Choosing the suitable pole – errors and misconceptions – part 2 weight-index and „flex“-number

There are digits on the top of each pole refering to „the athletes weight“ – for europeans in kilogram for americans in pounds. First, the pole is not as heavy as this weight-index says;-)

UCS/Spirit Pole:Weight-Index: 75kg / 165 pounds

There are numbers in kilogram like 59, 61, 63, 66, 68, 70, 73 and in pounds like 125, 130, 135, 140, 145. One can see, that the americans where the inventors of this index, the graduation is 5 pounds, while the graduation in kilogramm sometimes is 2kg (rounded down) sometimes 3kg (rounded up). But this all doesn’t matter that much as you will see soon.

What is the weight-index all about?

Pretty few, I would say, but enough to begin with. First, it is an indication about the stiffness of a vaulting pole, meaning how easy the pole bends.

The weight-index is for security reasons and a rough orientation. About the aspect of security I talk at the end of this article.

The orientation is about that a person weighing 130 pounds can suppose that a 130 pounds pole (or 125 or 135) is not completely wrong choice. But even that statement is pretty daring, pole vault beeing so difficult you cannot choose your pole by only looking at the weight-index matching your body weight. It’s not a ski binding. For example: Me being 73kg(160lbs), I could make nice jumps from a short run (8 steps) on a 4.60m long pole with weight-index 73kg(160lbs). But if I would take a 4.00m / 77kg(170lbs) and run 16 steps, that pole would burst. For beginners this is not self-evident as you might think 4.00m/77kg(170lbs) is, only looking at the weight-index, above my body weight.

The answer is, that the weight-index is relative to the length of the pole. A 4.00m/70kg(155lbs) pole is always softer than a 4.30m/70kg(155lbs) pole. And that one is softer than 4.60m/70kg(155lbs) and so on. Using the weight-index assumes that you have a certain experience and know for example that a 4.60m/73kg(160lbs) is not something dangerously soft for a man and a 4.00m/68kg(150lbs) is not something dangerously soft for women. But don’t try inversely;-)

The difference between two poles 30cm different in length is about 15-20 pounds (7-8kg) to be about equaly stiff. A 4.30m/75kg(165lbs) is about as hard as a 4.60/68kg(150lbs) or a 4.00m/70kg (155lbs) is as hard as a 4.30m/63kg(140lbs). If the difference in length is 15cm then it is about 3.5-4kg (7,5-10lbs). A 4.30m/75kg(165lbs) pole beeing as hard as a 4.45m/73kg(160lbs) and a 4.60m/68kg (150lbs).

Where did the producers get this weight-index from?

I cannot answer this question. I assume it has to do with experience and perhaps also a bit mathematics.

How does a producer calculate the certain weight-index having a pole in front of him, how can he conclude: That is a pole with a weight-index of 82kg (180lbs)?

The producer does this: He measures the bending of the pole, hanging 50 pounds in the middle of the pole (there are a few details about this I spare). The bending, measured in centimeter, while the pole is bend by 50 pounds, compared to the state without load (when the pole is not bent by force) ist the so-called „flex“-number.

Bending while loaded with 50 pounds, measured in centimeter = „flex“-number.

Measurement of the bending of a pole under load of 50 pounds in the garage of my parents (not only music bands and computer-inventors started in their parents garage).

If you got a pole in your hands with a flex-number of 16.8, this does mean, that this pole bends 16,8 centimeter, if you load it with 50 pounds (see picture above). This flex of 16,8 you will find on a 4.60m/80kg (175lbs), you’ll find the digits 460/80, 175, 16,8. How you transfer from 16,8 flex-number to 80kg/175lbs weight-index, that’s what I don’t know, but that doesn’t matter.

Let’s take again the example of a 4.60m/80(175lbs) Flex 16,8. You may ask yourself now, how about 82kg(180lbs) or 77kg(170lbs)?

This works as follows: The weight-index (for example 80kg/175lbs) always covers a certain range. For example ucs/spirit poles of 4.60m in length and a flex-number of 16.5 to 15.5 are classified 82kg/180lbs. Is a pole only a tiny bit harder, bending of only 15,4 centimeter (only 1mm less), the pole is classified 84kg/185lbs. Is the pole a tiny bit softer, flex-number 16,6, it’s a 4.60m/80(175lbs).

Rule of thumb: The weight-index changes every 1 centimeter of more/less bending. For example poles with a flex-number from 19.0 – 19.9 have the same weight-index, then from 20.0 – 20.9 it is the next softer weight-index, then 21.0 – 21.9 and so on. That’s not always the case (the range gets shorter the harder the poles (0.9 or 0.8) and longer the softer the poles(1.1, 1.2)). So there are 10 poles of different flex-numbers all with the same weight index (for example 73kg/160lbs). That’s not a razzle-dazzle, but it shows, that only the flex-number matters.

You might conclude: Wait?! I can buy two poles of different weight-index, but they are almost the same pole: 460/82 flex 15.5 and 460/84 flex 15.4. You are right!

That’s why every pole vaulter and his coach should understand the principle of the flex-numbers, not only pros, but also intermediate athletes and decathlon athletes and ambitious beginners. You can throw a lot of money out of the window (as we say in german), if you buy poles only looking on the weight-index. Maybe the difference between two poles that should follow each other is very small (flex-difference of only 0,2 for example, you lost money) or very large (flex-difference of 1.8, dangerous in switching poles during jumping!). If the difference of the flex-number is very small it can irritate athletes, because they don’t feel any difference. If it is very large athletes may underestimate the difference and produce an acciedent. Only the flex-number matters.

Buying poles, you should know the flex-numbers of the poles you already have in your set, and you should think about what flex-number you want to buy. Otherwise your purchase is random and that’s not wise as poles do cost about 500 to 750 dollars (700 to 900 euros).

Let’s talk about safety: Coach and athlet should know, how big the difference is between two poles. Is it 0.2 or 1.8 in flex-numbers?

This knowledge is actually vitally important (for the athlete it is essential for survival). Many (or most) athletes and coaches lack this knowledge – this article helps to change that – and this lack does not show that it works without it – the level of swiss vaulters rather proves the contrary.

For numerous skills there are functionality certificates: drivers licence, diving, lawyers and so on. For pole vault, far more dangerous than many other skills you need a licence for, there’s no exam. You can simply do and coach it, without knowing the basics.

If an athlete asks me at a competition do you have a 4.30m/70kg (155lbs), we only got a 4.30/68kg(150lbs) witch got to soft now, then my first question always is, what’s the flex-number of your 4.30/68kg(150lbs)? 90% the person is perplex – and the athlet would miss his next attempt if I would try to explain to him what you just have read so far to this point. That’s why I write this article. Depending on what the flex-number of his pole is, „my 4.30/70kg(155lbs) might be almost the same pole (small difference of the flex-number) or I may put him at risk (hugh difference of the flex-number). Have you ever thought about that, borrowing poles? (I hope so). That’s why I look at the flex-numbers. If the difference is 0.4 or less and he is a beginner, I tell him the difference is almost zero so he should go on with „his“ pole that he is used to. If the difference is 0.8 to 1.2 we found a perfect match for a next harder pole. If the difference is 1.2 or more it might get dangerous.

(In short I point out the question of liability. If something bad happens…As Coach you should never advice an athlet to jump a certain pole by only looking at the weight index, without knowing how mutch harder this next pole is. For me as a lawyer (therefore you need an exam), this behaviour would be a default in taking charge of something you don’t have the necessary skills (like a medical doctor doing a surgery he is not spezialiced for). The situation is even more dangerous as there is almost everytime a superiour authority by the coach, the athlete trusts the coach giving him advice.)

That brings us to the queston, how big the difference of the flex-number from one pole to the next one should be?

As a rule of thumb: A difference of 1.0 is suitable for most of the athletes (female and male). All your poles of the same length should therefore have the same difference, for examplle: 4.30m/21,4 -> 20,4 -> 19.4 -> 18.4.

The mathematician may object this cannot continue until the flex-number is zero as the poles would get disproportionally harder as the flex-number approaches zero. A pole with the flex-number 0,5 might have a weight-index of 500kg (900lbs) and a flex-number 0,0 would rise the weight-index to „indefnite“… This is correct, thats why my rule of thumb is only suitable for the range of 25.0 down to about 18.0, if poles get harder you should make smaller steps like 0.8 or 0.6. If poles are softer than 24.0 you can make steps of 1.2 or 1.4.

Example for you vaulting pole set

My track club has 4.60m poles with flex-numbers: 21.1, 20.0, 18.9, 18.0, 16.7 (that’s a bit big 18.0 -> 16.7 that’s why we use there a 17.5 from another track club), then 16.0 and 15.5. What weight-index do these poles have? I don’t care. You only have to get used to look only at the flex-numbers and you will forget about the weight-index. The weight-index is only an orientation for the beginners: If you weigh about 80kg (175lbs) you should jump using a pole with a weight index of 68kg (150lbs). But also that isn’t accurate in every situation. For example if you grip a 4.60m/68(150lbs) at 4.10m from 8 steps, that might fit quite well (the bending might not be the best, but the pole might be suitable in stiffness).

A last example: In my track club we have a 460/82(180lbs) Flex 15.5. In Zurich track club we had a 460/84(185lbs) Flex 15.4. Again, this is „the same pole.“. For the „ignorant“ it’s two different poles, he might think, „wow now I jump a 84kg/185lbs pole. Only the flex-number matters.

Assessing the weight-index

In my view, it is an orientation for beginners but not more. Even a beginner might kill himself, if he picks a 4.60m pole and grips it at 4.50m no matter if the weight index might be suitable to his body weight. Maybe the pole will not burst but maybe some of his bones landing somewhere of the pit.

For the advanced athlete the standard that the weight-index of your poles should be higher than your body weight isn’t suitable any more. If I (73kg) would jump a 4.30m/73(160lbs), gripping at 4.20m the pole would probably burst or I would jump over the pit, the pole beeing so soft. Jumping 460/73(160), gripping at 4.50 the pole will burst. Jumping 490/73(160), gripping at 4.80 the pole will burst immediately.

There’s no „women weight-index or flex“, that again is why I think the weight-index is not more than a rough orientation. An orientation a beginner is overstrained and a pro does not use. And the intermediate relies on it but he shouldn’t, because it’s only the flex-number that matters.

Basically the weight-index is not very bad (I jump mostly poles with a weight-index of 75 to 84kg (165 – 185) having a body weight of 72kg (160), but if women with a body weight of 54kg (120lbs) jump 430/75(165) that just shows how useless the weight index is.

Safety

In the U.S. scholar are allowed to jump poles with a weight-index superiour than their body weight (I hope that still is the case, please call me if it’s wrong). Additionally there’s a mark about 4 or 5 inches from the top, you are not allowed to grip higher than this mark. So most of the world class athletes wouldn’t be allowed to jump under these guidelines because the majority of the world’s best pole vaulters grip their pole within the top 10cm – for good reason, but that’s the story of another article.