January 26, 2000

On the Need for a Standard Method for Measuring Vaulting Pole Stiffness/Flexibility

By: Roger W. Werne, PhD, Mechanical Engineer at Lawrence Livermore National Lab.

High School vault coach and Masters vaulter

Selection of a pole for a vaulter is governed by a number of factors. The most important of these, of course, are the vaulters weight and physical ability such as speed and vaulting technique. Other factors such as wind conditions and temperature also have an effect on pole selection. Because of the number of variables involved, a good vaulter will frequently take at least three or more poles to a competition each having a slightly different stiffness. Coaches, of young vaulters who are just learning the event, will typically have a graded selection of pole stiffness' to account for the rapid improvement in technique that frequently can happen. Moving the vaulter to stiffer poles as their technique improves, even in a single practice session, prevents the young vaulter from significantly over bending a given pole and creating a potentially hazardous situation.

Relative pole stiffness is expressed as a weight for which the pole is rated (and not to be exceeded) and a length, with a hand hold limit some distance from the top end. At a finer level of detail, the Flex Number for the pole is inscribed on it. The Flex Number is the deflection of the pole in inches or centimeters when a standard weight, usually 50 pounds, is suspended in the middle of a horizontal pole with simple supports at some distance from each end. The pole manufacturer determines the Flex Number for each pole at its factory and then labels the weight rating of the pole according to the range of Flex Numbers that fall within that weight limit for a given length of pole. Therefore, the Flex Number, the test by which it is determined, and the manufacture's algorithm for weight as a function of flex number are the final criteria that determine the rated weight on a new pole.

Any experienced pole vault coach or vaulter will know that for a given length and weight rating, the poles having slightly different flex numbers will, in fact, respond in a slightly different way. For example a 14' -160 # set of poles may actually correspond to weight ranges of approximately 14' -158 # to 14' -162#, depending on the exact Flex Number for each pole that makes up that range. This occurs because of the natural variability inherent in the manufacturing process for modern vaulting poles.

When fiberglass vaulting poles were first introduced in the late fifties, there was of course only one pole designer and manufacturer, and that company did most of the pioneering work on how to manufacture poles and determine their stiffness and therefore weight rating. Much of that technology and know-how has found its way into modern pole manufacturing, but different manufacturers have added their own refinements and technology, thus giving the vaulting community the rich selection of poles that it enjoys today. The concern is that the method for determining pole stiffness and therefore weight rating has also changed somewhat depending on the manufacturer.

Although all manufacturers utilize the simple pole deflection method mentioned above, there are enough small differences between manufacturers that differences in poles from those manufacturers will in fact respond differently to the experienced vaulter. For example, it is not uncommon for a 15' - 160 # from one manufacturer and a 15' -155 # from another to be closer in actual performance to an experienced vaulter, than would two 15' -160s from those same two manufacturers. It has to do with the details of how they measure Flex Number on their pole flex test. For example one such detail is the span of the pole between supports in the flex test. Whether a manufacturer uses a 14'-0" span or 14' 2" span can make a large difference in the measured pole deflection under a given weight. This is because the deflection, under otherwise identical conditions, varies as the cube of the span of the pole. Another important detail in the flex test is whether or not the supports at the end of the pole are rollers which are, for all practical purposes frictionless, or whether the supports are not rollers and have friction at the interface between the pole and its support. The magnitude of the weight and whether it is in the exact center of the span, and the accuracy of the method by which the deflection is actually measured, can make a difference.

The above discussion is leading up to the following question: Should there be standard method for measuring the Flex Number on a vaulting pole? From coaches and a vaulters point of view, the answer should be Yes. A number of advantages would occur as a result of such standardization. It would, improve the ability of a buyer to accurately purchase a pole of a desired stiffness. This is especially true if one is replacing a pole in an existing sequence of poles,

allow an easier and safer transition for a vaulter between poles from different manufacturers allow older poles to be reflexed according to the new standard and more accurately reflect the range of poles in a given inventory demonstrate a proactive approach by the vaulting community to improve the safety of the sport of pole vaulting.

Others ?

The Task Force understands that invoking a standard on the pole manufacturers will involve some time and expense on their part to meet the new standard. However, it is believed that the incremental expenses incurred will be small, and well worth the benefit to the vaulting community.

The appropriate way to move toward a standard test is to do it through a standards organization such as the American Society of Testing & Materials(ASTM). Such organizations develop and maintain testing standards for virtually all aspects of commercial enterprise where standards are important to public safety and/or commercial success.

The members of the USA Track And Field Pole Vault Equipment Task Force listed below unanimously recommend the adoption of a standard method for measuring pole stiffness.

Please feel free to comment to Eddie Seese at prsport1@aol.com or Fax 707 645-0550

Task Force Membership:

Mathew Kendall, PhD

Mechanical Engineer at Lawrence Livermore National Lab.

High School vault coach and Masters National Champion Vaulter

2473 Lexington Pl.

Livermore, CA 94550

Michael Philpott, PhD

Professor of Mechanical Engineering at University of Illinois

William Singhose, PhD

Professor of Mechanical Engineering at Georgia Tech.

Masters vaulter

Bob Slover

High School Track Coach

Pole Vault Coach

Former nationally ranked vaulter

Wilson SooHoo, MD

Masters vaulter and high school coach

Chairman, Roger W. Werne, PhD

Mechanical Engineer at Lawrence Livermore National Lab.

High School vault coach and Masters vaulter

163 Berkshire Ct.

San Ramon, CA 94583