Cardio and Muscle Growth
Does cardio kill your gains? Mike Matthews (Muscle for Life) argues that moderate cardio helps more than it hurts when you're trying to build muscle.
Three ways cardio helps
- 1. Faster recovery
- Hard training damages muscle fibres (hence soreness, or DOMS). Repair depends on getting nutrients in and waste out, and cardio increases blood flow to do both. He does cardio on leg day to cut next-day soreness. Mostly the legs benefit; for the upper body, use a rowing machine or an elliptical with arms.
- 2. Better use of food
- Some people store more fat when they overeat and lose more muscle when they diet, partly down to hormones you can't change much (testosterone, cortisol). Insulin sensitivity you can improve. Being insulin-sensitive helps your muscles take up nutrients during a surplus instead of storing them as fat, and cardio improves it: the more you do, the greater the effect.
- 3. Staying conditioned
- Bulking for months with no cardio means your fitness crashes, so starting a cut becomes a shock. That extra stress can even speed up muscle loss. Keeping some cardio in helps you keep your ability to burn fat and makes the switch to cutting smoother.
Two ways it can hurt
- Eating into your surplus. A normal session burns a few hundred calories, so just eat a bit more. (Light cardio can even boost appetite, useful for "hardgainers".)
- Overtraining. Too much, too intense, especially for the legs, interferes with strength and growth.
The recommendation
- Include cardio while bulking, but cap it at 2–3 sessions a week, 30 minutes max.
- He prefers HIIT, which research suggests preserves muscle better than long steady-state cardio. If it hurts your strength, switch to low-to-moderate sessions.
- Cycling beats running for muscle gain, perhaps because it resembles lifting movements. His leg strength jumped after he switched.
See also
Summary of an article by Mike Matthews (Muscle for Life), with the studies it cites.