title: Is myoelectric activity distributed equally within the rectus femoris muscle during loaded, squat exercises?
abstract: Recent evidence suggests different regions of the rectus femoris (RF) muscle respond differently to squat exercises. Such differential adaptation may result from neural inputs distributed locally within RF, as previously reported for isometric contractions, walking and in response to fatigue. Here we therefore investigate whether myoelectric activity distributes evenly within RF during squat. Surface electromyograms (EMGs) were sampled proximally and distally from RF with arrays of electrodes, while thirteen healthy volunteers performed 10 consecutive squats with 20% and 40% of their body weight. The root mean square (RMS) value, computed separately for thirds of the concentric and eccentric phases, was considered to assess the proximo-distal changes in EMG amplitude during squat. The channels with variations in EMG amplitude during squat associated with shifts in the muscle innervation zone were excluded from analysis. No significant differences were observed between RF regions when considering squat phases and knee joint angles individually (P>0.16) while a significant interaction between phase and knee joint angle with detection site was observed (P<0.005). For the two loads considered, proximal RMS values were greater during the eccentric phase and for the more flexed knee joint position (P<0.001). Our results suggest inferences on the degree of RF activation during squat must be made cautiously from surface EMGs. Of more practical relevance, there may be a potential for the differential adaption of RF proximal and distal regions to squat exercises.
authors.affiliation: Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Leonardo Mendes Leal
authors.initials: LM
authors.lastname: de Souza
authors.affiliation: Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Desirée Barros
authors.initials: DB
authors.lastname: da Fonseca
authors.affiliation: Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Hélio da Veiga
authors.initials: HD
authors.lastname: Cabral
authors.affiliation: Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Programa de Engenharia Biomédica (COPPE), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil. Electronic address: liliam@peb.ufrj.br.
authors.forename: Liliam Fernandes
authors.initials: LF
authors.lastname: de Oliveira
authors.affiliation: Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Torino, Italy.
authors.forename: Taian Martins
authors.initials: TM
authors.lastname: Vieira
mesh_terms: D000328:Adult; D004576:Electromyography; D015444:Exercise; D006801:Humans; D007537:Isometric Contraction; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D052097:Quadriceps Muscle / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology
keywords: Rectus femoris; Resistance training; Squat; Surface electromyography