4. Discussion
incongruity, HIT
Our purpose was to examine the substrate oxidation rates of reproductive-age eumenorrheic women by indirect calorimetry during SWRE at two hormonally distinctive menstrual cycle phases, pre- and post-HIT. The present substrate metabolism finding indicated a greater dependency upon lipid versus carbohydrate in the menstrual cycle luteal phase compared to the follicular phase in pre-intervention. This finding agrees with other studies that measured exercise RER at the low and moderate intensities of maximal oxygen consumption (VOHackney et al. reported greater LT lipid oxidation only when exercise was performed at 35–60% of the VODuring FL there is a high concentration of 17β-estradiol, progressive increase of estrogen, and absence of progesterone, which favors the absorption of glucose by the muscle and its oxidation, reducing LIPox and protein oxidation [When the reactions of these hormones to different exercise intensities were studied, variations in substrate oxidation rates were mentioned, in which low rates of CHOox and high rates of LIPox were found in the LT in low and moderate-intensity exercises [In contrast, other studies have found greater carbohydrate oxidation and lower lipid oxidation in LT compared to FL during the menstrual cycle with exercise intensity of 45% [For Vaiksaar et al. [The present study’s results show that eight HIT sessions promoted beneficial effects for other parameters, such as Vpeak in FL. Data that corroborate those presented by Gibala et al. [According to Aparecido et al. [The comparison between groups showed significant differences in relative energy derived from CHOox pre- and post-training of −61.4% and −59.3%, respectively, and LIPox pre- and post-training of 27.5% and 34.4%, respectively. The relative energy derived from CHOox after the training period was 18.9% and 25.5% higher for FPG and LPG, respectively; consequently, the relative energy derived from LIPox after the training period was 8,45% and 3.46% lower for FL and LT, respectively. The greater sensitivity of alpha- and beta-adrenergic receptors, with increased glucose uptake, greater glycolytic enzyme activation, and modulation of substrate oxidation due to moderate-to-high strength or resistance exercise can explain this phenomenon [This discrepancy in the results of the studies reinforces that the impact of HIT on women of reproductive age is still controversial. This incongruity can be justified by the wide variety of HIT protocols applied or even by the inherent characteristics of the female sex—totally ignored in the methodology and discussion of the studies selected [Studies have demonstrated that estrogen has a direct and indirect (via growth hormone [GH] and cortisol) lipolytic action on adipose tissue. Several studies have reported elevated resting and exercise levels of GH in women during the LT. However, it was recently reported that there is no enhanced GH response to exercise in the LT compared to the FL. Data from the same study also showed increased cortisol during exercise in the LT but no increase during the FL [At this point, it seems important to investigate women’s hormonal status and physiological exercise-induced responses to clarify specific hormonal and metabolic responses leading to specific fuel selection. Moreover, cellular studies must consider the complex inherent mechanisms of such adaptations.The novelty of the current study was that the oxidation substrate post-HIT ratio and the female characteristics had not been previously investigated and/or discussed in women of reproductive age. Thus, further research is needed to test the potential superiority of HIT vs. moderate-intensity continuous training (MICT) on body composition and general oxidative metabolism. Moreover, it will be vital to elucidate whether hormonal changes in the female ovarian cycle or the use of different types of contraceptives (estrogen and progesterone) could induce a state of both metabolic “flexibility or inflexibility” effects in this population under different protocols of HIT training.Our current data, although showing extreme values, probably due to the small sample size, suggest an important relationship between the training model adopted and the adaptations promoted on the oxidation capacity of CHO and LIP throughout the monthly sexual cycle. Undoubtedly, this is an important limitation of this study, which is why we classify it as a preliminary or pilot study.