Maximal amplitude postures of the scapula : simulations with the Anybody software

8th World Congress of Biomechanics, DUBLIN, IRELANDE, 08-/07/2018 - 12/07/2018Scapular dyskinesis is often associated to shoulder joint injuries. However, as stated by Kibler (2003), 'no specific pattern of dyskinesis is associated with a specific shoulder diagnosis'. To better understand the pathomechanisms associated to scapular dyskinesis, the effect of scapular position and orientation still need to be investigated

Kinematics of the bow arm of violinists: effect of tempo, string played and play style and their interactions

8th World Congress of Biomechanics, DUBLIN, IRELANDE, 08-/07/2018 - 12/07/2018Bowed string musicians are especially at risk of upper limb injuries (Cayea and Manchester, 1998). While a few risk factors were identified, no causal relations could be found (Baadjou et al., 2016), highlighting the need for biomechanical investigations. Among the music parameters impacting violinists' biomechanics, the tempo, string played and play style have been investigated (Visentin and Shan, 2003; Berque and Gray, 2002). However, interactions between these parameters are not clear. Their knowledge could help defining relevant experimental research plans. The objective was to assess the interactions of the tempo, string played and play style on the bow arm biomechanic

Moving horizon estimation of human kinematics and muscle forces

Human-robot interaction based on real-time kinematics or electromyography (EMG) feedback improves rehabilitation using assist-as-needed strategies. Muscle forces are expected to provide even more comprehensive information than EMG to control these assistive rehabilitation devices. Measuring in vivo muscle force is challenging, leading to the development of numerical methods to estimate them. Due to their high computational cost, forward dynamics-based optimization algorithms were not viable for real-time estimation until recently. To achieve muscle forces estimation in real time, a moving horizon estimator (MHE) algorithm was used to track experimental biosignals. Two participants were equipped with EMG sensors and skin markers that were streamed in real time and used as targets for the MHE. The upper-limb musculoskeletal (MSK) model was composed of 10 degrees-of-freedom actuated by 31 muscles. The MHE relies on a series of overlapping trajectory optimization subproblems of which the following parameters have been adjusted: the fixed duration and the frame to export. We based this adjustment on the estimation delay, the muscle saturation, the joint kinematic mean power frequency, and errors to experimental data. Our algorithm provided consistent estimates of muscle forces and kinematics with visual feedback at 30 Hz with a 110 ms delay. This method is promising to guide rehabilitation and enrich assistive device control laws with personalized force estimations

Shoulder muscle activation strategies differ when lifting or lowering a load

Purpose Lowering a load could be associated with abnormal shoulder and scapular motion. We tested the hypothesis that lowering a load involves different shoulder muscle coordination strategies compared to lifting a load. Methods EMG activity of 13 muscles was recorded in 30 healthy volunteers who lifted and lowered a 6, 12 or 18 kg box between three shelves. Kinematics, EMG levels and muscle synergies, extracted using non-negative matrix factorization, were analyzed. Results We found greater muscle activity level during lowering in four muscles (+ 1–2% MVC in anterior deltoid, biceps brachii, serratus anterior and pectoralis major). The movements were performed faster during lifting (18.2 vs. 15.9 cm/s) but with similar hand paths and segment kinematics. The number of synergies was the same in both tasks. Two synergies were identified in ~ 75% of subjects, and one synergy in the others. Synergy #1 mainly activated prime movers’ muscles, while synergy #2 co-activated several antagonist muscles. Synergies’ structure was similar between lifting and lowering (Pearson’s r ≈ 0.9 for synergy #1 and 0.7–08 for synergy #2). Synergy #2 was more activated during lowering and explained the greater activity observed in anterior deltoid, serratus anterior and pectoralis. Conclusion Lifting and lowering a load were associated with similar synergy structure. In 3/4 of subjects, lowering movements involved greater activation of a “multiple antagonists” synergy. The other subjects co-contracted all shoulder muscles as a unit in both conditions. These inter-individual differences should be investigated in the occurrence of shoulder musculoskeletal disorders

RELATIVE CONTRIBUTION OF CONTACT AND AERIAL COMPONENTS IN THE CONTROL OF AERIAL ROTATION TO GUIDE ACROBATICS SKILLS LEARNING

The contribution of release state, change in inertia moment, and angular momentum transfer to the performance of a transition move on asymmetrical bars was analysed to better guide acrobatics learning in novices and experts. Numerical simulation based on actual release state was used to optimise aerial technique in novices and experts. Optimised novice performances did not reach actual expert ones. Thereafter, it may be crucial to orient novice learning toward improving release state. In addition for both groups, adjustments of inertia moment and momentum transfer in optimised techniques significantly increased performances. Finally in all actual or optimised techniques, the level of contribution of inertia moment correlated the most with the level of performance. Therefore technique enabling larger change in inertia moment should be preferred