Should You Do Cardio While Building Muscle?

The Fear of Cardio

Walk into any bodybuilding forum and you'll find people terrified of cardio. "It kills gains." "It burns muscle." "Stay off the treadmill."

Is this fear justified? Let's look at the evidence.

What the Research Says

The "interference effect"—the idea that cardio blunts muscle growth—is real, but massively overstated in fitness culture.

A 2012 meta-analysis found that combining cardio and strength training does slightly reduce strength and hypertrophy gains compared to strength training alone. But the effect size was small, and depends heavily on how you do your cardio.

When Cardio Hurts Gains

High Volume + Same Muscle Groups

Running 10 miles and then trying to grow your legs is counterproductive. The fatigue accumulates, recovery suffers, and adaptation is compromised.

Pre-Workout Cardio

Doing intensive cardio immediately before lifting fatigues you and reduces performance. You'll lift less weight and accumulate less volume.

Inadequate Nutrition

If you're in a caloric deficit AND doing lots of cardio, you're creating a larger deficit. Your body may catabolize muscle for energy.

When Cardio Helps Gains

Improved Work Capacity

Better cardiovascular conditioning means faster recovery between sets and better endurance during high-volume sessions.

Health Benefits

Strong heart, healthy blood pressure, better insulin sensitivity—these support your training and longevity in the gym.

Active Recovery

Light cardio increases blood flow, which can speed recovery without adding significant stress.

Body Composition

Cardio makes it easier to maintain a lean physique without extreme dietary restriction.

How to Program Cardio for Lifters

Recommended Approach

• 2-3 sessions per week of low-to-moderate intensity cardio
• 20-30 minutes per session
• Separate from lifting (different day or 6+ hours apart)
• Low-impact options preferred (cycling, rowing, walking on incline)

What to Avoid

• High-intensity running before leg day
• Excessive HIIT (more than 1-2 sessions per week)
• Cardio immediately before or after heavy lifting

The Bottom Line

Cardio won't kill your gains if programmed intelligently. A few moderate sessions per week will improve your health, work capacity, and body composition without meaningfully impacting muscle growth.

Don't fear the cardio. Just do it smart.