VO2 max is defined as the maximal amount of oxygen the body is able to extract and use to support work performed by the body. It is therefore an indirect measure of the aerobic power of the body, which is controlled by complex interactions between neural (brain and nervous system), cardiovascular (heart and lungs) and skeletal muscle factors. The equation for VO2 max it is equal to the product of stroke volume (the maximum volume of blood the heart ejects in a contraction) and the arterio-venous difference (the difference between the saturation of the arterial blood and that of the venous blood). The aerobic power of the body will change constantly throughout a well-designed running program due to physiological changes and therefore its usefulness in designing a program and determining running capabilities is questionable. This article aims to explain the reason VO2 max is a better indicator of fitness levels than running potential and conditioning program design.
Many physiological adaptations occur as one becomes more fit, some of these include: an increased size and efficiency of the heart, increased blood volume, increased muscle capillarization (more capillaries developed) and increased mitochondria (small bodies in the muscle cell that use oxygen to burn fat and make energy) density. So it should be obvious then that if we increase the stroke volume or the a-v difference (or both), the VO2 max will increase. With a more muscular heart and an increased blood volume you may increase the stroke volume and with a greater extraction of oxygen from the blood at the muscle level (more mitochondria) you can increase the a-v difference, which equals a higher VO2 max. Thus, VO2 max is a good indicator of physical condition or fitness.
The question arises whether it is beneficial to know your VO2 max to develop an ideal training regimen or whether a high VO2 max automatically determines you as a great runner. From evidence accumulated by Prof. Tim Noakes and his colleagues at the Sports Science Institute of South Africa the answer is that knowing your VO2 max will not answer either question. Here’s the explanation according to Dr. Andrew Bosch at the Institute. Dr Bosch questions whether VO2 max is genetically determined (i.e. an athlete with a high value has muscles that are capable of utilizing large amounts of oxygen and has a cardiovascular system capable of delivering this quantity of oxygen). This athlete can then run at a maximum aerobic speed that can be sustained by this amount of oxygen. If VO2 max was determined genetically, then it would make no difference if the athlete was highly unfit or superbly fit since the result of the test would be the same. However, it should be intuitively obvious that a fit and more conditioned runner can run at a higher speed (higher power output) on a treadmill than when unfit. Dr. Bosch suggests that in this situation the (high) VO2 max value would be attained at a very low running speed, which would be impossibly inefficient.
Dr. Bosch confirms the common knowledge that oxygen demand increases incrementally as the speed (power output) of the runner increases. This increase in oxygen consumption continues until the athlete can no longer continue running at that speed and stops. The volume of oxygen consumed at that instant is termed the VO2 max and the running speed, the peak running speed. Historically, exercise scientists have attributed a leveling out or a plateau to VO2 max and that at the point this occurs determines the value. Research by Noakes and colleagues indicate that half of athletes tested in laboratories fail to demonstrate a plateau and that their VO2 or oxygen consumption is still increasing when they cannot continue further. This poses a question as to why these runners stopped if their oxygen consumption (the supposed limiting factor) was still on the increase. Prof. Noakes feels and is continuing to search for evidence that some “central governor” regulates the power output to the exercising limbs to help protect the body from “running itself to death” via a heart attack (see VO2 Max or the Brain?). The fact that oxygen consumption continues to increase until ultimate fatigue indicates that as the fitness level of the athlete increases and he is able to run faster, so does his VO2 max. Therefore, the inability to use the VO2 max test as a predictor of future performance of an athlete that can still improve his running by using a scientifically devised program becomes obvious – a great training induced increase in running speed (decrease in race times) will transfer into a substantial increase in VO2 max and visa versa. Even knowing the peak speed is unlikely to help an individual for the same reasons and also possibly because of the unlikelihood of being able to sustain such a speed/intensity for the duration of a long distance run.
Professor Tim Noakes feels that running economy is the true measure of performance. Running economy is the relationship between maximal power output and oxygen consumption. Good running economy in this context means that a highly economical runner may actually achieve a higher treadmill speed or power output at a relatively low VO2 max and is therefore more efficient. A less economical runner will require a higher volume of oxygen to achieve the same power output. Noakes is proposes that biomechanical efficiency contributes to running economy – for example, a runner with good core stability will waste less energy and power than a competitor with poor core strength that allows for inefficent movement. Also, Dr. Noakes considers superior runners to have superior fatigue resistance. That is, they have a superior heart that can maintain a high cardiac output at the maximum coronary blood flow and skeletal muscles that are efficient, elastic and possess a high degree of contractility.
Dr. Bosch concedes that even though it may be of little use in predicting running ability or program design, there are some uses for the VO2 max test. He advises that if a program is being designed for a beginning runner who has not run any races and therefore has no running times, a VO2 max test will give a good indication of the current condition of the athlete and how to base running schedules. Also, if performed regularly, a VO2 max test can give an indication of the effectiveness of the training program. Lastly, it is fun to compare own VO2 max to those of elite runners who often have values exceeding 70ml/kg/min.