The interaction between body position and vibration frequency on acute response to whole body vibration.

PURPOSE: The present study was designed to investigate the electromyographic (EMG) response in leg muscles to whole-body vibration while using different body positions and vibration frequencies. METHODS: Twenty male sport sciences students voluntarily participated in this single-group, repeated-measures study in which EMG data from the vastus lateralis (VL) and the lateral gastrocnemius (LG) were collected over a total of 36 trials for each subject (4 static positions × 9 frequencies). RESULTS: We found that vibration frequency, body position and the muscle stimulated had a significant effect (P-values ranged from 0.001 to 0.031) on the EMG response. Similarly, the muscle × frequency and position × muscle interactions were significant (P < 0.001). Interestingly, the frequency × positions interactions were not significant (P > 0.05). CONCLUSIONS: Our results indicate that lower frequencies of vibration (25-35 Hz) result in maximal activation of LG, whereas higher frequencies (45-55 Hz) elicit the highest responses in the VL. In addition, the position P2 (half squat position with the heels raised) is beneficial both for VL and LG, independently of the vibration frequency.

Involvement of mitochondrial activity in mediating ELF-EMF stimulatory effect on human sperm motility.

It has recently been reported that the exposure of human spermatozoa to an extremely low frequency (ELF) electromagnetic field (EMF) with a square waveform of 5 mT amplitude and frequency of 50 Hz improves sperm motility. The functional relationship between the energy metabolism and the enhancement of human sperm motility induced by ELF-EMF was investigated. Sperm exposure to ELF-EMF resulted in a progressive and significant increase of mitochondrial membrane potential and levels of ATP, ADP and NAD(+) that was associated with a progressive and significant increase in the sperm kinematic parameters. No significant effects were detected on other parameters such as ATP/ADP ratio and energy charge. When carbamoyl cyanide m-chlorophenylhydrazone (CICCP) was applied to inhibit the oxidative phosphorylation in the mitochondria, the values of energy parameters and motility in the sperm incubated in the presence of glucose and exposed to ELF-EMF did not change, thus indicating that the glycolysis was not involved in mediating ELF-EMF stimulatory effect on motility. By contrast, when pyruvate and lactate were provided instead of glucose, the energy status and motility increased significantly in ELF-EMF-treated sperm. Under these culture conditions, the inhibition of glycolitic metabolism by 2-deoxy-D-glucose (DOG) again resulted in increased values of energy and kinematic parameters, indicating that gluconeogenesis was not involved in producing glucose for use in glycolysis. We concluded that the key role in mediating the stimulatory effects exerted by ELF-EMF on human sperm motility is played by mitochondrial oxidative phosphorylation rather than glycolysis.

The effects of vibration on explosive and reactive strength when applying individualized vibration frequencies.

The aim of this study was to assess the effects of 8 weeks of whole-body vibrations on explosive and reactive leg strength. Thirty-three physically active students took part in the study and were randomly assigned to an individualized-vibration group, a fixed-vibration group or a control group. The frequency of vibration was set to 30 Hz for the fixed-vibration group, whereas the frequency for the individualized-vibration group was determined by monitoring the participants' EMGrms activity. The participants in the two vibration groups were exposed three times a week for 8 weeks to a series of 10 x 1-min whole-body vibrations with a 1-min pause between series of vibrations and a 4-min pause after the first five series of vibrations. Jump height in the squat jump increased significantly in all three groups (by 11% for the individualized-vibration group, p=0.001; by 3% for the fixed-vibration group, p=0.011; and by 2% for the control group, p=0.006), but countermovement jump height was not affected. In continuous rebound jumps by the individualized-vibration group, jumping height increased by 22% (p=0.006) and power increased by 18% (p=0.002). The results of this study suggest that the use of an individualized vibration frequency produces a greater response from the neuromuscular system and is more beneficial than vibrations at a fixed pre-selected frequency.

The use of a syncytium model of the crystalline lens of the eye as a new tool to study the light flashes phenomenon seen by astronauts.

A syncytium model to study some electrical properties of the eye is proposed to study the phenomenon of anomalous light flashes (LF) perceived by astronauts in orbit. The crystalline lens is modelled as an ellipsoidal syncytium with a variable relative dielectric constant. The corresponding mathematical model is a boundary value problem for a system of two coupled elliptic partial differential equations in the two unknown syncytial electrical potentials. A numerical method to compute an approximate solution of this mathematical model is used, and some numerical results are shown. The model can be regarded as a new tool to study the LF phenomenon. In particular, the energy lost in the syncytium by a transversing cosmic charged particle is calculated and the results obtained with the syncytium model are compared with those obtained using the previously available Geant 3.21 simulation program. In addition, the interaction of antimatter-syncytium is studied, and the Creme96 computer program is used to evaluate the cosmic ray fluxes encountered by the International Space Station in its standard mission.