Does Cardio Kill Your Gains? What 43 Studies Found

Not for muscle size or maximal strength. A 2022 review of 43 studies found that adding cardio to a lifting program didn't blunt strength or muscle growth on average. What it did dent was explosive strength, the kind you use to jump and sprint, and mostly when cardio and lifting were done in the same session.

The short answer

Cardio doesn't kill your gains. For most people who lift and run, the research says you can build muscle and strength just as well as if you only lifted.¹

There are three real exceptions:

• Explosive strength grew less when people added cardio, especially when both happened in one session.
• Experienced lifters chasing a bigger squat or leg press saw some interference, mainly when they combined both in one session.
• Muscle fibers may grow slightly less, particularly with running, though the evidence is early.

The first two have the same practical fix: keep hard runs and heavy leg days apart. The third is too uncertain to plan your week around.

What the 43-study review found

The main evidence here is a 2022 systematic review and meta-analysis by Schumann and colleagues in the journal Sports Medicine.¹ It pooled 43 studies with 1,090 healthy adults. Every study ran for at least four weeks and compared two groups doing the identical lifting program, one of which also did cardio.

The results are reported as standardized mean differences. Zero means the two groups improved equally. A negative number means the group that added cardio improved less.

The explosive strength dip depended on timing. When cardio and lifting were done within 20 minutes of each other, the gap was −0.31. When the two were separated by at least three hours, there was no significant effect.¹

Several things you might expect to matter didn't change the results: running versus cycling, how many combined sessions people did each week, whether they started untrained or already active, and whether they were under or over 40.¹

Why does explosive strength take the hit?

Explosive strength is how quickly you can produce force, rather than how much. The review measured it with jump tests, how fast force rose during a held contraction, and leg-press power.¹

The authors don't know exactly why it suffers while maximal strength doesn't. Their best guess is that leftover fatigue from cardio dulls the fast nerve signals that rapid force depends on. That could lower the quality of a lifting session without cutting how much work gets done, which would hurt speed and power more than raw strength or size.¹

If your sport is built on jumping or sprinting, this is the part of the research that applies to you most.

What the review can't tell you

• Study quality was middling. The included studies averaged 4.3 out of 10 on a standard quality scale, and seven were rated low quality.
• It was mostly about legs. Strength was measured with leg press, squat or knee extension, and muscle size mostly at the front of the thigh.
• Muscle size meant whole-muscle size, measured with scans such as ultrasound or MRI. It didn't look at individual muscle fibers.
• Well-trained lifters weren't analyzed separately. Anyone not described as untrained was grouped as "active," which could hide effects in experienced lifters.
• Cardio intensity wasn't analyzed, because the studies reported it too inconsistently.

When does cardio interfere with lifting?

Other reviews add useful detail about who's most likely to notice an effect.

Experienced lifters, in the same session. A 2021 review of 27 studies looked only at lower-body one-rep max strength.² Adding endurance training reduced gains in trained people (effect size −0.35) but not clearly in moderately trained or untrained people. In trained people, the drop showed up when both were done in the same session (−0.66), not when they were in separate sessions (−0.10, not significant). The authors suggest trained lifters separate the two during phases focused on maximal strength.

Muscle fibers, possibly with running. A 2022 review of 15 studies, from the same research group as the 43-study review, measured growth of individual muscle fibers.³ Adding cardio produced a small, borderline reduction in fiber growth overall (−0.23, right at the edge of statistical significance). Slow-twitch fibers grew noticeably less when the cardio was running (−0.81) but not when it was cycling. The authors call this preliminary.

Lots of long cardio sessions. An older 2012 review of 21 studies found that running, but not cycling, was tied to smaller gains in muscle size and strength, and that more frequent and longer cardio sessions went with smaller gains.⁴ The 2022 review didn't confirm these patterns, and its authors point to differences in methods, but the older finding is a reason not to pile on cardio volume all at once.

So the honest summary is this. For the average person who lifts and runs a few times a week, the interference effect was too small to detect in whole-muscle size and maximal strength. If you're an experienced lifter peaking for a heavy squat, or an athlete who needs to jump and sprint, scheduling matters more.

Should you lift or run first?

If they have to share a session and strength is the goal, lift first. A 2018 review of 10 studies found that lifting before endurance work led to bigger gains in lower-body strength, about 7 percentage points more improvement than the reverse order.⁵ Order made no difference to muscle size, aerobic fitness or body fat.

The 43-study review found the same-session dip in explosive strength regardless of which came first.¹ So lifting first protects strength, but only separating the sessions avoided the explosive strength dip.

How to schedule lifting and running

These rules come from the findings above. Where the research doesn't reach, they're standard coaching guidance, and we've said so.

1. Keep hard runs and leg days apart. Put intervals, tempo runs and long runs on different days from squats and deadlifts. Rep Labs builds lifting and running into one plan, so you never get an intense run and a leg day on the same day, and hard days get recovery yoga.
2. If they share a day, split them by three hours or more. With that gap, the explosive strength dip was no longer statistically significant in the 43-study review.¹
3. If they share a session, lift first when strength is your priority.⁵
4. Place easy runs near leg days, not hard ones. The studies couldn't analyze cardio intensity, so this is coaching judgment: an easy run leaves your legs fresher than intervals.
5. Add cardio gradually. Build running volume a little at a time and watch whether your lifts still go up. If they stall, cut back on the hardest runs first.
6. Consider cycling for some sessions if leg muscle growth is your top priority. The evidence on running versus cycling is mixed, so this is a hedge, not a rule.

An example week

This is an example layout, not a schedule tested in a study. Adjust the days to fit your life.

If you're new to either side, start smaller. Our guides on your first 12 weeks of lifting and going from zero to 30 minutes of running each give a gentler on-ramp.

Is it worth doing both?

For most people, yes. The 43-study review's authors conclude that most people, recreational athletes included, can combine the two and get the benefits of both, with separate sessions mainly helping those who prioritize explosive strength.¹

Lifting and cardio build different things. Skipping running to protect your gains means giving up the fitness it brings for a cost the research mostly can't find. Plan the week so the hard sessions don't collide, and you can have both.