Study Finds No Difference in Muscle Growth Between High-Load and Low-Load Resistance Training

A recent study conducted at the State University of Campinas (UNICAMP) in São Paulo, Brazil, has shed light on the question of which type of resistance training promotes greater muscle growth: high load with fewer repetitions or low load with more repetitions. Surprisingly, the study found that it makes no difference.

The eight-week study involved 18 volunteers who were divided into two groups following different training protocols. One group performed high-load (HL) exercises with fewer repetitions, while the other group engaged in low-load (LL) exercises with higher repetitions. Muscle mass was measured before and after the exercise sessions, and an analysis of substances released into the bloodstream during the exercises was conducted to assess metabolic stress. The findings, published in the journal Metabolites, revealed no significant difference in muscle growth or metabolic stress between the two groups.

In the HL group, participants lifted weights up to 80% of their own body weight. In contrast, the LL group lifted weights limited to 30% but repeated the exercises until their muscles reached exhaustion.

Renato Barroso, a professor at UNICAMP’s School of Physical Education, explained, “Resistance training is known to promote muscle growth, but it’s still not completely clear whether the key to muscle hypertrophy is the load or the number of repetitions. Our study supports the theory that both types have the same effect. We also showed that muscle activation occurs in a different manner in each type, although metabolic stress is the same, and the effect on hypertrophy is therefore also the same.”

During the study, blood samples were collected before exercises began, five minutes after exercise completion, and an hour after. Metabolomic analysis, which detects metabolites in the bloodstream, was performed on these samples. Muscle activation was monitored in real-time using surface electromyography, a method that measures electrical activity in the muscles.

Barroso noted that although the HL group demonstrated higher muscle activation, metabolic stress was similar in both groups. He said, “The similarity of the metabolic responses suggests that both types of training may act on the same pathways to induce hypertrophy.”

The metabolomic analysis revealed variations in 50 metabolites in response to muscle activation in both types of training. However, only a few of these metabolites differed between the two groups. The researchers focused on six specific metabolites, including asparagine, 3-hydroxyisovalerate, acetoacetate, carnitine, creatine, and phosphocreatine.

While no significant differences were found in the overall metabolic response, certain metabolites were found to correlate with muscle hypertrophy in both groups. The researchers concluded that these correlations may be associated with the characteristics of the muscle fibers activated during exercise (type 1 or type 2) and the metabolic demands of the training protocols.

Barroso explained, “Some of the metabolites studied come from anaerobic energy systems and are produced by glycolysis in the muscles or the breakdown of creatine and phosphocreatine, which supplies sufficient energy to maintain exercise intensity for a few seconds. Asparagine and acetoacetate are associated mainly with the Krebs cycle, which uses oxygen and nutrients to produce energy for the muscles over a more extended period.”

Higher expression of creatine and phosphocreatine was expected in response to anaerobic exercise, which primarily activates type 2 muscle fibers. On the other hand, LL training, with its greater number of repetitions, preferentially activates type 1 fibers, which are highly fatigue-resistant and have high oxidative capacity.

The study’s findings provide valuable insights into resistance training and suggest that both high-load and low-load exercises yield similar results in terms of muscle growth and metabolic stress.

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