Hipertermijos ir dehidratacijos poveikis suaugusiųjų griaučių raumenų nuovargiui atliekant maksimalaus intensyvumo izometrinius pratimus

The aim of the study was to establish the impact of hyperthermia and dehydration to not actively engaged in sports male and female adults on the functions of skeletal muscles, evaluate the impact of rehydration to central (CNS) fatigue under the conditions of hyperthermia during the maximum intensity isometric load. The research participants were male (n = 10) and female (n = 10) adults not actively engaged in sports. The male were 22.4 ± 3.4 years old, with body mass of 75.1 ± 8.0 kg, and height — 177.6 ± 7.2 cm, and the females were 21.2 ± 2.4 years old, with body mass of 64.84 ± 8.4 kg, and height —170.8 ± 2.5 cm. Three studies were carried out — one control study and the other two — experimental. During the hyperthermia experiment the bodies of the research participants experienced hyperthermia and dehydration (research participants kept their legs up to the pelvis in the bath with hot water (44 ± 1oC) for 45 minutes). During the rehydration experiment, using the same methods of increasing hyperthermia, the organisms experienced peroral rehydration with the1000 ml solution of 37oC NaCl 0.9%. The load of maximum voluntary strength lasted for 120 seconds (MVC-2 min), every 15 seconds the muscle was stimulated by electrical impulses — the duration of the stimulation was 250 ms, the frequency was 100 Hz, and the voltage was 85—105 V. We registered the moment of maximal voluntary contraction force (MVC) (N•m) and the central activation ratio (CAR%). CAR% = MVC / (MVC + TT-100 Hz) × 100. After hyperthermia, dehydration and hyperthermia were applied, the rectal male and female body temperature averagely increased by ~3° C (p < 0.001). During the hyperthermia experiment the male research participants lost 1.17 ± 0.4% of their body mass (I° dehydration) and the females lost 0.62 ± 0.13% of their body mass. Having analyzed the physiological index of heat stress (in the 10 point system) we established that the research male participants experienced average and high level physiological stress — in the case of hyperthermia it was 6.42 ± 0.71, and in the case of rehydration — 7.16 ± 0.91, and female participants experienced high level physiological stress — in the case of hyperthermia it was 8.85 ± 1.13, and in the case of rehydration — 8,38±0,98. At the end of the load the MVC decreased signifi cantly in all the cases (p < 0.001), compared to the indices which were established before the load. After 15 seconds during the recovery time the strength regained the level witch was established before the load was applied. Two-factor dispersion analysis revealed that the changes in the analyzed strength indices depended on time (p < 0.001); however, the level of hyperthermia and their interaction did not impact the results (p > 0.05). After the analysis of the indices of muscle voluntary activation we noticed that hyperthermia (p < 0.05) and rehydration (p < 0.01) signifi cantly decreased CAR% compared to the one established before the load. Applying the methods of passive heating of muscles the research participants were made to experience hyperthermia and I° dehydration. Hyperthermia increased the central fatigue. During the experiments of hyperthermia and dehydration MVC fatigue altered at the same level. After performing rehydration under the conditions of hyperthermia before the load central fatigue of men and women not engaged in sports increased.