## 1 Introduction  
The sensations that accompany a person during their lifetime, especially superficial (sensory) feelings, i.e., tactile perception and the sensations referred to as pain, are associated with different factors that can affect their interpretation, modification, and level of feeling [1; 2; 3; 4]. The receptors located in the skin, muscles, ligaments, and joints receive somatosensory information to be processed by the brain, specifically in the cerebellum, thalamus, posterior parietal cortex, insula, and primary and secondary somatosensory cortex regions. A distinction is made between exteroceptive and proprioceptive somatosensory, with the former including touch and pain and the latter sensing movement and body position [5].  
The sensory threshold is the point at which sensation is consciously perceived, and it is always the first effect of a stimulus, recognized by a human, such as the electrical impulse applied during standard electrotherapy procedures in clinics and hospitals. A sensory impression is based on a subjective assessment of a stimulus acting on the human body, which therefore differs from person to person [6; 7; 8].  
The human skin, the largest sensory organ, is innervated by complex combinations of low- and high-threshold mechanoreceptors (LTMRs and HTMRs, respectively; approximately 17,000), each with its unique physiological profile and response properties elicited by distinct tactile stimuli [2]. Tactile sensations and their perception rely on mechanosensitive sensory neurons: LTMRs that react to innocuous mechanical stimulation and HTMRs that respond to harmful (nociceptive) mechanical stimuli. Thus, the perception of stimulation that does not damage tissues initiates the activation of cutaneous LTMR mechanoreceptors, and then the sensory neurons are activated, the cell bodies of which are located in the dorsal root ganglia and the sensory ganglia of the brain [1; 2; 3; 4].  
Therefore, an external stimulus, including an electrical impulse, is felt differently depending on the treatment parameters applied, particularly the frequency and the duration of the applied electrical impulse, the physical properties of the skin [9] (how warm, cool or moisturized it is), and changing external conditions, e.g., air humidity [10; 11; 12; 13]. The perception of the stimulus may also be influenced by the current somatic state of a person (health or illness), their mental state (e.g., happy, anxious, or depressed), and the physiological properties of the peripheral and central nervous system [14; 15; 16]. In humans, other factors that may contribute to the modification of somatosensory impressions and differences in the degree of external stimuli perception include age, sex, changing hormone levels such as during the monthly cycle in women (especially estrogen E2 and progesterone P2) [17], personality traits, and effects of endogenous opioids or medication taken, including painkillers. The perception of stimuli from the environment may also depend on genetic determinants, as well as a system of sociological and cultural beliefs in which a given person functions [18; 19; 20].  
The standard electrical stimulation used for electrotherapeutic procedures performed in health centers and often used in scientific research is transcutaneous electrical nerve stimulation (TENS) [8]. This stimulation is non-invasive and widely accepted, and its pulse time is short--in the range of 50-350 us depending on the aperture, which makes it safe for patients' skin. The amplitude of the current is variable and individually selected, depending on the person's neurosensory threshold. Each person needs a different electrical current intensity value to reach the sensory threshold. Thus, the aim of this research was to assess the sensory threshold in response to TENS, taking into account selected personal factors, such as participant's sex, body composition, and the phase of the monthly cycle. The results of this type of research may contribute to a better understanding of an individual's sensitivity to TENS stimuli.