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