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Original articles  EXERCISE PHYSIOLOGY AND BIOMECHANICS


The Journal of Sports Medicine and Physical Fitness 2007 Marzo;47(1):1-12

lingua: Inglese

Effect of slow movement and stretch-shortening cycle on lower extremity muscle activity and joint moments during squat

Manabe Y. 1, Shimada K. 1, Ogata M. 2

1 Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan
2 Institute of Health and Sport Sciences University of Tsukuba, Tsukuba, Japan


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Aim. The purpose of the present study was to compare activity patterns of 8 muscles that cross the ankle, knee and hip joints under different conditions of squatting.
Methods. Ten male athletes performed squats at 3 different speeds (slow, normal, quick). Variables such as net moment and power about the joint were calculated during the descending and ascending phases of each squat. Using surface electrodes placed over the 8 lower extremity muscles, %iEMG was calculated during the ascending phase of each squat.
Results. In the descending phase, activities of the following 7 muscles were significantly greater for the quick squat (QS) than the normal squat (NS) or slow squat (SS): erector spinae (ES), gluteus maximus (Gmax), gluteus medius (Gmed), rectus femoris (RF), biceps femoris (BF), adductor longus (AL), and vastus lateralis (VL). Median frequency (MDF) of the Gmax muscle was significantly lower for NS than QS, and activity of the BF was significantly lower for NS than QS or SS. Mean moment of the hip joint was significantly lower for SS than QS. In the ascending phase, activities of the following 7 muscles were significantly greater for QS and NS than SS: ES, Gmax, Gmed, RF, BF, AL, and VL. MDF of the Gmax muscle was significantly lower for NS than QS, and the activity of the BF was significantly lower for NS than QS or SS. Mean moment of the hip joint was significantly higher for QS than SS or NS. Mean moment of the knee was significantly lower for SS than NS or QS.
Conclusion. For QS, a stretch-shortening cycle increased the load on the Gmax. Mean muscle activity was less for SS than NS, and MDF was greater for SS than NS. These results suggest that SS mobilizes type-2 muscle fibers, despite the slow movement involved and the low risk of injury.

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