The Electro-mechanical Response Law Of Quadriceps At Different Knee Angles

Purposes: The knee is one of the most important joints, while the patellar buttonenthesiopathy and other knee disease caused great distress to people’s lives. The patellartendon is a continuation of the quadriceps, while the quadriceps is the main device ofthe extension of the knee, so the electro-mechanical law of the quadriceps have a majorimpact on the knee. Surface EMG acquisition and motor response test during isometrictesting of quadriceps at different knee angles, designed to investigate theelectro-mechanical response law of the quadriceps in the different knee angle, and theresponse of fatigue on the electro-mechanical law.Methods: In this study, the isokinetic dynamometer system is used to10subjectswith the maximum isometric knee extension test at different angles, together withsurface EMG acquisition and records on quadriceps. Analysis the surface EMGcharacteristics and motor response characteristics at different angles, and the responseof fatigue.Results:(1) In the isometric knee extension mode, from10°to90°, the quadriceps’PT/BW is the maximum in the knee joint80°, there is a very significant difference(p<0.01).(2) In the isometric knee extension mode, the RT of the quadriceps is decreasing asthe angle increases, and there is a very significant difference (p<0.01); the PMT ofquadriceps has no significant change; the EMD of quadriceps is gradually reduced, andthere is a significant difference (p <0.01)(3) In the isometric knee extension mode, the iEMG VM/VL increases at first andthen decreases as the angle increases, it reaches to the climax at the knee joint40°, butthere is no significant difference (p>0.05); the iEMG%of the vastus medialis and rectus femoris have no significant difference, but at the same angle,40°、50°、60°and90°,three is a very significant difference (p<0.01).(4) After fatigue, the PMTs of vastus lateralis, vastus medialis, rectus femoris aresmaller than before, and it shows a significant difference (p <0.05); the EMDs of vastuslateralis, vastus medialis, rectus femoris are longer than before, and it shows asignificant difference (p <0.05).(5) After fatigue, the iEMG VM/VL reduced, but there is no significant difference(p>0.05); the iEMG%s of the vastus lateralis and vastus medialis reduce but nosignificant difference (p>0.05), the iEMG%of rectus femoris increase, and there is asignificant difference (p<0.05); the contribution of the vastus medialis muscle is thesmallest, the three show a very significant difference (p<0.01).Conclusions:(1) In some hip angle, in the isometric knee extension mode, from10°to90°, theknee extensor power reach to the climax at knee joint80°.(2) The quadriceps reaction rate is related with knee joint angle, to a certain extent,knee angle increases, resulting in faster movement speed.(3)At different knee joint angles, each muscle’s contribution of quadricep isdifferent, after knee joint40°, the vastus lateralis is the main contribution muscle.(4) Fatigue is an important factor in causing EMD to extend.