Hand Dexterity Impairment in Patients with Cervical Myelopathy: A New Quantitative Assessment Using a Natural Prehension Movement.

Cervical myelopathy (CM) caused by spinal cord compression can lead to reduced hand dexterity. However, except for the 10 sec grip-and-release test, there is no objective assessment system for hand dexterity in patients with CM. Therefore, we evaluated the hand dexterity impairment of patients with CM objectively by asking them to perform a natural prehension movement. Twenty-three patients with CM and 30 age-matched controls were asked to reach for and grasp a small object with their right thumb and index finger and to subsequently lift and hold it. To examine the effects of tactile afferents from the fingers, objects with surface materials of differing textures (silk, suede, and sandpaper) were used. All patients also underwent the Japanese Orthopedic Association (JOA) test. Preoperative patients showed significantly greater grip aperture during reach-to-grasp movements and weaker grip force than controls only while attempting to lift the most slippery object (silk). Patients, immediately after surgery, (n = 15) tended to show improvements in the JOA score and in reaction time and movement time with respect to reaching movements. Multiple regression analysis demonstrated that some parameters of the prehension task could successfully predict subjective evaluations of dexterous hand movements based on JOA scores. These results suggest that quantitative assessments using prehension movements could be useful to objectively evaluate hand dexterity impairment in patients with CM.

Polarity-dependent improvement of maximal-effort sprint cycling performance by direct current stimulation of the central nervous system.

Sprint motor performance, such as in short-distance running or cycling, gradually decreases after reaching a maximum speed or cadence. This may be attributed to the central nervous system. Brain stimulation studies have recently revealed the plastic nature of the human brain and spinal cord, but it is unclear how direct current stimulation (DCS) affects sprint motor performance. To address this issue, we investigated DCS's effect on healthy volunteers' sprint cycling performance. DCS was applied to the lumbar spinal cord (3mA) or the leg area of the motor cortex (2mA) for 15min with 3 different polarities: anodal, cathodal, and sham. After DCS, the subjects performed maximal-effort sprint cycling for 30s under a constant load. Pooled mean power during the 30s was significantly greater after cathodal transcutaneous spinal DCS to the lumbar spinal cord (tsDCS) than anodal or sham tsDCS. The improvement with cathodal stimulation was notable both 0-5 and 20-25s after the performance onset. There were no significant inter-conditional differences in peak power. Pooled mean power was significantly greater after anodal transcranial DCS to the motor cortex (tDCS) than after cathodal tDCS, although mean powers of anodal and sham tDCS were not significantly different. The increase in mean power after cathodal tsDCS could result from a reduction in central fatigue. This stimulus method might improve sprint performance.

Reassessment of Non-Monosynaptic Excitation from the Motor Cortex to Motoneurons in Single Motor Units of the Human Biceps Brachii.

Corticospinal excitation is mediated by polysynaptic pathways in several vertebrates, including dexterous monkeys. However, indirect non-monosynaptic excitation has not been clearly observed following transcranial electrical stimulation (TES) or cervicomedullary stimulation (CMS) in humans. The present study evaluated indirect motor pathways in normal human subjects by recording the activities of single motor units (MUs) in the biceps brachii (BB) muscle. The pyramidal tract was stimulated with weak TES, CMS, and transcranial magnetic stimulation (TMS) contralateral to the recording side. During tasks involving weak co-contraction of the BB and hand muscles, all stimulation methods activated MUs with short latencies. Peristimulus time histograms (PSTHs) showed that responses with similar durations were induced by TES (1.9 ± 1.4 ms) and CMS (2.0 ± 1.4 ms), and these responses often showed multiple peaks with the PSTH peak having a long duration (65.3% and 44.9%, respectively). Such long-duration excitatory responses with multiple peaks were rarely observed in the finger muscles following TES or in the BB following stimulation of the Ia fibers. The responses obtained with TES were compared in the same 14 BB MUs during the co-contraction and isolated BB contraction tasks. Eleven and three units, respectively, exhibited activation with multiple peaks during the two tasks. In order to determine the dispersion effects on the axon conduction velocities (CVs) and synaptic noise, a simulation study that was comparable to the TES experiments was performed with a biologically plausible neuromuscular model. When the model included the monosynaptic-pyramidal tract, multiple peaks were obtained in about 34.5% of the motoneurons (MNs). The experimental and simulation results indicated the existence of task-dependent disparate inputs from the pyramidal tract to the MNs of the upper limb. These results suggested that intercalated interneurons are present in the spinal cord and that these interneurons might be equivalent to those identified in animal experiments.

Polarity specific effects of transcranial direct current stimulation on interhemispheric inhibition.

Transcranial direct current stimulation (tDCS) has been used as a useful interventional brain stimulation technique to improve unilateral upper-limb motor function in healthy humans, as well as in stroke patients. Although tDCS applications are supposed to modify the interhemispheric balance between the motor cortices, the tDCS after-effects on interhemispheric interactions are still poorly understood. To address this issue, we investigated the tDCS after-effects on interhemispheric inhibition (IHI) between the primary motor cortices (M1) in healthy humans. Three types of tDCS electrode montage were tested on separate days; anodal tDCS over the right M1, cathodal tDCS over the left M1, bilateral tDCS with anode over the right M1 and cathode over the left M1. Single-pulse and paired-pulse transcranial magnetic stimulations were given to the left M1 and right M1 before and after tDCS to assess the bilateral corticospinal excitabilities and mutual direction of IHI. Regardless of the electrode montages, corticospinal excitability was increased on the same side of anodal stimulation and decreased on the same side of cathodal stimulation. However, neither unilateral tDCS changed the corticospinal excitability at the unstimulated side. Unilateral anodal tDCS increased IHI from the facilitated side M1 to the unchanged side M1, but it did not change IHI in the other direction. Unilateral cathodal tDCS suppressed IHI both from the inhibited side M1 to the unchanged side M1 and from the unchanged side M1 to the inhibited side M1. Bilateral tDCS increased IHI from the facilitated side M1 to the inhibited side M1 and attenuated IHI in the opposite direction. Sham-tDCS affected neither corticospinal excitability nor IHI. These findings indicate that tDCS produced polarity-specific after-effects on the interhemispheric interactions between M1 and that those after-effects on interhemispheric interactions were mainly dependent on whether tDCS resulted in the facilitation or inhibition of the M1 sending interhemispheric volleys.

Corticospinal excitability of the ankle extensor muscles is enhanced in ballet dancers.

We tested the corticospinal excitability of the soleus muscle in ballet dancers to clarify whether the presumed long-term repetition of the specific plantarflexion results in changes of excitability in this neural pathway. We compared motor evoked potentials of the soleus muscle at rest and during isometric contraction of the plantar flexors in dancers and non-dancers. The amplitudes of motor evoked potentials elicited by transcranial magnetic stimulation during contraction were examined against the background electromyographic activity. A regression line was calculated for each subject. Results showed that the slope of the regression line is significantly greater in the dancer group than in the control group, suggesting that the corticospinal tract of ballet dancers has adapted to long-term repetition of plantarflexion in daily ballet training.

Leg automaticity is stronger than arm automaticity during simultaneous arm and leg cycling.

Recent studies indicate that human locomotion is quadrupedal in nature. An automatic rhythm-generating system is thought to play a crucial role in controlling arm and leg movements. In the present study, we attempted to elucidate differences between intrinsic arm and leg automaticity by investigating cadence variability during simultaneous arm and leg (AL) cycling. Participants performed AL cycling with visual feedback of arm or leg cadence. Participants were asked to focus their attention to match the predetermined cadence; this affects the automaticity of the rhythm-generating system. Leg cadence variability was only mildly affected when the participants intended to precisely adjust either their arm or leg cycling cadence to a predetermined value. In contrast, arm cadence variability significantly increased when the participants adjusted their leg cycling cadence to a predetermined value. These findings suggest that different neural mechanisms underlie the automaticities of arm and leg cycling and that the latter is stronger than the former during AL cycling.

Asymmetrical modulation of corticospinal excitability in the contracting and resting contralateral wrist flexors during unilateral shortening, lengthening and isometric contractions.

Unilateral isometric muscle contractions increase motor-evoked potentials (MEPs) produced by transcranial magnetic stimulation not only in the contracting muscle but also in the resting contralateral homologous muscle. Corticospinal excitability in the M1 contralateral to the contracting muscle changes depending on the type of muscle contraction. Here, we investigated the possibility that corticospinal excitability in M1 ipsilateral to the contracting muscle is modulated in a contraction-type-dependent manner. To this end, we evaluated MEPs in the resting left flexor carpi radialis (FCR) during unilateral shortening, lengthening, and isometric muscle contractions of the right wrist flexors at 10, 20, and 30% of maximal isometric contraction force. To compare the effects of different unilateral contractions on MEPs between the contracting and resting sides, MEPs in the right FCR were recorded on two separate days. In a separate experiment, we investigated the contraction specificity of the crossed effect at the spinal level by recording H-reflexes from the resting left FCR during contraction of the right wrist flexors. The results showed that MEPs in the contracting right FCR were the smallest during lengthening contraction. By contrast, MEPs in the resting left FCR were the largest during lengthening contraction, whereas the H-reflex was similar in the resting left FCR during the three types of muscle contraction. These results suggest that different types of unilateral muscle contraction asymmetrically modulate MEP size in the resting contralateral homologous muscle and in the contracting muscle and that this regulation occurs at the supraspinal level.

A single circularly permuted GFP sensor for inositol-1,3,4,5-tetrakisphosphate based on a split PH domain.

A fluorescent sensor for the detection of inositol-1,3,4,5-tetrakisphosphate, Ins(1,3,4,5)P(4), was constructed from a split PH domain and a single circularly permuted GFP. A structure-based design was conducted to transduce a ligand-induced subtle structural perturbation of the split PH domain to an alteration in the population of the protonated and the deprotonated states of the GFP chromophore. Excitation of each distinct absorption band corresponding to the protonated or the deprotonated state of GFP resulted an increase and a decrease, respectively, in the intensity of emission spectra upon addition of Ins(1,3,4,5)P(4) to the split PH domain-based sensor. The Ins(1,3,4,5)P(4) sensor retained the ligand affinity and the selectivity of the parent PH domain, and realized the ratiometric fluorescence detection of Ins(1,3,4,5)P(4).

Remote facilitation of supraspinal motor excitability depends on the level of effort.

Stretch reflexes and motor-evoked potentials (MEPs) of a muscle are facilitated when performing intensive contraction of muscles located in a different segment (remote effect). We investigated to what extent the remote effect on MEPs in the flexor carpi radialis (FCR) in humans is modulated during sustained maximal and submaximal voluntary contractions of the ipsilateral quadriceps (remote muscle). We found that even when the force of maximal voluntary contraction (MVC) of the remote muscle declined during sustained MVC, the magnitude of the remote effect on MEPs remained constant. Maximal electrical stimulation of the remote muscle and transcranial magnetic stimulation of the corresponding motor cortex revealed that the level of voluntary activation gradually decreased during the sustained MVC. The motor response in the FCR following magnetic stimulation at the level of the foramen magnum, which preferentially elicits muscle response as a direct response of the corticospinal tract, was not modified by the remote effect during the sustained MVC. This finding suggested that the excitability of the spinal motoneuron pool remained constant. In contrast to the sustained MVC, during sustained submaximal contraction of the remote muscle, the magnitude of the remote effect on MEPs gradually increased as muscle fatigue developed. These findings suggest that the remote effect on MEPs was dependent on the level of effort driving the remote muscle, but not on the actual level of force output of the remote muscle, and that the origin of the remote effect was supraspinal, putatively upstream of the primary motor cortex.

Location-specific modulations of plantar cutaneous reflexes in human (peroneus longus muscle) are dependent on co-activation of ankle muscles.

Cutaneous reflexes induced in lower leg muscles by non-noxious electrical stimulation to the foot sole are strongly modified depending on the stimulated location. Little is known, however, about the functional importance of this location-specificity. We examined modulation of cutaneous reflexes in the peroneus longus muscle during co-activation of the peroneus longus (PL), soleus, and tibialis anterior muscles in ten healthy volunteers. We successfully recorded 121 intramuscular single motor units (MU) of cutaneous reflexes in PL elicited by stimulating either fore-medial, fore-lateral, or heel regions of the plantar foot while performing plantarflexion and eversion (PF + EV), dorsiflexion and eversion (DF + EV), or isolated eversion (EV). Firing probability increased following fore-lateral stimulation during the PF + EV and EV tasks, but not during the DF + EV. Fore-medial stimulation, irrespective of the task, suppressed the reflex. Heel stimulation facilitated the reflex only during the PF + EV and DF + EV tasks. In general, cutaneous reflex magnitudes were larger during the PF + EV task than during the others, irrespective of whether the effects were facilitatory or suppressive. These results suggest that the magnitude of the reflex effects on the PL motoneurons strongly depends on activation of plantarflexors and dorsiflexors.

Effective approaches for the production of heterologous proteins using the Thermococcus kodakaraensis-based translation system.

We have previously established a system for cell-free protein synthesis that can be operated at high temperatures using the cell lysate of a hyperthermophilic archaeon, Thermococcus kodakaraensis. To apply this system to practical use in the field of heterologous protein production, the performance of our system in the synthesis of green fluorescent protein (GFP) was examined. As the wild-type GFP is a thermolabile protein, a thermostable GFP derivative (tGFP) was selected as a candidate for protein synthesis. The first attempt of tGFP synthesis at 60 degrees C using the system resulted in a detection of small amount of protein (<0.1 microg/mL) by Western blot analysis. Using a newly synthesized tGFP gene in which codon usage was optimized for T. kodakaraensis as a template, tGFP was clearly detectable at temperatures between 50 and 65 degrees C. The tGFP production was further enhanced over 10 microg/mL with the addition of stem-loop structure at the 3'-end of mRNA. Determination of fluorescences of tGFP in the reaction mixtures indicated that active tGFP constituted ca. 30% of the total protein synthesized. Addition of T. kodakaraensis chaperonin to the system significantly increased the ratio of active tGFP content to ca. 50%. Through these approaches to the system, the production of tGFP increased over 100-fold, and the yield of active tGFP synthesized reached to 6.5 microg/mL.

Effects of remote muscle contraction on transcranial magnetic stimulation-induced motor evoked potentials and silent periods in humans.

OBJECTIVE: To determine to what extent tonic contraction of the testing muscle modulates the effect of remote muscle contraction on motor evoked potentials (MEPs) and cortical silent periods (CSPs) in resting and active proximal and distal muscles following transcranial magnetic stimulation (TMS). In addition, we tested whether the remote effect on MEP was observable when the test MEP was small. METHODS: While performing tonic abductions of the first dorsal interosseous (FDI), flexor carpi radialis, or anterior deltoid muscles, subjects made phasic dorsiflexions of the right ankle at various forces. MEPs and CSPs were induced by separately optimized TMS intensities and locations in the left motor cortex and recorded electromyographically. RESULTS: Phasic dorsiflexion increased MEP amplitude and shortened CSP duration in a dorsiflexion intensity-dependent manner in all muscles tested. At test MEPs <10% of Mmax, remote effects on MEP amplitude and CSP duration were significantly attenuated while the testing muscle was active. CONCLUSIONS: Phasic contraction of remote muscles potentiates excitatory- and suppresses inhibitory intracortical neuronal pathways converging on corticospinal tract cells innervating the upper limb muscles even when they are active. However, the magnitude of the remote effect on MEP amplitude strongly depends on the test MEP amplitude. SIGNIFICANCE: Although remote effects on MEP amplitude and CSP duration are observed even when the test muscle is active, the magnitude of the remote effect strongly depends on TMS intensity.

Voluntary changes in leg cadence modulate arm cadence during simultaneous arm and leg cycling.

Although there is some evidence showing that neural coupling plays an important role in regulating coordination between the upper and lower limbs during walking, it is unclear how tightly the upper and lower limbs are linked during rhythmic movements in humans. The present study was conducted to investigate how coupling of both limbs is coordinated during independent rhythmic movement of the upper and lower limbs. Ten subjects performed simultaneous arm and leg cycling (AL cycling) at their preferred cadences without feedback for 10 s, and then were asked to voluntarily change the cadence (increase, decrease, or stop) of arm or leg cycling. Leg cycling cadence was not affected by voluntary changes in arm cadence. By contrast, arm cycling cadence was significantly altered when leg cycling cadence was changed. These results suggest the existence of a predominant lumbocervical influence of leg cycling on arm cycling during AL cycling.

A highly productive system for cell-free protein synthesis using a lysate of the hyperthermophilic archaeon, Thermococcus kodakaraensis.

We report in this study an improved system for cell-free protein synthesis at high temperatures using the lysate of Thermococcus kodakaraensis. Previous work indicated that cell-free protein synthesis of ChiADelta4, a derivative of T. kodakaraensis chitinase, was observed within a temperature range of 40-80 degrees C, and the maximum yield of the ChiADelta4 synthesized was approximately 1.3 microg/ml. To increase productivity of the system, the following approaches were taken. First, the process of lysate preparation was examined, and we found that omitting the preincubation (runoff) step was especially effective to increase the translational activity of lysate. Second, the concentrations of each reaction mixture were optimized. Among them, the requirement of a high concentration of potassium acetate (250 mM) was characteristic to the T. kodakaraensis system. Third, a mutant strain of T. kodakaraensis was constructed in which a heat shock transcriptional regulator gene, phr, was disrupted. By using the lysate made from the mutant, we observed an increase in the optimum reaction temperature by 5 degrees C. Through these modifications to the system, the yield of ChiADelta4 was dramatically increased to 115.4 microg/ml in a batch reaction at 65 degrees C, which was about 90 times higher than that in the previous study. Moreover, in the optimized system, a high speed of protein synthesis was achieved: over 100 microg/ml of ChiADelta4 was produced in the first 15 min of reaction. These results indicate that the system for cell-free protein synthesis based on T. kodakaraensis lysate has a high production potential comparable to the Escherichia coli system.

Disinhibition of upper limb motor area by voluntary contraction of the lower limb muscle.

It is well known that monosynaptic spinal reflexes and motor evoked potentials following transcranial magnetic stimulation (TMS) are reinforced during phasic and intensive voluntary contraction in the remote segment (remote effect). However, the remote effect on the cortical silent period (CSP) is less known. The purpose of the present study is to determine to what extent the CSP in the intrinsic hand muscle following TMS is modified by voluntary ankle dorsiflexion and to elucidate the origin of the modulation of CSP by the remote effect. CSP was recorded in the right first dorsal interosseous while subjects performed phasic dorsiflexion in the ipsilateral side under self-paced and reaction-time conditions. Modulation of the peripherally-induced silent period (PSP) induced by electrical stimulation of the ulnar nerve was also investigated under the same conditions. In addition, modulation of the CSP was investigated during ischemic nerve block of the lower limb and during application of vibration to the tibialis anterior tendon. The duration of CSP was significantly shortened by phasic dorsiflexion, and the extent of shortening was proportional to dorsiflexion force. Shortening of the CSP duration was also observed during tonic dorsiflexion. In contrast, the PSP duration following ulnar nerve stimulation was not altered during phasic dorsiflexion. Furthermore, the remote effect on the CSP duration was seen during ischemic nerve block of the lower limb and the pre-movement period in the reaction-time paradigm, but shortening of the CSP was not observed during tendon vibration. These findings suggest that phasic muscle contraction in the remote segment results in a decrease in intracortical inhibitory pathways to the corticospinal tract innervating the muscle involved in reflex testing and that the remote effect on the CSP is predominantly cortical in origin.

Location specificity of plantar cutaneous reflexes involving lower limb muscles in humans.

It is known that cutaneous reflexes in human hand muscles show strong location-specificity dependent on the digit stimulated. We hypothesized that in lower leg muscles the cutaneous reflex following tactile sensation of the plantar surface of the foot is also organized in a location-specific manner. The purpose of the present study was to test this hypothesis. Middle latency reflexes (approximately 70-110 ms, MLR) following non-noxious electrical stimulation to different locations on the plantar foot were recorded from 16 neurologically intact volunteers (15 males, 1 female). Electrical stimulation was given to the fore-medial (f-M), fore-lateral (f-L) and heel (HL) regions of the plantar surface of the right foot while the subjects performed isometric dorsiflexion (tibialis anterior, TA), plantarflexion (soleus, Sol and medial gastrocnemius, MG), eversion (peroneus longus, PL) and knee extension (vastus lateralis, VL) while sitting and standing. In the Sol and MG, an excitatory response was observed following HL stimulation, which was switched to an inhibitory response following f-M or f-L stimulation (P < 0.001). A reciprocal pattern in contrast to Sol was observed in the TA. In the PL, MLR exhibited significant excitation following both f-L and HL stimulation, which, however, was switched to an inhibitory response following f-M stimulation (P < 0.001). Moderate inhibition of the MLR was seen in the VL for all stimulated positions. Systematic stimulation along the lateral side of the plantar foot demonstrated that the reflex reversal occurred around the middle of the plantar foot in the Sol and TA. In all muscles tested, the slope of the regression line between the magnitude of the MLR and background electromyographic activity significantly decreased during standing compared with sitting except for the PL following f-L simulation. These results suggest that reflex effects from cutaneous nerves in the plantar foot onto the motoneurons innervating the lower leg muscles are organized in a highly topographic manner in humans. The organization of these reflexes may play an important role in the alteration of limb loading and/or ground contact in response to tactile sensation of the plantar foot while sitting and standing.

Modulations of interlimb and intralimb cutaneous reflexes during simultaneous arm and leg cycling in humans.

OBJECTIVE: We investigated to what extent intralimb and interlimb cutaneous reflexes are altered while simultaneously performing arm and leg cycling (AL cycling) under different kinematic and postural conditions. METHODS: Eleven subjects performed AL cycling under conditions in which the arm and leg crank ipsilateral to the stimulation side were moved synchronously (in-phase cycling) or asynchronously (anti-phase cycling) while sitting or standing. Cutaneous reflexes following superficial radial or superficial peroneal nerve stimulation (2.0-2.5 times radiating threshold, 5 pulses at 333 Hz) were recorded at 4 different pedal positions from 12 muscles in the upper and lower limbs. Cutaneous reflexes with a peak latency of 80-120 ms were then analyzed. RESULTS: The magnitude of interlimb and intralimb cutaneous reflexes in the arm and leg muscles was significantly modulated depending on the crank position for the relevant limb (phase-dependent modulation). A significant correlation between the magnitude of the cutaneous reflex and background EMG was observed in the majority of muscles during static contraction, but not during AL cycling (task-dependent modulation). No significant difference was found in comparisons of the magnitude of intralimb and interlimb cutaneous reflexes obtained during in- and anti-phase AL cycling. Qualitatively, the same results were obtained during AL cycling while sitting or standing. In addition, the modulation of cutaneous reflexes in arm muscles was identical among in-phase, anti-phase and isolated arm cycling. Results were the same for leg muscles. CONCLUSIONS: Cutaneous reflexes in arm muscles are little influenced by rhythmic movement of the legs and vice versa during AL cycling. It is likely that neural components that control interlimb reflexes are loosely coupled during AL cycling while sitting or standing. SIGNIFICANCE: Our results provide a better understanding of the coordination between the upper and lower limbs during rhythmic movement.

Cell-free protein synthesis at high temperatures using the lysate of a hyperthermophile.

Systems for cell-free protein synthesis available today are usually based on the lysates of either Escherichia coli, wheat germ or rabbit reticulocyte, and protein synthesis reactions using these extracts are performed at moderate temperatures (20-40 degrees C). We report here the development of a novel system for cell-free protein synthesis that can be operated at high temperatures using a lysate of the hyperthermophilic archaeon, Thermococcus kodakaraensis. With the system, cell-free protein synthesis of ChiADelta4, a derivative of T. kodakaraensis chitinase (ChiA), was observed within a temperature range of 40-80 degrees C, with an optimum at 65 degrees C. Corresponding chitinase activity was also detected in the reaction mixtures after cell-free protein synthesis, indicating that the synthesized ChiADelta4 folded in a proper tertiary structure. The maximum concentration of active ChiADelta4 synthesized was determined to be approximately 1.3 microg/mL. A time course experiment indicated that the amount of synthesized ChiADelta4 saturated within 30 min at 65 degrees C, and energy depletion was suggested to be the main cause of this saturation. We further developed a system for transcription and translation-coupled protein synthesis at high temperatures using a combination of T. kodakaraensis lysate and thermostable T7 RNA polymerase.

Location-specific and task-dependent modulation of cutaneous reflexes in intrinsic human hand muscles.

OBJECTIVE: The current study was designed to determine location-specificity in long latency cutaneous reflexes in intrinsic human hand muscles while performing a simple abduction and a manual task. METHODS: Subjects comprised of 13 neurologically intact healthy volunteers. Cutaneous reflexes following non-noxious electrical stimulation to the digits of the hand (digit 1, D1; digit 2, D2; and digit 5, D5) were elicited while the subjects performed isolated isometric contraction of the abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi muscles (ADM). The cutaneous reflexes were also elicited while the subjects performed a pincer grip with D1 and D2 while slightly lifting the hand from the supporting surface by abduction of D5 (manual task). RESULTS: While performing isolated tonic voluntary contraction of the APB, FDI and ADM, the magnitude of E2 (peak latency approximately 60-90 ms) was larger when stimulation was delivered to the homotopic digit (e.g. APB response following D1 stimulation) than to the heterotopic nearby (e.g. APB response following D2 stimulation) or heterotopic distant digit (e.g. APB response following D5 stimulation). I2 ( approximately 90-120 ms) and E3 ( approximately 120-180 ms) were significantly larger following D5 stimulation than D1 or D2 stimulation in all muscles tested. The size of each component in the ADM following D1 and D2 stimulation did not increase even when the contraction level of the ADM increased. However, while performing the manual task, the E2 response in the ADM following both D1 and D2 stimulation was significantly increased as compared to that recorded during isolated D5 abduction. CONCLUSIONS: Long latency cutaneous reflexes following non-noxious electrical stimulation are organized in a highly location-specific as well as task-dependent manner. SIGNIFICANCE: Our findings provide further insight into the nature and functional significance of long latency cutaneous reflexes in human intrinsic hand muscles.

Effects of muscle damage induced by eccentric exercise on muscle fatigue.

PURPOSE: The present study was designed to determine to what extent muscle damage induced by repetitive eccentric exercise with maximal voluntary effort (ECC) affects the time course of central and peripheral fatigue during sustained maximal voluntary contraction (MVC). METHODS: Ten healthy male volunteers were asked to perform brief (control MVC) and sustained MVC (fatigue test of 60 s in duration) with elbow flexion before and 2 and 4 d after ECC. Transcranial magnetic stimulation (TMS) was applied to the motor cortex to determine changes in voluntary activation (VA), the size of the motor evoked potential (MEP), and length of electromyographic (EMG) silencing. The ratio of the root mean square value for the surface EMG of the biceps brachii and exerted force within 50 ms before TMS was also calculated (RMS/F). RESULTS: In two subjects, no significant changes in MVC and muscle soreness were seen after ECC so that their data was excluded from further analysis. Control MVC and muscle soreness was significantly decreased and increased, respectively, 2 and 4 d after ECC compared with that before ECC (P < 0.001). During the fatigue test, VA, which was determined by a phasic increase in the twitch force after TMS, significantly decreased 2 and 4 d after ECC compared with that beforehand (P < 0.01). In addition, the RMS/F was significantly increased 2 and 4 d after ECC (P < 0.001). Although the degree of facilitation of the MEP was significantly increased (P < 0.05), the length of EMG silencing was less affected by ECC. CONCLUSIONS: Muscle damage and/or muscle soreness induced by repetitive eccentric exercise with maximal effort may be a strong modifier of central and peripheral fatigue during sustained MVC.