Análisis de las respuestas neuromusculares durante dos diferentes sesiones de entrenamiento intervalado de alta intensidad en atletas de deportes cíclicos y acíclicos

The purpose of the present study was to investigate the acute effects of two high-intensity interval training (HIIT) sessions on countermovement jump performance. Twenty-two male regional-level athletes (cyclic, n = 11; acyclic, n = 11) completed two HIIT sessions consisted of multiple running bouts on a treadmill. A different work-interval duration was applied in each session. To determine the effect of fatigue on jumping performance, countermovement jump tests were executed pre-effort and at the end of all series. The results showed a decrease in jump performance at the end of the third series respect to the pre-effort condition (p < .001). In addition., the acyclic athletes jumped higher than the cyclic ones (p < .001), revealing a different jumping strategy based on a higher velocity component, and a more efficient elastic energy utilization (p < .01). The neuromuscular mechanisms affected by fatigue, were also different between groups. In conclusion, during HIIT sessions the neuromuscular status is principally conditioned by the total volume rather than by the work-interval duration, affecting specific performance variables depending on the sport discipline. The present findings may be useful when conducting HIIT concurrently with other training contents in athletes of both cyclic and acyclic sports.El propósito del presente estudio ha sido investigar los efectos agudos de dos sesiones de entrenamiento intervalado de alta intensidad (HIIT) sobre el rendimiento en el salto contramovimiento. Veintidós atletas hombres, de nivel regional (cíclicos, n = 11; acíclicos, n = 11) completaron dos sesiones de HIIT, que consistían en series repetidas de carrera sobre un tapiz rodante. Se aplicaron intervalos de trabajo de diferente duración en cada sesión. Para determinar el efecto de la fatiga sobre el rendimiento en el salto, se ejecutaron pruebas de salto contramovimiento antes del esfuerzo y al final de todas las series. Los resultados mostraron una disminución en el rendimiento del salto al final de las tercera serie respecto a la condición pre-esfuerzo (p < .001). Asimismo, los atletas acíclicos saltaron más alto que los cíclicos, (p < .001), revelando una estrategia de salto diferente, basada en un mayor componente de velocidad y una utilización más eficiente de la energía elástica (p < .01). Los mecanismos neuromusculares afectados por la fatiga también fueron diferentes entre los grupos. En conclusión, durante sesiones de HIIT, el estatus neuromuscular está principalmente condicionado por el volumen total, más que por la duración del intervalo de trabajo, afectando variables específicas dependiendo de la disciplina deportiva. Los presentes hallazgos pueden ser de utilidad cuando se prescribe HIIT de manera concurrente a otros contenidos de entrenamiento tanto en atletas de deportes cíclicos como acíclicos.Actividad Física y Deport

Low temperature magnetic properties of a Ni50Mn34In16 ball-milled metamagnetic shape memory alloy

[EN] The effect of the atomic disorder induced by ball-milling on the structure and the magnetic properties has been analyzed in a Ni50Mn34In16 metamagnetic shape memory alloy. The as-milled samples displayed an amorphous structure which crystallizes to a disordered B2 structure on annealing. On further annealing, several recovery processes leading to the austenitic L21 structure and the subsequent martensitic transformation are observed. As a result of the recovery processes, the magnetic order drastically varies concurrent with the long-range atomic order. In particular, the magnetism evolves from a frustrated magnetic state compatible with a canonical spin-glass, observed in the amorphous structure, to the well-developed ferromagnetic state.This work has been carried out with the financial support of the Spanish “Ministerio de Economía y Competitividad” and FEDER funding, projects no. MAT2012-37923 and MAT2015-65165-C2-R. I. Unzueta acknowledges financial support from the Basque Government Grant nos. IT-443-10 and PRE_2014_214

Identification of Ni-vacancy defect in Ni-Mn-Z (Z = Ga, Sn, In): An experimental and DFT positron annihilation study

[EN] By means of experimental positron-annihilation-lifetime measurements and theoretical density functional theory (DFT) positron-lifetime calculations, vacancy-type defects in Ni50Mn50−xSnx (x=25, 20,15,13,10) and Ni50Mn50−xInx (x=25,20,16,13) systems are systematically studied. The study is extended to Ni-Mn-Ga systems as well. Experimental results are complemented with electron-positron DFT calculations carried out within the local density approximation and generalized gradient approximation, where five different parametrizations accounting for the γ(r) enhancement factor are analyzed. Theoretical results indicate that the Boronski-Nieminen parametrization of γ(r) is the one that best predicts the experimental results, which ultimately enables us to identify VNi as the vacancy present in the studied samples. The characteristic positron lifetime related to VNi ranges between 181 and 191 ps in Ni-Mn-Sn/In systems. Positron-annihilation-lifetime spectroscopy results in these two systems delimit the lower bound of the achievable vacancy concentration, which is much larger compared with the reported values in Ni-Mn-Ga systems. The present work, along with setting the basis for positron simulations in Ni-Mn based Heusler alloys, delimits the effect that the variation of vacancies has in the martensitic transformation in Ni-Mn-Sn systemsThis work is supported by the Basque Government and Spanish Ministry of Economy and Competitiveness under grants IT-1005-16, IT-756-13 and MAT2015-65165-C2-R (MINECO/FEDER). I. Unzueta also wants to acknowledge the Basque Government Grant PRE-2014-214