underwater gliding and undulatory swimming after the · pdf fileunderwater gliding and...

Underwater gliding and undulatory

swimming after the start

Biomechanics and motor control approaches

Marc Elipot

French Swimming Federation – Research Department

University of Paris Descartes

French Institute of Sport (INSEP) – Performance Analysis Department

Philippe Hellard, Gilles Dietrich and Nicolas Houel

[email protected]

mailto:[email protected]

Some facts

Why we built a 10 years research and training program

A few facts :

- During the 50m Freestyle at the Athens OG, the difference in time between

the 3 medallists was 0,11s at the end of the race while it had already reached

0,10s after the 15th meter.

- In 2004 – 2006: French athletes scored some of the worse start times during

international events

Some facts

During the 2005 World Championships (Montreal):

Alshammar Veldhuis Lenton Metella Couderc

Race time 24,92 24,99 25,14 25,7 25,64

Time to reach the 15th meter 6,34 6,30 6,34 7,02 7,18

Time swum during the 15 first meters 2,77 1,85 1,69 3,90 3,5

Schoeman Draganja Kizierowski Bousquet Sicot

Race time 21,69 21,89 21,94 22,26 22,31

Time to reach the 15th meter 5,28 5,44 5,48 5,72 5,8

Time swum during the 15 first meters 2,13 2,18 2,39 2,53 2,74


Consequences

As a result of those observations we started in 2006 a brand new program to

improve french athletes performances during starts

- Program research aiming:1- To produce a biomechanical analysis of the start (aerial and underwater phases)

2- To gather knownledge on how the underwater undulatory movements are produced,

controled and learned

- Performance evaluation team using new technologies to measure start

performance

- Applied communications, coaches education, …


What we knew

Two main phases:

Phases

1- The glide

- No propulsive actions

- Hold a streamlined position

- Re-orientation of the body after the water entry

2- The underwater undulatory swimming

- Synchronised undulatory legs movements

- No arms movements untill reaching the water surface

What we knew

Objectives

Main objectives

1- The glide :Maintain as long as possible the over-speed collected during to the previous phases of the start

- Decrease the hydrodynamic resistances

- Smooth re-orientation of the body from the initial position after the water entry to a

position suitable for the underwater propulsion

2- The underwater undulatory swimming :Maintain a velocity higher than the maximal surface swimming velocity (untill the 15th meter)

- Decrease the hydrodynamic resistances

- Increase the propulsive forces

- Build an appropriate trajectory to assure a smooth return to the surface

What we knew

Which factors have to be controlled ?

To decrease the hydrodynamic resistances

- Posture and position

(body full extension, ventral vs lateral position, …)

- Depth of the swimmer body

- Anthropometric data

- Limbs’ angles of attack

Form drag

Vawe drag

Frictional drag

Hydrodynamic resistances

What we knew

Orientation of the limb according to

the water dispacement

or the velocity vector of the swimmer’s centre of mass

Angles of attack

Velocity vector

Direction of the water displacement

Important angle of attack

Small angle of attack

Angle of attack = 90° Angle of attack = 45° Angle of attack = 0°

What we knew

Propulsive forces

How propulsive forces are created ?

Creation of a Karman vortex street

Adapted from Arellano et al., 2008

Undulatory movements create vortices behind the

swimmer’s feets

What we knew

Propulsive forces

How do those vortices work ?

Limbs’ angles of attack (amplitude)

Adapted from Arellano et al., 2008

Inappropriate(for a given frequency)

Appropriate(for a given frequency)

Regular Karman vortex street Reverse Karman vortex street

Creates resistive forces Creates propulsive forces

Swimmer Swimmer

Vortex Vortex

Forces Forces

To manage the limbs’ angles of attack in a way to find a comprise between holding a

streamlined position and re-orientating the body during the glide or increasing the

propulsive forces and at the same time lowering the resistances.

A story of compromises ?

Performance

What we knew

Angles of

attackJoins angles

Muscles

contractionsBrain

Motor control and coordination

Biomechanical measurements during the glide

Energy wasted during 70% of the underwater phase of the start

Vel

icit

y (

m.s

-1)

Kin

etic

en

erg

y o

utp

ut

(J ✖️

10

4)

Underwater distance (m) Underwater distance (m)

Swimmers’ efficiency during the underwater phase of the start

Velocities comparisonInternal and external kinetic energy comparison

Starts with underwater undulatory movements Starts without underwater undulatory movements

(hold a streamlined position as long as possible)

Measurements done in 2006/2007 on top french swimmers


Sources of explanation

Measurements done in 2007 on top french swimmers

Increase of the swimmer’s drag




Speed threshold (Lyttle et al., 2000)

Optimal CM position around 6m Optimal head position around 6,5m




By initiating the legs propulsion too early, swimmers :

1- Create higher hydrodynamic resistances

2- Lose very quickly the extra-velocity obtained thanks to previous phases of the start

3- Waste energy

Optimal distance from

which legs propulsion has

to be initiated (m)

Real distance from

which legs propulsion

are initiated (m)

Difference (m)

Mean 5,8 4,09 1,69

SD 0,56 0,53 0,75

Problem to be fixed

General representation Take the appropriate information

A quick glance at the motor control

basic principles

CerveauMuscle

Moelle épinière

1- The brain sends a motor command to the effectors (muscles)

2- The brain receives a feedback from the effectors (but not only)

Motor control and learning basis

Complexe movements

Multiple commands to send

Huge quantity of information to process

Maximal capacity of the brain ?


basic principles


Creation of a group of muscles and joins controlled thanks

only 1 motor command (task sharing)

Simplification = Optimisation



basic principles

Complexe movements

Motor coordination during the glide

Body re-orientation


How to control the angles of attack

Motor Coordinations

Synergistic action of the hip and

the shoulder

Synergistic action of the knee

and the ankle

Controls the trunk angle of

attackControls the angles of attack of

the legs and the feet

Angle of attack of the thighs

Coordinations identified using

PCA and cross correlation

functions

The fastest, the strongest synergy

Motor coordination during the legs propulsion

Legs movements


How to control the angles of attack

Actions of the hip and the ankle

Action of the knee

Angle of attack of the thigh Angle of attack of the trunk

Coordinations identified using

PCA and cross correlation

functions

The fastest, the strongest synergy

Angle of attack of the feet1 synergy



Legs movements

A) Streamlined position B) Upbeat beginning C) End of the upbeat

D) Downbeat beginning E) End of the downbeat F) Begnning of a new upbeat

MC 1: Hip extension – ankle

flexion

MC 2: Knee flexion

Reaction 1: Increase of the trunk and

legs angles of attack

Reaction 2: Increase of the thighs

angles of attack

MC 1: Hip flexion – Ankle extension

MC 2: Knee extension

Reaction 1: Decrease of the trunk and

the legs angles of attack

Reaction 2: Decrease of the thigh

angles of attack

MC 1: Hip extension – Ankle flexion

MC 2: Knee flexion

MC : Motor Command

And so on

Existing model versus those observations

Information found in previous studies or in books:

1- Their conclusions pointed out that the action of a single join can explain

the difference of performance between athletes

Hip, Knee, Ankle, … depending on the source

2- Their conclusions pointed out the existance of a top-down activation starting

from the shoulders or the hip and going to the ankles.

Important modifications in training the UUS


Our Paradism

1- We tried to understand the cooperations existing between the joins and have

observed some very specific synergies

2- We have observed a motor control organised around a loop where all joins are

working at the same time

Can we improve the UUS of young athletes using those

informations ?

Training the UUS

Training program

Measurements done in 2012/2013 on young french national level swimmers

The program

3 sessions per week

20 à 30 min during each session (sometimes specific exercises, sometimes

« hidden » during the regular training)

3 axes (in and out the water) :

- Sensori-motor training

- Motor conditionning using Biofeedback protocoles (mostly video)

- Exercises stimulating the postural control and the dynamical

interactions between joins

8 weeks

Modifications Observations

Velocity (m.s-1) Improvement

Distance per cycle (m) Individual strategies

Frequency (cycle/s)

Adjustment or stabilisation

of the ratio F/AAmplitude (m)

Kinematical analysis

Thanks to which adaptions, swimmers were able to

swim faster under the water ?

Training the UUS


Angles of attack

HandImportant decrease

of the drag generated

by the superior parts

of the body

Fore-Arm

Arm

Trunk

Join angles

Wrist

No trendElbow

Shoulder

Uper limbs

We cannot associate the decrease of the angles of

attack to a specific join action…

Postural component

Training the UUS


Propulsion

efficiency(evaluted regarding of the angle

of attack and the velocity)

ThighImprovement or stabilisation

of the « propulsion

efficiency »

Leg

Foot

Join angles

Hip

No trendKnee

Ankle

Lower limbs

We cannot associate the modification to the

propulsion efficiency to a specific join action…

propulsive component

=

=

Training the UUS

Time (s)

Act

ivat

ion (

mV

)

Movement 1 Movement 2 Movement 3 Movement 4 Movement 5

Beginning of the

contractionPeak of contraction and lag

Duration of contraction

Quantity of contraction

Training the UUS

Muscular activations


Duration of

contraction

Harmstrings

Decrease of the durationQuadri

Gluteus Max

Calf

Lumbar Decrease of the duration

Quantity of

contraction

Harmstrings

Increase of the quantity of

contraction

Quadri

Gluteus Max

Calf

Lumbar Stabilisation

=

Training the UUS

=

Inversion of contraction mode … Tonic versus phasic


-0,1

-0,05

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

Nageur 1 Nageur 3 Nageur 5 Nageur 6 Nageur 8

Grand fessier

Quadriceps

-0,1

-0,05

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

Nageur 1 Nageur 3 Nageur 5 Nageur 6 Nageur 8

Tim

e(s)

Tim

e(s)

Pre-test Post-test

Re-synchronisation of the muscles on the beginning of the movement

Synchronised contraction of the muscles


Gluteus

Max

Harm.

Training the UUS

Tim

e(s)

Tim

e (s

)

Pre-test Post-test

Synchronised contraction of the muscles

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

Nageur 2 Nageur 5 Nageur 6 Nageur 8

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

Nageur 2 Nageur 5 Nageur 6 Nageur 8

Ischio-

Jambiers

Mollet


Quadri

Calf.

Training the UUS

What’s the result

1- Modification of the theoritical model

Newton action-reaction to votex mechanisms

Modifications

3- The start is a step by step process… take the time to glide…

2- Frequency over the amplitude

4- the motor control during the start involved a synergistic control of the

joins. No join should be seen a single element

Modification of the exercices and the vocabulary used with the coaches

5- Attention should be put on the type of muscle contraction and their

synchronisations

6- A short motor learning program can lead to real and strong improvements

What’s the result

Fred Bouquet’s performances during the french national championships

over the last 8 years

50m Free 100m Free

Dist (m) Speed (m.s-1) Dist (m) Speed (m.s-1)

2006 Bernard / Bernard 9 2,61 9 2,53

2015 Manaudou/Stravius 14,45 3,51 15 3,20

2,5

2,6

2,7

2,8

2,9

3

3,1

3,2

3,3

3,4

7

8

9

10

11

12

13

14

15

2007 2008 2009 2010 2011 2012 2013 2014 2015

Vel

oci

ty (

m/s

)

Dis

tan

ce (

m)

Distance (m)

Velocity (m/s)

Underwater performance of the best french sprinters in 2006 and 2015

Thank you

Marc Elipot

French Swimming Federation – Research Department

University of Paris Descartes

French Institute of Sport (INSEP) – Performance Analysis Department

Philippe Hellard, Gilles Dietrich and Nicolas Houel

[email protected]

mailto:[email protected]

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