Guide · By the FitSum team
Why mixing running and lifting can hold back your gains
What the 'interference effect' means for people who run and lift, and practical ways to keep making progress at both.
The interference effect
Researchers use the term 'interference effect' for the idea that doing a lot of endurance training alongside strength training can hold back some strength and muscle gains. How much it matters varies from person to person and depends on how much, how hard, and what type of cardio you do.
It's mostly about fatigue and recovery
For most people, the practical problem is simple: if you arrive at a lifting session tired from a hard run, you can't lift as well — and the reverse is true too. Over weeks, that adds up.
Ways to reduce it
Build cardio volume gradually rather than jumping straight to hard sessions. Keep most of your cardio easy. Space hard runs and heavy leg days apart where you can. Sleep and eat enough to recover from both.
Low-impact cardio such as cycling can be easier to combine with leg training for some people.
How FitSum helps
FitSum's endurance coaching builds your aerobic base by prioritising volume before intensity, and its strength coaching progresses each exercise separately from your own performance. Because both are coached in one app, a hard day in one is taken into account in the other.