Effect of speed varition and stretch-shortening cycle on lower muscles activity and joint torque during parallel squat

Abstract

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 significantly 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.