VO2 Max, or maximal oxygen uptake, is one of the qualities we test for as part of our metabolic panel. We’ll be following up this post in the near future with more discussion about the rest of the metabolic panel, what the results mean, and why they are important, so stay tuned for more!
When it comes to VO2max, perhaps the most important question that arises is this:
How can an athlete use VO2max to achieve peak performance?
For starters, VO2 Max is an important physiological measure of cardiovascular fitness, which can also help to explain differences in athletic performance between individuals. VO2 Max is defined as the maximum volume (V) of Oxygen (O2) that the body can consume during intense full-body exercise, and is usually expressed relative to body weight to allow for fair comparison between different people. This is commonly expressed as ml/kg/min, or milliliters per kilogram bodyweight per minute.
There is a linear relationship between exercise intensity and oxygen consumption up until a point at which intensity increases without a corresponding rise in oxygen consumption. This point of plateau is regarded as an individual’s maximum aerobic capacity.
VO2 Max values can vary greatly between individuals, with an untrained individual or average Joe typically having a VO2max in the range of 25 to 45 ml/kg/min.
On the other hand, elite endurance athletes typically record much higher VO2max values than those recorded for untrained, and even trained individuals. Elite endurance athletes may have a VO2max in the region of 60 to 85 ml/kg/min—60 to 75 in women and 70 to 85 in men.
In fact, some athletes record values of greater than 90ml/kg/min!
A high VO2 Max is important since it means there will be a greater absorption and utilization of oxygen in the working muscles, thus giving the athlete the potential to work at higher work rates before the muscles demand for oxygen exceeds the supply. It is considered to be one of the best indicators of cardiovascular fitness and has been shown to be a key determinant of endurance exercise performance (Conley and Krahenbuhl, 1980; Morgan et al., 1989; Jacobs et al., 2011).
A further consideration is that a high VO2 Max indicates that an athlete has an extremely efficient cardiovascular system that will not only allow them to maximize their potential, but likely allow them to better recover more quickly from the physiological demands of the large training volumes and intensities utilized during endurance training.
This is supported by research looking at the effects of interval training on excess post-exercise consumption (EPOC) in which the researchers found that those with greater cardiovascular fitness (i.e. higher VO2max) had a reduced magnitude of EPOC (Matsuo et al., 2012) – in other words they had a quicker return to resting metabolism than those with lower VO2max.
From all this, one might wager that it is in his/her best interest to improve VO2max in order to improve performance in endurance modalities, such as marathons, triathlons, charity runs, and so on and so forth. This is true to a certain extent, but I would argue that VO2max is actually a better indicator of cardiovascular fitness that can leave clues as to where to start in this pursuit.
Is VO2max the be-all and end-all of aerobic endurance? Certainly not, but one would be mistaken not to consider the physiological adaptations that occur in athletes who possess such high levels of oxygen consumption. There are a number of factors that affect an individual's VO2max, including: age, gender, genetic physiology, body composition, and training status.
Age – One's VO2max is at its highest between the ages of 20-25. As we age our VO2max's are known to decrease at a rate of approximately 0.5ml/kg/min per year. The decrease is due in part to the age-related decline in maximum heart rate and stroke volume.
Gender – Men generally have a slightly higher VO2max (approximately 15-30% higher) than women. The difference in VO2max between men and women is influenced by a number of factors including differences in %body fat, muscle mass, blood volume, and hemoglobin levels.
Genetics/physiology – These factors play a significant role in VO2max, with approximately 10-30% of the variability in VO2max being accounted for by genetics. Genetics appears to influence VO2max through a number of factors including: cardiac output, which is known to significantly influence VO2max (Poole and Richardson, 1997), muscle fiber composition, body size, muscle mass, body fat %, mitochondrial density, aerobic enzyme levels, capillary density, lung capacity, blood, viscosity, and red blood cell concentration. Some people just picked the right parents; they were built to run long distances.
On this note, researchers studied 30 boys and girls in Nandi, a district in Kenyan’s Rift Valley responsible for producing many elite runners. They recorded the number of minutes over a 14-hour day that the children were sedentary and active, and how far they walked to and from school. The kids, who ranged in age from 10 to 16, also completely a multitude of fitness tests, including VO2max. The boys had a VO2max of 73.9, and the girls, 61.5! That’s mind-boggling, and it’s no surprise that Kenyans also hold 8 of the top 10 marathon times in the entire world.
Body composition – Since VO2max is expressed relative to bodyweight, any variation in bodyweight will affect VO2max. Body composition, though, is also known to influence VO2max—an athlete with a higher % body fat will tend to have a lower VO2max than a similarly sized athlete with a lower % body fat.
Training status – Training can significantly influence VO2max. The extent of improvement varies greatly between individuals, but VO2max may be increased by up to 20% depending on current fitness status, previous training history, and one's training regimen. Highly trained elite athletes are unlikely to see further significant improvements in VO2max, and any further improvements in exercise performance will likely come from improved lactate threshold, % sustainable VO2max, and improved exercise economy.
Exercise Type – The type of exercise is known to affect VO2max, with greater values generally recorded in weight-bearing exercises such as running rather than non-weight-bearing exercises like swimming.
As you can see from the above, a lot of people can start improving VO2max through training, which will affect both fitness status and body composition. Knowing this variable helps people determine the best course of action to improve their endurance performance.
Performance in endurance modalities isn’t the only thing that can be predicted by VO2max, however. Many of you may not recognize the hockey player pictured here, so for the uninitiated, that’s Duncan Keith. He’s a 3-time Stanley Cup Champion defenseman for the Chicago Blackhawks, and unanimous Conn Smythe trophy winner. He consistently averages among the most minutes played among NHL players. As a side note…he's also been reported to have a VO2max of 71 ml/kg/min.
One may not think of hockey as an aerobic sport; after all, most players will only be on the ice and completing hauling ass for about 45 seconds at a time before being subbed out in line changes throughout the game. However, the ability of an athlete to recover fully between these shifts, periods, and games is an invaluable advantage. This is all dependent on having a good aerobic base, and one of the markers of this is VO2max.
To better understand all these concepts, it would be worthwhile to explain some basic bioenergetics--or how energy is made in the body--with regards to exercise and performance.
The human body is dependent on fats (lipids), and carbohydrates (blood glucose and muscle glycogen) to support ATP (the body's unit of energy) regeneration to power muscle contraction during exercise (Roberts & Robergs 1997). Availability and utilization of these substrates plays a significant role in the limitations to endurance exercise.
The intensity of endurance exercise determines the substrate utilized to provide energy. During low-intensity endurance exercise (<60% VO2max), both fats and carbohydrates are used to support metabolism. With increasing exercise intensity (at or above 70% VO2max), there is a shift towards more carbohydrate metabolism to support continuous exercise (Roberts & Robergs 1997). While carbohydrate supply is limited, lipid supply in most individuals is unlimited. However, after approximately 2 hours of intense steady state exercise, muscle glycogen stores become significantly depleted, resulting in fatigue regardless of the presence of an adequate oxygen supply.
Research has demonstrated that the ingestion of carbohydrates during exercise can prolong the duration of exercise beyond the time supplied by muscle glycogen stores (Coggan & Coyle 1989). When muscle glycogen stores are exhausted, individuals experience fatigue and muscular pain. In marathon running, this physiological event is commonly referred to as “hitting the wall”.
One of the most noted physiological adaptations to endurance training is an increased reliance on fats at the same relative intensity workload. This is a desirable adaptation, and is commonly known as the crossover concept. This carbohydrate sparing modification increases an individual’s potential for endurance activity and performance at lower intensity (<60% VO2max).
This concept is illustrated above. With training, the graph shifts to the right. At a certain % of VO2 Max, you will be utilizing more fat and less carbohydrate to fuel your exercise than before, allowing you to conserve your carbohydrate stores.
As an example, let’s say you jog at a rate of 7 miles/hour, and consume oxygen at a rate of 70% VO2max. Through proper training, you increase your VO2max and running at 7 mph is now 60% VO2max for you. Because of this, you are better able to conserve your carbohydrate/glycogen stores, and thus, you can run longer before hitting a wall.
Regardless of training status though, at exercise intensities nearing lactate threshold (which we’ll explain in another blog soon!) there is a greater predominance of carbohydrate utilization for energy because the metabolism of carbohydrates (resulting in the formation of ATP) is less dependent on oxygen consumption (Robergs & Roberts 1997). The body requires less oxygen to burn carbohydrate as compared to protein or fat, and thus carbohydrate is considered the body’s most efficient fuel source. Carbohydrates are increasingly critical during high-intensity exercise when the body cannot process enough oxygen to meet its demands.
Most endurance competitions are performed at intensities near the anaerobic threshold in which substrate utilization relies almost entirely on blood glucose and muscle glycogen. Long-term training in multiple endurance sports including cycling, running, and swimming has been shown to increase muscle glycogen levels (Robergs & Roberts 1997). This training adaptation delays muscle glycogen depletion, and extends the duration and intensity of the endurance exercise.
The Implications of VO2max on Future Training
When someone has knowledge of their VO2max, s/he can easily integrate that into training utilizing heart rate training zones. Heart rate monitoring is a convenient method to monitor intensity once a metabolic profile has been established. Due to the correlation between heart rate and oxygen consumption, once a valid VO2 max test has been completed, an athlete may be prescribed exact heart rate zones for their cardiovascular training that match well with percentages of VO2 max.
Current recommendations for improving VO2 Max include interval training between 90 and 100% VO2 Max. This method, often labeled high intensity interval training, is believed to be one of the best training methods for placing the greatest physiological stress on aerobic energy systems. It involves performing repeated work/rest intervals, such as 4-8 sets of 3 minute of work alternating with 60-90 seconds of recovery, at speeds or intensities that correspond to 90-100% VO2 Max.
While VO2 Max values determine the capacity of which an athlete is able to achieve during training, it is only one physiological marker that explains improvements in performance across endurance athletes. Stay tuned for more; we’ll be talking about anaerobic threshold next!