Impact of hyperthermia on the skeletal muscle fatigue of men performing isometric exercices of maximum intensity

The aim of the study was to establish the impact of hyperthermia on the functions of skeletal muscles performing 2 min maximum intensity isometric load under the conditions of hyperthermia. The research participants were male adults actively engaged in sports (n = 6), aged 22.4 ± 3.4 years, with body mass of 75.1 ± 8.0 kg, and height — 177.6 ± 7.2 cm. Two studies were carried out — one control study and one — experimental. The load of maximum voluntary strength (MVS) lasted for 120 seconds, 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. During the experiment the bodies of the research participants experienced hyperthermia participants kept their legs up to the pelvis in the bath with hot water (44 ± 1oC) for 45 minutes). We registered the moment of MVS (N*m) and the degree of voluntary activation of muscles VA% = (MVS + electrical impulse) / MVS × 100.When the load was applied the research participants were motivated verbally, and they were provided with the visual feedback of changes in strength signals.). Having analyzed the physiological index of heat stress (in the 10 point system) we established that the research participants experienced average and high level physiological stress — in the case of hyperthermia it was 6.42 ± 0.71. After 15 seconds during the recovery time the strength regained the level witch was established before the load was applied. After the analysis of the indices of voluntary activation we noticed that hyperthermia (p < 0.05) signifi cantly increased the degree of voluntary activation VA% compared to the one established before the load. During the recovery time, 15 seconds after the application of the load, the strength index of voluntary activation regained the level which was before the load.. Under the conditions of hyperthermia had impact on the central fatigue and increased it even more when the 2 min maximum isometric load was performed