Kinematic Analysis of Soccer Players in Shuttle Running

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Training & Testing

Padulo J et al. Kinematic Analysis of Soccer Int J Sports Med

accepted after revision

January 23, 2012

Bibliography

DOI http://dx.doi.org/

10.1055/s-0032-1304641

Published online: 2012Int J Sports Med

Georg Thieme

Verlag KG Stuttgart New York

ISSN 0172-4622

Correspondence

Dr. Johnny Padulo, PhD St

Faculty of Medicine and Surgery

University of Rome

Via Columbia s.n.c.

00133 ROME

Italy

Tel.: +39/06/2042 7573

Fax: +39/06/2042 7258

[email protected]

Key words

footstep analysis

fi

eld testing heart rate

Kinematic Analysis of Soccer Players in ShuttleRunning

running economy [7]. Despite the fact that taking

into consideration kinematic parameters can

shed light on an athletes efficiency, no previous

study has investigated soccer players step char-

acteristics during both incremental (as Y1) or

constant speeds. Furthermore, specific training

using the intermittent shuttle run is used within

soccer to improve both cardiovascular and mus-

cular strength conditions with little considera-

tion of the biomechanical patterns of this training

tool.

We hypothesized that heart rate and the maxi-

mal run velocity performed in this test wouldrepresent the most important parameters to

evaluate the aerobic conditions of each player. It

is widely known that metabolic variations gener-

ate alterations within the kinematic parameters

[4]. We therefore studied kinematic parameters

both at increasing velocity (Y1) and constant

velocity [95 % maximal aerobic velocity (MAV95 %)]

when the subjects complied with the standard

run (at the centre of the shuttle) and also heart

rates of soccer players during all phases tested

(Y1 MAV95 %).

Introduction

The intermittent shuttle running test, the Yo-Yo

Endurance Lv1(Y1), is mainly used within soccer

to assess aerobic power in young soccer players

[1]. Consequently, intermittent training and test-

ing protocols have been proposed to improve

soccer players fitness and to guide talent selec-

tion [5, 8, 12]. However, during the Y1 test and

during exercise at a specific percentage of oxygen

uptake (VO2max) various authors have predomi-

nantly considered metabolic parameters (VO2

heart rate and lactate) only, neglecting themechanical parameters [10, 13]. In all forms of

locomotion [11], biomechanical parameters

including mechanical parameters associated

with muscle strength are pertinent as intensity

changes as a function of time [10]. For instance it

is well known that a reduction in contact time is

associated with an increased ground reaction

force (GRF) as a consequence of increased step

length [14]. Research advocates that kinematic

parameters, as well as metabolic factors, may

contribute to running performance. Hasegawa et

al. state that step strategy changes at higher

speeds and therefore presumably influences the

Authors J. Padulo1, S. DOttavio1, F. Pizzolato2, L. Smith3, G. Annino1

Affiliations 1Faculty of Medicine and Surgery, University of Rome, Italy 2Faculty of Sport Science, University of Verona, Italy 3School of Health, Sport and Rehabilitation Sciences, University of Salford, United Kingdom

Abstract

The intermittent shuttle running test is mainlyused within soccer to assess aerobic power. For

this reason we studied kinematic parameters

and heart rate at both an increasing speed, [Yo-

Yo Endurance Lv 1 (Y1)] and at constant veloc-

ity [95 % maximal aerobic velocity (MAV95 %)].

12 soccer players were selected for this study.

A high-speed digital camera (210 Hz) was used

to record motion; Dartfish5.5Pro was used to

perform 2D video analysis and heart rate was

also recorded and computed during the test.

The parameters considered (baseline measures

with respect to the end of each test) in this

study were: step length (SL), contact time (CT)

and heart rate (HR). SL: 40 % in Y1and 22 % inMAV95 %. CT: 31 % in Y1and 29 % in MAV95 %. HR:

increased 96 % in Y1and 17 % in MAV95 %. These

results highlight 2 different neuromechanical

strategies adopted under fatigued conditions.

In light of the clear changes of the CT in MAV 95 %

(29 %) and with respect to the moderate changes

in HR (17 %) it is clear that the CT is the most

important parameter, as it experiences greater

adaptations associated with neuromuscular pat-

terns, under a fatigued condition as opposed to HR.


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Training & Testing


Material and Methods

Subjects12 junior level athletes (age 19.22 0.4 years; body mass

73 14 kg; height 1.76 0.06 m; BMI 22.60 2.60 kg/m2) partici-

pated in the study. Local ethical approval was gained. Players

possessed at least 6 years of experience in both soccer training

(with shuttle running) and competitions and had participated in

national/international championships at the time of the investi-gation. The subjects were healthy, without any muscular, neuro-

logical and tendineous injuries and reported they were clear of

any drug consumption. The groups were homogeneous with

regard to their training status, in which none of the subjects

underwent any endurance strenuous activity and resistance

training outside of their normal endurance training protocol.

After being informed of the procedures, methods, benefits and

possible risks involved in the study, each subject reviewed and

signed an informed consent to participate in the study in accord-

ance with the ethical standards of the IJSM [6].

Experimental setting

All the tests were carried out in November 2010 at the GiulioOnesti sport centre in Rome on the synthetic turf of the pitch,

which is certified for national matches. Testing took place on 2

separate days, Monday and Friday. All participants were in good

general health conditions at the time of the study and they car-

ried out the test during the same period of the sporting season.

The relevant data were acquired during 2 separate occasions,

starting at 4 p.m. up until 6 p.m. under the following weather

conditions (first and second day): no rain, average temperature

1517 C, relative average humidity 8682 % and average wind

speed 3.303.40 ms1. Each participant completed a standard-

ized 10-min warm-up, which consisted of running at low speeds

and familiarization with shuttle running, following 5-min active

muscular stretching. Subjects wore soccer shoes during testing.

ProcedureOn the first day (Monday), the Y1was conducted. The test lasted

for 810 min and consisted of repeated 20-m shuttle runs at pro-

gressively increasing velocities dictated by an audio bleep emit-

ted from a CD player [1]. Failure to achieve the shuttle run in

time on 2 occasions resulted in termination of the test and the

distance covered in the last successfully completed shuttle was

recorded and represented the test result.

On the second day (Friday), the constant velocity test was con-

ducted. The constant velocity was calculated from the results of

Y1test (95 % maximal aerobic velocity (MAV95 %). The constant

velocity test lasted for ~4 min and consisted of repeated shuttle

runs at MAV95 %dictated by an audio bleep emitted from a CD

player every 5 s, with changed distance (18.75 1.15 m). Failure

to achieve the shuttle run in time on 2 occasions resulted in ter-

mination of the test and the distance covered in the last success-

fully completed shuttle was recorded and represented the test

result. During the tests HR recordings from a given number of

shuttles were used as a marker of performance. HR was recorded

by a Polar heart rate monitor (Sport Tester PE 3000; Polar Elec-tro, Kempele, Finland) which was securely fitted around the

chest for continuous HR recordings throughout selected steps of

the test. All testing sessions were performed on the soccer pitch,

approximately 20 meter from and perpendicular to the goal. The

running lane was marked by cones. An area of 3.0 0.6 m (in the

middle of the track) was used for the data acquisition space

( Fig. 1), excluding change of direction.

During the test each subject was recorded with a digital camera

(Casio Exilim FH20), the sampling rate was 210 Hz. The camera

was located on a 1.5 meter high tripod, 6 meter from the running

lane, and perpendicular to the acquisition space and the sub-

jects sagittal plane [2]. The studied variables were step length

(SL), contact time (CT), step frequency (SF) and heart rate (HR);all footsteps within the data acquisition space were sampled. We

taped kinematic markers on the feet of each subject. Each sub-

ject performed the tests individually, in order to avoid obstruc-

tion issues. The film sequences were analyzed off-line using

Dartfish 5.5Pro motion analysis software (Dartfish, Fribourg,

CH). During the tests, the procedure was never interrupted and

the involved players suffered no injuries. SL was defined as the

distance between successive foot contacts and CT was calculated

as time from initial contact through to toe-offof the ipsilateral

foot, this was in line with the protocol proposed by Cavanagh et

al. [3]. Furthermore, step frequency was calculated applying the

following formula for MAV95 %: [(speed kmh-1/3.6)/SL m].

Statistical analysisThe data from the investigation are presented as mean SDand

coefficient of variation [CV = (SD/mean)100]. In order to deter-

mine difference between Y1and MAV95 %and difference between

baseline measures and the end of the single test, an ANOVA with

repeated measures was applied on (i) step length, (ii) contact

time (iii) heart rate data. Assumption of normality was verified

using the Shapiro-Wilk W test. Statistical analyses were per-

formed using the software IBM SPSS Statistic version 15.0

(IBM Corporation, Somers, NY, USA). The level set for significance

wasp0.05.

8.50 m 3 m 8.50 m

60cm

60cm

ACQUISITION SPACE

Fig. 1 The upper image presents a representa-

tion of the shuttle run performed.


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Training & Testing


Results

ANOVAs with repeated measures revealed significant differences

between 2 tests in all the variables investigated. For HR

F(1,11) = 410.05, p < 0.0001 and 2 = 0.974, (Y1 146 5.2 and

MAV95 % 168 5.3 beatsmin-1). SL F(1,11)= 6.72, p = 0.025 and

2= 0.379, (Y1 138 6.4 and MAV95 % 144 5.2 cm). CT

F(1,11)= 179.37, p < 0.0001 and 2= 0.942, (Y1194 8.3 and MAV95 %

175 2.6 ms). The difference between thefi

rst step and the laststep in all the variables investigated was also significant. For HR

F(1,11)= 2455.83, p < 0.0001 and 2= 0.996, (first step 126 5.5 and

last step 187 4.9 beatsmin1). SL F(1,11)= 25.94, p < 0.0001 and

2= 0.702, (first step 138 6.4 and last step 143 7.2 cm). CT

F(1,11)= 28.413, p < 0.0001 and 2= 0.721 (first step 191 6.7 and

last step 178 4.3 ms). Moreover also the interaction of test x

time was significant: HR F(1,11)= 1 384.22, p < 0.0001 and

2= 0.992; SL F(1,11)= 1 553.72, p < 0.0001 and 2= 0.993; CT

F(1,11)= 712.33, p < 0.0001 and 2= 0.985.

Y1. HR increased 94 % with respect to the start of the test

(p< 0.0001). The maximum HR was 194 5.02 beatsmin-1 (CV

2.57 %) which was achieved at 523 58.89 sec ( Fig. 2a). SL dur-

ing thefi

rst step was 115 7.40 (CV 6.44 %) and 161 5.44 cm (CV3.38 %) on the last step (6 < 14.22 0.89 kmh1) an increase of

40 % (p< 0.0001) ( Fig. 2b). CT of the first step was 239 11.99

(CV 5.22 %) and 158 4.69 ms (CV 2.96 %) during the last step

( Fig. 2c) a decrease of 31 % (p< 0.0001).

MAV95 %: The velocity was 13.50 0.81 kmh1 and distance

18.75 1.15 m. HR increased 17 % (p < 0.0001) in which the maxi-

mum HR of the 95 % MAV95 % was 181 4.81 beatsmin1 (CV

2.65 %) and achieved at 188 10.95 s ( Fig. 2a). SL ( Fig. 2b)

during the first step was 162 6.91 (CV 4.26 %) and 126 3.52 cm

(CV 2.79 %) during the last step (22 %,p< 0.0001). CT ( Fig. 2c)

during the first step was 153 1.48 (CV 0.97 %) and 197 3.82 ms

(CV 2.94 %) during the last step (29 %, withp< 0.0001). Step fre-

quency increased from 2.32 0.10 Hz (CV 4.31 %) during thefi

rststep to 2.98 0.08 Hz (CV 2.83 %) during the last step (29 %, with

p< 0.0001).

Discussion

The aim of this study was to examine the changes in kinematic

parameters and heart rate during an intermittent shuttle run-

ning at both incremental and constant speeds. Heart rate

increased linearly during both tests (Y1and MAV95 %), however

reached greater intensity during the end of the incremental test

(Y1). The results for both tests showed a trend between CT and

SL. In which greater CT was associated with smaller SL and vice-versa ( Fig. 2b, c). This leads to the first consideration, that the

CT is associated with SL. Due to the fact CT is the phase in which

the athlete has ground contact, this parameter raises great inter-

est in which the primary component relates to ground reaction

forces. We believe CT has a central role within soccer, not only as

Step

HeartRate(beat.min1)

StepLength(cm)

ContactTime(ms)

a

b

c

210

200

190

180

170

160

150

140

160

150

140

130

120

110

100

250

230

210

190

170

150

1300

6 7 8 9 12 13 14 16151110km.h1

0

170

0

5 10 15 20 25 30 35 40 45 50 55

Y1

MAV95%

Fig. 2 a= Heart Rate, b= Step length, c= Contact

Time; during MAV95 % (upper x-axis represents

number of shuttle runs) and Y1 (x-axis in lower

represents the increased velocity).


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Training & Testing


the study has showed a very tight relationship with the SL

( Fig. 2a, b) but also as an index of fatigue; which has also been

observed by other authors [9]. This is evident within the MAV95 %

testing where speed was constant and determined a priori, in

which we analyzed the phenomenon and observed the effect of

fatigue. For example at the beginning of the test SL was ~162 cm,

and halfway through had decreased 17.72 %, which coincides

perfectly with step 30 at 11 kmh-1whereby the CT had increased

by 20 %. This suggests that already the mid-parametric testswere strongly influenced kinematically. Furthermore during the

MAV95 %test, with a reduction in SL and a corresponding increase

in CT it was evident that maintenance of speed would be

achieved through increases in step frequency, which is sup-

ported by previous research [10]. An increase in step frequency

suggests that during the MAV95 %test there was a greater energy

cost due to increased lower limb muscle activity [9]. This view is

reflected, as during the shuttle run, there are several stages:

accelerated phase, intermediate run and deceleration, which

require a high muscle activity. These results highlight 2 different

neuromechanical strategies adopted in fatigue conditions: dur-

ing the incremental test (Y1), the CT decreased and the SL

increased whereas in the MAV95 %, the CT increased and the SLdecreased. In light of the clear adaptations of the CT during

MAV95 %(29 %) and with respect to the moderate changes in HR

(17 %) it is clear that the CT is the key parameter. This is also

because when the fatigue condition increased [9] the associated

adaptations within the neuromuscular patterns affected CT

more than HR.

In conclusion, whereas in the middle phase there was a reduc-

tion of~20 % in both CT and SL, SF conversely increased by 20 %.

We believe that continuing training beyond this threshold is

counterproductive as it would allow the athlete to take other

steps during the day and cause a state of very low fitness in the

game of football. We believe that knowledge of these parameters

would allow the coach to improve the quality of training by pay-ing attention to mechanical parameters that are easily measur-

able. In fact, the knowledge of the number of steps per shuttle

run allows to observe possible reductions of the SF: in this case,

if the SF is decreased by 20 %, then a passive recovery or another

training session will be the best choice. Finally, the use of MAV95 %

allows to improve the specific strength in lower limbs by keep-

ing the number of steps constant as shown by Padulo et al. [11];

for example, given the number of steps per shuttle run, it is then

possible to require the soccer player to maintain a constant fre-

quency of steps per shuttle run.

Acknowledgements

The authors are grateful to Domenico Arestia and Cristiano

Palermiti for technical suggestions and encouragement.

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Kinematic Analysis of Soccer Players in Shuttle Running

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