José Antonio R. Piedrabuena -- Why do we need to exercise?

We are alive because all our organs communicate with each other through molecular signals, and we age when these signals decline or encounter resistance, or fail to output or have difficulty in inputting them.

Exercise stimulates communication between organs: skeletal muscle, heart, bone, liver and adipose tissue, endocrine glands, intestinal flora and the brain are sending or receiving signals indicating the need for each other's work. All of this is modulated by the muscle through its myokines.

Organ-to-organ communication is regulated by cell-to-cell signalling for the whole body and facilitates the subsequent reprogramming of multiple regulatory systems, including metabolism and immunity, which are disrupted by sedentary lifestyles and poor diet. Exercise, so to speak, resets the communication between organs: they return to stability, being essential for the proper functioning of the body and mind, preventing and inhibiting numerous diseases.

Physical exercise is able to increase in skeletal muscle the expression of several genes involved in energy expenditure and particularly in glucose and lipid metabolism.

The muscle

Muscle contraction secretes a series of molecules (lactate, cathepsin B and irisin), which communicate with other organs such as the liver, colon and brain, send signals to the brain and improve cognition and memory, send signals to the liver and improve its metabolism, export signals to adipose tissue and increase energy expenditure by using fat as fuel.

During exercise, muscle secretes 300 proteins and 600 factors, a whole host of commands and signals to the rest of the body. These include irisin and cathepsin B, a muscle-secreting factor necessary for neuroregeneration and cognition.

We improve our heart

Regular exercise may have anti-atherogenic effects: improving the balance of the autonomic nervous system (thus reducing the risk of malignant arrhythmias) and inducing cardioprotection against ischaemia-reperfusion injury.

It promotes an anti-inflammatory environment, stimulates myocardial regeneration and improves age-related loss of muscle mass and strength.

Molecules secreted by exercising skeletal muscle such as irisin, released by skeletal muscle into the circulation after exercise, protects the heart from injury due to insufficient blood supply through a free radical scavenging mechanism. Similarly, the protein myonectin is an exercise-induced myokine that also protects the heart from injury due to insufficient blood supply.

Daily exercise increases the number of mitochondria in cardiomyocytes, which are largely lost with age, as well as fat oxidation, cell survival and protein synthesis.

Both ageing and cardiovascular disease culminate in impaired cardiac function, so exercise is able to induce reverse remodelling of the left ventricle, bringing cardiac morphology closer to that of a young, healthy heart. Together, these adaptations result in recovery of cardiac function.

We maintain and protect the brain

Many of the myokines and hepatokines produced during exercise have also been found to flow through the brain. One such peptide is brain-derived neurotrophic factor (BDNF), a member of the neurotrophic protein family that facilitates neurogenesis, synaptic plasticity and brain cell survival - yes, all of which exercise provides. BDNF has also been linked to cognition and memory, because its expression in the hippocampus is decreased in people with depression and/or Alzheimer's disease. Conversely, studies in both rodents and humans have indicated that the resulting physical training and fitness are associated with maintenance or improvements in brain biology and function. The protective role of exercise may be due to several mechanisms. One of these is that it increases brain blood flow by 20%.

Life without exercise is associated with mobilisation, recruitment, retention of aberrant cell types and specific molecules that deregulate our metabolism, hormonal system, immunity and oxidative balance, favouring a tumour microenvironment.

Exercise activates genes that induce vascular vasodilation. The heart, lungs, vascular system and skeletal muscle adapt to the new situation and increase the supply of oxygen to the mitochondria of the muscular system, in a process called the oxygen cascade, and will increase their oxidative enzymes. The mitochondria are the thermal, energy powerhouses of the cells, which, by the way, increase in number, so we will have more energy and live longer, and less oxidised. Energy always comes from oxidising sugars, fats and proteins.

The adrenal glands release adrenaline and cortisol, which are so important for life's challenges, and through them energy is generated, in this case by the pancreas releasing glucagon, a sugar reserve that will be transformed into energy. All this explains why we start running or swimming and after a few minutes we feel tired, because all this machinery has to be put to work. Then after half an hour we can feel tired again, it is another turn of the screw in which the liver deposits, although it continues to synthesise proteins, have run out of glucagon and the fats we have around our waist or "love handles" and also the bad cholesterol, the good cholesterol increases. The liver stops synthesising lipids and proceeds to oxidise them, a way of transforming fat into energy. In total, in half an hour we have used up the reserves we have in our body and those we have in our body start to be used, we have exhaled a lot of CO2 and water and we are dehydrated, but not only water, we have lost minerals; so a broth, a glass of milk, or a shake and we also replenish minerals.

Exercise also increases glucose entry into cells and decreases circulating insulin, which is why it is so important for older people to exercise daily and to monitor their basal insulin level, as it tends to rise due to several known factors. In addition, it decreases circulating myeloid cells and increases the number of natural killer (NK) cells and their cytotoxic capacity. They kill bacteria through toxins, which are the ones that are depleted in severe cases of COVID-19 and defend us from infections. Another way of saying that the blood content is improved and our defences are strengthened.

This text may be reproduced provided that PROA is credited as the original source.