For those whose primary goal is to build muscle (or increase strength), aerobic exercise can be a source of anxiety and even fear. They worry that cardio might hinder their progress and diminish their gains.
However, just as weight loss can't be simply solved by "eating less and exercising more," the impact of aerobic exercise on muscle growth (or strength) also depends on many factors.
Aerobic exercise can indeed inhibit muscle growth in various ways.
Firstly, doing too much (or high-intensity) cardio will inevitably accumulate fatigue, which can affect your performance in weight training. Weaker performance means less stimulation to the target muscles, and consequently, poorer muscle-building results.
Of course, this refers to excessive (or high-intensity) aerobic exercise. What does that mean? Let's say you do high-intensity interval training (HIIT) on a spin bike before leg day; you'll likely feel drained during your workout. Due to the residual fatigue from HIIT, you won't be able to lift as much weight or perform as many repetitions.
As a result, the intensity of the growth signal sent to the muscles weakens, which means slower muscle growth.
Aerobic exercise can also affect your ability to recover from weight training.
Suppose you have weight training sessions on days 1, 3, and 5. Then, you schedule a lot of aerobic exercises on days 2, 4, and 6. In that case, you're reducing the opportunities for your muscles to recover and grow.
Additionally, aerobic exercise can disrupt some molecular signaling pathways related to muscle hypertrophy, meaning that the "grow bigger" signals sent to muscle fibers in the hours or days after training will be weaker, slowing the rate of muscle protein synthesis.
However, please note the adjective before "aerobic exercise" in the previous paragraph. Don't generalize and say that doing cardio hinders muscle growth. It might impede your progress, but it might not damage your gains, as the extent to which aerobic exercise interferes with muscle hypertrophy depends on many factors, including:
- The time interval between aerobic and weight training
- The type of aerobic exercise (e.g., jogging or cycling)
- The duration of the aerobic exercise
- The order of training completion
- The frequency of aerobic exercise
- The intensity of aerobic exercise
In fact, if arranged properly, aerobic exercise might help rather than harm your gains.
Firstly, certain types of aerobic exercise can aid recovery by promoting blood flow to muscles without causing further damage. For example, after completing a high-intensity workout at the gym, riding a bike for 20-30 minutes at a low to moderate intensity daily can usually reduce post-exercise muscle soreness and may even speed up the repair of muscle damage.
Some interesting studies have shown that differences in capillary density can partly explain why some people grow faster than others. In a review, researchers reported that after 6 months of resistance training, men with higher capillary density gained more muscle mass than those with lower capillary density.
One of the best ways to improve capillary density is through some aerobic exercise. Additionally, using low-intensity steady-state aerobic exercise as part of the warm-up for weight training might enhance your performance in the gym.
This is because warmed-up muscles tend to perform better and have a stronger recovery capacity from injuries compared to cold muscles.
However, the situation is different for higher intensity or longer duration aerobic exercises. In a study, weight training performance was adversely affected after aerobic exercise, with high-intensity interval training causing the greatest decline in performance. Over time, this decline in performance is likely to mean slower gains in strength and size.
So, how much aerobic exercise is needed in the process of building muscle? There are no strict rules.
No matter how much aerobic exercise you do and when you do it, there's a lot of individualization. Some high-level professional athletes maintain at least one hour of steady-state aerobic exercise every morning, but some might only do 3-4 hours of aerobic exercise per week.
You need to explore based on your own situation and goals, but the following general guidelines can help minimize the interference of aerobic exercise on muscle growth.
- Limit the time you spend on moderate to high-intensity aerobic exercise to within 2 hours per week, and change the rest of your aerobic exercise to low-intensity steady-state aerobic exercise.
- Avoid any vigorous aerobic exercise before weight training. It's best to do aerobic exercise after resistance training is finished, or separate them on the same day, or do them on a separate day.
- Incorporate some light aerobic exercise as part of your general warm-up, such as 10 minutes on an elliptical machine, with a slight incline on the treadmill, and walk at a moderate speed for 5 minutes.
- If muscle growth is your primary goal, try to do more low-intensity aerobic exercises, such as cycling, climbing stairs, or using an elliptical machine, rather than running.
