| Objective: The amount of marathon runners has recently skyrocketed.Correspondingly,running-related injuries were common.Among them,the knee was the most common site,which often occurred during or shortly after a marathon.However,the potential mechanism of knee injury is still unclear.And there was a lack of convenient and feasible equipment to test the biomechanical characteristics of knee joint.Therefore,the purposes of this study were:(1)to propose a new portable system to evaluate knee kinematics in 6 degrees of freedom(6-DOF)and to evaluate knee proprioception.The test-retest reliability was to be clarified.(2)to comprehensively explore the effects of a marathon on the knee biomechanical characteristics and their recovery,including: i).knee proprioception and its recovery;ii).knee muscle strength and the recovery under various contraction modes;iii).knee 6-DOF kinematics during walking and running and the recovery;iv).muscle activation around knee joint during gait.Methods: Three experiments were performed in this study,which covered five studies.The study one was to clarify the test-retest reliability of the new portable knee motion analysis system,including two experiments.In the first experiment,the new system was used to assess the knee kinematics in 6-DOF during gait.10 healthy adults were enrolled.Each completed 6 tests(2 testers × 3 different days).Intraclass correlation coefficients(ICC),standard error of the measurement(SEM),and the Bland–Altman(B-A)method were used to statistically analyze the intra-and inter-rater reliability.In the second experiment,the new motion analysis system and the manual measurement were used to assess the active joint position sense(AJPS)of knee joint.21 adults were tested(2 days × 2 methods)to evaluate the reliability of both methods.The third experiment covered four studies.21 male runners with similar running experience were included through the questionnaire(298 questionnaires collected),who would certainly participate in 2018 Shanghai International Marathon Race.All participants conducted the tests before the marathon(T0),the day after the marathon(T1)and one week after the marathon(T2),respectively.The following biomechanical characteristics were evaluated,including: i)knee proprioception(including kinesthesia,passive joint position sense(PJPS)and AJPS);ii)knee muscle strength with the following modes: isokinetic concentric contraction at 60/120/240 °/s,isokinetic eccentric contraction at 120°/s,as well as isometric contraction;iii)knee 6-DOF kinematics during walking and running;iv)the muscle activation of knee flexors and extensors(including vastus medialis,rectus femoris,vastus lateralis,biceps femoris,semitendinosus,medial and lateral head of gastrocnemius).Another 21 adults were included as the control group for comparing the knee proprioception.Repeated measurement analysis of variance was used to observe the alterations of the biomechanical characteristics.Results: 1.Test-retest reliability:(1)For the evaluation of knee 6-DOF kinematics,intra-rater reliability showed average ICC values ranged 0.78~0.95,average SEM values ranged 1.49°~2.99° for rotations and 1.25mm~3.89 mm for translations,respectively;inter-rater reliability showed average ICC values ranged 0.73~0.94,average SEM values ranged 1.07°~3.33° for rotations and 1.72mm~4.61 mm for translations,respectively.B-A plots showed good consistency.(2)For the evaluation of knee AJPS,the ICC values ranged 0.74~0.80,while the SEM value ranged 0.52° ~ 0.61° using the new method;the ICC values ranged 0.23~0.43,while the SEM value ranged 0.89°~2.07° using manual measurement.The B-A plots showed the agreement was better with the new method than that with manual measurement.2.Proprioception:(1)For kinesthesia,compared with the control,the marathon runners significantly increased(p<0.01);for the marathon group,T0 significantly increased compared with T1 in knee flexion(p<0.001).(2)For PJPS,compared with the control,marathon runners significantly increased(p<0.05).(3)For AJPS, compared with the control,marathon runners significantly increased at knee 60° on T1(p<0.01).The trend within the marathon group was line with the control.3.Muscle strength:(1)For the peak torque,compared with T0,T1 significantly decreased(p<0.05);the values in eccentric contractions were significantly greater than concentric and isometric contractions,respectively(p<0.05);the peak torque of knee extensors significantly increased as the contraction speed decreased(p<0.05).(2)For the peak power,T1 was significantly lower than T0 in concentric contractions of knee flexor(240°/s)and extensor(60°/s and 120°/s)(p<0.05).(3)For total work,T1 was significantly lower than T0 in concentric contractions of knee flexor(60°/s and 240°/s)and extensor(all speed)(p<0.05).T2 partially or completely recovered.4.Knee kinematics: walking and running showed consistent changes.(1)For walking,compared with T0,knee flexion significantly decreased on T1 during early and middle stance phase,as well as middle and end swing phase(p<0.05).Internal rotation was significantly lower on T1 than T0 during initial contact and end swing phase(p<0.05).Anterior translation was significantly lower on T1 than T0 during end phase of stance and swing(p<0.05).(2)For running,knee flexion significantly decreased on T1 during middle stance phase,as well as middle and end swing phase,respectively(p<0.05).Moreover,the range of medial-lateral translation significantly decreased(p<0.05).Distal translation was significantly smaller on T2 than T0(p <0.05).5.The muscle activation functions of knee joint: walking and running showed consistent changes.(1)For the EMG amplitudes,T0 were significantly lower than T2 for knee extensors during initial contact and end swing phase(p<0.05);and for biceps femoris and semitendinosus during end swing phase,medial and lateral head of gastrocnemius during middle stance phase(p<0.05).(2)For MVC test,T0 was significantly lower than T2 for all knee muscles(p<0.05).T1 was significantly lower than T2 for the muscles except for vastus medialis and lateral head of gastrocnemius(p<0.05).(3)For the median frequency,T0 was significantly lower than T1 for the medial head of gastrocnemius during walking,as well as vastus medialis,vastus lateralis and medial head of gastrocnemius during running(p<0.05).(4)For the co-activation,the ratio of knee flexion-extension on T2 was significantly smaller than T1 during running(p<0.05),that is,the co-activation extent was better.Conclusion: 1.For the application of the new motion analysis system to evaluate the knee 6-DOF kinematics,the intra-rater reliability was well.For the evaluation of knee AJPS,the reliability was well and better than the manual measurement.2.Compared with the pre-marathon,the proprioception was not significantly reduced in post-marathon.Kinesthesia was more sensitive in post-marathon,which may be due to neuromuscular regulation.The marathon runners had lower kinesthesia and PJPS than the control,which may be associated with the more cumulative load.3.The peak torque,peak power and total work of the knee flexors and extensors decreased at various speeds and contraction modes after the marathon,which may potentially increase the risk of knee injury.The parameters recovered partially or completely one week after the marathon.4.For the knee kinematics,the flexion significantly reduced during the stance phase,which may increase the risk of knee injury.The changes in the other degrees of freedom mainly be due to the 6-DOF coupling motion and neuromuscular adaptation.5.The muscle activation was the lowest in pre-marathon,followed by the day after the marathon,and the highest one week after the marathon.It indicates that neuromodulation strategies and recovery with time may exist after the marathon running,which result in no reduction of muscle activation after the marathon. |
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