OBJECTIVES: During a longer car drive there are changes in rheological properties of driver's or passenger's connective tissues taking place as a consequence of monotonous and vibration load. These changes show more among the pregnant drivers, whose motion system is under heavier demands due to pregnancy. To asses these changes we have used the TVS (transfer vibration through the spine) method. METHODS: The TVS is based on application of γ excitation pulses with half-length 5 ms and then harmonic excitation continuously periodically changing from 5 Hz to 160 Hz on C7 and L5 vertebrae. This wave is transferred along the axial system and the acceleration of all the spinous tips of the vertebrae, along which the waves spread between C7 and S1, is detected by accelerometric sensors. The measurement was carried out on three drivers before and after a 4-hours driving. The same measurements of wave transfer along the spine with just one pregnant woman were carried out in th 16th, 26th and 32nd week of pregnancy. Consequently we constructed a simplified model of the spine in order to analyze gathered data by discovering elementary properties of the measured system. RESULTS: After both vibration and physical load there is a more significant dampening of the spinal tissues apparent, i.e. lower acceleration amplitude and the tissues resonance frequency also shifts towards the lower frequencies. On the other hand after long lasting relaxation on a bed an opposite tendency showed, the acceleration amplitude was higher, tissues were relaxed and dampening was lower. The same tendency manifested among the pregnant women. The influence of progressing pregnancy on the spinal segment transfer function showed through a shifting of peaks above 20Hz. Their size also changes monotonously. An absorption area moves towards higher frequencies, rigidity of axial system connections grows. CONCLUSION: The results say that drivers, including pregnant women, show changes in mechanical properties of examined tissues before and after vibration or other type of load. Or conversely before and after relaxation on a bed. Results of this work will be further analyzed, verified and evaluation procedures will be improved. We expect to find dependencies between excitation and resonance frequencies during the transfer via the axial system, the rheological properties of the axial system components and the physical nature of the load of the axial system. They are then going to be applicable for the prevention of injuries of the axial system, physiotherapy practices in the rehabilitation of post-operative conditions, the dosage of training loads of athletes, in determining the effects of job stress regimes and their prevention.

Department of Anatomy and Biomechanics Charles University Prague Czech Republic