| Menu | Introduction |Shoe Design | Lab Tools | Activities | Glossary | References |
Note: This activity was co-developed with Mark Blaser and was funded,
in part, by an NSTA TAPESTRY Grant. One of the most easily overlooked characteristics of an athletic
shoe is its ability to flex. If a shoe flexes easily, it requires
little force to bend and uses a small fraction of an athlete's
available energy. However, shoes that flex easily can provide
less support and cushioning--possibly increasing the chance of
injury. The need for shoes to flex varies from sport to sport.
Shoes that are designed for basketball, for example, will have
significantly different flexion characteristics than a shoe designed
for bike racing. Sport researchers and shoe designers try to find
the optimal amount of flex that best match the requirements of
a particular sport. Figure 1 - Students Test Different Shoes With Flex Test. What are the flex characteristics an athelete would require in
a bike shoe vs. a basketball shoe? The primary area of the shoe that needs to flex, for most sports,
is in the forefoot area. This may seem logical when one considers
the structure of the foot. When walking barefoot and observing
from the side, it is apparent that the foot flexes naturally near
the "ball" of the foot. However, sport researchers and shoe designers
virtually ignored this "natural" consequence of locomotion until
the 1980's. First, wear tests on shoes with the new innovation showed that
flex lines tended to be areas where the mid-sole and out-sole
would crack. The flex lines actually weakened these areas of the
shoe and caused them to break down too quickly. Second, foot morphology studies showed that the flex lines had
to be placed differently depending on the size of the foot. Placing
the flex lines was not a simple matter of putting them "one-third"
of the way from the front of the shoe. What the scientists found
by studying thousands of feet was that an equation, or a model,
could be developed that fit how the foot changed, or "scaled",
for different size feet. Scaling is an interesting concept that is applied in many areas
of science. Scaling is the study of how various characteristics
change as an object, like an organism, or some characteristic
of an organism, is increased or decreased in size. In shoe design,
scaling allows for the proper placement of the flex lines by describing
variations in size (i.e. foot size) with a mathematical model.
Figure 3 - A Foot Morphology Platform. Sport researchers took thousands of pictures of different feet
to see how they varied. How many different ways do you think you
might group feet to study variation? (Hint: One of the first studies
was to look at variation between the sexes.) The flex test was developed by sport researchers to test the effectiveness
of placement of flex lines; to see if a flex line hurt the overall
durability of the shoe; and lastly, whether too much force was
required to flex the shoe. In this activity students will set up, run, and apply a flex test.
At the end of this activity students will understand: This activity provides an overview of setting up and running flex
tests similar to those run in a sport research lab. The format,
like all Slam Dunk Science Activities, is designed to leave further
avenues of research up to the student. This procedure uses MacMotion, a force probe, and a ULI available
through Vernier Software. This setup, running on a Macintosh computer,
provides a good balance between ease of use, features, and cost.
Other hardware and software can be substituted. In fact, a "low
tech" version of the flex test can be run without computers using
spring scales and careful observation. It is suggested that you
familiarize yourself with the MacMotion software, force probe,
and ULI before you start this procedure. This activity is based
on the assumption that you have done so before you start. It is important to realize that the flex test as outlined here
is relatively simple. You will most likely see how you can modify
the test to improve its accuracy. For example, adding a potentiometer
and recording the angle via the software and ULI will greatly
improve the accuracy of the data collected. The authors encourage
students and teachers to develop their own improvements, to share
them with us (via the Internet) and, in turn, to share them with
other schools. Setting up a Flex Testing Device (See Figure 1 as a guide for setting up the flex test) Setting up the Force Probe, ULI, and MacMotion Collecting Flexion Data Presenting the Results Graphically By itself, merely collecting a bunch of data is not very useful.
In order to have meaning, the results must be analyzed and interpreted.
For example, simply measuring that the Super HangTime Basketball
Shoe requires 12.7 N to flex through an angle of 45° does not
convey much information. However, by knowing that the Super HangTime
shoe requires 12.7 N of flexion force, while the SkyJammer Special
needs 18.4 N to bend through the same angle, you can compare the
forces involved in using each shoe--a 45% larger force is needed
to flex the SkyJammer than the Super HangTime shoe. As a result,
energy costs for flexing can be compared from shoe to shoe. In addition, energy required for flexion can be determined as a
fraction of total energy requirements for a specific sport, and
effects on sport performance estimated. Finally, other important
design properties--such as cushioning and motion control--can
be considered to best balance performance characteristics with
the demands of the specific sport the shoe is designed for. Use your data to answer the following questions:
Introduction
With the advent of sport research labs it became apparent that
flexion, in most sports, was absolutely necessary, and, in fact,
if not allowed could lead to injury. Initially this realization
led to the advent of "flex lines, or grooves" (Figure 2) in the
forefoot area of the shoe. These indentations allow for the shoe
to flex more easily. However, further study pointed out two factors
not considered in designing early flex lines.
Figure 2 - Flex Lines in Basketball Outsole.
Objectives
Materials
Procedure
Discussion
| Menu | Introduction |Shoe Design | Lab Tools | Activities | Glossary | References |