When skeletal muscle contracts, oxygen consumption increases obviously. The response of cardiovascular system is to increase cardiac output to increase blood supply, so as to meet the oxygen consumption of muscle tissue and transport excessive metabolites in time, otherwise muscle exercise will not last long.
(1) Changes of cardiac output during muscle exercise: Cardiac output is sensitive to acute exercise, and its purpose is to quickly adapt to the needs of body activities. At the beginning of exercise, the cardiac output increased rapidly, then gradually increased and gradually reached a stable state. At this time, the blood flow state of the body and the metabolic demand of muscle activity have reached a relatively balanced state.
During exercise, due to the rhythmic relaxation and contraction of muscles and the strengthening of respiratory movement, the amount of blood returning to the heart is greatly increased, which is the guarantee to increase the input and output of the heart. On the basis of the increase of blood volume, the heart rate is accelerated and the myocardial contractility is enhanced, so the cardiac output is increased.
(2) Changes of blood volume of various organs during muscle exercise: The cardiac output increases during exercise, but the increased cardiac output is not evenly distributed to all organs of the whole body. Through the regulation mechanism in the body, the blood flow of various organs will be redistributed. In this way, the blood flow of the exercise heart and muscle increases obviously, while the blood flow of the skeletal muscle and viscera that do not participate in exercise decreases. At the beginning of exercise, the blood flow of the skin also decreased, but later, due to the increase of muscle heat production, the body temperature increased. Through the thermoregulation mechanism, the skin blood vessels are relaxed, the blood flow is increased, and the skin heat dissipation is increased.
The redistribution of blood volume of various organs during exercise has important physiological significance, that is, by reducing the blood flow distribution of organs that are not involved in activities, more blood flow is ensured to be distributed to the muscles that exercise. The physiological significance of blood flow redistribution during exercise is to maintain a certain arterial blood pressure.
(3) Changes of arterial blood pressure during exercise: The changes of arterial blood pressure during exercise depend on the relationship between cardiac output and peripheral resistance, and are related to exercise intensity and exercise mode. At the beginning of intensity-by-intensity exercise, the systolic blood pressure increased rapidly from a quiet state, and then increased with the increase of exercise intensity, reaching a maximum of more than 200mmHg. Although the total peripheral resistance decreased at this time, the diastolic pressure remained stable or slightly increased.
In terms of exercise mode, during dynamic exercise, due to the increase of cardiac output, the total resistance of peripheral blood vessels has little change, so blood pressure increases, but mainly systolic blood pressure increases; During static exercise, the cardiac output increases slightly, but due to the continuous contraction of muscles and the contraction of abdominal visceral vessels, the total peripheral resistance increases, so the blood pressure increases obviously during diastolic blood pressure. In addition, compared with the exercise of lower limb muscles, the arterial blood pressure changes obviously when the body completes the upper limb exercise with the same maximum oxygen uptake intensity; Compared with upright exercise, systolic blood pressure and diastolic blood pressure increased significantly during inverted exercise.
2. Adaptability of cardiovascular system to exercise.
Regular physical exercise or exercise training can promote the shape, function and adjustment ability of human cardiovascular system to adapt well, thus improving people's working ability. The long-term effects of exercise on cardiovascular system can be summarized as follows.
(1) Sinus bradycardia: Fitness exercise or exercise training, especially endurance exercise, can slow down the resting heart rate. The resting heart rate of some excellent endurance athletes can be as low as 40 ~ 60 beats/min, which is called sinus bradycardia. Sinus bradycardia is a good response to the improvement of cardiac function after long-term training. Sinus bradycardia is reversible.
(2) Exercise-induced heart enlargement: It is found that physical exercise or exercise training can enlarge the heart. The heart with increased exercise has rich appearance, strong contractility and high heart reserve. Exercise-induced cardiac enlargement is a good adaptation to long-term exercise load.
Exercise-induced cardiac enlargement has exercise specificity to some extent. For people who often do endurance exercise, the enlargement of the heart is mainly due to the enlargement of the ventricular cavity and the increase of the heart volume, but the ventricular wall is not thickened or only slightly thickened; People who often do strength exercises, their adaptation performance is that the ventricular wall is thickened, while the cardiac cavity is not enlarged or slightly enlarged.
(3) Improvement of cardiovascular function: At rest, there is not much difference in cardiac output between ordinary people and athletes, because athletes' heart rate is low, so their stroke output is high. When they are engaged in maximum exercise, their heart rates can reach the same height, but the increase of athletes' stroke output and cardiac output is obviously higher than that of ordinary people at rest. The increase of athletes' stroke output and cardiac output is the adaptation of the heart to sports training.
In addition, the myocardial microstructure will also change after training, which will increase the myocardial contractility.
Exercise training not only makes the heart adapt well in shape and function, but also improves the regulation function. When some trainers do quantitative work, the cardiovascular function is mobilized quickly, with great potential and rapid recovery. After the start of exercise, the function of cardiovascular system can be quickly mobilized to meet the needs of sports activities. When carrying out maximum intensity exercise, the cardiovascular system can exert its maximum functional potential and fully mobilize the heart reserve under the regulation of nerves and body fluids. The recovery period after exercise is short, which means that the timing of exercise can change greatly, but once the exercise stops, it can quickly return to a quiet level.