3. Discussion
This study consisted of a rigorous randomized, double-blind, sham-controlled, parallel-design trial that evaluated the effects of the IMT at different exercise intensities on chronic systemic metabolic adaptations in apparently healthy recreational male cyclists based on Interestingly, IMT promoted several changes in lipid metabolism, evidenced by decreased levels of serum fatty acids. Serum fatty acids are derived almost entirely from adipose tissue and play an important role in providing a source of energy for muscle, particularly in the fasting state, its reduced levels likely being attributed to the increased demand for energy of the respiratory muscle after IMT [Other lipids were also altered by IMT. We observed an increase in serum levels of LysoPC (14:0/0:0), a glycerophospholipid that plays a number of protective or anti-inflammatory effects [Considering the serum ketone bodies, IMT promoted an increase in serum levels of 3-Hydroxybutyrate and Acetone but a decrease in Acetoacetate levels. 3-Hydroxybutyrate and Acetoacetate are produced in hepatic mitochondria in conditions of reduced carbohydrate availability (i.e., during fasting and starvation) and serve as an alternative fuel source for peripheral tissues including skeletal muscle [Simultaneously, alterations to amino acid metabolism were observed after IMT, mainly for essential amino acids involved in the translational process through the aminoacyl-tRNA biosynthesis pathway. Although the effects of IMT on this pathway have not been shown in the literature, previous studies demonstrated a positive relationship between the regulation of aminoacyl-tRNA biosynthesis pathway and gains in cardiorespiratory fitness after endurance training programs [IMT also promoted changes in intermediate metabolites from the Citrate cycle, such as Citrate and Succinate. Citrate can be transported out of the mitochondria and into the cytoplasm, then undergoing breakdown into acetyl-CoA for fatty acid synthesis and oxaloacetate [Finally, some strengths and limitations should be further discussed in the present study. Even though the study was sufficiently designed to detect significant main effects and interactions of IMT on the serum metabolic profile, it was based on a small number of apparently healthy recreational male cyclists. Therefore, extrapolation of our findings to other populations should be performed with caution. On the other hand, the current study is comparable in sample size to previous studies related to this topic [