Activity Characteristics Of Major Knee Muscles And Mechanical Characteristics During Different Modes Of Flexion And Extension Exercise

Porpose:Knee is one of the most important joints,whose main funtion is flextion and extention.Exercises were carried out on a isokinetic machine,and at the same time bipolar electromyographic signals(sEMG)were recorded from surface electrodes on major muscles of knee.The aim of this study was to verify the mechanical characteristics of knee and the activity characteristics of knee muscles during flexion and extension exercise.Methods:Twelve young healthy men volunteered to participate in the study. Paticipants were requested to perform the following tasks:(1)maximal voluntary isometric contractions at knee joint 30°,45°,60°,75°and 90°(0°=full extention);(2)maximal flextion and extention isokinetic concentric contraction at 60°,120°,180°and 240°/s; (3) maximal flextion and extention isokinetic eccentric contraction at 60°,120°and 180°/s. Simultaneously,the sEMG signals were recorded from retus femoris(RF),vastus medialis(VM),vastus lateralis(VL),semitendinous(ST),biceps femoris(BF),gastrocnemius medialis(GM) and gastrocnemius lateralis(GL)muscles.Peak torque(PT) and average power(AP) were calculated as mechanical parameter; Normalized root mean square(RMS)of sEMG was calculated as an index of sEMG amplitude.Results:1.In maximal voluntary isometric contraction mode,the torque of knee flexors gradually decreases from the knee joint 30°to 90°;the torque of knee extensors first increases and then decreases(reaches to the climax at the knee joint 75°)。2.In isokinetic concentric mode,PT and relative PT both significantly reduce from 60°/s to 240°/s during both flextion and extention exercises(P<0.05);H/Q of knee increases slightly from60°/s to 240°/s;but AP shows a remarkable increasing from 60°/s to 240°/s.3.In isokinetic eccentric mode,PT and relative PT of both flexors and extensors see a slight decreasing from 60°/s to 180°/s,but it has no significant difference(P>0.05);However,AP shows a significant increasing (P<0.05).4. In maximal voluntary isometric contraction mode,RMS of knee extensors all first increase and then decrease from knee 30°to 90°,but RMS of VL and VM is up to a maximum value at knee joint 75°,RMS of RF is up to a maximum value at knee joint 45°;RMS of BF anf ST gradually decreases from knee joint 30°to 90°,however RMS of GL and GM has no significant difference.5. In isokinetic concentric mode,RMS of knee extensors all first increase and then decrease as knee moving from 30°to 90°,but RMS of VL and VM reach top value at knee joint 65°, RMS of RF reaches top value at knee joint 55°;RMS of BF anf ST first increase and then decrease(reaches to the climax at the knee joint 55°),RMS of GL and GM also first increase and then decrease(reaches to the climax at the knee joint 65°).6. In isokinetic eccentric mode,RMS of knee flexsors all first increase and then decrease as knee moving from 30°to 90°,but RMS of VL and VM reach top value at knee joint 75°,RMS of RF reaches top value at knee joint 55°;RMS of BF anf ST first increase and then decrease(reaches to the climax at the knee joint 45°),RMS of GL and GM also first increase and then decrease(reaches to the climax at the knee joint 55°).Conclusions:1.In maximal voluntary isometric contraction mode,knee entensors reach to the maximun strength at knee joint 75°;Strength of knee flexsors gradually decreases from knee joint 30°to 90°.2.In isokinetic concentric mode,strength of knee flexsors and extensors decrease with the increase of joint speed;H/Q of knee incrases with joint speed;AP also increases with joint speed.3. In isokinetic eccentric mode,strength of knee flexsors and extensors has no significant difference with the increase of joint speed. 4.Activation of the knee muscle has certain law with the increase of joint angle under different sports modes.Activation pattern of different muscle shows a evident difference.5.Activation of VL is higher than that of VM; Activation of BF is higher than that of ST.So VL makes larger contribution to knee extention than VM;BF makes bigger contribution to knee flextion than ST.