sports engineering

SPORTS ENGINEERING
Steve Haake
INSTANT
EXPERT
24
00 Month 2010 | NewScientist | 1
1,000
BIKES (old)
OARS, BIKES, POLE VAULT (new)
100
YOUNG’S MODULUS
10
POLE VAULT
(old)
OARS
(old)
ARCHERY BOWS (new)
P O RO U S
C ER A MI C S
ARCHERY
BOWS (old)
1
Knowing the physical
properties required, the
chart tells you which
material to use
0.1
FOA MS
0.01
100
Light
RU B B ER S
300
1000
3000
DENSITY (kg/m3)
10,000
The birth of sports technology
30,000
Heavy
material world
Sports equipment designers have to work out what
materials might be best for a bicycle frame or a tennis
racket. With such a vast range of materials available,
where do they start? One valuable tool is a materials
selection chart. Routinely used by engineers, these
charts show combinations of properties plotted
against each other, such as density versus stiffness.
The result is a “material space” populated with blobs,
each describing a class of materials, such as wood,
polymers and metals (see chart, above).
In 1995 Ulrike Wegst and Michael Ashby, both then
at the University of Cambridge, published the first
paper showing how selection charts could be used to
identify which materials would work best for sports.
With rowing, for instance, an oar must be able t
o withstand large forces during the stroke and yet
must bend just the right amount to give the athlete
the correct feel. An oar should also be as light as
possible to minimise energy in
accelerating its mass and also to keep
the boat high in the water and to
minimise drag. This points towards
wood, glass fibre or carbon-fibre
reinforced plastics.
Or consider the pole vault. The pole
must be able to store large amounts
of energy without breaking, while
its mass is kept to the minimum.
Bamboo comes out highly in the
selection process, which explains
why it was still in use in the 1950s.
Today glass fibre and carbon fibre
are the materials of choice because
they are more flexible, store more
energy and can be shaped to enhance
performance further.
Record breakers
World record
How times for the 100-metre sprint have changed. The introduction of automated timing led to an apparent 0.2-second increase
Second world war
Mean of top 25 sprinters
Fully automated timing
Usain Bolt
9.72 seconds, 9.69 seconds 2008
9.58 seconds 2009
11.2
Time (seconds)
META LS
A ND
A LLOYS
P O LY MER S
Sport is one of the
earliest adopters of
new technologies
11.4
For millions of years, humans have used tools and technology to
enhance the things we do. Throughout human evolution, our
imaginative minds have invented games, which help us to learn
useful physical and mental skills as well as have fun. It was
inevitable, then, that technology and sport would eventually
marry up, and sports engineering is the basis of that union. Any
technology is considered fair game – as long as it is within the rules
of sport – and sport is quicker than almost any other industry to
take up new ideas. So what has shaped the engineering of sport
up to now?
GOLF DRIVERS
CO MP O S I T ES
WO O D A N D
WO O D
P RO D U C T S
generation of large-headed drivers which, like
tennis rackets, have a larger hitting area and
peripheral weighting so that the club twists less
in golfers’ hands when they hit a ball off-centre.
Probably at the pinnacle of sports equipment
design is British bicycle designer Mike Burrows.
Working with engineering firm Lotus, he applied
good design principles to create a bike with a
carbon-fibre frame for Chris Boardman in the
1992 Barcelona Olympics, on which he won the
4000 metres pursuit. Apart from the psychological
effect of the bike’s style and beauty, Burrows’s
design reduced mass and increased stiffness so that
less energy was lost through bending of the frame.
More importantly, it improved the aerodynamic
efficiency and optimised the rider’s position.
First world war
HOW TECHNOLOGY TRANSFORMED SPORT
C ER A MI C S
11.0
10.8
10.6
10.4
Luther Cary 1891
10.8 seconds
Maurice Greene 1999
9.79 seconds
10.2
10.0
9.8
Jim Hines 1968
9.95 seconds
9.6
9.4
1890
1898
1906
ii | NewScientist | 7 July 2012
1914
1922
1930
1938
1946
1954
1962
Carl Lewis 1991
9.86 seconds
1970
1978
1986
1994
2002
2010
The inaugural Olympic games was one of the key
moments in human civilisation. It took place in ancient
Olympia in 776 BC to honour the Greek god Zeus. There
was only one event, the stadion – a foot race about
200 metres down a track and back again. Soon rules
were established that included simple technological
advances, such as a grooved sill for the starting block
and poles to mark the track. The Greeks introduced
a plethora of other sports in the 300 or so Olympiads
that led up to the last ancient games in the 4th century
AD. Chariot racing, running in armour and the javelin all
had their own technological intricacies and sets of rules.
Fast-forward 15 centuries to Victorian Britain and
the industrial revolution. Societal changes had as
much to do with the rise of sport as the technological
advances taking place at the time. Sport profited from
the introduction of regular leisure time, the rise in
the middle classes, increased levels of disposable
income and cheaper sports equipment produced in
large quantities.
Until then, sport had mostly used readily available
materials such as wood and leather. But that changed
in the 1850s when Thomas Hancock, Charles Goodyear
and Charles Macintosh invented ways to produce
vulcanised rubber on an industrial scale. By heating
a mixture of rubber and sulphur, they transformed
a naturally sticky substance into a durable material
with superior mechanical properties.
This transformed modern ball sports in the mid to
late 1800s. Rubber bladders replaced real animal
bladders, so balls could be mass-produced with almost
identical properties. Rubber was also used in shoes
and clothing. The introduction of the pneumatic
rubber tyre by John Dunlop in the 1880s led to more
comfortable bicycles and the transition from the
rather cumbersome penny-farthing to the modern
safety bicycle.
As professionalism increased and competitors
improved, techniques to monitor and measure
performance became more important. The invention
of photographic film in 1885 allowed Eadweard
Muybridge to create his classic stop-motion
technique for studying galloping horses.
Flash photography and cine-film followed and
sports coaches began to use high-speed film
with rates of hundreds of frames per second
to measure athletes’ technique and improve
their performance.
By the 1930s developments in timing allowed
measurements to be made with an accuracy
of 0.1 seconds. In the 1970s timing to 0.01 s
became mandatory in athletics. By then it was
possible to synchronise the starter’s pistol
with quartz timing and light beams crossing the
finish line. One consequence was that athletes
appeared to get slower by around 0.2 s because
the slight pause as the timekeeper reacted to
the gun and activated the watch was no longer
a factor (see chart, bottom left).
Technology has revitalised
the Olympics since the first
modern games in 1896
I.O.C./Getty Images
Stiff
New materials have changed the design of
traditional sports equipment. Graphite tennis
rackets, for instance, made the wooden rackets
used for more than a century obsolete within a
few years. The stiffer graphite frame meant that
rackets could be made longer and wider, increasing
the hitting area and the size of the “sweet spot”
where ball impact is most effective. It also shifted
the frame’s centre of mass away from the long
axis through the handle, so that the racket was
less likely to spin in the player’s hand if the ball
was off-centre. These new racket features made
tennis easier for beginners to learn and, some
argue, increased the speed of the elite game.
Graphite shafts are also popular in golf, and
titanium has had a significant effect on the design
of golf drivers. Being light, strong and corrosionresistant, both materials are ideal for the new
Flexible
Below: Gouhier-Hahn-Nebinger/ABACA/Press Association Images, right: Umit Bektas / Reuters
elite design
7 July 2012 | NewScientist | iii
THE PHYSICS OF SPORT
Aerodynamics
Fluid flow plays an important part in sport, with the
most obvious example being a swimmer in water.
For cycling, athletics and many other sports, the
fluid is the air. While sports scientists seek to
improve an athlete’s biological performance, sports
engineers seek to reduce energy losses, particularly
those that are the result of interactions with a fluid.
Probably the most important force to minimise is
drag, which is controlled by a number of factors. It is
proportional to the square of the speed, so doubling
the speed means four times as much drag. It is also
proportional to the density of the fluid. Water is
almost 1000 times as dense as air, so a triathlete
experiences far greater drag when swimming than
running or cycling.
Another factor is the cross-sectional area of
the body in relation to the fluid. Doubling the area
doubles the drag force and this is why cyclists crouch
when riding. One of the main effects of polyurethane
all-in-one swimsuits is to compact the body. The
smaller cross-sectional area reduces drag.
More subtle effects are important too. In the
1970s, Elmar Achenbach at the Jülich Nuclear
Research Centre in Germany carried out a series
of experiments on spheres in a wind tunnel. He
showed that the roughness of a sphere’s surface
influences the way that a fluid flows over it and
thus affects drag. Even scratches a hundredth of
a millimetre deep are significant.
One of the clearest examples of this is the dimples
on a golf ball. In the late 1800s, golf balls were
smooth, and because they were expensive players
Sport is not just about maximising the performance of the athlete,
it is also about minimising the energy that is lost as we run, swim
or slide through the fluids around us. Engineers now know that
understanding the forces that dominate a particular sport is crucial
to performing well
Computational fluid
dynamics helps to improve
design and performance
Newton’s insights
the numbers game
kept them for as long as possible. It turned out that
older balls travelled further as they accumulated
more nicks and bumps. The roughness creates
turbulence in the layer of air in contact with the ball.
This actually stabilises the flow of air around the
ball, allowing it to follow the ball’s contours and
reducing drag. Thus, golf ball dimples were born.
The late fluid dynamicist Milton Van Dyke
produced a beautiful book called An Album of Fluid
Motion (Parabolic Press, 1982). It shows numerous
examples of the way in which fluids can be coaxed
to separate or attach to a body using geometry,
steps and even trip wires. One of the clearest
examples of good aerodynamic design in sport is
the helmets used in cycling and the bobsled. The
helmet’s main job is to direct the airflow along the
back of the athlete and keep it attached to the body
as long as possible, thus reducing the size of the
wake and the drag.
iv | NewScientist | 7 July 2012
”One of the main
effects of all-in-one
swimsuits is to
compact the body.
This reduces drag
in the water”
Left: CSER/Sheffield Hallam University, Background: Richard Bartz/Wikimedia
Above: Dylan Martinez/Reuters; Top: john hart/Sheffield Hallam University
Sports equipment is often too complicated to
analyse using mathematical equations such as those
in Newton’s laws. But in the 1990s, increasingly
powerful computers enabled Keith Hanna, of
engineering company Fluent in Sheffield, UK, to
show that sport could use numerical methods to
improve design, including finite element analysis
and computational fluid dynamics.
Both methods start with a 3D representation
of the athlete or equipment, created either with
a software design package or
from a 3D body scanner. Finite
element analysis breaks down a
complex structure such as the
handlebars of a bike into a large
number of small elements, whose
movements are easier to work
out than the structure as a whole.
A computer program analyses the
forces acting on each element
separately, then combines them
to give an overall picture of what
is happening.
Computational fluid dynamics
is similar, though it is the fluid
rather than the object that is split
up into small elements. Large
models can take hours or even
days to run and require clusters
of computers, lots of memory
and many processors.
These numerical methods
have, however, made it possible
to gain insights about sporting
equipment where experiments
would be just too costly or difficult
to do. And they have helped
with the design of equipment as
diverse as archery bows, America’s
Cup yachts and golf clubs.
Natural philosopher Isaac Newton realised that forces
were important in sport, and said as much in a letter to
Henry Oldenburg, the secretary of the Royal Society in
1671. Newton’s three laws of motion are still the basis
for modern sporting analysis. Using them, physicist
Howard Brody at the University of Pennsylvania in
Philadelphia pioneered studies of the interaction
between a tennis racket and a ball. He found that the
best racket designs optimise three parameters. Mass
is crucial because if the racket is too heavy players
find it difficult to hold, if too light the racket transfers
little momentum to the ball. The centre of mass must
also be optimised – too far from the hand and the
racket feels “head heavy”. Finally, the moment of
inertia is a product of the mass of the racket and the
square of the distance of the balance point from the
hand. If it is too high, players cannot swing the racket
fast enough to give momentum to the ball.
Newton also coined the phrase “coefficient of
restitution” to describe the ratio of rebound to impact
velocity of an object. Simply speaking, it quantifies
the bounciness of sports balls and the effectiveness
of most bats, clubs, rackets and sticks.
Newton’s laws of motion
are the starting point for
sports engineers
7 July 2012 | NewScientist | v
game on
iSport
Gaming and sport are moving ever closer.
Nintendo’s Wii console introduced a level
of sporting activity into the home and uses
accelerometers and gyroscopes to track the
motion of the hand controller. The introduction
of Microsoft’s Kinect in 2010, however, has
taken video capture to a whole new level.
The Kinect is a 3D depth-sensing camera – it
projects an infrared pattern of dots that bounce
off an object or person and are picked up by an
infrared camera. Complex algorithms convert
the pattern into a depth field, while a standard
video camera picks up colour images.
In effect, the Kinect does for less than
$100 what complex motion-tracking systems
do for a thousand times as much – albeit
at only 30 times per second and with less
accuracy so far. Initial testing shows that,
without much modification, Kinect can
measure the volume of a typical human torso
to within a few per cent and knee angles to
within 10 degrees. The beauty of the Kinect
is that it tracks hundreds of thousands of
points in each picture, giving a complete 3D
image of the body.
It is early days yet, but already prototype
systems have appeared that can track the
centre of mass of badminton players, or can
simply gather measurements such as the
players’ height and the length and width of
their limbs. For now these systems are only
available to those at the higher end of sport,
When attached to the body, sensors such as
3D accelerometers, gyroscopes and GPS can
provide a wealth of information about an athlete’s
position and orientation. Until recently they
were so expensive that only university research
departments and sport’s ruling bodies could
afford them. But all that has changed. Today’s
smartphones and gaming devices include such
sensors, and this has driven down their price
so much that commercial athlete tracking
systems are readily available. Indeed,
many football, rugby, hockey and rowing
Sport is an early adopter of technology and at the turn of the 21st
century, better performances were characterised by new materials and
cheaper manufacturing. The biggest change happens when a technology
is introduced – for example, carbon fibre led to radical redesigns of bikes,
boots and boats. But after a while there are diminishing returns with
each new design.
What will be the next big thing to prompt a step change in performance?
Mobile devices such as phones, cameras and gaming consoles are one
of the fastest expanding markets. They are likely to enhance sport with
their ability to measure an athlete’s performance and analyse it. For the
first time, we will be able to quantify and understand the effect of a
piece of kit in action on the pitch or court. Buy a new tennis racket or set
of football boots and they may have sensors in them that tell you not
only how well you are playing, but how you can improve. Amassing data
out in the field without interrupting play has long been the ultimate
goal for sports engineers – the humble cellphone might just do the trick.
force, motion, speed
teams are using the technology.
There are now even portable wireless
systems that can measure heart activity
using electrocardiography, and muscle
activity using electromyography. Air pressure
and temperature measurements are there if
athletes need them too. If it can be measured,
it is being measured.
Just as the technology found in smartphones
is helping elite athletes, now everyone with a
smartphone can access the basics. There are
already hundreds of sports apps for phones and
many measure performance, mostly for outdoor
pursuits. There are of course places where GPS
doesn’t work, such as a squash court or bowling
alley, and other technologies that would be useful,
such as integration with video. Here, the solutions
are coming from the gaming industry…
Sports engineers develop new equipment and
technology and then have to work out whether it
actually makes a difference. One way is to give an
athlete a new golf club, for example, or a pair of
shoes and test them before and after to see what
changes. The test usually involves measuring the
position, speed, acceleration or force of both the
athlete and their equipment.
For instance, divers jumping from a 10-metre
platform are interested in the forces beneath their
feet and how they translate into a high jump with
more time to execute their complex twists and
rotations. Runners tend to be obsessed with time
and distance, so tracking their position is key.
Archers must be stable when they release the
arrow, so measuring how still they stay is important
to them. Here are some of the techniques used,
together with their pros and cons.
but it will not be too long before Kinect-like
derivatives are available in leisure centres or
sports stores.
The implications of this are not hard to see.
Before long there will be low-cost devices –
possibly on our phones – with depth-sensing
cameras to measure 3D motion in the field.
This will solve the long-standing problem
of tracking athletes cheaply in action, and
without using any kind of marker. And it will
be available to anyone, at any level, who just
wants to perform a little bit better.
vi | NewScientist | 7 July 2012
Markers on his body
track every movement
and can be analysed in
great detail afterwards
Ethan Miller/Getty Images
Top: J.C.Moschetti /R.E.A/ Retna Pictures, Right: Erik Jacobs/The New York Times/Redux/eyevine
THE FUTURE OF SPORTS ENGINEERING
”Tracking technologies
will soon be available
to everyone who
wants to perform
a little bit better”
n Motion tracking generally uses an
array of digital speed cameras taking
pictures at around 500 frames per
second. For comparison, a standard
camcorder takes 30 frames per
second. Multiple cameras around a
room can track reflective spherical
markers attached to an athlete’s body
at joints such as the knee and key
points such as the hands. The same
motion-capture system was used in
movies such as The Lord of the Rings
to track actors and turn them into
realistic avatars.
The results can be impressive,
with immediate video replay of the
athlete’s skeleton in motion. The
systems also give copious amounts
of data for each marker. The flip
side is the cost – often as much as
$100,000 per session, plus the need
for special lights and a lab setting.
Computers can only keep track of a
The results are usually instantaneous
and can be integrated with video
or motion capture. But only ground
reaction forces can be measured
and it is difficult to make these
measurements outside a lab. Again,
the systems are relatively expensive.
n Acceleration can be measured
directly using body-mounted sensors.
Accelerometers have shrunk in
recent years with wireless devices
becoming almost ubiquitous.
However, speed and position are
often more important to an athlete
than force and acceleration. While
it is possible to work out them out,
it takes a trained eye to manipulate
the data to avoid noise and errors
creeping in.
So what would be the perfect
system for sport? It would be cheap,
but also able to measure position,
speed, acceleration, physiology
limited number of markers, and when
they are covered by the athletes’
movements, working out what is
happening may take hours of tedious
manual reconstruction.
n Three-dimensional forces under
the feet can be measured using
sensitive plates sunk into the floor.
and be synchronised with 3D video.
And ideally, markers or sensors
would be unobtrusive or not
necessary at all. Complex data
analysis would be hidden from view
and only the important pieces of
information would be fed back,
just as with TV replays.
7 July 2012 | NewScientist | vii
Steve Haake
Steve Haake is director of the
Centre for Sports Engineering
Research at Sheffield Hallam
University in the UK. He advises
the International Tennis
Federation on the effect
of equipment design on the
rules of tennis and is also a
consultant to Adidas
Next
INSTANT
EXPERT
Pat Shipman
fossils
4 August
IS TECHNOLOGY CHEATING?
Most talks I give on sports engineering
end with the question: don’t state-of-theart technologies amount to cheating?
A cheat is someone who acts dishonestly
or unfairly in order to gain an advantage.
The crux, then, is to know what
constitutes being dishonest from a
technological point of view for a particular
sport. Technology and its possibilities
are grounded in Newton’s laws and the
manufacturing techniques of the day.
The definition of dishonesty, on the other
hand, is enshrined in the rather looser
rules of sport. What cheating in sport
amounts to, therefore, is the mismatch
between what is possible with current
technology and what the rules allow.
Both of these change over time, so any
sports ruling body has to be pretty sharp
to ensure that their rules match the
possibilities of the day.
Sometimes both sport and the rules
evolve in unison, at other times they are
out of sync. In tennis, for instance, no rule
for the tennis racket existed before 1978
because wooden rackets had remained
largely unchanged for over 100 years. But
the development of the “spaghetti” racket
that produced extraordinary amounts of
spin threatened to change the game and
it was duly banned. This was followed
by successive rules to limit racket size
as new materials allowed longer rackets.
An important turning point in athletics
came in 1984 when Uwe Hohn of what
was then East Germany threw the javelin
an enormous 104.8 metres. One of the
main issues with the javelin – apart from
viii | NewScientist | 7 July 2012
running out of space in the stadiums –
was the ambiguous flat landings, where
it was unclear if the javelin had landed tip
first. A technological solution was found;
the centre of mass was moved forwards
by 4 centimetres to ensure the javelin tip
always landed first. As a result javelins
travel dramatically shorter distances, less
than 100 metres and Hohn’s record stands
as the ultimate “old rules” javelin record.
More recently, the world governing
body for swimming, FINA, banned the
use of all-in-one polyurethane swimsuits.
Athletes were breaking an unseemly
number of world records because of
the reduced drag and extra buoyancy
the suits gave them. New rules were
introduced limiting the size of suits to
nothing above the navel or below the
knee for men and nothing extending
past the shoulder or below the knee for
women. Their buoyancy is also limited
to a maximum of 0.5 newtons (equivalent
to the weight of a small coin). It remains
to be seen if these rules will stop the
rapid rise in performance.
Sports engineering and technology
have an important role to play in sport.
New technologies can keep a sport alive
and relevant, but overuse can cause
a sport to lose credibility. Whose job is
it to keep the correct balance? The ruling
bodies of sport have to step up to the
mark. They need to keep an eye on
current and future technologies and
acquire the skills to understand the
implications. If they don’t, they will
always be playing catch-up.
Further information
An Album of Fluid Motion
by Milton van Dyke (Parabolic Press)
“The impact of technology on sporting
performance in Olympic sports” by
Steve Haake, Journal of Sports Sciences,
vol 27, p 1421
Engineering Sport blog
engineeringsport.co.uk
Video
richannel.org/collections/2012/
engineering-sport
Twitter
@stevehaake
Cover image
Karwai Tang/Alpha Press