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Background: Kinematics is studied by practitioners and researchers in different fields of practice. It is therefore critically important to adhere to a taxonomy that explicitly describes positions and movements. However, current representation methods such as cardan and Euler angles fail to report shoulder angles in a way that is easily and correctly interpreted by practitioners, and that is free from numerical instability such as gimbal lock. Methods: In this paper, we comprehensively describe the recent Tilt-and-Torsion method and compare it to the Euler YXY method currently recommended by the International Society of Biomechanics. While using the same three rotations (plane of elevation, elevation, humeral rotation), the Tilt-and-Torsion method reports humeral rotation independently from the plane of elevation. We assess how it can be used to describe shoulder angles (1) in a simulated assessment of humeral rotation with the arm at the side, which constitutes a gimbal lock position, and (2) during an experimental functional task, with 10 wheelchair basketball athletes who sprint in straight line using a sports wheelchair. Findings: In the simulated gimbal lock experiment, the Tilt-and-Torsion method provided both humeral elevation and rotation measurements, contrary to the Euler YXY method. During the wheelchair sprints, humeral rotation ranged from 14{\deg} (externally) to 13{\deg} (internally), which is consistent with typical maximal ranges of humeral rotation, compared to 65{\deg} to 50{\deg} with the Euler YXY method. Interpretation: Based on our results, we recommend that shoulder angles be expressed using Tilt-and-Torsion angles instead of Euler YXY., Comment: 19 pages, 5 figures, 2 tables

Purpose: This study aims to analyze learning differences between synchronous and asynchronous propulsion mode in manual wheelchairs.Materials and methods: Twenty novice and abled-bodied subjects (19.9 ± 1.3 years, 65.4 ± 8.8 kg, 173.6 ± 6.5 cm) participated in this study. Two sprints, in synchronous and asynchronous conditions, before and after twelve hours of sport practice including the learning of these two modes of propulsion, were realized. The rate of increase of the total force when entering the handrail, cadence, total and tangential force, speed and power were measured.Results: Significant differences before and after the twelve hours of practice are highlighted for speed (P < 0.0001), power (P = 0.006), rate of increase in total force (P = 0.02) and the tangential force (P = 0.005). The ANOVA performed also shows significant differences for the total force (P = 0.01), the velocity (P = 0.0002), the power (P = 0.002) and the tangential force (P = 0.005) between asynchronous and synchronous. Statistical analysis shows no significant interaction. The measured parameters tend to increase more significantly for the asynchronous vs. synchronous mode.Conclusion: The learning of the two modes of propulsion had significant effects on the main parameter of propulsive performance, speed. However, two of the biomechanical parameters related to the risk of injury, the rate of increase of the total force and the total force, increase significantly for the two modes of propulsion. It would be interesting to propose adapted muscle strengthening sessions during the learning phase. In addition, evolution percentages tend to be higher in asynchronous vs. synchronous propulsion. These results suggest that asynchronous instruction should be favored early on in the learning of manual wheelchair basketball., Objectifs: Cette étude vise à analyser les différences d’apprentissage existantes entre le mode de propulsion synchrone et asynchrone en fauteuil roulant manuel.Matériels et méthode: Vingt sujets valides novices (19,9 ± 1,3 ans ; 65,4 ± 8,8 kg ; 173,6 ± 6,5 cm) ont pris part à cette étude. Deux sprints, en conditions synchrone et asynchrone, avant et après douze heures de pratique sportive incluant l’apprentissage de ces deux modes de propulsion, ont été réalisés. Le taux d’augmentation de la force totale lors de la saisie de la main courante, la cadence, la force totale et tangentielle, la vitesse et la puissance ont été mesurés.Résultats: Des différences significatives avant et après les douze heures de pratique sont mises en évidence pour la vitesse (p < 0,0001), la puissance (p = 0,006), le taux d’augmentation de la force totale (p = 0,02) et la force tangentielle (p = 0,005). L’Anova réalisée montre également des différences significatives pour la force totale (p = 0,01), la vitesse (p = 0,0002), la puissance (p = 0,002) et la force tangentielle (p = 0,005) entre asynchrone et synchrone. L’analyse statistique ne montre pas d’interaction significative. Les paramètres mesurés tendent à augmenter de manière plus importante pour le mode asynchrone vs synchrone.Conclusion: L’apprentissage des deux modes de propulsion a eu des effets significatifs sur le principal paramètre de performance propulsive, la vitesse. Or, deux des paramètres biomécaniques liés aux risques de blessures, le taux d’augmentation de la force totale et la force totale, augmentent significativement pour les deux modes de propulsion. Il serait alors intéressant de proposer des séances de renforcement musculaire adaptées durant la phase d’apprentissage. De plus, les pourcentages d’évolution tendent à être plus importants en propulsion asynchrone vs synchrone. Ces résultats amènent à penser qu’il faudrait privilégier l’enseignement asynchrone de manière précoce durant l’apprentissage du basket en fauteuil roulant manuel.