Surface electromyography in ballistic movement: a comparative methodological analysis from taekwondo athletes (Electromiografía de superficie en movimientos balísticos: un análisis metodológico comparativo en atletas de taekwondo)

Surface electromyography (sEMG) signal processing methods used to assess combat sports are heterogeneous. This research aims to compare the electromyography peak (peak EMG) in taekwondo athletes with five processing methods. Secondarily, the coefficient of variation (CV) and the noise percentage regarding the peak EMG (NPRP) were compared. The sEMG record of eight leg muscles of sixteen athletes (12 male and 4 female, ages 20.31+4.1 years) was consulted. The processing methods were: a) Smoothing 1, b) Smoothing 2, c) Root mean square (RMS) 1, d) RMS 2, and e) Empirical mode decomposition (EMD). Results indicate that the peak EMG differs among Smoothing 1 vs. EMD; Smoothing 2 vs. EMD; Smoothing 1 vs. RMS 2; Smoothing 2 vs. RMS 2; Smoothing 1 vs. RMS 1; RMS 1 vs. RMS 2; RMS 1 vs. EMD, and RMS 2 vs. EMD. For all cases p<.05 in seven of the eight muscles studied. No differences were found for the CV. The EMD NPRP was lower than the other methods analyzed (p<.05). As a conclusion, there are differences among the studied methods and should be considered when interpreting the peak EMG. The EMD seems to be a useful alternative for reducing noise and artifact movement. Resumen. Los métodos de procesamiento de señales de electromiografía de superficie (sEMG) utilizados para evaluar los deportes de combate son heterogéneos. Esta investigación tiene como objetivo comparar el pico de electromiografía (pico EMG) en atletas de taekwondo con cinco métodos de procesamiento. En segundo lugar, se compararon tanto el coeficiente de variación (CV) como el porcentaje de ruido con respecto al pico EMG (NPRP). Se consultó el registro sEMG de ocho músculos de las piernas de dieciséis atletas (12 hombres y 4 mujeres, edades 20,31+4,1). Los métodos de procesamiento fueron: a) Suavizado 1, b) Suavizado 2, c) Raíz cuadrada media (RMS) 1, d) RMS 2 y e) Descomposición en modo empírico (EMD). Los resultados indican que el pico de EMG difiere entre el suavizado vs. EMD; Suavizado 2 vs. a EMD; Suavizado 1 vs. a RMS 2; Suavizado 2 vs. a RMS 2; Suavizado 1 vs. a RMS 1; RMS 1 vs. a RMS 2; RMS 1 vs. a EMD y RMS 2 vs. a EMD. Para todos los casos p <.05 en siete de los ocho músculos estudiados. No se encontraron diferencias para el CV. El EMD NPRP fue menor que los otros métodos analizados (p <.05). En conclusión, existen diferencias entre los métodos estudiados y deben tenerse en cuenta al interpretar el pico EMG. El EMD parece ser una alternativa útil para reducir el ruido y el movimiento de artefactos.

The Self-Prioritization Effect: Self-referential processing in movement highlights modulation at multiple stages

A wealth of recent research supports the validity of the Self-Prioritization Effect (SPE)—the performance advantage for responses to self-associated as compared with other-person-associated stimuli in a shape–label matching task. However, inconsistent findings have been reported regarding the particular stage(s) of information processing that are influenced. In one account, self-prioritization modulates multiple stages of processing, whereas according to a competing account, self-prioritization is driven solely by a modulation in central-stage information-processing. To decide between these two possibilities, the present study tested whether the self-advantage in arm movements previously reported could reflect a response bias using visual feedback (Experiment 1), or approach motivation processes (Experiments 1 and 2). In Experiment 1, visual feedback was occluded in a ballistic movement-time variant of the matching task, whereas in Experiment 2, task responses were directed away from the stimuli and the participant’s body. The advantage for self in arm-movement responses emerged in both experiments. The findings indicate that the self-advantage in arm-movement responses does not depend on the use of visual feedback or on a self/stimuli-directed response. They further indicate that self-relevance can modulate movement responses (predominantly) using proprioceptive, kinaesthetic, and tactile information. These findings support the view that self-relevance modulates arm-movement responses, countering the suggestion that self-prioritization only influences central-stage processes, and consistent with a multiple-stage influence instead.

A controllable dual-catapult system inspired by the biomechanics of the dragonfly larvae’s predatory strike

The biomechanics underlying the predatory strike of dragonfly larvae is not yet understood. Dragonfly larvae are aquatic ambush predators, capturing their prey with a strongly modified extensible mouthpart. The current theory of hydraulic pressure being the driving force of the predatory strike can be refuted by our manipulation experiments and reinterpretation of former studies. Here, we report evidence for an independently loaded synchronized dual-catapult system. To power the ballistic movement of a single specialized mouthpart, two independently loaded springs simultaneously release and actuate two separate joints in a kinematic chain. Energy for the movement is stored by straining an elastic structure at each joint and, possibly, the surrounding cuticle, which is preloaded by muscle contraction. As a proof of concept, we developed a bioinspired robotic model resembling the morphology and functional principle of the extensible mouthpart. Understanding the biomechanics of the independently loaded synchronized dual-catapult system found in dragonfly larvae can be used to control the extension direction and, thereby, thrust vector of a power-modulated robotic system.

Hunting with catapults: the predatory strike of the dragonfly larva

Dragonfly larvae capture their prey with a strongly modified -extensible- mouthpart using a biomechanically unique but not yet understood mechanism. The current opinion of hydraulic pressure being the driving force of the predatory strike can be refuted by our manipulation experiments and reinterpretation of former studies. On this fact, we present evidence for a synchronized dual-catapult system powered by two spring-loaded catapults. The power output of the system exceeds generally the maximum power achievable by musculature. Energy for the movement is stored by straining a resilin-containing structure at each joint and possibly the surrounding cuticle which is preloaded by muscle contraction. To achieve the precise timing required to catch fast-moving prey, accessory structures are used to lock and actively trigger the system, ensuring the synchronisation of both catapults. As a proof of concept, we developed a bio-inspired robotic arm resembling the morphology and functional principle of the extensible mouthpart. Our study elucidates the predatory strike of dragonfly larvae by proposing a novel mechanism, where two synchronized catapults power the ballistic movement of prey capturing in dragonfly larvae – a so-called synchronized dual-catapult system. Understanding this complex biomechanical system may further our understanding in related fields of bio inspired robotics and biomimetics.One Sentence SummaryThe synchronized dual-catapult, a biomechanically novel mechanism for the ballistic movement of prey capturing in dragonfly larvae