Homeostasis and Exercise
A hub on the regulation of the body's internal environment as exercise progresses.
What happens as we exercise?
The following hub will outline someone of the physiological responses that occur with the onset of exercise, and how the body looks to maintain homeostasis as exercise progresses, and after its conclusion.
Moments before a race or match, it is common for an athlete’s heart and respiratory rates to increase. These changes are due to the ‘fight or flight response’ of the sympathetic nervous system (SNS) and is caused by the release of catecholamine’s. Catcholamines are hormones, and the catecholamines released in this situation are epinephrine and norepinephrine (Wortsman, 2002), or more commonly known as adrenaline and noradrenaline.
Although the elevated heart rate may be perceived by an athlete as a physical manifestation of feelings of nervousness, this is not necessarily the case. In fact, the elevated heart rate allows the heart to achieve a greater cardiac output (Q), flooding working muscles with the oxygen necessary for them to function during exercise. Again the SNS is involved as, combined with a greater Q, it controls the redistribution of blood from the gastrointestinal tract to the working muscles by increasing and decreasing arteriolar diameters.
A few minutes in
After a few minutes of exercise temperature will rise, and in an attempt to return it to 37°C and maintain homeostasis, the preoptic-anterior hypothalamus sends impulses through the SNS to the eccrine sweat glands to secrete sweat (Wilmore, Costill & Kenney, 2008). Heat is then reduced by the evaporation of this sweat however it does lower water stores, which athletes must be careful to maintain as it will increase chances of dehydration. Additionally, blood is sent to the surface of the skin to dissipate heat. This is a good mechanism post-match however during physical activity a conflict is created here due to the need for blood to be sent to the working muscles to meet oxygen demands.
As exercise duration and intensity increases, a burning sensation in the muscles is common. Although widely believed to be caused by lactic acid, it is in fact caused by the accumulation of hydrogen ions which lower the muscle pH, a process termed acidosis (Maughan, 2008).
After a match hyponatremia is possible and explains why you should only take sips of water after a match. Without the combined effects of the restoration of sodium and the consumption of too much water, the osmatic balance across the blood-brain barrier is disrupted and can cause water to rush into the brain causing potentially life threatening swelling (Murray, Stofan & Eichner, 2003). Therefore drinking large volumes of water devoid of electrolytes will only further reduce the sodium concentration increasing chances of hyponatremia (Quinn, 2008). Although it is important to be aware of hyponatremia the chances of suffering from it depend upon exercise duration, with the condition being more prevalent among endurance events (Schurman & Schurman, 2009).
At the end of a match respiratory rates will remain high for around ten minutes after its conclusion. This elevated breathing rate, or excessive post-exercise oxygen consumption (EPOC), allows for the replenishment of oxygen stores and rids the body of carbon dioxide. EPOC can be thought of as the total amount of oxygen that would be needed to complete the whole activity aerobically. Furthermore 10% of EPOC is used to rephosphorylate creatine and adenosine diphosphate to phosphocreatine and adenosine triphosphate (Plowman & Smith, 2008), replenishing energy stores.
Maughan, R. J. (2008). The Olympic Textbook of Science in Sport. 1st Edition. Wiley-Blackwell.
Murray, B., Stofan, J. & Eichner, E. R. (2003). Hyponatremia in athletes. Online. Available at: http://www.gssiweb.com/Article_Detail.aspx?articleid=604&level=2&topic=6. Accessed on 22/2/2010.
Plowman, S. & Smith, D. L. (2008). Exercise Physiology for Health, Fitness, and Performance. 2nd Edition. Lippincott Williams & Wilkins.
Quinn, E. (2008). Can athletes drink too much water?. Online. Available at: http://sportsmedicine.about.com/od/hydrationandfluid/a/Hyponatremia.htm. Accessed on 10/3/2010.
Schurman, C. & Schurman, D. (2009). The Outdoor Athlete. 1st Edition. Human Kinetics.
Wilmore, J. H., Costill, D. L. & Kenney, W. L. (2008). Physiology of Sport and Exercise. 4th Edition. Human Kinetics.
Wortsman, J. (2002). Role of epinephrine in acute stress. North American Journal of Clinical Endocrinology and Metabolism, 31(1): 79-106.