## 4 Discussion  
The assessment of the impact of therapy duration on the immediate effects of short-term GR-HCT application on specific biomechanical properties of muscles, such as tone, stiffness, and elasticity, as well as the effect on improving muscle perfusion and tissue temperature, reducing pain, and increase in effectiveness of recovery of isometric strength of the forearm were the main objectives of our research. The obtained results show that the duration of 5 min of GR-HCT versus 10 min is sufficient to evoke significant changes and that increasing the time of GR-HCT from 5 to 10 min does not bring better effects in the aspect of recovery effectiveness. In our studies, we demonstrated the importance of the influence of the time of GR-HCT application on MFCR and MBR perfusion. Some authors suggested that skin perfusion measured by LDF may have a parallel in muscle hyperemia responses [56; 57; 58]. Research on the effects of heat on the vascular system published by [PERSON] and colleagues in The Journal of Physiology indicated the ability of heat therapy to exert improvement in many subclinical markers of cardiovascular disease [13]. One of the analyzed functional variables is tissue perfusion, which is also included in our research. Functional changes (flow-dependent dilation; FMD) were determined by improved endothelial function [59; 60]. A variety of interventions, including heat stress, can prompt a rapid improvement in these responses. The hemodynamic changes that occur after these interventions are described as mechanistic adaptations of the vascular system [14; 60; 61]. Figure 4: Presents the differences between post-rest values of PU, T, S, E, PPT, and temperature for 5 and 10 min therapy for both muscles (MFCR and MBR). [PERSON] et al. showed, in an animal experiment, that 15 min of daily heat stimulation in a dry far infrared sauna at 41 \({}^{\circ}\)C improves limb perfusion [26]. The authors showed that repeated thermal therapy increased eNOS protein expression, blood flow, and capillary density in an ischemic hind limb in mice. The endothelium plays a vital role in the mechanism of local microcirculation autoregulation as a source of numerous mediators, of which NO and prostacyclin are the strongest vasodilators, and EDCF2 and endothelin (EDCF1) are the most potent vasoconstrtictors [62]. [PERSON] et al. showed that the time of tissue heating is essential for the hyperemia reaction [63]. In our study, the GR-HCT application provided a rapid temperature rise. Differences in plateau protocols and skin heating rates trigger different contributions of vasodilatory pathways to the local heat response [63]. Rapid local heating (0.5 \({}^{\circ}\)C for 5 s) induces a transient axonal reflex (5-10 min) triggered by the activation of heat-sensitive sensory and adrenergic nerves. This is followed by a vasodilatory response (20-30 min) mediated by NO. Some authors suggest that maintaining the plateau phase at 39 \({}^{\circ}\)C leads to a higher proportion of NO in the plateau phase [64]. One of the important results in our study shows that despite the increase in temperature and PU during 10 min of GR-HCT, it did not show statistical significance in reducing the value of individual biomechanical properties of muscles (T, S, E). The immediate effect of hyperemia in 5 min GR-HCT was sufficient to obtain similar results for 10 min GR-HCT of MFCR and MBR. The explanation for this phenomenon underlies recent evidence suggesting that up to about 80% of the capillaries are perfused in a resting state for many animal preparations. Thus, any stimulation, including heat, is unable to recruit more than once, and capillary recruitment alone is not a major contributor to congestion and gas exchange in contracting skeletal muscles [65; 66]. Muscle tone, elasticity, and muscle stiffness are mainly maintained by the complex interplay of spinal and supraspinal mechanisms, the disruption of which can cause many changes in the biomechanical properties of muscles [44; 67].