Cardio doesn't automatically burn your muscle. But it can burn muscle if you (1) do it too much, (2) do it before your weight training session, or (3) do 'high impact' cardio. There are other factors involved as well so it's important to look just beyond the equation that cardio equals muscle catabolism.

Is running bad for gaining muscle?

Although long distance running may inhibit muscle growth, high intensity, short duration running may promote it. Doing HIIT several times per week can help you build lower body muscle. Make sure you follow a balanced diet and stay hydrated to support the muscle building process.

Can you lose muscle by running?

Losing muscle mass from running is a possibility, but good news: with the right diet and strength training regimen, it's avoidable.