Does Cardio Kill Your Gains?
Not muscle size, and not max strength. A 2022 meta-analysis of 43 studies and 1,090 people found that adding cardio to a lifting programme left muscle growth unchanged. The one thing that did dip was explosive strength, such as jump height, and mostly when the cardio came straight before or after the lifting.
Where “cardio kills gains” comes from
The idea has a name, the interference effect: the worry that training for endurance and for size at the same time leaves you worse at the second. It sounds plausible, and for decades it hardened into a gym rule.
The rule was supported by a 2012 meta-analysis in the Journal of Strength and Conditioning Research (Wilson et al.), which pooled 21 studies. Its summary: interference depends on the modality, frequency and duration of the endurance work, and resistance training combined with running, but not cycling, led to significant decrements in both hypertrophy and strength. It also found the penalty grew with how often and how long people did endurance training.
What the larger, newer analysis found
Ten years later, Schumann and colleagues repeated the exercise with more studies and a stricter design. Every study compared the same strength programme with and without added aerobic training, for at least four weeks, in healthy adults. Forty-three studies and 1,090 participants met that bar (590 doing both, 500 lifting only).
| Outcome (cardio + lifting vs lifting alone) | Effect size (SMD) | Verdict |
|---|---|---|
| Muscle hypertrophy | −0.01 (p = 0.919) | No difference |
| Maximal strength | −0.06 (p = 0.446) | No difference |
| Explosive strength | −0.28 (p = 0.007) | Small but real reduction |
An SMD of −0.01 for hypertrophy is as close to zero as these analyses get. The hypertrophy result rests on 15 studies with 201 people doing both and 188 lifting only, so it is the thinnest of the three rows, but it points the same way as the other analyses.
Running vs cycling, frequency, age: nothing split it
The 2012 paper’s running-versus-cycling finding is the part gym advice kept repeating. The 2022 analysis tested it directly and found no significant effect of the type of aerobic training. It also found no significant effect of weekly frequency (more than five sessions versus fewer), training status (untrained versus active) or age (under versus over 40). The authors conclude the results appeared independent of all of them.
This is a case where the field changed its mind, and the older answer is still the one most articles repeat. A 2016 review by Murach and Bagley in Sports Medicine had already argued that the evidence for interference on muscle growth in humans “is not as compelling as previously thought”, and that under certain conditions concurrent training may even add to hypertrophy.
The part that is real: explosive strength and timing
Explosive strength, the ability to produce force fast, fell by a small amount (SMD −0.28). The subgroup split is the useful bit. When aerobic and strength work were done within 20 minutes of each other in the same session, the reduction was significant (SMD −0.31). When sessions were separated by at least 3 hours, it was not.
For a lifter chasing size, that barely matters. For someone whose sport rewards jumping, sprinting or throwing, it is the reason to put the run and the squat session in different parts of the day, or on different days.
What this means for your week
- If you are training for muscle or general strength: do the cardio you want. The pooled data show no hypertrophy or max-strength penalty for it, and the heart-health case for it stands on its own. Our guide to how much cardio per week covers the amounts.
- If you can pick the order: lift first, so your heaviest sets are not done on tired legs. This is a practical call, not a finding of the meta-analysis, which found no hypertrophy difference by order.
- If explosive power matters: separate the two by hours, or put them on different days.
- If you are cutting: the thing that costs muscle is a deficit that is too large with too little protein, not the treadmill. See the body recomposition guide and check your numbers with the protein calculator and the TDEE calculator.
A caveat the studies cannot remove
The studies in the meta-analysis compared two training programmes. They do not tell you what happens in your own week if the cardio makes you eat less than you need or sleep less than you should. That is an energy and recovery problem, and it can cost you gains whatever the interference research says. If your lifts are stalling as your mileage climbs, look at food and sleep before you drop the running. Our piece on how many rest days you need is the next place to look.
The short version
The best current evidence says cardio does not kill your gains. Muscle size and max strength came through intact in 43 pooled studies; explosive strength took a small hit that was clearest when the sessions were back to back. Run, cycle or row as much as you enjoy, eat enough, and if power is the goal, give the two sessions some space.
Sources
- Schumann M, Feuerbacher JF, Sünkeler M, Freitag N, Rønnestad BR, Doma K, Lundberg TR. Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Med. 2022. doi:10.1007/s40279-021-01587-7
- Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP, Anderson JC. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res. 2012. doi:10.1519/JSC.0b013e31823a3e2d
- Murach KA, Bagley JR. Skeletal muscle hypertrophy with concurrent exercise training: contrary evidence for an interference effect. Sports Med. 2016. doi:10.1007/s40279-016-0496-y
General information, not medical advice. Effect sizes are pooled averages from supervised trials in healthy adults; individuals vary. If you have a heart condition or another medical issue, check with your doctor before changing your training.