During exercise there are a wide range of metabolic demands put on the body, especially with endurance activities. Endurance exercises place demands on the heart and blood vessels to deliver oxygen, remove carbon dioxide, and dissipate heat from the muscles. The primary purpose of the cardiovascular system during physical exertion is to deliver oxygen to the exercising muscles. Exercise performance greatly depends on the ability of the cardiovascular system to respond to the increased metabolic demands.
When at rest the metabolic requirements of the body are dominated by the brain, liver, and kidneys. Most people have a resting metabolic rate of 3.5 mL/min/kg or 1 MET (metabolic equivalent). As the workload increases the working muscles have an increased demand for oxygen. More than 80% of the blood flow during exercise can be directed toward the exercising muscles. Cardiac output (heart rate x stroke volume) increases to meet the increased demands of blood flow toward the muscles. During maximal aerobic exercise cardiac output can reach 4 to 6 times that of at rest. This can be even greater in well-conditioned endurance athletes. In well-conditioned athletes we can see a cardiac output of more than 40 L/min.
Maximal aerobic power or maximal VO2 defines the aerobic limits of the cardiovascular system. It is useful in measuring a person’s overall fitness because it provides an integrated measurement of cardiopulmonary and skeletal muscle function. VO2 max is the greatest rate of oxygen uptake by the body measured during maximal dynamic exercise. This is usually tested on a treadmill or while cycling, however there are other test that can be performed to calculate VO2 max. A person’s body weight, age, and sex influence their VO2 max.
Regular exercise leads to favorable changes in cardiac structure and function. The physiologic hypertrophy that occurs with repetitive aerobic training is termed the athlete’s heart. The cardiovascular system adapts to ensure adequate delivery of oxygen to the exercising muscles. One can see an increased cardiac chamber size with 4 to 5 sessions per week of moderate aerobic exercise within one year, in previously sedentary individuals. With significant training, changes to the left and right ventricular morphology can be seen in three months. Athlete’s hearts also show a reduction in the estimated peak wall tension. The athlete’s heart is much larger and distensible than the non-athlete’s heart.
Exercise testing can provide a comprehensive evaluation of an athlete’s performance capabilities. Supervised exercise testing is controlled exercise activity where an individual is put through exercises with gradual increase of workloads.
The purpose of exercise testing is
- To evaluate baseline fitness and prescribe an exercise program
- To evaluate continued progress after engaging in exercise training over a period of time.
- To diagnose cardiopulmonary conditions affecting exercise performance.
- To provoke arrhythmias or evaluate hemodynamic response to exercise in an athlete with a known cardiovascular condition, and to determine safety of competitive sports.
Measurements of maximal oxygen uptake (VO2 max), maximal steady state, economy, and anaerobic capacity describe an individual‘s exercise abilities. There are risks associated with exercise testing. Major complications can arise with exercise testing, however, when done under proper supervision exercise testing entails a very small risk. The American College of Sports Medicine recommend that testing should be performed under the supervision of a properly trained physician or individual incorporating appropriate technique and safety measures. A medical history, physical examination, and standard 12-lead electrocardiogram obtained before exercise testing can guide the determination of the level of supervision required for the test.
A. (n.d.). Determinants of Myocardial Oxygen Consumption. Retrieved September 07, 2016, from http://www.cvphysiology.com/CAD/CAD004.htm
Opondo, M. A., Md, Sarma, S., Md, & Levine, B. D., MD. (2015). The Cardiovascular Physiology of Sports and Exercise. Clinical Journal of Sports Medicine, 34, 391-404.
Orenstein, T. L., Parker, T. G., Butany, J. W., Goodman, J. M., Dawood, F., Wen, W. H., . . . Liu, P. P. (1995). Favorable left ventricular remodeling following large myocardial infarction by exercise training. Effect on ventricular morphology and gene expression. Retrieved September 07, 2016, from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC185272/