In the fitness industry, we hear multiple acronyms thrown around - HIIT, LISS, EPOC etc etc.... But what do they all mean? With trends coming and going and research proving and disproving the same theories, it can be difficult as a consumer to ascertain fact from fiction. So, in this blog I decided to give you a run down of the basic science behind training and how different formats of exercise impact different body systems accordingly.
Heart rate- A good place to start is working out your heart rate zones. On average, an adults resting heart rate should sit between 60 and 100 beats per minute. A simple way to calculate your heart rate is to find your radial pulse (on the thumb side of your forearm at the wrist). I usually count the beats for 10 seconds and then multiply it by 6 - for example I just counted mine over 10 seconds which was 9. Multiple that by 6 and my resting heart rate is 54. As a general rule, the fitter you are, the lower your resting heart rate.
So what happens during exercise?
As we place more demands on the body, the heart must keep up with the metabolic needs accordingly. Cardiac output (amount of blood pumped out of the heart each minute) must increase in order to supply more oxygen to the skeletal muscles and remove waste products such as lactic acid, hydrogen and carbon dioxide. On average, the cardiac output is about 5 litres per minute at rest. During exercise, sympathetic stimulation causes heart rate to increase and veins to constrict returning more blood to the heart. The resultant effects means we increase our cardiac output to about 20-25 litres per minute! See the graph below to track how our cardiac output increases as intensity on a treadmill goes up.
Lungs- obviously our heart and lungs work together during exercise. Again sympathetic nerve stimulation makes the respiratory muscles work harder to increase rate and depth of breathing. Also, the increased, heart rate, cardiac output and blood pressure enables more blood flow to the tiny air sacs in the lungs. This increases ventilation and allows more oxygen to enter the blood stream, therefore providing more oxygen to the working skeletal muscles. At rest your lungs move around 6 litres of air per minute at a breathing rate of about 12 breaths per minute. During exercise, you can move up to a staggering 192 litres of air per minute at a respiratory rate of 48 breaths per minute!
So how do all these changes effect us post exercise?
During training, you have caused a huge deficit and your body must now continue burning increased levels of energy (metabolism) in order to restore your body to its normal state (homeostasis). This effect is known as EPOC - Exercise Post Oxygen Consumption. Depending on intensity of exercise, this can last anywhere from 15 minutes to 48 hours post exercise! Interestingly, studies continue to show that High Intensity Interval Training (HIIT) creates a greater EPOC than steady state training. In HIIT training, we use the anaerobic energy system more which is less efficient than the aerobic system used in steady state training. Consequently there are more by-products (lactic acid) and the body works harder to utilise energy from glucose which is only short acting. See the graph below depicting the different EPOC for HIIT and steady state:
So as you can see, there's a lot going on to our bodies when we're exercising! I am fascinated with sports science and I love understanding the metabolic effects of training on our body systems. The human body is quite remarkable at adaptation and as we get fitter, its amazing to see how far we can push ourselves. Through better understanding of adaptations during exercise, we can work out what form of exercise suits us best by harnessing our natural abilities. Being cognisant of things like heart rate zones also enables us to achieve different fitness goals. We can determine our maximum heart rate by doing 220 minus our age. This rough estimate then enables us to ascertain what intensity levels we achieve in our workout. See the picture below for heart rate zones.
Well I hope you enjoyed this blog and can take away some basic information about sport science. I think it really highlights how amazing the human body is and how you as an individual can harness the science to reach new fitness goals! Good luck!