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

Abstract

[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.

Keywords: Gravitational physiology; Skeletal muscle function; Tonic vibration reflex.

Figures

Fig. 1.

Experimental setup of simulation 1. (A) Upper figure: the horizontal line represents the position of the tip of the pen prior to WBV. (B) Middle and (C) lower figures: the vertical lines show that the elastic band simulated muscle movement in both the upward and downward directions during WBV. The displayed trace was plotted during 25 Hz WBV.

Fig. 2.

Measurements of the reflex latencies. Representative latency values of one male participant. The solid circle represents the onset of the EMG spike, and the open circle represents the stimulus onset point. The dotted arrow represents the positive peak of the time derivative of the rectified EMG that was used as the trigger to average the accelerometer data and the rectified EMG data. The solid square shows the lowest position of the vibration platform during the vibration cycle and the onset point of the increase in force of the upward thrust of the platform. The mean time difference between the stimulus onset and the lowest position of the vibration platform was 3.5 ± 1.9 ms (n = 20). ACC: acceleration

Fig. 3.

Simulation 2. (a) Platform Accelerometer Record: the peak appears at a vibration frequency of 50 Hz. (b) Stretch Sensor Record: the sensor stretches two times during a complete vibration cycle, once during the upward movement and once during the downward movement. (c) Stretch Sensor Record (Rectified): the cumulative frequency of the upward and downward stretches was 100 Hz. (d) SEMG Record: the rectified SEMG; the vertical arrows separate the vibration cycles in the time domain traces.

Fig. 4.

Measurements of the reflex latencies using the method of Ritzmann et al.14). Drawn using data from the present study, this figure illustrates that the time period between the lowest point of the vibration platform and the onset of the first spike in the EMG signal varies depending on the frequency of vibration. The vertical arrow indicates the lowest point of the vibration platform.