The work of the heart during exercise
The frequency and strength of heart muscle contractions during operation increase significantly. Muscular work quickens the pulse lying less than sitting or standing.
Maximum blood pressure increased to 200 mmHg. and more. The increase in blood pressure occurs in the first 3-5 minutes of the start of work and then have the strengths of people trained in the long and intensive muscle work is kept at a relatively constant level of fitness due to a reflex of self-regulation. In weak and untrained people blood pressure starts to fall even during operation due to lack of training or lack of training of reflex self-regulation, leading to the loss of ability to work due to reduced blood supply to the brain, heart, muscles and other organs.
In people trained to muscular work, the number of heartbeats at rest less than that of the untrained, and usually no more than 50-60 per minute, and in particularly trained – even 40-42. It is believed that this decrease is due to heartbeats expressed in exercise that develop endurance. When a rare heart rate increased duration isometric contraction phase and diastole. The duration of the expulsion phase is almost unchanged.
Stroke volume at rest in trained same as that of the untrained, but with increasing fitness it decreases. Therefore, they alone and reduced cardiac output. However, in trained stroke volume at rest, as well as by untrained, combined with the increase in the ventricular cavity. Note that the ventricular cavity comprises:
- 1) a systolic volume which is ejected with its contraction, 2) reserve volume which is used at muscular activity and other conditions associated with increased blood circulation, and 3) a residual volume which is almost never used even if the most intense of the heart.
Unlike untrained in trained especially increased reserve volume and systolic and residual almost identical. Large reserve capacity in trained allows you to immediately increase the systolic ejection of blood at the beginning of the work. Bradycardia, elongation phase of isometric tension, decrease in systolic volume and other changes indicate the economical activity of the heart at rest, which is designated as a controlled physical inactivity infarction. In the transition from rest to the muscle activity in trained immediately evident hyperdynamia heart, which is the quickening of the heart rate, increasing systole, shortening, or even the disappearance of isometric contraction phase.
Minute volume of blood increases after exercise that depends on the increase in systolic volume and force of cardiac contraction, cardiac muscle development and improvement of its power.
During muscle work and in proportion to the magnitude of cardiac output in man rises to 25-30 dm3, and in exceptional cases up to 40-50 dm3. This increase in cardiac output occurs (especially untrained) mainly due to the systolic volume, which a person can reach 200-220 cm3. Less significant role in increasing cardiac output in adults playing palpitations, which is particularly increased when systolic volume reaches the limit. The more exercise, a relatively more powerful the work the person can perform at optimum increased heart rate to 170-180 in 1 min. Increased heart rate above this level makes it difficult to fill the heart with blood and its blood supply through the coronary vessels. At the most intensive work at the train human heart rate can reach up to 260-280 per minute.
During muscular work and increases the blood supply to the heart muscle itself. If after coronary heart man alone takes 200-250 cm3 of blood in 1 minute, during intensive muscle work the amount of blood flowing through the coronary vessels, reaches 3.0-4.0 dm3 to 1 min. With an increase in blood pressure by 50% at the advanced coronary vessels occurs 3 times more blood than in the resting position. Expansion of coronary vessels occurs reflexively, as well as due to the accumulation of metabolic products and the admission to the adrenaline.
Increased blood pressure in the aortic arch and carotid sinus reflex expands coronary vessels. Coronary vessels extend cardiac sympathetic nerve fibers excited by and by adrenaline and acetylcholine.
We trained people mass of the heart grows in direct proportion to the development of skeletal muscle. At trained male heart volume greater than that of the untrained, 100-300 cm3 and women – 100 cm3, and more.
When muscular work increases cardiac output and blood pressure increases, and so the work of the heart is 9,8-24,5 kJ per hour. If a person performs a muscular work for 8 hours a day, the heart during the day makes the work of approximately 196-588 kJ. In other words, the heart does the work of a day, equal to that which expends person weighing 70 kg and to rise to 250-300 meters. Productivity increases when the heart muscle activity, not only by increasing cardiac output and an increase in heart rate, but also a greater acceleration of blood circulation, as the systolic ejection speed increases 4 times and more.
Increasing and strengthening the heart and constriction of blood vessels in the muscle occurs due to reflex stimulation of the receptors in skeletal muscles at their reduction.
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