butterfly stroke coordination

8/12/2019 Butterfly Stroke Coordination

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Seifert, L., Delignires, D., Boulesteix, L., & Chollet, D. (2007). Effect of expertise on Butterfly stroke

coordination.Journal of Sport Science, 25, 131-141.

EFFECT OF EXPERTISE ON BUTTERFLY STROKECOORDINATION

L. Seifert**, D. Delignieres, L. Boulesteix, D. Chollet

C.E.T.A.P.S. Laboratory UPRES EA 3832 : University of Rouen, Faculty of Sports Sciences, France

Motor Efficiency and Deficiency EA 2991: University of Montpellier, Faculty of Sports Sciences, France

Abstract

The aim of this study was to compare the arm to leg coordination in the butterfly stroke

among three groups of male swimmers with different skill levels (10 elite, 10 non-elite and 10

young rising swimmers) at four race paces (400-m, 200-m, 100-m and 50-m). Using aqualitative video analysis and a hip velocity-video system (50 Hz), key events of the arm and

leg movement cycle were defined and four point estimates of relative phase (RP1, RP2, RP3,

RP4) assessed the arm to leg coordination between the propulsive (pull and push of arms and

downward movement of leg undulation) and non-propulsive times (entry, catch and recovery

of arms and upward of leg undulation). The relative phase was based on the time difference

between: entry of the hands in the water and high break point of the first undulation for RP1;

beginning of the hands backward movement and low break point of the first undulation for

RP2; hands arrival in a vertical plane to the shoulders and high break point of the second

undulation fro RP3; hands release from the water and low break point of the second

undulation for RP4.

With increased velocity, stroke rate and/or expertise, the swimmers increased the

synchronization between the arm and leg key points. On the mean swimmer groups, the RP1

get closer to in-phase coordination mode (from 11.6 to 0.5), while RP2 switched from anti-

phase (186.5) to 226.7 out-of-phase when velocity and stroke rate increased. On the mean

of the four paces, RP1 and RP4 showed a closer in-phase coupling between arm and leg with

increased skill level, while RP3 was in out-of-phase for the two less expert groups (316.2

and 312.8) and was closed to an in-phase mode for the elite swimmers (333.3). The RP2

also changed from anti-phase (187) to 225.6 out-of-phase with increased expertise. Finally,

these changes led to a higher continuity between the propulsive actions, which is propitious to

improving the swim velocity, suggesting that coaches and swimmers should monitor arm to

leg coordination.

Key words coordination, butterfly, motor control, biomechanics, expertise

** Author to whom all correspondence should be addressed:

M. Ludovic Seifert, University of Rouen, Faculty of Sports Sciences, CETAPS Laboratory, Bld Siegfried, 76821

Mont Saint Aignan Cedex, France. Tel: (33) 232 10 77 93, Fax: (33) 232 10 77 93, E-mail:

[email protected].


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Introduction

In the butterfly stroke, the movements of the two arms are identical and are performed

simultaneously, as are the leg movements, and the logic of this stroke is such that the arm

movements alternate with those of the legs. This alternation does not favour propulsive

continuity, however, but leads to high resistances that are overcome by the leg undulations.

This stroke pattern results in a body wave motion (Sanders et al., 1995) that must be wellcoordinated to be effective. Butterfly coordination in expert swimmers is based on two

undulations of the legs for each complete arm cycle, i.e.a 2:1 frequency ratio (Colwin, 2002;

Costill et al., 1992; Maglischo 2003). These authors showed that the downward time of the

first undulation of the legs should occur during the catch time of the arms; the upward time of

the first undulation of the legs should occur during the pull time of the arms; the downward

time of the second undulation of the legs should occur during the push time of the arms; and

the upward time of the second undulation should occur during the recovery of the arms. Yet

while the theoretical arm to leg coordination has been globally described, the perfect timing

between these two motor limbs has been difficult to achieve. Some swimmers, for example,

use only a 1:1 frequency ratio between leg and arm actions. Moreover, the coordination canbe constrained by the head inhalation, which may occur at each arm stroke (1:1 frequency

ratio) or every two arm strokes (1:2 frequency ratio).

As described by dynamical theory, relative coordination mode (oscillators with different

eigenfrequencie) is less stable than absolute coordination (von Holst, 1973). In bimanual

coordination, the coupling between left and right arms is more stable in a 1:1 than in a 1:2

frequency ratio (Sternad et al., 1999). Moreover, in two-limb (in ipsilateral and controlateral

condition) and four-limb human coordination, the coupling between non-homologous limbs

(arm with leg) is less stable than between homologous limbs (right arm with left arm and right

leg with left leg) (Baldissera et al., 1991; Kelso and Jeka, 1992; Jeka et al.,1993). In fact,

when frequency increases, the wrist to foot coupling switches from anti-phase (wrist flexion

with foot extension and wrist extension with foot flexion) to in-phase (wrist flexion with footflexion and wrist extension with foot extension), indicating that for non-homologous limbs

the iso-contraction mode (flexion for the two limbs or extension for the two limbs) is less

stable than the iso-direction mode (flexion of one limb with extension of the other limb)

(Baldissera et al., 1991). Similarly, transitions occur between the anti-phase and in-phase

modes in non-homologous limbs, whereas homologous limbs display no transitions between

the two modes (Kelso and Jeka, 1992). Indeed, when frequency increases, the right with the

left arm coupling (or the right with the left leg) is as stable in anti-phase as it is in in-phase

(Kelso and Jeka, 1992). Donker et al.(2001) studied different walking velocities and showedthat the interlimb coupling was lower for the arm movements and for the ipsilateral and

controlateral combinations of arm and leg movements than for the leg movements. Indeed,

whatever the walking velocity, the right and left legs were in anti-phase (180). Conversely,

when walking velocity increased, the frequency coordination of the arms to legs switched

from a 2:1 to a 1:1 ratio. Thus in the ipsilateral combination, the interlimb coupling

approached anti-phase (2x100 in 2:1 frequency coordination and 190 in 1:1 frequency

coordination); in the controlateral combination, the coupling switched from anti-phase (2x90

in 2:1 frequency coordination) to in-phase (10 in 1:1 frequency coordination); and the right

and left arm coordination switched from in-phase (20) at low velocity to anti-phase (180) at

high velocity. In quadrupedal animal gaits, four patterns have been observed: the jump, in

which all limbs move in-phase; the gallop or bound, in which homologous limbs are in-

phase and non-homologous limbs are anti-phase; the pace, in which homologous limbs are

anti-phase and ipsilateral limbs are in-phase; and the trot, in which all limbs are anti-phase(Schner et al.,1990). Based on this four-component model, Jeka et al.(1993) showed that in


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four-limb human coordination, the non-homologous limbs change their coupling with

increased frequency in 70% of the cases, while the homologous limbs maintain their initial

coordination mode.

In swimming, studies have shown that when velocity or stroke rate increases in relationships

to race paces, the coordination changes as much in the simultaneous strokes (breaststroke and

butterfly), in which arm to leg coordination was investigated (Chollet et al., 2004; Leblanc et

al., in press; Seifert and Chollet, in press), as in the alternating strokes (backstroke and front

crawl), in which right to left arm coordination was analysed (Chollet et al., 2000, Seifert et

al., 2004). In the simultaneous strokes, the FINA rules require temporal and spatial

simultaneity in the arm movements, as well as in the leg movements, so studying the

coordination mode between homologous limbs makes few interest. However, arm to leg

coordination has a key role in determining swimming performance, as observed in the

breaststroke (Chollet et al., 2004; Leblanc et al., in press; Seifert and Chollet, in press).

Indeed, when velocity and/or stroke rate increases, elite swimmers decrease the different

temporal gaps between arm and leg movements (Chollet et al., 2004), resulting in a higher

continuity between propulsive actions. Propulsive continuity has also been shown to increasewith expertise (Leblanc et al., in press) and to be higher in men (Seifert and Chollet, in press).

The study of the coordination between homologous limbs is of great interest for the

alternating strokes. For example, in the front crawl, the index of coordination quantifies the

time lag between the propulsive actions of the two arms (Chollet et al., 2000). With increases

in velocity, stroke rate and expertise, the index of coordination switches from catch-up

coordination (time lag between the propulsion of the two arms) at the long-distance paces to a

relative superposition coordination of the arms (overlapping between the propulsion of the

two arms) at the sprint paces, confirming that this change in arm coordination depends on

different control parameters (velocity, stroke rate and the ratio of stroke rate to stroke length)

(Seifert et al., 2004).

Based on the coordination data accumulated for other modes of locomotion and the other

swim strokes, several questions arise concerning the butterfly: Can butterfly coordination be

assessed by temporal gaps between the propulsive phases? Considering the in-phase mode as

a perfect synchronisation between the arm and leg key points of the stroke, are expert

butterfly swimmers characterized by an in-phase mode of coordination between arms and

legs? And does the coordination get closer to in-phase mode with increases in velocity, stroke

rate and higher expertise? We hypothesized that in the butterfly stroke swimmers would

increase the continuity between arm and leg propulsions when velocity and/or stroke rate

increased. Indeed, as observed in human locomotion and quadrupedal gaits, where the

increase in oscillation frequency involves a transition from anti-phase to in-phase

coordination mode, butterfly swimmers may get closer to in-phase mode of coordination bysynchronising the arm and leg key points. Moreover, the higher the expertise, the closer to in-

phase mode the coordination should be.

Material and Methods

Subjects

Thirty male swimmers, 10 elite (G1), 10 non-elite (G2) and 10 young rising swimmers (G3),

voluntarily participated in this study. The protocol was fully explained to all of them and they

provided written consent to participate in the study, which was approved by the university

ethics committee. The elite group (G1) included a national finalist and international levelswimmers and the non-elite group (G2) corresponded to a second national division level. The


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young rising swimmer group (G3) had the lowest level of expertise because they were still

mastering swim techniques; they therefore had a regional-national level for their age category.

A one-way ANOVA showed that G3 was younger than G2 and G1, but it failed to evidence

any significant difference in terms of height, arm span or weight (Table 1). For all groups,

expertise was expressed in percentage of the world record (% of WR) for a 100-m butterfly

(Table 1).

Swim Trials

In a 25-m pool, the swimmers performed four butterfly trials at successively increasing

velocity. Each trial required an individually imposed swim pace corresponding to a specific

race distance or training distance, as previously detailed for the front crawl and the

breaststroke (Chollet et al., 2004; Seifert and Chollet, in press; Seifert et al., 2004): the 400-

m, the 200-m, the 100-m and the 50-m paces. After each trial, all swimmers were informed of

their performance time, which was expected to be within 2.5% of the targeted race velocity.

If this was not the case, the subject repeated the trial. During the test, pace and stroke rate

were monitored with a chronometer and a Seiko Base 3-frequency meter. These measures

served only to validate each trial, i.e.to ensure minimal discrepancy between the swim pace

expected of each swimmer and the velocity at which he actually swam. The experimental data

of this study, on the other hand, were obtained by the video device.

Video Analysis

An aerial lateral video camera was superposed on an underwater lateral video camera (Sony

compact FCB-EX10L, Paris, France) with rapid shutter speed (1/1000s) and a sampling rate

of 50Hz, and both were fixed on a trolley. The trolley was pulled along the side of the pool by

an operator which followed the swimmers, using each subjects head as the mark to controlparallax. The cameras were connected to a four-entry audio-visual mixer (Videonics MX-1,

Campbell, USA), a video timer, a video recorder and a monitoring screen to mix the lateral

underwater and aerial views on the same screen, from which stroke rate was calculated. At

each hand entry, one stroke was completed so that the stroke rate was expressed for each

stroke. A third camera (fixed on the wall, 50 Hz, Sony compact FCB-EX10L, Paris, France)

filmed the swimmer from a frontal underwater view and was mixed and genlocked by the

audio-visual mixer (Videonics MX-1, Campbell, USA) with the underwater lateral view on

another screen. The two lateral views and the frontal view completed the velocity-video

system and were used to analyse the arm and leg stroke phases.

A fourth camera (50 Hz, Panasonic NV-MS1 HQ S-VHS, Paris, France), mixed with thelateral underwater view for time synchronisation, filmed all the trials of each swimmer with a

profile view from above the pool. This camera measured the time over a distance of 12.5 m

(between the 10-m and the 22.5-m marks to remove the wall constraint) to obtain the velocity.

The stroke length was calculated for each stroke from the mean velocity and stroke rate values

(stroke length = velocity x (stroke rate / 60)).


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Table 1. Mean and standard deviation values of swimmer characteristics.

Group Age (yr) Height (cm) Mass (kg) Arm Span (cm)

M SD M SD M SD M SD

G1: Elite swimmers 20.3 4.2 180.6 5.7 73.9 9 192.6 2.1

n= 10

G2: Non-elite swimmers 19.5 3.2 180.7 6.2 73.1 6.5 188.4 6.2

n=10

G3: Young rising swimmers 15.7 1.6 179.6 4.3 70.4 7.5 193.8 4.3

n=10 a b

Statistics n=30 F(2,27)=5.73

M: mean, SD: standard deviation, n: number of swimmers, W.R.: world record,

a: significant difference with preceding group, b: significant difference with G1, P < 0.05


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Velocity -Video System

The velocity-video system completed the qualitative analysis of the operators and enabled us

to determine the key points in both arm and leg movements and thus to accurately delimit the

propulsive (pull and push of arms and downward movement of leg undulation) and non-

propulsive times (entry, catch and recovery of arms and upward of leg undulation) (Fig. 1).

The video analysis was synchronised with a swim-speedometer (Fahnemann 12 045,Bockenem, Germany) as already described for the breaststroke (Chollet et al., 2004; Costill et

al., 1987; Craig et al., 1988; Seifert and Chollet, in press; Tourny et al., 1992) and the

butterfly (Buckwitz et al., 2003). The swimmers wore waist belts attached by cable to an

electric generator. The voltage produced by the generator was proportional to the swim

velocity, and this was recorded on computer. The lateral view of the underwater video camera

and the video timer were mixed and genlocked (by audio-visual mixer Videonics MX-1,

Campbell, USA) with the instantaneous velocity curve read on the computer. Four complete

strokes were filmed for each subject. The accelerations and decelerations of the hip calculated

by the swim speedometer (at 0.01s) were synchronised with the arm and leg movements

recorded by the video device (at 0.02s).

RP1: relative phase based on the time difference between the entry of the hands in the water and the high break-

even point of the 1stundulation.

RP2: relative phase based on the time difference between the beginning of the hands backwards movement and

the low break-even point of the 1stundulation.

RP3: relative phase based on the time difference between the hands arrival in a vertical plane to the shoulders

and the high break-even point of the 2nd

undulation.RP4: relative phase based on the time difference between the hands release from the water and the low break-

even point of the 2ndundulation.

PT1: first propulsive time: downward movement of leg undulation.

PT2: second propulsive time: pull and push of arms.

Figure 1. Synchronised structure of the arms and legs for butterfly swimming


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Arm and leg stroke times

The arm stroke was divided into four distinct times (Fig. 1), similar to those made for the

front crawl by Chollet et al.(2000). But unlike this latter study, which analysed two strokes,

and more recent works analysing three strokes (Chollet et al., 2004; Seifert and Chollet, inpress; Seifert et al., 2004), four strokes were analysed by three operators who analysed the

key points of each phase at 0.02s with a blind technique, i.e. without knowing the analyses of

the two other operators. The three analyses were compared only when each operator had

completed his own analysis. When the difference between the analyses did not exceed an

error of 0.04s, the mean of the three analyses was accepted to validate the key point of each

phase. When the error exceeded 0.04s, the three operators together proceeded to a new

assessment of the phase key point. The times were as follows:

Entry and catchof the hands in the water, which corresponds to the time between the entry of

the hands into the water and the beginning of their backward movement. In fact, this time was

composed of four parts: entry and stretch, outsweep, glide, and catch (Maglischo, 2003).

Pull, which corresponds to the time between the beginning of the backward movement of the

hands and their entry into the plane vertical to the shoulders.

Push, which corresponds to the time between the positioning of the hands below the shoulders

to their exit from the water. The pull and push times correspond to the arm propulsive time

(PT2 in Fig. 1).

Recovery, which corresponds to the time between the exit of the hands from the water and

their re-entry into the water.

The duration of each time was measured for each stroke with a precision of 0.02 s and was

expressed as a percentage of the duration of a complete arm stroke.

The leg stroke was composed of two times (Fig. 1):

Downward, which corresponds to the time between the high and low break-even points of the

feet during the undulation.

Upward, which corresponds to the time between the low and high break-even points of the

feet during the undulation.

The duration of each time was measured for each stroke with a precision of 0.02 s and was

expressed as a percentage of the duration of a complete leg stroke.

According to Jensen and McIlwain (1979), the downward time of the undulation correspondsto the leg propulsive time (PT1 in Fig. 1), whereas the upward time is not propulsive.

Arm to leg coordination

The arm to leg coordination was assessed by the point-estimated relative phase (Diedrich and

Warren, 1995; Hamill et al., 2000; Zanone and Kelso, 1992).This discrete method illustrates

the relative timing of key events, or key points, in a movement cycle. In the butterfly stroke, it

corresponds to the latency of a key point in the arm stroke time with respect to a key point in

the leg stroke time. Costill et al. (1992) and Maglischo (2003) described expert butterfly

coordination as two leg undulations for one arm stroke, so the coupling between arm and legcorresponds to a 2:1 frequency coordination. Swimmers with only one leg undulation were


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thus not admitted to this study. These authors also reported that four arm and leg key points,

which can be assessed by four point-estimated relative phases, should be in-phase during a

complete stroke (Costill et al., 1992, Maglischo, 2003). Each relative phase (RP) is calculated

with the formula: RP = ((ttarget - t0) / (treference- t0)) x 360. For the four RP, t0was the entry of

the hands in the water at the first stroke. The RPs are as follows:

RP1: the time difference between the high break-even point of the first undulation (ttarget) andt0 was measured. This duration was expressed in degrees relative to the time difference

between the entry of the hands in the water at the second stroke (treference) and t0(Fig. 1).

RP2: the time difference between the low break-even point of the first undulation (t target) and

t0 was measured. This duration was expressed in degrees relative to the time difference

between the beginning of the hands backwards movement (treference) and t0 (Fig. 1). During

this time the down and upper limbs did not realise a propulsive time, therefore RP2 measured

the glide of the body.

RP3: the time difference between the high break-even point of the second undulation (t target)

and t0was measured. This duration was expressed in degrees relative to the time difference

between the hands arrival in a vertical plane to the shoulders (treference) and t0(Fig. 1).

RP4: the time difference between the low break-even point of the second undulation (t target)

and t0was measured. This duration was expressed in degrees relative to the time difference

between the hands release from the water (treference) and t0(Fig. 1).

In each trial, each relative phase was measured for four arm strokes and was expressed in

degrees.

Two theoretical coordination modes existed: in-phase mode (0 or 360) and anti-phase mode

(180); but a lag of 30 was accepted to estimate a coordination mode. Therefore, between

330-360 and 0-30 an in-phase mode occurs, while the anti-phase mode is between 150 and

210. Over this step, a coordination mode in out-of-phase could be considered. The conceptsof anti-phase, out-of-phase and in-phase thus seem well adapted to characterise a coordination

mode at a given moment in this stroke (by the point estimate of the relative phase), instead of

the analysis of the continuous interlimb coupling over the course of the stroke (by the

continuous relative phase).

Statistical analysis

Spatial-temporal and stroke time parameters

On the mean of the four paces and the three groups, the distribution normality (Ryan Joiner

test) and the homogeneity of variance (Bartlett test) were verified for each variable andallowed parametric statistics (Minitab 13.20, Minitab Inc., 2000). Two-way repeated-measure(RM) ANOVAs assessed the main factor effect and the interaction between group (3 levels)

and pace (4 levels), and were completed by post-hoc Tukey tests (Tables 2, 3 and 4) (Minitab

13.20, Minitab Inc., 2000). For this statistical analysis, the mean of four strokes of each pace

was considered: n= 4 paces x 3 groups x 10 subjects = 120. Then, one-way RM ANOVAs

detailed the group effect at each pace (n= 3 groups x 10 subjects = 30) and the pace effect for

each group (n= 4 paces x 10 subjects = 40). For all tests, the level of significance was set at P

< 0.05.


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Table 2: Mean and standard deviation values of spatial-temporal parameters, according to the

Spatial-temporal Groups 400-m 200-m 100-m 50-m

parameters M SD M SD M SD M SD

G1 1.47 0.11 1.57c 0.08 1.7 c d 0.08 1.74d e 0.08Velocity G2 1.42 0.1 1.48 a 0.12 1.57 a d 0.1 1.64 a d e 0.09

(m.s-1) G3 1.3 a b 0.11 1.41 b c 0.09 1.5b d 0.09 1.58 b d e 0.1

Mean 1.39 0.13 1.49 c 0.12 1.59 c d 0.12 1.65 c d e 0.11

Statistics group effect F(2,27)=6.3 F(2,27)=6.7 F(2,27)=11,5 F(2,27)=7.6

G1 40 2.7 43.9 2.6 50.2 2.9 53.1 c d e 3

Stroke rate G2 41.3 2.7 43.8 3.5 48.5 cd 3 52.6 c d e 3.8

(stroke.min-1) G3 35.7 a b 4.6 39.1 a b 4 45.6c d 5 49.6 d e 5.8

Mean 39 4.3 42.3 c 4.3 48.1 c d 4.7 51.7 c d e 4.3

Statistics group effect F(2,27)=6.4 F(2,27)=5.1

G1 2.2 0.11 2.16 0.13 2.03 c d 0.12 1.97 d e 0.12

Stroke length G2 2.07 0.23 2.03 0.24 1.95 0.2 1.88 0.18

(m.stroke-1

) G3 2.2 0.29 2.18 0.22 1.99 0.28 1.94 0.3

Mean 2.16 0.23 2.13 0.21 1.99 c d 0.21 1.93 d e 0.22

Statistics group effect

M: mean, SD: standard deviation


c: significant difference with preceding pace, d: significant difference with the 400-m, e: significant difference with the 200-m, P


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Tables 3: Mean and standard deviation values of arm and leg times, according to the imp

Arm times Groups 400-m 200-m 100-m 50-m Mea

M SD M SD M SD M SD M G1 34.9 3.1 29.5c 5.5 26.5 d 5.3 26.4 d 4.8 29.2

Catch time G2 36.1 3.7 32.5 4.8 30 d 4.6 26.7 d e 4.9 31.3

(%) G3 42.6 a b 7.7 39.6 a b 5.6 33.7 bd e 5.5 32.4 abd e 6.6 37.1 a b

Mean 37.9 6.2 33.4 c 6.8 30.1 c d 5.8 28.6 d e 6.0 32.6

Statistics group effect F(2,27)=5.9 F(2,27)=9.5 F(2,27)=4.7 F(2,27)=3.6 F(2,109)=22.

G1 20.4 2.6 23.2 3.8 24.7 d 3.5 24.1 d 4.2 23.2

Pull time G2 20.9 2.3 22.5 2.8 23.7 3.6 25.7 d 5.2 23.2

(%) G3 19.4 4.1 20.5 2.8 22.5 d 3.2 23.3 d 3.2 21.4

Mean 20.3 3.1 22.1 3.3 23.7 d 3.5 24.4 d e 4.3 22.6

Statistics group effectG1 21.8 2.7 22.1 3.2 22.4 2.9 22.2 2.7 22.1

Push time G2 20.0 2.1 20.3 2.7 20.8 2.4 21.5 2.4 20.6 a

(%) G3 17.5 a b 2.9 17.7 b 3.1 19.1 b 1.8 18.6a b 3.5 18.2 a b

Mean 19.6 3.1 20.1 3.4 20.7 2.7 20.7 3.2 20.3

Statistics group effect F(2,27)=6.7 F(2,27)=5.2 F(2,27)=4.3 F(2,27)=3.9 F(2,109)=19.

G1 22.9 1.6 25.2 3,0 26.4 d 2.3 27.3 d 3,0 25.5

Recovery time G2 23.0 2.6 24.7 3.3 25.5 3.8 26.1 3.8 24.8

(%) G3 20.5 b 3.1 22.2 2.9 24.7 d 3.4 25.7 d e 4.8 23.3 b

Mean 22.1 2.7 24.0 3.3 25.5 d 3.2 26.3 d e 3.9 24.5

Statistics group effect F(2,27)=2.9 F(2,109)=4.6

M:mean, SD:standard deviation




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Tables 4: Mean and standard deviation values of arm and leg times, according to the imp

Leg times Groups 400-m 200-m 100-m 50-m Mean

M SD M SD M SD M SD M

G1 15.1 2 16.4 1.7 17.4 d 1.1 17.2 d 1.9 16.5 1 Downward G2 16.6 2.6 15.8 2 17 2.2 17.7 1.6 16.9

undulation G3 16 1.5 15.9 1.8 16.9 1.6 17.3 1.6 16.5

(%) Mean 15.9 2.1 16,0 1.8 17.1d 1.7 17.4 d e 1.7 16.6


G1 33.2 2.2 29.9 4.2 29.3 d 3.2 30.8 4.7 30.7

1 Upward G2 31.5 4.1 30.6 4.1 28.9 3.9 28 3.7 29.7

undulation G3 32.5 3.5 31.3 2.7 30.1 3.1 31 2.8 31.3

(%) Mean 32.3 3.4 30.6 3.7 29.5 d 3.4 29.9 d 3.9 30.6


G1 23.5 4.6 24.2 5.4 24.6 4.9 22.8 4.4 23.8

2 Downward G2 23.6 2.9 23.7 3.3 24.2 3.5 25 3.4 24.1

undulation G3 23.8 4.7 23.5 4.2 24.6 4.1 22.8 2.9 23.6

(%) Mean 23.6 4.0 23.7 4.2 24.4 4.1 23.6 3.6 23.9


G1 28.2 4.7 29.5 4.4 28.7 4.2 29.2 4.5 28.9

2 Upward G2 28.3 2.9 29.9 3.3 29.9 3.3 29.3 3.3 29.3

undulation G3 27.7 4.8 29.3 3.9 28.4 4.2 28.9 4 28.5

(%) Mean 28.0 4.1 29.5 3.8 28.9 3.8 29.1 3.8 28.9


M: mean, SD: standard deviation




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Coordination parameters

The Watson-Williams F-tests (Oriana 2.0, W. Kovach Computing Services, 1994-2003) for

circular data (Baschelet, 1981) showed coordination differences between groups (3 levels) on

the mean of the paces, and coordination differences between paces (4 levels) on the mean of

the groups. For this statistical analysis, the four strokes of each pace were considered: n= 4

strokes x 4 paces x 3 groups x 10 subjects = 480. The Watson-Williams F-tests then describedcoordination differences between groups at each pace (n= 4 strokes x 3 groups x 10 subjects

= 120) and coordination differences between paces for each group (n= 4 strokes x 4 paces x

10 subjects = 160) (Table 5). For all tests, the level of significance was set at P < 0.05.

Results

Velocity, Stroke Rate, Stroke Length

The two-way (pace x group) RM ANOVAs did not show significant interactions, but revealed

spatial-temporal differences between groups on the mean of the four paces and between paces

on the mean of the three groups (Table 2). The one-way (pace) RM ANOVA revealed that forall groups velocity and stroke rate increased throughout the paces, while stroke length

decreased only for elite swimmers (Table 2). The one-way (group) RM ANOVA showed that

the higher expertise was, the higher the velocity and stroke rate were (Table 2).

Arm and leg stroke times

The two-way (pace x group) RM ANOVAs did not show significant interactions, but revealed

stroke time differences between groups on the mean of the four paces and between paces on

the mean of the three groups (Tables 3 and 4). These changes in stroke times principally

occurred for the arms, because the leg stroke times only changed during the first undulation.

On the group mean and for elite swimmers, the first downward undulation took longer while

the first upward undulation took shorter between paces. Moreover, expertise was not related

to the relative duration of the leg stroke times because no significant difference was noted

between groups. Conversely, Table 3 shows that on the mean of the three groups (two-way

pace x group RM ANOVA) and for each group (one-way pace RM ANOVA), the catch

time took shorter while the pull and recovery times took longer with paces. On the other hand,

on the mean of the four paces (two-way pace x group RM ANOVA) and for each pace

(one-way group RM ANOVA), the catch time took shorter while the push time took longer

with greater expertise (Table 3).

Arm to leg coordination

On the mean of the four paces and for the whole population, RP1 (6.8), RP3 (320.8) and

RP4 (348) showed an arm to leg coordination close to the in-phase mode (Table 5).

Nevertheless, on the meanof the three groups and for each group, the Watson-Williams F-

tests revealed differences between paces for RP1 and RP2 (Table 5). From the 400-m to the

50-m pace, the arm to leg coordination get closer to the in-phase mode, with a shifting of RP1

from 11.6 to 0.5 (on the mean of the three groups). In contrast, RP2 switched from an anti-

phase mode at the 400-m pace (186.5) to an out-of-phase mode at the 50-m pace (226.7).

On the mean of the four paces, the Watson-Williams F-tests revealed differences between

groups for the four relative phases (RP1, RP2, RP3, RP4), indicating that with expertise, the

arm to leg coordination approached an in-phase mode (Table 5). These results on the mean of

the four paces was due to closer in-phase RP2 and RP3, which were different between groups

at each pace, while RP1 and RP4 only changed between groups at the 200-m pace (Table 5).


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Table 5: Mean and standard deviation values of arm to leg coordination parameters, according to

Relative phases Groups 400-m 200-m 100-m 50-m

M SD M SD M SD M SD M

G1 10.3 13.4 8.7 12.4 4.6d 13.5 1.5 d e 20.4 6

RP1 G2 9.6 16 5.9 16.8 2.2 c d 16.3 356.4 c d e 17.1 3

() G3 14.9 10.7 15.2 a b 10.4 9 c d 13.6 3.5 d e 11.9 10.7

Mean 11.6 13.7 9.9 14 5.3 c d 14.8 0.5 d e 17.1 6

Statistics group effect F(2,117)=4.9 F(2,477

G1 192.3 56.5 218 75 248.3 65.5 244.1 d e 57.1 22

RP2 G2 195 36.4 199.4 c 44.4 214.5 ad 60.4 235.9 d e 54.9 209

() G3 174.7 a b 25.9 184.8 b 31.2 192.3b 54.2 201.4 a b d 51.5 187

Mean 186.5 41.6 197 52.3 216.2 c d 64.3 226.7 d e 57.7 20

Statistics group effect F(2,117)=3.1 F(2,117)=3.5 F(2,117)=7.9 F(2,117)=6.6 F(2,477

G1 332.9 30.4 326.5 27.8 331.2 24.4 342.5 25 33

RP3 G2 321 a 19.1 315.8 a 15.7 315 a 25.5 312.8 a 25 316

() G3 307.8 a b 27 309.8 b 27.9 315.2 b 36.1 319.1b 36 312

Mean 320.5 27.8 317.4 25.3 320.6 30 324.9 31.8 32

Statistics group effect F(2,117)=7.6 F(2,117)=4.6 F(2,117)=6.3 F(2,117)=11.7 F(2,477

G1 352.9 10.9 353 13.6 352.1 20.2 349.8 12.5 35

RP4 G2 347.7 11.8 343.7 a 10.9 343 12.8 341.9 14.2 344

() G3 346.5 25.1 346.6 24.4 353.4 27.3 346.1 34.9 348

Mean 349.1 17.3 347.8 17.7 349.3 21.3 345.9 22.7 34

Statistics group effect F(2,117)=3.1 F(2,477M: mean, SD: standard deviation




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14

Discussion

Effect of velocity and stroke rate on coordination

On the mean of the four paces and for the whole population, the arm to leg butterfly

coordination approached in-phase mode at three key points of the stroke (at the entry, at the

passing under the shoulder and at the release of the hand), showing that the movements of thetwo pairs of motor limbs were linked. Moreover, with increases in velocity and stroke rate,

coordination mostly became closer to an in-phase mode. In human locomotion, when walking

velocity increases, the coupling between all pairs of limb movement was found to increase

(Donker et al., 2001). In quadrupedal coordination (Kelso and Jeka, 1992; Schner et al.,

1990) and in walking-running (Diedrich and Warren, 1995), when the frequency of the

oscillator movements or the velocity increases, the coordination of the non-homologous limbs

switches from anti-phase to in-phase, suggesting that frequency or velocity can be considered

as control parameters. In the butterfly stroke, velocity and stroke rate may be control

parameters of coordination because their increase led to a closer in-phase mode of arm to leg

coordination (particularly RP1 and RP2). This was due to the increase in the propulsive time

(pull time of arms and first downward undulation of legs) and the decrease in the non-propulsive time (catch time of arms and first upward undulation of legs), which leads to a

better timing between arm and leg key points (Delignires and Chollet, 1999).

The closer in-phase mode of RP1 with velocity could be due to the faster entry of the head

after inhalation and to the lesser trunk inclination when swimmer adopt high race pace. Alves

et al. (1999) noted a 8 decrease of the trunk inclination (from 32 to 24) and a shorter

downsweep of the arms when breathing was restrained. At high velocity and stroke rate,

swimmers must reduce the time during which the head is over the water to facilitate the aerial

and lateral recovery of the arms.

Concerning RP2, with increasing velocity and stroke rate, all groups shifted from an anti-

phase to an out-of-phase relation (excepted G3 for which the shifting took longer) betweenthe first low break-even point of the first undulation and the beginning of the pull time of the

arms. This change in coordination corresponded to a decrease in the lag between the

propulsive time of the legs and the propulsive time of the arms, usually called the glide.

Swimmers have to overcome high active drag at high velocity by reducing glide duration and

increasing propulsive times (Kolmogorov et al.,1997).

Finally, coaches could manipulate velocity and stroke rate to emerge appropriate coordination

mode. On the other hand coaches should not automatically advocate a high stroke rate in the

hope of obtaining arm to leg coordination in the in-phase mode. This advice should be given

only if a higher stroke rate does not result in too great a decrease in velocity, stroke length and

technique. For example, a swimmer could adopt the imposed stroke rate and show an in-phasecoordination, but with an ineffective hand sweep which slips through the water.

Effect of expertise on coordination

Concerning RP1, all groups became significantly closer to an in-phase relation between the

entry of the hands in the water and the high break-even point of the first undulation.

Nevertheless, the non-elite swimmers (G2) reduced the phase shifting between their first

downward undulation and the hand entry from the 400-m to the 100-m pace (RP1 was from

9.6 to 2.2) so much that at the 50-m pace, they began their first downward undulation before

the hand entry (RP1 was 356.4). This coordination was not adequate because, although the

legs were propelling, the arms and hands were not streamlined in an extended position toprepare the catch time (Colwin, 2002). Because the body decelerates during the arm recovery,


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15

the timing between the arm entry and the first downward undulation is critical. Indeed, this

undulation is the strongest in the stroke (Hahn and Krug, 1992) and should occur soon after

the arm entry (Colwin, 2002). Costill et al.(1992) advised striving for perfect synchronisation

between the arm entry and the first downward undulation, because the active drag caused by

the arm entry can be overcome by the leg propulsion. Unlike elite swimmers (G1), the least

skilled swimmers (G3) did not manage to synchronise these two key points to any great extent(Fig. 2) and consequently opposed more active drag.

a) Arm to leg coordination in the 50-m for a swimmer of the elite group (G1)

-20% 0% 20% 40% 60% 80% 100% 120%

arms

legs

RP1 = 8.5 RP2 = 253.6 RP3 = 309.3 RP4 = 349.8

Stroke Duration in %

b) Arm to leg coordination in the 400-m for a swimmer of the elite group (G1)

-20% 0% 20% 40% 60% 80% 100% 120%

arms

legs

RP1 = 16.7 RP2 = 195.3 RP3 = 319.4 RP4 = 343.9


c) Arm to leg coordination in the 400-m for a swimmer of the young rising swimmer group

(G3)

-20% 0% 20% 40% 60% 80% 100% 120%

arms

legs

RP1 = 22.5 RP2 = 184.4 RP3 = 279.4 RP4 = 344.1


Figure 2. Comparison of arm to leg coordination between different skill levels and different

race paces.

Concerning RP2, with increasing pace, the non elite swimmers (G2) shifted slower to out-of-phase than elite swimmers (G1), showing a longer glide duration with the arms extended


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16

forward and a non-propulsive time of the legs. An overly long glide, corresponding to an anti-

phase coordination between arms and legs, decreases the velocity (Mason et al., 1992;

Sanders, 1996); this was the case in the least expert swimmers (G3) who presented the

greatest time lag (see the catch time in Table 3 and Fig. 2c). Conversely, too short a glide,

which corresponds to in-phase coordination, did not enable an effective catch of the arms and

led to slippage throughout the water. Thus, Costill et al. (1992) advised finishing thedownward undulation just before the catch time of the arms. Finally, with an out-of-phase

coordination near 210-250 (Table 5 and Figs. 2a and 2b), the first downward undulation of

the elite swimmers provided acceleration to project the hips forward (Jensen and McIlwain,

1979) and enabled an effective catch time to prepare the pull time. So, logically, the first

upward undulation occurred during the pull time (i.e. the insweep of the arms) to bring the

body into a streamlined position.

RP3 was based on the difference between the beginnings of two propulsive times: the push

time of the arms and the second downward undulation. The higher the expertise was, the more

the swimmers began the push time early after the high break-even point of the secondundulation, and the more the arm to leg coordination became closer to the in-phase. Indeed,

the mean RP3 showed that the less skilled swimmers adopted an out-of-phase coupling

between arms and legs (316.2 for G2 and 312.8 for G3), whereas the elite coordination was

close to in-phase mode (333.3 for G1). In fact, the perfect timing of these two propulsive

times is important for great propulsion (Reischle, 1979; Sanders, 1996) because it provides

the biggest body acceleration in the stroke (Barthels and Adrian, 1975; Martin-Silva et al.,

1999; Mason et al., 1992), whereas a lack of coordination means large velocity fluctuations

that are detrimental to propulsion (Hahn and Krug, 1992). Figure 2c shows the case of one

swimmer from G3 presenting an out-of-phase coordination mode with marked shifting

between the two limbs (RP3 = 279.4). This lack of coordination could lead some of the less

skilled swimmers to forget the second downward undulation and to wait with the legssmoothly flexed. Thus, the hips remain in too deep a position and oppose great active drag.

Conversely, the second downward undulation counters the drop of the hips caused by the push

time of the arms upward (Colwin, 2002).

Like RP3, RP4, which was based on the time difference between the hand exit and the low

break-even point of the second undulation, showed an in-phase coordination mode. The elite

swimmers had a greater relative duration of the push time than the least experts (G3) (Table

3), which could explain their better coordination and which allowed a high force (Schleihauf

et al., 1988). Elite swimmers (mean RP4 = 351.9) revealed a closer in-phase mode of

coordination than G2 and G3 (respectively, 344.1 and 348.2), which was propitious to better

arm release. In fact, according to Colwin (2002), the timing of downward undulations has

three important functions: 1) to ensure continuous propulsion between arms and legs, 2) to

maintain the body in a streamlined position by keeping the hips high, 3) to aid head

mechanics, notably to favour the head inhalation. The closer the end of the second downward

undulation is to the end of the push time, the more the second downward undulation will

compensate the upsweep of the hands to provide hip elevation (Colwin, 2002; Maglischo,

2003); therefore, the hand exit and the release of the arm forward will be easy. The downward

undulation should not be too strong, however, because if the hips are above the water, the arm

recovery will be hampered. Therefore, the most important finding was not only the force

applied during the propulsive times, but also the coordination between these times. Moreover,elite swimmers were closer in-phase mode of coordination (for RP4), which favoured the

head inhalation and could explain why, although the relative duration of their arm recovery


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17

was greater than that of G3 (Table 3), it did not disturb their general propulsion. In fact, their

arm recovery occurred during the second upward undulation and influenced the coordination

of the next beginning stroke (as assessed by RP1).

ConclusionWith increases in velocity, stroke rate and/or expertise, the swimmers became closer to an in-

phase mode of coordination by synchronising the key points of the arm and leg movements.

These differences in coordination revealed greater continuity between propulsive actions at

high velocity and high expertise, which was propitious to decreasing the instantaneous

velocity fluctuations and improving the swim velocity. This suggests that coaches and

swimmers should monitor the arm to leg coordination by manipulating control parameters

(velocity, stroke rate) as regards to biomechanical (active drag and velocity) constraints.

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