Does Cardio Kill Your Gains?

The fear that cardio erases your hard won muscle has kept a lot of lifters away from conditioning they would genuinely benefit from. There is a real phenomenon here, the "interference effect" of training for strength and endurance at the same time, but the modern evidence says it is smaller, and far more manageable, than gym folklore suggests.

What the research shows

The landmark meta analysis by Wilson and colleagues (2012), pooling 21 studies, found that adding endurance work to resistance training produced a small to moderate blunting of strength and, most noticeably, power, while muscle size was not significantly compromised overall. Crucially, the interference was much more pronounced when the endurance mode was running than when it was cycling.

More recent and larger reviews have softened the picture further. An updated meta analysis by Schumann and colleagues (2022) found no meaningful overall interference for muscle growth, suggesting the effect is smaller than once believed when the type, timing, and amount of cardio are handled sensibly.

How to keep cardio from eating your gains

A few simple choices minimize any interference. Favor lower impact modes like cycling, the rower, or incline walking over high volumes of running when muscle and strength are the priority, since running's eccentric loading and muscle damage drive most of the interference. Separate your cardio and lifting by several hours, or put them on different days, rather than stacking a long run right before squats.

Keep cardio frequency and duration moderate rather than marathon length, and if you must do both in one session with strength as the goal, lift first. None of this requires eliminating conditioning, just sequencing it thoughtfully.

Don't skip it

Cardio's benefits for heart health, work capacity, and recovery between sets are real and worth having. A fitter cardiovascular system actually helps you recover within and between lifting sessions. The interference effect is a reason to be smart about programming your conditioning, not a reason to avoid it.