1. Introduction
obesity, metabolic inflexibility, HIT
OBESITY, INSULIN RESISTANCE, CARDIOVASCULAR DISEASES, TYPE II DIABETES
Women of childbearing age have variations in substrate oxidation rates that can lead to overweight, type II diabetes, and other conditions that may be associated with metabolic inflexibility and the variations in estrogen concentrations observed during the monthly ovarian cycle. Purpose: This study aimed to verify and compare the influence of eight treadmill high-intensity interval training (HIT) sessions on carbohydrate and lipid oxidation rates (CHOox and LIPox, respectively) and intensities of ventilatory anaerobic thresholds (VATs) of women in different phases of the monthly ovarian cycle. Methods: Eleven irregularly active women performed incremental treadmill exercise testing followed by submaximal work-rate running for 45 min to determine VATs, VOWomen of childbearing age, apparently healthy, may have a high propensity for changes in the oxidation of energy substrates (lipids and carbohydrates) and insulin resistance development, which, if not detected, can progress to type II diabetes, obesity, or other associated pathologies. This insulin resistance can occur due to metabolic inflexibility, the body’s inability to use energy substrates as fuel, and the transition between them in response to dietary change, energy availability, or circulating substrate concentrations [During the fertile period, women experience a monthly rhythm called the menstrual cycle. Each cycle lasts an average of 23 to 28 days and can be divided into follicular and luteal phases, in which hormonal fluctuations (estrogen and progesterone) occur. These hormones regulate reproductive function and other physiological systems, such as the respiratory, thermoregulatory, and cardiovascular systems, which can affect exercise performance. Most studies carried out with women prefer the follicular phase and close to ovulation, in which estrogen has its highest concentration. During this phase, more remarkable changes are noted in the oxidation rates of energy substrates, including increased availability of fatty acids, oxidative capacity, and suppression of protein catabolism, favoring better performance during exercise. On the other hand, in the luteal phase, high concentrations of progesterone are found, which has a physiological role during the menstrual cycle, exerting pituitary effects; in addition, the literature suggests that its high concentration affects the fertilization process [The literature has consistently shown that regular cardiorespiratory endurance training improves the performance of tasks that fundamentally depend on oxidative energy metabolism due to the increased ability of skeletal muscles to transport and utilize oxygen (OWhen analyzing the literature, it becomes noticeable that few studies with HIT or other training methods associate women’s energy metabolism in different phases of the menstrual cycle with possible modulation of metabolic flexibility and different impacts on health. Nevertheless, this combination is critical in preventing cardiovascular diseases [