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  • Author: Ludovic Seifert x
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Does Floatation Influence Breaststroke Technique?

Hugues Leblanc, Ludovic Seifert, and Didier Chollet

This study is aimed at examining the relationships between floatation parameters, assessed by field tests and the stroking characteristics of breaststroke swimmers. The floatation parameters were evaluated for 23 males and 23 females by the hydrostatic lift test, the sinking force acting at the ankle test and the maximal glide length after a push-off from the pool wall test. The swimmers performed two trials at submaximal and sprint pace, and then, from the data given by a PC-video velocity system, the duration and velocity of their propulsive, recovery and glide phases were analyzed. In the female group and at slow pace, glide duration is correlated with hydrostatic lift (r = .62) and with maximal glide length (r = .44); mean glide velocity is correlated with hydrostatic lift (r = .73). In the male group and at slow pace, the sinking force was correlated with the glide phase (r = –0.66) and with the mean glide velocity (r = –0.78). At sprint velocity, the hydrostatic lift is correlated with the glide phase in the female group (r = .52). Floatation parameters have an impact on the gliding phase of the breaststroke cycle.

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Upper-Limb Kinematics and Coordination of Short Grip and Classic Drives in Field Hockey

Perrine Brétigny, Ludovic Seifert, David Leroy, and Didier Chollet

The aim of this study was to compare the upper-limb kinematics and coordination of the short grip and classic drives in field hockey. Ten elite female players participated in the experiment. The VICON system was used to record the displacement of markers placed on the stick and the players’ joints during five short grip and five classic drives. Kinematic and coordination parameters were analyzed. The ball’s velocity was recorded by a radar device that also served as the drive target. Kinematic differences were noted between the two drive conditions, with shorter duration and smaller overall amplitude in the short grip drive, explained by the shorter lever arm and the specific context in which it is used. No differences were noted for upper-limb coordination. In both types of stick holding, an interlimb dissociation was noted on the left side, whereas the right interlimb coordination was in phase. Moreover, the time lag increased in the disto-proximal direction, suggesting wrist uncocking before impact and the initiation of descent motion by the left shoulder. Mediolateral analysis confirmed these results: coordination of left-right limbs converged at the wrist but dissociated with more proximal joints (elbows and shoulders).

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Do Qualitative Changes in Interlimb Coordination Lead to Effectiveness of Aquatic Locomotion Rather Than Efficiency?

John Komar, Ross H. Sanders, Didier Chollet, and Ludovic Seifert

This study compared interlimb coordination and indicators of swim efficiency and effectiveness between expert and recreational breaststroke swimmers. Arm-leg coordination of 8 expert and 10 recreational swimmers at two different paces, slow and sprint, were compared using relative phase between elbow and knee. For each participant, knee and elbow angles were assessed using a 3-dimensional video analysis system with four below and two above cameras. During each phase of the cycle, indicators of swim efficiency (intracyclic velocity variations) and effectiveness (horizontal distance, velocity peaks, acceleration peaks) were calculated. Two coordination patterns emerged between expert and recreational swimmers, with significant differences in the relative phase at the beginning of a cycle (−172.4° for experts and −106.6° for recreational swimmers) and the maximum value of relative phase (9.1° for experts and 45.9° for recreational swimmers; all P < .05). Experts’ coordination was associated with higher swim effectiveness (higher acceleration peak: 2.4 m/s2 for experts and 1.6 m/s2 for recreational swimmers) and higher distance covered by the center of mass during each phase of the cycle (all P < .05). This study emphasized how experts coordinate arms and legs to achieve effective behavior, therefore exhibiting flexibility, mainly in the timing of the glide phase, to adapt to different speed.

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Climbing Skill and Complexity of Climbing Wall Design: Assessment of Jerk as a Novel Indicator of Performance Fluency

Ludovic Seifert, Dominic Orth, Jérémie Boulanger, Vladislavs Dovgalecs, Romain Hérault, and Keith Davids

This study investigated a new performance indicator to assess climbing fluency (smoothness of the hip trajectory and orientation of a climber using normalized jerk coefficients) to explore effects of practice and hold design on performance. Eight experienced climbers completed four repetitions of two, 10-m high routes with similar difficulty levels, but varying in hold graspability (holds with one edge vs holds with two edges). An inertial measurement unit was attached to the hips of each climber to collect 3D acceleration and 3D orientation data to compute jerk coefficients. Results showed high correlations (r = .99, P < .05) between the normalized jerk coefficient of hip trajectory and orientation. Results showed higher normalized jerk coefficients for the route with two graspable edges, perhaps due to more complex route finding and action regulation behaviors. This effect decreased with practice. Jerk coefficient of hip trajectory and orientation could be a useful indicator of climbing fluency for coaches as its computation takes into account both spatial and temporal parameters (ie, changes in both climbing trajectory and time to travel this trajectory).