardio back. Build any new cardio up gradually to avoid overuse niggles.
Limitations and uncertainty
The reassuring "no effect on muscle size" is at the whole muscle level; a separate pooled analysis found a small negative effect at the muscle fibre level, worst with running. Both can be true. The largest older pooled analysis is from 2012 and methodologically dated; it is used here only for the dose response and running versus cycling points, which the newer reviews broadly echo. The "two to three sessions a week is fine" dose is a reasoned synthesis, not a tested threshold. Most studies are a few weeks to a few months long. This is about muscle size and strength, not endurance performance or whether lifting helps your running.
What would change our conclusion
A large trial mapping the interference effect against a measured weekly endurance dose, giving an actual "how much is too much" number. Consistent evidence that a specific, common recreational cardio pattern meaningfully reduces hypertrophy in trained lifters. Or evidence that the fibre level running effect does or does not translate into visible differences in leg size over a year.
How NST assessed this
NST ran no training studies. This article is built from published research: an updated pooled analysis of concurrent aerobic and strength training for muscle size and function, a pooled analysis of the same at the muscle fibre level, a pooled analysis of sex and training status effects, a pooled analysis of within session exercise order, and an older pooled analysis on endurance dose and modality. Bibliographic details were checked against PubMed in September 2026. Each claim is tied to a named source, and the underlying evidence records still need a human editor to read the full texts, assign a plain language certainty, and confirm nothing newer changes the picture.
Practical meaning
If you lift and also want general fitness, do roughly 2 to 3 moderate cardio sessions a week, on non lifting days or separated from lifting by several hours. Lift first when they share a session. Favour cycling, rowing or incline walking over hard running around leg training days. Done this way there is no meaningful cost to muscle or maximal strength. Only competitive strength or power athletes in a peaking phase need to cut cardio back. Build new cardio up gradually.
Limitations and uncertainty
The reassuring 'no effect on muscle size' is whole muscle; a separate pooled analysis found a small negative fibre level effect, worst with running, and both can be true. The largest older pooled analysis is from 2012 and dated, used only for the dose response and modality points. The '2 to 3 sessions a week is fine' dose is a reasoned synthesis, not a tested threshold. Most trials run weeks to months. This is about muscle and strength, not endurance performance.
No product needed
This page is here to answer the question, not force a product.
Some research pages are deliberately product-free because adding a retailer link would not help the reader make a better decision. When a product is genuinely relevant, it appears after the evidence and is clearly labelled.