Muscle architecture and EMG activity changes during isotonic and isokinetic eccentric exercises

Abstract

The present study aimed to compare muscle architecture and electromyographic activity during isotonic (IT) and isokinetic (IK) knee extensors eccentric contractions. Seventeen subjects were assigned in test and reproducibility groups. During test session, subjects performed two IT and two IK sets of eccentric contractions of knee extensor muscles. Torque, angular velocity, VL architecture and EMG activity of agonist (vastus lateralis, VL; vastus medialis; rectus femoris) and antagonist (semitendinosus; biceps femoris, BF) muscles were simultaneously recorded and averaged on a 5° window. Torque-angle and angular velocity-angle relationships exhibited differences in mechanical load between the IT and IK modes. Changes in muscle architecture were similar in both modes, since VL fascicles length increased and fascicle angle decreased, resulting in a decrease in muscle thickness during eccentric contraction. Agonist activity and BF co-activity levels were higher in IT mode than in IK mode at short muscle lengths, whereas agonist activity was higher in IK mode than in IT mode at long muscle lengths. Differences in mechanical load between both modes induced specific neuromuscular responses in terms of agonist activity and antagonist co-activity. These results suggest that specific neural adaptations may occur after IT or IK eccentric training. This hypothesis needs to be tested in order to gain new insights concerning the most effective eccentric protocols based on whether the objective is sportive or clinical.

Efeito do treino isocinético excêntrico sobre a razão I/Q do torque e EMGs em sujeitos saudáveis

“…), especialmente do modo de treino (isométrico, concêntrico ou excêntrico) 27 . Guilhem et al 21 , que além de outras variáveis (torque, velocidade angular e arquitetura muscular), compararam a atividade da RMS do EMGs de extensores (VM, VL e RF) do joelho, na contração excêntrica isocinética versus isotônica, observaram uma menor amplitude do sinal eletromiográfico associada ao exercício isocinético. Embora estes achados se coadunem, em parte, com nossos resultados, eles não avaliaram o efeito do treino, nem fizeram a comparação entre contração excêntrica e isométrica.…”

“…Eletromiografia de superfície (EMGs): Para o registro do sinal elétrico dos músculos vasto medial (VM), vasto lateral (VL), reto femoral (RF), semitendinoso (ST) e bíceps femoral (BF) 5,21 , foi utilizado um eletromiógrafo (modelo 800C, EMG System do Brasil) com as seguintes características técnicas: hardware com placa de conversão analógico-digital (A/D) de 12 bits; amplificador com ganho de 1000 vezes; filtro passa banda de 20 a 500 Hz (Butterworth de 2 a ordem); razão de rejeição de modo comum (RRMC) >100 dB; taxa de ruído do sinal < 3 µV RMS; impedância de 10 9 Ohms; eletrodos superficiais (bipolares, ativos) com pré-amplificação de 20 vezes e um software Aqdados para coleta e análise de sinais com frequência de amostragem de 1000 Hz, por canal, montado em plataforma Windows.…”

Effect of Ramadan intermittent fasting on body composition and neuromuscular performance in young athletes: a pilot study

“…The novelty of this pilot study is to use surface electyromyographic (EMG) activity to better explain putative changes associated with Ramadan. In fact, EMG activity can be used to assess neural drive during maximal voluntary contraction (Guilhem et al 2011) and to evaluate muscle fatigue during submaximal exercises as performed in numerous works (for review, see Cifrek et al 2009). …”

Reactive oxygen species generation is not different during isometric and lengthening contractions of mouse muscle

“…Strains as large as 30 -50% relative to fascicle length (an estimate of L f) have been reported in vivo for human gastrocnemius muscles during dorsiflexion (41,16) and vastus lateralis muscles during knee flexion (12). Modeling studies incorporating subject data have also found that fascicles actively lengthened as much as 37% (splenius capitis) and 50% (semispinalis capitis) during low-velocity automobile impacts (46), and 64% near the myotendinous junction of the biceps femoris muscle (36).…”