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Monday, June 18, 2007

The Comrades - inside the medical tent

So Durban (and South Africa) woke up to the sad news this morning that two runners had died during yesterday's race. As I promised yesterday, today we'll have a look at what goes on behind the scenes, especially in the medical tent (since that's about all I saw of the race), and I suppose we should start with this sad event.

Both deaths happened at the finish line, the first was a 34-year old man who collapsed at some point during the final kilometer and was then carried to the finish line by other runners, as is the Comrades tradition. It makes for stirring television and high drama, befitting the race, but unfortunately, can lead to complications for the affected runners. In fact, we had a celebratory dinner after finishing in the tent and when our Austrian colleague, who is also a cardiologist, heard that runners had picked up and carried a man across the line, he was shocked and amazed to say the least, since it can worsen the problem, especially if carried vertically (it's better to be horizontal). That this is a tradition at Comrades was even more amazing to him, he was incredulous that they would be allowed to do this.

The second runner collapsed after finishing, and was tended to immediately by doctors, both on the line and in the tent. They in fact resuscitated him meters from where we were doing our testing, and he was taken to hospital, where he unfortunately passed away. So these two sad days spoiled an otherwise very good day for the medical team, with the Chief Medical Officer saying it was one of the quitest days in many years. I've worked in the tent the last three years and it certainly was not nearly as busy as in the past.

But what of these two deaths? One happened in a runner who had done 14 Comrades before, an experienced runner who was by no means unfit. The other was in a young man, also fit, since he ran under 11 hours before collapsing. So these events are reminders that anyone can be affected - be it by genetic abnormalities, perhaps flu, or some problem related to cholesterol or coronary artery disease. Of course, all of this doesn't help anything, and we must avoid playing the blame game - was it the lack of medical treatment, was it the other runners, was it the race organizers? It doesn't really matter right now, though lessons would need to be learned. My personal opinion is that runners should be educated, perhaps by a campaign before the race, to assess the situation a little more - if a runner has cramp, by all means pick him up, but if a runner is lying still and does not respond to talking, rather get medical help to him as quickly as possible. Perhaps in future years, this is the way to go.

As for the rest of the day's action in the medical tent, most people come in simply because they are exhausted, or have severe cramp, brought on by the steep downhills. Almost all just need to lie down for 30 minutes, rest up and then they are fine. There is a common problem of nausea, which is brought on by a number of factors, and then worsened by the fact that for 10 hours, most runners drink and eat nothing by jelly babies, Coke and Energade, which would be enough to make anyone feel ill! Blood pressure drops a lot as well and so the most effective treatment is simply to lie the runner down and raise his/her legs until the blood pressure normalizes.

What were we doing the medical tent? As mentioned, we worked with some Austrian scientists to look at how the cardiovascular system functions after the race. We tested 100 people at the expo on Friday and Saturday and then asked them to come back after the race. About 60 did, which was pretty good going, I think. We were measuring their cardiac output, which is the volume of blood pumped by the heart per minute and also the stroke volume, which is the amount pumped per contraction.

Very briefly, we found that in most people, the cardiac output and the stroke volume fall after the race, which is really very interesting, because their sympathetic nervous system (which is the body's fight or flight system) is hyperactivated. Normally, if the sympathetic system is active, the heart pumps more blood. But after Comrades, it pumps less, so that's a really interesting finding. We now have to think why that happens - there are a couple of possibilities, neither of which I'll get into now. But basically, you could think of it as a simple equation of supply and demand - the tissues, muscles and organs set the demand which is met by the cardiac output - the supply. So when the cardiac output is lower, it means that the demand is down, and that has all sorts of implications. Is the body in a mega-conservative state, where it tries to minimize demand by 'shutting off' blood to all parts of the body where it's not needed? A survival mechanism for 90 km perhaps? The next step will be to answer these questions.

So that's a bit of a technical post, tomorrow I'll post on a little more of the science that goes into preparing for Comrades and exactly what happens to the body during the race. I'll also try to paint a picture of what it's like at the finish area, to illustrate how the physiology responds to 90 km.

See you tomorrow!


Anonymous said...

Did you weight them before and after as well? To see how dehydrated they were? Severe dehydration could explain a drop in cardiac output.

Ross Tucker and Jonathan Dugas said...

Hey Anonymous

Yes, you're quite right, a reduction in plasma volume, caused by dehydration, could well explain the fall in cardiac output. And so yes, we did measure their weight before and after the race. So what we will do in the analysis of the measurement results is correlate any changes in cardiac output with possible changes in body weight.

However (and forgive me for getting technical, though I suspect you might enjoy the facts) one has to bear in mind that even weight loss caused by sweating/dehydration might not adequately indicate plasma volume, because the body is able to shift fluid between compartments specifically to prevent the plasma volume from dropping too much. So body weight changes are a relatively crude measurement.

For example, consider a 80 kg runner. It would be quite normal for this runner to finish the race weighing 78 kg, which means he's lost around 2 kg (or liters) of fluid. However, the starting plasma volume in the ECG (which is basically the blood volume) might be around 5 to 6 L. So even though this guy has lost 2L, his blood volume has still been defended, to a certain extent, anyway.

Also, for other reasons I won't go into here, we measured the cardio output one hour after exercise, and so the plasma volume contraction may well have been partially reversed by the time we made measurements. And the studies have shown surprisingly small reductions in plasma volume after even severe endurance exercise.

So you make a good point and we have the data to be able to account for it, but I have a feeling there's a lot more to it than just that, which makes life either very complicated or very interesting!

Thanks again!