The things that are marketed primarily towards women; cycling classes, yoga, Pilates, Zumba, and “fat blasting” interval training classes using light weights; paint the perception that the muscle-burning, heart-pounding nature of the activity will somehow divest them of body fat while building aesthetically-acceptable amounts of muscle.
While doing a lot of pretty much anything can help reduce body fat and build muscle if you are pushing to your limit, that doesn’t mean there aren’t more effective ways of doing so. What often happens with cardio-heavy, low-resistance modalities is that you’ll lose some fat and gain some muscle in the first month or two, then never again.
In fact, you can actually LOSE muscle by overdoing it, ending up with a worse body composition than you started with. That’s because you aren’t giving your body the right signals. You aren’t going to get a six-pack like your Peloton instructor by just peddling a bike. Did you think otherwise? Sorry.
Getting muscles to develop means targeting them specifically with weights heavy enough to create a stimulus. You’re not going to get ripped by just running. You’ll just get skinny perhaps, and that’s if you’re lucky. More likely than not you’ll see marginal improvements in body composition and lots of improvement in your cardiovascular health (which is the real reason to do it).