Is cardio really getting in the way of muscle building and how to avoid it?

Many athletes and hobbyists combine cardio and strength training in their program, and this is great: it helps you lose weight without losing muscle mass and reduces the risk of CVD even more than just aerobic exercise. But such a system also has its disadvantage, which is very significant for strength athletes and bodybuilders.

How Cardio Affects Strength and Muscle Growth

In a 1980 study, participants were divided into three groups: in the first, people did weights five days a week (C), in the second, they did cardio six days a week (C), and in the third, they did both (C + C).).

The K-group did not increase strength at all - only endurance. In groups C and C + K, strength indicators initially grew equally well, but in the ninth week, C + K began to lag behind, and by the end of the experiment, the strength training group became the absolute leader, despite the same volume of loads.

Subsequent studies have confirmed this effect: adding cardio sessions to strength training inhibits increases in muscle strength and size.

Over time, the term "concurrent training" was formed in the scientific community, and the decrease in performance from such exercises was called the interference effect.

Why does the interference effect occur?

Scientists still don't know exactly how cardio gets in the way of muscle growth. Moreover, this does not always happen: in some studies, competing training did not reduce the gain in strength. There are several theories about this. Some affect the mechanisms inside cells, others - the effect of exercise on the nervous system.

Adaptations interfere with each other

Scientists have suggested that since the body adapts differently to strength and cardio loads, certain mechanisms can interfere with each other. There is a theory that the interference effect is due to the protein sirtuin-1.

It is released in response to energy-intensive aerobic exercise and can inhibit the mTOR target of rapamycin, a complex that signals increased protein synthesis following strength training.

Another possible cause is stress in the endoplasmic reticulum, an important cell organelle. When it is dysfunctional, it triggers a specific unfolded protein response that decreases protein synthesis and thus interferes with muscle hypertrophy. And such stress can occur, among other things, after energy-intensive exercises like cardio sessions.

The central nervous system (CNS) gets tired

This is another explanation of the interference effect, based on the characteristics of the body's fatigue. In general, exercise fatigue is divided into two types:

Peripheral- this is when the brain sends signals to muscle fibers to contract, but some part of them cannot do this due to fatigue. As a result, the signals become larger and the body has to use fibers that did not work before. This is useful for hypertrophy: the more signals are sent to the muscle, the more fibers will receive the load as a result, and then increase in size.
Central- this is when the brain cannot send enough signals, so most of the fibers are not used. This negatively affects the performance of strength training, since the muscles do not receive enough stress, fatigue and growth do not occur.

Endurance exercise, especially long-term exercise, causes central nervous system fatigue, which reduces the ability to generate strength.

If you do a cardio session for 30-40 minutes before strength training, the central nervous system will fatigue and will not be able to activate muscle fibers as well as if you were training with fresh strength.

Research confirms this. When you put strength training before cardio, strength grows almost twice as fast as in the reverse order of training. In addition, when strength training is done before cardio, the interference effect is negligible even in highly trained people.

How to do cardio without getting in the way of building muscle

Cardio can only be removed from your program if you want to turn into a mountain of muscles in no time. If endurance is important for your sport, or if you want not only an impressive figure, but also a healthy heart, continue aerobic training, but keep a few points in mind.

Do an aerobic workout after strength

This does not apply to 5-10 minutes of light jogging or jumping rope to warm up. Brief aerobic activity warms up the muscles well and does not tire the central nervous system, so you can leave the usual warm-up unchanged. But long cardio sessions of 30 minutes or more are better to be rescheduled. Perform them either a few hours after the strength load, or on days free from the gym.

The more time elapses between your cardio session and strength training, the more chances that the central nervous system will have time to recover and you will be able to fully load the muscles.

Try high-intensity interval training (HIIT)

Despite the fact that HIIT can be difficult to perceive, short, intense exercise is much less stressful for the central nervous system than long, calm cardio sessions. At the same time, intense intervals develop endurance, help to lose weight and improve cardiovascular health as well or better than cardio.

Replace long runs with short HIIT sessions of 8-24 minutes: this will increase your aerobic capacity and won't stop you from building muscle.