The Influence Of Friction Properties Of Shoe Upper Materials On Kicking Velocity In Soccer
T. Sterzing1, E. M. Hennig2
Department of Human Locomotion, Chemnitz University of Technology, Germany, [email protected]
2
Biomechanics Laboratory, University of Duisburg-Essen, Germany
1
INTRODUCTION
Kicking is the most typical sport specific technique in soccer
and has received considerable attention in biomechanical
research [1].
Fast kicking may make the difference to score in a game and
thus kicking velocity is to be seen as a decisive factor for
success in soccer. It was shown that different soccer shoe
models evoke different ball velocities during full instep
kicking [2,3]. The underlying mechanisms of differing ball
velocities in different shoes have not been fully explored yet.
Obviously, the collision mechanics during the contact period
of foot/shoe and ball determine the quality of the kick with
respect to accuracy and velocity. However, the impact during
the collision phase cannot be described solely according to
Newton’s laws as these describe mechanics for purely elastic
impacts. In kicking, during the collision phase,
displacement (≈ 26 cm) of the ball takes place [4]. Therefore,
the propulsion procedure has to be regarded as a mixture of a
throwing-like and an impact-like situation. Friction
properties of shoe upper materials potentially have an
influence on ball velocity during kicking, especially during
kicks in which the core impact is located off-centered. This
naturally occurs in games and during biomechanical studies.
Therefore, the purpose of this study was to quantify the
influence of different shoe upper friction properties on ball
velocity during full instep kicking.
METHODS
This study was designed as a laboratory experiment on
artificial turf in which kicking took place towards a spanned
net. Peak ball velocity was measured by a Stalker Pro radar
gun (Applied Concepts Inc., Plano, TX, USA). 18
experienced soccer players participated in this study (age:
24,0±2,0 years; height: 177,1±3,7 cm; weight: 74,3±4,9 kg).
Subjects had to perform six maximum full instep kicks in
four different shoe conditions with a mandatory rest period
between single kicks to avoid the influence of fatigue. Shoe
order was randomized for the different subjects. The shoe
conditions differed only in their upper material friction
properties. The friction properties were altered by four
handcrafted cap constructions and were characterized as
follows: KR1: low friction, KR2: regular friction, KR3: high
friction, KR4: very high friction (Picture 1). The ball used in
this study was a FIFA approved Nike Geo Merlin Vapor.
Picture 1: Shoe Conditions
Ground reaction forces of the stance leg and action time from
foot strike to initial movement of the ball were taken by a
Kistler 9281 force plate in combination with a photo cell
construction. By this, it was ensured that the standardized
three-step-approach and the swing phase in preparation of the
collision phase of the kick was homogenous between the four
shoe conditions
RESULTS AND DISCUSSION
All ground reaction force parameters of the stance leg, as
expected, revealed no differences between the four shoe
conditions. Thus, potential differences in ball velocity values
were due to the different shoe upper materials.
Ball velocity for the four shoe conditions differed only by 1,2
km/h. A repeated measures ANOVA between the shoe
conditions was not statistically significant (p<0,07) but
showed a trend towards higher ball velocity of the KR2 shoe
condition.
Figure 2: Ball Velocity, Means and SEM
The KR2 shoe condition reflects friction properties that are
most closely to currently used regular shoe upper friction
properties. Therefore, by usage of lower friction properties
(KR1), kinetic energy seems to get lost due to off-center
impact locations. Usage of higher friction properties (KR3,
KR4) might result in the transfer of kinetic energy in a
rotational movement of the ball due to off-center impact
locations. By this, reduction of energy, originally intended
for propulsion of the ball in kicking direction, takes place.
CONCLUSIONS
Friction materials of soccer shoe uppers could not be shown
to take statistically significant influence in achieving
different ball velocities during instep kicking. However,
friction properties of shoe upper materials close to regular
shoe upper conditions seem to work best with regard to ball
velocity during full instep kicking.
REFERENCES
1. Barfield, W (1998) The biomechanics of kicking in soccer,
Clinics In Sport Medicine, 17, 4, 711-728.
2. Hennig, E. M., Zulbeck, O. (1999) The influence of soccer
boot construction on ball velocity and shock to the body, 4.
Symposium on Footwear Biomechanics, Canmore,
Alberta, Canada.
3. Sterzing, T. and Hennig, E. M. (2004) unpublished data.
4. Tsaousidis, N. and Zatsiorsky, V (1996) Two types of ball
– effector interaction and their relative contribution to
soccer kicking, Human Movement Science, 15, 861-876.
ACKNOWLEDGEMENTS
This research was supported by Nike Inc., USA.