Does Cardio Kill Gains? Here's Everything You Need To Know

If you're looking to build your muscles, whether to improve your overall health or achieve a bulky physique, you might've gotten the same advice from the bodybuilders and trainers at the gym: "Don't do cardio because it will kill your gains." This notion spread quickly in the community, considering that not many people like cardio.

With this collective idea in mind, you might be prompted to stick with weight and resistance training while minimizing or even wholly disregarding cardio exercises like walking, running, or elliptical.

You might even join the other people in the fitness community that take this idea to extremes, not using the stairs or refusing to take long walks lest they "burn muscle."

But do cardio workouts hamper muscle growth? Or is that just a belief that holds little truth to it? This article aims to shed light on this issue and help you determine whether you should include cardio in your routine.

How cardio affects muscle gains?

There is some kernel of truth to the saying, “Cardio kills gains.” Cardio exercises, like running or high-intensity interval training (HIIT), can negatively affect your muscle growth since they break down the contractile muscle proteins.

Fasted cardio, in which you wait for your last meal to digest before your cardio routine fully, can quickly deplete the muscle's glycogen levels. This glycogen breakdown causes the body to burn protein or muscle into amino acids, convert them into glucose, and use them as energy. [1]

This conversion makes building up that lost protein difficult, especially when you’re in a fasted state post-workout.

What’s more, cardio may also “interfere with the molecular pathways responsible for adaptations to strength training,” according to Exercise Physiologist Heather Hart in her interview with Live Science. [2]

Hart says combining cardio and strength or resistance training inhibits muscle buildup since it downregulates the mTOR pathway, which is stimulated during anaerobic exercise.

Meanwhile, some studies found that HIIT can interfere with muscle growth, though not for the same reason as fast cardio. [3] The main reason why this particular workout has an impact on muscular development is that it causes more muscle damage and fatigue, which then affects your performance during strength and resistance training.

Running has also been found to significantly affect your body’s ability to gain muscle the way HIIT does; by causing muscle damage and extreme exhaustion that impacts the body’s condition during strength training workouts.

Aerobic exercises can also affect the muscle growth of women, especially if they do so during their menstrual cycle. Women are likely to build up muscle more effectively during their menstrual cycle due to the low hormone levels in the body.

However, doing cardio exercises like brisk walking, jogging, and running while on your period can interfere with the signals responsible for adapting the effects of strength training. [4]

Depleting energy stores is another suspected reason cardio exercises, combined with muscle-building workouts, may inhibit strength or muscular gains. That’s because a person tries to do too much in a single workout session and fails to get adequate rest between routines.

A case for cardio exercises

• Cardio and Muscle Mass Impact: The effect of cardio on muscle mass and strength isn't clear-cut. Studies show mixed results, with some indicating reduced strength and muscle size when combined with strength training, while others show no significant impact. This suggests the effect varies based on individual factors and training specifics​​​​. [5][6]
• Combining Cardio with Lifting: Improperly mixing cardio and weightlifting can significantly impair muscle growth and strength gains. A 2012 meta-analysis indicated muscle growth could reduce by about 31% and strength gains by 18% under such conditions​​.[7]
• Cardio Duration: Longer cardio sessions are linked to more muscle loss. However, muscle and strength decreases are minimal when cardio is limited to less than 20 minutes per day​​.[8]
• Type of Cardio: Lower-intensity cardio, when combined with resistance training, suppresses muscle growth and power more than high-intensity cardio. Limiting lower-intensity cardio is advised for maximizing muscle mass​​. [9]
• Cardio After Strength Training: Doing cardio post strength training is a common recommendation. However, the effectiveness varies based on individual goals, cardio type, and overall training regimen. The key is in the balance and intensity of cardio relative to strength training​​. [10]
• Excessive Cardio's Impact: Too much cardio can hinder muscle growth, even if other training and recovery aspects are managed well. However, "too much" is subjective and varies per individual​​​​. [11][12]
• Generalization on Cardio Impact: Simplifying the impact of cardio on muscle gains can be misleading. The relationship is complex and influenced by factors like cardio type, intensity, training program, and nutrition​​​​​​​. [13][14][15][16]

Why should you still do cardio?

1. Endurance Training and Muscle Building:
   • Balance is Key: Endurance training negatively impacts muscle building only if disproportionate to strength training goals. [17]
   • Beneficial Combination: Properly combining endurance with resistance exercise can enhance muscle growth, though some studies suggest potential interference. [18]
2. Cardiovascular Health and Muscle Recovery:
   • Enhanced Circulation: Cardio improves blood flow, aiding in quicker recovery and reduced muscle soreness.[19]
3. Cardio and Skin Health:
   • Immediate Skin Benefits: Increased blood flow from exercise improves skin appearance and health. [20]
   • Cellular Improvements: Exercise boosts mitochondrial function, essential for skin repair and youthfulness. [21]
   • Stress and Sleep Benefits: Reduced stress and better sleep from exercise indirectly benefit skin health. [22]
   • Exercise Types: Weight, endurance training, and HIIT are effective for skin health. Enjoyable and consistent exercise routines are key. [23]

Benefits of combining cardio and strength workouts

1. Cardio Training Benefits:
   • Improves Endurance and Heart Health: Cardio training enhances endurance, oxygen utilization, and cardiac and respiratory function. It is effective for heart health and helps lower the risk of conditions like heart disease, diabetes, and cancer​​. [24]
2. Strength Training Benefits:
   • Increases Muscle Size and Strength: Strength training boosts muscle size, enhances coordination, and is useful for injury prevention and rehabilitation. It also helps in managing, treating, and preventing various health conditions, including diabetes, hypertension, arthritis, cancer, and depression​​​​. [25] [26]
3. Combining Cardio and Strength Training:
   • Reduces Injury Risk: Incorporating both strength and cardio workouts reduces the risk of injury by providing a break from repetitive cardio movements and strengthening stabilizing muscles​​. [27]
   • Balance is Essential: The American College of Sports Medicine suggests a mix of two-thirds cardio workouts to one-third strength training, although the exact ratio can vary based on personal preferences and fitness goals​​.[28]
4. Fat Loss and Metabolic Effects:
   • Different Fat-Burning Mechanisms: Cardio generally burns more calories during the workout, while strength training, particularly high intensity, can elevate metabolism long after the session ends. This prolonged metabolic boost is due to the afterburn effect known as excess post-exercise oxygen consumption (EPOC)​​. [29]
   • Sustainable Fat Loss: For sustainable fat loss, a combination of cardio and strength training is recommended. This approach helps burn more calories both during cardio sessions and post strength training due to EPOC​​. [30]
5. Muscle Mass and Long-Term Fat Loss:
   • Increased Caloric Burn: Muscle mass is metabolically active and burns more calories at rest compared to body fat. Building lean muscle through strength training can thus enhance long-term fat loss, especially in cardio-dominant routines that haven't yet achieved desired fat loss goals​​. [31]

Integrating cardio into strength training

If you’re primarily into strength training, it can be difficult to overhaul your routine and incorporate cardio exercises into your sessions. Here are some things you can do to make this process easier:

Pace yourself

• Avoiding Overload: It's indeed important not to overdo cardio, especially if you're primarily focused on muscle gains. Doing too much cardio can interfere with muscle building efforts.
• Balancing Cardio and Strength Training: Alternating between cardio and strength training, rather than doing them back-to-back on the same day, can be beneficial. This approach helps in avoiding fatigue and ensures that each type of workout is effective​​.[32]

Organize your routine

To organize your workout routine effectively for muscle growth, while integrating both strength training and cardio, consider these guidelines:

1. Strength Training First: Prioritize strength training before cardio in the same session. This approach ensures maximum energy and performance for resistance exercises​​.[33]
2. Separate Sessions: If planning moderate to high-intensity cardio (longer than 30 minutes), it's beneficial to perform cardio and strength workouts separately. Ideally, space them at least 6 hours apart or do cardio on a different day​​​​. [34] [35]
3. Limit Cardio Duration: To focus on muscle building, limit your cardio sessions. Aim for less than three times per week and keep each session under 20-30 minutes​​. [36]

Eat enough calories

For building muscle and endurance, it's vital to consume enough calories to fuel your workouts and aid recovery:

• Adequate Caloric Intake: Ensuring a sufficient calorie intake is crucial for providing the energy needed for both strength training and cardio sessions, as well as for muscle recovery. This is especially important if your routine includes both types of workouts​​.[37]
• Balanced Macronutrient Distribution: Include a mix of carbohydrates, proteins, and fats in your diet. Carbs provide immediate energy, proteins aid in muscle repair and growth, and fats offer sustained energy, especially important for longer or low-intensity cardio sessions.[38]

Cardio activities to include in strength training

There are many fun cardio exercises that you can incorporate into your resistance training to help improve your endurance and build up your strength. Here are some activities that will get your heart pumping without interfering with the effects of your strength training.

1. Burpees: Enhance muscle building and fat burning through high-intensity, full-body engagement.
2. Jogging/Running: Effective for leg muscle development, helps prevent muscle deterioration, and enhances muscle definition, especially in legs.
3. Jump Rope: A full-body workout improving coordination, targeting lower and upper body muscles.
4. Jumping Jacks: Builds leg strength, improves performance in strength exercises like squats and deadlifts.
5. Box Jumps: Focus on leg strength, working out lower body muscles, and improving stability and balance.

Conclusion

A long-standing notion in the fitness and weight-lifting community is that cardio should not be part of a body-building routine since it burns away muscle tissues.

It’s an understandable concern, considering aerobic training does affect muscle growth. However, it can also harm those who wish to stay on top of their cardiovascular health while also reaching for gains.

Finally, cardio and strength training are essential to your fitness routine. Instead of sacrificing one for the other, it’s best to create a balanced composition program that complements both exercises.

Answers And Questions

Guest Author

Myrtle Bautista

Myrtle is a journalism major, a social media marketer and is now exploring freelance writing. She's fond of anything related to health and wellness, and when she's not writing, you'll find her doing long-distance cycling, ultramarathons, hiking, or in a local cafe enjoying a good cold brew.

Contact her at myrtlebautista.writes@gmail.com.