Cardiorespiratory endurance is how effectively your heart, lungs and blood vessels work together to get oxygen to all of your body’s tissues and organs. The amount of oxygen your body uses is referred to as oxygen consumption or VO2, or volume of oxygen. As your intensity of exercise increases, VO2 rises and eventually reaches its peak value, known as V02max. VO2max, also known as aerobic capacity, is the measure of cardiorespiratory endurance.
VO2max is measured in a laboratory setting using a mask device that measures oxygen consumption. The test subject performs exercise that gradually becomes more intense. VO2 is monitored and the test is stopped when VO2 stops rising. The measured value of oxygen consumption, or VO2, at the conclusion of the test is the VO2max. According to “Exercise Physiology," by Scott Powers and Edward Howley, the cost and complexity of laboratory testing make it unpractical for a health club setting. Therefore, other methods have been developed for estimating cardiorespiratory fitness.
The “NASM Essentials of Personal Fitness Training” describes several methods for estimating cardiorespiratory fitness. In the three-minute step test, you step up and down on a step of a predetermined height at a pace set by a metronome for three minutes. Then your heart rate is measured for a specified time. This recovery heart rate is used to estimate your level of cardiorespiratory fitness. A lower heart rate means a higher cardiorespiratory endurance level.
Another method described by the National Academy of Sports Medicine is the Rockport Walk Test. You walk for a mile as fast as you can control on a treadmill. At the mile mark, your heart rate is measured. This heart rate measurement is then plugged into a formula with your height, weight, age and time. The calculation gives an estimate of VO2.
Measuring Relative Improvement
The common theme in all of these tests is that lower heart rate at any given intensity level indicates better cardiorespiratory endurance. This idea can be used to measure your relative improvement over time. For example, you can measure your heart rate while walking 3.2 miles per hour on a treadmill. Then two months later, measure again. Any improvements will show up as a reduced heart rate at the same exercise intensity.