Lab results vs race results

0:03 · Twenty four men, and a number that moved

Twenty four men had their oxygen uptake measured, then trained for six weeks. The ones whose number improved most were not the ones who got faster. The change in the laboratory number said nothing at all about the change in performance.

0:22 · What is a laboratory number worth?

So what is a laboratory number actually worth? A study finds four per cent, you work it out on your own marathon, and you land on about eight minutes. That is almost certainly too many, and there are three reasons, which I will number as they come. Later in this video a laboratory number predicts a marathon time so closely that it is almost uncomfortable.

0:49 · The sum everybody does in their head

First, the sum everybody does in their head, because it is not a silly one. It costs you four per cent less energy, so you run four per cent faster. On a three and a half hour marathon that sum is close enough. You would be looking at a bit under four per cent, which really is about seven or eight minutes. Hold on to that, because it means your eight minutes do not disappear into the arithmetic, and something else has to be taking them.

1:23 · Level predicts, change does not

So back to those twenty four men, because the study is worth seeing in full. They were untrained, and they cycled under supervision for six weeks. Two things were measured before and after: their maximal oxygen uptake, the classic laboratory number, and a fifteen minute time trial. Beforehand those two lined up nicely. The men with the higher oxygen uptake rode the faster time trial, and that relationship covered about eighty per cent of the differences between them. What you are seeing here is the shape of that result, not its data points. Then they trained for six weeks, and the question became a different one. Did the men whose oxygen uptake improved most also improve most in the time trial? In the words of the study, the change in oxygen uptake was completely unrelated to the change in aerobic performance.

2:28 · One study, twenty four untrained men

Now, how much weight can that carry? It is one study, of twenty four untrained men, over six weeks. We went looking for a second study that measured the same thing the same way and we did not find one. So this is the clearest illustration of a real distinction, and it is not a settled quantity. The next part does not depend on it.

2:56 · Cause one: they measure different things

Look at where that time trial was ridden: in the laboratory, with no wind, no corners, and nobody setting off too fast. Suppose the distance between a laboratory number and a performance were mostly about the mess outside. Then that gap could not have opened up where it did. What happens instead is that those two measure different things. Maximal oxygen uptake is a ceiling, the most oxygen your body can take in and use, under one fixed instruction. A race is not a ceiling at all. It is how fast you got from start to finish. That depends on the ceiling, on how economically you move, and on how much of that ceiling you can hold for an hour. It also depends on how well you judged your effort. Eighteen international experts were asked which factors they considered important for endurance performance. They came back with twenty six. The three familiar laboratory measures are on that list. So are the other twenty three. That is cause number one, and it is the one that takes most of your eight minutes.

4:25 · The test does not sit still either

There is a second thing about that laboratory number, and it is easy to miss. It does not sit still either. How far apart depends on which test you chose. In a time trial you go as hard as you can over a set distance. That varies by under five per cent from attempt to attempt. A test where you hold an intensity until you cannot continue varies by more than ten. The first of those also resembles a race more closely, because it asks the athlete to do what a race asks. There is a quieter version of the same problem. Between a first and a second attempt, people improve by about one point two per cent on average. Between later attempts, by about zero point two. The first of those is learning the test. A study with no practice run hands that improvement to whatever it was testing.

5:36 · Cause two: the exchange rate

So that is why a laboratory number can move without you moving. Now try it the other way around. When a laboratory gain does carry over, how much of it actually arrives? That is where the strongest number in this video sits. Suppose something genuinely lowers the energy it costs you to run at a given speed. You now have energy to spare, so how much faster can you go on it? Two things are in the way, and both are physics. Oxygen uptake climbs more steeply the faster you run. And pushing air aside costs energy with the cube of your speed. So at racing speeds a good part of any saving disappears into the going faster itself. Where the line crosses matters more than you would think. It sits at about three point two metres per second, which is a marathon of about three hours and forty minutes. Run faster than that and you keep less than you saved. Run slower and you keep more. At a gentle jog, a marathon of about four and three quarter hours, it flips the other way. A ten per cent saving is then worth about twelve point eight per cent more speed, because the air is barely charging you anything. At the pace a world class marathon is run, about two thirds arrives. And at three and a half hours, where we started, you are almost exactly on the line. So that is cause number two, and for you it is a small one.

7:29 · The shoe, from laboratory to finish line

Back to that four per cent, because the number is real. Eighteen high calibre male runners ran in a prototype racing shoe with a stiff plate in a springy sole. At fourteen to eighteen kilometres an hour it cost about four per cent less energy than two established marathon shoes. The same researchers later put a saving through the exchange rate, and they had to assume its size. Start from a marathon pace of two hours and four minutes. A three per cent improvement in running economy buys one point nine seven per cent more speed. That is a finishing time of two hours, one minute, thirty six. The world record when that calculation was published stood at two hours, one minute, thirty nine. Three seconds, over forty two kilometres. The three per cent was an assumption, so this is a good fit rather than a proof. The sum that goes wrong is the one in your head. Take three per cent straight off that same two hours and four minutes. You get two hours and seventeen seconds, a minute and twenty two seconds faster than the record that actually stood.

8:53 · Cause three: the road

Then the layer everybody thinks of first. A treadmill in a room has still air, a surface that never changes, and a speed chosen for you. A race has wind, corners, camber, weather, and a pace you have to judge yourself. Laboratories know this and they correct for it. In nineteen ninety six, two researchers had nine trained male runners run at six speeds. On the belt at several gradients, and once outdoors on level road. At a one per cent gradient the cost on the belt matched the road across the middle of that range. That correction has been standard equipment ever since. In twenty twenty six a review looked back over thirty years of evidence. Its conclusion was that the equivalence depends on speed, on conditions, on the method, and on who is running. One fixed value does not fit every case. That is not a laboratory failing. That is thirty years of measuring. And that was cause number three.

10:14 · Three questions to take with you

So what does this leave you with? Three questions, for the next time a number like that comes past. Better at what: measured as a result, or as something that correlates with one. Measured where: on a belt in still air, or on the road, and at which pace. And in whom: untrained or trained, and at what speed, because the rate moves with the pace. A laboratory number is real currency. It is simply a different currency from the clock, and nobody prints the rate on the headline. The whole piece is on enduranceproof dot com, with all fourteen sources. The next video is about the calculators that predict your finishing time, and the one constant almost all of them share. Subscribe if you want that one.