a) Maximum oxygen consumption. Aerobic and static loads increase the body’s need for oxygen to provide energy to working muscle groups. The amount of energy used during FN is determined through oxygen consumption (VO2). The modified Fick formula: CB = VO2 / L (A – B) 02, where CB is a cardiac output, VO2 is oxygen consumption, Δ (A – B) O2 is the difference in 02 between arteries (A) and veins (B). In other words, the oxygen consumption depends on the CB and Δ (A – B) O2.
Thus, the metabolic needs when performing FN require an increase in oxygen delivery, which is provided by an increase in Δ (A – B) O2 and an increase in CB, which, in turn, depends on the heart rate and stroke volume (EI) of the heart. Δ (A – B) O2 during the execution of FN increases due to the redistribution of blood and, accordingly, oxygen from non-working tissues (for example, the kidneys and organs of the abdominal cavity) to working muscles. In addition, in working muscles, blood viscosity increases due to the transition of a certain part of blood plasma into the interstitial space. An increase in CB during FN is closely related to VO2. Thus, an increase in VO2 per liter leads to an increase in the total nitrogen concentration by = 6 l.
The maximum power of FN is defined as the maximum oxygen consumption (VO2max) that is transported in a person when performing FN until the moment when it is stopped due to fatigue or shortness of breath. Individual VO2max is a stable and reproducible indicator of physical performance. It is expressed either in absolute terms (l / min) or relative to MT (ml / kg / min). The maximum increase in Δ (A – B) O2 is a fixed value and is = 15-17 vol%. Since the intensity of the FN determines the oxygen consumption, which depends on the CB and Δ (A – B) O2, and the maximum Δ (A – B) O2 is a relatively constant value, the maximum power of the FN and VO2max indirectly indicate the maximum myocardial contractility (or maximum CB) and PP).
b) Myocardial oxygen consumption. Oxygen consumption by the myocardium (MVO2) is determined by the levels of HR and SBP through the so-called dual product: HR (beats / min) x CAD (mm Hg). Human physical performance depends on the consumption of oxygen and CB, and the degree of increase in heart rate and SBP during the FN is determined by the increase in oxygen demand (as a percentage of VO2max). Consequently, for any absolute value of the FN, a person with a large VO2max uses less of his reserve and, at a high FN, has a lower heart rate and an AAD. The key point: the myocardial oxygen demand is determined not only by the severity of the FN, but by the ratio of the severity of the load to the maximum physical performance.
c) Respiratory threshold. Carbon dioxide emissions (VCO2) with FN also increase. The increase in VO2 and VCO2 occurs in parallel, but the intensity of the release of CO2 increases faster. The amount at which an increase in oxygen demand is not accompanied by a further increase in carbon dioxide emissions is called a respiratory threshold (VT). This discrepancy is due to the formation of lactate, the buffering of H + lactate ions with bicarbonate and the subsequent formation of additional CO 2. The respiratory threshold is also called the anaerobic threshold and the onset of lactate accumulation in the blood. Since CO2 stimulates the respiratory center, a nonlinear increase in the respiratory rate occurs at the respiratory threshold and moderate shortness of breath appears. The respiratory threshold during FN is usually marked at 50% of VO2max in untrained people and makes up a higher percentage of VO2max in trained individuals. Respiratory threshold is an important indicator of TFN, because it reflects the maximum sustainable level of performance that can be achieved during submaximal loads.
d) The effect of heart disease on physical performance. Physical performance in some cardiac patients may be normal and age and sex, while others may be limited if the heart’s CR decreases, the heart rate response to the FN is disturbed, there is myocardial ischemia, which, in turn, limits the FA of patients or increase in PP at peak FN. Drugs such as β-AB, which limit the changes in heart rate during FN, as well as the limitations of FA in patients with heart disease, which cause the effect of detraining, make a definite contribution to the reduction of TFN.
e) The effect of physical training on physical performance. The main purpose of FT (aerobic or static) is to increase the physical performance of patients with heart disease. With static loads, an increase in muscle strength and endurance occurs in a trained muscle. The main effect of aerobic exercise is to increase VO2max. This provides a lower percentage of VO2max at submaximal FN, which reduces the increase in heart rate and SBP during FN and myocardial oxygen demand. Increased endurance also increases both the absolute respiratory threshold and the respiratory threshold as a percentage of VO2max.
Many mechanisms contribute to the increase in TFN after FT, including PP and Δ (A – B) O2, although the magnitude of the latter has clear physiological limitations.
The degree of increase in VO2max during static loads depends on a number of factors, including the patient’s age, the intensity and duration of PT, the genetic characteristics of the patient and the clinical condition, as well as whether similar exercises are used in FT and testing. Usually the degree of increase in TFN is greatest in young people who have been intensively trained. The degree of increase in VO2max in patients after cardiac rehabilitation averages 11–36%, but depends on the severity of the underlying disease. For example, in patients with significantly reduced cardiac contractility, an increase in physical performance can be achieved by increasing Δ (A – B) O2, although in some patients after 12 months of TF an increase in CV is also observed.
In addition to increasing the maximum physical performance, endurance exercises increase stamina due to the effect on the respiratory threshold. This influence is extremely important because increased submaximal physical performance reduces shortness of breath with submaximal fn and provides for the implementation of most daily tasks, none of which require maximum effort.