VO2 max. or maximum oxygen uptake, is considered the gold standard of cardiovascular, pulmonary, and muscule cell fitness. It is usually standardized per body weight and expressed in milliliters of oxygen per kilogram of body weight per minute, and is the maximum amount of oxygen your body (basically your muscles) can utilize. The VO2 max for an elite cyclist can range from 70 to more than 80 ml/kg/minute. It is generally measured on a treadmill or bicycle ergometer at a sports medicine clinic with the appropriate equipment. Exertion at or beyond 100% VO2max can be sustained for a few minutes at most. With training, you will increase your VO2max. as well as the ability to ride for longer periods at any % of your VO2max.

The following all indicate that an individual's VO2max has been reached:

VO2 plateau - no further increase in oxygen use per minute even with an increase in work performed
heart rate within 10 beats of the age predicted maximum heart rate -this is the basis for using your maximum heart rate as a surrogate for your VO2 max when designing your personal training program)
plasma (blood) lactate levels > 7 mmol/liter
For those of you interested in the mathematical expression of VO2max, it is the product of the arterio-venous oxygen difference (the oxygen content of blood leaving the heart minus that returning to the heart and thus the amount being extracted by the working skeletal muscles) and the maximal cardiac output (the maximal heart rate times the volume of blood pumped per beat). This is called the Fick equation.

Ranges of VO2max by age/sex
Calculating %VO2max based on your % of your MHR (Maximum Heart Rate).
Anaerobic Threshold (AT; also known as lactate threshold)is the level of physical performance at which the muscles produce more lactic acid than can be removed (by the liver and muscle enzyme systems). It is expressed as a percentage of VO2 max - or as indicated above as a % of its surrogate or maximum heart rate. At levels of exertion appraoching VO2max, there is a rapid increase in blood lactate levels. Cr. Concimi, a physiologist, suggested that it can be identified as the pulse rate deflection point with increasing exrcise (see the Concini test below).

Your AT limits your rate of maximal exertion (remember it can be exceeded for only a few minutes as you build up oxygen debt) and thus can be assumed to be reflected as the maximum physical effort you can maintain continuously for 30 to 60 minutes. The more you exceed your LT or AT, the more quickly lactic acid will accumulate and thus limit further increases in your performance. As most cyclists don’t have access to lab facilities, you can estimate your AT with a 30 minute (about 10 mile) time trial. The average heart rate you can maintain is a good approximation of your AT.

An individual's AT will improve with training, and cyclists with a higher AT can work at a higher level of energy expenditure for longer periods, defeating opponents of equal (or even greater) physical strength but with lower ATs. This concept explains why interval training, which is generally anaerobic, will improve performance.

Concini Test Another method of measuring your AT (and LT) is the Concini test. As a cyclist’s efforts increase, their heart rate generally increases in a direct relationship to the energy expended (a linear relationship). But at some point the heart rate begins to level off even as the speed (and energy expenditure) continues to increase. This is the anaerobic threshold, that point at which oxygen cannot reach the muscles fast enough, lactate accumulates, and performance suffers. After an appropriate warm up, using a single gear and a relatively high speed, the rider gradually increases his or her speed by 1 km per hour every 300 meters or so. Heart rate is graphed versus speed, and the break point on the graph is the AT.

Lactate Threshhold Recent work has focused on the blood lactate threshold (LT) as a reflection of an individual's level of training. The lactate threshold is that % of VO2 max. at which the cardiovascular system can no longer provide adequate oxygen for all the exercising muscle cells and lactic acid starts to accumulate in those muscle cells (and subsequently in the blood as well). At high levels of activity (but below 100% VO@max), there are always a few muscle cells (not entire muscles, but a small number of cells within those muscles) that are relatively deficient in oxygen and thus producing lactic acid. But this lactic acid is quickly metabolized by other cells that are still operating on an aerobic level. At some point, however, the balance between production of lactic acid and its removal shifts towards accumulation. This point is the LT. It is usually slightly below 100% VO2 max., and will improve with training (move closer to 100% VO2max). Those with an increased LT not only experience less physical deterioration in muscle cell performance for any level of %VO2max, but also use less glycogen for ATP production at any level of performance. Thus an improvement in LT allows the individual to perform at maximal levels for a longer period of time before running out of adequate energy (glycogen) stores.

Resting heart rate, your heart rate on awakening in the morning, is a simple but effective indicator of your level of training. It will fall as you train, but then begin to rise again with overtraining.

Cardiac Stress Testing for asymptomatic coronary artery disease.