VO2max - Maximal Oxygen Consumption and the Anaerobic Threshold
One of the most common measured, physiological variables in sports medicine is the maximal oxygen consumption. It is simply a measure of aerobic capacity and cardiorespertory and is the most amount of oxygen used to produce ATP. In order to reach VO2max you must do an extensive, intense workout normally done on a treadmill or bicycle.
The differences between VO2max and the stroke volume and cardiac output are directly related and are similar in type of capacity. Maximal oxygen consumption is a sign of what the cardiac output is doing. While running your muscles are, in a sense, sent a message to do more work, in order for this to happen you need an increase of oxygen to these muscles so they can produce ATP. The oxygen is then delivered to the muscles; the muscles withdraw the oxygen and use it in the aerobic energy processes to create ATP to allow you to continue on running. Without this increase of cardiac output, that delivers more oxygen to the muscles when needed, oxygen absorption could not reach the levels needed to support the increase in work effort.
Skeletal muscles that are trained must have an immense capacity to absorb oxygen to the blood and make ATP. A developed muscle has the volume to absorb all the oxygen that can be delivered to the muscle. As a result, the restrictions in a personís VO2max are the ability to carry oxygen to the muscle or in the cardiac output, as was in other areas. VO2max and cardiac output are measures of the same capacity - the capacity to give oxygen to the muscles and the volume of the muscles to consume the oxygen to produce ATP. People with extreme maximal cardiac outputs will have high VO2max. The higher your VO2max, the better your aerobic capacity.
Endurance activities is the anaerobic threshold is also a contributor to you performance. The anaerobic threshold is the percentage of your maximal oxygen consumption that you can endure for a prolonged amount of time. If you work at or just below the anaerobic threshold, lactic acid will not build up and you can continue working for a longer period. When you begin to work above your anaerobic threshold, lactic acid begins to accumulate because you are doing more of the work anaerobically when this happens you will not be able to work for much longer.
An average untrained adult has an aerobic threshold of about half of VO2 max, but a trained person may have an aerobic threshold as high as 80% of VO2 max. For any value of VO2 max, a higher anaerobic threshold results in being able to do more work for longer periods. A high anaerobic threshold can countervail a low VO2max and a high VO2max can countervail a low anaerobic threshold. The best of course is to have both.
Just as it builds VO2max, training builds the anaerobic threshold and intensifies lactic acid removal.