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 1RM) . 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 1RM used in squat exercise increases the load on the hip joint extensor muscles.

The purpose of this study was to compare hip and knee joint extension torque and the activity of eight muscles around the hip and knee joints during three squat exercises with different movements.
Ten male athletes performed three different squats (Normal squat : NS, Knee push squat : KPS, Hip drive squat : HDS) . KPS is the type of squat which emphasizes knee joint movement without moving the hip joint position back and forth. On the other hand, HDS is the type of squat which emphasizes hip joint movement, while keeping the knee joint position fixed. Kinematic and kinetic variables such as angle, angular velocity, net torque and power of the joints of the lower extremity were calculated during the descending and ascending phase of each squat. At the same time, surface electrodes were placed on eight muscles of the lower extremity, and %iEMG was also calculated during the same phases.
During the descending phase, Elector spinae muscle activity and hip joint extension torque was significantly greater for HDS than KPS. Rectus femoris and Vastus lateralis muscle activity was significantly greater for KPS than HDS. In addition, KPS showed significantly greater knee joint extension torque than HDS and NS. At the ascending phase, Elector spinae, Glueus maximus and Biceps femoris muscle activity, and hip joint extension torque was significantly greater for HDS than KPS and NS. Rectus femoris muscle activity and knee joint extension torque was significantly greater for KPS than HDS and NS.
These results suggest that HDS is effective for selectively training the hip extensor, and KPS is effective for training the Rectus femoris muscle.

A study was conducted to investigate the relationships among changes of joint torque of the lower limbs, sprint ability such as sprint speed, stride length and stride frequency in 400 m running, and muscular endurance of the lower limbs. Subjects were 11 male track and field athletes who had a 400m running time of 48.75±1.32s. The experiment was composed of videotaping sprint form at 160 m and 360 m points during 400 m running, and measuring muscular endurance of hip and knee flexion and extension using Cybex NormTM.
The main results were as follows:
1) There was a significant relationship between 400 m running time and ability to maintain a higher running speed at the 360 m point.
2) Running speed, stride length and stride frequency decreased significantly at the 360 m point.
3) Subjects who showed a smaller decrease in stride frequency at the 360 m could maintain higher running speed.
4) Subjects who showed smaller decrease in maximal joint torque of the lower limbs at the 360 m could maintain a higher running speed.
5) There was a significant relationship between an increase in support time and decrease in maximal joint torque of hip extension for the recovery leg.
6) Ability to maintain joint torque during 400 m running was influenced by muscular endurance of the lower limbs.
These results suggest that the ability to maintain torque needed for higher performance in 400 m running is influenced by muscular endurance of the lower limbs.

The purpose of this study was to compare joint torque and the activity pattern of eight muscles crossing the ankle, knee and hip joints during three kinds of squats with different speeds (Slow, Normal, Quick) . Ten male athletes performed squats at three different speeds. Variables such as net torque and power about the joint were calculated during the descending and ascending phase of each squat. At the same time, surface electrodes were placed over the eight lower extremity muscles, and %iEMG was also measured during the ascending phase of each squat.
During the descending phase, the activity of elector spinae (ES), Gluteus maximus (Gmax), Gluteus medius (Gmed), Rectus femoris (RF), Biceps femoris (BF), Adductor longus (AL), and Vastus lateralis (VL) muscles was significantly greater for Quick squats than Normal and Slow squats, whereas during the ascending phase, activity was significantly greater for Quick and Normal squats than for Slow squats. Mean torque around the hip joint increased significantly when switching from Slow to Quick squats in the descending phase; and during the ascending phase, mean torque was sig nificantly greater for Quick and Normal squats than for Slow squats. The median frequency (MDF) of an electromyogram of the Gmax was significantly lower for Normal squats than for Quick squats ; and in the ascending phase, the MDF of the BF was significantly lower for Normal squats than for Quick and Slow squats.
Quick squats use the stretch-shortening cycle so that the load around the Gmax may increase. Although mean muscle activity for Slow squats was smaller than for Nomal squats, MDF was greater. MDF was greater for Slow squats suggesting that Slow squats mobilize type-II fibers in spite of the slow movement ; and is, therefore, useful for strength training with low risk of injury.