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Titre du document / Document title

EMG analysis of lower extremity muscle recruitment patterns during an unloaded squat

Auteur(s) / Author(s)

ISEAR J. A. (1) ; ERICKSON J. C. (1) ; WORRELL T. W. (1) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

(1) Krannert School of Physical Therapy, University of Indianapolis, Indianapolis, IN 46227, ETATS-UNIS

Résumé / Abstract

During an unloaded squat, hamstring and quadriceps co-contraction has been documented and explained via a co-contraction hypothesis. This hypothesis suggests that the hamstrings provide a stabilizing force at the knee by producing a posteriorly-directed force on the tibia to counteract the anterior tibial force imparted by the quadriceps. Research support for this hypothesis, however, is equivocal. Therefore, the purposes of this study were 1) to determine muscle recruitment patterns of the gluteus maximus, hamstrings, quadriceps, and gastrocnemius during an unloaded squat exercise via EMG and 2) to describe the amount of hamstring-quadriceps co-contraction during an unloaded squat. Surface electrodes were used to monitor the EMG activity of six muscles of 41 healthy subjects during an unloaded squat. Each subject performed three 4-s maximal voluntary isometric contractions (MVIC) for each of the six muscles. Electrogoniometers were applied to the knee and hip to monitor joint angles, and each subject performed three series of four complete squats in cadence with a metronome (50 beats.min-1). Each squat consisted of a 1.2-s eccentric, hold, and concentric phase. A two-way repeated measures ANOVA (6 muscles X 7 arcs) was used to compare normalized EMG (percent MVIC) values during each arc of motion (0-30°, 30-60°, 60-90°, hold, 90-60°, 60-30°, 30-0°) of the squat. Tukey post-hoc analyses were used to quantify and interpret the significant two-way interactions. Results revealed minimal hamstring activity (4-12% MVIC) as compared with quadriceps activity (VMO: 22-68%, VL: 21-63% of MVIC) during an unloaded squat in healthy subjects. This low level of hamstring EMG activity was interpreted to reflect the low demand placed on the hamstring muscles to counter anterior shear forces acting at the proximal tibia.

Revue / Journal Title

Medicine and science in sports and exercise    ISSN  0195-9131   CODEN MSPEDA 

Source / Source

1997, vol. 29, no4, pp. 532-539 (22 ref.)

Langue / Language

Anglais

Editeur / Publisher

Lippincott Williams & Wilkins, Hagerstown, MD, ETATS-UNIS  (1980) (Revue)

Mots-clés anglais / English Keywords

Electromyography

;

Knee

;

Lower limb

;

Recruitment

;

Muscular fiber

;

Gluteus maximus muscle

;

Gastrocnemius muscle

;

Quadriceps muscle

;

Muscle contraction

;

Posture

;

Human

;

Electrophysiology

;

Striated muscle

;

Mots-clés français / French Keywords

Electromyographie

;

Genou

;

Membre inférieur

;

Recrutement

;

Fibre musculaire

;

Muscle grand fessier

;

Muscle gastrocnémien

;

Muscle quadriceps

;

Contraction musculaire

;

Posture

;

Homme

;

Accroupissement

;

Electrophysiologie

;

Muscle strié

;

Mots-clés espagnols / Spanish Keywords

Electromiografía

;

Rodilla

;

Miembro inferior

;

Reclutamiento

;

Fibra muscular

;

Músculo glúteo mayor

;

Músculo gastrocnémio

;

Músculo cuadriceps

;

Contracción muscular

;

Postura

;

Hombre

;

Electrofisiología

;

Músculo estriado

;

Localisation / Location

INIST-CNRS, Cote INIST : 17103, 35400006522263.0160

Nº notice refdoc (ud4) : 2649800



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