The Effects Of Stride Frequency On The Muscle Tunning And The Stiffness Of Lower Limbs During Running

ObjectiveThis study integrated application of biomechanics of dynamics and kinematics methods and methods of electric technology to discuss the changes of muscle tuning and the stiffness of lower limbs in the course of the running of different stride frequency.Understanding the mechanism of neuromuscular regulation during running on different stride frequency,,and the mechanism of muscle tuning in preventing sports injury.Put forward rationalization suggestion to runners.Methods21 male college students were recruited in this research,running with 2.5±0.2m/s),3.25±0.2 m/s,4±0.2 m/s.8 cameras high-speed infrared motion capture system(Qualisys,200Hz)?three-dimensional force plates and sEMG(Delsys,2000Hz)were synchronized to collect kinematic,kinetics and iEMG signals.According to the measured running frequency,the subjects were divided into low frequency group and high frequency group.The lower limb stiffness was calculated according to the maximum reaction force in the vertical direction and the vertical displacement of the center of gravity.Muscle tuning was analyzed according to the integrated electromyography(iEMG),root-mean-square amplitude(RMS)and the muscle vibration frequency of 0-100 ms and 100-200 ms after the maximum impact on the lower limb.Results1.The high frequency group shows shorter stride length,gait cycle time.(p<0.05),and stance duration(p<0.01 at slow speed).During stance duration,the high frequency group shows deeper center of mass vertical excursion(p<0.05 at 2.5m/s and 4m/s,p<0.01 at 3.25m/s),and smaller kneeflexion and extension(p<0.01 at 3.25m/s,p<0.05 at 4m/s),internal rotation and external rotation,ankle varus valgus,internal rotation and external rotation.At the moment of landing,the high frequency group shows greater hip,knee abduction,ankle varus,larger knee internal rotation,and smaller hip internal rotation,ankle flexion dorsiflexion(p<0.05 at 3.25m/s,4m/s),and the external rotation(p<0.01 at 2.5m/s and p<0.05 at 3.25m/s).At the moment of leaving the ground,the high frequency group shows greater hip flexion and extension,adduction and abduction(p<0.05 at 3.25m/s,p<0.01 at4m/s),smaller knee abduction,ankle varus.At the moment of maximum ground reaction force,the high frequency group shows greater hip flexion and extension,knee adduction abduction,internal rotation external rotation,smaller hip adduction,and ankle internal rotation angle(p<0.05 at3.25m/s).2.During the support period,the high frequency group shows deeper stiffness at the stretching stage.3.The higher the running frequency,the smaller the RMS during support period(GM p<0.05 at 3.25m/s),50 ms before landing(BF p<0.05 at 3.25m/s)and 50 ms after landing(GM p<0.05 at 3.25m/s).4.IEMG during 50 ms before landing is less than 50 ms after landing(RF,TA,GM at 2.5m/s,BF,TA at 3.25m/s,BF,RF,TA at 4m/s p<0.01,GM at 2.5m/s,RF,GM3.25m/s p<0.05).5.The muscle vibration frequency during 100-200 ms phase after the first peak of the ground reaction force was significantly reduced during the 0-100 ms phase(all of the muscles shows p<0.01 at three speeds).The low frequency group and the high frequency group show the same trend.6.In the high frequency group,the vibration frequency of the muscles during the0-100 ms and 100-200 ms phases after the first peak time is lower than that in the low frequency group(BF,RF,TA at 2.5m/s,BF at 4m/s p<0.05 during 100-200 ms phases).Conclusion and Suggestion1.Running frequency has an effect on time and space parameters and joint angle.2.Different running frequencies have no influence on the ground reaction force of lower limbs.3.The adjustment of the lower limb stiffness is mainly manifested in the active stretching stage,and the lower limb stiffness of the low frequency group is greater.4.Muscle tuning is mainly manifested in the buffer phase,and the muscle tuning effect of the low step group is more obvious.5.The adjustment of the lower limb stiffness mainly plays a role in the stretching stage,and the muscle tuning mainly acts in the buffer stage.6.It is recommended that when people run for fitness,they should try to choose a relatively high stride frequency at the same speed,while runners who are used to lower stride frequency should choose more professional sports equipment to reduce the risk of sports injury.