Does cardio negatively affect muscle growth?

Yes and no. This discussion largely comes down to muscle fibers and the demand placed upon them by the type of training a person is doing. What is the stimulus? And how will the body adapt?

First and foremost, the body is not a robot. We don’t use energy systems like on/off switches. The same applies to muscle fibers. If you want to gain muscle mass, size, or strength, you’ll be after type 2a and 2b muscle fibers. But type 1 are also going to be used in that process. They’re simply smaller in size, don’t produce as much force and are favored in endurance based exercise because they have high oxidative capacity and mitochondrial density.

There is a threshold where cardio, more specifically, endurance, type 1 muscle fiber dominant exercise modalities, will hinder your ability to hold on to muscle mass and/or strength abilities. Which tend to be more type 2a & b dominant tasks.

BUT. But. It’s probably a higher threshold than you think. Crossfit and the UFC have shown us this. These athletes are “hybrid” in a sense. Have high levels of strength and muscle mass but also have very high work capacities. Now, I don’t have EMGs and VO2 max numbers to back that claim. But generally speaking, a larger factor than your actual training methodology might be the determiner in your ability to hold onto muscle mass and performance while also training endurance.

If you can: eat enough fuel (carbs, protein, fat) for both of these modalities and recover adequately from both cardio and lifting, THEN YOU CAN HAVE BOTH GAINS.

Factors will also include your training split (how strength and endurance are scheduled), and which you’re prioritizing if you need to perform strength and endurance in the same session.

• Strength/muscle is the priority? Lift first.
• Conditioning is the priority? Cardio first.

I’ve answered this questions a million times and will likely answer it a million more. This is the fitness industry. I’m happy to help if I can.

Do you find a difference in strength when you add in conditioning? I feel better in my lifts typically. Like I have more gas in the tank.

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