Cardio doesn't 'eat' your muscle — unless you overdo it

The fear of cardio among people bulking is usually overblown

Among people building muscle, there's a common fear that any cardio competes with strength training for recovery resources and 'burns off' hard-earned muscle. Moderate cardio — 2–3 sessions of 20–30 minutes a week — doesn't show a meaningful negative effect on muscle growth or strength in studies for most people who train, and can even help via improved blood flow and general conditioning that carries over into the strength work itself.

The real problem shows up with excessive cardio volume — daily long runs stacked on top of an intense strength program without accounting for total fatigue. In that case, competition for the body's recovery resources (the so-called interference effect) can genuinely slow strength and size gains, especially if nutrition isn't sufficient to cover both types of demand.

Practical guideline: as long as total calories and protein are adequate and cardio volume stays moderate and isn't done right before a strength session, cardio tends to complement progress rather than undermine it.