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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.

Unilateral spatial neglect is a common neurological syndrome following predominantly right hemispheric stroke. While most patients lack insight into their neglect behaviour and do not initiate compensatory behaviours in the early recovery phase, some patients recognize it and start to pay attention towards the neglected space. We aimed to characterize visual attention capacity in patients with unilateral spatial neglect with specific focus on cortical processes underlying compensatory gaze shift towards the neglected space during the recovery process. Based on the Behavioural Inattention Test score and presence or absence of experience of neglect in their daily life from stroke onset to the enrolment date, participants were divided into USN+‰‰+ (do not compensate, n = 15), USN+ (compensate, n = 10), and right hemisphere damage groups (no neglect, n = 24). The patients participated in eye pursuit-based choice reaction tasks and were asked to pursue one of five horizontally located circular objects flashed on a computer display. The task consisted of 25 trials with 4-s intervals, and the order of highlighted objects was randomly determined. From the recorded eye tracking data, eye movement onset and gaze shift were calculated. To elucidate the cortical mechanism underlying behavioural results, electroencephalagram activities were recorded in three USN+‰‰+, 13 USN+ and eight patients with right hemisphere damage. We found that while lower Behavioural Inattention Test scoring patients (USN+‰‰+) showed gaze shift to non-neglected space, some higher scoring patients (USN+) showed clear leftward gaze shift at visual stimuli onset. Moreover, we found a significant correlation between Behavioural Inattention Test score and gaze shift extent in the unilateral spatial neglect group (r = -0.62, P < 0.01). Electroencephalography data clearly demonstrated that the extent of increase in theta power in the frontal cortex strongly correlated with the leftward gaze shift extent in the USN+‰‰+ and USN+ groups. Our results revealed a compensatory strategy (continuous attention to the neglected space) and its neural correlates in patients with unilateral spatial neglect. In conclusion, patients with unilateral spatial neglect who recognized their own neglect behaviour intentionally focused on the neglected space as a compensatory strategy to avoid careless oversight.

Studies of robot-assisted passive stepping paradigms have reported that movement-related afferent inputs strongly inhibit the excitability of the Hoffmann (H) reflex in the soleus (Sol) during walking. However, it is unknown if movement-related afferent inputs have the same effect on the excitability of spinal reflexes in the other lower-limb muscles that are involved in normal walking in healthy subjects. The aim of this study was to examine the effects of movement-related afferent inputs on the spinal reflexes in lower-limb muscles during walking. Spinal reflexes that were elicited by transcutaneous spinal cord stimulation (tSCS) were recorded during passive air standing and air stepping at three stepping velocities (stride frequencies: 14, 25, and 36 strides/min). The amplitude of the spinal reflexes was reduced in most of the recorded muscles during passive air stepping compared with air standing. Furthermore, in the Sol and lateral gastrocnemius, the amplitude of the reflexes during air stepping significantly decreased as stride frequency increased. These results demonstrate that movement-related afferent inputs inhibit spinal reflexes in the Sol and other lower-limb muscles during walking.

Limb-sparing resection of malignant pelvic tumours provides the opportunity for patients to obtain better post-operative mobility. However, because few studies have examined in detail the gait function of patients following pelvic tumour resection, the factors affecting gait performance remain to be clarified. Here, with the laboratory-based computer-assisted gait analysis, we evaluated these patients' gait objectively and the impact of a hip-stabilising supporter on gait improvement was simultaneously examined. Three-dimensional gait analysis was performed to obtain cross-sectional data for seven post-operative patients (mean age, 42.7 years; range, 20–61 years) who underwent various types of resection, including P1/4 internal hemipelvectomy (IH), P1/2/3 IH, and proximal femur resection with prosthetic reconstruction. To assess the immediate effects of a hip joint stabiliser, we instructed subjects to walk at their self-selected preferred speed and compared gait parameters with and without use of the hip stabiliser. At baseline, the average walking speed was 0.75 m/s (95 % CI 0.53–0.97). As shown by the intra-subject comparison, the hip stabiliser increased walking speed in all but one subject, increasing both temporal and spatial parameters. Ground reaction force of operated limbs increased for some subjects, while step length increased on at least one side in all subjects. Improvement in the gait parameters is indicative of better control provided by the external hip stabiliser over the affected limb. Moreover, our findings show the potential of a biomechanical approach to improve gait function following pelvic tumour resection.

The purpose of this study was to investigate the effect of electrical stimulation to the common peroneal nerve (CPN) on the spinal reflex and reciprocal inhibition (RI) during robot-assisted passive ground stepping (PGS) in healthy subjects. Five interventions were applied for 30 min in healthy subjects: PGS alone; strong CPN stimulation [50% of the maximal tibialis anterior (TA) M-wave, functional electrical stimulation (FES)] alone; weak CPN stimulation [just above the MT for the TA muscle, therapeutic electrical stimulation (TES)] alone; PGS with FES; and PGS with TES. FES and TES were applied intermittently to the CPN at 25 Hz. The soleus (Sol) H-reflex and RI, which was assessed by conditioning the Sol H-reflex with CPN stimulation, were investigated before (baseline), and 5, 15 and 30 min after each intervention. The amplitudes of the Sol H-reflex were not significantly different after each intervention as compared with the baseline values. The amounts of RI were significantly decreased 5 min after PGS with FES as compared with the baseline values, whereas they were significantly increased 5 and 15 min after PGS with TES. The other interventions did not affect the amount of RI. These results suggest that interventions that combined PGS with CPN stimulation changed the spinal RI in an intensity-dependent manner.

Cross-sectional study. To determine the effect of injury duration on plantar-flexor elastic properties in individuals with chronic spinal cord injury (SCI) and spasticity. National Rehabilitation Center for Persons with Disabilities, Japan. A total of 16 chronic SCI patients (age, 33±9.3 years; injury localization, C6-T12; injury duration, 11–371 months) participated. Spasticity of the ankle plantar-flexors was assessed using the Modified Ashworth Scale (MAS). The calf circumference and muscle thickness of the medial gastrocnemius (MG), lateral gastrocnemius and soleus were assessed using tape measure and ultrasonography. In addition, the ankle was rotated from 10° plantar-flexion to 20° dorsiflexion at 5 deg s−1 with a dynamometer, and the ankle angle and torque were recorded. After normalizing the data (the initial points of angle and torque were set to zero), we calculated the peak torque and energy. Furthermore, angle–torque data (before and after normalization) were fitted with a second- and fourth-order polynomial, and exponential (Sten–Knudsen) models, and stiffness indices (SISOP, SIFOP, SISK) and AngleSLACK (the angle at which plantar-flexor passive torque equals zero) were calculated. The stretch reflex gain and offset were determined from 0–10° dorsiflexion at 50, 90, 120 and 150 deg s−1. After logarithmic transformation, Pearson’s correlation coefficients were calculated. MAS, calf circumference, MG thickness, peak torque and SIFOP significantly decreased with injury duration (r log-log=−0.63, −0.69, −0.63, −0.53 and −0.55, respectively, P

Split-belt treadmill walking has been extensively utilized as a useful model to reveal the adaptability of human bipedal locomotion. While previous studies have clearly identified different types of locomotor adaptation, such as reactive and predictive adjustments, details of how the gait pattern would be adjusted are not fully understood. To gain further knowledge of the strategies underlying split-belt treadmill adaptation, we examined the three-dimensional ground reaction forces (GRF) and lower limb muscle activities during and after split-belt treadmill walking in 22 healthy subjects. The results demonstrated that the anterior component of the GRF (braking force) showed a clear pattern of adaptation and subsequent aftereffects. The muscle activity in the tibialis anterior muscle during the early stance phase was associated with the change of braking force. In contrast, the posterior component of GRF (propulsive force) showed a consistent increase/decrease in the fast/slow leg during the adaptation period and was not followed by subsequent aftereffects. The muscle activity in the gastrocnemius muscle during the stance phase gradually decreased during the adaptation phase and then showed a compensatory reaction during the washout phase. The results indicate that predictive feedforward control is required to set the optimal ankle stiffness in preparation for the impact at the heel contact and passive feedback control is used for the production of reflexively induced propulsive force at the end of the stance phase during split-belt treadmill adaptation. The present study provides information about the detailed mechanisms underlying split-belt adaptation and should be useful for the construction of specific rehabilitation protocols.

Although recent vertebrate studies have revealed that different spinal networks are recruited in locomotor mode- and speed-dependent manners, it is unknown whether humans share similar neural mechanisms. Here, we tested whether speed- and mode-dependence in the recruitment of human locomotor networks exists or not by statistically extracting locomotor networks. From electromyographic activity during walking and running over a wide speed range, locomotor modules generating basic patterns of muscle activities were extracted using non-negative matrix factorization. The results showed that the number of modules changed depending on the modes and speeds. Different combinations of modules were extracted during walking and running, and at different speeds even during the same locomotor mode. These results strongly suggest that, in humans, different spinal locomotor networks are recruited while walking and running, and even in the same locomotor mode different networks are probably recruited at different speeds.

A phantom limb is the sensation that an amputated limb is still attached to the body and is moving together with other body parts. Phantom limb phenomenon is often described on the basis of the patient’s subjective sense, for example as represented using a visual analog scale (VAS). The aim of this study was to propose a novel quantification method for behavioral aspect of phantom limb by psychophysics. Twelve unilateral forearm amputees were asked to perform phantom wrist motion with various motion frequencies (60, 80, 100, 120, 140, 160, 180, 200, 220, 240% of preferred speed). The attainment of phantom limb motion in each session was rated by the VAS ranging from 0 (hard) to 10 (easy). The relationship between the VAS and motion frequency was mathematically fitted by quadric function, and the value of shift and the degree of steepness were obtained as evaluation variables for the phantom limb movement. In order to test whether the proposed method can reasonably quantify the characteristics of phantom limb motion, we compared the variables among three different phantom limb movement conditions: (1) unilateral (phantom only), (2) bimanual, and (3) bimanual wrist movement with mirror reflection-induced visual feedback (MVF). While VAS rating showed a larger extent of inter- and intra-subject variability, the relationship of the VAS in response to motion frequency could be fitted by quadric curve, and the obtained parameters based on quadric function well characterize task-dependent changes in phantom limb movement. The present results suggest the potential usefulness of psychophysical evaluation as a validate assessment tool of phantom limb condition.

Congenital insensitivity to pain (CIP), which is an extremely rare sensory neuropathy, is defined as the absence of normal responses to noxious stimuli. Although motor function is not directly impaired in CIP patients, it is likely that the sensory deficit affects the motor control system. In order to characterize motor capacity in CIP patients, we here measured grip force and acceleration of a held object in 12 patients with CIP and 12 age-matched able-bodied subjects. The results demonstrated that the grip force during the object grasp-lift-holding task was significantly greater, less reproducibility and greater fluctuation in the acceleration of the object in CIP patients than in normal subjects. Moreover, some patients showed absence of temporal coupling between the grip and load force, suggesting that anticipatory modulation of the grip force was at least partly impaired. As far as the authors know, this is the first study to characterize motor control ability in patients with CIP. The observed abnormal motor capacity can be at least partly attributed to a lack of sensory inputs mediated by Aδ and unmyelinated C-, specifically C-tactile, fibers. The present results may provide information useful for the prevention of secondary injury and education for patients during the developmental stage.

The purpose of this study was to examine the effects of aging on posture-related changes of the stretch reflex excitability in the ankle extensor, soleus (SOL), and flexor, tibialis anterior (TA) muscles. Fourteen neurologically normal elderly (mean 68±6years) and 12 young (mean 27±3years) subjects participated. Under two postural conditions, upright standing (STD) and sitting (SIT), stretch reflex electromyographic (EMG) responses in the SOL/TA muscle were elicited by imposing rapid ankle dorsi-/plantar-flexion. Under the SIT condition, subjects were asked to keep the SOL background EMG level, which is identical to that under the STD condition. In the SOL muscle, both groups showed significant enhancement of the short-latency stretch reflex (SLR) response when the posture changed from SIT to STD. In the TA muscle, the young group showed significant enhancement of the middle- (MLR) and long-latency stretch reflex (LLR) when the posture changed from SIT to STD; no such modulation was observed in the elderly group. Since the TA stretch reflex responses under the STD condition were comparable in the young and elderly groups, the lack of posture-related modulation of the TA muscle in the elderly group might be explained by augmented stretch reflex excitability under the SIT condition. The present results suggest that the (1) SOL SLR responses are modulated both in the young and elderly subjects when the posture is changed from SIT to STD, (2) TA MLR and LLR responses are not modulated in the elderly subjects when the posture is changed from SIT to STD, while each response is same between the young and elderly in STD, and (3) the effect of aging on the posture-related stretch reflex differs in the SOL and TA muscles.

The purpose of this study was to test whether the spinal reflex excitability of the soleus muscle is modulated as posture changes from a supine to a passive upright position. Eight healthy subjects (29.6+/-5.4 yrs) participated in this study. Stretch and H-reflex responses were elicited while the subjects maintained passive standing (ST) and supine (SP) postures. The passive standing posture was accomplished by using a gait orthosis to which a custom-made device was mounted to elicit stretch reflex in the soleus muscle. This orthosis makes it possible to elicit stretch and H-reflexes without background muscle activity in the soleus muscle. The results revealed that the H-reflex amplitude in the ST was smaller than that in the SP condition, which is in good agreement with previous reports. On the other hand, the stretch reflex was significantly larger in the ST than in the SP condition. Since the experimental conditions of both the stretch and H-reflex measurements were exactly the same, the results were attributed to differences in the underlying neural mechanisms of the two reflex systems: different sensitivity of the presynaptic inhibition onto the spinal motoneuron pool and/or a change in the muscle spindle sensitivity.

The present study hypothesized that if subliminal facilitation of the ankle flexor motoneurons is related to preparatory state to a mechanical perturbation while standing, different standing conditions such as standing with eyes-closed or touching a bar should have different influences on the facilitation levels. While the subjects were maintaining an upright stance posture, sudden drops of support surface were applied several times in the following four different conditions: (1) standing with eyes-open, (2) with eyes-closed, (3) with eyes-open and warning of the drop, and (4) with eyes-open and touching a bar with both hands. The results demonstrated that the EMG responses in the ankle flexor TA muscle increased in the eyes-closed condition, while it reduced in the conditions, such as that the subjects had prior warning or touched a bar. The preparatory state of supraspinal neural centers was suggested to be related to the observed variation in the EMG responses.

Background The dynamic role of the trunk musculature, with respect to stability, has not been fully explored to date. The purpose of this study was, using a transient and multi-directional perturbation, to: (1) quantify the tonic level of activity in the superficial trunk musculature prior to any perturbation; (2) quantify the phasic activity in those same muscles following application of a transient, horizontally directed load; and (3) quantify the direction-dependent behavior of this phasic response. Methods Twelve healthy individuals were perturbed during sitting via a chest harness in eight horizontal directions. Surface electromyograms were measured bilaterally from the abdominal (rectus abdominis, internal and external obliques) and back musculature (thoracic and lumbar erector spinae) to determine the tonic muscle activity prior to perturbation, and the phasic response following perturbation. A descriptive model was used to characterize the relationship between the phasic response of the muscles due to perturbation and the pulling direction. Findings Tonic activity in the trunk musculature in upright sitting is low, but still above resting levels by at about 1–3% of the MVC for the abdominal muscles, and 4–6% for the back muscles. Each trunk muscle also showed a direction-specific, phasic activation in response to perturbation, above these tonic levels of activation. This phasic activation was accurately modeled using a descriptive model for each muscle. Interpretation The obtained muscle activation level and the identified descriptive model will be applied in the design of a closed-loop controller for functional electrical stimulation.

The delay of the sensory-motor feedback loop is a destabilizing factor within the neural control mechanism of quiet standing. The purposes of this study were 1) to experimentally identify the neuromusculoskeletal torque-generation process during standing posture and 2) to investigate the effect of the delay induced by this system on the control mechanism of balance during quiet standing. Ten healthy adults participated in this study. The ankle torque, ankle angle, and electromyograms from the right lower leg muscles were measured. A ground-fixed support device was used to support the subject at his/her knees, without changing the natural ankle angle during quiet standing. Each subject was asked to mimic the ankle torque fluctuation by exerting voluntary ankle extension while keeping the supported standing posture. Using the rectified soleus electromyogram as the input and the ankle torque as the output, a critically damped, second-order system (twitch contraction time of 0.152 ± 0.027 s) successfully described the dynamics of the torque-generation process. According to the performed Bode analysis, the phase delay induced by this torque-generation process in the frequency region of spontaneous body sway during quiet standing was considerably large, corresponding to an effective time delay of about 200 to 380 ms. We compared the stability of the balance control system with and without the torque-generation process and demonstrated that a much smaller number of gain combinations can stabilize the model with the torque-generation process than without it. We concluded that the phase delay induced by the torque-generation process is a more destabilizing factor in the control mechanism of quiet standing than previously assumed, which restricts the control strategies that can stabilize the entire system.

We previously found that orthotic gait training can induce 'locomotor-like' coordinated muscle activity of the paralyzed lower limb in persons with spinal cord injury (SCI). The purpose of the present study was to characterize the locomotor-like muscle activity based on data obtained from electromyographic recordings and motion analysis during orthotic gait in nine motor complete SCI subjects. Seven of nine subjects showed a common EMG activation pattern mainly in the ankle (soleus: Sol) and hip extensor (biceps femoris: BF) muscles. The locomotor-like muscle activity was well synchronized with the gait cycle, namely, the EMG amplitude of both Sol and BF muscle had common temporal relationships with the ground reaction force, and hip and ankle joint motions. While the presence or absence of the EMG activity during orthotic gait was consistent with those of mechanically-induced stretch reflex, the duration and amount area of the locomotor-like muscle activity were significantly longer than those of the stretch reflex in the Sol muscle. Moreover, the Sol EMG magnitude had strong relevance to hip as well as ankle angular velocities. These results indicate that the locomotor-like muscle activity during orthotic gait is not a mere reflex response, but includes an activity of the central pattern generator (CPG) and its interaction with afferent inputs. Orthotic gait training for complete SCI persons might have a potential to activate the spinal locomotor center.

The purpose of the present study was to investigate the association of neural control between walking and running, and in particular, how these two gait modes at different velocities are controlled (thus, either dependent on the gait mode or on velocity) by the central nervous system (CNS). The subjects were fully-adapted (acquiring modified motor patterns) to either walk or run on a split-belt treadmill driven in split mode (asymmetry in the velocities of two belts at 1.0 and 2.0 m s−1). Subsequently, the extent of adaptation transfer (i.e., how the adaptation affected the subsequent task execution) to walking and running at three different velocities in the tied mode (symmetrical velocities) at 0.75 m s−1: reflecting a preference to walk, 1.50 m s−1: a preference to both walk and to run, 2.25 m s−1: and a preference to run) was tested. Both walking and running on the split-belt resulted in the emergence of a significant aftereffect (asymmetrical movement) at all of the velocities tested when the adapted modes were executed subsequently (i.e., walking after adapting to walk and running after adapting to run). For contrasting modes (i.e., running after adapting to walk and walking after adapting to run), in contrast, such aftereffects were far less evident under all the velocities, thus showing only limited transfer across gait modes. The results demonstrate a clear mode-dependency in the neural control between human walking and running. In addition, only for walking, there was a degree of velocity-dependency.

The purpose of this study was to investigate the effects of hip proprioceptors on soleus stretch reflex excitability in standing humans. A custom-made device to stretch the ankle extensors was mounted on the lower leg portion of a gait orthosis and was used to elicit stretch reflex responses while standing. Six subjects with motor complete spinal cord injury (SCI) and six spinal intact subjects were placed in the orthosis, and stretch reflex responses were elicited when static and/or dynamic hip joint angle changes were imposed. We found that static hip extension significantly enhanced the stretch reflex responses as compared to the neutral position and the hip flexion position only in the SCI group. The EMG magnitude induced by hip extension was 142 +/- 16.6% greater than that induced by the neutral position. When the leg was dynamically swung, the reflex responses also changed with the phase of the hip angle in the SCI group; in particular, the reflex amplitude was enhanced with hip extension and in the transition phase from flexion to extension. Although the magnitude of the changes was less than that in the SCI group, a similar type of modulation was found in the normal group. Given the fact that the persons with SCI had lost the neural connection between higher nervous center and the paralyzed lower limb muscles, the mechanism underlying the present results can be attributed to the peripheral afferent input due to the hip angle changes. We concluded that hip mediated afferent input has a significant influence on the excitability modulation of the soleus stretch reflex pathway. Such neural modulation may play a role in the mechanism responsible for the phase-dependent modulation of the stretch reflex while walking.

Cross-sectional and comparative investigation using quadriplegics (QP) and nondisabled subjects (ND).To evaluate cardiorespiratory responses during passive walking-like exercise (PWE) in QP.National Rehabilitation Center for Persons with Disabilities in Japan.The subjects were seven male QP with complete lesion (age: 27.0 +/- 5.4, injured level: C6-C7) and six male ND (age: 26.3 +/- 4.5). Cardiorespiratory responses were measured until voluntary fatigue during PWE, the rhythmical activity of paralyzed lower limbs synchronized with arm movements.There were no significant differences in oxygen consumption (VO(2)), pulmonary ventilation (VE), heart rate (HR) and oxygen pulse (O(2) pulse) between QP and ND during PWE. ND showed increased ventilatory equivalent for oxygen (VE/VO(2) ratio) during exercise, while QP showed a significantly greater respiratory rate (RR) during exercise than ND (P0.05).PWE elicited an increase in VO(2) with workload increment in QP similar to ND. However, higher RR suggested the intrinsic dysfunction of RR control during submaximal exercise in QP. From these results, it was thought that respiratory response would be the restriction factor of efficient oxygen transportation during PWE in QP.

Even in the paralyzed lower limb muscle, EMG activity can be induced by imposing passive leg movement in standing posture in persons with spinal cord injury (SCI). The purpose of the present study was to ascertain whether the oxygenation level of the paralyzed lower limb muscle covaried with the muscle EMG activity during imposed passive leg movement.Six motor-complete SCI subjects and four neurologically normal controls were placed on a gait-training apparatus that enabled the SCI subjects to stand and move their legs passively. After a 1-min resting stage, consecutive passive alternate leg movements were performed at different frequencies (0.8, 1, 1.2, and 1 Hz, for 3 min at each stage). To obtain postexercise data, subjects were kept in a standing posture for 5 min after passive movement ceased. The EMG activity and concentration changes in the oxygenated (oxy-) and deoxygenated hemoglobin (Hb) (deoxy-Hb) were continuously measured using near-infrared spectroscopy (NIRS) from the gastrocnemius muscle.In all SCI subjects, muscle EMG activity was observed during passive leg movement. The oxy-Hb level gradually increased, whereas the deoxy-Hb decreased, and these changes were independent of the total Hb changes. In the recovery stage, the total Hb level was found to exceed the preexercise level. In contrast to the SCI patients, the normal subjects showed neither EMG activity nor changes in oxy- or deoxy-Hb.The present results demonstrate that passive leg movement can induce not only muscular activity but also alteration of muscle oxygenation level in the paralyzed lower leg. Particularly, induced muscular activity seems to correlate with increased perfusion of the muscle.

It is now well recognized that muscle activity can be induced even in the paralyzed lower limb muscles of persons with spinal cord injury (SCI) by imposing locomotion-like movements on both of their legs. Although the significant role of the afferent input related to hip joint movement and body load has been emphasized considerably in previous studies, the contribution of the “alternate” leg movement pattern has not been fully investigated. This study was designed to investigate to what extent the alternate leg movement influenced this “locomotor-like” muscle activity. The knee-locked leg swing movement was imposed on 10 complete SCI subjects using a gait training apparatus. The following three different experimental conditions were adopted: 1) bilateral alternate leg movement, 2) unilateral leg movement, and 3) bilateral synchronous (in-phase) leg movement. In all experimental conditions, the passive leg movement induced EMG activity in the soleus and medial head of the gastrocnemius muscles in all SCI subjects and in the biceps femoris muscle in 8 of 10 SCI subjects. On the other hand, the EMG activity was not observed in the tibialis anterior and rectus femoris muscles. The EMG level of these activated muscles, as quantified by integrating the rectified EMG activity recorded from the right leg, was significantly larger for bilateral alternate leg movement than for unilateral and bilateral synchronous movements, although the right hip and ankle joint movements were identical in all experimental conditions. In addition, the difference in the pattern of the load applied to the leg among conditions was unable to explain the enhancement of EMG activity in the bilateral alternate leg movement condition. These results suggest that the sensory information generated by alternate leg movements plays a substantial role in amplifying the induced locomotor-like muscle activity in the lower limbs.

This is, to our knowledge, the first report demonstrating the effects of orthotic gait training on the activity of the spinal locomotor neural networks. Three subjects with complete spinal cord injury (SCI) performed 1-h training with reciprocating gait orthosis 5 days/week for 12 weeks. The results showed that after 3 (n=1) or 6 weeks (n=2) of training, EMG activities synchronized with locomotor rhythm appeared in the soleus muscle (SOL) in all subjects, although very little EMG activity accompanied the orthotic gait at the early training stage. Our results suggest that the induced modulation in the SOL EMG waveforms might be attributable to changes in the orthotic gait movement pattern, and/or changes in the interneuronal activities of the spinal locomotor neural networks, as a result of orthotic gait training.

Study design: Prospective before–after trial. Objective: To examine the changes of natural killer (NK) cell activity in response to orthotic gait exercise in thoracic level of spinal cord-injured (SCI) patients. Setting: National Rehabilitation Center for Persons with Disabilities, Japan. Methods: In all, 10 thoracic level of SCI patients (ranging Th5–Th12), who experienced orthotic gait training, participated in this study. NK cell activity at an effector:target (E/T) ratio (20:1) was examined in a sample of peripheral blood taken before and just after orthotic gait exercise for 20 min. On a separate day, to evaluate the physical intensity of the orthotic gait exercise, cardiorespiratory responses at rest and during exercise were measured. Results: The resting value of the NK cell activity in our SCI patients was remarkably lower than that in normal subjects reported in previous studies. The NK cell activity was significantly increased through a 20 min orthotic gait exercise (pre versus post; 12.7±5.28 versus 17.76±6.71, P

Aim: To examine whether the stretch reflex excitability of the soleus muscle changes with age, stretch reflexes at rest (REST) and during weak voluntary contractions (ACT) were elicited in 18 older and 14 younger subjects. Method: The amplitude of the stretch reflex responses and gain, defined as the gradient of the regression line for the relation between stretch reflex responses against the angular velocity of the applied perturbation, were evaluated in each short-latency (M1) and two long-latency components (M2 and M3). Results: It was found that in the older group, both the amplitude and gain of the M1 component did not change from the REST to the ACT conditions, whereas in the younger group both variables significantly increased from the REST to ACT conditions. The latency of the M1 component was significantly shorter under the REST condition (older vs. younger: 51.8 ± 7.37 vs. 55.1 ± 8.69 ms), while no group differences were found in those variables under the ACT condition, suggesting that the muscle-tendon complexes of SOL muscles of the older subjects were less elastic and had less slack, probably due to age-related histochemical alterations. Further, the Hoffman reflex (H-reflex), elicited during the REST condition in 10 older and 11 younger subjects showed no significant differences, suggesting that the soleus motoneuron response to the Ia input was comparable between the two subject groups. Conclusion: The histochemical alterations occurring with the ageing process might augment the short-latency stretch reflex in the SOL muscle without enhancement of motoneuronal excitability, and this effect might be masked when the muscle is voluntarily activated.

It is well known that muscle contraction can be easily evoked in the human soleus muscle by applying single-pulse electrical stimulation to the tibial nerve at the popliteal fossa. We herein reveal the unexpected phenomenon of muscle contractions that can be observed when train stimulation is used instead. We found, in 11 human subjects, that transient electrical train stimulation (1-ms pulses, 50 Hz, 2 s) was able to induce sustained muscle contractions in the soleus muscle that outlasted the stimulation period for greater than 1 min. Subjects were unaware of their own muscle activity, suggesting that this is an involuntary muscle contraction. In fact, the excitability of the primary motor cortex (M1) with the sustained muscle contractions evaluated by transcranial magnetic stimulation was lower than the excitability with voluntary muscle contractions even when both muscle contraction levels were matched. This finding indicates that M1 was less involved in maintaining the muscle contractions. Furthermore, the muscle contractions did not come from spontaneous activity of muscle fibers or from reverberating activity within closed neuronal circuits involving motoneurons. These conclusions were made based on the respective evidence: 1) the electromyographic activity was inhibited by stimulation of the common peroneal nerve that has inhibitory connections to the soleus motoneuron pool and 2) it was not abolished after stopping the reverberation (if any) for approximately 100 ms by inducing the silent period that followed an H-reflex. These findings indicate that the sustained muscle contractions induced in this study are most likely to be maintained by autonomous activity of motoneurons and/or interneurons within the human spinal cord.

Comparative study of the effectiveness of walking exercise with a newly developed gait orthosis, the weight-bearing control (WBC) orthosis, for thoracic level of paraplegic patients.To test its feasibility as a rehabilitation alternative for paraplegic patients, the energy consumption and cost during walking with WBC were calculated and compared with the values of conventional orthoses given in previous reports.National Rehabilitation Center for the Disabled, Japan.Four paraplegic patients with traumatic spinal cord injuries ranging from T8 to T12 participated. Experiments were conducted after 3 months of the orthotic gait training with WBC. The cardiorespiratory parameters were continuously measured at rest and during walking with a telemetric device. The steady-state value of the oxygen uptake (V(O2)), heart rate (HR), the energy consumption (J/kg/s) and energy cost (J/kg/m) were calculated.The average walking speed was 19.0 +/- 2.58 m/min. The steady-state value of the V(O2) and HR were 16.08 +/- 1.93 ml/kg and 147.3 +/- 10.94 b/min, respectively. The energy cost during orthotic walking tended to be better than the values of conventional orthoses, whereas the energy consumption was almost similar.WBC enables thoracic level of paraplegic patients to walk at relatively higher speed than conventional orthoses under similar energy expenditure. The special devices equipped with WBC are therefore considered to lead to improvement of the energy cost of walking. The physical intensity presumed by cardiorespiratory responses during walking with WBC is suited to promote their aerobic capacity. Therefore, it is concluded that the WBC orthosis could be an effective alternative in rehabilitation for thoracic level of paraplegic patients.

The purpose of the present study was to ascertain the contribution of peripheral sensory inputs to posture-related Hoffman reflex (H-reflex) modulation in the human soleus muscle. The soleus H-reflexes were elicited in the sitting (SI) and passive standing (ST) conditions in patients with clinically complete spinal cord injuries (SCI) and in neurologically normal subjects. The results clearly showed suppression of the H-reflex amplitude during the ST compared with the SI condition especially in the SCI group. Considering the lack of a descending neural command in the SCI patients, our findings suggest that peripheral sensory inputs primarily contribute to the reduction of the soleus H-reflex during the upright standing posture.

The purpose of this study was to investigate the cortical activities during two types of Go/NoGo task with different movement instructions (Push-Go and Release-Go) using transcranial magnetic stimulation (TMS) and event-related potential (ERP) recordings. In the Push-Go condition, ten subjects were instructed either to push a button with their right index finger as fast as possible after a Go signal or not to push it after a NoGo signal. In the Release-Go condition, they were asked beforehand to continually depress a button by pushing, and instructed either to release it as fast as possible after a Go signal or not to release it after a NoGo signal. TMS was applied to the left primary motor cortex at 20--300 ms after each signal. In the Push-Go condition trials, the amplitude of the motor evoked potentials (MEPs) recorded from the right first dorsal interosseous muscle significantly increased at 120--300 ms after the Go signals and decreased at 160--200 ms after the NoGo signals. In contrast, the MEP amplitudes recorded during the Release-Go condition trials significantly decreased at 160--300 ms after the Go signals and significantly increased at 160--180 and 220--300 ms after the NoGo signals. On the other hand, the ERPs recorded in the frontocentral cortex after each signal for five of the subjects were identical in both the Push-Go and Release-Go condition trials. These results indicated that, while the cortical activities related to the Go/NoGo decision were similar in the two task conditions, the corticospinal excitability was modulated so as to suppress or facilitate the required Go responses depending on the given movement instructions. This suggests that the Go/NoGo decision may be separate from the subsequent motor program.

While previous studies have shown that muscle stretching suppresses monosynaptic spinal reflex excitability in stretched muscles, its effects on non-stretched muscles is still largely unknown. The purpose of this study was to examine the effects of muscle stretching on monosynaptic spinal reflex in non-stretched muscles. Ten healthy male subjects participated in this study. Muscle stretching of the right triceps surae muscle was performed using a motor torque device for 1 minute. Three different dorsiflexion torques (at approximately 5, 10, and 15 Nm) were applied during muscle stretching. Spinal reflexes evoked by transcutaneous spinal cord stimulation were recorded in both the lower-limb muscles before, during, and at 0 and 5 min following muscle stretching. The amplitudes of the spinal reflexes in both the stretched and non-stretched muscles in the right (ipsilateral) leg were smaller during stretching compared to before, and at 0 and 5 min after stretching. Furthermore, the degree of reduction in the amplitude of the spinal reflexes in the right (ipsilateral) leg muscles increased significantly as the dorsiflexion torque (i.e., stretching of the right triceps surae muscles) increased. In contrast, reduction in the amplitude of the spinal reflexes with increasing dorsiflexion torque was not seen in the left (contralateral) leg muscles. Our results clearly indicate that muscle stretching has inhibitory effects on monosynaptic spinal reflexes, not only in stretched muscles, but also in non-stretched muscles of the ipsilateral leg.

The amplitude of the Hoffmann (H)-reflex in the soleus (Sol) muscle is known to be suppressed during passive stepping compared with during passive standing. The reduction of the H-reflex is not due to load-related afferent inputs, but rather to movement-related afferent inputs from the lower limbs. To elucidate the underlying neural mechanisms of this inhibition, we investigated the effects of the stepping velocity on the Sol H-reflex during robot-assisted passive stepping in 11 healthy subjects. The Sol H-reflexes were recorded during passive standing and stepping at five stepping velocities (stride frequencies: 14, 21, 28, 35, and 42 min(-1)) in the air. The Sol H-reflexes were significantly inhibited during passive stepping as compared with during passive standing, and reduced in size as the stepping velocity increased. These results indicate that the extent of H-reflex suppression increases with increasing movement-related afferent inputs from the lower limbs during passive stepping. The velocity dependence suggests that the Ia afferent inputs from lower-limb muscles around the hip and knee joints are most probably related to this inhibition.

OBJECTIVE: To test whether the phantom limb awareness could be altered by observing mirror reflection-induced visual feedback (MVF) in unilateral forearm amputees. METHODS: Ten unilateral forearm amputees were asked to perform bilateral (intact and phantom) synchronous wrist motions with and without MVF. During wrist motion, electromyographic activities in the extensor digitorum longus (EDL) and flexor carpi radialis muscles (FCR) were recorded with bipolar electrodes. Degree of wrist range of motion (ROM) was also recorded by electrogoniometry attached to the wrist joint of intact side. Subjects were asked to answer the degree of attainment of phantom limb motion using a visual analog scale (VAS: ranging from 0 (hard) to 10 (easy)). RESULTS: VAS and ROM were significantly increased by utilizing MVF, and the extent of an enhancement of the VAS and wrist ROM was positively correlated (r = 0.72, p

The purpose of the present study was to investigate how stretch reflex (SR) responses in the ankle extensor (soleus: SOL) and flexor (tibialis anterior: TA) muscles would be modulated with temporal and/or spatial predictions of external perturbations and whether their effects are specific to the standing posture. SR responses in the SOL/TA were elicited by imposing quick ankle toes-up/toes-down rotations while standing upright and in the supine position. We designed four experimental conditions based on pre-information about perturbations: no information (No Cue), the timing of the perturbation onset (TIM), the direction of the perturbation (DIR), and both the timing and direction of the perturbation (TIM/DIR). Each condition was separated and its order was counterbalanced. In the SR of TA evoked by toes-down rotation, integrated electromyography activities of the late component were significantly reduced in the TIM and TIM/DIR conditions as compared with those in the No Cue and DIR conditions. The occurrence rate of late SR components that reflects how often the reflex response was observed was also lower in the TIM and TIM/DIR conditions as compared with that in the No Cue and DIR conditions. On the other hand, no significant changes were seen among the four conditions in the early SR component in the TA and both SR components in the SOL. The same results in the occurrence rate were found in the supine position. The present results suggest (1) only temporal predictions have a remarkable effect on the SR excitability of the TA, and (2) this effect is independent of posture.

The two major modes of locomotion in humans, walking and running, may be regarded as a function of different speed (walking as slower and running as faster). Recent results using motor learning tasks in humans, as well as more direct evidence from animal models, advocate for independence in the neural control mechanisms underlying different locomotion tasks. In the current study, we investigated the possible independence of the neural mechanisms underlying human walking and running. Subjects were tested on a split-belt treadmill and adapted to walking or running on an asymmetrically driven treadmill surface. Despite the acquisition of asymmetrical movement patterns in the respective modes, the emergence of asymmetrical movement patterns in the subsequent trials was evident only within the same modes (walking after learning to walk and running after learning to run) and only partial in the opposite modes (walking after learning to run and running after learning to walk) (thus transferred only limitedly across the modes). Further, the storage of the acquired movement pattern in each mode was maintained independently of the opposite mode. Combined, these results provide indirect evidence for independence in the neural control mechanisms underlying the two locomotive modes.

Direct evidence supporting the contribution of upper limb motion on the generation of locomotive motor output in humans is still limited. Here, we aimed to examine the effect of upper limb motion on locomotor-like muscle activities in the lower limb in persons with spinal cord injury (SCI). By imposing passive locomotion-like leg movements, all cervical incomplete ( n = 7) and thoracic complete SCI subjects ( n = 5) exhibited locomotor-like muscle activity in their paralyzed soleus muscles. Upper limb movements in thoracic complete SCI subjects did not affect the electromyographic (EMG) pattern of the muscle activities. This is quite natural since neural connections in the spinal cord between regions controlling upper and lower limbs were completely lost in these subjects. On the other hand, in cervical incomplete SCI subjects, in whom such neural connections were at least partially preserved, the locomotor-like muscle activity was significantly affected by passively imposed upper limb movements. Specifically, the upper limb movements generally increased the soleus EMG activity during the backward swing phase, which corresponds to the stance phase in normal gait. Although some subjects showed a reduction of the EMG magnitude when arm motion was imposed, this was still consistent with locomotor-like motor output because the reduction of the EMG occurred during the forward swing phase corresponding to the swing phase. The present results indicate that the neural signal induced by the upper limb movements contributes not merely to enhance but also to shape the lower limb locomotive motor output, possibly through interlimb neural pathways. Such neural interaction between upper and lower limb motions could be an underlying neural mechanism of human bipedal locomotion.

Yu E, Abe M, Masani K, Kawashima N, Eto F, Haga N, Nakazawa K. Evaluation of postural control in quiet standing using center of mass acceleration: comparison among the young, the elderly, and people with stroke. Objective To determine center of mass (COM) acceleration usefulness in the evaluation of postural control during quiet standing. Design Three-group comparison design. Setting A research laboratory. Participants Poststroke subjects (n=12), healthy elderly subjects (n=22), and healthy young subjects (n=25). Interventions Not applicable. Main Outcome Measures With a force platform, postural sway was evaluated by using the standard deviations of COM acceleration and center of pressure (COP) and COM (COP-COM) in which COP-COM represents the distance between the COP and the COM. Results COM acceleration and COP-COM variables were greater in the poststroke group than in the healthy groups (elderly and young) in the mediolateral (ML) direction. Both variables in the anteroposterior (AP) direction were greater in the poststroke group and the elderly group than in the young group. Furthermore, the correlations between COM acceleration and COP-COM in each group in each direction were shown to be significantly high (r range, .906–.979; P Conclusions COM acceleration was useful in the evaluation of postural control during quiet standing when comparing the young, the elderly, and poststroke patients. Additionally, COM acceleration and COP-COM in both the AP and ML directions during quiet standing were significantly and highly correlated. Thus, we proposed that COM acceleration can be an alternative and convenient measure instead of COP-COM in the evaluation of postural control.

Cross-sectional, experimental research.To clarify the effect of lesion level on cardio-respiratory responses and biomechanical characteristics of walking with a reciprocating gait orthosis in complete paraplegia with spinal cord injury (SCI).National Rehabilitation Center for Persons with Disabilities, Japan.Ten SCI individuals (age: 20-34 years, injured level: Th5-12) who experienced orthotic gait training at least for 10 weeks participated in two experiments: (1) measurement of the cardiorespiratory responses during 20 min of orthotic gait exercise; and (2) three-dimensional motion analysis and ground reaction force measurement using the VICON system. We calculated the following parameters: pulmonary ventilation, oxygen consumption (VO(2)), heart rate (HR), gait speed, cadence, stride length, crutch force (CF), hip range of motion (ROM), and hip angular velocity (VEL). Further, energy consumption and energy cost were calculated using the steady-state value of VO(2) and gait speed.The steady-state value of the VO(2) (18.2 +/- 3.80 ml/kg) and HR (133.0 +/- 21.63 b/min) tended to be larger in higher thoracic SCI subjects. There were strong positive correlations between the lesion level and walking speed (r = 0.74), energy cost (r = 0.85), and hip ROM (r = 0.78). On the other hand, negative correlation between the lesion level and peak CF (r = -0.78) was clarified.The physiological intensity of the orthotic gait strongly depended on the level of lesion. It seems likely that a limited hip range of motion and excess upper limb load result in the low energy cost of orthotic gait for the higher thoracic level of paraplegic patients.

Recent studies have revealed that the stretch reflex responses of both ankle flexor and extensor muscles are coaugmented in the early stance phase of human walking, suggesting that these coaugmented reflex responses contribute to secure foot stabilization around the heel strike. To test whether the reflex responses mediated by the stretch reflex pathway are actually induced in both the ankle flexor and extensor muscles when the supportive surface is suddenly destabilized, we investigated the electromyographic (EMG) responses induced after a sudden drop of the supportive surface at the early stance phase of human walking. While subjects walked on a walkway, the specially designed movable supportive surface was unexpectedly dropped 10 mm during the early stance phase. The results showed that short-latency reflex EMG responses after the impact of the drop (

Excitability of both stretch reflex (SR) and motor evoked potential (MEP) elicited in the tibialis anterior (TA) muscle by transcranial magnetic stimulation were tested in standing humans. The results demonstrated significantly greater values for both SR and MEP in the TA while standing than while in the supine posture, although background electromyographic activity was silent in the two conditions. Taken together with previous reports that both pathways are facilitated in the TA at the early stance phase of human walking, our findings suggest that a common neural mechanism underlies both observations, one that might be functionally relevant for securing ankle joint stabilization during upright standing.