Cardio training is very useful. They improve heart health, reduce the risk of cardiovascular disease (CVD), help you lose extra pounds and get rid of dangerous visceral fat.
Many athletes and amateurs combine cardio and strength training in their program, and this is great: such a mix helps to lose weight without losing muscle mass and reduces the risk of cardiovascular diseases. span> even more than aerobic exercise. But such a system has its downside, which is very significant for power sports athletes and bodybuilders.
How cardio training affects strength and muscle growth
In a 1980 study, participants were divided into three groups: in the first group, people exercised with weights five days a week (C), in the second group they did cardio six days a week (K), and in the third group they did both of these activities (C + K) ).
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.
Further studies confirmed this effect: adding strength cardio sessions inhibits the increase in strength and muscle size.
Subsequently, the term "concurrent training" was formed in the scientific community, and the decrease in the performance of such classes was called the interference effect.
Why does the interference effect occur?
Scientists still don't know exactly how cardio interferes with muscle growth. Especially since this is not always the case: in some studies, competitive training did not reduce strength gains. There are several theories about this. Some touch on the mechanisms inside cells, others on the effect of exercise on the nervous system.
Adaptations interfere with each other
Scientists have suggested that when the body adapts differently to strength and cardio loads, certain mechanisms can interfere with each other. There is a theory that the barrier effect occurs due to the sirtuin protein.
It is produced in response to energy-consuming aerobic exercise and can inhibit the activity of the mTOR target of rapamycin, a complex that signals to increase protein synthesis after strength training.
Another possible cause is stress in the endoplasmic reticulum, an important cell organelle. When its functioning is disturbed, it triggers a specific response to misfolding (unfolded protein response), which reduces protein synthesis and thus prevents muscle hypertrophy. And such stress can occur, among other things, after energy-consuming exercises such as cardio sessions.
The central nervous system (CNS) gets tired
This is another explanation of the hindrance effect based on the characteristics of body fatigue. In general, fatigue from exercises is divided into two types:
- Peripheral is when the brain sends signals to the muscle fibers to contract, but some part of them cannot do so due to fatigue. As a result, there are more signals 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 a load as a result, and then increase in size.
- Central is when the brain is unable to send enough signals, so most fibers are not involved. This has a negative effect on the performance of strength training, as the muscles do not receive enough load, fatigue and growth do not occur.
Endurance exercise, especially prolonged exercise, fatigues the central nervous system, but this reduces the ability to exert force.
If you do a cardio session for 30-40 minutes before strength training, the central nervous system will get tired and will not be able to activate muscle fibers as well as if you were training with fresh strength.
This is confirmed by research. If you put strength training before cardio, strength increases almost twice as fast as if you do it in the reverse order. In addition, when strength training is performed before cardio, the interference effect is negligible even in highly trained individuals.
How to do cardio so that it does not interfere with growing muscles
Cardio can be deleted from your program only if you want to turn into a mountain of muscles in the shortest possible time. If endurance is important for your sport or you want not only an impressive figure, but also a healthy heart - continue aerobic training, but consider a few points.
Do aerobic training after strength training
This does not apply to 5-10 minutes of easy jogging or jumping rope in the warm-up. Short 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 it is better to postpone long cardio sessions of 30 minutes or more. Do them a few hours after strenuous exercise, or on days off from the gym.
The more time that passes 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
Although high-intensity interval training can feel difficult, short bursts of intense exercise are much less taxing on the central nervous system than long, leisurely cardio sessions. At the same time, intense intervals develop endurance, help you lose weight and improve the health of the cardiovascular system as much or even better than cardio.
Replace long runs with short high-intensity interval training sessions of 8-24 minutes: this will increase aerobic capacity and will not prevent you from growing muscles.
Tell us how you combine strength and cardio in your program.
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