Basic Course in Training Science Part 2 - Training Physiology
4,5 min read
Updated: 6 December 2018
After gaining an understanding of how the body converts nutrition into energy and how muscles are structured, it is now time to move on to the two systems that connect everything in the body: the cardiovascular system and the nervous system.
Cardiovascular System
The heart, lungs, blood, and blood vessels make up the cardiovascular system. Its main task is to supply the body's organs and muscles with oxygen-rich blood.
The heart, this small muscle weighs about 200-600g and is the organ that so many of us endurance athletes strive to train, making it stronger so it can pump out enough oxygen-rich blood at 195 beats per minute! In a well-trained athlete, the heart can pump about 40 liters of blood per minute! The frequency at which the heart beats is called the pulse, and it can be easily measured manually or with a heart rate monitor to keep track of resting heart rate and maximum heart rate. By testing one’s resting heart rate and maximum heart rate, one can also find their threshold heart rate. Maximum heart rate decreases with age but actually says very little about how well-trained a person is. Resting heart rate, on the other hand, is a good personal indicator as it decreases somewhat as you become more well-trained. The heart becomes more efficient and stronger through endurance training, allowing it to pump more blood per beat and thus not have to beat as many times each minute. For elite athletes, it is not uncommon to have a resting heart rate down to 30 beats/min.
As mentioned, the heart pumps blood. Blood consists of 99% red blood cells and blood plasma; in addition, there are also platelets and white blood cells. The function of blood during activity is to transport essential substances such as oxygen, carbohydrates, and fatty acids to the muscles and organs, as well as remove carbon dioxide and lactate. The heat generated during activity also helps blood to transport away to the skin for cooling. Furthermore, proteins (enzymes) and salts/minerals are transported in the blood. Blood is pumped through the arteries leading out from the heart to the muscles and organs. The blood vessels branch out and become increasingly thinner, eventually becoming capillaries, which are super thin and can transport blood all the way to the muscle where the exchange of blood between the capillary and muscle occurs. Endurance training stimulates the body to create more capillaries, enabling oxygen transport to occur more efficiently. After the exchange, waste products are transported away, and the deoxygenated blood returns to the lungs via the veins.
Last in the cardiovascular system, we have the lungs. These two sacs provide the body with oxygen and help us get rid of the carbon dioxide formed during energy processes. An adult human has about 4-7 liters of lung volume, and here the size of the person plays a significant role. In the alveoli of the lungs, the exchange of oxygen and carbon dioxide takes place, allowing oxygen-rich blood to continue to the heart and be pumped out into the body. By measuring how much oxygen we inhale and exhale, one can determine the oxygen uptake; more about oxygen uptake and how it affects performance will be discussed in part 3.
Nervous System
The nervous system is probably the most advanced system in the body, next to the brain, and is incredibly important for our performance capability, although it is a bit more complicated to explain. It is divided into the Central Nervous System (CNS), which consists of the brain and spinal cord, and the Peripheral Nervous System (PNS), which includes the remaining nerves in the body. The precision and speed of the nervous system are genetic and vary from person to person. However, it can be trained to function faster and more accurately (for example, we can learn new movement patterns). During childhood, we find ourselves in the "motor golden age" where we have a significantly easier time learning new things and movement patterns.
In addition to CNS and PNS, the nervous system is divided into the Autonomic and Somatic Nervous Systems. The autonomic nervous system controls the parts of the body that we do not consciously influence, such as vital functions like heartbeat, breathing, and metabolic functions in the digestive system. Within the autonomic nervous system, there are the sympathetic and parasympathetic nervous systems that accelerate and decelerate the body's functions. For instance, when we engage in intense physical activity, the parasympathetic nervous system slows down the digestive process as more blood is needed in the working muscles, while the sympathetic nervous system increases blood flow and raises the heart rate (pulse).
The part of the nervous system that we can influence with our will is called the Somatic Nervous System, which also includes sensation in the skin and muscles. Through this system, muscle fibers are activated when a motor neuron (nerve cell) stimulates the muscle fiber through an axon (nerve fiber). Different types of stress engage different muscle fibers. The higher the force required, the more motor units (motor neurons + muscle fibers) are activated.
This concludes the overview of the four categories of physiological systems that govern the body and, consequently, our performance. In part 3 of training science, the focus will be more on performance and the physiological factors that limit our physical capabilities.
