Muscle Activation Differs between Three Different Knee Joint-Angle Positions during a Maximal Isometric Back Squat Exercise

The purpose of this study was to compare muscle activation of the lower limb muscles when performing a maximal isometric back squat exercise over three different positions. Fifteen young, healthy, resistance-trained men performed an isometric back squat at three knee joint angles (20∘, 90∘, and 140∘) in a randomized, counterbalanced fashion. Surface electromyography was used to measure muscle activation of the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteusmaximus (GM). In general,muscle activity was the highest at 90∘ for the three quadricepsmuscles, yet differences in muscle activation between knee angles were muscle specific. Activity of the GM was significantly greater at 20∘ and 90∘ compared to 140∘.The BF and ST displayed similar activation at all joint angles. In conclusion, knee position altersmuscles activation of the quadriceps and gluteus maximus muscles. An isometric back squat at 90∘ generates the highest overall muscle activation, yet an isometric back squat at 140∘ generates the lowest overall muscle activation of the VL and GM only

ALONGAMENTO ESTÁTICO MONOARTICULAR AUMENTA A AMPLITUDE DE MOVIMENTO E ALTERA O SINERGISMO MUSCULAR DURANTE O EXERCÍCIO LEG PRESS ISOMÉTRICO

ResumoDevido ao sincronismo muscular necessário para a execução de um exercício multiarticular como o leg press, o alongamento estático agudo monoarticular poderia produzir alterações no controle articular individual afetando, desta forma, o controle dos músculos primários em outras articulações a fim de manter a ação isométrica. Assim, o presente estudo avaliou o efeito agudo de um protocolo de alongamento estático monoarticular, no sinergismo muscular, durante a execução do exercício leg press unilateral (LPU) isométrico. A amostra foi composta por 15 sujeitos adultos, hígidos, do sexo masculino (idade: 25±4 anos, estatura: 174±8 cm, massa corporal total: 71±6 kg, e 2±1 ano de experiência em musculação). O sinal eletromiográfico advindo dos músculos vasto lateral (VL) e glúteo máximo (GM) foram mensurados durante uma ação isométrica de 10" no exercício LPU contra 60% 1RM em três condições de alongamento estático monoarticular (6 séries de 45” / 15” e 70-90% da percepção subjetiva de desconforto): sem alongamento, alongamento do joelho (CAQ) e alongamento de quadril (CAG). Uma ANOVA (2x2) foi utilizada para verificar as diferenças entre condições (CAQ e CAG) e músculos (VL e GM) para as variáveis dependentes: eletromiografia integrada (IEMG) e frequência mediana (FMed). Houve aumento da amplitude máxima passiva para articulação do quadril e do joelho (P<0,001). Os resultados da IEMG revelaram diferenças significantes entre as condições CAQ e CAG para o músculo vasto lateral (P=0,004; d=1,22; Δ%=12,1%) e glúteo máximo (P=0,024; d=1,44; Δ%=35,5). Foi observada diferença significante entre músculos apenas na condição CAQ (P=0,012; d=1,5; Δ%=36,9). Concluiu-se que o protocolo de alongamento estático monoarticular aumentou a amplitude de movimento em ambas as articulações avaliadas e afetou o sinergismo muscular durante a execução do exercício LPU isométrico.AbstractDue to muscular synchronism of a multi-joint exercise such as the leg press, an acute single-joint static-stretching may produce changes in individual joint control and affect the primer muscle control in correlated joints in order to maintain the isometric action. Thus, the present study aimed to evaluate the acute effect of a single-joint static-stretching protocol on muscle synergy during a submaximal isometric leg press exercise. The sample was composed by fifteen adult subjects, healthy male (age: 25±4 years, height: 174±8 cm, total body mass: 71±6 kg, and 2±1 year of experience in resistance training). The electromyographic signal from the muscle Vastus Lateralis (VL) and Gluteus Maximus (GM) were measured during 10sec of a single-leg isometric contraction in leg press exercise against 60%1RM, in three conditions of single-join static-stretching protocols (6sets x 45sec/15sec, and 70-90% of the point of discomfort): without stretching, knee flexion (CAQ) and hip flexion and external rotation (CAG). An ANOVA (2 x 2) was used to evaluate differences between conditions (CAQ and CAG) and muscles (VL and GM) for the dependent variables: IEMG, median frequency. There was an increase of maximum amplitude passive to the hip joint and the knee (P < 0.001). The IEMG results revealed significant differences between conditions CAQ and CAG for the Vastus Lateralis muscle (P=0.004; d=1.22; Δ%=12.1%), and Gluteus Maximus (P=0.024; d=1.44; Δ%=35.5). Significant difference was observed between muscles only to CAQ (P=0.012; d=1.5; Δ=36.9%). It was concluded that the single-joint static-stretching protocol increased the range of motion in both joints (knee and hip), and affected the muscular synergy during the single-leg isometric leg press exercise. figshare DOI: 10.6084/m9.figshare.819839

Muscle Activation Differs between Three Different Knee Joint-Angle Positions during a Maximal Isometric Back Squat Exercise

The purpose of this study was to compare muscle activation of the lower limb muscles when performing a maximal isometric back squat exercise over three different positions. Fifteen young, healthy, resistance-trained men performed an isometric back squat at three knee joint angles (20°, 90°, and 140°) in a randomized, counterbalanced fashion. Surface electromyography was used to measure muscle activation of the vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM). In general, muscle activity was the highest at 90° for the three quadriceps muscles, yet differences in muscle activation between knee angles were muscle specific. Activity of the GM was significantly greater at 20° and 90° compared to 140°. The BF and ST displayed similar activation at all joint angles. In conclusion, knee position alters muscles activation of the quadriceps and gluteus maximus muscles. An isometric back squat at 90° generates the highest overall muscle activation, yet an isometric back squat at 140° generates the lowest overall muscle activation of the VL and GM only