Mechanical interaction between neighboring muscles in human upper limb: evidence for epimuscular myofascial force transmission in humans

To confirm the existence of epimuscular myofascial force transmission in humans, this study examined if manipulating joint angle to stretch the muscle can alter the shear modulus of a resting adjacent muscle, and whether there are regional differences in this response. The biceps brachii (BB: manipulated muscle) and the brachialis (BRA: resting adjacent muscle) were deemed suitable for this study because they are neighboring, yet have independent tendons that insert onto different bones. In order to manipulate the muscle length of BB only, the forearm was passively set at supination, neutral, and pronation positions. For thirteen healthy young adult men, the shear modulus of BB and BRA was measured with shear-wave elastography at proximal and distal muscle regions for each forearm position and with the elbow joint angle at either 100° or 160°. At both muscle regions and both elbow positions, BB shear modulus increased as the forearm was rotated from a supinated to pronated position. Conversely, BRA shear modulus decreased as function of forearm position. The effect of forearm position on shear modulus was most pronounced in the distal muscle region when the elbow was at 160°. The observed alteration of shear modulus of the resting adjacent muscle indicates that epimuscular myofascial force transmission is present in the human upper limb. Consistent with this assertion, we found that the effect of muscle length on shear modulus in both muscles was region-dependent. Our results also suggest that epimuscular myofascial force transmission may be facilitated at stretched muscle lengths

節収縮特性の電気生理学・エネルギー代謝的解明

京都大学0048新制・課程博士博士(人間・環境学)甲第7915号人博第58号10||140(吉田南総合図書館)新制||人||15(附属図書館)UT51-99-G509京都大学大学院人間・環境学研究科文化・地域環境学専攻(主査)教授 家森 幸男, 教授 田口 貞善, 助教授 森谷 敏夫学位規則第4条第1項該当Doctor of Human and Environmental StudiesKyoto UniversityDA

Automatic analysis of ultrasound shear-wave elastography in skeletal muscle without non-contractile tissue contamination

Current analysis methods for obtaining mean shear modulus of skeletal muscles with ultrasound shear-wave elastography are limited by contamination with non-contractile tissues and manual operation of video processing. In this work, we develop new ultrasound image processing methods to assess muscle activities. We build upon previous research by using a 6-DOF robotic manipulator system and indirectly quantifying extensor carpi ulnaris (ECU) and triceps brachii longus (TRI) muscle elasticity during loading using ultrasound shear-wave shear modulus elastography. The purposes of this study were to (1) develop an automatic image-processing algorithm for removing non-contractile tissues from muscle elastography videos and (2) understand the effect of the removal on comparison of mean shear modulus of muscles across static motor tasks with variable muscle loadings in healthy humans. The developed algorithm with optimized clustering and thresholding identified and removed non-contractile tissues from muscle elastography videos with > 90% accuracy in arm muscles, causing reductions in the spatial variability of shear modulus data within the region of interest in healthy young adults. Removal of non-contractile tissues can alter the mean shear modulus of the muscles and influenced task comparisons by substantially altering the ranking of tasks by mean shear modulus

Motor unit data - FHB recordings

Analysed motor unit dat

Corticospinal excitability during actual and imaginary motor tasks of varied difficulty

The present study examined corticospinal excitability of the contralateral and ipsilateral hemispheres during actual (ACT) and imaginary (IMG) unilateral hand force-matching tasks of different difficulty. Seventeen young male adults (21.2 +/- 2.2 yrs) actually and imaginarily matched their left index finger abduction force to a displayed target force. Task difficulty was manipulated by varying the acceptable force range about each mean target force (5 and 15% MVC for ACT, 15% MVC for IMG). Specifically, easy (EASY) and difficult (DIFF) tasks were assigned an acceptable force range of +/- 7% and +/- 0% of target force, respectively. Single pulse transcranial magnetic stimulation was applied to the both hemispheres in ACT and over the left hemisphere in IMG. Motor evoked potentials (MEPs) were collected from the first dorsal interosseous muscle during tasks. In ACT, MEPs in both the contracting and resting hands were significantly larger (P < 0.05) during DIFF than EASY when collapsed across target force levels. In IMG, MEPs in the resting right hand were significantly larger (P < 0.05) during DIFF than during EASY. The relative change in MEP amplitude in the right hand from EASY to DIFF in ACT was positively correlated (r = 0.63) with that in IMG. These results indicate that greater task difficulty increases corticospinal excitability of the contralateral hemisphere in ACT, and increases corticospinal excitability of the ipsilateral hemisphere in both ACT and IMG. The relative changes in corticospinal excitability of the ipsilateral hemisphere with increasing task difficulty are correlated between ACT and IMG. (C) 2018 IBRO. Published by Elsevier Ltd. All rights reserved

Validity of measurement of shear modulus by ultrasound shear wave elastography in human pennate muscle.

Ultrasound shear wave elastography is becoming a valuable tool for measuring mechanical properties of individual muscles. Since ultrasound shear wave elastography measures shear modulus along the principal axis of the probe (i.e., along the transverse axis of the imaging plane), the measured shear modulus most accurately represents the mechanical property of the muscle along the fascicle direction when the probe's principal axis is parallel to the fascicle direction in the plane of the ultrasound image. However, it is unclear how the measured shear modulus is affected by the probe angle relative to the fascicle direction in the same plane. The purpose of the present study was therefore to examine whether the angle between the principal axis of the probe and the fascicle direction in the same plane affects the measured shear modulus. Shear modulus in seven specially-designed tissue-mimicking phantoms, and in eleven human in-vivo biceps brachii and medial gastrocnemius were determined by using ultrasound shear wave elastography. The probe was positioned parallel or 20° obliquely to the fascicle across the B-mode images. The reproducibility of shear modulus measurements was high for both parallel and oblique conditions. Although there was a significant effect of the probe angle relative to the fascicle on the shear modulus in human experiment, the magnitude was negligibly small. These findings indicate that the ultrasound shear wave elastography is a valid tool for evaluating the mechanical property of pennate muscles along the fascicle direction

Fine-wire recordings of flexor hallucis brevis motor units up to maximal voluntary contraction reveal a flexible, non-rigid mechanism for force control

Our current knowledge on the neurophysiological properties of intrinsic foot muscles is limited, especially at high forces. This study therefore aimed to investigate the discharge characteristics of single motor units in an intrinsic foot muscle, namely flexor hallucis brevis, during voluntary contractions up to 100% of maximal voluntary contraction. We measured the recruitment threshold and discharge rate of flexor hallucis brevis motor units using indwelling fine-wire electrodes. Ten participants followed a target ramp up to maximal voluntary contraction by applying a metatarso-phalangeal flexion torque. We observed motor unit recruitment thresholds across a wide range of isometric forces (ranging from 10 to 98% of maximal voluntary contraction) as well as across a wide range of discharge rates (ranging from 4.8 to 23.3 Hz for initial discharge rate and 9.5 to 34.2 Hz for peak discharge rate). We further observed patterns of high variability in recruitment threshold and discharge rate as well as crossover in discharge rate between motor units within the same participant. These findings suggest that the force output of a muscle is generated through a mechanism with substantial variability rather than relying on a rigid organisation, which is in contrast to the proposed onion-skin theory. The demands placed on the plantar intrinsic foot muscles during high and low force tasks may explain these observed neurophysiological properties