Tutorial: Golf Swing
Biomechanics
Dave
Tutelman  started
February 26, 2020
Straight
to
table of
contents
What can you get out of this tutorial?
You have undoubtedly heard of "biomechanics"  whatever that is 
becoming important in golf performance. This should help give you a
little insight into what golf biomechanics is and what it says.
My intent is for this insight to be sufficient that:
 It will help golf instructors understand the new things they are
hearing that could apply to what they teach. It may also disabuse them
of things they have heard over and over in the past that are, frankly,
wrong.
 It will show golfers diligent enough to slog through it, and
moreover to practice as much as it takes, some new things about how to
swing that are different from the traditional golf swing.
 It will allow you to read some of the published papers and
articles in journals on biomechanics, sports medicine, and kinesiology.
You might, or might not, be able to read and follow the details, but
you should be able to understand what the results are. You will also
gain an appreciation of how science figures out what is going on in a
golf swing.
 You may be able to better understand other things about golf
besides swing biomechanics, because now you know the physics. Some of
my examples relate to golf, but not specifically the biomechanics of
the swing; I talk about golf clubs, golf balls, and their interaction.
I hear golf instructors and golfers discuss these topics at length, so
I am not hesitating to bring them up in this discussion. They
illustrate a golfrelevant point of physics, and they may be easier to
understand in terms of a club or a ball.
A few points in the use of this tutorial:
 If you choose to read or skim it from beginning to end,
there are "next page"
and "previous page"
arrows at the top and bottom of each page.
 Below is a table of contents of the course, with links to
the
pages. You can dive in where you wish, but be forewarned that the
material assumes you know and understand what came in earlier pages.
 It is organized in two "books": Principles
and Applications.
 The "Principles" section is a tutorial on the physics and
biology you will need for a quantitative understanding of golf
biomechanics.
 The "Applications" section applies those principles to golf. It
covers my current (2023) understanding of the swing, and draws upon
published papers and articles  and gives you links to them for more
detail.
 I do expect you to know a little math. It is all stuff you
should have learned before or in high school, including:
 Eighth grade algebra. Solving simple equations, and
manipulating equations with multiple letters as unknowns.
 Eighth grade trigonometry. We may use a bit of ninth and
tenth grade stuff, but we'll develop what we need; I don't expect you
to know it when we start.
 Basic geometry, at least the terminology.
 How to read and understand graphs. Seriously, folks!
Understanding graphs
is a survival skill in today's world anyway.
Every now and then, I hear someone say (or see them write on
social media), "Well, how many equations have you had to solve this
year? Learning that was a waste of time." And I shake my head. If you
are like that, I hope I can convince you otherwise. A sense for
algebra is
absolutely essential to thinking quantitatively  about golf and about
almost anything.
 You
should pay attention to the examples. The deeper we get
into the principles, the more opportunity to include golf situations as
examples, and I try to do so whenever I can. Even if you don't sweat
the numbers in the examples, it is essential to understand what the
problem was and roughly how we got to the answer. Often, the answer
itself is enlightening; I will try to discuss the message in the answer
whenever possible.
 Occasionally there will be an optional
point where you may get some deeper insight if you can handle
the math. Such optional notes will be inserts
with a green background,
and might even be listed in green in the table of contents. But they are optional!
You can
skip it if your math skills can't deal with it. You will not have as
deep a grasp of the material if you skip it, but you will still have a
decent
working knowledge.
 Some, certainly not all, of those green notes will require more
math than the bullets in the list above. Occasionally, I may explain
something in terms of calculus or some other branch of math or science.
Again, it may be an opportunity to grasp a little better the concept I
am explaining, but you will still have a decent working knowledge of my
point even without the green note.
Book 1  Principles
Book 2  Application to the golf swing
Concepts
Coordinate systems
World coordinates  x,y,z
Swing plane coordinates 
alpha,beta,gamma
Club coordinates
Functional swing plane
Stability
Allows 2D analysis
The swing
The kinematic sequence
Torques in the downswing
Ground reaction force
Weight and pressure shift
Net GRF and its moment
Kinetic and kinematic sequence
Classic kinematic sequence
Some consequences
Rory McIlroy's hip reversal.
(Lots of
reaction torque)
Andreas Zanardelli's Facebook post. (Too little reaction torque)
Scottie Scheffler's slipping right foot. (Pressure shift too
early for reaction torque)
Recent published results
What produces clubhead speed?
What does shaft flex do?
How do we know this stuff?
Empirical studies
Instrumenting the swing
Direct kinetic measurement
Force plates
Transducer in grip
Launch monitor
Motion capture
Modeling the swing
Forward dynamics
Numerical integration
Inverse dynamics
I've been planning to write this tutorial for a halfdozen years. Once,
I even got started. But the enthusiasm lasted for only a few days.
There was never a clear organization to the material in my mind.
Then, in early February of 2020, Kathy Ricci, an instructor at our
Monmouth County Parks golf courses, called and asked for a tutorial on
the physics that is increasingly important to understand the new
biomechanics research on the golf swing. That motivated me to put
together a few pages of notes as a
"lesson plan" for my meeting with Kathy. We met at the Shark River Park
clubhouse on February 8 and spent about two hours going over the
material I had planned, plus detours for her questions. At the end, she
felt she understood the things we talked about. This sounded pretty
much like what I originally intended the tutorial
to do, and for the sort of person I hoped to help: a professional golf
instructor without a lot of physics or biomechanics background. So I
used the lesson plan as
the outline for the tutorial. As I made progress, the outline has
evolved.
At this point, I'm making the draft public for comment. It is still a
work in progress, but I think it is ready for reader input. Any
comments you have to make are welcome. Anything from errors of fact to
topics you'd like to see covered to the smallest typo. Thanks in
advance for any help you can give.
DaveT
Last
modified  Apr 25, 2023
