Changes of Agonist and Antagonist Spinal Motor Neurons Excitability by Muscle Fatigue : analysis of H-reflex and M waves of evoked electromyogram

本研究では, 筋疲労に伴う主動筋および拮抗筋脊髄運動ニューロン興奮性の変化を明らかにするため, 等尺性足関節底・背屈運動前後のヒラメ筋H波およびM波の経時的な変化を観察した。対象は健康な男子10名とし, 最大随意筋収縮(MVC)の50%の足関節等尺性運動を行った。その結果, (1)底屈運動によるヒラメ筋の疲労後, Hmax/Mmax(最大H波とM波の振幅比)は, 安静時と比較して57.37±12.97%に低下し, この低下は運動終了30分後においても74.90±10.89%であった。このことから, 筋疲労に伴い, 筋を支配する脊髄運動ニューロンが長時間抑制されることが示唆された。(2)背屈運動による前脛骨筋の疲労後, 拮抗筋であるヒラメ筋のHmax/Mmaxが, 安静時と比較して70.13±8.85%に低下した。運動終了後, 徐々に回復し, 8分程で安静時のレベルに回復した。(3)前脛骨筋の疲労後, 拮抗筋であるヒラメ筋のHthr(H波閾値)は安静時と比較して有意に増加した。(2)と(3)により, 主動筋の疲労によって, 主動筋のみならず運動を行っていない拮抗筋脊髄運動ニューロンも抑制を受けていることが明らかになった。This study examined the chronological changes of H-reflex and M waves in soleus muscle before and after fatigue induced by isometric ankle joint plantar/dorsal flexion to clarify the changes of agonist/antagonist spinal motor neurons excitability involved in muscle fatigue. Subjects were 10 healthy males who performed ankle joint isometric exercise at 50Invalid or incomplete multibyte or wide characteraximum voluntary contraction (MVC). Results were : (1) After plantar flexion caused soleus muscle fatigue, the soleus muscle Hmax/Mmax (amplitude ratio between maximum H-reflex and M waves) stayed at a low value for a long time. (2) After dorsal flexion caused tibialis anterior muscle fatigue, the soleus muscle (antagonist) Hmax/Mmax fell to 70.13±8.850f the resting value and then gradually recovered. (3) After the tibialis anterior muscle fatigue, the soleus muscle (antagonist) Hthr (H-reflex threshold) significantly increased as compared with the resting value. Results (2) and (3) showed that the agonist's fatigue inhibits not only the agonist but also non-exercised antagonist spinal motor neurons

Influence of Visual Stimulation-Induced Passive Reproduction of Motor Images in the Brain on Motor Paralysis After Stroke

Finger flexor spasticity, which is commonly observed among patients with stroke, disrupts finger extension movement, consequently influencing not only upper limb function in daily life but also the outcomes of upper limb therapeutic exercise. Kinesthetic illusion induced by visual stimulation (KINVIS) has been proposed as a potential treatment for spasticity in patients with stroke. However, it remains unclear whether KINVIS intervention alone could improve finger flexor spasticity and finger extension movements without other intervention modalities. Therefore, the current study investigated the effects of a single KINVIS session on finger flexor spasticity, including its underlying neurophysiological mechanisms, and finger extension movements. To this end, 14 patients who experienced their first episode of stroke participated in this study. A computer screen placed over the patient’s forearm displayed a pre-recorded mirror image video of the patient’s non-paretic hand performing flexion–extension movements during KINVIS. The position and size of the artificial hand were adjusted appropriately to create a perception that the artificial hand was the patient’s own. Before and after the 20-min intervention, Modified Ashworth Scale (MAS) scores and active range of finger extension movements of the paretic hand were determined. Accordingly, MAS scores and active metacarpophalangeal joint extension range of motion improved significantly after the intervention. Moreover, additional experimentation was performed using F-waves on eight patients whose spasticity was reduced by KINVIS to determine whether the same intervention also decreased spinal excitability. Our results showed no change in F-wave amplitude and persistence after the intervention. These results demonstrate the potential clinical significance of KINVIS as a novel intervention for improving finger flexor spasticity and extension movements, one of the most significant impairments among patients with stroke. The decrease in finger flexor spasticity following KINVIS may be attributed to neurophysiological changes not detectable by the F-wave, such as changes in presynaptic inhibition of Ia afferents. Further studies are certainly needed to determine the long-term effects of KINVIS on finger spasticity, as well as the neurophysiological mechanisms explaining the reduction in spasticity

Discrimination of athletic characteristics based on exercise physiology and serum biochemistry

The purpose of the present study is to determine whether athletic characteristics can be discriminated by changes in serum components during exercise which are considered to reflect systemic endurance capacity, muscle strength, and the energy metabolism system. Thirteen male long-distance athletes and 8 male short-distance and field athletes performed an incremental exercise test, muscle strength, and endurance test. They were also observed for changes in serum components during exercise. According to data analysis, the discriminant function thus obtained was: Z=0.8220×peakVO2+0.0037×AT+0.0010×MVC+(-0.0276)×60deg/sec+0.2629×MVC500me+(-0.8715)×UN+36.1659(peakVO2: measured value of peak VO2, AT: 0xbfffa670eakVO2, MVC: measured value of the isometric muscle strength, 60deg/sec: peak torque of the isokinetic muscle contraction at 60deg/sec, MVC50-1230722560me: the time for the previously determined isometric muscle strength value to become less than 50%, UN: the increase rate of UN from the value at rest to the maximum value). Subjects were classified into the actual group correctly, while the erroneous discriminant rate was 0.73%.0 In particular, weighting of the discriminant coefficient of peakVO2 and UN was large, indicating that these are useful as parameters for discriminating athletic characteristics

The Main Factor Causing Prolonged Reaction Time on Force Producing Process Following Anterior Cruciate Ligament Reconstruction

This study investigated the electromechanical properties of atrophied human quadriceps femoris muscle during a voluntarily elicited maximal isometric contraction (MVC) and a peripherally stimulated twitch contraction. Nineteen patients were recruited 2-3 months following a unilateral anterior cruciate ligament (ACL) reconstruction. Both the involved leg as well as the uninvolved leg were studied. Maximal twitch response was elicited and surface electromyograms (EMG) were recorded from the vastus lateralis. Total reaction time (TRT) for both MVC and twitch on involved leg was prolonged (251.47 msec, 26.01 msec). This prolongation suggests an extended lag in avoiding injury such as during sports. Pre-motor time during both MVC and twitch (PMTmvc, PMTtwitch) did not differ between both groups. Electromechanical delay during MVC (EMDmvc) was prolonged on involved leg (53.42 msec), and also evoked twitch EMD (EMDtwitch) (20.04 msec) as compared to the opposit side. Prolonged EMDtwitch may be due to a decrease in stiffness of the series elastic component, changes of peripheral muscle composition to containing more slow type muscle fibers, or a decrease in function of the excitation-contraction (E-C) coupling process. A prolonged EMDtwitch can also explain the prolonged EMDmvc. These findings also suggested that prolonged TRTmvc to visual stimulus during MVC in atrophied human quadriceps femoris muscle after disuse was principally due to prolongation of EMDmvc. Prolonged EMDmvc may have resulted from decreased muscle stiffness, which was evident in the prolongation of the EMDtwitch

The Effect of Fatigued External Rotator Muscles of the Shoulder on the Shoulder Position Sense

This study aimed to investigate the effect of fatigue in shoulder external rotator muscles on position sense of shoulder abduction, internal rotation, and external rotation. The study included 10 healthy subjects. Shoulder position sense was measured before and after a fatigue task involving shoulder external rotator muscles. The fatigue task was performed using an isokinetic machine. To confirm the muscle fatigue, electromyography (EMG) was recorded, and an integrated EMG and median power frequency (MDF) during 3 sec performed target torque were calculated. After the fatigue task, the MDF of the infraspinatus muscle significantly decreased. This indicates that the infraspinatus muscle was involved in the fatigue task. In addition, the shoulder position sense of internal and external rotation significantly decreased after the fatigue task. These results suggest that the fatigue reduced the accuracy of sensory input from muscle spindles. However, no significant difference was observed in shoulder position sense of abduction before and after the fatigue task. This may be due to the fact that infraspinatus muscle did not act as prime movers in shoulder abduction. These results suggest that muscle fatigue decreased position sense during movements in which the affected muscles acted as prime movers

The Long-Term Potentiation-Like Effect in the Corticomotor Area after Transcranial Direct Current Stimulation with Motor Imagery

The purpose of the present study was to clarify a long-term potentiation like effect in the corticomotor area after anodal transcranial direct current stimulation (tDCS), which had been done with motor imagery. Anodal tDCS was applied transcranially as an intervention to the left hand motor area in the right hemisphere for 15 min with the intensity of 1.0 mA during resting or motor imagery (MI) conditions. In the MI condition, subjects performed motor imagery of index finger abduction. Motor-evoked potentials (MEPs) were recorded from the first dorsal interossei (FDI) of the left hand before the intervention and at 0 min, 15 min, 30 min and 60 min after the intervention. The stimulus intensities of TMS were set at 1.05, 1.15, and 1.25 times the strength of the resting motor threshold (RMth). Increases of MEPs were detected with all intensities of TMS at 0 min and 15 min after tDCS with motor imagery. However, in the resting condition, MEP amplitudes were elevated only at 15 min after tDCS and at the highest TMS intensity of 1.25×RMth. The facilitatory effect induced by tDCS with motor imagery was significantly long-lasting and definite compared to that after tDCS without motor imagery

Brain Regions Associated to a Kinesthetic Illusion Evoked by Watching a Video of One's Own Moving Hand

International audienceIt is well known that kinesthetic illusions can be induced by stimulation of several sensory systems (proprioception, touch, vision...). In this study we investigated the cerebral network underlying a kinesthetic illusion induced by visual stimulation by using functionalmagnetic resonance imaging (fMRI) in humans. Participants were instructed to keep their hand still while watching the video of their own moving hand (Self Hand) or that of someone else's moving hand (Other Hand). In the Self Hand condition they experienced an illusory sensation that their hand was moving whereas the Other Hand condition did not induce any kinesthetic illusion. The contrast between the Self Hand and Other Hand conditions showed significant activation in the left dorsal and ventral premotor cortices, in the left Superior and Inferior Parietal lobules, at the right Occipito-Temporal junction as well as in bilateral Insula and Putamen. Most strikingly, there was no activation in the primary motor and somatosensory cortices, whilst previous studies have reported significant activation in these regions for vibrationinduced kinesthetic illusions. To our knowledge, this is the first study that indicates that humans can experience kinesthetic perception without activation in the primarymotor and somatosensory areas. We conclude that under some conditions watching a video of one's ownmoving hand could lead to activation of a network that is usually involved in processing copies of efference, thus leading to the illusory perception that the real hand is indeed moving