Effects of vibration frequency and postural changes on human responses to seated whole-body vibration exposure

Abstract

The present investigation evaluated the effects of changes in pelvic orientation and vibration frequency on the seated human's response to wholebody vibration (WBV). Seat-to-trunk and seat-to-head acceleration transmissibility, peak-to-peak pelvic motion and erector spinae EMG and mean erector spinae EMG was collected across three pelvic orientations (9 degrees anterior pelvic tilt, neutral pelvis, and 9 degrees posterior pelvic tilt) and frequencies ranging from 4.5 to 16 Hz. Subjects included 30 healthy males between the ages of 18 and 35. Ensemble averages, two vibration cycles in length, were produced for each subject within each frequency-pelvic orientation combination. Group ensemble averages within each frequency-pelvic orientation combination were then compared using ANOVA. Changes in pelvic orientation produced significant differences in acceleration transmissibility, pelvic motion, and erector spinae EMG. At frequencies below 6 Hz, acceleration transmissibility at the head and pelvic motion were significantly greater in the posterior pelvic orientation than in the other two. At frequencies above 6 Hz, acceleration transmissibility at the head and trunk were significantly greater in the anterior pelvic orientation than in the other two. Peak-to-peak EMG responses were similar across all pelvic orientations at frequencies below 6 Hz. However, above 6 Hz, the response was significantly greater in the anterior pelvic orientation than in the other two. Thus, vibration frequency and pelvic orientation were shown to have significant interactive effects on the seated human's response to WBV. These interactive effects need to be considered when determining appropriate vibration exposure guidelines.

Effect of Backrest and Torso Twist on the Apparent Mass of the Seated Body Exposed to Vertical Vibration

“…Several studies have been reported that show EMGs of back muscles whilst exposed to vibration [19][20][21] . These consistently show a muscular response that is correlated to the driving acceleration.…”

Study of the biodynamic response of the foot to vibration exposure

“…Second, although participants' foot placement was controlled and all were given the same instruction with regard to how to stand, it could not be confirmed that all participants' maintained the same posture throughout the 45-second FTV exposure period. Deviations in posture can influence vibration transmissibility due to changes in the surface contact area with the vibrating surface, which can influence the position of the bony structures and the degree of tension in different muscle groups of the trunk and the extremities, in turn changing the resonant frequency of the body structure [1,19,21,25,36,[38][39][40][41]. Thus, variations in the ankle and knee angles could have influenced the transmission of vibration from the platform through the feet and into the lower limbs.…”

A Quasi-static Discomfort Measure in Whole-body Vibration

“…With WBV, the scenario is different because many parameters, such as frequency and human-machine interface, can affect discomfort. Also, there is a significant contribution of posture to discomfort measures in WBV [7][8][9][10][11] . However, all studies in this regard consider posture as a static form and instruct the subjects to maintain the same posture during the testing.…”