Sunday, March 7, 2010

Physiological Fitness - Aerobic Capacity

Exercise physiologists generally agree that there are only three things you can improve to become physiologically more fit for endurance sports performance: aerobic capacity, lactate threshold and economy. Ultimately, these are the reasons you train. So what are they and how do you improve them? I'll discuss aerobic capacity now and come back to lactate threshold and economy in a few days.

Also referred to as VO2 max, aerobic capacity is your ability to use oxygen to produce energy. The more oxygen your body can process the more energy you can produce and the greater your output (power or pace). It’s common to find that the fastest athletes in a race have the highest aerobic capacities of the entrants. The farther down the race results you go typically the lower the athletes’ aerobic capacities. But don’t take this to mean that knowing your VO2 max tells you how fast you will go or how well you will do compared with others in your race category. The two other physiological factors – lactate threshold and economy – also play a major role in race outcomes. One of these by itself does not constitute all of what it takes to race fast.

Aerobic capacity is literally at the heart of success in endurance sport. Improvements in aerobic capacity have largely to do with how much blood (which contains oxygen) the heart pumps out to the working muscles with every beat. This is called “stroke volume” and has a lot to do with how much aerobic capacity you have. A purpose of training is to improve your stroke volume. There are basically two ways to do this. The first is to focus on the volume of your training. The heart responds to lots of time spent at higher-than-resting intensity (above about 50 percent of VO2 max) by becoming more efficient and effective which ultimately means pumping more blood per beat.

The other way to improve aerobic capacity is by doing high-intensity intervals, especially those done at about the power or pace associated with your VO2 max. At that intensity your heart rate is approaching maximum, so these are very hard efforts. This method will produce a higher stroke volume sooner than by relying only on volume. Most experienced athletes employ both strategies.

There are other physiological contributors to aerobic capacity such as aerobic enzymes found in the muscles, blood vessel diameter and ability to dilate, blood volume and related hematocrit (red blood cells). Many athletes seem to believe their lungs are the deciding factor when it comes to aerobic capacity. Training produces insignificant changes in lung volume.

Body weight also has a lot to do with aerobic capacity. The formula for determining VO2 max is expressed in terms of milliliters of oxygen consumed per kilogram of body weight per minute. What this means is that as you lose body weight, especially fat as opposed to sport-specific muscle, your VO2 max increases. And most of us have experienced this at both ends of the weight spectrum. When we have gained weight it’s harder to run or ride a bike uphill. Conversely, when body weight has been low the effort of exercise is decreased at any given power or pace. This is clearly the affect of body weight on aerobic capacity.

Aerobic capacity is largely dependent on who your parents were. Research (Bouchard, 1986) has shown that identical twins have nearly identical aerobic capacities. While genetics probably sets the boundaries for the upper limit of your VO2 max, proper training can take you to near the upper limit. But also bear in mind that there are two other physiological factors that contribute to endurance performance. I'll come back to them soon (I hope).

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At March 7, 2010 11:14 PM , Blogger Nate Spangler Chiropractic Student 2011 said...

Excellent post Joe. Your explanation of the training paradigm is insightful and inspiring.



At March 8, 2010 2:22 AM , Blogger AMR said...

Many thanks for this informative post on the basics of Physiological Fitness. Looking forward to the next part.

At March 8, 2010 8:00 AM , Blogger Steelcyclist said...

So while it is not possible to train your lung volume greater, it is possible to increase aerobic capacity?

I'm a bit confused, as later you say that aerobic capacity is dependent on genetics. Through heavy training what kinds of improvements have folks seen in their aerobic capacity overall? The increase must be in both the stroke volume as well as the 'other physiological' traits like vessel diameter and blood volume?

Great article as always Joe, thank you. I was just speaking with a coach friend who suggested VOC/Lactate testing, got any suggestions for the Seattle area?

At March 8, 2010 9:00 AM , Blogger Joe Friel said...

steelcyclist--Right. It's not lung capacity. It's the other stuff mentioned. Don't know of Sattle test facilities ut perhaps a reader can suggest one.

At March 8, 2010 10:09 AM , Blogger velobob said...

Joe - can one extend this concept then and say that by losing weight (fat) and increasing VO2Max that you would also increase your power at VO2Max (ie your MAP)?

At March 8, 2010 10:10 AM , Blogger velobob said...

Joe - can one extend this concept then and say that by losing weight (fat) and increasing VO2Max that you would also increase your power at VO2Max (ie your MAP)?

At March 8, 2010 1:46 PM , Blogger Josh said...

Steel - Who says you can't train lung capacity? If your body recognizes the physiological benefits, there's no reason that this can't become a long-term adaptation that occurs with improved fitness.

At March 9, 2010 5:19 AM , Blogger Joe Friel said...

velobob--No, not necessarily. But powr to weight ratio is likely to increase.

At March 9, 2010 5:40 PM , Blogger vlp said...

VO2max is sport dependent. Are we so sure that the limiting factor is the heart? The highest VO2max has been observed by cross country skiing, a sport that is weight bearing and uses the legs, core, and upper body. Weight bearing running produce higher VO2max than non-weight bearing cycling, etc.

It seems to me that the great limiter to VO2max is not the cardiovascular system, but mitochondrial density of sport specific muscles. While genes probably put an upper limit on this and probably provide the strongest correlation, I would bet there is a correlation between VO2max and training volume. The higher your training volume, the greater your mitochondrial density. High intensity training also matters because mitochondrial density in fast twitch muscles goes up best in response to high intensity training. Although, if you're an ironman, I don't know how much it matters that your fast twitch muscles have lots of mitochondria. Great for lab testing results, not so much in real world performance.

At March 11, 2010 9:28 AM , Blogger vlp said...

Upon further reflection, maybe the limiter is capillarization in sport-specific skeletal muscles. We know that altitude training (or EPO) also boosts VO2max. The amount of O2 delivered to working muscles is limited by the surface area of capillaries. Raising hematocrit levels increases the amount of O2 delivered per unit area of capillaries.

This would still explain why cross country skiers have the highest VO2max, their active muscles have more capillaries because they're using more musculature to produce power.

At March 13, 2010 1:28 PM , Blogger Laura Wheatley said...

Great post, and great comments! I think there is too much emphasis placed on VO2max, especially in the realm of trained athletes.

It can change pretty significantly when someone goes from sedentary to an active lifestyle, or from recreational to competitive endurance sport training, but genetics does place a "cap" on it. When trained triathletes come in wanting to know their VO2max, it's really more for bragging rights than actual training guidance...

However, actual WORK DONE at max can change with TRAINING - i.e. a recreational athlete may run a 6minute mile at MAX...after 8 weeks of consistent and smart training, they may be able to run a 5:45mile at the same rate of oxygen uptake/utilization.

I think the most useful lab tests are submaximal exercise metabolic rate tests. At common training and racing intensities, athletes can determine what their oxygen uptake is, what their heart rate is, how many calories they are burning, and whether they are using carbohydrate (inefficient, must be replaced during exercise) or fat (efficient, doesn't need to be replaced during exercise). The really cool part is when they come back later in the season and that at the SAME workloads, their VO2/HR/calories decrease, and their substrate utilization switches from carbs to fat!

Love your blog Joe! Sorry for the long comment, can't wait for the next edition of the "training paradigm"

At March 13, 2010 2:14 PM , Blogger Rodrigo Langeani said...

How much dependent on genetics is Vo2max?
Why cross-country skiers have high VO2max?
Excelent article!

At March 13, 2010 3:00 PM , Blogger Joe Friel said...

Rodrigo--The theory is that the upper limit of one's aerobic capacity is determined by genetics. As for XC skiers, they are using a lot of muscle to propel themselves--both upper and lower body. The more muscle is used, the more O2 is used. The more O2 is used, the hgher the VO2max (VO2max = volume of O2 used / body weight / time).

At March 13, 2010 9:49 PM , Blogger Ken said...


Interesting that training does not change lung volume. But does large lung volume (presumably inherited) correlate with high VO2 max? In other words, is lung volume an aerobic limiter?

Long time fan :-)

At March 14, 2010 1:57 PM , Blogger Joe Friel said...

Ken - No, it's not a sgnificant factor. You exhale O2 with every breath. It isn't hom much you take in, it's how much you use.

At March 15, 2010 1:26 AM , Blogger Pete F said...

Hi Joe, another terrific article as always. From my understanding VO2 max can be increased in a sedentary person by exercise, up to close to their genetic potential whereby any increase will be minimal regardless of any additional training load. In other words, VO2 max generally won't increase much in cyclists who have been training regularly for several years. Nevertheless, the POWER produced at VO2 max can be increased by systematic training, especially at or around VO2 max power. Can you confirm this understanding and explain (in a follow-up article perhaps) the mechanism by which VO2 max may remain constant, but power at VO2 max can be increased?


At March 15, 2010 7:18 AM , Blogger Joe Friel said...

Pete F--This will become more evident when I post about the third element of endurance fitness - economy (if I can find time).

At March 21, 2010 11:17 AM , Blogger Folkert said...

Hi Joe, read all about the three parameters of fitness: Aerobic capacity, Lactate threshold and economy (and am working on all of them). Recently I went to a sport laboratory in Turku, Finland, and they identify three points: Aerobic Threshold (the point where your lactic acid level starts to rise), anaerobic threshold (I guess it is the same as your Lactate threshold) and Maximum (the point where you cannot sustain effort). You do not use the term aerobic threshold, are you aware of the concept, and how does it relate to the training zones you (and I) use?


* Folkert/

At March 22, 2010 5:08 AM , Blogger Joe Friel said...

Folkert--I've written several posts on aerobic thresold(AeT) and decoupling which is associated with it. For example, see

At March 23, 2010 10:18 AM , Anonymous Anonymous said...

Hi Joe,

Great Post, Especially one of your answers "You exhale O2 with every breath. It isn't how much you take in, it's how much you use."

Do you think using decoupling to set (build phase) steady state duration at a 4 / 5A intensity is useful in increasing aerobic capacity .

thanks JD


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