Biomechanics of a Wrist Shot
BIOLOGY 438
A P R I L 5 TH, 2 0 1 2
PARTH PATEL
Basic Principles
 Three types of shots
 Slap Shot
 Snap Shot
 Wrist Shot
 Power generation
 Weight transfer
 Stick Flexion
 Wrist Snap
Muscles Used for Power Generation
 Legs – Weight Transfer
 Hamstrings
 Quadriceps
 Gluteus maximus
 Gluteus medius
 Gluteus minimus
 Hips / Core - Rotation
 Hip abductors
 Rectus Abdominus
 Obliques
Muscles Used for Power Generation
 Upper Body
 Energy Harnessing and Release
Shoulders
 Biceps/Triceps
 Forearms

 Uses the momentum created from weight transfer
and rotation, converts it into a quick, powerful wrist
snap
 Recruits the use of fast-twitch fibers in the forearms

High Vmax , high force, and high power
More About Stick Flex
 During any kind of shot, the stick turns into a spring
storing energy
 When the spring is released, the energy accelerates
the puck
 Proper slap shot technique
Source: http://hockeystickexpert.com/hockey-stick-flex/
Wrist Shot Flex
 Stick flex is usually seen in
more violent movements
 It takes a considerable
amount of force to “load”
the shaft
 Do the principles of stick
flex for slap shots and
snap shots apply to wrist
shots?
Experimental Question
 How does shaft stiffness on a hockey stick influence
potential energy storage and subsequent shot
velocity during a wrist shot?
 Approach:
 Analyze and compare the biomechanics of wrist shots with
both a flexible composite stick, and a stiffer wooden stick
Wood Stick
Composite Stick
Kinematic Descriptions
Composite
Wood
Lower hand acceleration
45.40 m/s2
45.64 m/s2
Lower hand peak velocity
7.295 m/s
7.064 m/s
Kinematic Descriptions
Composite
Wood
Stick Blade Velocity
19.24 m/s
17.60 m/s
Puck Speed
28.32 m/s (63.7 mph)
25.22 m/s (56.7 mph)
Narrowing Our Question
 Assuming that wrist, arm, and body movements are
identical regardless of which stick is being used

Can we explain the extra shot speed from the flex in the stick?
 And assuming that the wrist snap is the same with
both sticks

Can we explain the extra stick speed from the flex in the stick?
Force and Energy Measurements
 In a three-point bending test:
 Where
 E is the Young’s Modulus of the material
 I is the second area moment of the cross section
 L is the length of the beam
 𝛿 is the static deflection at the midpoint of the beam
Source: Russell, Dan, and Linda Hunt. "Spring Constants for Hockey Sticks."
Flex Ratings
 All composite sticks
have a flex rating on
the shaft
 Flex is measured by
the number of pounds
of force needed to
bend the shaft 1 inch
from its equilibrium
Converting Flex to SI Units
 Composite stick with Flex rating of 65
 65 lbs of force needed to bend the shaft at the midpoint by 1
inch
 Wooden stick with approximated Flex of 100
 100 lbs of force needed to bend the shaft at the midpoint by 1
inch
Comparisons to Literature
 Most professionals use sticks with Flex Ratings
anywhere from 80 – 160
 According to the cited study, shaft stiffness was
classified under four categories:




Medium (13 kN m-1)
Stiff (16 kN m-1)
Extra Stiff (17 kN m-1)
Pro Stiff (19 kN m-1)
Source: Pearsall, D. J., D. L. Montgomery, N. Rothsching, and R. A. Turcotte.
"The Influence of Stick Stiffness on the Performance of Ice Hockey Slap Shots."
Potential Energy Storage
U = ½ (11,383) (.07837)2
U =34.96 Joules
U = ½ (17,513) (.04237)2
U = 15.72 Joules
What happens to this energy?
 Obviously, this energy is not released back into the
shot


For reference, there were 35 (composite) and 16 (wood) joules
stored in the sticks.
The launch velocities measured correspond to 40 (composite)
and 32 (wood) joules into the puck.
 But can it at least account for the difference in stick
blade velocity at the release point?
Elastic Energy to Rotational Energy
 The motion we’re interested in is the speed of the
stick blade as it rotates through the puck
 Choose to ignore the loss of stored energy, and
instead focus on how much energy goes into rotating
the stick blade
 Rotational kinetic energy can be calculated
KE = ½ I ω2
Elastic Energy to Rotational Energy
 Consider the upper hand as stationary, and assume
that the stick rotates around that point
Calculations
 Velocity = R ω
 Composite stick blade release velocity = 19.24 m/s
 Radius = 1.12 meters
 ω = V/R = 17.18 radians/sec
(2.7 rev/sec)
 Wood stick blade release velocity = 17.60 m/s
 Radius = 1.12 meters
 ω = V/R = 15.71 radians/sec
(2.5 rev/sec)
Calculations
 I = moment of inertia = Istick + Iblade+puck
 I = moment of inertia = 1/3 ML2 + MR2
 I = 1/3 (.400 kg) (1.20 m)2 + (.100 kg + .102 kg) (1.20 m)2
 I = 0.4829 kg m2
 Difference in Kinetic Energy
 KE = ½ I ωcomposite2 – ½ I ωwood2
 KE = ½ I (ωc2 – ωw2 )
 KE = ½ (0.4829) [17.182 – 15.712]
 KE = 11.67 joules
Results
Composite
Wood
Spring Constant, k
11,383 N/m
17,513 N/m
Max Deflection, Δx
0.07837 m
0.04237
34.96 J
15.72 J
Potential Energy Stored
Potential Energy
Difference
Angular Speed of Stick
at Time of Puck Release
Rotational Kinetic
Energy
Kinetic Energy
Difference
Storage Efficiency
19.24 Joules
17.18 radians/sec
15.71 radians/sec
71.26 J
59.59 J
11.67 Joules
60.65%
Summary
 The composite stick is able to store more energy than
the wood stick
 The excess energy storage is used to increase the
rotational kinetic energy of the stick at the time of
puck release
 The efficiency of this conversion from elastic
potential to rotational kinetic energy is 60%
 Under the same movement, the composite stick is
able to launch the puck 7 miles per hour faster than
the wood stick
Implications
 This supports evidence that advises hockey players to
buy the stiffest hockey stick they can flex easily
 Also explains why only a handful of NHL players still
use wood sticks
Conclusions
 This finding should not be surprising, as this
relationship is also common in nature.
Recover the most
energy from a given
force using a spring
with the lowest
spring constant
Further Investigation
 The effect of different kickpoints on shot velocity
 Mid flex vs. Low kickpoints
Sources
 "Ice Hockey Sticks | Hockey Stick Flex: Produce Better Shots With The Right
Flex/Stiffness." Web log post. Hockey Stick Flex: Produce Better Shots With
The Right Flex/Stiffness. Web. 28 Mar. 2012.
<http://hockeystickexpert.com/hockey-stick-flex/>.
 Russell, Dan, and Linda Hunt. "Spring Constants for Hockey Sticks." The
Physics Teacher (2009). Print.
 Laliberte, David. "Biomechanics of Ice Hockey Slap Shots: Which Stick Is
Best?" Biomechanics of Ice Hockey Slap Shots: Which Stick Is Best? The Sports
Journal, 2009. Web. 02 Apr. 2012.
<http://www.thesportjournal.org/article/biomechanics-ice-hockey-slap-shotswhich-stick-best>.
 Pearsall, D. J., D. L. Montgomery, N. Rothsching, and R. A. Turcotte. "The
Influence of Stick Stiffness on the Performance of Ice Hockey Slap Shots."
Sports Engineering 2.1 (1999): 3-11. Print.