For Peer Review

The anthropometry manual work. 1 space for the seated .... 12709. 14.79 s. EgTini + 1. 9794. 5100. 32509. 10506. 30.26 s. EgTini + 1.5. 7063. 3832. 32842.
285KB taille 10 téléchargements 390 vues
Journal of Applied Biomechanics

High-level swimmers kinematic efficiency during the underwater phase of a grab start

r Fo Journal:

Manuscript ID: Manuscript Type:

draft Technical Note

Pe

Keywords:

Journal of Applied Biomechanics

swimming performance, start, underwater, kinematic energy

er ew

vi

Re Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 1 of 19

Journal of Applied Biomechanics

1

Title:

2

underwater phase of a grab start

3

Authors:

4

Affiliations:

5 6

1

swimmers

kinematic

efficiency

during

the

Elipot, M.1,2, Dietrich, G.2, Hellard, P.1, Houel, N.1

Département Recherche Fédération Française de Natation, Pôle Natation

INSEP, 11 Avenue du Tremblay, 75012 Paris, France. 2

Fo

7

High-level

Laboratoire Ergonomie Comportement et Interaction, EA 4070 – LAMA,

Université Paris Descartes, France.

9

Type of manuscript: Technical note.

ee

rP

8

Key words: swimming performance, start, underwater, kinematic energy.

11

Email: [email protected]

12

Mailing address:

13

Phone number: +33 610 32 06 75

14

iew

ev

rR

10

15

16

Number of tables: 3.

17

Number of figures: 3.

18

Number of words (main text): 1890 (max: 2000).

19

Number of words (abstract): 190 (between 150 and 200).

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

ABSTRACT The purpose of the present work was to study swimmers’ efficiency during the underwater

2

phase of the grab start. Eight high-level swimmers participated in this study. They performed

3

two types of start: a regular grab start (with underwater leg propulsion after the glide) and a

4

grab start with no underwater movement (swimmers had to remain in a streamlined position).

5

Four cameras filmed the entire underwater phase of all starts. Nine anatomic landmarks were

6

identified on the swimmers’ bodies and their positions were calculated using a modified

7

double plan DLT technique. From these positions and Dempster’s anthropometric data, the

8

centre of mass position and velocity were also determined. Kinematic energies were also

9

calculated. This velocity and kinematic energies for the two types of start were compared.

10

Swimmers began underwater leg propulsion 1.69 m too soon. The global and external

11

energies were significantly higher for the start with underwater leg propulsion. Nevertheless,

12

swimmers’ velocities were equivalent for both starts. These results suggest that the swimmers

13

did not use the underwater phase of the start efficiently: By kicking too soon, they did not

14

succeed in producing higher velocities and thus wasted energy.

iew

ev

rR

ee

rP

Fo

1

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 2 of 19

Page 3 of 19

Journal of Applied Biomechanics

INTRODUCTION The start is an important part of swimming events. It can account for 0.5 and 11% of the total

2

event time, as observed for the 1000-yard and 50-yard freestyle events, respectively (Hay,

3

1986). The importance of the start is further emphasised by the observation that the

4

differences between the individual performances of high-level swimmers are quite small. For

5

example, during the 50-m freestyle event at the Athens Olympic Games (2004), the difference

6

between the three Olympic medallists was only 0.11 s at the end of the race but had already

7

reached 0.1 s at the 15th meter. Differences in starting efficiency could explain nearly all of

8

the small differences in final time.

9

Start performance is defined as the performance observed between the start signal and the

10

moment when the swimmer’s head reaches the 10th (Alves, 1993; Arellano et al., 1996) or the

11

15th meter (Mason & Cossor, 2000; Issurin & Verbitsky, 2002). The global analysis of starts

12

has shown that the underwater phase is determinant to achieve a good start performance

13

(Clothier et al., 2000; Cossor & Mason, 2001; Shin & Groppel, 1986). Guimaeres & Hay

14

(1985) showed that 95% of the differences observed between swimmers’ starts could be

15

explained by differences in the underwater phase, yet surprisingly few studies have focused

16

on this phase (Blanksby et al., 1996; Lyttle et al., 1998; Clothier et al., 2000; Lyttle et al.,

17

2000).

18

The underwater phase of the start is divided into the glide and underwater undulatory

19

swimming. An optimised underwater phase aims to maintain the velocity created during the

20

aerial phase up to the resumption of arm stroking. To achieve the best performance, the

21

transition between the glide and underwater undulatory swimming is determinant (Lyttle et

22

al., 2000). Blanksby et al. (1996) showed that swimmers can lose time by kicking too late or

23

too soon after the glide phase. Swimmers starting underwater undulatory swimming too soon

iew

ev

rR

ee

rP

Fo

1

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

would create higher hydrodynamic resistance and would lose speed. Although these studies

2

pointed out the benefits of an efficient underwater phase, none of them presented the optimal

3

conditions for an efficient start.

4

During the underwater phase of a start, swimmers create hydrodynamic resistances

5

(Karpovich, 1933) that are directly influenced by the velocity and depth (Lyttle et al., 1998;

6

Lyttle et al., 2000; Toussaint et al., 2002; Vennel et al., 2006). Hertel (1966) and Larsen et al.

7

(1981) showed that the coefficient of drag decreases rapidly as the swimmer’s body depth

8

increases. Vennel et al. (2006) showed that at underwater swimming velocities (i.e. about 2

9

m.s-1) hydrodynamic resistances are 2.4 times smaller when the swimmer is fully immersed.

rP

Fo

1

10

The kinematic energy expended by athletes during sport performance has often been

11

calculated as a means to assess their movement efficiency (Winter, 1990; Duboy, 1994)

ee

12

rR

13

16

With Eg: The global kinematic energy

17 18

Ei: The internal kinematic energy

19

Ee: The external kinematic energy

20

Ii: Segment mass moment of inertia

21

ωi: Segment transversal rotation velocity

iew

ev

14 15

Page 4 of 19

mi: Segment weight 22

VGi/R*: Segment centre of mass velocity expressed in the centre of mass frame of reference

23 24

VG/R: Body centre of mass velocity expressed in the global Galilean frame of reference. To our knowledge, however, this variable has never been used to study swimmer efficiency

25

during the underwater phase of the start.

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 5 of 19

Journal of Applied Biomechanics

1

Although some investigations have sought to optimise the underwater phase of the start, the

2

efficiency of swimmers during this phase remains unknown. The aim of the present work was

3

to study the swimmer efficiency during the underwater phase of the start. METHODS Eight high-level swimmers voluntarily participated in this study (Table 1). All were informed

5

of the objectives and signed a consent form. The swimmers were asked to perform grab starts

6

as efficiently as possible. They practised this type of start on a regular basis and used it for

7

competitive racing. The swimmers had to perform six grab starts. Three starts had to be

8

performed without any subsequent propulsion during the underwater phase of the start.

9

During this phase, the swimmers maintained the streamlined position with no further

10

propulsive movement. Three regular grab starts had then to be performed (i.e. with

11

underwater leg propulsion). For each condition, the best start was analysed.

12

Four mini-DV cameras (Panasonic NV-GS17 and Sony DCR-HC20E) were used to record the

13

entire underwater phase of the start, i.e. from the start wall to the 15th meter. Three cameras

14

(camera 1, 2 and 3) were placed behind portholes and the fourth was placed in waterproof

15

housing (Figure 1). The cameras were positioned so as to minimise optical refraction effects

16

(Snell’s law) (Kwon, 1999; Kwon & Casebolt, 2006): A large distance separated the cameras

17

and the centre filmed zone. The optical axes of the cameras were perpendicular (± 5°) to the

18

air-water interface plane. The angles between the principal axis of camera 1 and the other

19

cameras were between 55° and 70°.

20

The underwater experimental area was divided into three field of view measuring 5 × 2 × 2 m:

21

The first zone was from the start wall to the 5th meter, the second zone from the 5th to the 10th

22

meter, and the third zone from the 10th to the 15th meter. To limit the effects of image

23

distortion (due to camera lens deformations) on reconstruction accuracy, particularly maximal

iew

ev

rR

ee

rP

Fo

4

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

error reconstruction, only the points within the 2/3 centre of the camera field were

2

reconstructed (Figure 1). The sampling frequency was 25 frames per second. The video was

3

interlaced scan and the odd and even fields were used. The cameras were synchronised using

4

light signal.

5

The entire underwater phase was recorded (i.e. from the instant at which the swimmers were

6

completely under water until the instant they broke the water surface, stopped gliding or

7

began arm propulsion).

8

To minimise errors during the digitizing process, the two sides of the swimmer’s body were

9

assumed to be symmetric. Only the right side was digitalized. Nine anatomic landmarks were

10

identified on the swimmers: a toe, the lateral malleolus, the knee, the iliac spine, the

11

acromion, a finger tip, the wrist, the elbow, and the centre of the head. A modified double

12

plane direct linear transformation method (inspired from Drenk et al., 1999) was used to

13

calculate the landmark coordinates in space. Space reconstruction accuracy was calculated as

14

described by Kwon & Casebolt (2006) and was 6.2 mm (maximal reconstruction error was

15

12.2 mm). These positions, together with Dempster’s anthropometric data (1959), were used

16

to determine the trajectory of the centre of mass. Data were filtered with a Butterworth II

17

filter (Winter, 1990). Cut-off frequencies were included between 5 and 7 Hz.

18

During the entire underwater phase of the start, each swimmer’s centre of mass depth and

19

velocity and swimmer’s kinematic energy were calculated.

20

The results obtained (velocities, depths, external and internal kinematic energies) for starts

21

with and without underwater leg propulsion were compared using one-way analysis of

22

variance for repeated measures. These comparisons were made at specific instants (Figure 2):

iew

ev

rR

ee

rP

23

Fo

1

-

At T0, i.e. the instant at which the swimmer’s body was fully immersed.

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 6 of 19

Page 7 of 19

Journal of Applied Biomechanics

1

-

At Tini, i.e. the instant when the swimmer initiated underwater leg propulsion.

2

-

Once leg propulsion began, every 0.5 m up to 3 m (Tini + 3 m) (6 comparisons). The centre of mass position was used to identify these positions.

3

4

The compared parameters were the internal, external and global kinematic energies, the centre

5

of mass velocity and depth, and the position and velocity at T0. The effect of underwater

6

propulsion on depth was analysed using two-way analysis of variance for repeated measures.

7

All statistical tests were performed with a level of confidence set at 99% (p < 0.01).

rP

Fo

RESULTS

Table 2 shows the optimal distance (from the start wall) for initiating underwater leg

9

propulsion compared with the real distance at which the swimmers began propulsion. It

10

appears that swimmers initiated underwater undulatory swimming 1.69 m too soon (SD =

11

0.75).

12

The comparison of the starts with and without underwater leg propulsion is presented in Table

13

3. The analysis of variance revealed no significant difference in the distance covered at the

14

instant of full immersion (DistT0) or the velocity at the same instant (VT0).

15

The two starts significantly differed at each instant in terms of global kinematic energy (EgTX)

16

and internal kinematic energy (EiTX), with the exception of the instant at which underwater

17

leg propulsion began (Tini). The start with underwater leg propulsion showed significantly

18

higher values than the start without propulsion.

19

Significant differences between the two starts were also noted in the swimmers’ centre of

20

mass velocity (VTX) and external kinematic energy (EeTX) 3 meters after underwater leg

21

propulsion began (Tini + 3). At this instant, the start with underwater leg propulsion showed

iew

ev

rR

ee

8

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

1

significantly higher values than the start without. At the other instants, no significant

2

differences were observed in these variables.

3

Significant differences between the two starts were also observed at all instants for the

4

swimmers’ centre of mass depth (DTX), with the exception of Tini and Tini + 0.5 m. The two-

5

way analysis of variance revealed significant type of start–distance interactions from Tini + 1

6

m (Figure 3). DISCUSSION

Fo

Choosing the optimal instant to initiate underwater undulatory movement directly influences

8

start performance. This choice has a direct impact on the decrease in underwater deceleration

9

(caused by hydrodynamic resistance) and the decrease in energy expenditure (Lyttle et al.,

ee

rP

7

2000).

11

The combined results of the present study and the study of Lyttle et al. (2000) suggest that

12

swimmers initiate underwater undulatory movement too soon. Our start comparison also

13

showed that, at the first instant of full body immersion, the distance covered by the swimmers

14

and their velocity seemed to be the same for starts with and without underwater leg

15

propulsion (respectively, 3.8 m versus 3.73 m and 3.87 m.s-1 versus 3.61 m.s-1). Furthermore,

16

none of the studied variables were significantly different at the instant when the swimmers

17

initiated underwater undulatory movement (Table 3). This implies that the swimmers’ actions

18

during the impulsion, aerial and gliding phases led to equivalent velocity, depth, and

19

kinematic energy expenditure for the two types of start.

20

In contrast, once underwater leg propulsion began, the swimmers’ global and internal

21

kinematic energy expenditure was higher for the start with underwater leg propulsion. The

22

swimmers did not, however, produce higher velocities and the external kinematic energy was

23

equivalent. This indicates that the difference in global kinematic energy was due only to the

iew

ev

rR

10

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 8 of 19

Page 9 of 19

Journal of Applied Biomechanics

internal kinematic energy difference. These results seem to suggest that the kinematic energy

2

produced by all segment movements relative to the centre of mass did not contribute to centre

3

of mass propulsion. This infers that, by beginning underwater undulatory movements too

4

soon, the swimmers wasted energy.

5

The results also showed that once underwater leg propulsion began, the swimmers’ depth

6

quickly decreased. One meter after leg propulsion began, the type of start had an effect on the

7

swimmer’s depth. Figure 3 shows that the start with underwater propulsion was characterised

8

by quicker surface resumption. Previous studies of the hydrodynamic resistances of towed

9

swimmers or mannequins have shown that hydrodynamic resistances are directly influenced

10

by centre of mass velocity and depth. Indeed, when the swimmers approach the water surface

11

with a high velocity, drag strongly increases (Hertel, 1966; Larsen et al., 1981; Lyttle et al.,

12

1998; Toussaint et al., 2002; Vennel et al., 2006). By returning to the water surface too soon

13

(with too high velocity), swimmers are faced with higher hydrodynamic resistances. The

14

energy waste observed in the present study could be explained by this effect of the start with

15

underwater propulsion.

16

In conclusion, the results of this study tend to suggest that swimmers do not use the

17

underwater phase efficiently during competitive starts. Indeed, during underwater leg

18

propulsion, the swimmers’ kinematic energy expenditure was higher during a glide velocities

19

are the same.

iew

ev

rR

ee

rP

Fo

1

ACKNOWLEDGEMENTS 20

The authors wish to thank the “Ministère de la Jeunesse, des Sports et de la Vie Associative”

21

and the “Fédération Française de Natation” for financing this study. The authors also wish to

22

thank Frédéric Frontier, Frédéric Clerc, Isabelle Amaudry and the “INSEP” for logistic

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

Page 10 of 19

1

support, and Jean-Lyonel Rey, Stéphane Lecat, Eric Boissière and Yves Thomassin for their

2

contributions. REFERENCES Alves, F. (1993). Analysis of swimming races. Proceedings of the XIVth Congress of

4

International Society of Biomechanics (pp. 88-89). Paris, France: International Society of

5

Biomechanics.

6

Arellano, R., Moreno, F. J., Martinez, M., & Ona, A. (1996). A device for quantitative

7

measurement of starting time in swimming. In J. P. Troup, A. P. Hollander, D. Strasse, S. W.

8

Trappe, J. M. Cappaert, & T. A. Trappe (Eds.), Biomechanics and Medicine in Swimming VII

9

(pp. 195-200). London, United Kingdom: E & FN Spon.

ee

rP

Fo

3

Blanksby, B. A., Gathercole, D. G., & Marshall, R. N. (1996). Force plate and video analysis

11

of the tumble turn by age-group swimmers. Journal of Swimming Research, 11, 40-45.

12

Issurin, V. B., & Verbitsky, O., 2002. Track start vs. Grab start: evidence of the Sydney

13

Olympic Games. In J. C. Chatard (Ed.), Biomechanics and Medicine in Swimming IX (pp. 92).

14

Saint Etienne, France: Université de Saint-Etienne.

15

Clothier, P. J., Mac Elroy, G. K., Blansby, B. A., & Payne, W. R. (2000). Traditional and

16

modified exits following freestyle tumble turns by skilled swimmers. South African Journal

17

for Research In Sport Physical Education and Recreation, 22, 41-55.

18

Cossor, M. J., & Mason, B. R. (2001). Swim start performances at the Sydney 2000 Olympic

19

Games. In J. R. Blackwell (Ed.), Proceedings of XIX International Symposium on

20

Biomechanics in Sports (pp. 65-69). San Francisco, California: University of San Francisco.

iew

ev

rR

10

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 11 of 19

Journal of Applied Biomechanics

Dempster, W. T., Gabel, W. C., & Felts, W. J. L. (1959). The anthropometry manual work

2

space for the seated subject. American Journal of Physiology and Anthropometry, 17, 289-

3

317.

4

Drenk, V., Hildebrand, F., Kindler, M., & Kliche, D. (1999). A 3D video technique for

5

analysis of swimming in a flume. In R. H. Sanders, & B. J. Gibson (eds.), Proceedings of the

6

XVII International Symposium on Biomechanics in Sports (pp. 361-364). Perth, Australia:

7

Edith-Cowan University.

8

Gamaraes, A., C., S., & Hay, J., G. (1985). A kinematic analysis of the grab starting technique

9

in swimming. International Journal of Sport Biomechanics, 1, 25-35.

rP

Fo

1

Hay, J. G. (1986). Swimming biomechanics: a brief review. Swimming technique, 23, 15-21.

11

Hertel, H. (1966). Structure-Form-Movement. New York, New Jersey: Reinhold Publishing

12

Corporation.

13

Karpovich, P. V. (1933). Water resistance in swimming. Research Quarterly, 4, 21-28.

14

Kwon, Y. H. (1999). Object plane deformation due to refraction in two-dimensional

15

underwater motion analysis. Journal of Applied Biomechanics, 15, 396-403.

16

Kwon, Y. H., & Casebolt, J. B. (2006). Effects of light refraction on the accuracy of camera

17

calibration and reconstruction in underwater motion analysis. Sports Biomechanics, 5, 95-120.

18

Larsen, O., W., Yancher, R., P., & Baer, C., L., H. (1981). Boat design and swimming

19

performance. Swimming Technique, Aug-Oct, 38-44.

20

Lyttle, A., D., Blanksby, B., A., Elliott, B., C., & Lloyd, D., G. (1998). The role of drag in the

21

streamlined glide. Journal of Swimming Research, 13, 15-22.

iew

ev

rR

ee

10

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

Page 12 of 19

Lyttle, A., D., Blanksby, B., A., Elliott, B., C., & Lloyd, D., G. (2000). Net forces during

2

tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle

3

turn. Journal of Sports Sciences, 18, 801-807.

4

Mason, B., & Cossor, J. (2000). What can we learn from competition analysis at the 1999 Pan

5

Pacific Swimming Championships? In R. Sanders & Y. Hong (Eds.), Proceedings of XVIII

6

Symposium on Biomechanics in Sports (pp. 75-82). Hong Kong, China: The Chinese

7

University of Hong Kong.

8

Shin, I., & Groppel, J. (1986). A comparison of the grab start and track start as utilized by

9

competitive swimmers. In D. L. Landers (Ed.), Sport and Elite Performers (pp. 171-175).

rP

Fo

1

Champaign, Illinois: Human Kinematics Publishers.

11

Toussaint, H., M., van Stralen, M, & Stevens, E. (2002). Wave drag in front crawl swimming.

12

In Gianikellis, K. (Ed.), Proceedings of the XXth International Symposium on Biomechanics

13

in Sports (pp. 279-282). Extremadura, Spain: Universidad de Extremadura.

14

Vennell, R., Pease, D., & Wilson, B. (2006). Wave drag on human swimmers. Journal of

15

Biomechanics, 39, 664-671.

16

Winter, D., A. (2000). Biomechanics and motor control of human movement. New York, New

17

Jersey: A. Wiley-Interscience Publication.

iew

ev

rR

ee

10

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 13 of 19

Journal of Applied Biomechanics

List of tables

1

2

Tables 1 - Swimmers’ general characteristics

3

Tables 2 - Lag between the optimal instant to initiate underwater leg propulsion and the

4

instant at which swimmers really began leg propulsion

5

Table 3 - Comparison between the start with underwater leg propulsion and the start without

6

underwater leg propulsion

Fo

7

List of figures

rP

Figure 1 - Experimental set-up

9

Figure 2 - Comparison between the two types of start: With and without leg propulsion

ee

8

Figure 3 - Interaction effect of the distance covered and the type of start on the swimmer’s

11

depth

iew

ev

rR

10

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

1

Tables

2

Table 1

3

Swimmers’ general characteristics

6

iew

ev

rR

ee

rP

5

Fo

4

Mean SD

Best performances (s) 50-m 100-m Body mass Height (m) 50-m freestyle (% 100-m freestyle (% (kg) freestyle (s) of the world freestyle (s) of the world record) record) 1.85 78.5 24.41 114.7 51.84 110 0.05 4.66 1.62 7.49 1.49 3.12

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 14 of 19

Page 15 of 19

Journal of Applied Biomechanics

1

Table 2:

2

Lag between the optimal instant to initiate underwater leg propulsion and the instant at which

3

swimmers really began leg propulsion

Distance at which Optimal distance to swimmers really initiated initiate underwater leg underwater leg propulsion propulsion (m)* (m) 4.9 4.28 3.81 3.97 4.82 3.51 3.82 3.59

-0.51 -0.97 -1.85 -1.83 -1.85 -2.09 -1.44 -2.99

4.09 0.53

-1.69 0.75

rR

ee

5.78 0.56

rP

Mean SD

5.41 5.25 5.66 5.8 6.67 5.6 5.26 6.58

Fo

Subject 1 Subject 2 Subject 3 Subject 4 Subject 5 Subject 6 Subject 7 Subject 8

Lag (m)

The distance were calculated from the start wall

4

* i.e. when the swimmer's centre of mass reached a velocity between 2.2 and 1.9 m.s-1 (Lyttle et al, 1998)

iew

ev Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

Page 16 of 19

1

Table 3

2

Comparison between the start with underwater leg propulsion and the start without

3

underwater leg propulsion Start without underwater undulatory movements

Start with underwater undulatory movements

Comparison

SD

Mean

SD

F

p

DistT0 VT0

3.8 3.87

0.26 0.55

3.73 3.61

0.19 0.31

0.33 1.3

n.s n.s

VTini VTini + 0.5 VTini + 1 VTini + 1.5 VTini + 2 VTini + 2.5 VTini + 3

3.36 2.93 2.53 2.19 1.91 1.68 1.51

0.49 0.52 0.46 0.39 0.33 0.3 0.27

3.11 2.7 2.46 2.18 2.07 1.95 1.92

0.44 0.41 0.29 0.3 0.24 0.23 0.2

1.13 0.95 0.13 0.004 1.29 3.77 10.18

n.s n.s n.s n.s n.s n.s s

DTini DTini + 0.5 DTini + 1 DTini + 1.5 DTini + 2 DTini + 2.5 DTini + 3

-0.92 -0.97 -1.03 -1.05 -1.06 -1.06 -1.04

0.18 0.15 0.12 0.14 0.16 0.18 0.2

-0.73 -0.82 -0.87 -0.85 -0.79 -0.73 -0.65

0.12 0.09 0.08 0.13 0.13 0.21 0.25

5.53 11.26 15.37 12.14 11.48 27.42 31.7

n.s n.s s s s s s

EgTini

34515

11546

56615

15548

2.44

n.s

EgTini + 0.5

15419

7988

36897

12709

14.79

s

EgTini + 1

9794

5100

32509

10506

30.26

s

EgTini + 1.5

7063

3832

32842

33.77

s

EgTini + 2

2741

32279

11767

40.48

s

EgTini + 2.5

4363

2138

32533

13228

30.93

s

EgTini + 3

3505

1643

322891

13758

31.48

s

EiTini

34050

11247

rR

11946

5100

56158

16548

2.444

n.s

EiTini + 0.5

15070

7990

36552

12747

14.72

s

EiTini + 1

9516

5118

32171

10509

30.04

s

EiTini + 1.5

6838

3853

32547

11963

EiTini + 2

4913

2761

32013

EiTini + 2.5

4205

2152

32292

EiTini + 3

3367

1657

32811

EeTini

464

148

457

EeTini + 0.5

348

105

389

EeTini + 1

278

73

EeTini + 1.5

224

ee

rP

Fo

Mean

ev

s

40.07

s

13250

30.64

s

14074

30.21

s

108

0.01

n.s

92

0.64

n.s

338

70

2.81

n.s

60

294

59

5.36

n.s

EeTini + 2

190

50

266

55

8.23

n.s

EeTini + 2.5

167

55

231

57

4.48

n.s

EeTini + 3

138

40

223

50

12.12

s

iew

33.47

11789

With: DistT0 (m): The distance from the start wall when the swimmer is fully immersed -1

VTX (m.s ): The swimmer's velocity at T0, Tini, Tini + 0.5, 1, 1.5, 2, 2.5 and 3m DTx (m): The swimmer's depth at T0, Tini, Tini + 0.5, 1, 1.5, 2, 2.5 and 3m EgTX (J): The global mechanical energy at Tini, Tini + 0.5, 1, 1.5, 2, 2.5 and 3m EiTX (J): The internal mechanical energy at Tini, Tini + 0.5, 1, 1.5, 2, 2.5 and 3m

4

EeTX (J): The external mechanical energy at Tini, Tini + 0.5, 1, 1.5, 2, 2.5 and 3m

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Page 17 of 19

Journal of Applied Biomechanics

1

Figures

2

Figure 1

3

Experimental set-up

5m

0m Zone 1

10 m Zone 2

15 m Zone 3

Start wall

rP

Fo Camera 4

Camera 1

Camera 2

: 2/3 centre of the camera field

4

iew

: Set of four calibration points

Camera 3

ev

Behind portholes

rR

ee

In waterproof housing

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Journal of Applied Biomechanics

Page 18 of 19

1

Figure 2

2

Comparison between the two types of start: With and without leg propulsion Start wall First comparison

Second comparison

Third comparison

Start with underwater leg movements

etc

T0 :

rP

Fo

Start without any underwater movement

7

iew

6

Beginning of underwater undulatory swimming

ev

5

Dini + 0.5 m

rR

4

Dini

ee

The swimmer is fully immerged

3

Sixth comparison

8

9

10

11

12

Human Kinetics, 1607 N Market St, Champaign, IL 61825

Dini + 3 m

Page 19 of 19

Journal of Applied Biomechanics

1

Figure 3

2

Interaction effect of the distance covered and the type of start on the swimmer’s depth

-0,5 Tini

Tini + 0.5 m Tini + 1 m Tini + 1.5 m Tini + 2 m

Tini 2.5 m

Tini + 3 m

-0,7

-0,8

-0,9

No significant interaction (distance-type of start) on swimmer's depth

Start with underwater undulatory movement

Significant interaction (distance-type of start) on swimmer's depth

iew

ev

rR

ee

-1,2

rP

-1

-1,1

3

Start without underwater undulatory movement

Fo

Swimmer's centre of mass depth

-0,6

Human Kinetics, 1607 N Market St, Champaign, IL 61825