Increasing insulin sensitivity and nitric oxide (NO) bioavailability and promoting vasodilation and tissue perfusion.
-
2.5. Muscle-Building Effects of Exercise and Cardiovascular Health
Skeletal muscle represents approximately 40% of the human body’s mass, which makes it the most conspicuous organ. In addition to carrying out the body’s motor function, skeletal muscle is one of the major organs involved in glucose metabolism and, by extension, glucose homeostasis. A decrease in skeletal muscle mass may impair glucose metabolism and tolerance. In addition to enhancing insulin sensitivity, the muscle-building effect of exercise promotes glucose metabolism and tolerance by enhancing blood glucose “pathways” (into the skeletal muscle) that serve to buffer increases in blood glucose. Moreover, muscle is an essential endocrine organ of the body that can regulate cardiovascular metabolism and function via the production of various exercise factors. Recently, it has shown an association between the amount of human muscle tissue and the incidence and mortality of cardiovascular disease
[36,37][36][37]. Muscular atrophy (e.g., sarcopenia) is characterized by a decrease in muscle-derived carnitine, which is essential for fatty acid transport in the heart and skeletal muscle and thus leads to abnormal fatty acid metabolism. Sarcopenia is common in patients with heart failure due to the retention of the ejection fraction, which may result in cardiovascular dysfunction due to abnormal glucose and lipid metabolism and decreased production of exercise hormones
[38,39][38][39].
2.6. Other
In recent years, many studies have investigated the mechanism through which the biological function of gut bacteria can influence cardiovascular health via their metabolites. Indeed, the time it takes for physical exercise to affect intestinal flora is linked to higher body fat, higher triglycerides, and better circulation of high-density lipoprotein cholesterol (HDL-c) and blood pressure. Intriguingly, the intestinal microbiota of top athletes and inactive individuals exhibit metagenomic and metabolomic differences, which shows that regular exercise might enhance metabolic health by improving the intestinal microbiota
[40,41,42][40][41][42]. For instance, Liu et al. reported that exercise may boost short-chain fatty acids and decrease branched-chain amino acid (BCAA) levels by enhancing the gut flora and thus improve glucose metabolism and insulin sensitivity
[43]. Also, mental and psychological variables contribute to the onset and progression of ischaemic heart disease. Exercise may alleviate psychological stress, lower the moderate=to-severe anxiety prevalence in coronary heart disease patients by 56% to 69%, and facilitate cardiac rehabilitation
[44]. In addition, physical activity may increase stem cell mobilization and tissue healing
[45]. These interactions are principal contributors to cardiovascular health (
Figure 2).
Figure 2. Exercise-induced cardiovascular benefits and underlying mechanisms: Exercise benefits cardiovascular health through its effects on the body. The primary mechanisms include enhancement of insulin sensitivity and metabolism in the cardiovascular system, reductions in oxidative stress and inflammation, the initiation of structural and functional remodelling in the cardiovascular system, the promotion of exerkine secretion from skeletal muscles and other tissues, and decreases in the risk factors for cardiovascular disease.
3. Exercise Improves the Cardiovascular Structure and Function
3.1. Remodeling of the Cardiovascular Structure and Function
Even moderate exercise reduces pathological ventricular hypertrophy, such as that caused by heart failure, and improves cardiac shape and function under pathological conditions. Exercise-induced vascular remodelling is characterized by increases in the arterial vessel diameter and arterial vessel wall thickness (including coronary arteries)
[46]. Likewise, exercise increases collagen and elastin content in atherosclerotic plaques while decreasing atherosclerosis-related adverse outcomes
[47]. This effect may be one of the mechanisms through which physical activity protects vital organ function and retards ageing
[48].
Exercise impacts blood vessels and increases the development of new blood vessels. Exercise, may increase the capillary formation and promote angiogenesis, while it may widen the arterial lumen through a process known as arteriogenesis (
Figure 3). This process may occur in existing blood vessels (including coronary arteries) and thus demonstrates substantial vascular system adaptability. A key regulator of angiogenesis is the vascular endothelial growth factor (VEGF), whose expression in skeletal and cardiac muscle may be increased by exercise
[49,50][49][50].
Figure 3. Long-term moderate- and high-intensity exercise induces cardiovascular remodelling: Moderate- and high-intensity exercise performed over a prolonged period both causes and promotes structural and functional remodelling in the cardiovascular system. The structural remodeling process involves physiological cardiac hypertrophy, a decrease in the vascular wall thickness, and increases in the luminal width of conduit arteries. The process of functional remodelling is characterized by increases in cardiac contraction and dilatation and reductions in the heart rate and blood pressure.
Conversely, in atherosclerosis, exercise may enhance the amount of circulating endostatin and angiogenesis in plaque tissue, thus preventing the progression of atherosclerotic plaque, which may have important implications for the prevention and treatment of coronary heart disease
[51]. However, certain circumstances are required for angiogenesis and arteriogenesis to maintain tissue perfusion. The disturbance of these systems is one of the pathogenic mechanisms underlying several diseases, such as coronary heart disease. Angiogenesis and arteriogenesis may boost coronary collateral circulation, reduce myocardial damage during myocardial infarction, and improve blood perfusion and tissue healing
[52]. Exercise may stimulate the ischaemic myocardium, and angiogenesis and arteriogenesis can increase coronary collateral circulation and improve blood vessel and tissue healing perfusion. Endothelial dysfunction is one of the pathogenic mechanisms contributing to the development and progression of certain cardiovascular diseases. Physical activity may improve vascular endothelial function through mechanisms independent of cholesterol, blood pressure, glucose tolerance, and body weight
[53].
The effect of exercise on cardiovascular health is partially attributable to its direct mechanical stimulation of the cardiovascular system. One of the primary variables of cardiovascular function is mechanical force. For example, exercise-induced acceleration of the tissue blood flow increases shear forces, stimulating nitric oxide generation by vascular endothelial cells, widening capillaries, and improving blood perfusion to tissues and organs
[54]. Similarly, shear stress-induced movement increases blood flow and can directly induce vascular endothelial cells to secrete a movement factor. The latter, which is absorbed by heart muscle cells from outside the blood circulation and plays a role in cardiac protection, promotes interactions between the heart and blood vessels to affect cardiovascular regulation and protection
[55]. In a recent population-controlled study, stretching was found to be more effective for lowering blood pressure than brisk walking. The process may be related to the enhancement of vascular stiffness by mechanical stretching stimulation
[56].
The mechanism through which mechanical force stimulates and garners a response in the cardiovascular system remains unknown. Piezo receptors on the cell membranes of vascular endothelial cells, smooth muscle cells, and other tissues may sense mechanical force stimulation and initiate cellular calcium influx, resulting in changes in cellular functional activities. These receptors regulate cardiovascular function in response to exercise and are linked to the initiation and progression of cardiovascular diseases such as atherosclerosis, heart failure, and hypertension
[57,58][57][58].
3.2. Improvements in Myocardial Mitochondrial Function and Metabolism
Numerous studies have shown that increased mitochondrial activity is directly connected to the cardioprotective benefits of exercise. Mitochondria govern metabolic, redox, and cell fate processes. The myocardium is the most mitochondrially dense tissue in the body, accounts for approximately 40% of the volume of cardiomyocytes, and serves as the heart’s main energy source. During exercise, the energy demands of the heart increase substantially, leading to an increase in ATP generation. In addition, the heart has access to almost all metabolic substrates. Under normal conditions, the major metabolic substrate of the heart is lipoic acid (40–70%). During exercise, the myocardium increases its use of fatty acids and lactic acid while decreasing its glucose usage. Prolonged exercise increases myocardial glucose use, particularly the glycolysis level, which is related to the establishment and progression of cardiac physiological hypertrophy
[59,60][59][60]. Under normal conditions, the major metabolic substrate of the heart is lipoic acid (40–70%). During exercise, the myocardium increases its use of fatty acids and lactic acid while decreasing its glucose usage. Prolonged exercise increases myocardial glucose use, especially the glycolysis level, which is related to the establishment and progression of cardiac physiological hypertrophy
[61,62][61][62]. Long-term exercise may increase mitochondrial dynamics and function and thus increases the pace and efficiency of cardiac metabolism and the adaptability of the metabolic switch and strengthen myocardial damage resistance
[63]. Exercise increases the transcription factors PGC-1, PPAR, NRF2, and others that govern cell function and mitochondrial homeostasis
[64].
3.3. Other
In addition to the abovementioned mechanisms, exercise influences cardiovascular function. For example, prolonged hyperexcitation of sympathetic neurons has a negative impact on the structure and function of the cardiovascular system, which is one of the causes of several cardiovascular diseases
[65]. Long-term aerobic exercise may enhance cardiovascular autonomic nervous system function and homeostasis, increase parasympathetic nerve activity, decrease sympathetic nervous activity, increase heart rate variability (HRV), thereby exerting a cardioprotective effect. Cardiorespiratory fitness (CRF) reduction due to ageing or long-term inactivity is also connected to the onset and development of cardiovascular diseases. According to a meta-analysis, all-cause mortality and cardiovascular mortality are lowered by 13 and 15%, respectively, for each additional metabolic equivalent (MET) of cardiopulmonary fitness
[66,67][66][67]. Aerobic and resistance exercise may improve both cardiorespiratory fitness and cardiovascular health.