Acute effects of the intensity in the agonistantagonist paired-set on the neuromuscular performance / Efeito agudo da intensidade no sistema agonista-antagonista pareado por série sobre o desempenho neuromuscular

The intensity employed in the agonist-antagonist paired-set (AAPS) system may influence neuromuscular performance due to increased fatigue and decreased antagonist coactivation. However, it is not yet known whether performing submaximal repetitions at different intensities (i.e., wit h out m uscle failure) negatively affects agonist muscle performance. The aim of this study was to verify the acute effect of the AAPSsystem performed at different intensities with submaximal repetitions. 20 trained m ales in resistance training (RT) (21.8 [3.1] years; 76.9 [9.7] kg; 1.7 [0.0] m; 24.3 [2.6] kg/m2 ) participated of this investigation. All the participants were allocated in a randomized order in one of the two AAPS configurations: high-load (HL) or low-load (LL). In the HL condition, the individuals were submit t ed to one set of eight repetitions at 75% of one-repetition maximum (1RM) in the knee flexion (i.e., antagonist), followed by 75% 1RM knee extension (i.e., agonist) exercise until momentary concentric failure. In t he LL condition, they performed one set of 12 repetitions at 50% 1RMin the knee flexion, followed by knee extension at 75%1RM also until momentary concentric failure. Both experimental conditions p resented similar values for the number of repetitions, without significant difference (p= 0.66, ES= 0.15). Thus, our data suggest that the adoption of AAPS system without an increase of the antagonist fatigue and consequently no reduction of coactivation, acutely, may not lead to increased p erfo rm an ce o f target musculature during a resistance exercise session...(AU)

A intensidade empregada no sistema agonista-antagonista pareado por série ( AAPS) pode influenciar o desempenho neuromuscular devido ao aumento da fadiga e diminuição da co ativação do antagonista. No entanto, ainda não se sabe se realizar repetições submáximas em diferentes intensidades (i.e., sem falha muscular) afeta negativamente o desempenho muscular. O objetivo deste estudo foi verificar o efeito agudo do sistema AAPS realizado em diferentes intensidades com repetições submáximas. 20 homens treinados em treinamento resistido (TR) (21.8 ± 3.1 anos; 76.9 ± 9.7 kg; 1.7 ± 0.0 m; 24.3 ± 2.6 kg/m2 ) participaram desta investigação. Todos os participantes foram alocados, de forma aleatória, em uma das duas configurações do sistema AAPS: alta-carga (AC) ou baixa- carga (BC). Na condição AC, os indivíduos foram submetidos a uma série de oito repetições a 75% 1RMno exercício de flexão do joelho (i.e., antagonista), seguido por uma série a 75% 1RM de extensão do joelho até a falha oncêntrica momentânea. Ambas as condições experimentais apresentaram v alores sim ilares para o número de repetições, sem diferença significante (p = 0.66, TE = 0.15). Assim, nossos dados sugerem que a adoção do sistema AAPSsem aumento da fadiga do antagonista e consequentemente sem redução da coativação, agudamente, pode não levar ao aumento do desempenho da musculatura alvo durante uma sessão de exercício resistido...(AU)

Avaliação eletromiográfica do exercício swan na Wunda Chair: Co-ativação dos músculos do core / Electromyographic evaluation of the swan exercise in the Wunda Chair: Co-activation of the core muscles

A principal finalidade do método Pilates é desenvolver uma automação dos músculos do core. Sendo assim, o objetivo deste estudo foi analisar a razão eletromiográfica dos músculos Oblíquo Interno (OI) e Reto do Abdômen (RA) localizados na parte anterior do tronco, a razão eletromiográfica dos músculos Multífido (MU) e Longuíssimo do Tórax (LO) localizados na parte posterior do tronco, e também a razão ântero-posterior (A/P=RA+IO/LO+MU) desses músculos durante o exercício swan do método Pilates, realizado sobre a Wunda Chair. Na comparação entre as três razões, foram encontradas diferenças estatísticas (p = 0,0103), apenas entre as razões ântero-posterior (A/P), e entre a razão dos músculos localizados na parte posterior do tronco (MU/LO). Os resultados demonstraram que houve um predomínio na atividade eletromiográfica dos músculos da região posterior em relação aos músculos da região anterior do tronco e que os músculos estabilizadores apresentaram maior atividade eletromiográfica em comparação com os músculos globais ou mobilizadores. O exercício swan pode ser utilizado como forma de treinamento para a musculatura do tronco, e como consequência gerar maior estabilidade a coluna vertebral, pois o exercício prioriza a diminuição da carga sobre a coluna vertebral. (AU)

The main purpose of the Pilates method is to develop an automation of core muscles. Thus, the aim of this study was to analyze the electromyographic ratio of the Internal Oblique (IO) and Rectus Abdominis (RA) muscles located in the anterior part of the trunk, the electromyographic ratio of the Multifidus (MU) and Longissimus Thoracis (LO) muscles, located in the posterior part of the trunk, and also the ratio antero- posterior (A/P=RA+IO/LO+MU) of these muscles during the swan exercise of the Pilates, performed on the Wunda Chair. In the comparison between the three ratios, statistical differences (p = 0.0013) were found only between the antero-posterior (A/P) ratios and the ratio of the muscles located in the posterior part of the trunk (MU/LO). The results showed a predominance of the electromyographic activity in the muscles of the posterior region in relation to the muscles of the anterior region of the trunk. The stabilizing muscles presented greater electromyographic activity in comparison to the global or mobilizing muscles. The swan can be used as training for the trunk muscles, and therefore generates greater stability of the spine, since exercise prioritizes the decrease of the load on the spine. (AU)

Study on Neural Co-activation during Human Upper Limb Muscle Fatigue Based on Surface Electromyography / 中国运动医学杂志

Objectives To observe the co-activation phenomenon during exercise fatigue induced by the proximal muscles on the upper limbs.Methods Sixteen undergraduates not majoring in sports participated in this study,and their left arms were chosen as the observed arms and right arms were selected as the weighted arms.The weighted arm was alternatively in the state of relaxation without any load and fatigue after bending and extending elbow joints to uphold a 5 kg dumbbell.However,the observed arm kept weighing a 4 kg dumbbell with 90 degrees elbow flexion until the muscles were exhausted.The surface electromyography of biceps brachii and triceps brachii of the observed arms was measured using the ME6000.And the integrated surface electromyography (IEMG),root of mean square (RMS),mean power frequency (MPF)and median frequency (MF)were further analyzed.Results The IEMG and RMS of biceps brachii and triceps brachii of the observed arms increased gradually after the exercise began (P＜0.05)regardless of in the relaxed state or in the in the state of weighing a 5 kg dumbbell for the weighted arm,but in the state of weighting a 5 kg dumbbell the IEMG and RMS increased more significantly (P＜0.01),Meanwhile the electrical activities of the triceps brachii as an antagonistic muscle were intensively inhibited.The changes of MPF and MF of biceps brachii in the observed arms were more significant in the state of exercise fatigue than in the relaxed state (P＜0.01),but without such an impact on the triceps brachii.Conclusions The fatigue in one arm can trigger contingent changes in sEMG time domain and frequency domain indexes of its contralateral parallel muscles,suggesting that sEMG changes of upper limb proximal muscles have the co-activation effect.

Triple redundant signals effect in the visual modality / Efecto de señales triple redundantes en la modalidad visual

Response times in a visual object recognition task decrease significantly if targets can be distinguished by two redundant attributes. Redundancy gain for two attributes has been commonly found, but redundancy gain from three attributes has been found only for stimuli from three different modalities (tactile, auditory, and visual). This study extends those results by showing that redundancy gain from three attributes within the same visual modality (color, form and direction of movement) is possible. It also presents evidence that the separate activation model cannot account for such a gain.

Los tiempos de respuesta en las tareas de reconocimiento visual de objetos disminuye significativamente si los objetivos pueden ser distinguidos por dos atributos redundantes. La ganancia de redundancia para dos atributos se ha encontrado comúnmente, pero la ganancia de redundancia de tres atributos ha sido encontrada solo para estímulos desde tres modalidades diferentes (táctil, auditivo y visual). Este estudio se extiende a aquellos resultados mostrando que el aumento de la redundancia es posible en tres atributos dentro de la misma modalidad visual (color, forma y dirección del movimiento). También se presenta evidencia de que el modelo de activación separada no puede dar cuenta de una ganancia como tal.

Coactivación muscular del miembro inferior de jóvenes y ancianos saludables durante la marcha con doble tarea funcional / Coativação muscular dos membros inferiores de jovens e idosas saudáveis durante marcha com dupla tarefa funcional / Lower limb muscle coactivation levels in healthy younger and older adults during functional dual-task gait

The purpose of this study was to investigate the influence of daily cognitive task on stiffness of old and young female adults during the gait. The study included 17 physically active younger and 18 older women, with low risk of falls. The volunteers were asked to walk on the treadmill at two different gait conditions: normal gait and functional dual-task gait. The electromyographic signals were collected of the lower limb muscles. The percentage of coactivation for the tibialis anterior/gastrocnemius lateralis and tibialis anterior/soleus were significantly higher in elderly than in younger in the normal gait and dual-task gait. Our results suggest that the elderly have a greater stiffness in the ankle joint during gait normal and daily dual task gait. Thus, we conclude that challenging cognitively situations during the gait may increase the risk of falls in this population.

O objetivo deste estudo foi investigar a influência de uma tarefa cognitiva cotidiana sobre a coativação muscular de mulheres idosas e jovens durante a marcha. Participaram do estudo 17 mulheres jovens fisicamente ativas e 18 mulheres idosas com baixo risco de quedas. Os voluntários foram orientados a caminhar sobre uma esteira em duas diferentes condições de marcha: marcha normal e marcha com dupla-tarefa cotidiana. Os sinais eletromiográficos foram coletados dos músculos dos membros inferiores. A porcentagem de coativação para tibial anterior/gastrocnêmio lateral e tibial anterior/sóleo foram significativamente maiores em idosos do que em jovens na marcha normal e marcha com dupla-tarefa. Nossos resultados sugerem que os idosos tem maior coativação muscular no tornozelo durante a marcha normal e marcha com dupla tarefa cotidiana. Assim, nós concluimos que situações cognitivamente desafiadoras durante a marcha podem aumentar o risco de quedas em idosos.

El objetivo de este estudio fue investigar la influencia de una tarea cognitiva diaria en la co-activación muscular en ancianos y jóvenes durante la marcha. Los participantes del estudio fueron 17 ancianos y 18 jóvenes físicamente activos con bajo riesgo de caídas. Los voluntarios caminaron sobre una cinta de correr en dos condiciones diferentes: la marcha normal y la marcha con doble tarea cotidiana. Las electromiografía se obtuvo de los músculos de las extremidades inferiores. El porcentaje de co-activación de los tibialis anterior/gastrocnemius lateralis and tibialis anterior /soleus fueron significativamente mayores en los ancianos que en los sujetos jóvenes durante la marcha normal y marcha con doble tarea. Nuestros resultados sugieren que los ancianos tienen un mayor coactivación muscular en el tobillo durante la marcha normal y marcha con doble tarea cotidiana. Por lo tanto, se concluye que las situaciones cognitivamente desafiantes durante la marcha puede aumentar el riesgo de caídas en los ancianos.

Efeito da facilitação neuromuscular proprioceptiva e pré-ativação dinâmica dos antagonistas sobre a força isométrica máxima e sinal eletromiográfico / Effects of proprioceptive neuromuscular facilitation and antagonist dynamic pre-activation on maximal isometric force and electromyographic signal

Uma das principais adaptações neurais relacionadas ao treinamento de força é a redução progressiva na coativação dos músculos antagonistas e aumento da ativação dos agonistas. Recentemente, evidências sugerem que a pré-ativação dos antagonistas pode melhorar o desempenho dos agonistas, entretanto, não há evidências consistentes que suportem tal hipótese. O objetivo do estudo foi verificar as respostas eletromiográficas (EMG) do latíssimo do dorso (LD), porção espinal do deltoide (DE), porção clavicular do peitoral maior (PC), porção clavicular do deltoide (DC) e força isométrica máxima (Fmáx) durante o exercício de remada aberta (RA) em isometria após facilitação neuromuscular proprioceptiva (FNPA) e pré-ativação dinâmica dos antagonistas no teste de flexão de braços (PADA). Participaram do estudo 10 homens (23,1 ± 3 anos de idade, 77,7 ± 6,5 kg de massa corporal, 167,5 ± 4,8 cm de estatura e 25,6 ± 2,3 kg/m2 de índice de massa corporal) recreacionalmente treinados. A amplitude do sinal EMG foi normalizada por ações isométricas voluntárias máximas (AIVMs). Na análise estatística, foi aplicada a ANOVA two-way e post hoc de Bonferroni para realizar as devidas comparações (p < 0,05). Não foram observadas diferenças significativas na Fmáx após os protocolos FNPA e PADA comparados ao exercício de RA sem estímulo prévio (RSEP). Em relação à amplitude EMG dos músculos LD, DE (agonistas), PC e DC (antagonistas), não foram observadas diferenças significativas entre os protocolos RSEP, FNPA e PADA. Esses resultados sugerem que parece não haver benefícios adicionais na aplicação da técnica de FNP contract-relax e pré-ativação nos antagonistas sobre o sinal EMG e Fmáx dos agonistas baseado na hipótese de inibição neurológica dos antagonistas.

One of the main related neural adaptations to strength training is the progressive reduction in the antagonist coactivation and increased in agonist activation. Recently, evidence suggests that antagonist pre-activation can improve the agonist performance, however, there is no consistent evidence to support this hypothesis. The purpose of this study was to investigate electromyographic responses (EMG) of the latissimus dorsi (LD), spinal portion of deltoid (DE), clavicular portion of pectoralis major (PC), clavicular portion of deltoid (DC) and maximal isometric force (Fmax) during the isometric exercise of wide grip seated row (SR) after proprioceptive neuromuscular facilitation (FNPA) and antagonist dynamics pre-activation in the push up test (PADA). The study included 10 men (23.1 ± 3 years of age, 77.7 ± 6.5 kg body weight, 167.5 ± 4.8 cm in height and 25.6 ± 2.3 kg/m2 index body weight) recreationally trained. The EMG amplitude was normalized by maximum voluntary isometric actions (MVIAs). Statistical analysis was applied the two-way ANOVA and post hoc Bonferroni to perform the comparisons (p < 0.05). There were no significant differences in Fmax after the protocols FNPA and PADA compared the performance of SR without previous stimulus (RSEP). Regarding the EMG amplitude LD, DE (agonists), PC and DC (antagonists), there were no significant differences between the protocols RSEP, FNPA and PADA. These results suggest that there is no additional benefits in applying the technique of PNF contract-relax and pre-activation in the antagonists on the EMG signal and Fmax based on the hypothesis of neurological inhibition of antagonists.

A simple test of muscle coactivation estimation using electromyography

In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A variety of indexes based on electromyography signals have been presented in the literature to quantify muscle coactivation. However, it is not known how to estimate it reliably using such indexes. The goal of this study was to test the reliability of the estimation of muscle coactivation using electromyography. Isometric coactivation was obtained at various muscle activation levels. For this task, any coactivation measurement/index should present the maximal score (100% of coactivation). Two coactivation indexes were applied. In the first, the antagonistic muscle activity (the lower electromyographic signal between two muscles that generate opposite joint torques) is divided by the mean between the agonistic and antagonistic muscle activations. In the second, the ratio between antagonistic and agonistic muscle activation is calculated. Moreover, we computed these indexes considering different electromyographic amplitude normalization procedures. It was found that the first algorithm, with all signals normalized by their respective maximal voluntary coactivation, generates the index closest to the true value (100%), reaching 92 ± 6%. In contrast, the coactivation index value was 82 ± 12% when the second algorithm was applied and the electromyographic signal was not normalized (P < 0.04). The new finding of the present study is that muscle coactivation is more reliably estimated if the EMG signals are normalized by their respective maximal voluntary contraction obtained during maximal coactivation prior to dividing the antagonistic muscle activity by the mean between the agonistic and antagonistic muscle activations.

Effect of Flexion Angle of Knee Joint on Co-contractions of Agonist and Antagonist Muscles / 中国康复理论与实践

@# Objective To test the effect of different flexion angles of knee joint on the myoelectric activity and torque of quadriceps femoris and hamstring muscle when these muscles contracting.MethodsElectromyographic activities and isometric torque measurements were performed on 10 healthy subjects at 30°, 60° and 90° of knee joint flexion.ResultsThe results indicated that the greatest maximal voluntary isometric contracture-torque of quadriceps femoris occurred during knee extension at 60° of knee flexion ( P<0.01). However, no significant relationship of maximal voluntary isometric contracture-electromyography and maximal voluntary isometric contracture-torque of quadriceps femoris were found in 10 subjects. But when knee joint was at 90° flexion, hamstring muscle had a greatest neuro-myoelectric activity.ConclusionThe exercise of maximal voluntary isometric contraction of quadriceps femoris and hamstrings muscles at certain knee joint angle can help to maintain the stability of knee joint.