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

A ROTAÇÃO DE OMBRO NÃO AFETA A ATIVAÇÃO MUSCULAR DO PEITORAL MAIOR E DELTOIDE ANTERIOR DURANTE O EXERCÍCIO PEC DECK

ResumoObjetivo: comparar a atividade mioelétrica do peitoral maior (PM) e deltoide anterior (DA) durante o exercício pec deck, em contração voluntária máxima isométrica (CVMI), em rotação interna (RI) e externa (RE) de ombro em diferentes posições articulares. Materiais e Métodos: dez homens saudáveis (idade: 30 ± 6,37 anos, massa corporal total: 84,6 ± 9,43 kg, estatura: 178,6 ± 5,60 cm), treinados em força (tempo de prática: 82,8 ± 63,35 meses), realizaram três CVMI’s durante cinco segundos, e intervalo de 15 segundos entre contrações no exercício pec deck tanto em RI, quanto em RE da articulação do ombro. Um intervalo de 10 minutos foi fornecido aos sujeitos entre condições experimentais em três diferentes posições articulares: máxima adução de ombros (0°), adução dos ombros a 45° e 90°. A atividade mioelétrica do PM e DA foi avaliada por meio de eletromiografia superficial. Resultados: não foram verificadas diferenças significantes entre as rotações de ombro para a ativação muscular em nenhuma das posições articulares analisadas para o DA (0°: d=0,89; Δ%=22,46; 45°: d= 0,65; Δ%=17,95 e 90°: d= 1,26; Δ%=21,16) e para o PM (0°: d= 0,18; Δ%=5,42; 45°: d=0,29; Δ%=10,08 e 90°: d=0,41; Δ%=16,24). Foi verificado aumento significante da ativação muscular do PM em RI na posição de 90° de abdução horizontal de ombro quando comparado a 45° (P<0,05 d=1,85; Δ%=47,00). Conclusão: a realização do exercício pec deck em RI e RE não altera a atividade muscular do PM e do DA, independentemente da posição articular realizada.Palavras-chave: força; eletromiografia; exercício. AbstractObjective: to compare the myoelectric activity of the pectoralis major (PM) and anterior deltoid (AD) during the pec deck exercise, in maximal isometric voluntary contraction (MIVC) in internal rotation (IR) and external (ER) rotation of the shoulder in different joint positions. Methods: ten healthy male (age: 30 ± 6.37 years, total body mass: 84.6 ± 9.43 kg, height: 178.6 ± 5.60 cm), trained in strength (time of practice: 82.8 ± 63.35 months) performed through three MIVC's for five seconds, and a 15-second interval between contractions in the pec deck exercise in both RI and ER of the shoulder joint. A 10-minute interval was provided to subjects between experimental conditions at three different joint positions: maximum shoulder adduction (0°), shoulder adduction at 45° and 90°. The myoelectric activity of the PM and anterior deltoid AD was evaluated by surface electromyography. Results: there were no significant differences between shoulder rotations for muscle activation in any of the joint positions analyzed for the AD (0°: d=0.89; Δ%=22.46; 45°: d= 0.65; Δ%=17.95 e 90°: d= 1.26; Δ%=21.16) and the PM (0°: d= 0.18; Δ%=5.42; 45°: d=0.29; Δ%=10.08 e 90°: d=0.41; Δ%=16.24). There was a significant increase in muscle activation of the PM in IR at the 90° horizontal abduction position of the shoulder when compared to 45° (P<0.05 d=1.85; Δ%=47.00). Conclusion: the performance of the pec deck exercise in IR and RE does not alter the muscular activity of the PM and the AD, independently of the joint position performed.Keywords: strength; electromyography; exercise. Figshare DOI: 10.6084/m9.figshare.1119571

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

The range of motion of the back squat exercise affects absolute volume load without changing the rating of perceived exertion

The range of motion (ROM) may affect the external maximal load during back squat (BS) exercise. The correct ROM manipulation can be useful as an exercise load manipulation strategy, changing the volume load during a resistance training session. The aim of this study was to evaluate the acute effects of ROM on relative load, absolute load and the rating of perceived exertion (RPE) during partial and full BS exercise with adjusted loads. Fifteen male individuals (age: 26.5±4.5 years; height: 173±6 cm; body mass: 80.6 ± 8.8 kg; resistance training experience 5±3 years) participated in this study. The experimental procedure was conducted in two sessions. In the first session, brief familiarization and a 10-repetition maximal test (10-RM) was performed for partial (PBS) and full BS exercise (FBS) with 30-min of rest interval. During the second session, all subjects performed 1 set of 10-RM in both conditions (partial and full ROM), and relative load, absolute load, and RPE were evaluated. A paired t-test was used to compare means. The results showed higher values for PBS when compared to FE exercise: relative load (PBS: 1.14±0.24xBW vs. FBS: 0.87±0.24xBW; P<0.001), and absolute load (PBS: 925±249 kg x FBS: 708±232 kg, P<0.001). Similar RPE was observed between conditions (PBS: 8.6±1.3 IEP x FBS: 8.5±1.0 IEP, P=0.855). It was concluded that PBS allowed higher relative load and absolute load during 10RM, without effects on RPE

Unilateral Plantar Flexors Static-Stretching Effects on Ipsilateral and Contralateral Jump Measures

The aim of this study was to evaluate the acute effects of unilateral ankle plantar flexors static-stretching (SS) on the passive range of movement (ROM) of the stretched limb, surface electromyography (sEMG) and single-leg bounce drop jump (SBDJ) performance measures of the ipsilateral stretched and contralateral non-stretched lower limbs. Seventeen young men (24 ± 5 years) performed SBDJ before and after (stretched limb: immediately post-stretch, 10 and 20 minutes and non-stretched limb: immediately post-stretch) unilateral ankle plantar flexor SS (6 sets of 45s/15s, 70-90% point of discomfort). SBDJ performance measures included jump height, impulse, time to reach peak force, contact time as well as the sEMG integral (IEMG) and pre-activation (IEMGpre-activation) of the gastrocnemius lateralis. Ankle dorsiflexion passive ROM increased in the stretched limb after the SS (pre-test: 21 ± 4° and post-test: 26.5 ± 5°, p < 0.001). Post-stretching decreases were observed with peak force (p = 0.029), IEMG (P<0.001), and IEMGpre-activation (p = 0.015) in the stretched limb; as well as impulse (p = 0.03), and jump height (p = 0.032) in the non-stretched limb. In conclusion, SS effectively increased passive ankle ROM of the stretched limb, and transiently (less than 10 minutes) decreased muscle peak force and pre-activation. The decrease of jump height and impulse for the non-stretched limb suggests a SS-induced central nervous system inhibitory effect