## 4 Discussion  
In this study, an attempt was made to determine the factors that may affect the individual variability in the perception of external stimuli. An electrical impulse based on the principles and characteristics of TENS stimulation was used as the sensory stimulus. The use of this type of impulse in the study ensured that the stimulus used was safe, non-invasive, and painless, while being objectively measurable and expressed numerically in milliamperes (mA) [10; 11; 12; 13]. The results obtained showed that the sensory threshold in women was lower than in men. Comparing the results of this study to the results of other authors concerning differences in sensitivity to external stimuli broken down by sex, it was found that women showed a lower perception threshold than men, regardless of changing locations of the electrodes, as demonstrated, for example, in a study in which perception threshold measurements were also carried out using an electric stimulus [8]. The mean differences between male and female subjects were 0.18, 0.22, 0.44, 0.88, and 0.61 mA at five different measurement points [8]. A study by [PERSON] et al. [23] also found a lower sensory threshold in women compared to men--13.77 vs. 19.57 mA. The authors pointed out the anatomical and physiological discrepancies that can generate differences in sensory response, including size of the neuromotor course and amounts of neurotransmitters [23]. A study by [PERSON] et al. [24] showed that even using two different current frequencies, i.e., 5 and 50 Hz, the threshold of sensory perception in women was lower than that in young and elderly men. Men and women differ significantly in their body composition, as noted in our own study, so it is difficult to establish unequivocally whether the key factor in the perception of stimuli is sex or the content of individual components of body composition. [PERSON] et al. [25] proposed selecting men and women with a similar water content (50-55%) for tests on the sensory threshold and to perform a log transformation of the obtained results. After doing this, they showed that there are no statistically significant differences in the sensitivity threshold to electric current between men and women, and the body water content together with the fat content are more important than sex and are strongly correlated with each other. The authors of the discussed article suggest that these factors should be used in sensory research in order to minimize the sex influence. However, the results described above raise some doubts. Perhaps, no statistically significant differences were found because the number of men and women included in the analysis was reduced (initially 35 men and 35 women; afterward, 15 men and 15 women). The group selection and logarithmic transformations also could play a significant role. Examining the interrelationship of the sensory threshold and the changing phases of the menstrual cycle in women, it was found that the level of the external stimulus perception did not depend on the phase of the menstrual cycle, the time of menarche, the number of days of menstruation, or the declared pain level during menstrual bleeding. It is worth noting, however, that the basic problem and limitation of most scientific studies examining the differences between the sexes in the perception of external stimuli are hormonal changes in a woman's body during their menstrual cycle. In the available scientific literature, there are ambiguous and sometimes even contradictory reports about the impact of hormonal changes occurring in women during the phases of the menstrual cycle, i.e., the follicular (including the proliferative phase and ovulation), luteal, and menstrual phases, on the level of perception of an external stimulus [26; 27; 28]. It should be noted, however, that the research of other authors most often focuses on differences in the perception of experimentally induced pain and not the threshold of sensation; therefore, not all of the results of the present study can be compared to such papers.