Reliability of measurements during countermovement jump assessments: Analysis of performance across subphases

The aim of this study was to examine the reliability of performance measures in the different phases and sub-phases of the countermovement jump (CMJ). Seventeen male athletes competing at a regional level completed 204 valid trails consisting of the execution of maximal hands-on-waist CMJs performed on a force platform. The vertical ground reaction force (VGRF) data obtained at a sampling frequency of 1000 Hz were used to calculate performance-derived variables and determine key points and jump subphases. The relative reliability of 92 variables was assessed using the intraclass correlation coefficient (ICC) from a two-way mixed effects model analyzing the time, force, power, velocity, and displacement variables across the different phases and sub-phases of the jump. The contact phase serves as a consistent approach (range ICC = .806 to .987), providing reliable information about the jump as a unit. Mean force was the only measure that presented high reliable values throughout all sub-phases (ICC = .931 to .963). The power and velocity variables were reliable from the point where force turned into an increasing value while displacement from minimum velocity was reached. Net impulse and ratios of force development showed high and acceptable values, respectively. Timerelated variables were the least reliable measures (ICC = .587 to .720), showing acceptable reliability only in the contact phase and propulsive sub-phase. In conclusion, VGRF may be used to determine specific parameters during CMJ execution, although the appropriate variables should be selected based on acceptable levels of reliability.S

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