Training

Does cardio kill your gains? The truth about the interference effect

Combining endurance and strength training can slightly blunt some adaptations, but for most people the effect is small and easy to manage.

The interference effect is the idea that doing endurance training alongside strength training reduces the gains you would get from lifting alone. The concept comes from studies in the 1980s and has been examined many times since. Modern reviews suggest the effect is real but generally modest: combining both types of training does not meaningfully reduce gains in muscle size or maximal strength for most people, while explosive power and very high training volumes appear somewhat more sensitive to interference.

The details of the cardio matter more than the fact that you do it. Large amounts of running, especially long or very intense sessions done close to lifting, tend to interfere more than cycling, rowing or walking, probably because running adds more muscle damage and impact to the legs. Fatigue is also a practical issue: a hard interval session right before squats will lower the quality of the lifting, regardless of any molecular signaling effects. Low to moderate amounts of cardio, on the other hand, support recovery, heart health and work capacity.

To get the benefits of both, separate hard cardio and heavy lifting by several hours or put them on different days when possible, and do the session that matters most to you first. Favor cycling or other low-impact options if leg strength is the priority, and increase endurance volume gradually rather than all at once. Eating enough total energy and protein also limits interference, since many problems blamed on cardio are actually caused by under-eating while training a lot.

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