Post-exercise depression of motor evoked potentials as a function of exercise duration

Post-exercise facilitation and post-exercise depression are phenomena described in motor evoked potentials (MEPs) elicited to transcranial magnetic stimulation. Brief, non-fatiguing muscle activation produces post-exercise facilitation, and prolonged fatiguing muscle activation produces post-exercise depression. We studied 12 normal subjects to determine whether post-exercise depression occurs before fatigue is reached. We recorded MEPs from the resting extensor carpi radialis muscle after increasing the duration of isometric wrist extension, at 50% of maximum voluntary contraction, until the muscle fatigued. Fatigue was defined as the inability to maintain that force. The mean exercise duration before the muscle fatigued was 130 s, and post-exercise depression occurred only beyond 90 s of exercise. We conclude that post-exercise depression is detectable only after prolonged muscle activation.     

Crossed effects of muscle vibration on motor-evoked potentials.

OBJECTIVES: Muscle vibration (MV) to a forearm muscle augments motor-evoked potentials (MEPs) following transcranial magnetic stimulation (TMS) and the underlying mechanism involves cortical structures. Although MV-induced cortical activation is bilateral, the effects of MV on MEPs in contralateral muscles have not been investigated. METHODS: Low-amplitude MV (80 Hz, amplitude 0.5 mm, duration 4 s), subthreshold for the tonic vibration reflex, was applied to the right extensor carpi radialis muscle (ECR). MEPs were elicited (0.5, 3 and 5 s after MV onset) in the left and right ECR and flexor carpi radialis muscle (FCR) by TMS (120% of threshold at rest) to the left and right hemisphere, respectively. RESULTS: During MV of right ECR the left ECR revealed a slight non-significant augmentation of MEPs. In contrast, the left FCR showed a gradual depression of MEPs with ongoing MV and at 3 s the reduction of MEPs was significant. The time course of MEP changes in left FCR correlated with the facilitation of the vibrated right ECR. Post-vibration MEPs at 1 s after the offset of MV were still significantly decreased. CONCLUSIONS: The study demonstrates crossed effects of MV on motor cortex excitability, suggesting transcallosal MEP modulation.     

Delayed facilitation of motor cortical excitability following repetitive finger movements.

OBJECTIVES: To define motor cortical excitability changes occurring at various times after non-fatiguing bimanual exercise of the index fingers. METHODS: Twenty healthy right-handed subjects were studied with transcranial magnetic stimulation (TMS) of the right non-dominant hemisphere. They performed regular (3-4/s) repetitive opening-closing bilateral movements of the index finger onto the thumb. Motor evoked potentials (MEPs) of the left first dorsal interosseus (FDI) and rate of the repetitive finger movements were determined (1) before exercise, (2) immediately following 3 exercise periods of 30, 60 and 90 s, and (3) over a subsequent 30 min rest period. RESULTS: Rate of movement did not show significant change during any of the exercise periods but did increase significantly when tested after 15 min of rest. MEPs immediately after 30 and 60 s of exercise were facilitated whereas MEPs after 90 s of exercise did not differ from baseline measures. MEP amplitudes were significantly increased after rest of approximately 15 min compared to the baseline MEPs. In contrast, motor potentials evoked by peripheral nerve stimulation were unchanged throughout the experimental test periods. CONCLUSIONS: Motor cortical excitability relating to an intrinsic finger muscle (FDI) was facilitated beginning 15 min after a brief period of non-forceful, repetitive activity of that muscle. This delayed facilitation of motor cortex after exercise may represent a form of short-term potentiation of motor cortical excitability.     

Motor cortex excitability in chronic fatigue syndrome.

OBJECTIVE: To use transcranial magnetic stimulation (TMS) to define motor cortical excitability in chronic fatigue syndrome (CFS) subjects during a repetitive, bilateral finger movement task. METHODS: A total of 14 CFS patients were tested and compared with 14 age-matched healthy control subjects. TMS of the motor cortex (5% above threshold) was used to elicit motor evoked potentials (MEPs). Subjects performed regular (3-4/s) repetitive bilateral opening-closing movements of the index finger onto the thumb. MEPs of the first dorsal interosseus (FDI) were measured before, immediately following exercise periods of 30, 60 and 90 s, and after 15 min of rest. RESULTS: Performance, defined by rate of movement, was significantly slower in CFS subjects (3.5/s) than in controls (4. 0/s) independent of the hand measured. The rate, however, was not significantly affected by the exercise duration for either group. The threshold of TMS to evoke MEPs from the FDI muscle was significantly higher in CFS than in control subjects, independent of the hemisphere tested. A transient post-exercise facilitation of MEP amplitudes immediately after the exercise periods was present in controls independent of the hemisphere tested, but was absent in CFS subjects. A delayed facilitation of MEPs after 15-30 min of rest was restricted to the non-dominant hemisphere in controls; delayed facilitation was absent in CFS subjects. CONCLUSIONS: Individuals with CFS do not show the normal fluctuations of motor cortical excitability that accompany and follow non-fatiguing repetitive bimanual finger movements.     

Postexercise facilitation of motor evoked potentials elicited by ipsilateral voluntary contraction

Motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) increase in amplitude when obtained immediately after a period of exercise of the target muscle (postexercise facilitation). We studied postexercise facilitation of MEPs to TMS after periods of voluntary activation of either the ipsilateral or contralateral primary motor cortex (simple finger movements) or supplementary motor area (complex finger movements). Postexercise facilitation of the first dorsal interosseous MEPs occurred ipsilaterally even after simple, unilateral finger movements of the dominant hand. The findings are taken to suggest transcallosal transfer of excitability from the dominant to nondominant cerebral hemisphere, perhaps related to mechanisms involved in bimanual motor coordination.     

Cortical excitability of psychiatric disorders: reduced post-exercise facilitation in depression compared to schizophrenia and controls

OBJECTIVE: In normal subjects, motor evoked potentials (MEPs) produced by transcranial magnetic stimulation (TMS) from the motor cortex are increased after non-fatiguing exercise of hand muscles. This phenomenon is called post-exercise facilitation. This study aims to test the hypothesis that psychiatric syndromes (major depressive episode, schizophrenia) have different levels of post-exercise facilitation compared to controls. METHODS: Patients with DSM-IV major depressive episode (six female, four male), schizophrenia (two female, nine male) and a control group (nine female, four male) participated. MEPs were elicited pre- and post-exercise from the contralateral abductor pollicis brevis by TMS over the primary motor cortex. RESULTS: Post-exercise facilitation expressed as a percentage of baseline was 510% in controls, 110% in depression and 190% in schizophrenia. There were significant differences in patients with depression and schizophrenia compared to controls (p = 0.0001, p = 0.0008). CONCLUSIONS: Post-exercise facilitation was reduced in depression and schizophrenia, suggesting impaired cortical excitability in these disorders. Further studies may discriminate between the two groups.     

Motor strategies and excitability changes of human hand motor area are dependent on different voluntary drives

The present study examined whether there were different voluntary drives between intended and non-intended muscle contractions. In experiment 1, during intended and non-intended muscle contractions, electromyograms (EMGs) were recorded from the first dorsal interosseous (FDI) and extensor carpi radialis (ECR) muscles when force levels were varied from 10% to 50% maximal voluntary contraction (MVC) in 10% MVC steps. In experiment 2, using transcranial magnetic stimulation, motor-evoked potentials (MEPs) were recorded from the FDI muscle when EMGs were varied from 10% to 40% EMGmax (EMG activities during MVC) in 10% EMGmax steps during intended and non-intended muscle contractions. In experiment 3, at 10% MVC force level MEPs were recorded before and after practice. The results showed that, in the FDI muscle, EMGs during intended muscle contractions were larger than those during non-intended ones at higher force levels (30-50% MVC). In the ECR muscle, reverse results were observed. At comparable EMG levels of the FDI muscle MEPs were the same during intended and non-intended muscle contractions. After practice, MEPs during intended muscle contraction became larger than those during non-intended at 10% MVC force level, while EMGs were the same between two muscle contractions. It is concluded that motor strategies and excitability changes of hand motor area are different during intended and non-intended muscle contractions, and these differences are due to the different voluntary drives of intended and non-intended. The present findings may contribute to the understanding of rehabilitation for patients suffering from damages of the central motor system.     

Investigation of paroxysmal dystonia in a patient with multiple sclerosis: a transcranial magnetic stimulation study.

OBJECTIVE: To study the pathogenesis of paroxysmal dystonia affecting the right body side in a patient with a demyelinating lesion in the descending motor pathways, also involving the basal ganglia. METHODS: Single-pulse transcranial magnetic stimulation (TMS) was applied to study motor evoked potentials (MEPs) and the following silent periods (SPs) in the first dorsal interosseous muscle (FDI) of both sides and in the right extensor carpi radialis muscle (ECR) during voluntary contractions performed outside the dystonic attacks. During the dystonic paroxysms, single-pulse TMS was used to investigate the time course of MEPs and SPs in both FDI and ECR of the right side. Furthermore, paired-pulse TMS was applied at rest to investigate short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) in both FDI muscles. RESULTS: At rest SICI and ICF were normal in both motor cortices. During voluntary contraction the MEP was smaller and the SP was longer in the affected FDI than in the contralateral. During the paroxysms, the MEPs and SPs were suppressed in comparison with the responses elicited during voluntary contraction. CONCLUSIONS: These results fit well with the theory of ephaptic excitement of corticospinal axons for the pathogenesis of paroxysmal dystonia due to a demyelinating lesion. SIGNIFICANCE: Identification of the mechanisms underlying paroxysmal dystonia in demyelinating disorders extends our knowledge on the pathophysiology of dystonia.     

Post-exercise facilitation and depression of motor evoked potentials to transcranial magnetic stimulation: a study in multiple sclerosis.

OBJECTIVE: To evaluate motor cortex excitability changes by transcranial magnetic stimulation (TMS) following repetitive muscle contractions in patients with multiple sclerosis (MS); to state whether a typical pattern of post-exercise motor evoked potentials (MEPs) is related to clinical fatigue in MS. METHODS: In 41 patients with definite MS (32 with fatigue and 9 without fatigue according to Fatigue Severity Scale) and 13 controls, MEPs were recorded at rest: at baseline condition, following repetitive contractions until fatigue, and after fatigue, to evaluate post-exercise MEP facilitation (PEF) and depression (PED). RESULTS: After exercise, MEP amplitude significantly increased both in patients and controls (PEF). When fatigue set in, MEP amplitude was significantly reduced in normal subjects (PED), but not in patients. Post-exercise MEP findings were similar both in patients with and without fatigue. CONCLUSIONS: Our findings suggest an intracortical motor dysfunction following a voluntary contraction in MS patients, possibly due to failure of depression of facilitatory cortical circuits, or alternatively of inhibitory mechanisms.     

Changes in motor cortex excitability during ipsilateral hand muscle activation in humans.

OBJECTIVES: To test whether unilateral hand muscle activation involves changes in ipsilateral primary motor cortex (M1) excitability. METHODS: Single- and paired-pulse transcranial magnetic stimulation (TMS) of the right hemisphere was used to evoke motor evoked potentials (MEPs) from the resting left abductor pollicis brevis (APB) in 9 normal volunteers. We monitored changes in motor threshold (MT), MEP recruitment, intracortical inhibition (ICI) and intracortical facilitation (ICF) while the ipsilateral right APB was either at rest or voluntarily activated. Spinal motoneuron excitability was assessed using F-wave recording procedures. RESULTS: Voluntary muscle activation of the ipsilateral APB significantly facilitated the MEPs and F-waves recorded from the contralateral APB. Facilitation was observed with muscle activation >50% of the maximum voluntary force and with stimulus intensities >20% above the individual resting motor threshold. Intracortical inhibition significantly decreased in the ipsilateral M , while there was no significant change in intracortical facilitation during this maneuver. CONCLUSIONS: Unilateral hand muscle activation changes the excitability of homotopic hand muscle representations in both the ipsilateral M1 and the contralateral spinal cord. While the large proportion of MEP facilitation most likely occurred at a spinal level, involvement of the ipsilateral hemisphere may have contributed to the enlargement of magnetic responses.     

Effects of somatosensory input on central fatigue: a pilot study.

OBJECTIVE: Depression of motor evoked potentials (MEPs) following transcranial magnetic stimulation (TMS) may be a sign of central motor fatigue. As a pilot study, we have examined whether post-exercise MEP depression can be compensated by application of sensory stimuli prior to TMS. METHODS: We studied 15 healthy volunteers (aged 21-28 years) who were required to perform an exercise protocol of ankle dorsiflexion until force fell below 66% of maximum force. MEPs were recorded from the right tibialis anterior muscle. Prior to TMS, electrical stimuli were applied to the ipsilateral sural nerve with an individual interstimulus interval between 50 and 80 ms. RESULTS: MEP areas decreased after exercise. When a sensory stimulus was administered MEPs did not change. CONCLUSION: We conclude that the effects of central fatigue may be influenced by application of sensory stimuli.     

Selective effect of repetitive hand movements on intracortical excitability

Repetitive training of isolated movements induces local reorganization of the motor cortex. To investigate the effect of repetitive movements on intracortical inhibition and facilitation shortly after the movements, we performed paired-pulse transcranial magnetic stimulation in 12 healthy subjects by using interstimulus intervals of 2 and 8 ms, respectively. Motor evoked potentials (MEPs) were recorded simultaneously from the extensor carpi radialis (ECR) and the flexor carpi ulnaris muscle (FCU) following paired stimuli at rest or 1 s after repetitive (every 6 s) active or passive wrist extensions and compared with MEPs produced by single stimuli at rest. The active movements produced significantly larger MEPs in the ECR but not the FCU muscle. Passive movements had no effect. Intracortical facilitation increased significantly after movements in the ECR only. Intracortical inhibition, however, did not change significantly after repetitive movements in either muscle. These findings support the notion that intracortical inhibition and facilitation may be controlled independently. Further, these data suggest that shortly after repetitive movements the excitability of the primary motor cortex representing the agonist muscle is increased by interaction with intracortical facilitatory circuits rather than by inactivating inhibitory circuits.     

Immediate plasticity in the motor pathways after spinal cord hemisection: implications for transcranial magnetic motor-evoked potentials

The present study evaluates motor functional recovery after C2 spinal cord hemisection with or without contralateral brachial root transection, which causes a condition that is similar to the crossed phrenic phenomenon on rats. Descending motor pathways, including the reticulospinal extrapyramidal tract and corticospinal pyramidal tracts, were evaluated by transcranial magnetic motor-evoked potentials (mMEPs) and direct cortical electrical motor-evoked potentials (eMEP), respectively. All MEPs recorded from the left forelimb were abolished immediately after the left C2 hemisection. Left mMEPs recovered dramatically immediately after contralateral right brachial root transection. Corticospinal eMEPs never recovered, regardless of transection. The facilitation of mMEPs in animals that had undergone combined contralateral root transection was well correlated with open-field behavioral motor performance. Both electrophysiological and neurological facilitations were significantly attenuated by the selective serotonin synthesis inhibitor para-chlorophenylalanine (p-CPA). These results suggest that serotonergic reticulospinal fibers located contralateral to hemisection contribute to the behavioral and electrophysiological improvement that immediately follows spinal cord injury (SCI).     

Alteration of sensorimotor integration in musician's cramp: impaired focusing of proprioception.

OBJECTIVE: The influence of muscle vibration (MV) as a strong proprioceptive input on motorcortical excitability was studied in 5 patients with musician's cramp, 5 musician controls and 5 non-musician controls. METHODS: The relaxed flexor carpi radialis (FCR), involved in the dystonic movement in all patients, was vibrated using low frequency (80 Hz) and low amplitude (0.5 mm). Transcranial magnetic stimulation (TMS; intensity, 120% of motor threshold) was applied without MV, 3 and 9 s after the onset of MV. Motor-evoked potentials (MEPs) in the FCR and in the antagonistic extensor carpi radialis (ECR) were recorded. RESULTS: With MV, musician and non-musician controls showed a facilitation of MEPs in the FCR and a decrease of MEPs in the ECR. In musician's cramp, both phenomena were significantly less pronounced. CONCLUSIONS: The reduced facilitation of MEPs in musician's cramp indicates a reduced MV-induced activation of motorcortical areas representing the FCR. The less pronounced inhibition by MV reflects a reduced inhibitory control of the antagonistic ECR. As there were no differences between musician and non-musician controls, the observed changes in musician's cramp refer to this special form of focal dystonia. An impairment of focused motorcortical activation by proprioceptive input from a muscle involved in the dystonic movement is suggested.     

Inhibition of motor system excitability at cortical and spinal level by tonic muscle pain.

OBJECTIVE: To assess whether the motor system excitability can be modified by experimental tonic pain induced either in muscles or in subcutis. METHODS: Transcranial magnetic stimulation of the left primary motor cortex was used to record motor evoked potentials (MEPs) from the right abductor digiti minimi (ADM) muscle. Recordings were made before, during and after experimental pain induced by (1) injection of hypertonic (5%) saline into the right ADM, the right first dorsal interosseum (FDI) and the left ADM muscles, and (2) injection of hypertonic saline in the subcutaneous region of the right ADM. Both MEPs and H-reflex were recorded also from the right flexor carpi radialis (FCR) before, during and after muscle pain. RESULTS: MEPs recorded from the ADM muscle were significantly reduced in amplitude during pain induced in the right ADM and right FDI muscles, but not during pain in the left ADM muscle or during subcutaneous pain. This inhibitory effect was observed during the peak-pain and persisted also after the disappearance of the pain sensation. In the FCR muscle, the MEP inhibition was observed during the peak-pain, while a significant reduction of the H-reflex's amplitude was observed starting 1 min after the peak-pain. CONCLUSIONS: Tonic muscle pain can inhibit the motor system. The motor cortex inhibition observed at an early phase is followed by a reduction of the excitability of both cortical and spinal motoneurones.     

Inhibition of ipsilateral motor cortex during phasic generation of low force.

OBJECTIVE: To study the effect of different types of unilateral pinch grips on excitability of the ipsilateral motor cortex. METHODS: In 9 healthy volunteers, transcranial magnetic stimuli (TMS) were applied over one motor cortex while the subjects performed either phasic or tonic ipsilateral pinch grips with different force levels (range 1-40% maximum voluntary contraction, MVC). Motor evoked potentials (MEP) were recorded from the relaxed contralateral first dorsal interosseous muscle (FDI) and were compared to MEPs obtained during muscle relaxation of both hands. In additional experiments, transcranial electrical stimuli (TES) were administered and F waves were recorded after electrical stimulation of the ulnar nerve. RESULTS: Phasic pinch grips with low force (1 and 2% MVC) induced a significant decrease of TMS-induced MEP amplitudes. The effect lasted for about 100 ms after reaching the force level and was similar for both right and left-handed pinch grips. TES-induced MEPs and F waves remained unchanged. In contrast, tonic contractions (20 and 40% MVC) enhanced MEPs in the homologous FDI. CONCLUSIONS: Phasic pinch grips with low force inhibit the motor cortex responsible for the contralateral homologous hand muscle. This effect, which is probably mediated transcallosally, might act at the level of the motor cortex.     

Modulation of motor evoked potentials by muscle vibration: the role of vibration frequency.

Augmentation of motor evoked potentials (MEPs) by muscle vibration (MV) was studied in 10 healthy subjects with regard to the vibration frequency (VF). The extensor carpi radialis muscle (ECR) was vibrated using VFs of 80, 120, and 160 Hz. Motor evoked potentials following transcranial magnetic stimulation were recorded simultaneously from the vibrated ECR and the antagonist flexor carpi radialis muscle (FCR) without MV, 0.5 s and 3 s after onset of MV and 1 s after offset. Only the VFs of 80 Hz and 120 Hz caused MEP augmentation and latency shortening in ECR, whereas depression of MEPs in FCR was induced by all VFs used. It appears that MEP augmentation and latency shortening in ECR are mediated by the primary muscle spindle endings which respond with optimal discharge rates to VFs of up to 100 Hz. Motor evoked potential depression in FCR, being well expressed also with VF 160 Hz, seems to involve other dynamic mechanoreceptors.     

推拿对一次性离心运动后延迟性肌肉酸痛的影响

背景：推拿是运动性疲劳防治的常用手段之一,但有关推拿防治延迟性肌肉酸痛疗效的客观评价较少。 目的：评价推拿对一次性离心运动后延迟性肌肉酸痛的影响。 设计、时间及地点：对比观察,于2008-04/07在南京中医药大学完成。 对象：将30名健康男性学生按照条件对等原则随机分成对照组和运动前推拿组、运动后推拿组共3组,每组10名。 方法：运动前推拿组学生于训练前在左上肢进行30 min的推拿,推拿结束5 min后开始训练。运动后推拿组学生于训练后30 min在左上肢进行30 min的推拿,并在此后的3 d内按规定的时间继续接受推拿治疗,30 min/次,1次/d。对照组学生仅参加训练,不做任何的准备活动或整理活动,也不接受任何治疗。 主要观察指标：观察训练前、训练后即刻、训练后24,48,72 h测定肌肉酸痛程度和持续时间、最大等长收缩力量、臂围、肘关节的屈伸度,训练前1 h、训练后即刻、训练后24,48 h血清肌酸激酶的变化。 结果：与对照组相比,运动前推拿组、运动后推拿组的肌肉酸痛持续时间明显缩短,酸痛的程度明显减轻(P < 0.01,P < 0.05),运动后72 h的肌肉最大等长收缩力量的恢复明显(P < 0.01),运动后72 h的血清肌酸激酶升高幅度明显降低。运动前推拿组运动后即刻的肘关节屈曲程度变化明显小于对照组(P < 0.05),运动后推拿组在运动后72 h的肘关节伸直程度的恢复明显优于对照组(P < 0.05);运动前推拿组、运动后推拿组的臂围变化与对照组无明显差异。 结论：运动前推拿能一定程度预防延迟性肌肉酸痛,减轻延迟性肌肉酸痛的严重程度,而运动后推拿能一定程度促进延迟性肌肉酸痛的恢复。     

Focal enhancement of motor cortex excitability during motor imagery: a transcranial magnetic stimulation study

OBJECTIVES: In order to learn more about the physiology of the motor cortex during motor imagery, we evaluated the changes in excitability of two different hand muscle representations in the primary motor cortex (M1) of both hemispheres during two imagery conditions. MATERIALS AND METHODS: We applied focal transcranial magnetic stimulation (TMS) over each M1, recording motor evoked potentials (MEPs) from the contralateral abductor pollicis brevis (APB) and first dorsal interosseus (FDI) muscles during rest, imagery of contralateral thumb abduction (C-APB), and imagery of ipsilateral thumb abduction (I-APB). We obtained measures of motor threshold (MT), MEP recruitment curve (MEP-rc) and F waves. RESULTS: Motor imagery compared with rest significantly decreased the MT and increased MEPs amplitude at stimulation intensities clearly above MT in condition C-APB, but not in condition I-APB. These effects were not significantly different between right and left hemisphere. MEPs simultaneously recorded from the FDI, which was not involved in the task, did not show facilitatory effects. There were no significant changes in F wave amplitude during motor imagery compared with rest. CONCLUSIONS: Imagery of unilateral simple movements is associated with increased excitability only of a highly specific representation in the contralateral M1 and does not differ between hemispheres.     

The role of cutaneous inputs during magnetic transcranial stimulation

Latency and amplitude characteristics of motor evoked potentials (MEPs) from abductor digiti minimi (ADM) and first dorsal interosseus (FDI) muscles were evaluated in 7 healthy volunteers via magnetic transcranial stimulation of the hemiscalp overlying contralateral motor areas. MEPs in complete relaxation and during contraction were recorded in two different experimental conditions: before and following anesthesia of median (sensory + motor) and radial (sensory) nerve fibers at wrist. This procedure induced a complete loss of skin sensation from dorsal and palmar aspects of the hand area “enveloping” the FDI muscle. On the other hand, the skin overlying the ADM muscle, as well as the strength of ulnar nerve-supplied muscles were spared. This selective sensory deprivation lead to the following short-term changes: the physiological latency “jump” toward shorter values in contracted MEPs vs. relaxation was partially lost in the FDI (3.0 ± 1.4 ms in basal condition, 1.8 ± 1.1 ms after anesthesia, P = 0.028), while it was still clearly evident in the ADM (3.7 ± 0.9 ms and 3.3 ± 1.0 ms, respectively). Moreover, minor amplitude changes of MEPs during active contraction in the two muscles were detected: MEPs recorded from the FDI muscle were less potentiated during voluntary contraction than those recorded from the ADM muscle. The role of the cutaneous input in governing latency/amplitude characteristics of MEPs is discussed. © 1996 John Wiley & Sons, Inc.