A COMPARISON OF TIBIOFEMORAL JOINT FORCES AND ELECTROMYOGRAPHIC ACTIVITY DURING OPEN AND CLOSED KINETIC CHAIN EXERCISES

We chose to investigate tibiofemoral joint kinetics (compressive force , anteroposterior shear force, and extension torque) and electromyogra phic activity of the quadriceps, hamstring, and gastrocnemius muscles during open kinetic chain knee extension and closed kinetic chain leg press and squat. Ten uninjured male subjects performed 4 isotonic repe titions with a 12 repetition maximal weight for each exercise. Tibiofe moral forces were calculated using electromyographic, kinematic, and k inetic data. During the squat, the maximal compressive force was 6139 +/- 1708 N, occurring at 91 degrees of knee flexion; whereas the maxim al compressive force for the knee extension exercise was 4598 +/- 2546 N (at 90 degrees knee flexion). During the closed kinetic chain exerc ises, a posterior shear force (posterior cruciate ligament stress) occ urred throughout the range of motion, with the peak occurring from 85 degrees to 105 degrees of knee flexion, An anterior shear force (anter ior cruciate ligament stress) was noted during open kinetic chain knee extension from 40 degrees to full extension; a peak force of 248 +/- 259 N was noted at 14 degrees of knee flexion. Electromyographic data indicated greater hamstring and quadriceps muscle co-contraction durin g the squat compared with the other two exercises. During the leg pres s, the quadriceps muscle electromyographic activity was approximately 39% to 52% of maximal velocity isometric contraction; whereas hamstrin g muscle activity was minimal (12% maximal velocity isometric contract ion). This study demonstrated significant differences in tibiofemoral forces and muscle activity between the two closed kinetic chain exerci ses, and between the open and closed kinetic chain exercises.