Modulation of soleus stretch reflexes during walking in people with chronic incomplete spinal cord injury.

In people with spasticity due to chronic incomplete spinal cord injury (SCI), it has been presumed that the abnormal stretch reflex activity impairs gait. However, locomotor stretch reflexes across all phases of walking have not been investigated in people with SCI. Thus, to understand modulation of stretch reflex excitability during spastic gait, we investigated soleus stretch reflexes across the entire gait cycle in nine neurologically normal participants and nine participants with spasticity due to chronic incomplete SCI (2.5-11 year post-injury). While the participant walked on the treadmill at his/her preferred speed, unexpected ankle dorsiflexion perturbations (6° at 250°/s) were imposed every 4-6 steps. The soleus H-reflex was also examined. In participants without SCI, spinal short-latency "M1", spinal medium latency "M2", and long-latency "M3" were clearly modulated throughout the step cycle; the responses were largest in the mid-stance and almost completely suppressed during the stance-swing transition and swing phases. In participants with SCI, M1 and M2 were abnormally large in the mid-late-swing phase, while M3 modulation was similar to that in participants without SCI. The H-reflex was also large in the mid-late-swing phase. Elicitation of H-reflex and stretch reflexes in the late swing often triggered clonus and affected the soleus activity in the following stance. In individuals without SCI, moderate positive correlation was found between H-reflex and stretch reflex sizes across the step cycle, whereas in participants with SCI, such correlation was weak to non-existing, suggesting that H-reflex investigation would not substitute for stretch reflex investigation in individuals after SCI.

Acquisition of a simple motor skill: task-dependent adaptation and long-term changes in the human soleus stretch reflex.

Changing the H reflex through operant conditioning leads to CNS multisite plasticity and can affect previously learned skills. To further understand the mechanisms of this plasticity, we operantly conditioned the initial component (M1) of the soleus stretch reflex. Unlike the H reflex, the stretch reflex is affected by fusimotor control, comprises several bursts of activity resulting from temporally dispersed afferent inputs, and may activate spinal motoneurons via several different spinal and supraspinal pathways. Neurologically normal participants completed 6 baseline sessions and 24 operant conditioning sessions in which they were encouraged to increase (M1up) or decrease (M1down) M1 size. Five of eight M1up participants significantly increased M1; the final M1 size of those five participants was 143 ± 15% (mean ± SE) of the baseline value. All eight M1down participants significantly decreased M1; their final M1 size was 62 ± 6% of baseline. Similar to the previous H-reflex conditioning studies, conditioned reflex change consisted of within-session task-dependent adaptation and across-session long-term change. Task-dependent adaptation was evident in conditioning session 1 with M1up and by session 4 with M1down. Long-term change was evident by session 10 with M1up and by session 16 with M1down. Task-dependent adaptation was greater with M1up than with the previous H-reflex upconditioning. This may reflect adaptive changes in muscle spindle sensitivity, which affects the stretch reflex but not the H reflex. Because the stretch reflex is related to motor function more directly than the H reflex, M1 conditioning may provide a valuable tool for exploring the functional impact of reflex conditioning and its potential therapeutic applications. NEW & NOTEWORTHY Since the activity of stretch reflex pathways contributes to locomotion, changing it through training may improve locomotor rehabilitation in people with CNS disorders. Here we show for the first time that people can change the size of the soleus spinal stretch reflex through operant conditioning. Conditioned stretch reflex change is the sum of task-dependent adaptation and long-term change, consistent with H-reflex conditioning yet different from it in the composition and amount of the two components.

Short-latency crossed spinal responses are impaired differently in sub-acute and chronic stroke patients.

OBJECTIVE: Investigate if patients with supraspinal lesions have impaired interlimb spinal reflex pathways. The short-latency crossed spinal response will be investigated during sitting from the non-paretic to paretic and paretic to non-paretic extremities at different stimulation intensities in chronic and sub-acute stroke patients. METHODS: The ipsilateral tibial nerve of the paretic and non-paretic extremities were stimulated at motor threshold, 35% M-max and 85% M-max of the ipsilateral soleus while the contralateral soleus was contracted from 5% to 15% of the maximum voluntary contraction of the paretic soleus. RESULTS: Chronic patients (from both extremities) had significantly less prominent inhibitory responses than healthy controls (post hoc tests: P<.01-P<.05). The responses were significantly modulated by stimulus intensity in healthy controls and chronic patients (P<.001-P<.05) but not sub-acute patients (P>.05). Some sub-acute patients had significantly more variable responses than chronic patients and healthy controls (P<.001-P⩽.05). CONCLUSIONS: Short-latency interlimb reflexes are impaired differently in sub-acute vs. chronic patients, are impaired from the non-paretic and paretic extremity, and abnormal when compared to healthy controls. SIGNIFICANCE: The inappropriate coordination could result in an inability to quickly avoid obstacles following a mechanical disturbance to the ipsilateral extremity. It also indicates that bilateral descending projections affect the response.

Afferent contribution to locomotor muscle activity during unconstrained overground human walking: an analysis of triceps surae muscle fascicles.

Plantar flexor series elasticity can be used to dissociate muscle-fascicle and muscle-tendon behavior and thus afferent feedback during human walking. We used electromyography (EMG) and high-speed ultrasonography concomitantly to monitor muscle activity and muscle fascicle behavior in 19 healthy volunteers as they walked across a platform. On random trials, the platform was dropped (8 cm, 0.9 g acceleration) or held at a small inclination (up to +/-3 degrees in the parasagittal plane) with respect to level ground. Dropping the platform in the mid and late phases of stance produced a depression in the soleus muscle activity with an onset latency of about 50 ms. The reduction in ground reaction force also unloaded the plantar flexor muscles. The soleus muscle fascicles shortened with a minimum delay of 14 ms. Small variations in platform inclination produced significant changes in triceps surae muscle activity; EMG increased when stepping on an inclined surface and decreased when stepping on a declined surface. This sensory modulation of the locomotor output was concomitant with changes in triceps surae muscle fascicle and gastrocnemius tendon length. Assuming that afferent activity correlates to these mechanical changes, our results indicate that within-step sensory feedback from the plantar flexor muscles automatically adjusts muscle activity to compensate for small ground irregularities. The delayed onset of muscle fascicle movement after dropping the platform indicates that at least the initial part of the soleus depression is more likely mediated by a decrease in force feedback than length-sensitive feedback, indicating that force feedback contributes to the locomotor activity in human walking.

Neuromodulation of lower limb monoparesis: functional electrical therapy of walking.

After Cerebro-Vascular Accident (CVA), restoration of normal function, such as locomotion, depends on reorganization of existing central nervous system (CNS) circuitry. This capacity for reorganization, generally referred to as plasticity, is thought to underlie many instances of functional recovery after injury as well as learning and memory in the undamaged CNS. Both the reorganization of the supraspinal and spinal circuitry are highly important for the recovery of walking. The neural mechanisms responsible for learning and adapting processes are thought to involve changes both in the efficacy of synaptic function and the pattern of synaptic connections within neural circuits. In the uninjured CNS, these changes occur as a result of alterations in the amount of neural activity within circuits and are, therefore, termed activity-dependent. In this chapter, we will present several therapies of walking that provide effective input for the training of the existing CNS circuitry; thereby, contribute to long term recovery of sensory-motor functions. The focus of this chapter is Functional Electrical Therapy (FET) of walking, that is, the multi-channel electrical stimulation of sensory-motor systems that lead to more normal stance and swing of the paretic leg during the walking exercise.

Changes in excitability of the cortical projections to the human tibialis anterior after paired associative stimulation.

Paired associative stimulation (PAS) based on Hebb's law of association can induce plastic changes in the intact human. The optimal interstimulus interval (ISI) between the peripheral nerve and transcranial magnetic stimulus is not known for muscles of the lower leg. The aims of this study were to investigate the effect of PAS for a variety of ISIs and to explore the efficacy of PAS when applied during dynamic activation of the target muscle. PAS was applied at 0.2 Hz for 30 min with the tibialis anterior (TA) at rest. The ISI was varied randomly in seven sessions (n = 5). Subsequently, PAS was applied (n = 14, ISI = 55 ms) with the TA relaxed or dorsi-flexing. Finally, an optimized ISI based on the subject somatosensory evoked potential (SEP) latency plus a central processing delay (6 ms) was used (n = 13). Motor-evoked potentials (MEPs) were elicited in the TA before and after the intervention, and the size of the TA MEP was extracted. ISIs of 45, 50, and 55 ms increased and 40 ms decreased TA MEP significantly (P = 0.01). PAS during dorsi-flexion increased TA MEP size by 92% (P = 0.001). PAS delivered at rest resulted in a nonsignificant increase; however, when the ISI was optimized from SEP latency recordings, all subjects showed significant increases (P = 0.002). No changes in MEP size occurred in the antagonist. Results confirm that the excitability of the corticospinal projections to the TA but not the antagonist can be increased after PAS. This is strongly dependent on the individualized ISI and on the activation state of the muscle.

Symmetry of post-movement beta-ERS and motor recovery from stroke: a low-resolution EEG pilot study.

The inter-hemispheric symmetry of electroencephalographic (EEG) post-movement beta-event-related synchronization (PMBS) after movements on a drawing board was studied in eight acute stroke subjects with mild hemiparesis and eight normal subjects. A follow-up testing was conducted 3 months after the initial recordings with a twofold purpose: (1) to validate the reproducibility of the experimental protocol in normal subjects; and (2) to study changes of inter-hemispheric PMBS-symmetry as a response to recovery of motor function. PMBS values were calculated and their topographic distributions illustrated at various time instances following movement offset. Significant PMBS patterns were present in all normal subjects, with only minor differences within consecutive recordings. The side of hemiparesis in acute stroke subjects could be distinguished (P = 0.04) on the basis of the signed symmetry index, a quantitative measure of lateralization. The follow-up testing on three recovered stroke subjects revealed a trend of changes in the lateralization towards the contralateral side of movement, an indication that the cortical organization of movement following recovery turned out as reported for normal subjects. Further clinical investigations need to be carried out to evaluate the relationship between recovery and PMBS symmetry on a large number of subjects, using the method presented here.

Evidence for a supraspinal contribution to the human quadriceps long-latency stretch reflex.

In sitting humans a rapid unexpected lengthening of the knee extensors elicits a stretch reflex (SR) response as recorded by the electromyogram (EMG) which comprises multiple bursts. These are termed short latency responses (SLR), medium latency responses (MLR) and long latency responses (LLR). The aim of this study was to determine if a transcortical pathway contributes to any of these bursts. Flexion perturbations (amplitude =4 degrees, velocity=150 degrees/s) were imposed on the right knee joint of sitting subjects (n=11). The effect of the perturbation on the electromyographic (EMG) response of the pre-contracted quadriceps muscle to magnetic stimulation of the contralateral motor cortex was quantified. Transcranial magnetic stimulation (TMS) was applied to elicit a compound motor evoked potential (MEP) in the target muscle rectus femoris (RF), in the vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF). The MEP and SR were elicited either in combination or separately. When applied in combination the delay between the SR and the MEP varied from 0 to 150 ms in steps of 4, 5 and 10 ms. Somatosensory evoked potentials (SEPs) were recorded from four subjects during the imposed stretch to quantify the latency of the resulting afferent volley. Onset latencies of responses in RF were 25+/-2 ms for the SR and 20+/-4 ms for the MEP. The average SEP latency was 24+/-2 ms. A transcortical pathway thus has the potential to contribute to the RF SR no earlier than 54+/-6 ms (SEP + MEP + 10 ms central processing delay) following the stretch onset. The duration of the total reflex burst was 85+/-6 ms. Significant facilitation of the MEP commenced at 78 ms, coinciding with the LLR component of the stretch response. No such facilitation was observed in the synergists VL and VM, or in the antagonist BF. Our results indicate that the LLR of the RF likely involves supraspinal pathways. More importantly, of the investigated muscles, this involvement of higher centers in the shaping of the LLR is specific to the RF muscle during the investigated task.

Intraoperative recording of electroneurographic signals from cuff electrodes on extradural sacral roots in spinal cord injured patients.

PURPOSE: A safe and reliable method for monitoring intravesical pressure on a long-term basis is needed for conditional electrical stimulation to be feasible as a treatment option for neurogenic detrusor overactivity in patients with a spinal cord injury. Therefore, we investigated the possibility of recording afferent nerve activity related to mechanical activity of the bladder and other pelvic organs from the extradural sacral nerve root in human. MATERIALS AND METHODS: Nerve cuff electrodes were temporary placed on the extradural S3 sacral root in 6 spinal cord injured patients who underwent implantation of an extradural FineTech-Brindley Bladder System (Finetech Medical Lt., Welwyn Garden City, United Kingdom). The dorsal penile/clitoral nerve was electrically stimulated to evoke compound action potentials. Electroneurographic signals were recorded together with bladder and rectal pressure during mechanical stimulation of the dermatome rapid bladder filling and rectal distention, and during bladder contraction evoked by electrical stimulation of the contralateral sacral root. RESULTS: Compound action potentials and electroneurographic responses during stimulation of the dermatome and rectum were present in all 6 patients and during bladder filling in 5 of 6. However, recorded responses from the bladder and rectum were small and mainly phasic in nature. Nerve responses following bladder contractions were present in 4 of 5 stimulated patients. CONCLUSIONS: Afferent nerve activity from the dermatome, bladder and rectum can be recorded using cuff electrodes placed on the extradural S3 sacral root in humans but improvements in recording quality and sophisticated signal processing methods are needed for chronic application.

Propulsive activity induced by sequential electrical stimulation in the descending colon of the pig.

UNLABELLED: This work was performed to study electrically induced contractions in the descending colon of pigs. Contractions were monitored using impedance planimetry and manometry. The luminal pressure, cross-sectional area (CSA), latency and velocity of CSA decrease were compared when using 3 ms, 9, 12, 15 or 30 mA pulses at 10 Hz for 10 s, and 15 mA, 0.03, 0.3 or 3 ms pulses at 10 Hz for 10 s. Stimulation was performed prior and after the application of N(G)-nitro-L-arginine methyl ester (L-NAME) and atropine. In the untreated colon, contraction was always of an 'off' type. A current increase from 9 to 30 mA increased the pressure. An increase of pulse duration from 0.03 to 3 ms shortened the latency, accelerated contraction and increased pressure. By sequential stimulation, contractions were coordinated to propel semi-fluid and solid luminal contents. L-NAME increased the magnitude of CSA decrease. Atropine induced inhibitory effects on contractions elicited by 3 ms pulses and abolished contractions induced by 0.03 and 0.3 ms pulses. IN CONCLUSION: (i) electrical stimulation evokes'off' colon contractions, which can be coordinated to result in propulsion; (ii) the best combination for current and pulse duration to induce propulsive contractions is 15 mA and 3 ms; (iii) nitrergic and cholinergic pathways mediate responses to electrical stimulation.

Treatment of neurogenic detrusor overactivity in spinal cord injured patients by conditional electrical stimulation.

PURPOSE: The feasibility of automatic event driven electrical stimulation of the dorsal penile/clitoral nerve in the treatment of neurogenic detrusor overactivity (NDO) was evaluated in individuals with spinal cord injury. MATERIALS AND METHODS: The study included 2 women and 14 men older than 18 years with NDO, bladder capacity below 500 ml and complete or incomplete suprasacral spinal cord injury. Detrusor pressure (Pdet) was recorded during ordinary, natural bladder filling. In a similar subsequent recording Pdet was used to trigger electrical stimulation when pressure exceeded 10 cm H2O. RESULTS: Of the 16 patients enrolled in this study 13 had increased bladder capacity together with a storage pressure decrease as a result of automatic, event driven electrical stimulation. In 2 patients stimulation could not inhibit the first undesired contraction, leakage occurred and finally 1 could not tolerate stimulation. During stimulated filling Pdet never exceeded 55 cm H2O. Thus, storage pressure was sufficiently low to prevent kidney damage. An average bladder capacity increase of 53% was achieved. CONCLUSIONS: This study demonstrates the feasibility of automatic, event driven electrical stimulation in the treatment of NDO. Although the setup in this experiment is not suitable in a clinical setting, the treatment modality is promising and it warrants further investigation.

No correlation between number of MRI-evident lesions in cerebrum and the soleus stretch reflex in multiple sclerosis patients.

The aim of the study was to investigate if the stretch reflex of the soleus muscle was useful in quantifying upper motor neuron lesions. The soleus stretch reflex was recorded in 10 healthy subjects and 20 patients with active relapsing-remitting multiple sclerosis and correlated to the number of MRI lesions in cerebrum and clinical scores (expanded disability status scale and regional functional scoring system). The short latency stretch reflex was elicited by rotating the left ankle joint 4 degrees with a rise time in the interval of 40-640 ms. The amplitude of the stretch was larger in multiple sclerosis patients being 88.5 microV in patients and 12.8 microV in controls, P = 0.007. The sensitivity of the stretch reflex expressed as the slope of the best linear fit was increased in MS patients to 2.6 microVs/degree compared with 0.6 microVs/degree (0.1-2.2) in controls, P = 0.009. There was no correlation between amplitude of the stretch reflex and number of MRI lesions (r = -0.03). In conclusion, the soleus stretch reflex might be useful to quantify spasticity but is not useful in detecting dysfunction of upper motor neurons in MS.

Guided intrathecal baclofen administration by using soleus stretch reflex in moderate-severe spastic multiple sclerosis patients with implanted pump.

We tested the hypothesis that changes in soleus stretch reflex was correlated to changes in intrathecal baclofen dose in 12 multiple sclerosis patients with moderate-severe spasticity treated with intrathecal baclofen pump. Twice patients were evaluated clinically and biomechanically. The short-latency soleus stretch reflex was elicited by rotating the ankle joint 4 degrees with a velocity from 3.1 to 180 degrees/s. There was a strong correlation between changes in intrathecal baclofen dose and amplitude of the short-latency stretch reflex (r=-0.88, P<0.001), which means that with an increase in baclofen dose there is a decrease in the amplitude. In contrast, no correlation exists between changes in intrathecal baclofen dose and clinical assessment of spasticity by using the Ashworth scale. The amplitude of the stretch reflex was very small (5 microV) compared with previous findings (>50 microV), which indicates an effective antispastic effect of intrathecal baclofen. We suggest that clinical evaluation of spasticity using Ashworth scale is insensitive to detect minor changes in moderate-severe spasticity and consequently might not be very useful in evaluating spasticity in relation to ambulatory filling of baclofen pumps. The soleus stretch reflex might be useful in situations when there is doubt about the effect of intrathecally administered baclofen.

Characterisation of the quadriceps stretch reflex during the transition from swing to stance phase of human walking.

The main objective of this study was to characterize the stretch reflex response of the human thigh muscles to an unexpected knee flexion at the transition from stance to swing during walking. Eleven healthy subjects walked on a treadmill at their preferred speed. Reliable and constant knee flexions (6-12 degrees amplitude, 230-350 degrees /s velocity, 220 ms duration) were applied during the late swing and early stance phase of human walking by rotating the knee joint with a specifically designed portable stretch apparatus affixed to the left knee. Responses from rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), medial hamstrings (MH) and medial gastrocnemius (GM) were recorded via bipolar surface electromyograms (EMG). The onset of the response in the RF, VL and VM, remained stable and independent of the time in the step cycle when the stretch was applied. Across all subjects the response onset (mean +/- SD) occurred at 23+/-1, 24+/-1 and 23+/-1 ms for RF, VL and VM, respectively. The duration of the initial response was 90-110 ms, at which time the EMG signal returned towards baseline levels. Three reflex response windows, labelled the short latency reflex (SLR), the medium latency reflex (MLR) and the late latency reflex response (LLR), were analysed. The medium and late reflex responses of all knee extensors increased significantly ( p=0.008) as the gait cycle progressed from swing to stance. This was not related to the background EMG activity. In contrast, during standing at extensor EMG levels similar to those attained during walking the reflex responses were dependent on background EMG. During walking, LLR amplitudes expressed as a function of the background activity were on average two to three times greater than SLR and MLR reflex amplitudes. Distinct differences in SLR and LLR amplitude were observed for RF, VL and VM but not in the MLR amplitude. This may be related to the different pathways mediating the SLR, MLR and LLR components of the stretch response. As for the knee extensor antagonists, they exhibited a response to the stretch of the quadriceps at latencies short enough to be monosynaptic. This is in agreement with the suggestion by Eccles and Lundberg (1958) that there may be functional excitatory connections between the knee extensors and flexors in mammals.

Decreased stiffness at the ankle joint in patients with long-term Type 1 diabetes.

AIMS: To evaluate contractile and reflex properties of the soleus muscle together with ankle joint stiffness in long-term Type 1 patients. METHODS: Stretch reflex and muscle function of the soleus muscle was tested in 15 Type 1 diabetes mellitus patients and 15 controls. M-wave amplitude and maximal twitch torque was elicited by supramaximal stimulation of the tibial nerve. The stretch reflex was elicited by a 4 degree rotation of the ankle. RESULTS: Rise time and fall time of the maximal twitch torque were increased compared with controls. The amplitude of the short latency stretch reflex was significantly reduced in patients at contraction levels of 5-30 Nm. At a contraction level of 5 Nm the median stretch reflex threshold was 10 degrees/s in patients and 6 degrees/s in controls (P = 0.03). Stiffness was decreased in diabetic patients, especially at lower contraction levels. There was no significant correlation between the clinical neuropathy score and stiffness. In contrast, high neuropathy score was correlated with low amplitude of the reflex amplitude (rho = -0.51, P = 0.05). CONCLUSIONS: We demonstrate altered contractile properties, a decrease in stretch reflex of the soleus muscle, and a reduced stiffness at the ankle joint in patients with long-term Type 1 diabetes. These changes may cause delayed muscle contraction and impaired reflex modulation which could contribute to gait disturbances and increased number of falls in diabetic patients.

Implantable telemeter for long-term electroneurographic recordings in animals and humans.

A system is described that amplifies an electroneurographic signal (ENG) from a tripolar electrode nerve cuff and transmits it from the implanted amplifier to an external drive box. The output was raw ENG, bandpass filtered from 800 to 8000 Hz. The implant was powered by radio-frequency induction and operated for coil-to-coil separations up to 30 mm. The testing and performance of the system is described. The input-referred noise was never more than 1 microV RMS, and, at some positions of the radio-frequency field, was 0.7 microV, close to the expected value for the amplifier used. The common-mode rejection ratio (CMRR) depended on the impedance imbalance from the cuff and the length of input cable. Devices with a short cable and low source impedance had CMRR of 84 dB, but, with 31 cm of cable and a real cuff, the CMRR fell to 66 dB. Recovery from a stimulus artifact took 5 ms. The responses of the cuff to external potential gradients and to common-mode signals are described theoretically or by simulation. The devices are available for use in neuroprosthetic or neurophysiological research.

Modified implanted drop foot stimulator system with graphical user interface for customised stimulation pulse-width profiles.

A modified implanted drop foot stimulator that allows cyclic modulation of the stimulation pulse-width during gait has been developed. Stimulation was on two channels of a four-channel 12 polar cuff electrode. The stimulator allowed modulation of stimulation pulse-width, between 0 and 255 micros, on both channels throughout the swing and stance phases of gait. Stimulation was applied between 17 and 40 Hz. The clinician can specify an infinite range of stimulation profiles on a desktop computer, using a user-friendly LabVIEW interface. The desktop program generated a stimulation profile table of 100 values, which was then downloaded to the drop foot stimulator. As each phase of gait imposed different biomechanical demands on the ankle dorsiflexor muscles, different stimulation intensities were desirable, throughout gait, to match these demands. Moreover, as the gait of each person with hemiplegia is unique, the biomechanical demands imposed throughout the gait cycle for each user of a drop foot stimulator are unique. This stimulator architecture allowed the clinician to, specify stimulation intensities individually, at each phase of the gait cycle for each drop foot stimulator user. The stimulator was evaluated on a male hemiplegic subject. It was used to increase the stimulation pulse-width by 150% at 5% of gait cycle prior to heel strike. The system performed well, with the ankle angle at heel strike increasing by 5 degrees owing to this increased pulse-width.

Reflex and non-reflex torque responses to stretch of the human knee extensors.

Reflex responses to unexpected stretches are well documented for selected muscles in both animal and human. Moreover, investigations of their possible functional significance have revealed that stretch reflexes can contribute substantially to the overall stiffness of a joint. In the lower extremity only the muscles spanning the human ankle joint have been investigated in the past. This study implemented a unique hydraulic actuator to study the contributions of the knee extensor stretch reflex to the overall knee joint torque. The quadriceps muscles were stretched at various background torques, produced either voluntarily or by electrical stimulation, and thus the purely reflex mediated torque could be calculated. The stretch had a velocity of 67 degrees /s and an amplitude of 20 degrees. A reflex response as measured by electromyography (EMG) was observed in all knee extensors at latencies of 26 - 36 ms. Both phasic and tonic EMG stretch responses increased with increasing background torques. Lines of best fit produced correlation coefficients of 0.59 - 0.78. This study is the first to examine the reflex contribution of the knee extensors to the total torque at background torques of 0 - 90% MVC. The contribution of the reflex mediated torque is initially low and peaked at background torques of 20 - 40% MVC. In terms of the total torque the reflex contributed 16 - 52% across all levels of background torque. It is concluded that during medium background torque levels such as those obtained during walking, the stretch reflex of the quadriceps muscle group contributes substantially to the total torque around the knee joint.

Conditional stimulation of the dorsal penile/clitoral nerve may increase cystometric capacity in patients with spinal cord injury.

AIMS: To investigate the feasibility of conditional short duration electrical stimulation of the penile/clitoral nerve as treatment for detrusor hyperreflexia, the present study was initiated. METHODS: Ten patients with spinal cord injury, 4 women and 6 men, with lesions at different levels above the sacral micturition center had a standard cystometry performed. During a subsequent cystometry, conditional short duration electrical stimulation of the penile/clitoral nerve was performed as treatment for one or more detrusor hyperreflexic contractions. RESULTS: In all patients, at least one contraction (mean, 7.8; range, 1-16 contractions) was inhibited by the stimulations. The mean cystometric capacity was increased significantly by conditional electrical stimulation, from 210 mL in the control cystometries to 349 mL in the stimulation cystometries (P=0.016). The maximal detrusor pressure during the first contraction in the control cystometries was mean 51 cm H(2)O, whereas the maximal pressure of the first contraction in the stimulation cystometries was reduced to mean 33 cm H(2)O (P=0.045). CONCLUSIONS: The authors conclude that repeated conditional short duration electrical stimulation significantly increased cystometric capacity in patients with spinal cord injury. The increase was caused mainly by an inhibition of detrusor contractions. The need for a reliable technique for chronic bladder activity monitoring is emphasized, as it is a prerequisite for clinical application of this treatment modality.

Control of posture with FES systems.

One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints.