Vibration-related extrusion of capillary blood from the calf musculature depends upon directions of vibration of the leg and of the gravity vector.

PURPOSE: In this study, we investigated the effects of vibration of the whole lower leg on the content and the oxygenation of hemoglobin in the unloaded relaxed lateral gastrocnemius muscle. Vibration was applied orthogonal to and in parallel with leg axis to examine whether the extrusion of blood depends on an alignment of main vessel direction, axis of vibration and gravity. METHOD: The blood volume in the muscles was altered by horizontal and 30° upright body posture. Fifteen male subjects were exposed to 4 sets of experiments with both vibration directions and both tilt angles applied in permutated order. The absence of voluntary muscular activity and the potential occurrence of compound action potentials by stretch reflexes were monitored using electromyography. Total hemoglobin and tissue saturation index were measured with near infrared spectroscopy. Changes of lower leg circumference were measured with strain gauge system placed around the calf. RESULT: Vibration caused decrease in tHb and increase in TSI indicating extrusion of predominantly venous blood from the muscle. In 30° tilted position, muscles contained more blood at baseline and vibration ejected more blood from the muscle compared with horizontal posture (p < 0.01). At 30° tilting deeper drop in tHb and steeper increase in TSI (p < 0.01) were observed when vibration was applied in parallel with the length axis of muscle. CONCLUSION: It is concluded that the vibration extrudes more blood in 30° head up posture and the vibration applied in parallel with the length axis of the muscle is more effective than orthogonal vibration.

Vibration parameters affecting vibration-induced reflex muscle activity.

PURPOSE: To determine vibration parameters affecting the amplitude of the reflex activity of soleus muscle during low-amplitude whole-body vibration (WBV). MATERIALS AND METHODS: This study was conducted on 19 participants. Vibration frequencies of 25, 30, 35, 40, 45, and 50 Hz were used. Surface electromyography, collision force between vibration platform and participant's heel measured using a force sensor, and acceleration measured using an accelerometer fixed to the vibration platform were simultaneously recorded. RESULTS: The collision force was the main independent predictor of electromyographic amplitude. CONCLUSION: The essential parameter of vibration affecting the amplitude of the reflex muscle activity is the collision force.

Tendon reflex is suppressed during whole-body vibration.

In this study we have investigated the effect of whole body vibration (WBV) on the tendon reflex (T-reflex) amplitude. Fifteen young adult healthy volunteer males were included in this study. Records of surface EMG of the right soleus muscle and accelerometer taped onto the right Achilles tendon were obtained while participant stood upright with the knees in extension, on the vibration platform. Tendon reflex was elicited before and during WBV. Subjects completed a set of WBV. Each WBV set consisted of six vibration sessions using different frequencies (25, 30, 35, 40, 45, 50Hz) applied randomly. In each WBV session the Achilles tendon was tapped five times with a custom-made reflex hammer. The mean peak-to-peak (PP) amplitude of T-reflex was 1139.11±498.99µV before vibration. It decreased significantly during WBV (p<0.0001). The maximum PP amplitude of T-reflex was 1333±515µV before vibration. It decreased significantly during WBV (p<0.0001). No significant differences were obtained in the mean acceleration values of Achilles tendon with tapping between before and during vibration sessions. This study showed that T-reflex is suppressed during WBV. T-reflex suppression indicates that the spindle primary afferents must have been pre-synaptically inhibited during WBV similar to the findings in high frequency tendon vibration studies.

Whole-body vibration-induced muscular reflex: Is it a stretch-induced reflex?

[Purpose] Whole-body vibration (WBV) can induce reflex responses in muscles. A number of studies have reported that the physiological mechanisms underlying this type of reflex activity can be explained by reference to a stretch-induced reflex. Thus, the primary objective of this study was to test whether the WBV-induced muscular reflex (WBV-IMR) can be explained as a stretch-induced reflex. [Subjects and Methods] The present study assessed 20 healthy males using surface electrodes placed on their right soleus muscle. The latency of the tendon reflex (T-reflex) as a stretch-induced reflex was compared with the reflex latency of the WBV-IMR. In addition, simulations were performed at 25, 30, 35, 40, 45, and 50 Hz to determine the stretch frequency of the muscle during WBV. [Results] WBV-IMR latency (40.5 ± 0.8 ms; 95% confidence interval [CI]: 39.0-41.9 ms) was significantly longer than T-reflex latency (34.6 ± 0.5 ms; 95% CI: 33.6-35.5 ms) and the mean difference was 6.2 ms (95% CI of the difference: 4.7-7.7 ms). The simulations performed in the present study demonstrated that the frequency of the stretch signal would be twice the frequency of the vibration. [Conclusion] These findings do not support the notion that WBV-IMR can be explained by reference to a stretch-induced reflex.

The effect of single extremity-vibration on the serum sclerostin level.

[Purpose] Sclerostin is mechanosensitive protein that is produced exclusively by osteocytes. It was reported that the plasma sclerostin level increases in the 10th minute after the application of Whole-Body Vibration. The aim of this study was to determine whether single extremity-vibration induces any change in the serum sclerostin level. [Subjects and Methods] Eight healthy young-adult volunteers were recruited for this pilot study. The participants sat on a chair with their left hip and knee joints flexed at 90 degrees. The lower leg was exposed to vibration: 40 Hz, 4 mm, 60 s. Blood samples were collected before and after the vibration. The serum sclerostin levels were blindly measured in dual-controlled blood samples. [Results] The serum sclerostin level before vibration was 328.2±589.9 pg/ml, and it showed no significant change after vibration. [Conclusion] Unlike Whole-Body Vibration, Single-Extremity Vibration did not affect the serum sclerostin level significantly. This finding can be explained by the limited bone volume exposed to vibration. Bone volume exposed to vibration is less during Single-Extremity Vibration than during Whole-Body Vibration.