Updated: Dec 11, 2019
The human body has the most amazing ability to adapt both acutely and chronically, this article takes a closer look at what happens when we begin to exercise and why we get better after continuous endurance activity. Understanding this can help with your training, race preparation and motivation.
The very first thing that happens during activity is the use of a complex chemical called Adenosine Triphosphate (ATP). ATP stores and releases energy into muscles to allow them to contract and create movement throughout the body. ATP is in constant use as muscle contractions are occurring all day everyday (involuntary muscles such as the heart), however it is only when muscle contractions (mostly voluntary muscles) become elevated when the body begins major adaptations to cope. The body stores a small amount of ATP within the muscles; this is constantly being broken down and resynthesized to sustain life and movement. This process is called ATP resynthesis and requires oxygen (O2) to take place, simply put the more ATP we use the more O2 is require to sustain movement.
Increased blood supply
Every other change within the human body is because of the increased use of ATP. The muscles begin to demand more O2 as this is required to resynthesis ATP at a higher rate; therefore the heart begins the first of its two acute adaptations. The nervous system sends signals to the heart to beat faster than it does at rest, this means more blood is being pumped around the body carrying more O2 to working muscles. The second adaptation the heart makes is an increase in stroke volume (the amount of blood pumped out with each beat), heart rate multiplied by stroke volume equals cardiac output which at rest is around 5 litres of blood pumped out of the heart per minute, whereas elite endurance athletes can increase this rate to around 35 litres per minute.
Increased breathing rate
When we begin to exercise we begin to breathe harder, however this is not in response to the body needing more O2 to resynthesis ATP. A by-product of ATP resynthesis is carbon dioxide (CO2), like O2 this is carried by the blood. The body needs to get rid of the carbon dioxide and it does so via a process called gaseous exchange, this takes place in capillaries within the lungs (where CO2 is dropped off and O2 collected by the blood) and within the muscles (Where O2 is dropped off and CO2 is collected). The body begins to breathe harder primarily in an attempt to get rid of CO2 rather than to take in O2, this is why our first action after holding our breath is to exhale as oppose to inhale. As intensity of activity increases the body struggles to supply enough O2 to working muscles, this is known as VO2 max and is a significant factor for endurance performance. There will be another article on this separate to this as it can be a major performance factor and training can be specifically adapted to improve this.
So next time you begin exercising you can understand just how amazing your body is and will be able to feel each stage kicking in. Please feel free to leave a comment or ask about this during your next treatment.