What most promotes muscle mass gain, a weight training workout that values the load or the number of repetitions? According to a study carried out at the State University of Campinas (Unicamp), it doesn't matter.
The researchers followed 18 individuals over eight weeks who underwent different training protocols. Some exercised with a heavier weight and fewer repetitions, while the others did longer sets and with less load. Muscle mass was measured at the first and last exercise session. When the two groups were compared, no difference was observed in terms of mass gain or metabolic stress – measured by the analysis of substances released into the bloodstream after exertion.
In high-load training, participants carried up to 80% of their own weight. In resistance training, with low load, this percentage reached a maximum of 30%, but the repetitions were done until exhaustion (when the muscle no longer responds). The complete data from the research, supported by Fapesp, was published in the journal Metabolites.
“Strength training is a recognized means of promoting muscle growth. However, it is still not completely clear whether it is more efficient to value the load or the number of repetitions to achieve hypertrophy. Our study reinforces the theory that both types of training work in a similar way. Furthermore, we were able to show that muscle activation occurs differently in each training session, but the metabolic stress is the same and, therefore, the hypertrophy result was the same”, explains Renato Barroso, professor at the Faculty of Physical Education at Unicamp.
In the assessments carried out during the first and last weight training session, blood samples were collected at three different times: before training, five minutes after exercise and one hour later. The collected material was subjected to a metabolomic analysis, the objective of which is to identify the set of metabolites (metabolism products) present in the circulation. Muscle activation was measured using an exam called electromyography, carried out with electrodes capable of monitoring the electrical activity of the muscles in real time.
“What was expected was that in the group that trained with low load, metabolic stress responses would be more exacerbated. This is because, in theory, this stress would compensate for the lower muscle activation. However, that is not what we found”, says Barroso.
The analyzes indicate that, although muscle activation was greater in the group that trained with higher loads, metabolic stress was similar in both groups. “This result suggests that, eventually, the two types of training, as they have very similar metabolic responses, can act through the same pathways to induce hypertrophy”, he says.
Variations
The metabolomic analysis detected the variation of 50 metabolites in the blood when muscle activation occurred in both types of training. However, of the 50 metabolites selected, few showed any difference between the groups of volunteers. Of those few, the researchers looked at six (asparagine, 3-hydroxyvalerate, aceto-acetate, carnitine, creatine and phosphocreatine).
Although the researchers found no difference in the overall metabolic response, it was observed that some metabolites correlated with muscle hypertrophy in both training groups. According to the researchers, some of these correlations may be associated with the characteristics of the muscle fibers activated by exercise (type 1 or type 2) and also with the metabolic demand of the training protocols used in the study.
“Some metabolites studied come from anaerobic energy systems, produced by glycolysis [the breakdown of glucose] that occurs in the muscle or by the breakdown of creatine and phosphocreatine – a process that provides enough energy to maintain an exercise intensity of a few seconds. Asparagine and aceto-acetate are more associated with the Krebs cycle, which uses oxygen and nutrients such as fat, protein and carbohydrates to produce energy for the muscle and lasts much longer”, explains Barroso.
Therefore, what is expected is that creatine and phosphocreatine are at their highest expression when using anaerobic metabolism. “This type of metabolism is a characteristic of type 2 fiber, a fast-twitch fiber. While asparagine, for example, could be found when the stage of cellular respiration known as the Krebs cycle is more activated, that is, a characteristic of type 1 muscle fiber”, he explains.
Barroso highlights that, during training sessions that emphasize load, type 2 muscle fibers are activated with greater predominance. “These muscle fibers have low oxidative activity but high glycolytic activity and may be more responsive to hypertrophy compared to type 1 muscle fibers. On the other hand, training that values repetition may preferentially activate type 1 muscle fibers, which have low glycolytic capacity, but high oxidative capacity and are highly resistant to fatigue”, he concludes.
Access the article: Serum Metabolites Associated with Muscle Hypertrophy after 8 Weeks of High- and Low-Load Resistance Training
