Finite Element Investigation of the Effects of the Low-Frequency Vibration Generated by Vehicle Driving on the Human Lumbar Mechanical Properties.

Long-term exposure to low-frequency vibration generated by vehicle driving impairs human lumbar spine health. However, few studies have investigated how low-frequency vibration affects human lumbar mechanical properties. This study established a poroelastic finite element model of human lumbar spinal segments L2-L3 to perform time-dependent vibrational simulation analysis and investigated the effects of different vibrational frequencies generated by normal vehicle driving on the lumbar mechanical properties in one hour. Analysis results showed that vibrational load caused more injury to lumbar health than static load, and vibration at the resonant frequency generated the most serious injury. The axial effective stress and the radial displacement in the intervertebral disc, as well as the fluid loss in the nucleus pulposus, increased, whereas the pore pressure in the nucleus pulposus decreased with increased vibrational frequency under the same vibrational time, which may aggravate the injury degree of human lumbar spine. Therefore, long-term driving on a well-paved road also induces negative effects on human lumbar spine health. When driving on a nonpaved road or operating engineering machinery under poor navigating condition, the auto seat transmits relatively high vibrational frequency, which is highly detrimental to the lumbar spine health of a driver.

High-frequency and low-magnitude whole body vibration with rest days is more effective in improving skeletal micro-morphology and biomechanical properties in ovariectomised rodents.

We explored the optimal regime in preventing or treating bone loss, using ovariectomised rodents loaded by mechanical stimuli with rest days during the loading cycle. Eighty-four Sprague-Dawley rats, aged 6 months, were randomly divided into 7 groups after bilateral ovariectomy. Mechanical vibration with 1-day rest (ML1R), with 3-day rest (ML3R), with 5-day rest (ML5R), with 7-day rest (ML7R), daily loading (DL), comparing the ovariectomised group (OVX) with baseline (BCL) measurements. After a recovery of one week, all the rodents were loaded daily by whole body vibration at 35 Hz and 0.25 g for 15 minutes. Eight weeks later, a three-point bending test of the radius and micro-CT scanning of the femoral head were performed after animal sacrifice. Large improvements in biomechanical properties occurred in all the experimental groups for failure load, elastic modulus and deflection, while a significantly enhanced efficacy was detected in ML7R compared with daily loading (p<0.05). In micro-CT scanning, bone volume fraction, trabecular thickness, number and separation were improved by the regime in all experimental groups, while ML7R showed a significant improvement over daily loading (p<0.05). Early bone loss in human subjects may be improved by high-frequency and low-magnitude whole body vibration with rest days or daily stimuli. Mechanical stimulus with a 7-day rest was more effective in improving biomechanical properties and micro-morphology compared with daily loading. This may have clinical implications in relation to the prevention and treatment of hip fractures, and in postoperative management following hip arthroplasty.