The Effect of Different Muscle Strength on the Transmission of Impact Vibration in Human Body
|School||Shanghai Institute of Physical Education|
|Course||Human Movement Science|
|Keywords||Impact Vibration Joint Torque Muscle Activity Knee Angle Acceleration Vibration Transmission|
Background:During exercise in the human body, impact vibration waves generated along the body and on the next spread, due to physical differences between different individuals. Lower limb muscle strength will be different, the vibration transmission in the human body will also have Corresponding impact.Purpose:Two groups whose lower limb muscle strength are different, through changing the test control conditions:load, impact wave magnitude and knee angles. In the different experimental conditions, to discuss the transmission characteristics of impact vibration in the human body and the lower limb muscles response to the impact vibration.Methods:According to the experimental purposes, through reading the related literatures, there are 16 subjects for the study, eight of them are athletes, the others are ordinary people. The subjects upright stand on the surface of the vibrator, using the angle and the bar which is made by myself, to control the experimental conditions, the knee position maintained at 90°,120°,150°and 180°. They take the weight in 0% BW,10% BW,20% BW and 30% BW. DY-600-5 produce acceleration in 2 and 4,using shaking table speed of subjects produce 2g and 4g (duration 20ms) of the triangular wave shock and vibration. Experiment was divided into two groups, according to the experimental conditions change, a total of 32 conditions. During the experiment, using Endevco accelerometer (sampling frequency of 2000hz) shaking table collecting surface, the lateral malleolus, knee joint center and the fourth lumbar vertebra the vertical component of acceleration. Dasylab produced by Biovision acquisition system recorded test EMG tibialis anterior muscle, gastrocnemius, vastus medialis, rectus femoris, vastus lateralis, biceps femoris and gluteus maximus muscle surface, the angle meter to use measuring the angle of the knee in the experiment variation.Results:(1) In the experiments, the largest vibration attenuation is from the tibia to the fourth lumbar spine. The In the experimental conditions 0kg4g90°,15kg4g120°, 10kg4g90°, The vibration attenuation from the knee center to the fourth lumbar vertebra is significant (p<0.05). Attenuation is 55.7±6.08% and 45.31±20.2% and so on. With the changes of the input impact vibration, vibration attenuation will increase, but when it come to 5kg, it is the biggest impact and the greater attenuation from the center of the knee to ankle. With the increase of knee flexion, vibration attenuation is gradually increased, but from the waist to the knee, the most greatest attenuation is when the knee angle 150°, but the knee-ankle-decay, the attenuation is the most powerful in the knee 90°. In addition to 120°and 150°,the knee-ankle-decay is not significant, the other departs of attenuation in the waist-knee attenuation, knee-ankle-attenuation and ankle-plate form attenuation were significant differences.(2) From the knee angle, with the increase of weight, the knee angle tends to decrease. In the normal group, this trend is obviously. However between the two groups don’t have significant differences. With the knee angle increasing in the impact experimental process, the knee angle movement increases, it is maybe with the knee flexion angle increases, to reduce the damage to the torso and head, people don’t need to increase the knee flexion angle to attenuate the vibration. Except the 150°and 180°, the other groups in different angles are significant. The different magnitudes of impact have a very significant difference to the changes of the knee angle. Whether the ordinary group or the exercise group,2g and 4g are significant differences, but between the two groups, there is no significant difference, with increasing the impact magnitude, people will increase the knee flex angle to decrease the magnitude of vibration.(3) In the delaying time of the peak vibration, the weight factor only has significant different when comparing the time delaying on the waist-knee between the 0% BW and 30% BW. There is no significant in time delayed when the knee angle changes. However, when the knee angle is 150°, the time delayed is obverse short. There is a significant different between the two groups. in these conditions, the force of the lower limb muscles changing, leading to lower extremity stiffness increases, the transmission speed up in it. The impact factor only has a significant differences on time delayed in ankle-plateform. in waist-knee and knee-ankle, there is a trends that the time delayed increases with the impact growing trend, but there is not a significant.(4) In the same experimental conditions, there is a signifitient different between the two groups in the vastus medialis. Gastrocnemius and rectus femoris.the tibialis anterior muscle will have much activity when the impact increasing or the knee angle decreases. The normal group has a significant difference when the weight factor changes. The exercise group has a significant difference in the angle and impact; the gastrocnemius EMG activity will increased gradually when the increasing the weight or the knee angle increasing.(5) Vastus medialis and vastus lateralis will increase activity when the knee angle decreasing or the bigger impact. The EMG activity of the normal group will exerse obviously under the same conditions, the EMG activity have a significant between the normal group and the exercise group. The weight bigger,the electromyographic activity stronger. Vastus medialis has a significant difference between the two groups; the rectus femoris shows a trend that with the weight, impact and knee flexion increase, the muscle activities rising. However, there is no significant difference; the gluteus maximus and biceps femoris activity will increase when the weight increasing, the main role in the maintenance of joints.Conclusion:(1)Lower limb muscle strength influce to the vibration attenuation, time delayed,in the same conditions, the larger muscle strength,the more vibration attenuation, the shorter time delayed. In the impact vibration, the people whose lower limb muscle strength is large changes a small knee angle.(2) In the experiments, the lower limb muscle strength can better control the knee angle, with the load and the impact increasing, the knee changing angle became bigger during the impact experiment, to increase the amount of vibration attenuation, Reducing the transmission of acceleration to the upper body.(3) When the transmission process of vibration waves transmit from bottom to up in the human body, the peak acceleration of impact vibration gradually decreases with distance increasing. The largest part of its fading is from the lateral ankle to the fourth lumbar vertebra. Therefore, the major part of the human body which cushion the impact force is the knee joint and the hip joint, the ankle joint has a certain buffer attenuation, but it isn’t very obverse. the vibration transmission from the lateral ankle to the fourth lumbar vertebrae is major related to knee flexion primarily. When the knee flexion angle increases, the vibration attenuation increasing and the vibration transmit fast in human body.