A kinematic analysis of jumping technique in elite Korean teeterboard athletes: a case-study.

Korean teeterboard is a circus discipline that consists of a board pivoted at its centre upon which two acrobats are catapulted in turn performing acrobatic jumps. This paper presents one of the first studies that focuses on investigating the factors that contribute to jump height in Korean teeterboard. A total of 120 jumps were recorded from two acrobats using motion capture. Selected variables were input to a Boosted Regression Trees (BRT) analysis, corresponding to three specific events: acrobat landing, rotation of the teeterboard and acrobat take-off. Significant predictor variables were identified as: 1) body's centre of mass vertical velocity at the first contact with the teeterboard (relative importance: 69.4%) for landing, 2) maximum downward vertical teeterboard velocity for teeterboard rotation (72.7%) and 3) maximum upward vertical teeterboard velocity for take-off (50.4%). Kinematic parameters such as hip range of motion during take-off also contributed significantly to jump height (37.2%). The results provide understanding of the complex kinematics between two acrobats and a flexible pivoting board. Teeterboard designers, acrobats and trainers should be aware that maximising these parameters are the best strategies to improve jump height.

Learned Overweight Internal Model Can Be Activated to Maintain Equilibrium When Tactile Cues Are Uncertain: Evidence From Cortical and Behavioral Approaches.

Human adaptive behavior in sensorimotor control is aimed to increase the confidence in feedforward mechanisms when sensory afferents are uncertain. It is thought that these feedforward mechanisms rely on predictions from internal models. We investigate whether the brain uses an internal model of physical laws (gravitational and inertial forces) to help estimate body equilibrium when tactile inputs from the foot sole are depressed by carrying extra weight. As direct experimental evidence for such a model is limited, we used Judoka athletes thought to have built up internal models of external loads (i.e., opponent weight management) as compared with Non-Athlete participants and Dancers (highly skilled in balance control). Using electroencephalography, we first (experiment 1) tested the hypothesis that the influence of tactile inputs was amplified by descending cortical efferent signals. We compared the amplitude of P1N1 somatosensory cortical potential evoked by electrical stimulation of the foot sole in participants standing still with their eyes closed. We showed smaller P1N1 amplitudes in the Load compared to No Load conditions in both Non-Athletes and Dancers. This decrease neural response to tactile stimulation was associated with greater postural oscillations. By contrast in the Judoka's group, the neural early response to tactile stimulation was unregulated in the Load condition. This suggests that the brain can selectively increase the functional gain of sensory inputs, during challenging equilibrium tasks when tactile inputs were mechanically depressed by wearing a weighted vest. In Judokas, the activation of regions such as the right posterior inferior parietal cortex (PPC) as early as the P1N1 is likely the source of the neural responses being maintained similar in both Load and No Load conditions. An overweight internal model stored in the right PPC known to be involved in maintaining a coherent representation of one's body in space can optimize predictive mechanisms in situations with high balance constraints (Experiment 2). This hypothesis has been confirmed by showing that postural reaction evoked by a translation of the support surface on which participants were standing wearing extra-weight was improved in Judokas.