[The function of the heart changes in implementation of the diving reactions in humans].

The changes of chronotropic function of the heart and of the myocardium in the implementation of the diving response in humans were studied by the electrocardiographic method. The study involved 80 students aged 18-20 years. Diving simulation was performed by immersing the face in cold water during breath-hold exhale. When the water temperature was 12.3 +/- 2.3 degrees C, average duration of apnea was 31 +/- 11 s. The oxygen content in the exhaled air after apnea was 98.8 +/- 8.7 mm Hg, carbon dioxide--49.1 +/- 3.5 mm Hg. It was observed slowing of the heart rate, mainly due to the increasing of diastole in 41 of the 80 surveyed during simulating diving. But it also can be observed symptoms of conduction deterioration: atrioventricular block type I (22% of reactive type and 29% of the highly reactive type subjects), and exceeds standards QTc-interval prolongation (at 7.5% of the subjects). These responses are adaptive in nature and disappear in the recovery process. But the fact abnormalities of conduction in the myocardium must be considered when using the diving reflex in medical practice, as may be due to a predisposition to a certain pathology of the cardiovascular system.

[Effect of exhaustive weightlifting exercise on EMG, biochemical markers of muscle damage and performance capacity in young male subjects].

The aim of this study was to examine the effect of exhaustive weightlifting exercise on electrical and biochemical variables and performance capacity in young male subjects. The onset of exercise (80-50% 1RM) was associated with a decrease in the amount of work performed, which was followed by a steady performance capacity at 40-10% 1RM. There were no significant changes of m. rectus femoris EMG maximal amplitude though it tended to be increased during the first half of exercise. A significant blood lactate concentration increase indicated that an anaerobic metabolism was a predominant mechanism of muscle contraction energy-supply. CK level in blood plasma did not change but plasma myoglobin concentration doubled immediately post-exercise. The data presented here suggest that decrease in performance capacity was likely due to progressive "refusal of work" of the fast motor units and work prolongation of weaker, intermediate and slow motor units. Unchangeable CK activity and relatively small increase in myoglobin concentration in plasma suggest that used weightlifting exercise did not induced substantial damage in myocytes' membranes in our subjects.

[Acute and remote biochemical and physiological effects of exhaustive weightlifting exercise].

The goal of the work was a study of exhaustive weightlifting exercise effect on prolonged changes in physiological and biochemical variables characterized functional status of skeletal muscles. An exercise gave rise to significant blood lactate concentration increase that was indicative of an anaerobic metabolism to be a predominant mechanism of muscle contraction energy supply. A reduction of m. rectus femoris EMG activity (amplitude and frequency), tonus of tension and an increase in tonus of relaxation were found immediately after exercise. Both EMG amplitude and frequency were increased 1 day post-exercise. However, after 3 days of recovery, EMG amplitude and frequency were decreased again and, in parallel, blood serum creatine kinase (CK) activity was significantly increased. After 9 recovery days, all measured variables with the exception of CK were normalized. A significant reverse correlation was found between blood serum lactate concentration and m. rectus femoris EMG activity at the same time points. Blood serum CK activity and m. rectus femoris EMG and tonus variables were observed to be significantly reversely correlated on the 3rd post-exercise day. Presented data demonstrate that exhaustive exercise-induced muscle injury resulted in phase alterations in electrical activity and tonus which correlated with lactate concentration and CK activity in blood serum.