EFFECT OF THE STARTING BLOCK POSTURE ON THE 3D JOINT ANGULAR VELOCITY IN SPRINTERS.
Jean Slawinski1,2, Guy Ontanon2, Raphaël Dumas3, Laurence Chèze3, Christian Miller2, Alice Mazure-Bonnefoy1,2.
1
Laboratoire d’analyse du mouvement, CIC-IT 805, AP-HP, CHU Raymond Poincaré, Garches, France
2
Team Lagardère, centre d’expertise, 26 avenue du général Sarrail 75016 PARIS.
3
Université de Lyon, F-69622, Lyon, France ; Université Lyon 1, F-69622, Villeurbanne, France ; INRETS, UMR_T9406
Laboratoire de Biomécanique et Mécanique des Chocs, F-69675, Bron, France.
SUMMARY
The aim of this study was to measure the effect of the
modification of the posture during a sprint start on 3D joint
angular velocity. This was performed using a 3D kinematic
analysis of the whole body. Ten trained sprinters started
using three different starting positions in the starting blocks
(bunched, medium and elongated). They were equipped with
63 passive reflective markers, and an opto-electronic Motion
Analysis® system (12 digital cameras 250 Hz) was used to
collect the 3D marker trajectories. During the pushing phase
on the blocks and the first step, the 3D angular velocity
(EJAV) and the norm of the joint angular velocity (NJAV)
were calculated. These results demonstrated that the
modification of the initial posture of the sprinter in the
starting block significantly influenced the NJAV of the rear
elbow, hip and knee. The 3D kinematic analysis of the
whole body demonstrated that joints such as shoulders,
thoracic or hips did not reach their maximal angular velocity
with a movement of flexion-extension, but with a
combination of flexion-extension, abduction-adduction and
internal-external rotation. To understand postural
adaptations in skilled movement the NJAV approach could
be a useful tool.
and the first step. A segment coordinate system (SCS) was
defined on each body segment based on the markers. The
orientation of their axes was carefully carried out using the
ISB recommendations (Wu et al. 2002; 2005). From the
reconstructed spatial trajectories of the markers, the segment
mass, position of the centre of mass and inertia tensor were
estimated from scaling equations [1]. The rotation sequence
proposed by the ISB to describe the lower and the upper
limbs joint movements was used. For this study, 16 rigid
segments were used in order to model the body.
The joint angular velocity and its norm
were computed from proximal and distal segment angular
velocities:
Ω i / i −1 = Ω i / 0 − Ω i −1 / 0 .
The contribution of each degree of freedom was also
computed. For this, the joint angular velocity was projected
on each axis of the joint coordinate system (JCS) in order to
(
MATERIAL AND METHODS
Ten trained sprinters started using three different starting
positions in the starting blocks (bunched, medium and
elongated). They were equipped with 63 passive reflective
markers, and an opto-electronic Motion Analysis® system
(12 digital cameras 250 Hz) was used to collect the 3D
marker trajectories during the pushing phase on the blocks
)
retrieve the Euler angles derivatives α& , β& , γ& :
Ω i / i−1 =
(e × e )• Ω e + (e × e )• Ω e + (e × e )• Ω e
(e × e )• e 1(e44×2e 4
)• 4
(e × e )• e
e
1442443
3
1442443
2
i / i −1
3
1
where
3
i / i −1
1
1
2
α&
INTRODUCTION
Biomechanical studies shown that the velocity of the centre
of mass (VCM) at block clearing is higher when the interblock spacing is increased as a result of a more effective
force-impulse [2, 3]. From Kisler or Henry the
biomechanical tools and the morphology of the sprinter have
been considerably modified and these modifications could
influence these old results. A Recent study demonstrated
that complex movement such as sprint start must be studied
using a 3D kinematical analysis because joints such as
shoulders, thoracic or hips did not reach their maximal
angular velocity with a movement of flexion-extension, but
with a combination of flexion-extension, abductionadduction and internal-external rotation [5]. The aim of this
study was to measure the effect of the modification of the
posture during a sprint start on 3D joint angular velocity.
Ω i / i −1 (NJAV),
3
1
i / i −1
2
2
1
2
3
β&
3
1
2
3
γ&
e1 is a selected axis from the matrix Ti −1 / 0 , e3 is a
selected axis from the matrix Ti / 0 and
e2 = e" × e1 . These
values, called Euler Angular Velocity (EAV), could be used,
in addition to the numerical value of NJAV, to know which
degree of freedom (flexion/extension, adduction/abduction
and internal/external rotation) is more important during the
pushing phase of the sprint start. From the NJAV, the
maximal values, NJAVmax were calculated to analyse the
data. Rear and front joints were respectively associated with
the side of the rear and the front legs in the starting blocks.
RESULTS
These results demonstrated that the modification of the
initial posture of the sprinter in the starting block
significantly influenced the NJAVmax of the rear elbow, hip
and knee. Indeed, NJAVmax of the rear shoulder tends to be
greater while NJAVmax of the rear hip and knee tends to be
lower in the bunched condition (fig. 1).
DISCUSSION AND CONCLUSION
The 3D kinematic analysis of the whole body demonstrated
that joints such as shoulders, thoracic or hips did not reach
their maximal angular velocity with a movement of flexion-
REFERENCES
extension, but with a combination of flexion-extension,
abduction-adduction and internal-external rotation. To
understand postural adaptations in skilled movement the
NJAV approach could be a useful tool.
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Figure 1: NJAV of the rear elbow, hip and knee during the
starting block phase and the first step of the run. †Significant
effect of the inter-block spacing (ANOVA).
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