The Characteristics Of Vibration Transmission On The Skin Surface Of Lower Limbs Under The Effect Of Multi-factors

Objective: Biodynamic response is widely used in the evaluation of vibration effects and safety.It is affected by factors such as excitation characteristics and medium properties.Based on the mechanism of vibration effects such as tonic vibration reflection,this study has investigated the effect of vibration on the skin surface of human lower limbs.The biodynamic response is measured,and multiple factors are analyzed(Factor 1: Vibration intensity;Factor 2: Posture;Factor 3: Calf orientation;Factor 4: Calf location)The transmission characteristics of vibration on the skin surface of the lower limbs(amplitude transmissibility during the transmission process,the range of spacing change between adjacent marker is used as a biodynamic response index),which provides a biomechanical analysis of the human body’s response under vibration.Methods: 15 students from Shanghai University of Sport(age: 23.5±1.4;height: 167.1±6.0cm;weight: 63.4±9.9kg)participant in this research.The kinematic of reflective markers(diameter: 2.5mm)attached to the skin surface of the lower limbs were collected.Four positions of the calf are defined as: Front side: tibial tuberosity to the height of the line connecting the tibial anterior muscle tendon and the medial and lateral malleolus;Back side: popliteal to heel;Medial: medial side of tibial plateau to medial malleolus;Lateral side: outside tibial plateau to the lateral malleolus,16 reflective markers are pasted at equal intervals in each orientation as factors for different positions of the calf.Participants stood on the shaking table in four positions to receive vibrations(knee flexion 10°,knee flexion 30°,knee flexion 60°,forefoot support),and received six vibration intensities in random order(23.4 Hz,1.32 g;30.1Hz,1.75g;35.4Hz,2.31g;40.5Hz,3.00g;45.8Hz,3.63g;51.1Hz,4.32g;g=9.8m/s2)whole body vertical vibration.Using the infrared optical motion capture system,the marker is used as the vibrator on the vibration transmission path,and the coordinates of the calf and the table vibrator are collected at a sampling frequency of 1000 Hz.The single intervention time is 15 s,the vibration intervention interval is 1min,and a total of 24 vibration conditions(4 posture * 6 frequency).Use Fourier transform to fit the z-axis motion trajectory of each vibrator,and calculate the amplitude transmissibility of the vibrator and the range of adjacent vibrator spacing changes(Range of Spacing Change,RSC)based on the parameters obtained by the fitting.Results: The four factors of vibration intensity,posture,orientation and position have no interaction effect on the amplitude transmissibility and RSC,but the combination of any three of them has a significant interaction effect on the transmissibility.Vibration intensity,posture,and orientation have a significant interaction effect on the transmission rate.The post-hoc test found that with the increase of the knee flexion angle,the transmissibility showed an increasing trend.When the vibration intensity reached(2.31 g,35Hz),the transmissibility of the posterior and medial knee joint flexion angle of 30° was significantly higher than that of knee joint flexion 10°(p<0.05).With the increase in intensity,the transmissibility also increased significantly with the increase in knee flexion angle on the front and outside of the calf(p<0.05).For the forefoot support posture,as the vibration intensity increases,the lower extremity transmissibility decreases significantly(p<0.05).Compared with the flexed knee joint,the forefoot transmissibility is lower(p<0.05).Vibration intensity,posture,and position also have a significant interaction effect on the transmissibility.After the inspection,it is found that when the vibration intensity is greater than(45.8Hz,3.63g),there is a significant difference between the three postures.With the increase of,the position of the vibrator with a significant difference is higher.As the knee flexion angle increases,the position of the vibrator with a significant difference is also higher.In this study,the number of significant differences in the transmissibility of the vibrator at different positions on the same side was taken as the degree of non-linearity.After chi-square test,it was found that there was no interaction between posture and orientation(x2=8.272,p= 0.219>0.05),there is an interaction between intensity and orientation(x2=68.341,p<0.05).For another index,RSC,it is affected by vibration intensity,posture and orientation.After the test,it was found that the RSC increased significantly with the increase in knee flexion angle only on the inner and outer sides of the calf(p<0.05),and The RSC on the posterior,medial,and lateral sides were significantly higher than the RSC on the front side of the calf(p<0.05),and this phenomenon became more obvious as the knee flexion angle increased.For the calculation of biological dynamic response,by fitting the spatial coordinates of the vibrator collected by the high-speed infrared optical motion capture system,the average Pearson correlation coefficient of the table vibrator is 0.96,and the average Pearson correlation coefficient of the vibrator on the calf is 0.90.Conclusion: 1.The biodynamic response of the lower limbs is affected by the vibration intensity,the posture when receiving the vibration,the orientation of the calf or location.The influence of the posture is consistent for the four orientations,while the influence of the intensity is not consistent for the four orientations,among them,the biodynamic response of the medial calf is the most sensitive to the change of intensity.2.The influence of 25Hz-50 Hz vibration on the calf is mainly reflected in the lower part of the calf(at the Achilles tendon).Based on mechanisms such as tonic vibration reflection(TVR),the range of spacing change(RSC)is used to support the vibration effect mechanism,ore directly,it may be more meaningful to select the vibration dose by referring to the RSC index.