Comparative physiology of aerobic scope

When surfing around looking for data on VO2max I found some interesting comparisons.

First we can have a look at different sports, you may remember that elite judo athletes had a maximal VO2 at around 60 ml/(min*kg). I guess most readers will have heard about the extremes of aerobic capacity. Who the best is depends on the unit used. Cross country skiers are the most extreme when compared to body weight. The highest ever published VO2max was Bjørn Dæhli, world champion from Norway. He had a VO2max over 90 ml/(min*kg), I have seen anything up to 96 ml/(min*kg), but cannot find the original publication.

If we ignore body weight, olympic rowers are reported with the highest oxygen consumption among athletes, but they can afford to be more massive than many other athletes and therefore get lower maximal uptake when related to body weight.

Then we can look at the real comparative physiology of endurance. Reported maximal oxygen consumption VO2max in running animals are quite a bit more impressive than humans. Note that these are extremes from non-original publications.

Human: 96 ml/(min*kg)

Horse, thoroughbred: 160 ml/(min*kg)

Dog, sledhound: 240 ml/(min*kg)

So, that's why I can run for an hour with my boxer, and when I am all done she wants to play fetch. For another hour.

Even more interesting than maximal aerobic capacity is the concept of aerobic scope. That is the difference between the rate of oxygen consumption at resting metabolic rate and at maximal aerobic exertion, i.e. VO2max.

Oxygen consumption at rest from original publications:

Human: 7.8 ml/(min*kg) (J Hum Kin vol 6, 2001, Andziulus et al)
Horse: 7.2 ml/(min*kg) (Am J Physiol vol 253, 1987, Weber et al)
Dog: 7.8 ml/(min*kg) (J Appl Physiol vol 19, 1961, Bailie et al)

This gives an aerobic scope of about 10 times in human endurance athletes, 20 times in racing horses and a whopping 30 times in racing dogs. This is not what is generally reported as aerobic scope because it is usually based on basal metabolic rate, which is a theoretical entity measured after sleep and fasting at a high ambient temperature. And, it is compared to popularly reported maxima for the different species. If you look at scaling and metabolic scope there are better articles with reproducible methods and averaged maxima e.g. Charles Bishop, Proc. R. Soc. Lond. B (1999) 266, 2275-2281.

In addition to being interesting, I am pretty satisfied to have combined science, dogs and photography in one post. 

SPS 2011 in Bergen

The annual meeting of the Scandinavian Physiological Society was held August 12-14. The difficulty of trying to combine working as a junior doctor with active research made itself evident by my trying to fly in the same morning. Since the airlines still believed it was summer, there were no direct flights. So I had to board at 05:40 in the morning in order to arrive in Bergen at 09:30 after a brief stop in Copenhagen. Yes, Copenhagen. That is 1217 km instead of 703 km according to Google Maps.

Anyway, that meant I missed the opening lectures. As far as I have heard they were brilliant. Polly Maltzinger talked about "Conversations between tissues and the immune system" and then Roger Seymour talked about "Homage to Scholander, Johansen and Schmidt-Nielsen: Ecophysiology of temperature regulation and energetics".

The most interesting presentation that I actually attended was Jens Titze's about how macrophages in the skin affect sodium balance and blood pressure. Apparently this happens completely without involving the kidneys. If you, like I, have a hard time grasping the idea you can read more in his Nature Medicine paper: "Macrophages regulate salt-dependent volume and blood pressure by a vascular endothelial growth factor-C-dependent buffering mechanism" (Machnik et al. Nat Med. 2009 May;15(5):545-52). The future developments in this field will be very interesting.

The social program was outstanding. The young investigators party included a free bar (Yay!) and a live band. Although they played a bit too loud for relaxed conversations, the lubrication was enough to get even young, more or less autistic, researchers to socialise and meet new people. Saturday evening there was the conference dinner, which was held at the top of mount Fløyen. The resturant managed to produce very nice, quite authentic Norwegian food, and similarly very good entertainment with some authentic Norwegian parts.

All in all, a very successful meeting. Thanks to the organisers in Bergen and the SPS for making it happen.

Bjarne Magnus Iversen (1942-03-30 - 2011-08-05)

My very good friend and mentor Bjarne Magnus Iversen died the night to august 5^th. He was born in March 1942 and became 69 years old. At the time of his death he was on a fishing trip with friends, one of whom found him dead in bed on Friday morning. The death was sudden and unexpected, but peaceful. He was in no way ready to leave us, but if he would have had a choice I am certain he would have liked nothing better than to die while fishing.

Bjarne was known for his modesty and great ability to make friends. He would describe him self as “just a fisherman from the fjords.” Everyone who had the benefit of meeting Bjarne got the feeling that he really cared about him or her and their lives. This was an ability that he used to great effect in his work as a physician, as a scientist and as an administrator. As outlined in any of the more formal obituaries he achieved much in his life and left us at the absolute peak of his career.

He was an avid fisherman and would never miss a chance to send pictures of his latest catch to everyone he knew. I used to take him hunting in Sweden, where he availed himself to several fine trophies and even better dinners of Swedish roe deer. A dream of his was to hunt moose, and although we did on one or two occasions he never got the chance to fell one. Our plans to rectify this in the autumn will now forever go unfulfilled.

Bjarne had the indomitable spirit to go from failure to failure without loosing enthusiasm for the project at hand, or loosing sight of the goal. As my thesis advisor and mentor this was his greatest asset. We will try to go on in his spirit and attack each new challenge with undiminished zeal.

Aerobic endurance

Today's post is about endurance. Physiologically, endurance is about energy delivery. In many ways the muscles are machines that can keep up a given amount of work for as long as there is sufficient energy. Chemically, fuel and oxygen is converted to carbon dioxide and water, which releases energy. This is the same thing that happens in a fire, but since we don't want to burn up, the energy release is very closely controlled by the use of the energy currency: adenosine triphosphate (ATP).

New ATP is produced through three basic mechanisms: nonaerobic metabolism, anaerobic metabolism and aerobic metabolism. The mechansims are listed in order of speed, that is the rate at which they can replenish ATP, which corresponds to the maximal level of effort that can be sustained by them.

Nonaerobic metabolism is the conversion adenosine diphosphate (ADP, with two phosphate groups), into ATP using creatine phosphate (CP). This is very fast and provides almost all energy the first 8-10 seconds of any exercise, and can produce around 1200 watt (Guyton & Hall, 10th ed.). It is limited by the intracellular stores of CP, which aren't that large.

Anaerobic metabolism is the breakdown of glucose or glycogen into lactic acid. The process is very fast, producing about 650 watt and can keep going for much longer than the CP-ATP conversion. However, it is limited by the acidity of lactate. All enzymes, including actin and myosin and the metabolic enzymes, have an optimal pH. When the pH varies from this they get less effective, and after about 60 seconds of pure anaerobic exercise the muscle pH will be far enough below the ideal for the process to be severely impaired and the muscle becomes fatigued. In judo, the combination of these first two kinds of metabolism is what provides energy during the intense parts of the workout.

Finally there is aerobic metabolism where glucose/glycogen, proteins, fat or lactate can be used to produce ATP through the Kreb's cycle, which requires oxygen. When burning glycogen, which is the most efficient, aerobic metabolism can produce about 280 watt. In judo this is what allows us to keep going for a full two hour session, and importantly what happens between the short periods of attack and defense to keep fatigue at bay. In the low intensity periods between bouts lactate can be removed from the muscle.

So, the most important part of endurance for judo training, and thus for keeping up with young elite athletes, is the aerobic capacity. The demands aren't as strenuous as for pure endurance sports like running or swimming, but you have to be fit enough to continuously recover from fatigue for a full two hours of training. Going back to our definition of endurance as energy delivery. This means the rate of oxygen consumption, which can be measured in ml/min. In order to be able to make comparisons between different athletes this in often normalised to body weight so that the most commonly used unit is ml/(min*kg).

According to the only english-language, judo-specific book on sports science I know of: "The sport science of elite judo athletes" by Wayland Pulkkinen, the maximal rate of oxygen uptake, or VO2max (that's "V" with a dot over it indicating volume over time, "O" with a "2" subscript as in oxygen, and max, as in max.), of judoka is around 60 ml/(min*kg).

The question then is: How do I measure up? To find out we have to find a way to measure VO2max, but actually measuring VO2max is impractical outside of a physiology laboratory. What remains is estimation from parameters we can easily measure. There are a number of more or less well validated methods to estimate VO2max. You can find them through your friendly, neighbourhood search engine (PubMed, not Google). Uth and co-workers presented their method in 2004 (Eur J Appl Physiol, 91(1), 111-115), so fairly recently, and they used well-trained men aged 21-51 years old by running while measuring their pulse.

The method by Uth et al calls for a resting heart rate, which I found to be about 50/min and a maximal heart rate which I found to be about 200/min. You then divide your maximum heart rate by your minimum heart rate and multiply by 15.3, let's say 15. That gives:

200 / 50 * 15 = 60 ml/(min*kg)

In conclusion, I can not blame my aerobic capacity for any of my shortcomings, but I did find out that I need to work on my running. My calves are killing me.

Fitness for judo

Physical fitness is a complex parameter that is not easily caught in any one number. As any role-playing gamer knows, there are three basic physical characteristics: constitution (CON), strength (STR) and dexterity (DEX).

In addition, judo competition is divided by weight categories so that each of the stats have to be optimised in relation to body weight. Some judoka have, apparently, rolled the perfect 18, 18, 18 and can beat everyone, but the rest of us will have to do with stats that aren't as stellar, and hopefully, bodies (and opponents) that aren't quite as large.

CON:

In judo constitution, or endurance, means that you have to be able to do two things: Control your opponent for at least five minutes, and launch your own attacks. The former is an inherently aerobic task because of it's length, but it is broken into shorter intervals by all sorts of breaks. At the same time the latter is anaerobic on the verge of nonaerobic. That is, during a match you use enormous amounts of energy very quickly, when attacking or defending, and then you have to re-coup this oxygen debt time and time again in the lulls of the fight.

STR:

For any given technical level, the stronger judoka always wins. The easiest way to get stronger is to increase muscle size, this increases the number of motor units and makes you stronger. It also makes you heavier. That's the reason for weight categories. Another way to become stronger is to learn how to activate as many muscle fibers as possible at the same time, while relaxing the opposing muscles as much as possible. This is an important reason for building strength using the movements that will actually be used in judo, and not only by lifting weights.

DEX:

Dexterity can be separated into speed and limberness, where speed is the most important. It is important to be limber enough to perform all techniques, but there are always techniques that require less flexibility. However, if you are faster than your opponent, he will be hard brought to avoid your attacks. Speed in judo means how quickly you can step and turn into your technique or out of your opponents. It also means how quickly you are able to notice and react to an opening in your opponent's defense. Both require very specific training, which is why years of recreational judo has surprisingly little impact on the ability to beat competitive judoka (not to mention that they have higher CON and STR as well, or do they?).

Next up will be a more detailed look at CON. How do competitive judoka perform, and how much do I have to catch up?

Judo!

I did include judo as something that the Nephrophysiologist blog would be about, but there hasn't been much about that. Actually, there hasn't been any judo here at all. It has been hard to find something sufficiently interesting to write about, something where I also feel I have enough to say that someone might find interesting.

So, what has changed? you might ask. My answer would be that my sights have been raised for me. As I moved home to Uppsala and changed labs and hospitals, I also changed clubs. From a small club with recent recruiting difficulties and therefore a clientele of slightly older, non-competetive judoka, to a large, competitive club with some recent successes. Anyway, while it is a lot of fun working out with the youngsters, they are in better shape than I am. It would be more fun if that wasn't the case.

To remedy the situation (so that I'm not that embarrassingly winded older guy) I started doing some supplemental training. At first I had the basic philosophy that anything is better than nothing (which is true). However, being a physiologist it's hard not to have a quick look at what the science says. The judo posts will try to handle the science of judo performance from a practical perspective as I play catch-up with elite judoka more than ten years younger than me.

Using the OS X clipboard in R

One annoyance with using a command line based statistical system, i.e. R, is that if you use a spreadsheet program to handle your data (as most of you do) you have to incessantly export to csv and import to R. For big data sheets and complex calculations this generally a Good Idea(tm). It improves reproducibility and readability when going back to the project at some later time. However, the complexity of that is enough that you often, at least I, end up doing statistics in Excel. This is generally a Bad Idea, and often entails much more work in the long run. In order to make importing and exporting data easier R can handle the clipboard directly, which is what this post is about.

In OS X the clipboard is easily accessed through the command line programs pbcopy and pbpaste (pb means "pasteboard" but everyone knows it as the clipboard so that's what I'm going to call it). These are easily scriptable programs that can be used with any unix command in the shell or scripts (enter "man pbpaste" in the terminal to learn more). "pbpaste" pastes the current clipboard to std-out (that is where you call it from), while "pbcopy" copies std-in (what you put there) to the clipboard. An important quirk is that they only handle plain text, RTF and EPS, that is formats that are transferred as plain text. This is because unix is a text based system. What it means is that you can't copy stuff from formatted text, e.g. word, but with spreadsheets you are OK.

As command line programs they can be handled through the R command: pipe(). Pipe does not produce the current clipboard contents, just a description of the pipe as such. You have to use a read command to get the actual contents.

> readLines(pipe("pbpaste"))

which will produce one string per line (completely useless as data, but often useful to see how a given copy is formatted). To format it for data you use the same as you would any import, using one of the higher level read-commands: read.table(), read.csv(), etc.

> x <- read.table(pipe("pbpaste"))

This will put your copied excel table directly into the table "x" in R. Often you will be forced to tweak the function a little to get a usable table.

> x <- read.table(pipe("pbpaste"), header=TRUE, sep="\t")

That should be able to read your copied Excel data ("header" specifies that the first row is the header, and "sep" specifies the separator which defaults to tab or "\t" in excel).

To write to the clipboard you use "pbcopy". It is a bit more involved, but not much. First you connect a variable to the pipe from pbcopy.

> osxclipboard <- pipe("pbcopy", "w")

Now you can write to the variable "osxclipboard" and it will turn up on the clipboard so that you can paste it into another application. You have to remember that it is a pipe to an external file, which means that you have to use "write()" to put data in the clipboard. If you just assign some data to "osxclipboard" it will be changed from a pipe to that data. Thus:

> write(x, file="osxclipboard")

where "x" is your data, will to the trick. Then you just have to clean up using:

> close(osxclipboard)

In the same way as with copying from the clipboard, this will not format your data optimally. so you have to add some formatting command for Excel to read it properly.

> write(x, file="osxclipboard", sep = "\t")

There we are, but that is rather alot of code. Not really that much easier than a regular export from excel and then import to R. So here are two simple functions to do it all at once, with the most used arguments (I'm sorry for the code, I haven't figured out how to get indenting to work properly in blogger).

Simple readlines from the clipboard:

clipboard.readlines <- function (

clipboardname = "pbpaste",

n = -1L) {

readLines(con = pipe(clipboardname),

n = n)}

Read table from the clipboard. I have only included the most commonly used arguments to read.table(). You could easily add all the rest if you need them:

clipboard.readtable <- function (

clipboardname = "pbpaste",

header = FALSE,

sep = "",

quote = "\"'",

dec = ".") {

read.table(file = pipe(clipboardname),

header = header,

sep = sep,

quote = quote,

dec = dec)}

Write to the clipboard:

clipboard.write <- function (x,

clipboardname = "pbcopy",

sep = " ") {

osxclipboard <- pipe(clipboardname, "w")

write(x = x,

file = clipboard,

sep = sep)

Close(osxclipboard)}

That was it for now. I hope someone finds it helpful. I'm probably not putting any of this into a formal extension, so you will just have to run the code to use it. Consider the code GPL-licensed, although the text is under regular copyright.