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Strength training regimen, hormones and muscle growth

The most effective way to increase the size of skeletal muscles is considered to be volumetric strength training of medium or high intensity, in which each exercise is repeated 8-12 times, and the pauses between sets are short, 1-2 minutes. Justifying this method, experts point out that after a workout carried out in this mode, the concentration of anabolic hormones in the circulating blood increases to the maximum. Anabolic hormones trigger a cascade of intracellular biochemical reactions that enhance muscle growth. 

However, the validity of this concept has been questionable in recent years. To affect the growth of skeletal muscle, hormones must interact with the corresponding receptors in muscle fibers. Meanwhile, according to some reports, when training with such a load and intensity, the number of receptors for anabolic hormones decreases. In addition, exercise-induced increases in circulating anabolic hormones – testosterone and insulin-like growth factor-1 (IGF-1) – are approximately the same for different training regimens. There is also evidence that skeletal muscle hypertrophy can be achieved without significant increases in testosterone, growth hormone, cortisol, or IGF-1. Observation of people who do strength training does not allow us to conclude that

There is little and conflicting data on how exercise affects anabolic hormone levels and how hormones affect muscle growth. These contradictions can be caused by the fact that different researchers use different methods of data analysis. American specialists, led by Assistant Professor of Kennesaw University Gerald Mangin, joined in the study of the problem. They showed that regardless of the training regimen, muscle growth occurs mainly under the influence of testosterone, and also depends on the initial muscle volume .

Who trained and how

The study involved men who had been involved in strength training for at least two years. To begin with, they all went through a two-week preparatory training consisting of six workouts: Monday, Tuesday, Thursday and Friday of the first week, Monday and Tuesday of the second week. During training, participants performed upper and lower body exercises, a total of six, each exercise consisted of four sets of 6-8 repetitions with a load of 80-85% maximum repetition with 1-2 minute breaks. The purpose of the training was to familiarize all participants with the exercises to be performed, to check the technique and to make sure that everyone is at about the same level.

The participants were then randomly divided into two groups of 13 people. They trained for eight weeks, during which time they had to conduct at least 28 workouts, 4 per week. Each training session consisted of six exercises performed under the supervision of certified professionals. Diet changes were monitored every three days (participants kept diaries). Immediately after training, each participant received a serving of chocolate milk (approximately 235 ml, 170 calories, 2.5 g fat, 29 g carbohydrates, 9 g protein) or Lactaid® (150 calories, 2.5 g fat, 24 g carbohydrates, 8 g protein).

One group, labeled VOL (for volume), performed each exercise four times for 10-12 repetitions, ~ 70% of maximum repetition, with 1 minute rest between sets. The participants in the second group, INT, trained at high intensity: 4 sets of 3-5 reps, ~ 90% maximum repetition, 3 minutes rest between sets.

The groups turned out to be quite uniform: the average age was about 24 years, the weight was 89 – 91 kg, only the height was noticeably different: in VOL 169.5 ± 30.1 cm, in INT – 180.1 ± 5.8 cm.

What was measured and how

At the end of the preparatory period and after 8 weeks of training, the thickness and cross-sectional area of ​​the vastus lateralis muscle and the rectus femoris muscle were determined in the subjects. All muscle measurements were performed by non-invasive ultrasonography.

On the first days of the 1st and 8th weeks of training, blood samples were taken from the subjects from the superficial veins of the forearm. We did it four times. The first time – before training, 3 hours after eating, then the subjects received a portion of chocolate milk or Lactaid® and went to train. The next sample was taken immediately after training, after which the participants drank their chocolate milk again. The third and fourth samples were taken 30 and 60 minutes after training. The subjects spent this time lying on their backs. In all blood samples, the content of anabolic hormones was determined: testosterone, cortisol, IGF-1, insulin and growth hormone.

The scientists analyzed the data obtained using the method of partial least squares, which, unlike traditional statistical measurements, allows you to establish relationships between several factors that change over time. In this case, the researchers calculated the relationship between the initial and final muscle size and the level of anabolic hormones that are released during training.

What the analysis showed

The average training load in the VOL group was 28.4% higher than in the INT group, but the researchers did not find differences between groups in the relative calorie and protein intake or in the increase in the size of the vastus or rectus femoris. Instead, they noticed significant differences in endocrine response. In the first week, post-workout growth hormone and cortisol levels in the VOL group were 42.4% and 29.22% higher, respectively; no difference was found for other hormones. At the 8th week of training, the difference remained only for cortisol, its level in the VOL group was 21.6% higher.

Muscle thickness and cross-sectional area after a series of strength training depended on what they were before the start of 8 weeks of training, as well as on the overall endocrine response and on the level of testosterone in the circulating blood. Growth hormone, cortisol, IGF-1, and insulin alone did not affect muscle size, although they were actively synthesized after strength training. These patterns are true for both groups.

The mechanism of the specific action of testosterone is not entirely clear. The researchers refer to literature data, according to which the effect of testosterone in this case may not depend on the presence of specific receptors for it. Testosterone increases muscle fiber calcium concentration, which temporarily increases maximum muscle strength. As a result, the muscles are able to handle more loads, train at higher intensity, and increase size effectively. In any case, testosterone, regardless of the mechanism of action, does indeed contribute to muscle hypertrophy.

The role of other hormones, taken together is less than that of testosterone, their synthesis explains only 42.6% of the increase in muscle volume. The effect of individual hormones on muscle hypertrophy is not noticeable. Growth hormone can interfere with IGF-1 secretion, but circulating IGF-1 levels are not associated with muscle hypertrophy. It is possible that this hormone affects muscle growth after it enters the cells, there is such information in the literature, but the researchers have not tested this effect. It is also known that temporary fluctuations in cortisol concentration do not affect muscle protein synthesis. Insulin regulates the same protein synthesis pathways as testosterone and IGF-1, but its effect immediately post-workout depends on food intake. According to the researchers, the existence of an ideal post-workout hormonal background for muscle growth cannot be ruled out. however, the model they created allows to isolate only the effect of testosterone. This result may be due to the fact that blood was taken for analysis only in the first and eighth weeks. Perhaps this circumstance influenced the sensitivity of the model, and the analysis of a larger number of samples will reveal the role of each of the hormones.