What is VO2 Max?
VO2 Max is the most amount of oxygen that can be used by your body (muscles)
in one minute. It is measured in units of mL per kg of body weight per minute.
Let's assume a healthy adult male has a VO2 max value of 50 mL/kg/min, which
is actually good for a trained individual and excellent for an untrained one.. If this
man weighed 71 kg (156 lbs) then his muscles, at maximum exercise would be
consuming 3550mL of oxygen every minute, or roughly the equivalent volume of
ten cans of soda.
VO2 Max correlates linearly with the amount of motor recruitment. At easy
exercise loads, not every muscle fiber is being used in any muscle. As we
exercise harder our brain's motor centers tell more motor units to start working to
enable this greater speed or force. If more muscle fibers are working then more
oxygen is being consumed than at lower work rates. This increase in muscle
fiber usage does not continue forever. There comes a point where our brain will
not recruit any more motor units. This is the first area that differentiates athletes'
VO2 Maxs. It is believed that some athlete's brains will not inhibit muscle usage
as much as other, less gifted athletes. Because they use a greater percentage
of their muscle fibers, they can sustain a greater speed and therefore consume
more oxygen.
Inactive people have lower muscle mass than active people, on average.
Greater amount of lean muscle mass means more oxygen can be consumed. It
would be easy to see that Michael Jordan is likely to have a higher VO2 max than
Dick Cheney.
Elite athletes have muscles that simply make use of more oxygen, and can then
sustain greater speeds and wattages. They may have just as many muscle
fibers working as another athlete, but if their muscles can consume more oxygen
per minute then it is possible they can sustain greater speeds (more later on
why this is "possible" and not definite). This may be due to improved enzyme
function within the muscle. There is plenty of oxygen inspired into the lungs, but
only a few can get high percentages of it into the muscle to be used. This ability
to use more oxygen is a double-edged sword as we will see in the next part.
Why do some runners with lower VO2 max values beat runners
with higher values?
Research has shown frequently that when you get a group of runners together
that have higher VO2 max values (>70), the one with the highest value is often
not the most successful runner. This puzzled scientists for a long time and the
root physiological reason still eludes them. It is apparent that (somehow)
athletes have different levels of running economy. Put simply, some athletes'
muscles need to consume less oxygen to run the same speed. Tim Noakes, MD
postulates that muscle elasticity is the key. Perhaps if we could quantify the
response of the contractile proteins of the muscle to Calcium, ATP, enzymes, etc
we might be able to then measure the elastic properties of muscle and determine
muscular efficiency.
So far we have discussed those with higher VO2 max values (>70). A lot of
research is done on elite athletes and so often discussions are skewed toward
the higher end of the spectrum. Noakes et al. have determined that there is a
point, above which you need to fall to be considered in the "elite athlete"
category. That magic number is 67. Most elite athletes are in the mid to high
70's. I have not heard of a case of a truly "elite" athlete having a VO2max below
67.
So how far can training take you?
If you have been competing in any sort of endurance sport for greater than 6
months, it is likely you will be able to train up your VO2max only about 5-15%. If
you are a couch potato who has never exercised a day in your life, it is possible
to raise you VO2max close to 40%. The reason for this is that when we first
undertake some endurance training (of almost any intensity) our bodies go
through a rapid compensatory phase in response to this exercise. Motor
recruitment is increased quickly which is why the early phases of our first training
endeavors saw our greatest and fastest improvements. It is because of this initial
improvement in motor recruitment that our VO2max rises.
More muscle working = more consumption of oxygen = greater VO2max value
After our initial training period the improvements come slower and they are more
hard fought. From this point we can train up our VO2max with specific high
intensity intervals, and again the increase would be on the order of 5-15%.
Where we start with our VO2max is genetically determined and consequently,
how high we can get it is genetically determined as well.
The injustice of this is that there are many hard working age group athletes out
there who, with all the intensive training they can muster, can work their VO2max
all the way up to 45, while some cigarette smoking, sedentary slug may have the
genetics that starts him off at 45 and he could train up to 63.
What about EPO? I hear someone ask. Synthetic EPO is chemically identical
to erythrpoietin....a chemical produced by our body that causes the production of
red blood cells (RBC). It is used in blood doping, illegally, to increase the
number of oxygen-carrying RBCs, so that more oxygen can be delivered to the
muscle. The hematocrit is the blood test determining oxygen-carrying capacity of
the blood. So will an athlete with a high hematocrit have a higher VO2 max than
someone with a lower hematocrit? Early research with EPO showed that it did
increase VO2 max, so oxygen-carrying capacity was thought to be one of the
limiting factors to VO2 max. More recent work (Celsing et al., 1987; Spriet et al.,
1986) is less clear, as blood doping does not solely increase maximal oxygen
uptake, but it also improves lactate metabolism. So, it is not unreasonable to
think that the runner with the high hematocrit may just buffer lactic acid better
than the athlete with a lower 'crit and that is why they won the race. It hasn't
been proven that oxygen carrying capacity is the limit to performance at maximal
exercise.
One question I have that I don't believe has been definitively disproved is this:
If you compete in Ironman triathlons and you have a low to moderate VO2max
(say 53) can you improve your economy (by years of dedicated, very distance
intensive aerobic training) so much that it will allow you to compete at an elite
level? My first impression is that I don't think you can. Why then are there no
elites with lower VO2max values? This distance intensive training would certainly
allow you to be very efficient over very long distances, but I don't think it would
dramatically allow you to run efficiently at the faster paces necessary to win big
races. Those speeds, I believe, just require a lot of oxygen, and to expect your
muscles to output that kind of power on very little oxygen is beyond the realm of
expected improvements in efficiency/economy.
Mark Allen wrote an article for Outside magazine about 8 years ago where he
stated that he would do a 1 mile time trial keeping his heart rate at 162 at the
beginning of his training season and his time would be about 7:30 or something
like that. He would then train with his heart rate always in a comfortable aerobic
zone....no speedwork, no intervals, etc. After about two months of training he
would do his mile time trial test again and his time would be 5:20, while his HR
always stayed at that low 160-something value. I was a little naive and terribly
excited that I might be able to have even some of these improvements, so I
religiously followed his training regimen. Well, I tested myself again after about 2
months of doing this and was more than a little dismayed that my mile time had
not changed at all. Effectively I had trained my body to run and be efficient at
that HR and consequently at that low speed as well. True, I could run farther,
just not any faster. So I started thinking....could Mark Allen do that because
1. He had done speed-training in the past and so his muscles were already used
to being efficient at those speeds or
2. Because he has an exceptional cardiovascular and muscular system that
allows him to consumes more oxygen and reach and maintain greater speeds?
I think it is a little of both.
That said, there are significant improvements that can be made in the
Back-of-the-Pack racer....they just might not become an elite athlete.