How long is the most beneficial interval for muscle building in the training group?

You train in the gym. After a group of exercises, drink water, walk around and play with your mobile phone. Some Laotie will come and say, "Brother, your interval is too long, and your rest is too long to improve your muscle.". When you look at the time, the interval is less than a minute. It seems that trainers in gyms, especially those who focus on bodybuilding, have a obsession with short intervals. They feel that a short rest time leads to a strong sense of muscle congestion, and the muscles also have a "feeling" during exercise. Therefore, it is "likely" that the stimulation of muscles will be better. The "conclusion" of old irons is based on their intuition and feelings. They don't care about the control group or double-blind experiment. The best way for them to persuade others is to show you their pectoral muscles and biceps muscles mixed with a lot of fat after 20 years of training (although they never actively show their legs that can be worn into jeans). But science is not empiricism. If we want to figure out the most beneficial training intervals for muscle building, we should return to principle analysis, empirical research, and data.

People who support training short intervals believe that short intervals can generate greater metabolic stress, and an increase in metabolic stress can further trigger changes in the body's endocrine levels, such as significant secretion of long hormone levels during shorter intervals. Experiments have shown that during bench press training, a 1-minute interval can achieve higher levels of growth hormone than a 3-minute interval, but there is no change in IGF-1 levels (the IGF-1 pathway is an important signaling pathway for muscle synthesis). But the increase in auxin levels is not without cost. Several studies have pointed out that [2], compared to a 2-minute (longer interval), subjects who took a 1-1.5 minute interval had significantly higher cortisol levels within 30 minutes after exercise. Cortisol is a muscle destroyer, which I believe my readers are well aware of. Secondly, shorter intervals can also have a negative impact on testosterone levels. A study has found that if the interval level between groups is less than 1.5 minutes, the serum testosterone response will be significantly limited. Another experiment found that after 85% RM of bench press and squat training using 1-minute, 1.5-minute, and 2-minute intervals, subjects with 1-minute and 1.5-minute intervals showed a decrease in immediate testosterone levels and an increase in cortisol levels, while subjects with 2-minute intervals were not affected.

What is the effect of elevated growth hormone on muscle growth. In fact, from the physiological function of growth hormone, we can know that its main function is to mobilize energy reserves (such as glycogen or fat) to participate in training at a higher proportion. Therefore, growth hormone does not promote synthetic metabolism. In addition, the increase in cortisol (increase in breakdown rate) and the decrease in testosterone (decrease in synthesis rate), combined with many factors, indicate that too short a group interval (less than 1.5 minutes) is harmful to muscle synthesis or muscle hypertrophy itself. How long does that interval of rest last for muscle building? In a randomized controlled experiment, it was found that participants in the 3-minute interval group experienced more muscle growth compared to those in the 1-minute interval group. Although participants in the 1-minute interval group did experience more metabolic stress, higher metabolic stress alone did not lead to muscle growth. In my previous article, I wrote about a training design concept: dividing a training session into three different days to complete (specific details can be found in the original text reading). We can consider this approach as an extreme form of group interval, where the rest between groups is measured in days. However, this approach resulted in more muscle growth for the participants compared to traditional methods. The essence of interval training is the same as rest after exercise, both of which affect the body's recovery situation, and the recovery situation affects the body's external grouping ability (i.e. the total amount of training). The interval is short, the pump sensation is strong, and the congestion is strong, but it will be exhausted after only a few sets; Long intervals may not cause muscle congestion or excitement, but it can still complete a large amount of training, which is beneficial for muscle growth in the medium to long term.

reference material

1、Boroujerdi SS, Rahimi R. Acute GH and IGF-I responses to short vs. long rest period between sets during forced repetitions resistance training system. S Afr J Res Sport Phys Educ Recreat. 2008;30(2):31–8.

2、 Rahimi R, Ghaderi M, Mirzaei B, et al. Effects of very short rest periods on immunoglobulin A and cortisol responses to resistance exercise in men. J Hum Sport Exerc. 2010;5(2):146–57.

3、Rahimi R, Rohani H, Ebrahimi M. Effects of very short rest periods on testosterone to cortisol ratio during heavy resistance exercise in men. Apunt Med l’Esport. 2011;46(171):145–9.

4、Acute and Long-term Responses to Different Rest Intervals in Low-load Resistance Training，Julius Etienne Fink, Brad Jon Schoenfeld, Naoki Kikuchi, Koichi Nakazato