Not at ordinary running volumes, and the fear is largely out of date. The idea comes from the “interference effect” — the observation that combining endurance and strength training blunts strength gains. Recent pooled evidence has shrunk that effect substantially: analyses covering more than 40 studies found concurrent training did not interfere with muscle growth or maximal strength.
Where the fear came from
The original 1980 study found that people doing both endurance and strength work gained less strength than people doing strength alone. That result is real, and it launched forty years of gym-floor anxiety about cardio.
What has changed is the size and the conditions. A systematic review and meta-analysis of 43 studies (1,090 participants) reported that concurrent training did not interfere with muscle growth (SMD −0.01, p = 0.919) or maximal strength (SMD −0.06, p = 0.446). A separate semi-systematic review covering 42 studies — a narrative review rather than a pooled analysis, and one that includes animal work — likewise found no consistent effect of training sequence on eventual gains in endurance, hypertrophy or maximal strength. That review does add a qualification worth carrying: it concluded that a strength-first arrangement optimises neuromuscular adaptation, and that endurance-first works better with more than three hours before the strength session.
One caveat that matters more here than anywhere: 24 of those 43 studies used cycling as the aerobic mode and only 16 used running — and in the breakdown by exercise type, the explosive-strength attenuation appeared in the cycling studies and not the running ones, then weakened further when an outlier was removed. For a guide about whether running burns muscle, that is the most relevant line in the paper.
Where interference does show up at all, it is narrower than the gym version and in one specific place: explosive strength — jumping, sprinting, rate of force development — which was attenuated (SMD −0.28, 95% CI −0.48 to −0.08, p = 0.007). Maximal strength and muscle size were not.
And it is worth being straight about who that applies to, because it is tempting to wave it away. That review classified participants only as untrained or active, with the active category covering everyone from recreationally active to well-trained, and training status was not a significant moderator. The subgroup analyses in that review found no statistically significant differences between subgroups, so nobody should claim a clean moderator here. What the authors do report is that the attenuation showed up in the group training both within about twenty minutes of each other, and not in the group separated by three hours or more — which is a direction worth acting on even though it is not a proven interaction.
Why do some runners lose muscle?
Runners who visibly lose muscle almost always have one of three things going on, and none of them is “running”:
- Not eating enough. A large energy deficit costs lean mass whatever exercise you do. This is by far the most common cause.
- Not lifting. Muscle that is never loaded heavily does not stay. Running is not a resistance stimulus for the upper body at all.
- Not enough protein, badly distributed. See how much protein runners actually need.
Should you lift before or after running?
If you do both, the evidence supports a few modest preferences rather than hard rules:
- Separate them where you can. Different days, or at least three hours apart. This is the one variable that showed a significant effect, so it is the one worth arranging your week around.
- If they must share a session, some evidence favours strength first for lower-body dynamic strength over programmes of five weeks or more — though the same reviews found no clear ordering advantage for hypertrophy or static strength.
- Do not put heavy legs the day before a quality run. This is about running the session well, not about interference.
- Two sessions a week is enough for most recreational runners. See our 12-week strength progression.
One thing to be honest about
Strength training is worth doing because it makes you a more durable, more economical runner and preserves muscle you will otherwise lose with age. It is not reliably proven to prevent running injuries — pooled across nine randomised trials of exercise-based prevention in 1,904 endurance runners the effect was not significant — though a supervised-only analysis within it did find lower injury risk, which cuts the other way. We set out that evidence in what actually prevents running injuries. Do it for the right reasons.
References
Schumann M, Feuerbacher JF, Sunkeler M, et al. Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Med, 2022;52(3):601–12. · Feng Z, Ying W, Jun W. The effects, mechanisms, and influencing factors of concurrent strength and endurance training with different sequences: a semi-systematic review. Front Sports Act Living, 2025;7:1692399. · Eddens L, van Someren K, Howatson G. The role of intra-session exercise sequence in the interference effect: a systematic review with meta-analysis. Sports Med, 2018;48(1):177–88. · Hickson RC. Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol, 1980.