The special questionnaire, which covered 974 respondents representing 16 sports, demonstrated that the majority of elite female athletes (98.9%) trained during menstruation and that one in every three athletes experienced menstrual function disorders such as delayed sexual development (late menarche), an impaired cyclical character of the MC, or a reduction or prolongation of menstruation. Each of the above factors indicates that the limits of physiological adaptation are being exceeded with an effect on this function. The highest percentage of disorders is ob- served amongst gymnasts, ski racers and acrobats. An analysis of the results of instrumental examinations has shown that changes of hormonal status during the MC significantly influence the functional state of athletes. According to our observations, body mass increases from the end of the postovulatory phase. It reaches maximum value during the premenstrual phase. slightly decreases during the phase of menstruation and reaches initial values at postmenstrual phase (Table 2). The results presented reflect the dynamics of body mass changes. Such changes may be explained by the impact of oestrogens on fluid and electrolyte balance; by means of aldosterone reabsorption of an increase in sodium which, in turn, enhances the reabsorption of water (4, 11 ). A change in the hormonal balance of oestrogens and progesterone may lead to a significant increase in body mass including premenstrual oedemas (8, 19, 29). The body oxygen regimes (BOR) of athletes change during the MC as well. The indices of respiration reflect changes at rest (sitting position) (Table 3). The highest indices of pulmonary minute volume (PMV) are noted during the ovulation phase (phase 3). It should be stated that during this phase the highest pulmonary ventilation is achieved as a result of high respiration volume (RV), but a relatively low respiration rate (RR) in comparison to other phases of the cycle. However, during the ovulation phase breathing is less economic. The premenstrual phase is characterised by the fastest respiratory rate and the lowest respiration volume: 02 is utilised by the body from 35.2% - 39.31% of the air entering the lungs (ventilatory equivalent) whereas during the postmenstrual and postovulatory phases 02 is utilised from 32.71% and 32.91% respectively. The highest values of oxygen uptake during the ovulation phase were due to the stimulating effect of cellular respiration by eostrogens, the concentration of which during this phase is the highest. An increase in the sensitivity threshold of the respiratory centre to C02 during the premenstrual and menstrual phases of the cycle (17, 18, 19, 20). together with a reduction of bronchial permeability and ventilatory capacity of the airways as a result of secretory changes under the impact of sex hormones (4, 10, 11, 17, 18, 19, 20), may be the cause of a compensatory increase in respiration rate and pulmonary ventilation, along with a de- creased respiratory volume during these phases (especially the premenstrual phase). More change is observed in the indices of circulation (Table 4). The heart rate (HR) increases at the beginning of the ovulation phase, its values maximising during the pre- menstrual phase. This may be related to the enhanced tone of the sympathetic part of the CNS beginning with the ovulation phase, whereas before ovulation the tone of the parasympathetic part of the CNS is dominant (4). An increased HR results in an augmentation of blood minute volume (BMV) during the postovulatory phase, and especially in the premenstrual phase. According to M. Rotaru this may be considered as a compensatory mechanism related to an increased reverse venous circulation to the right side of the heart and an enhanced blood volume. The lowest cardiac output is observed during the menstruation phase. The changes in stroke volume during the MC were found to be insignificant (P < 0.05). The same was true for arterial pressure differences in systolic pressure during different phases of the cycle, constituting a range from 3-5 mm Hg, whereas the differences in diastolic pressure ranged from 4-7 mm Hg. During the first and especially the third phases, the circulation system meets the body oxygen demand most economically- each litre of 02 during the menstrual and ovulatory phases is supplied from 19-20 litres of circulating blood. During the second half of the cycle. the circulation becomes less economic. The haemodynamic equivalent (HE) increases significantly (P < 0.05) whereas the oxygen pulse (02CC) diminishes (Table 4). Blood haemoglobin content changes are insignificant during different phases of the t MC-from 124.5 +/- 8.0 g/l during the first phase to 126.6 +/- 6.0 g/l during the fifth phase (P < 0.05). The saturation of arterial blood with oxygen changes slightly during each phase of the cycle, with the highest values being observed during the ovulation phase (Table 3). At rest the lowest speed of oxygen delivery to the lungs is observed during the postmenstrual and postovulatory phases, whereas the highest level is observed during the ovulation phase. During this phase the speed of oxygen delivery to the alveoles is significantly higher in comparison to the other phases. An increase in the speed of oxygen transport by arterial blood, which begins in the ovulation phase, becomes most evident during the postovulatory and postmenstrual phases. The level of oxygen uptake is the highest during the ovulation phase despite the greater speed of oxygen transport by arterial blood. The speed of its transport by mixed venous blood during the third phase is statistically low when compared with the values evident in the fourth and fifth phases. The highest values of oxygen intake which are evident in the ovulation and menstruation phases are probably due to the fact that these phases. being the phases of "physiological stress," establish increased energy demands to the body. Changes in hormonal status and the state of the respiration, circulation and BOR systems influence the manifestation of the physical capacities of female athletes and their work capacity. The total work capacity determined by means of an ergonometry test significantly differs during different phases of the MC (Fig. 3). Both maximum power and maximum volume of performed work show differences too. In modern pentathletes the highest values of the above parameters were noted during the postmenstrual and postovulatory phases, reduction of work capacity has been observed during premenstrual, menstrual whereas a significant reduction of work capacity has been observed during the pre- menstrual, menstrual and ovulatory phases of the cycle. The functional cost of work is also of interest. High values of maximum oxygen up- take and low volumes of performed work bring about a high oxygen cost in undertaking loads during the menstrual, ovulatory and premenstrual phases of the cycle. During these phases respiration is the most frequent and the least economic-ventilatory equivalent is the highest whereas the oxygen effect within the respiration cycle is the lowest. During maximum intensity, the blood minute volume (BMV) significantly increases during phases 1, 3 and 5 of the cycle at the expense of HR augmentation; the lowest stroke volume is observed during phase 5, the highest during phase 2. There is a high pulse cost of work respectively during phase 3 --0.46 HR/kg min; phase 1--0.44; phase 5 -- 0.41 HR/kg min. During the above phases the low oxygen pulse constituted 18.3 +/- 0.3 ml O2/HR, 17.0 +/- 0.4; 18.9 +/- 1.0 ml O2/HR. Optimum regimes of respiration and circulation functioning have been noted during phases 2 and 4 of the cycle; this is confirmed by much lower values of ventilatory and haemodynamic equivalents along with in- creased oxygen effects of respiration and cardiac cycles.The findings show that during the course of the MC, changes of hormonal status (complex reorganisation of neurohormonal regulations) are accompanied by changes in respiration, circulation, respiratory function of the blood and speed of oxygen utilisation in the body of the female. We have revealed a high economy in the functions of the respiratory and circulatory systems, as well as high reserves of respiration during the post- menstrual and postovulatory phases of the cycle. These factors determine the higher work capacity of athletes during these phases as compared to the ovulatory, premenstrual and menstrual phases. Taking into account the fact that strenuous physical loads are accompanied by hypoxic states, we were interested in the response of the female body to hypoxia during the MC. No data on this subject was found in the literature. There were only some notions about changes in such aspects as respiration, circulation, respiratory function of the blood and the oxygen regimes of the female body at an altitude of 2000-4000 m, but nothing in relation to the MC. Our studies have shown that the responses of the female body to HM-11 inhaling for 10 minutes have their own features in each phase (Table 3, 4). Under hypoxic conditions PMV increases at each phase, being at the highest during the ovulation phase. It's increase during phase 3 is due to an augmentation of respiratory volume (RV) which is indicative of an enhanced efficiency of lung respiration and economy (VE has decreased) (Table 3). While inhaling HM-11, the highest HR is observed during the premenstrual and menstrual phases. This contributes to the enhancement of BMV. Changes in stroke volume under these conditions have been insignificant (Table 4). A hypoxic mixture inhaled for 10 minutes has resulted in an insignificant increase of blood haemoglobin content during the ovulatory and premenstrual phases. During HM-11 inhalation, saturation of arterial blood with oxygen (Sa02) decreases to 82.0 +/- 0.4% during the postovulatory phases, 82.8 +/- 0.3% during the postmenstrual phases, and 85.0 +/- 0.6%during the ovulation phases. In revealing the peculiarities of changes in respiration and circulation, Sa02 determines the specifics of the body oxygen regimes in hypoxic conditions as well. Significant changes have been noted in both speed of stage-by-stage oxygen transport and cascades of 02 (Fig. 2.). Under hypoxic conditions the speed of oxygen delivery to the lungs and especially to the alveoles is lower than that of oxygen transport by arterial blood in all phases of the MC except the ovulation phase. During phase 5 the highest speed of oxygen transport by arterial blood is due to the highest values of BMV: PO2 during HM-11 inhaling decreases to a level lower than critical (Fig.2). On the basis of the studies carried out, we may conclude that the responses of respiration and circulation, changes of BOR under hypoxic conditions (whilst inhaling a hypoxic mixture containing 11% oxygen) depend on the phase of the menstrual cycle. One should pay attention to the fact that the better conditions for transport and utilisation of oxygen in the body are created during hypoxia at the expense of greater stimulation of respiration and circulation function during the most crucial phase for the female body which is phase 3 of the menstrual cycle, when the process of ovulation called upon for reproduction, dominates. The above results demonstrate that hormonal changes (complex neurohormonal reorganisation of regulatory mechanisms during the MC) determine the biological cyclical character of all the body system functions. A high economy in the functions of respiration, circulation, BOR and high respiration reserve during the postmenstrual and postovulatory phases of the cycle provides for the greater work capacity of female athletes during these phases as compared to the ovulatory, premenstrual and menstrual phases. We have also discovered that the female body's response to hypoxia is different in various phases of the MC. The most economic adaptation to hypoxia is observed during the postmenstrual and postovulatory phases. On the basis of what is outlined above, we may conclude that there is a need for a reorganisation in the training of the female body during the different phases of the menstrual cycle. By redistributing the training load planned according to volume, intensity and direction in each phase of the cycle, the coach is able to maintain the health of the athlete and future mother, provide an enhancement of her performance and an increase in the length of her career in sport.