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Swimming Biomechanics in
Practice
Koji Honda,AIS Biomechanist
What is Biomechanics?
Sport Biomechanics is the application of physics and mechanics to the human body during sport.
Biomechanics is a part of the Movement Science, which also includes Performance Analysis and Skill Acquisition
“Performance Analysis answers the ‘What’ and ‘When’ whereas Biomechanics answers the ‘How’, whilst Skill Acquisition helps to
create the change.”
Tools of the Trade
Basic EquipmentVideo Equipment
- Video camera, - Smart phone, - Tablet
Stop watch
Advance Equipment and analysisVideo based kinematic analysisInertial sensorsPhysical testing using
Force plates (Wetplate, KPASS),Drag lines/towing devices
Numerical modelling and analysis of recorded flowlines and vortex patterns
Particle Image VelocimetryComputer-based numerical modelling
Computational Fluid Dynamics (CFD)
SPARTA Race Analysis
How do we make Swimmers Faster?
How Do Swimmers Swim?
The Swimming Race
Swimming Velocity = Stroke Rate x Stroke Length
= x
Swimming Velcoity
How Do Swimmers Swim?
48
35.2
24
7.5
0
10
20
30
40
50
60
Killer Whales Dolphins &
Barracudas
Penguins Humans
Sw
imm
ing
Sp
ee
d (
kp
h)
Aquatic Creatures
• Blunt and smooth at the
front and tapered at the
back
• Minimises turbulence until
well past
The Swimming Body
So What Is the Problem?
• Body Shape
– Blunt cigar shape
VS
– Lumpy & irregular human body contour
• No limbs or rough edges to create resistance and, ideally, driven from the rear
How to Improve Swimming Performance?
Achieved by one of three alternatives:
(1) the swimmer can increase propulsive force, or
Swimming Propulsion
Traditional Ideas of Propulsion Generation:
•Action/Reaction
(Drag/Propulsion)
•Lift (Sculling)
Propulsive Force = ½ ρ CD A v
A – frontal surface areav – swimmer’s velocityCD – Coefficient if dragρ – density of water
2+ ρ CM V a
V – Volumea – swimmer’s accelerationCM – Coefficient of inertiaρ – density of water
Drag Effects Unsteady State Inertial Effects
Net Thrust Generation in Swimming
How to Improve Swimming Performance?
Achieved by one of three alternatives:
(1) the swimmer can increase propulsive force, or
(2) the swimmer can reduce resistive drag (both active and passive), or
(3) some combination of the two (i.e. increased propulsive force and reduced resistance).
Components of drag:
1) frictional drag: friction
produced between water and
a moving object
2) form drag: a combination of
frontal and eddy resistance
3) wave drag: energy loss due
to creation of waves
Skin
Frontal areaEddies
Waves
• Components of drag:
– Frictional drag: friction produced between water and swimmer
– Form drag: a combination of frontal and eddy resistance
– Wave drag: energy loss due to creation of waves
Resistance – Drag Forces
• Is directly proportional to velocity
• Skin with Hair vs Shaved Skin vs Suit
0
2
4
6
8
0 2 4 6 8Velocity
Frictional D
rag
Frictional Drag
• Combination of
– Frontal resistance
– Eddy resistance
• Quadratic relationships
– Velocity squared
0
2
4
6
8
0 2 4 6 8Velocity
Form
D
rag
Form Drag
• wave drag: energy loss due to creation of waves• Bow wave, stern wave & lateral waves• Most detrimental type of drag – related to the cube
of the velocity.
Wave Drag
Distance of Glide in 1s
1.7 1.8 1.9 2 2.1 2.2 2.3
Surface
0.2m Deep
0.4m Deep
0.6m Deep
Distance (m)
Practical Measure of the
Drag Force:
Over 25cm extra glide
distance in 1s by gliding
at 0.4m deep compared
with the surface.
Effect of Depth on Drag Force
Underwater Kick
UW Kick
Normal Range
10° Less Plantar Flexion
(Toe Pointing)
A 10° increase in plantar flexion created an extra 16N of propulsive force (an extra ~66% peak force).
-80
-60
-40
-20
0
20
40
60
0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4
Feet Orig Feet less flexion on downwards only
Downsweep
Propulsion
Drag
UW Kick
UW Kick Transition
Body Position
The 4 H’s
Hand Head Hips Heels
Freestyle
✓✓
Freestyle
Freestyle
Freestyle
Freestyle
Freestyle
Force component for Left Leg
-50
0
50
100
150
200
0 0.2 0.4 0.6 0.8 1 1.2
Time (sec)
Fo
rce (
N)
Left Calf Left Foot Total Left Leg
Kicking During Swimming
• Aim to keep the feet submerged at all times.
Freestyle
Backstroke
Hand Press
Backstroke
Breaststroke
Traditional
New
Breaststroke
Breaststroke
Butterfly
Butterfly
Butterfly
Dive Start
Dive Start
Before and After
Dive Start
Before and After
Full Extension in the Air
Entry: 2.97m Entry: 3.36m
Backstroke Start
Sequencing: Arm push / upper body drive (Unfold), Leg drive
Arms streamline
Full leg extension
Head neutral
Backstroke Start
Arms streamline
Full leg extension
Head neutral
No knee bend/flick
Hands apart = Approx 17% increase in drag
Hold body position on entry – Depth of start
Hold tight body position on entry
Tumble Turns
Touch Turns
Touch Turns
Touch Turns
6.52
5.95
5.605.705.805.906.006.106.206.306.406.506.60
15m Start Time
4.76
4.96
4.40
4.50
4.60
4.70
4.80
4.90
5.00Horizontal Velocity m/s
Skill Development
Thank You