Defined by Merriam-Webster's Collegiate Dictionary, 11th edition, "aerobic" means living, active, or occurring only in the presence of oxygen and "physiological" is characteristic of or appropriate to an organism's healthy or normal functioning. Physiological measures related to aerobic fitness are those variables that change in the body during cardiorespiratory activities. Many reactions occur in the body during any fitness activity, but there are a few that are particularly important during aerobic activities.
VO2max
VO2max is the standard measurement of cardiorespiratory fitness. VO2max is the product of cardiac output and arteriovenous oxygen difference--in effect, VO2max is the body's maximal oxygen uptake. Methods to measure your true VO2max are highly invasive and costly; thus indirect measures are used to arrive at an estimated VO2max. Higher VO2max readings are associated with improved physical activity and are typically higher in males versus females.
Heart Rate
Heart rate is one of the best known measures of aerobic fitness. Heart rate is the number of heart beats per unit of time. Typically readings of beats per minute are given. During activity as the body demands increased blood flow the heart rate increases. A general calculation that you should be aware of during activity is your maximum heart rate, which is calculated as 220 minus your age. As fitness level increases, resting heart rate decreases and the amount and intensity of activity needed to reach your max heart rate increase.
Blood Pressure
Blood pressure is the measure of the pressure that blood exerts throughout the vascular system. It is often measured in the arteries where pressure is the greatest. Most people are aware that blood pressure is actually not one number but two. The top number, which is the higher of the two, is systolic blood pressure, and it is the pressure created when blood is ejected from the heart. The bottom and lower number is your diastolic blood pressure, and it is the pressure created as your heart relaxes. Aerobic exercise has been found to lower resting blood pressure. During activity systolic pressure rises, while diastolic readings remain relatively unaltered.
Stroke Volume
Stroke volume is the amount of blood pumped by the ventricles in a single beat. Stroke volume increases as activity increases but has been found too plateau somewhere between 40 and 60 percent of VO2max for most individuals. Aerobic training has been found to increase resting stroke volume, which results in decrease of resting heart rate.
Cardiac Output
Cardiac output is the amount of blood pumped by the heart per unit of time. It is equal to the product of heart rate and stroke volume. Since both heart rate and stroke volume increase with increasing activity, cardiac output increases with increases in activity level. Increases in cardiac output beyond 40 to 60 percent of VO2max are caused by increases in heart rate because of the plateau of stroke volume.
References
- "Exercise Physiology;" Scott Powers, Edward Howley; 1997
- "Physiological Tests for Elite Athletes;" Christopher Gore, PhD; 2000
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