| Purpose The purpose of this study was to determine the changes in the lower extremity kinematics, ground reaction forces, and frequency content of the vertical ground reaction forces under the fatigue condition and the difference between two fatigue protocols during a landing task in order to provide a preliminary reference for the selection of fatigue protocols in laboratory tests.MethodFifteen trained male athletes(age: 20.9 ± 0.8 years, height: 175.5 ± 4.2 cm, mass:68.9 ± 5.5kg) volunteered to participate in the study. Two fatigue protocols, namely,constant speed running(running) and shuttle running + maximal vertical jumping(running + jumping) fatigue protocol separately, were randomly used to induce fatigue.The running fatigue protocol required participants to run at 4.0 m/s on a treadmill until fatigue. The running + jumping fatigue protocol required participants to first perform five consecutive countermovement jumps within a height above 70% of their maximal vertical jump height then completing a group of shuttle running(6×10 m)with their maximal effort. Participants repeated the said process until the average height of five consecutive countermovement jumps was below 70% of their maximal vertical jump height. Before and after the fatigue protocols, each participant was required to execute five successful trials of drop landings from a 60 cm platform. The3 D kinematics(Vicon, 240 Hz) of the dominant leg and ground reaction force(GRF)(Kistler, 1200 Hz) were measured simultaneously. The main variables included 1) the sagittal and frontal joint kinematics of the hip, knee, and ankle. 2) the maximal vertical ground reaction force(vGRF), the peak loading rate and the time to reach the above two measures during the impact phase of landings. 3) the frequency content of the vGRF. Paired t-test were used to determine the influence of independent variable(fatigue) on each of the dependent variables using SPSS 13.0(SPSS Inc., Chicago, IL,USA). The significance level was set at a = 0.05.Result1) Effects of fatigue on the kinematics of sagittal plane in the lower extremity during landingFor the joint angle characteristics, post-tests using both fatigue protocols showed a significant decrease in the minimum angle of hip and knee joints, and an increase in the range of motion of these two joints compared to pre-tests. Post-tests using running fatigue protocol showed a significant increase in the maximum angle of hip joint.Post-tests using running + jumping fatigue protocol showed a significant increase in the range of motion of ankle joint.For the joint angular velocity characteristics, post-tests using running fatigue protocol showed a significant decrease in the maximum angular velocity of ankle joint.Post-tests using running + jumping fatigue protocol showed a significant increase in the maximum angular velocity of knee joint.2) Effects of fatigue on the kinematics of frontal plane in the lower extremity during landingFor the joint angle characteristics, post-tests using running fatigue protocol showed a significant increase in the maximum angle of knee joint. Post-tests using running + jumping fatigue protocol showed a significant increase in the range of motion of hip joint.For the joint angular velocity characteristics, Post-tests using running + jumping fatigue protocol showed a significant decrease in the minimum angular velocity of both hip and knee joints.3) Effects of fatigue on the impact force, frequency content of vertical ground reaction force during landingFor impact forces, no changes were found in the peak vGRF, peak loading rate,and the time these two indicators were reached in both pre- and post-tests for both fatigue protocols.For frequency content of the vGRF: the results of post-tests using the running fatigue protocol showed lower amplitude than the results of pre-tests for frequencies at 3.51 Hz and 8.20 Hz. The results of post-tests using the running + jumping fatigueprotocol showed lower amplitude than the results of pre-tests for frequencies at 1.17Hz、3.51 Hz and 7.03 Hz.Conclusion1) Both running and running + jumping fatigue protocols would induce a decrease in the minimum angle of hip and knee joints, and an increase in the range of motion of these two joints which resulting in a more flexed landing posture. The differences between the effect of two fatigue protocols lie in that running and jumping fatigue protocol exert an influence on joint angle of three joints(hip、knee、ankle) while the effect of running fatigue protocol is limited to the hip and knee joints. From the perspective of intervention time, the time of running and jumping fatigue protocol is shorter than that of running. In conclusion, compared to running fatigue protocol,running and jumping fatigue protocol bring about shorter time and better effect; from the perspective of experimental methodology, running and jumping fatigue protocol have more advantages.2) No changes were found in the peak vertical ground reaction force and peak loading rate between pre- and post-test for both fatigue protocols which suggested that the magnitude of the impact force may not be the cause of injury. However, post-tests using both fatigue protocols showed lower amplitudes than pre-tests at some low frequency components indicate that frequency content of the vertical ground reaction force may work as a means of evaluating fatigue. |
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