Task-Dependent Inhomogeneous Muscle Activities within the Bi-Articular Human Rectus Femoris Muscle

Naokazu Miyamoto,Taku Wakahara,Yasuo Kawakami,Valdur Saks

doi:10.1371/journal.pone.0034269

Abstract

The motor nerve of the bi-articular rectus femoris muscle is generally split from the femoral nerve trunk into two sub-branches just before it reaches the distal and proximal regions of the muscle. In this study, we examined whether the regional difference in muscle activities exists within the human rectus femoris muscle during maximal voluntary isometric contractions of knee extension and hip flexion. Surface electromyographic signals were recorded from the distal, middle, and proximal regions. In addition, twitch responses were evoked by stimulating the femoral nerve with supramaximal intensity. The root mean square value of electromyographic amplitude during each voluntary task was normalized to the maximal compound muscle action potential amplitude (M-wave) for each region. The electromyographic amplitudes were significantly smaller during hip flexion than during knee extension task for all regions. There was no significant difference in the normalized electromyographic amplitude during knee extension among regions within the rectus femoris muscle, whereas those were significantly smaller in the distal than in the middle and proximal regions during hip flexion task. These results indicate that the bi-articular rectus femoris muscle is differentially controlled along the longitudinal direction and that in particular the distal region of the muscle cannot be fully activated during hip flexion.

Highlights

Some human skeletal muscles are anatomically subdivided into neuromuscular compartments, according to their architecture and/or innervation patterns [1,2]
Follow-up post hoc comparisons for the rectus femoris (RF) muscle revealed that both RMSMVC/AmpMwave and RMSMVC/RMSMwave were significantly smaller during hip flexion than during knee extension maximal voluntary isometric contractions (MVCs) task for all regions
There was no significant difference in both RMSMVC/AmpMwave and RMSMVC/RMSMwave values between regions for knee extension task, whereas for hip flexion task the distal region were significantly smaller than those of the middle and proximal regions of the RF muscle for the RMSMVC/AmpMwave value and for the RMSMVC/RMSMwave

Summary

Introduction

Some human skeletal muscles are anatomically subdivided into neuromuscular compartments, according to their architecture and/or innervation patterns [1,2]. The motor nerve of the bi-articular rectus femoris (RF) muscle is generally split from the femoral nerve trunk into two sub-branches just before it reaches the distal-middle and proximal regions of the muscle [1]. With such anatomical organization in the RF, it is hypothesized that the proximal and distal regions of RF demonstrate neuromuscular activation depending on the tasks (e.g. hip flexion and knee extension). This study was undertaken to compare electromyographic (EMG) activities recorded from the distal and proximal regions of the RF muscle during maximal voluntary isometric contractions (MVCs) of knee extension and hip flexion. The findings obtained in the present study can help in gaining insight into the functional role of the neuromuscular compartments within the RF muscle, and in designing injury prevention and rehabilitation program for muscle strain, because theoretically, in bi-articular muscle, the activity within a muscle results in equal force at both origin and insertion but this is not necessarily the case [7]

Methods

Results

Conclusion