Discussion
muscle mass, PGC-1α, sarcopenia, Skeletal muscle, skeletal muscle hypertrophy
SKELETAL MUSCLE ATROPHY, SARCOPENIA, CONTRACTION
Resistance training has been reported as the most effective approach to significantly improve muscle mass, size, and strength, as well as physical performance, in any type of individual [Our previous study, which employed a randomized control trial identical to the one utilized in this study, indicated that resistance training increases muscular fitness and improves body composition on untrained young males. Although the body composition indices did not exhibit significant alterations, the results of the current study regarding the reduction in the percentage of body fat and the increase in lean body mass are similar to the results of our previous study [Our study revealed no difference in muscular fitness following the training program between the two groups. Participants in both groups exhibited comparable upper and lower limb 1RM strength, muscular endurance, and power under similar training volume. These findings are consistent with our previous hypothesis that training under unstable conditions results in neuromuscular adaptations similar to those induced by stable conditions. Our data is not without support; Maté-Muñoz [AMPK, a highly conserved regulator of cellular energy metabolism, plays a crucial role in the regulation of cell growth and the maintenance of the body’s energy homeostasis. Since AMPK can be activated by alterations in the AMP/ATP ratio during exercise [Nonetheless, the potential reasons for the lack of a significant increase in serum levels of AMPK following FRT may be as follows: first, FRT may not increase the AMP/ATP ratio; second, low-intensity FRT only engages a portion of the muscle fibers exhibiting high AMPK activity, whereas AMPK activity in other portions of the engaged muscle fibers remains unchanged, resulting in no significant change in the activity of the entire muscle [In this study, we investigated the effect of resistance training on serum levels of PGC-1α. The results indicated a significant increase in serum levels of PGC-1α, which is a key regulator of mitochondrial biogenesis, following six weeks of TRT and FRT. To the best of our knowledge, no study has compared the effects of various models or intensities of resistance training on serum levels of PGC-1α. Our findings are consistent with those of one study, which was conducted by Hooshmand-Moghadam et al. [In this study, serum levels of irisin were positively correlated with those of PGC-1α in both groups, indicating that an increase in the serum levels of irisin is accompanied by an increase in PGC-1α expression following acute training and six weeks of training. This suggests that the regulation of irisin in the blood of humans involves its hydrolysis and cleavage from FNDC5 by proteolytic enzymes and its subsequent release into the bloodstream [Skeletal muscle has been identified as an endocrine organ that regulates several physiological and metabolic pathways in response to muscle contraction. Certain myokines, such as IGF-1 and MSTN, may be involved in inducing skeletal muscle hypertrophy, enhancing strength, and suppressing skeletal muscle atrophy. Recent studies showed that an increase in circulating irisin is strongly correlated with an increase in IGF-1 levels and a decrease in MSTN levels [Our study has several limitations. First, given to the small sample size and the involvement of only young males as participants might limit the applicability of our findings to a wider population. Future studies should delve into the effects of TRT and FRT on large sample, including female participants and individuals with sarcopenia. Additionally, the lack of daily food intake records of these participants is a shortcoming in this study. Therefore, this should be considered more concretely and carefully when interpreted the results. Secondly, owing to the participants’ concerns regarding muscle biopsy techniques, we only analyzed blood samples. Muscle biopsy techniques are essential for accurately measuring protein and mRNA levels of AMPK and PGC-1α through western blotting and polymerase chain reaction analysis, which could further support our results at molecular level. Furthermore, this is the first study to compare the influence of resistance training of varying intensities on the regulatory factors associated with mitochondrial synthesis in the skeletal muscle of humans. Although our study did not reveal any differences in the AMPK/PGC-1α/irisin pathway across resistance training protocols of varying intensities, it suggests that resistance training may mitigate muscle function decline by activating the AMPK/PGC-1α/irisin pathway.