The question “does cardio kill gains?” has stirred debate for years among lifters, bodybuilders, and fitness enthusiasts. Many people fear that adding cardio to a training routine will somehow sabotage hard-earned muscle gains. But what does the science say — and what do experts like Dr. Mike Israetel have to add to the conversation?
The truth is, cardio doesn’t have to be the enemy of muscle growth. In fact, when used strategically, it can enhance overall fitness and even support gains, rather than destroy them.
The Interference Effect: Real, But Manageable
The term “interference effect” describes how concurrent endurance and resistance training may compete for your body’s resources, such as recovery ability and muscle protein synthesis. In poorly structured programs, this can lead to reduced hypertrophy and strength progress.
However, the interference effect is not a universal outcome. According to sports scientists and evidence-based coaches, including Dr. Mike Israetel, the issue isn’t cardio itself — it’s how and when it’s done.
When Cardio Hurts Gains
Cardio can negatively affect muscle growth under these conditions:
- Too much volume or frequency: Long, frequent sessions of high-intensity cardio can overwhelm your recovery systems.
- Poor timing: Doing cardio right before heavy lifting can leave you too fatigued to train effectively.
- Insufficient calories: If you’re not eating enough, cardio increases the calorie deficit, which may lead to muscle breakdown.
- Inadequate rest: Your body needs time to recover from both lifting and cardio. Without it, gains may stall.
How to Do Cardio Without Killing Gains
Here are practical tips to include cardio in your routine while protecting (and possibly enhancing) your muscle-building efforts:
1. Prioritize Strength Training
Lift first when doing both on the same day. Your body is fresh, and you’ll push more weight — crucial for muscle growth.
2. Keep Sessions Moderate
Stick to 2–3 cardio sessions per week, lasting 20–40 minutes. Go for low to moderate intensity, like brisk walking, cycling, or incline treadmill.
3. Separate Your Sessions
For best results, do cardio and weight training on different days. If that’s not possible, leave several hours between them.
4. Eat Enough
Fuel your workouts with sufficient protein and calories. Cardio burns extra energy, so compensate if you’re aiming for muscle growth.
5. Choose Cardio Wisely
Avoid excessive high-intensity interval training (HIIT) if your main goal is mass. While HIIT is time-efficient, it can interfere with strength recovery if overdone.
Why Cardio Can Actually Help
Used correctly, cardio offers several benefits that support muscle-building indirectly:
- Improved work capacity: Better cardio fitness can help you recover faster between sets.
- Enhanced recovery: Light cardio improves blood flow, helping nutrients reach muscles for repair.
- Heart health: A stronger cardiovascular system improves endurance and long-term training potential.
- Fat loss support: Cardio can help you stay lean while building or maintaining muscle.
Final Thoughts: Cardio Isn’t the Enemy
So, does cardio kill gains? No — not when it’s intelligently programmed. The idea that you must avoid all cardio to build muscle is outdated and misleading. Instead of seeing cardio as a threat, think of it as a tool. When used correctly, it complements your training, boosts recovery, and supports long-term health.
The key is balance. Pay attention to your training volume, recovery, and nutrition. Match your cardio to your goals. Whether you’re cutting, bulking, or maintaining, there’s a smart way to include cardio without sacrificing your gains.