About five years ago, I had several discussions
with colleagues regarding the status of biomechanics
in tennis. I was interested in knowing: who were
the "movers and the shakers" in the field, who was
really on the leading edge,
what were the best techniques
for motion capture and what were the best software
tools for performance analysis.
Let's back up first. What is biomechanics and
what to biomechanists do?
Biomechanics is the study of how living things
move using the sciences of biology and mechanics.
It is part of a broader field called kinesiology
which is the study of human movement. The study of kinesiology
includes exercise physiology,
motor development, motor learning and biomechanics.
Biomechanics is an interdisciplinary field combining
several different sciences. Clearly, the human
performance aspect of biomechanics requires a good
understanding of anatomy (the science of the structure
and parts of a living organism) or physiology (the biological
study of the functions of living organisms). However,
biomechanics also includes that part of physics known
as mechanics. Mechanics analyzes how forces affect
objects both at rest (statics) and in motion (dynamics).
Both external and internal (including muscles) forces
create human movement in sport and exercise. Putting
it all together, sports biomechanics is the study of how
internal and external forces affect the motion and
performance of the human body in an athletic endeavor.
There also are biomechanists that study human
motion in industrial settings or work in ergonomics.
These biomechanists study equipment design in the
workplace and focus on improving worker performance
by reducing fatigue or discomfort. There are scientists
that study animal and even plant biomechanics. For
example, studies have been conducted on how a tree's
structure develops or how fluid flows through a tomato.
Biomechanists also need to be knowledgeable and
comfortable with the tools of the trade: math,
computer science, and statistics.
Who uses and investigates sports related biomechanics?
Studies are often conducted by university researchers
and professors. Biomechanics is also important to the
national governing boards of sports, like the USTA for
tennis, and all the other sports represented in the Olympics,
like skiing and swimming.
Biomechanic studies have been used to:
Recognize and create new playing techniques;
Develop athlete physical training programs.
The U.S. Olympic committee has a sports science group
with biomechanists on staff. Not all sports focus on
biomechanic studies. Team or contact sports are
difficult to study. In wrestling, for example, there are
simply a lot of body parts hidden from view.
Coaches need to understand biomechanics as well as the
players themselves. Professional players benefit by understanding
areas of improvement. For beginners, biomechanics helps them
understand the basic stroke production.
Knowledge of biomechanics is important in the sports
industry for equipment designers. Groups like the
ASTM (American Society for Testing and Materials)
and NOCSAE (pronounced Noxsey, National Operating
Committee on Standards for Athletic Equipment) determine
the standards and testing for athletic equipment from bike
helmets to running shoes to racquets.
What are the types of questions related to tennis
biomechanists might study?
Is it a good idea to imitate the performance of a
Are there techniques that limit injury?
What are the best techniques to teach tennis?
should I teach tennis differently than the way I learned it?
How many hours should you train a day?
For example: What's an optimal training schedule? Many pros
train 4 hours a day, 6 days per week. Jimmy Connors
trained only 1 1/2 hours a day, but it was focused and
concentrated. Which is better? In general, is one training
method superior to another? Is it dependent on the
individual or the skill level?
A professional tennis player may
compete an average of 7 years. What if we could
extend that longevity to 8-9 years? We could
increase the time that they can compete injury free.
There's a monetary value that can be placed on that additional
1-2 years of professional play. The information can be
used to support the longevity for any player, not just the professionals.
Studies have been conducted that confirm that tighter
strings create more control, while looser strings create
more power. That's not "intuitive." You might
actually think that the ball has a longer "dwell time"
(remains on the strings longer) if the
strings are tighter, but that isn't so.
Should you imitate a champion? Not necessarily.
Although a tremendous amount can be learned from
watching them, their strength, agility and endurance is
probably far greater than yours.
Information learned from this research is then applied
to coaching and training techniques. Swing patterns have
changed, racquets have changed, so have the position or
stance that the athletes use as they play. However, it is very
common to find coaches that teach the way they were taught
years ago and those older coaching and training techniques
do not necessarily support the "modern game of tennis."
The USTA has summarized some of its research in
biomechanics in a video tape production for coaches.
Biomechanic studies are conducted to determine:
how to learn the skill, what works best and what's safest.
Another area of interest is to understand the racquet
strings and its effect on player performance. As the
equipment changes or rules change we need to be asking:
What are the ramifications to the game's techniques, the players'
performance, training and potential for injury?"
There are many ways to capture information in
scientific studies. An entire industry exists dedicated to
instrumentation (collection of information with
scientific equipment and instruments). A variety of
equipment exists to calibrate, accumulate and analyze motion data.
In sports, equipment such as in-sole sensors or force
plates measure the pressure that the athlete imposes
on the ground as he or she performs. It's not surprising
that equipment used to measure the gaits and motions
of the most elite athletes are also used in the medical
and rehabilitative fields to analyze the motions of
individuals with limited and restrictive movements.
The same equipment monitors and looks for
improvements as the person recovers from an injury.
There are four major methods of motion capture: optical,
electromagnetic, magnetic, and "non-invasive" video systems.
Motion capture techniques are not only used to study athletes,
but used in animated films and video games.
Today, computer animated characters can look very realistic.
How do they do that? One technique uses small reflective balls.
The balls are attached to key joints and points on a person's body.
Infra-red cameras are set up around the athlete or performer
and can track the movement of these little balls. If one of the
balls is out of view of the cameras, its position can be determined
by the other cameras. This is called an "optical" system
and is typically limited to an indoor studio setting.
Another technique uses magnetic sensors instead of balls.
There are wires leading from these sensors into computer
systems that collect the motion information. This is called a
"magnetic" system and although the motion capture is not
limited to a studio, the wires restrict very complicated motions.
There are also methods that are "electromagnetic."
These systems use body suits.
These motions are collected by a computer and then used
with animated or "synthetic" characters.
While these systems do an excellent job at motion
capture and analysis, they are invasive methods of
motion capture. Clearly tennis equipment and players
could not be tagged with these devices during a professional
Subsequently, some researchers use video or film
cameras to record motions. Your standard home video
camera collects 30 frames/second. Researchers will often
use high speed cameras at 250 or 500 frames/second
(sometimes even higher).
Motion capture and analysis has been a tool used by
the military, universities, and research groups from
industry (groups of people that conduct scientific
studies to develop new products or techniques).
The military has used motion capture and analysis to
study ballistics (the flight of objects that are not
self-propelled, for example bullets). These objects
have a shelf-life (a length of time that an object can
be kept without deteriorating). Researchers wanted
to understand if projectiles built today would still fly
the same way several years later. They used
high speed cameras to study the performance of
these objects over a period of time and observed differences.
Researchers and students at universities use
motion capture and analysis to study both
biomechanics (the science of how a living organism moves)
and fluid (liquid or gas) flow.
One very interesting project was funded by the
Navy and conducted at a university. The Navy
and other branches of the Department of Defense
are interested in unmanned vehicles. The researchers
used cameras under the water to study how sea
creatures maneuver on the ocean floor. How does a
crab move over the edge of a cliff? By understanding
how these creatures move over this difficult terrain, better
underwater droids (robots) can be constructed.
High speed cameras can be used whenever motion is
so fast that the motion can not be comprehended by
our eyes and brain. One example from industry was
an electronic toothbrush study. The cameras were
used to determine if and how the bristles of the
toothbrush reached the nooks and cracks on and
between the teeth and gums.
Today, advances in technology are making
machines and processes faster and smaller.
Motion capture and analysis is used in "quality
control" (techniques used to assure high quality
products). Cameras are used to monitor assembly
lines for products like raisin cereal and soft drinks.
For example, soda cans move quickly down an
assembly line as they are filled and packaged.
Automated camera systems watch the process
and are able to determine when problems occur
(dented cans, messy labels). A high speed camera
is used to pinpoint where the damage occurs on the assembly line.
One of the biggest users of motion capture and
analysis is the automobile industry and not just
to watch the performance of fast race cars!
Motion capture and analysis is used in airbag
performance and safety studies. Engineers and
scientists study how airbags deploy.
They study the impact of the airbag against a
person's body. They want to understand how
the airbag affects people of all ages and sizes,
especially small children.
Of course high speed cameras are used in sports to
capture biomechanics. Motion capture and analysis
has been used extensively in sports such as golf.
Researchers at companies that manufacture golf
equipment study how the contact between the golf
club and the ball affect the flight of the ball. There
are even training systems developed that videotape
and analyze your motion so that you can become a better player.
These last systems will be the focus of the next column.
I'd like to try and incorporate your questions on biomechanics
into this series of columns on biomechanics in tennis. Don't hesitate to
write me using this form with your questions.
Until Next Month ... Jani