Cortical oscillations and interareal synchronization as a preparatory activity for postural response.

Neural mechanisms of human standing are expected to be elucidated for preventing fallings. Postural response evoked by sudden external perturbation originates from various areas in the central nervous system. Recent studies have revealed that the corticospinal pathway is one of the key nodes for an appropriate postural response. The corticospinal pathway that mediates the early part of the electromyographic response is modulated with prediction before a perturbation occurs. Temporal prediction explicitly exhibiting an onset timing contributes to enhancing corticospinal excitability. However, how the cortical activities in the sensorimotor area with temporal prediction are processed before the corticospinal pathway enhancement remains unclear. In this study, using electroencephalography, we investigated how temporal prediction affects both neural oscillations and synchronization between sensorimotor and distal areas. Our results revealed that desynchronization of cortical oscillation at α- and ß-bands was observed in the sensorimotor and parietooccipital areas (Cz, CPz, Pz and POz), and those are nested in the phase at θ-band frequency. Furthermore, a reduction in the interareal phase synchrony in the α-band was induced after the timing cue for the perturbation onset. The phase synchrony at the low frequency can relay the temporal prediction among the distant areas and initiate the modulation of the local cortical activities. Such modulations contribute to the preparation for sensory processing and motor execution that are necessary for optimal responses.

Different functional networks underlying human walking with pulling force fields acting in forward or backward directions.

Walking with pulling force fields acting at the body center of mass (in the forward or backward directions) is compatible with inclined walking and is used in clinical practice for gait training. From the perspective of known differences in the motor strategies that underlie walking with the respective force fields, the present study elucidated whether the adaptation acquired by walking on a split-belt treadmill with either one of the force fields affects subsequent walking in a force field in the opposite directions. Walking with the force field induced an adaptive and de-adaptive behavior of the subjects, with the aspect evident in the braking and propulsive impulses of the ground reaction force (difference in the peak value between the left and right sides for each stride cycle) as parameters. In the parameters, the adaptation acquired during walking with a force field acting in one direction was transferred to that in the opposite direction only partially. Furthermore, the adaptation that occurred while walking in a force field in one direction was rarely washed out by subsequent walking in a force field in the opposite direction and thus was maintained independently of the other. These results demonstrated possible independence in the neural functional networks capable of controlling walking in each movement task with an opposing force field.

Effect of Long-Term Classical Ballet Dance Training on Postactivation Depression of the Soleus Hoffmann-Reflex.

Classical ballet dancing is a good model for studying the long-term activity-dependent plasticity of the central nervous system in humans, as it requires unique ankle movements to maintain ballet postures. The purpose of this study was to investigate whether postactivation depression is changed through long-term specific motor training. Eight ballet dancers and eight sedentary subjects participated in this study. The soleus Hoffmann reflexes were elicited at after the completion of a slow, passive dorsiflexion of the ankle. The results demonstrated that the depression of the soleus Hoffmann reflex (i.e., postactivation depression) was larger in classical ballet dancers than in sedentary subjects at two poststretch intervals. This suggests that the plastic change through long-term specific motor training is also expressed in postactivation depression of the soleus Hoffmann reflex. Increased postactivation depression would strengthen the supraspinal control of the plantarflexors and may contribute to fine ankle movements in classical ballet dancers.

Spatiotemporal characteristics of locomotor adaptation of walking with two handheld poles.

Pole walking (PW) has received attention not only as a whole-body exercise that can be adapted for elderly people with poor physical fitness but also as a possible intervention for the restoration of gait function in normal walking without the use of poles (i.e., conventional walking CW). However, the characteristics of PW, especially how and why PW training affects CW, remain unclear. The purpose of this study was to examine the characteristics of locomotor adaptation in PW from the perspective of kinematic variables. For this purpose, we compared the locomotor adaptation in PW and CW to that when walking on a split-belt treadmill in terms of spatial and temporal coordination. The result showed that adaptations to the split-belt treadmill in PW and CW were found only in interlimb parameters (step length and double support time ratios (fast/slow limb)), not in intralimb parameters (stride length and stance time ratios). In these interlimb parameters, the movement patterns acquired through split-belt locomotor adaptations (i.e., the aftereffects) were transferred between CW and PW regardless of whether the novel movement patterns were learned in CW or PW. The aftereffects of double support time and step length learned in CW were completely washed out by the subsequent execution in PW. On the other hand, the aftereffect of double support time learned in PW was not completely washed out by the subsequent execution in CW, whereas the aftereffect of step length learned in PW was completely washed out by the subsequent execution in CW. These results suggest that the neural mechanisms related to controlling interlimb parameters are shared between CW and PW, and it is possible that, in interlimb coordination, temporal coordination is preferentially stored in adaptation during PW.

Cross-sectional comparison of the probabilistic structure in the distribution of pitching location among baseball pitchers of different ages.

The present study was a cross-sectional comparison of probabilistic structure in the distribution of pitching location among baseball pitchers of various age groups (25 elementary school (ES), 20 junior high school (JH), 15 high school (HS), and 18 college students (CL)). In the results, despite the general age-dependent variations in pitching precision, the difference was reflected not only in error 'size' but also in the 'shape' of error as it was shown by fitting 95% confidence ellipse to the two dimensional distribution of pitch location. While the precision measure as a reflection of trial-by-trial variability of release timing (major axis length of the ellipse) was constant, minor axis length of the ellipse as a reflection of variability in the pitching form of each participant demonstrated significant differences among the groups. In the ES group particularly, the trial-by-trial variability in the trajectory angle of the throwing arm was significantly correlated with the minor axis length; this correlation was far greater than those in older groups. The present study is the first to demonstrate the detailed structure of the variability of pitching location of baseball dependent on age.

Effects on Postural Kinematics of Performing a Cognitive Task During Upright Standing.

The execution of cognitive tasks is known to alter postural sway during standing, but the underlying mechanisms are still debated. This study investigated how performing a mental task modified balance control during standing. We required 15 healthy adult males to maintain an upright stance under conditions of simply relaxing and maintaining normal quiet standing (control condition) or while performing a secondary cognitive task (mental arithmetic). Under each condition, we measured the participants' center of pressure and used kinematic measurements for a quantitative evaluation of postural control modulation. We calculated the standard deviation of the joint angles (ankle, knee, and hip) and the estimated joint stiffness to measure joint mobility changes in postural control. To estimate the kinematic pattern of covariation among these joints, we used uncontrolled manifold analysis, an assessment of the strength of multijoint coordination. Compared to normal standing, executing the cognitive task while standing led to reduced movements of the ankle and hip joints. There were no significant differences in ankle stiffness or uncontrolled manifold ratios between the conditions. Our results suggest that when performing a secondary cognitive task during standing, neither changes in the modification of stiffness nor the strength of multijoint coordination (both of which preserve the center of mass position) explains changes in postural sway.

"Paralympic Brain". Compensation and Reorganization of a Damaged Human Brain with Intensive Physical Training.

The main aim of the study was to evaluate how the brain of a Paralympic athlete with severe disability due to cerebral palsy has reorganized after continuous training geared to enhance performance. Both corticospinal excitability of upper-limb muscles and electromyographic activity during swimming were investigated for a Paralympic gold medalist in swimming competitions. Transcranial magnetic stimulation (TMS) to the affected and intact hand motor cortical area revealed that the affected side finger muscle cortical representation area shifted towards the temporal side, and cortico-spinal excitability of the target muscle was prominently facilitated, i.e., the maximum motor evoked potential in the affected side, 6.11 ± 0.19 mV was greater than that in the intact side, 4.52 ± 0.39 mV (mean ± standard error). Electromyographic activities during swimming demonstrated well-coordinated patterns as compared with rather spastic activities observed in the affected side during walking on land. These results suggest that the ability of the brain to reorganize through intensive training in Paralympic athletes can teach interesting lessons to the field neurorehabilitation.

Remarkable hand grip steadiness in individuals with complete spinal cord injury.

Although no damage occurs in the brains of individuals with spinal cord injury, structural and functional reorganization occurs in the sensorimotor cortex because of the deafferentation of afferent signal input from below the injury level. This brain reorganization that is specific to individuals with spinal cord injury is speculated to contribute to the improvement of the motor function of the remaining upper limbs. However, no study has investigated in detail the motor function above the injury level. To clarify this, we designed an experiment using the handgrip force steadiness task, which is a popular technique for evaluating motor function as the index of the variability of common synaptic input to motoneurons. Fourteen complete spinal cord injury (cSCI) individuals in the chronic phase, fifteen individuals with lower limb disabilities, and twelve healthy controls participated in the study. We clarified that the force steadiness in the cSCI group was significantly higher than that in the control groups, and that sports years were significantly correlated with this steadiness. Furthermore, multiple analyses revealed that force steadiness was significantly predicted by sports years. These results suggest that brain reorganization after spinal cord injury can functionally affect the remaining upper limb motor function. These findings may have implications in the clinical rehabilitation field, such as occupational rehabilitation of the upper limbs. They also indicate that individuals with complete spinal cord injury, based on their enhanced force adjustment skills, would excel at fine motor tasks such as manufacturing and handicrafts.

Repeatability of spinal reflexes of lower limb muscles evoked by transcutaneous spinal cord stimulation.

Transcutaneous electrical stimulation is a relatively new technique to evoke spinal reflexes in lower limb muscles. The advantage of this technique is that the spinal reflex responses can be obtained from multiple lower limb muscles simultaneously. However, repeatability of spinal reflexes evoked by transcutaneous spinal cord stimulation between days has not been evaluated. We aimed to examine repeatability of recruitment properties of the spinal reflexes evoked by transcutaneous spinal cord stimulation. Recruitment curves of the spinal reflexes evoked by transcutaneous spinal cord stimulation of 8 lower limb muscles (i.e., foot, lower leg, and thigh muscles) of 20 males were measured on two consecutive days. To confirm that responses were caused by activation of the sensory fiber, a double-pulse stimulation with 50 ms inter-pulse interval was delivered. Peak-to-peak amplitude of the first response was calculated for each muscle when no response was observed in the second response owing to post-activation depression. For comparison with the spinal reflexes evoked by transcutaneous spinal cord stimulation, the recruitment curves of the H-reflex amplitude of the soleus of 9 males were measured. Threshold intensity and maximal slope of the recruitment curves were calculated, and inter-day repeatability of the properties was quantified using intraclass correlation coefficients. For the spinal reflexes evoked by transcutaneous spinal cord stimulation, the intraclass correlation coefficient values of threshold intensity and maximal slope for each muscle ranged from 0.487 to 0.874 and from 0.471 to 0.964, respectively. Regarding the soleus H-reflex, the intraclass correlation coefficients of threshold intensity and maximal slope were 0.936 and 0.751, respectively. The present data showed that repeatability of the recruitment properties of the spinal reflexes evoked by transcutaneous spinal cord stimulation in the lower limb was moderate to high. Measurement of the spinal reflexes evoked by transcutaneous spinal cord stimulation would be useful for longitudinal neurophysiological studies.

Unique controlling mechanisms underlying walking with two handheld poles in contrast to those of conventional walking as revealed by split-belt locomotor adaptation.

Pole walking (PW), a form of locomotion in which a person holds a pole in each hand, enhances the involvement of alternating upper-limb movement. While this quadruped-like walking increases postural stability for bipedal conventional walking (CW), in terms of the neural controlling mechanisms underlying the two locomotion forms (PW and CW), the similarities and differences remain unknown. The purpose of this study was to compare the neural control of PW and CW from the perspective of locomotor adaptation to a novel environment on a split-belt treadmill. We measured the anterior component of the ground reaction (braking) force during and after split-belt treadmill walking in 12 healthy subjects. The results demonstrated that (1) PW delayed locomotor adaptation when compared with CW; (2) the degrees of transfer of the acquired movement pattern to CW and PW were not different, regardless of whether the novel movement pattern was learned in CW or PW; and (3) the movement pattern learned in CW was washed out by subsequent execution in PW, whereas the movement pattern learned in PW was not completely washed out by subsequent execution in CW. These results suggest that the neural control mechanisms of PW and CW are not independent, and it is possible that PW could be a locomotor behavior built upon a basic locomotor pattern of CW.

Effect of Paired Associative Stimulation on Corticomotor Excitability in Chronic Smokers.

Chronic smoking has been shown to have deleterious effects on brain function and is an important risk factor for ischemic stroke. Reduced cortical excitability has been shown among chronic smokers compared with non-smokers to have a long-term effect and so far no study has assessed the effect of smoking on short-term motor learning. Paired associative stimulation (PAS) is a commonly used method for inducing changes in excitability of the motor cortex (M1) in a way that simulates short-term motor learning. This study employed PAS to investigate the effect of chronic cigarette smoking on plasticity of M1. Stimulator output required to elicit a motor-evoked potential (MEP) of approximately 1 mV was similar between the groups prior to PAS. MEP response to single pulse stimuli increased in the control group and remained above baseline level for at least 30 min after the intervention, but not in the smokers who showed no significant increase in MEP size. The silent period was similar between groups at all time points of the experiment. This study suggests that chronic smoking may have a negative effect on the response to PAS and infers that chronic smoking may have a deleterious effect on the adaptability of M1.

Presetting of the Corticospinal Excitability in the Tibialis Anterior Muscle in Relation to Prediction of the Magnitude and Direction of Postural Perturbations.

The prediction of upcoming perturbation modulates postural responses in the ankle muscles. The effects of this prediction on postural responses vary according to predictable factors. When the amplitude of perturbation can be predicted, the long-latency response is set at an appropriate size for the required response, whereas when the direction of perturbation can be predicted, there is no effect. The neural mechanisms underlying these phenomena are poorly understood. Here, we examined how the corticospinal excitability of the ankle muscles [i.e., the tibialis anterior (TA), the soleus (SOL), and the medial gastrocnemius (MG), with a focus on the TA], would be modulated in five experimental conditions: (1) No-perturbation; (2) Low (anterior translation with small amplitude); (3) High (anterior translation with large amplitude); (4) Posterior (posterior translation with large amplitude); and (5) Random (Low, High, and Posterior in randomized order). We measured the motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) at 50 ms before surface-translation in each condition. The electromyographic (EMG) responses evoked by surface-translations were also measured. The results showed that the TA-MEP amplitude was greater in the High condition (where the largest TA-EMG response was evoked among the five conditions) compared to that in the No-perturbation, Low, and Posterior conditions (High vs. No-perturbation, p < 0.001; High vs. Low, p = 0.001; High vs. Posterior, p = 0.001). In addition, the MEP amplitude in the Random condition was significantly greater than that in the No-perturbation and Low conditions (Random vs. No-perturbation, p = 0.002; Random vs. Low, p = 0.002). The EMG response in the TA evoked by perturbation was significantly smaller when a perturbation can be predicted (predictable vs. unpredictable, p < 0.001). In the SOL and MG muscles, no prominent modulations of the MEP amplitude or EMG response were observed, suggesting that the effects of prediction on corticospinal excitability differ between the dorsiflexor and plantar flexor muscles. These findings suggest that the corticospinal excitability in the TA is scaled in parallel with the prediction of the direction and magnitude of an upcoming perturbation in advance.

Short-term inhibition of spinal reflexes in multiple lower limb muscles after neuromuscular electrical stimulation of ankle plantar flexors.

Neuromuscular electrical stimulation (NMES) of lower limbs elicits muscle contractions through the activation of efferent fibers and concomitant recruitment of afferent fibers, which can modulate excitability of the central nervous system. However, neural mechanisms of NMES and how unilateral stimulation of the soleus affects spinal reflexes in multiple lower limb muscles bilaterally remains unknown. Twelve able-bodied participants were recruited, and spinal reflex excitability changes were tested after four interventions, each applied for 60 s, on the right plantar flexors: (1) motor-level NMES; (2) sensory-level NMES; (3) voluntary contraction; (4) rest. Spinal reflexes were elicited using single-pulse transcutaneous spinal cord stimulation applied on the lumbar level of the spinal cord to evoke bilateral responses in multiple lower limb muscles, while maximum motor response (Mmax) was tested in the soleus by stimulating the posterior tibial nerve. Spinal reflexes and Mmax before each intervention were compared to immediately after and every 5 min subsequently, for 15 min. Results showed that motor-level NMES inhibited spinal reflexes of the soleus and other studied muscles of the ipsilateral leg, but not the contralateral leg (except vastus medialis) for 15 min, while not affecting soleus muscle properties (Mmax). Voluntary contraction effect lasted less than 5 min, while sensory-level NMES and rest did not produce an effect. Short-term spinal reflex excitability was likely affected because antidromic impulses during motor-level NMES coincided in the spinal cord with afferent inputs to induce spinal neuroplasticity, whereas afferent input alone did not produce short-term effects. Such activation of muscles with NMES could reduce spasticity in individuals with neurological impairments.

Effects of breathing movement on the reduction of postural sway during postural-cognitive dual tasking.

An execution of cognitive processing interferes with postural sway during quiet standing. It reduces sway variability in young adults, but the mechanism is not clear. To elucidate the mechanisms, we focused on breathing in the present study. The purpose of this study was to clarify whether a decrease in postural sway amplitude during a postural-cognitive task is related to the change in breathing movement. The center of pressure (COP) was recorded via a force plate and the motion of leg joints (ankle, knee, and hip), and breathing movements were measured with a 3D motion capture system in quiet standing and standing with cognitive (mental arithmetic) task conditions. The change ratios of each variable from the quiet standing condition to the cognitive task were also calculated. It was shown that the MASt condition produced a significantly smaller RMS of COP displacement as compared to the QSt condition (p < 0.01). The results revealed that the breathing rate was faster and the amplitude of breathing movement smaller when subjects performed the cognitive task. A significant positive correlation (r = 0.75, p < 0.01) was found between the change ratio of breathing amplitude and the COP amplitude. The present results suggest that reduced standing postural sway during a cognitive task is related, at least in part, to a decrease in breathing amplitude.

Corticospinal Excitability Is Modulated as a Function of Postural Perturbation Predictability.

Recent studies demonstrated that the corticospinal pathway is one of the key nodes for the feedback control of human standing and that the excitability is flexibly changed according to the current state of posture. However, it has been unclear whether this pathway is also involved in a predictive control of human standing. Here, we investigated whether the corticospinal excitability of the soleus (SOL) and tibialis anterior (TA) muscles during standing would be modulated anticipatorily when perturbation was impending. We measured the motor-evoked potential (MEP) induced by transcranial magnetic stimulation over the motor cortex at six stimulus intensities. Three experimental conditions were set depending on predictabilities about perturbation occurrence and onset: No perturbation, No Cue, and Cue conditions. In the Cue condition, an acoustic signal was given as timing information of perturbation. The slope of the stimulus-response relation curve revealed that the TA-MEP was enhanced when postural perturbation was expected compared to when the perturbation was not expected (No Perturbation vs. No Cue, 0.023 ± 0.004 vs. 0.042 ± 0.007; No Perturbation vs. Cue, 0.023 ± 0.004 vs. 0.050 ± 0.009; Bonferroni correction, p = 0.01, respectively). In addition, two-way analysis of variance (intensity × condition) revealed the main effect of condition (F(1,13) = 6.31, p = 0.03) but not intensity and interaction when the MEP amplitude of the Cue and No Cue conditions was normalized by that in No Perturbation, suggesting the enhancement more apparent when timing information was given. The SOL-MEP was not modulated even when perturbation was expected, but it slightly reduced due to the timing information. The results of an additional experiment confirmed that the acoustic cue by itself did not affect the TA- and SOL-MEPs. Our findings suggest that a prediction of a future state of standing balance modulates the corticospinal excitability in the TA, and that the additional timing information facilitates this modulation. The corticospinal pathway thus appears to be involved in mechanisms of the predictive control as well as feedback control of standing posture.

Velocity-dependent transfer of adaptation in human running as revealed by split-belt treadmill adaptation.

Animal studies demonstrate that the neural mechanisms underlying locomotion are specific to the modes and/or speeds of locomotion. In line with animal results, human locomotor adaptation studies, particularly those focusing on walking, have revealed limited transfers of adaptation among movement contexts including different locomotion speeds. Running is another common gait that humans utilize in their daily lives and is distinct from walking in terms of the underlying neural mechanisms. The present study employed an adaptation paradigm on a split-belt treadmill to examine the possible independence of neural mechanisms mediating different running speeds. The adaptations learned with split-belt running resulted in aftereffects with magnitudes that varied in a speed-dependent matter. In the two components of the ground reaction force investigated, the anterior braking and posterior propulsive components exhibited different trends. The anterior braking component tended to show larger aftereffect under speeds near the slower side speed of the previously experienced split-belt in contrast to the posterior propulsive component in which the aftereffect size tended to be the largest at a speed that corresponded to the faster side speed of the split-belt. These results show that the neural mechanisms underlying different running speeds in humans may be independent, just as in human walking and animal studies.

Influence of motor imagery on spinal reflex excitability of multiple muscles.

The effects of motor imagery on spinal reflexes such as the H-reflex are unclear. One reason for this is that the muscles that can be used to record spinal reflexes are limited to traditional evoking methods Recently, transcutaneous spinal cord stimulation has been used for inducing spinal reflexes from multiple muscles and we aimed to examine the effect of motor imagery on spinal reflexes from multiple muscles. Spinal reflexes evoked by transcutaneous spinal cord stimulation were recorded from six muscles from lower limbs during motor imagery of right wrist extension and ankle plantarflexion with maximum isometric contraction. During both imaginary tasks, facilitation of spinal reflexes was detected in the ankle ipsilateral plantarflexor and dorsiflexor muscles, but not in thigh, toe or contralateral lower limb muscles. These results suggest that motor imagery of isometric contraction facilitates spinal reflex excitability in muscles of the ipsilateral lower leg and the facilitation does not correspond to the imaginary involved muscles.

On the skilled plantar flexor motor action and unique electromyographic activity of ballet dancers.

The study aimed to compare the ability of dance and non-dance subjects to perform fine control of a simple heel-raising/lowering movement, and to determine if there are any differences in motor unit activity in the primary plantar flexor muscles during the movement. Subjects were instructed to accurately track a sinusoidal trace with a heel-raising and lowering movement at four controlled frequencies (1, 0.5, 0.25, and 0.125 Hz). The ankle joint angle was used to characterize movement errors from the target. Surface electromyography was recorded from the soleus and medial gastrocnemius muscles. One trial including five sinusoidal traces was divided into two phases: an up phase and a down phase. To characterize motor unit activity of the plantar flexor muscles, a wavelet transform was applied to electromyographic signals recorded in each phase. For both phases, errors in movement accuracy were lower in dancers than in controls (8.7 ± 4.6 vs. 11.5 ± 6.8%, P < 0.05) regardless of the frequency of the sinusoidal wave traced. During the down phase, peak power of soleus electromyographic signals at ~ 10 Hz was statistically larger in control subjects than in dancers (10.4 ± 0.7 vs. 6.3 ± 0.4% total power, P < 0.05). These results indicate that dancers have a higher degree of motor skill in a heel raise tracking task and exhibit adaptations in the motor unit activity during skilled dynamic movements.

Short-term effects of electrical nerve stimulation on spinal reciprocal inhibition depend on gait phase during passive stepping.

A combination of electrical nerve stimulation (ENS) and passive or active cyclic movements (i.e., pedaling and stepping) has been suggested to induce stronger short-term effects in spinal circuits as compared to either intervention alone. The purpose of the present study is to determine whether the effects of ENS during passive stepping are dependent on the timing of the stimulation during the stepping cycle. A total of 10 able-bodied participants were recruited for the study. Two interventions were assessed during passive ground stepping: (1) ENS of the common peroneal nerve (CPN) during the swing phase (ENSswing) and (2) stance phase (ENSstance). ENS was applied at the motor threshold intensity on the tibialis anterior muscle for a total of 30 min. Spinal reciprocal inhibition (RI) was assessed by conditioning the H-reflex in the soleus muscle with electrical stimulation to the CPN before (baseline), as well as 5, 15, and 30 min after each intervention. Compared to the baseline, the amount of RI was increased 5 and 15 min after the ENSswing intervention, whereas it was decreased after the ENSstance intervention. This suggests that ENS has a phase-dependent effect on RI during passive stepping. Overall, the results imply that phase-dependent timing of ENS is essential for guiding plasticity in the spinal circuits.

Effects of anode position on the responses elicited by transcutaneous spinal cord stimulation.

The purpose of this study was to investigate the effect of anode position on the spinal reflex responses evoked by transcutaneous spinal cord stimulation. Healthy males participated in two experiments. In Experiment 1 (Exp. 1, n = 3), we investigated the effect of anode position on the spinal reflex responses in multiple lower-limb muscles. Experiment 2 (Exp. 2, n = 8) focused on the effect of anode position on the spinal reflex response in the vastus medialis (VM) muscle. In each experiment, electromyographic signals were recorded in the right leg muscle(s). The cathode was placed over the area between the spinous processes of the L1 and L2 vertebrae. The anode was placed over (1) the abdomen (ABD), (2) the ipsilateral (right) anterior superior iliac spine (iASIS), or (3) the contralateral (left) anterior superior iliac spine (cASIS). A double pulse stimulation test was conducted to confirm that the response was due to activation of sensory fibers (i.e. spinal reflex). The results showed that the anode position was critical for inducing the spinal reflex in the VM (Exp. 1). The ratio of second to first responses was smaller when the anode was placed over the ABD or cASIS than when the anode was placed over the iASIS (Exp. 2). In addition, the onset latency of the first response was longer when the anode was placed over the ABD or cASIS than when the anode was placed over the iASIS (Exp. 2). These results showed that the anode should be placed over the ABD or cASIS to effectively elicit spinal reflexes in lower-limb muscles.