The menstrual cycle is considered one of the factors associated with variations in body composition in women, due to the recognized physiological and hormonal changes that occur during this time. Reliable measurement methods during the menstrual cycle are therefore required for an accurate assessment of body composition. The aim of our study was to use a bioimpedance analyzer (Tanita MC-780MA) and anthropometry to investigate whether and how hormonal fluctuations during the menstrual cycle and the use of contraceptives affect body composition changes in women at different phases of the menstrual cycle. The study involved 50 participants, who were divided into three groups: a research group (girls without hormonal contraception) and two control groups (girls with hormonal contraception and boys). The measurements were taken during four phases of the menstrual cycle: menstrual phase, follicular phase, ovulation phase and luteal phase. For boys, measurements were taken on random days but with the same weekly delay. Our results indicated that the measured indices of body composition – including body mass, body fat percentage and fat mass, muscle mass, extracellular water, body circumferences, and skinfold thicknesses – did not differ significantly across the phases of the menstrual cycle within each study group or between the groups. The absence of statistically significant differences indicates that body composition measurements using bioelectrical impedance analysis (BIA) are stable and reliable throughout the menstrual cycle. This means there is no need to adjust the timing of measurements according to the menstrual cycle phase, which simplifies and enhances the practical application of this method in clinical and research settings. Nevertheless, it is important to consider that certain factors may have influenced the consistency of the results, such as the limited sample size (particularly in the group of females using hormonal contraception), the lack of objective confirmation of menstrual cycle phases (e.g., through hormonal assessments), interindividual differences in cycle length, and the use of various types of hormonal contraceptives. These limitations provide a basis for further research but do not diminish the practical utility and value of the findings obtained.
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