As one study reported, the type of resistance training—high load with fewer reps or low load with more reps—makes no difference in promoting muscle growth.
The study lasted 8 weeks and involved 18 participants in 2 different training protocols. 1 group performed high-load exercises with fewer repetitions, while the other performed low-load exercises with more repetitions. Muscle mass was measured in the first and last training session.
No differences were seen in metabolic stress or muscle growth when the 2 groups were compared by measuring compounds released into the bloodstream from exercise.
Each participant lifted up to 80% of their body weight in the high-load group. The limit was 30% in the low-load group, but the exercises were repeated until their muscles could no longer lift the weight.
Resistance training promotes muscle growth, but it’s still unclear whether the key to muscle growth is the load or the number of repetitions. The study supports the idea that both types have the same impact.
The researchers also demonstrated that muscle activation occurs differently in each type, even though the metabolic stress is identical and the impact on hypertrophy is also subsequently the same.
In the evaluations performed before and after the 1st and last exercise session, blood samples were taken before the start of the exercises, 5 minutes after the end of the exercises and one hour after the end of the exercises. A metabolomics assay was used to detect metabolites in blood samples.
Surface electromyography has been used to measure muscle activation, in which electrodes monitor the electrical activity of muscles in real time.
A stronger metabolic stress response was expected in the low-load group because, in theory, this additional stress should have canceled out the reduced level of muscle activation, but it did not.
The analysis revealed that although the level of muscle activation was higher in the high-load group, metabolic stress was comparable in both groups. The similarities in metabolic response indicate that both types of training could induce hypertrophy by acting on the same pathways.
Changes in 50 blood metabolites were found in response to muscle activation during both types of training. However, not many of these metabolites differed between the 2 groups and 6 of these metabolites were analysed: phosphocreatine, creatine, carnitine, acetoacetate, 3-hydroxyisovalerate and asparagine.
Although no differences in overall metabolic response were found, there were some metabolite correlations with muscle hypertrophy in both groups. Some of these correlations could be related to the characteristics of type 1 or 2 muscle fibers activated by exercise and also by the metabolic demands of the study training protocol.
Some of the metabolites examined are produced by anaerobic energy systems and are the result of muscle glycolysis (breakdown of glucose) or phosphocreatine and the breakdown of creatine, which provides sufficient energy to maintain exercise intensity for several seconds.
Acetoacetate and asparagine are mainly connected to the Krebs cycle, which uses oxygen and nutrients including carbohydrates, proteins and fats to produce energy for muscles and lasts much longer.
Phosphocreatine and creatine expression were predicted to have a higher response to anaerobic exercise. The metabolism that takes part in it is typical of type 2 muscle fiber, called ‘fast twitch’ fiber, while asparagine, for example, could be present when the cellular respiration phase called Krebs cycle is more activated, and is type 1 characteristic of the muscle fiber.
Type 2 muscle fiber activation predominates due to the higher load in high-load training. These muscle fibers are low in oxidative activity but high in glycolytic activity and may be more sensitive to hypertrophy than type 1 fibers. However, low-load training with more repetitions activates type 1 fibers more preferentially, which have low glycolytic capacity and high oxidative capacity and are very resistant to fatigue.
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