The purpose of this study was to investigate the effect of whole body vibration (WBV) training on maximal strength, squat jump, and flexibility of well-trained combat athletes. Twelve female and 8 male combat athletes (age: 22.8 ± 3.1 years, mass: 65.4 ± 10.7 kg, height: 168.8 ± 8.8 cm, training experience: 11.6 ± 4.7 years, training volume: 9.3 ± 2.8 hours/week) participated in this study. The study consisted of three sessions separated by 48 hours. The first session was conducted for familiarization. In the subsequent two sessions, participants performed WBV or sham intervention in a randomized, balanced order. During WBV intervention, four isometric exercises were performed (26 Hz, 4 mm). During the sham intervention, participants performed the same WBV intervention without vibration treatment (0 Hz, 0 mm). Hand grip, squat jump, trunk flexion, and isometric leg strength tests were performed after each intervention. The results of a two-factor (pre-post[2] × intervention[2]) repeated measures ANOVA revealed a significant interaction (p = 0.018) of pre-post × intervention only for the hand grip test, indicating a significant performance increase of moderate effect (net increase of 2.48%, d = 0.61) after WBV intervention. Squat jump, trunk flexion, and isometric leg strength performances were not affected by WBV. In conclusion, the WBV protocol used in this study potentiated hand grip performance, but did not enhance squat jump, trunk flexion, or isometric leg strength in well-trained combat athletes.
We investigate the Alfvén wave propagation characteristics in the inner zone (r < 1.35 R⊙) of the North Polar Coronal Hole. The linear, incompressible magnetohydrodynamic (MHD) approximation reveals two wave modes with different phase velocities. Alfvén wave with the slower phase velocity is quickly damped; in other words it cannot propagate in the coronal plasma. On the other hand, the higher phase velocity Alfvén waves can propagate along the magnetic field lines. Mechanical energy flux density of these waves is found to be high enough to replace the coronal energy which is lost via optically thin emission and through heat conduction to the chromosphere below. We show that Alfvén waves propagating along the magnetic flux tubes go through refraction and get damped via viscous dissipation and resistivity. The energy flux density of the waves is of the order of 106 erg cm−2 s−1. The radial profile of the energy flux density in the region 1.05–1.35 R shows a rise until about 1.15 R where it peaks and further on declines less steeply than rising arm. This result is used to interpret Si viii data taken by the Solar Ultraviolet Measurements of Emitted Radiation instrument on board Solar and Heliospheric Observatory. Si viii lines like many other ionic lines show non‐thermal broadening. The observed radial profile of the non‐thermal line‐of‐sight velocity of Si viii shows a plateau which coincides with the peak of the energy flux density we derived. We claim that this coincidence is not accidental but indicates the fact that the decrease in the energy flux density of damped Alfvén waves causes the plateau formation in Si viii non‐thermal line‐of‐sight velocity profile.
We investigate the stability properties of a hot, dilute and differentially rotating weakly magnetized plasma which is believed to be found in the interstellar medium of galaxies and protogalaxies and in the low‐density accretion flows around some giant black holes like the one in the Galactic Centre. In the linear magnetohydrodynamic regime, we consider the combined effects of gyroviscosity and parallel viscosity on the magnetorotational instability. The helical magnetic field is considered in the investigation. We show that the gyroviscous effect and the pitch angles cause a powerful gyroviscous instability. Furthermore, in most of the cases, plasma with the above‐mentioned properties is unstable and the growth rates of the unstable modes are larger than that of the magnetorotational instability.
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