Effect of load variation on lower muscle activity and joint torque during parallel squats

The squat is used for strength training of the hip and knee joint muscles. The weight to be lifted is important for multi-joint movement like a squat, because weight differences are thought to directly affect joint load. The purpose of this study is to compare the activity of eight muscles crossing the ankle, knee and hip joints during three kinds of squats with different loads (60%, 75% and 90% of IRM). Eight male athletes performed squats with three different loads. Variables such as net torque, power and work about the joint were calculated only during the ascending phase of each squat. At the same time, surface electrodes was placed over the eight lower extremity muscles, and %iEMG was also calculated during the ascending phase of each squat. Elector spinae and Biceps femoris muscle activity of 90% was significantly greater than at 60%. Gluteus maximus muscle activity at 90% was significantly of 75% and 60%. Mean torque and work on the hip joint increased significantly as load increased from 60% and 75% to 90%. For the knee, mean torque increased significantly from 60% to 90%. These results that a heavy weight like 90% of IRM used in squat exercise increases the load on the hip joint extensor muscles. (Jpn. J. Phys. Fitness Sports Med. 2003, 52 : 89-98).