| | Comparison of Soleus H-Reflex Modulation After Incomplete Spinal Cord Injury in 2 Walking Environments: Treadmill With Body Weight Support and OvergroundAbstract Phadke CP, Wu SS, Thompson FJ, Behrman AL. Comparison of soleus H-reflex modulation after incomplete spinal cord injury in 2 walking environments: treadmill with body weight support and overground. ObjectiveTo investigate a walking environment effect on soleus H-reflex modulation during walking in persons with motor incomplete spinal cord injury (SCI) and noninjured controls. DesignPretest and posttest repeated-measures quasi-experimental controlled design. SettingLocomotor training laboratory. ParticipantsEight adults with incomplete SCI and 8 noninjured age- and speed-matched controls. InterventionWalking overground with a customary assistive device and brace at a self-selected, comfortable walking speed was compared with walking on treadmill with 40% body weight support (BWS) and manual trainers for leg and trunk movement guidance. Main Outcome MeasureMean soleus H-reflex amplitude (H/M ratio) was recorded during midstance and midswing phases of walking. ResultsThe H/M ratio was 33% smaller in stance phase (P=.078) and 56% smaller in the swing phase (P=.008) of walking on the treadmill with BWS and manual assistance compared with overground in the incomplete SCI group. The H/M ratio in the incomplete SCI group was significantly greater compared with noninjured controls in the stance and swing phases of overground walking (P=.001, P=.007, respectively). Soleus H-reflex modulation in the 2 walking environments did not differ significantly in the noninjured population. ConclusionsTraining walking on a treadmill with BWS and manual assistance to approximate the kinematics and spatiotemporal pattern of walking may be a more optimal environment to aid in normalizing reflex modulation after incomplete SCI when compared with conventional gait training overground. GENERATING AN IMPROVED stepping pattern after repetitive sensory stimulation specific to walking exemplifies the impact of activity-dependent plasticity in the human spinal cord injury (SCI).1, 2, 3, 4, 5, 6 This physiologically based strategy for rehabilitating walking after SCI is founded in basic science research by using a treadmill, body weight support (BWS), and manual assistance to achieve repetitive stepping in animal models of SCI.7, 8, 9, 10 Based on this model, Barbeau et al11 first described the use of a treadmill and BWS, which was subsequently incorporated to retrain walking after human SCI.1, 2, 6 Since then, the literature reporting benefits of training in this environment to overcome locomotor deficits after human motor incomplete SCI has grown.1, 2, 3, 4, 5, 12 This approach performed by using a cluster of modalities such as treadmill and BWS with the manual assistance of trainers to afford practice of the specific task of walking has been termed locomotor training.13 Locomotor training assists in producing rhythmic and repetitive stepping over the treadmill to afford experience of a relatively normal walking pattern that persons with incomplete SCI are typically unable to generate unassisted overground.6, 14 The practice of this rhythmic and repetitive stepping pattern is proposed to provide critical therapeutic shaping of the locomotor neurophysiology deemed essential to generate and relearn stepping after SCI.3 The principles of locomotor training propose that the combination of active leg loading, upright posture, normal range of hip extension, and good walking kinematics are particularly favorable to inducing an activity-dependent plasticity in the injured spinal cord and throughout the neural axis.13, 15 Conventional overground training also provides a repetitive mobility experience. Several difficulties, however, such as imbalance, inconsistent stepping pattern, and gait abnormalities, are associated with unassisted overground training. Without the use of BWS, treadmill, and trainers, orthoses and assistive devices are frequently used to compensate for gait deficits and motor-sensory impairments. Compensatory strategies result during such training overground and further contribute to a “novel compensated” pattern of walking. Assistive devices may not independently achieve improvement in a walking pattern and can thus alter the normal movement-related afferent feedback. Thus, in contrast to the unassisted overground walking environment, locomotor training over the treadmill with BWS and trainers theoretically provides an environment conducive to activity-dependent plasticity. The neurophysiology that underlies the improved locomotor performance induced by locomotor training is not understood. One strategy for increasing our understanding is to determine the influence of locomotor training on reflex excitability and fundamental processes that regulate the excitability of reflexes.16 As a starting point, it would be important to quantify the specific nature and magnitude of neurophysiologic changes induced by walking in the BWS, manual assistance, and treadmill (BWSMAT) environment and compare them with those produced in the unassisted overground environment. Furthermore, by comparing neurophysiologic changes induced by walking in 2 walking environments, such neurophysiologic data could provide quantitative insights into the comparison of the benefits of 1 modality or training environment over another. To study the locomotor neurophysiology, soleus H-reflex testing offers a noninvasive method to examine the altered patterns of reflex excitability after SCI17 and is a sensitive probe of changes induced by a specific therapeutic regimen.17, 18, 19 Typically, in noninjured subjects, the soleus H-reflex amplitude is low or completely depressed in the swing compared with the stance phase of walking.20 After SCI, the development of spasticity has been temporally correlated to specific changes in excitability patterns of the soleus H-reflex.21 These changes include impaired modulation22 and significantly greater reflex amplitudes (swing and stance phases) compared with noninjured controls while walking overground.17, 18 The greater amplitudes of the H-reflex after SCI suggest that soleus motoneurons may be significantly more excitable during lengthening of the soleus muscle.23 Such an increase in reflex activity of the soleus muscle could interfere with lengthening of the soleus muscle necessary for translation of the tibia over the stationary foot in the stance phase (propulsion) and foot clearance during the swing phase.20, 24, 25, 26 Accordingly, abnormal reflex excitability appears to be a significant contributor to spasticity27, 28, 29 and walking-related impairments associated with clonus.17 Although walking in the BWSMAT environment enables persons with incomplete SCI to generate improved stepping patterns, it is not clear to what extent these improvements in walking patterns are specifically correlated with clinically significant changes in soleus H-reflex excitability.19 We hypothesized that walking in the BWSMAT environment will induce a greater modulation of the soleus H-reflex compared with unassisted walking overground in persons with incomplete SCI. Because H-reflex modulation is reported to be impaired post-SCI,30, 31, 32, 33, 34 an environment that affords greater H-reflex modulation (decrease in H-reflex amplitude) would be viewed as providing a training experience consistent with normalizing the afferent experience deemed crucial to stepping recovery. We also hypothesized that the H-reflex amplitudes will be significantly greater in persons with incomplete SCI compared with noninjured controls. Our third hypothesis was that the walking environment will not affect H-reflex modulation in noninjured controls. The purpose of this experiment was to examine the immediate effect of 2 walking environments (treadmill, unassisted overground) on soleus H-reflex excitability in persons with incomplete SCI and noninjured controls. Methods  Eight persons with motor incomplete SCI (table 1) and 8 noninjured controls (mean age ± standard deviation, 51.37±7.17y) signed the informed consent. Subjects with incomplete SCI were included in the study if they had a diagnosis of first time SCI, a medically stable condition, the ability to walk independently a minimum of 12m with or without an assistive device, and spending a minimum of 30 minutes a day walking. Subjects with congenital SCI or other degenerative spinal disorders were not recruited. Noninjured subjects with no history of a neurologic or orthopedic condition that could impair walking were recruited. All experiments were conducted in accordance with the Declaration of Helsinki, and all procedures were performed with the adequate understanding and written informed consent of the study participants as approved by the University of Florida Health Science Center Institutional Review Board. These subjects were a sample of convenience and were recruited from a larger pool of subjects for a different study. | | |  | Subjects | Age (y)⁎ | Sex | Ethnicity | Assistive Device | Months Since Injury† | ASIA Grade | Lower-Limb ASIA Motor Score‡ | Upper-Limb ASIA Motor Score§ | Level of Lesion | Self-Selected Walking Speed (m/s) | |
|---|
| 1 | 43 | Male | White | RPW | 35 | D | 35 | 23 | C6 | 0.13 | | | 2 | 48 | Male | White | RPW | 20 | D | 32 | 19 | C5–6 | 0.10 | | | 3 | 60 | Male | White | Cane | 5 | D | 38 | 44 | C7 | 0.48 | | | 4 | 58 | Male | Black | Rolling walker | 26 | D | 37 | 50 | C5 | 0.34 | | | 5 | 46 | Male | White | None | 3 | D | 47 | 50 | C8, T1 | 1.30 | | | 6 | 49 | Male | White | None | 5 | D | 46 | 42 | C6–7 | 0.51 | | | 7 | 42 | Male | White | None | 72 | D | 44 | 44 | C4–5 | 0.98 | | | 8 | 56 | Male | White | Rolling walker + right AFO | 3 | D | 35 | 38 | C5–6 | 0.19 | | | | |
| ⁎ Mean age ± standard deviation (SD), 50.25±6.9 years. †Mean months ± SD, 21.12±23.85. ‡Mean score ± SD, 39±5.6 (score range, 1−50). §Mean score ± SD, 39±11.7 (score range, 1−50). The score from the following muscle groups was combined: elbow flexors, elbow extensors, wrist extensors, finger flexors, and finger abductor. |
The degree of motor and sensory impairment for persons with incomplete SCI was evaluated and classified according to the guidelines of the American Spinal Injury Association (ASIA).35 All persons with incomplete SCI first walked with their customary assistive device on a level walkwaya (3.86-m long digitized mat with embedded microswitches) at their self-selected walking speed. Three consecutive trials of walking were recorded, and comfortable walking velocity was determined by using GaitMat II software. All persons were then asked to walk overground and subsequently over the treadmill at this walking velocity. The 2 testing conditions for this study were walking overground unassisted (no manual assistance but with customary assistive device and/or brace) and walking over a treadmill with 40% BWS and manual assistance. BWS was provided by using a specialized harnessb with 1 thoracic band, 1 pelvic band, and 2 thigh straps. The harness was attached vertically overhead to a crossbar connected to pulleys supporting the person’s body weight. The BWS systemc was used to pneumatically adjust the support to 40% of the subject’s body weight. We chose to provide 40% BWS to test the persons with incomplete SCI over the treadmill because training protocols typically begin with 40% BWS1, 2, 36, 37 and greater than 50% BWS38 has shown to cause significant change in gait parameters and a decrease in mean electromyographic amplitudes. A treadmilld with about 0.5-m/s speed increments was used for the BWSMAT walking condition. Trainers provided manual assistance when necessary to initiate or maintain good kinematics while stepping on the treadmill. As soon as an adequate stepping pattern (coordinated, rhythmic steps) over the treadmill was established, soleus H-reflex testing was initiated. Thus, a relatively immediate effect of walking in the BWSMAT environment was measured. Because the H-reflex is prone to age-related changes,39 the noninjured controls were age matched to the persons with incomplete SCI and walked over the treadmill with 40% BWS. Subject Preparation for H-Reflex Assessment Soleus H-reflexes were evoked on the more involved side of persons with incomplete SCI (determined by ASIA motor score) and on the dominant side of the noninjured controls. The skin was shaved and cleaned for application of electrodes. A bipolar (interelectrode distance, 2cm) Ag-AgCl surface electrodee was placed longitudinally over the soleus muscle. Surface electromyography electrodes were placed over the soleus and tibialis anterior muscle belly. The electromyographic data were used to examine if the soleus H-reflex amplitude changed systematically with mean electromyographic activity. To evoke H-reflexes, current pulses were delivered via a constant-current stimulatorf by using a 2-cm half-sphere silver cathode placed in the popliteal fossa40 and a 10-cm silver anode positioned just superior to the patella. The tibial nerve was localized in the popliteal fossa by the electrode placement to evoke a soleus H-reflex at the least current intensity required. Data were acquired at a sample rate of 10kHz per channel and stored digitally by using Datapac software, a commercially available data acquisition systemg on a personal computer. Protocol Persons with incomplete SCI walked overground at a self-selected speed, and then this speed was matched over the treadmill, whereas the noninjured persons walked overground at self-selected speed and over the treadmill at 1.25m/s.41 Noninjured controls were tested under similar conditions (overground, treadmill), but no manual assistance was provided over the treadmill. Before the H-reflex was tested under the 2 loading conditions, H-M recruitment curves were recorded. The stimulus intensity was gradually increased from a level below the H-wave threshold to a level in which a stable maximum M wave (Mmax) was elicited. These recordings determined the test stimulus intensity for both walking conditions. Subsequently, the test stimulus intensity was set at an M-wave response of 10%±3% Mmax (chosen based on our experience that this range provides the minimum amplitude stable M wave for standardizing stimulus intensity).42, 43 During the testing, the M wave was constantly monitored and adjusted as necessary. In all persons, 15 H-reflexes each were evoked in the midstance and midswing phases of walking.44 The midstance and midswing phases of walking were determined visually and confirmed by using footfall data patterns from microfootswitches. Because the H-reflex amplitude is phasically modulated during the walking cycle, the amplitude increases gradually during the stance phase before falling sharply at toe-off; hence, we chose midpoints of stance and swing phases for stimulation.45, 46 Data Analysis H-reflex values were first normalized to Mmax (H/M ratio). Then Wilcoxon signed-rank tests47 were performed to compare the 2 walking environments separately for the noninjured and the incomplete SCI groups. These analyses were conducted separately for the 2 phases of walking: stance and swing. In addition, to compare the noninjured control group with the incomplete SCI group, Wilcoxon rank-sum tests47 were conducted separately for the 2 walking environments and the 2 phases of walking. We chose the nonparametric methods over the repeated-measure analysis of variance because, for small sample sizes as in this study, the validity of the later approach depends crucially on normality assumption. Results Comparison of the H-Reflex Amplitude (incomplete SCI: treadmill versus unassisted overground) The mean H/M ratio in the swing phase of persons with incomplete SCI in the BWSMAT environment was significantly smaller than walking overground (Wilcoxon signed-rank test, P=.008). The mean H/M ratio in the stance phase of walking did not differ significantly between the 2 walking environments (Wilcoxon signed-rank test, P=.078). The mean H/M ratio recorded during swing in the persons with incomplete SCI was approximately 50% smaller than those recorded during stance phase both for unassisted overground and BWSMAT walking environments (eg, fig 1; individual and mean data, table 2). Examining individual data revealed that all persons with incomplete SCI showed a decreased H/M ratio in either swing or stance or both phases of walking in the BWSMAT environment compared with unassisted overground environment (fig 2). In the BWSMAT walking environment, 4 of 8 persons with incomplete SCI showed a smaller H/M ratio in both the swing and the stance phase (subjects 1, 6, 7, 8; see tables 2, 3). In addition, it should be noted that in the incomplete SCI group, the H/M ratio decreased in the BWSMAT environment in 6 of 8 persons in the swing phase (subjects 1, 3, 4, 6, 7, 8) and 6 of 8 persons in the stance phase (subjects 1, 2, 5, 6, 7, 8; see Table 2, Table 3). Of the 2 persons with incomplete SCI who did not show a change in H/M ratio in the swing phase, 1 person already had a completely depressed H-reflex (subject 2). The electromyographic activity in the soleus and tibialis anterior muscles did not change systematically with the H/M ratio (see table 2). | | | | Subject | BWSMAT | Overground | |
|---|
| Stance | Swing | Mmax | Stance | Swing | Mmax | |
|---|
| M Wave | H Wave | M Wave | H Wave | M Wave | H Wave | M Wave | H Wave | |
|---|
| 1 | 1.47 | 2.60 | 1.69 | 1.43 | 4.60 | 0.75 | 3.58 | 0.72 | 3.48 | 4.05 | | | 2 | 0.55 | 1.95 | 0.50 | 0.07 | 5.07 | 0.63 | 1.83 | 0.51 | 0.06 | 4.09 | | | 3 | 0.13 | 0.52 | 0.15 | 0.07 | 1.01 | 0.23 | 0.97 | 0.20 | 0.47 | 2.05 | | | 4 | 0.66 | 4.99 | 0.65 | 2.31 | 5.78 | 0.90 | 7.12 | 0.95 | 4.51 | 9.68 | | | 5 | 0.24 | 1.43 | 0.26 | 0.64 | 2.49 | 0.26 | 2.02 | 0.25 | 0.60 | 2.31 | | | 6 | 0.23 | 0.87 | 0.23 | 0.16 | 2.38 | 0.32 | 1.40 | 0.30 | 0.58 | 3.26 | | | 7 | 0.45 | 0.35 | 0.33 | 0.10 | 8.50 | 0.44 | 3.69 | 0.52 | 2.52 | 4.73 | | | 8 | 0.32 | 1.08 | 0.32 | 0.98 | 3.21 | 0.65 | 3.14 | 0.59 | 2.85 | 3.66 | | | Mean | 0.51 | 1.73 | 0.52 | 0.72 | 4.13 | 0.52 | 2.97 | 0.51 | 1.88 | 4.23 | | | | |
Comparison of the H-Reflex Amplitude (incomplete SCI versus noninjured) Wilcoxon rank-sum tests revealed that the mean H/M ratio in persons with incomplete SCI walking overground was significantly greater than noninjured controls for both stance and swing phases of walking (P=.001, P=.007, respectively). On the other hand, the mean H/M ratio in persons with incomplete SCI and noninjured persons did not differ significantly in the BWSMAT walking environment for both stance and swing phases of walking (P=.052, P=.128, respectively). H-Reflexes in Noninjured Controls The mean H/M ratio in the noninjured persons did not differ significantly between the 2 walking environments (P=.742 for the stance phase, P=.945 for the swing phase). The amplitude of the soleus H-reflex recorded during swing was approximately 80% smaller than recorded during stance, both for overground and treadmill locomotion (see table 2). Discussion The primary finding of this study was that for the incomplete SCI group walking in the BWSMAT environment, the mean H/M ratio was significantly smaller in the swing phase (56% smaller, P=.008) than recorded during the swing phase of unassisted overground walking. In addition, there was a robust trend of a smaller H/M ratio recorded during the stance phase (33% smaller, P=.078) of walking in the BWSMAT environment compared with the H/M ratio recorded in the stance phase of overground walking in the incomplete SCI group. All subjects with incomplete SCI showed a decrease in H/M ratio in the BWSMAT environment either in swing, stance, or both phases (see table 2). Our methodology afforded a dynamic comparison of 2 diverse walking environments (BWSMAT, unassisted overground) and revealed significant differences in the swing phase between the 2 walking conditions. Compared with the unassisted overground environment, the BWSMAT environment produced an increase and thus an improved H-reflex modulation in the swing phase similar to that seen in noninjured subjects. Testing H-reflexes within the task of walking provided an opportunity to measure parameters (reflex excitability, modulation) that have a high degree of clinical relevance to the expression of spasticity. Thus, testing walking H-reflexes provides a task-specific approach to study the effect of walking rehabilitation interventions such as locomotor training on the impaired reflex modulation post-SCI. Although the time course was not determined, a previous study revealed that the H-reflex modulation induced by locomotor training may persist during an immediate subsequent period of unassisted overground walking. In subjects with incomplete SCI, Trimble et al33 tested overground H-reflexes before and after a single bout of locomotor training and reported a significant depression of H-reflexes after locomotor training (28% stance, 34% swing) alongside a 26% increase in walking speed. However, the soleus H-reflexes were not tested in the BWSMAT environment, and, hence, it is not known if the H-reflex depression is inherent to the BWSMAT environment.33 In addition, this change in H/M ratio was task specific because it was observed only during walking, but the H/M ratio tested in standing remained unchanged after locomotor training. To our knowledge, the report by Trimble33 is the first to suggest that greater depression of the soleus H-reflex post-SCI may be correlated with greater walking speed. In light of this report, the mean decrease of 33% (stance) and 56% (swing) that we report in our study appears to be a clinically significant change.27, 28, 33 The 2 persons with incomplete SCI who did not show a decrease in H/M ratio in the stance phase of BWSMAT environment were both older (subject 3, 60y; subject 4, 58y) than the rest of the study sample (range, 42−56y) (see table 1). The relatively older age of these 2 subjects may have affected the H-reflex response, which is consistent with previous reports39, 48, 49 that the H/M ratios are less likely to change in older compared with younger persons. Consistent with previous reports17, 18, 33 on subjects with SCI compared with intact subjects, the SCI subjects in this study showed significantly greater H-reflex amplitudes in both the swing and stance phases of walking. Interestingly, these same subjects showed improved modulation of H-reflexes (decreased amplitude) in the BWSMAT environment. Accordingly, it appears that modulation of the H-reflex in a task-specific manner is enhanced in response to the sensory input provided in the BWSMAT environment (compared with unassisted overground environment). This decrease in the H-reflex size was most likely caused by better propulsion and foot clearance in the BWSMAT environment. We found that the phase-specific H-reflex modulation in the BWSMAT environment in persons with incomplete SCI did not differ significantly from noninjured subjects. Because the BWSMAT environment afforded a modulation pattern similar to one seen in subjects with an intact spinal cord, this decrease in the H-reflex amplitude is perceived as a particularly desirable asset of this type of intervention and training environment.50 A second finding of this study was that the mean H/M ratio in persons with incomplete SCI was significantly greater compared with noninjured persons. The examination of individual data revealed that 2 persons with incomplete SCI (subjects 2, 6), with a clinical presentation of impaired walking speed, showed good phase-specific modulation in the unassisted overground environment comparable to noninjured controls (see table 2). Similar findings, suggesting that all subjects with SCI do not exhibit increased H-reflexes during walking, were also reported previously by Yang et al.17 In addition, studies performed in static positions in humans and animals51, 52, 53 report that the H-reflex does not increase post-SCI. However, a large majority of studies30, 31, 32, 33, 34, 54, 55 have reported that H-reflex modulation is impaired (seen as increase in reflex amplitude) post-SCI. A recent study by Lee et al51 indicates that the impairment of H-reflex modulation may be related to the severity of SCI. Although our finding of an increased mean H/M ratio in persons with incomplete SCI is consistent with a majority of past reports,17, 18, 19, 33 it is important to document this observation because there remains an ongoing controversy over this issue of SCI and H-reflex excitability.52 The third finding was that H-reflex modulation in noninjured persons in the 2 walking environments was similar; these results support previous findings that varying degrees of BWS56 did not change H-reflex amplitude. The primary purpose of this study was to examine the behavior of the soleus H-reflex during walking in the BWSMAT environment (a cluster of modalities such as treadmill, BWS, and manual assistance) in comparison to unassisted overground walking (patients’ customary mobility pattern with a choice of assistive device and/or bracing). At matched walking speeds, our results suggest that the BWSMAT environment improves modulation of the soleus H-reflex. In contrast to overground walking, training variables afforded in the locomotor training environment include BWS,14, 57 treadmill speed,58 and manual assistance, and each of these factors may have an independent59 or perhaps even an interactive or cumulative effect on the resulting H-reflex modulation. Effect of BWS on H-Reflex Ferris et al56 reported in noninjured subjects that H-reflex modulation was independent of muscle activity and BWS. The noninjured persons in this study also walked with 40% BWS over treadmill, and the H-reflex modulation did not differ significantly from walking overground. However, we did not test the independent effect of 40% BWS on H-reflexes in the SCI population. Increased limb extensor loading has been reported to reset locomotor rhythm in a task-specific manner in cat SCI model60 and assist the human lumbosacral spinal cord to modulate efferent output to facilitate the stepping pattern post-SCI.14, 61 Thus, it is likely that BWS may have independently contributed to the H-reflex modulation observed in persons with incomplete SCI. Future studies need to exclusively examine the effect of percent BWS on soleus H-reflex modulation during walking post-SCI. Effect of the Walking Environment on the H-Reflex Limb guidance provided by trainers assists with generation of appropriate walking kinematics, namely, walking phase–specific leg movements and timing of the swing and stance phases.3, 4 A combined use of treadmill, BWS, and manual assistance during locomotor training induces electromyographic patterns that are more similar to those recorded in noninjured persons,12, 14 particularly more reciprocal activity of agonist and antagonist muscles,61 which may have been responsible for depression of the H-reflex amplitude. The reflex pathways are known to show plasticity and can be modified62, 63; however, the nature of these neuroplastic changes as walking improves post-SCI is not known.64 H-reflexes are exaggerated post-SCI,29, 33, 43, 51, 65, 66 and it may be possible to normalize these reflexes by training. There have been previous reports of normalization of reflex excitability post-SCI after training programs such as step training in humans33, 34 and cats,64 passive bike training in rats,66 cutaneomuscular stimulation,18 and passive bicycling in humans.29 In all of these training studies, the reflexes were tested during nonlocomotor tasks. In contrast, to investigate the nature of neurophysiologic changes associated with training modalities, we chose to examine the H-reflex excitability within the task of walking. The decrease in the H/M ratio seen in our study during walking in the BWSMAT environment may be a precursor to ongoing plasticity of reflex pathways. Thus, it appears that a combination of all the previously mentioned factors involved in the BWSMAT environment (ie, treadmill, BWS, manual assistance, acute neural adaptation) were together instrumental in decreasing the soleus H-reflex amplitude. The effect of different combinations of variables overground or on the treadmill could certainly be tested; however, our interest was to examine these different variables as an ensemble of sensory information and a total experience rather than the individual effects. Study Limitations First, we only examined the effect of walking in the BWSMAT walking environment rather than individual components of the BWSMAT walking environment such as treadmill speed, BWS, and manual assistance. Separate investigation of the neurologic effects of walking over a treadmill and the effect of BWS will yield information on the unique effects of these training variables and their contribution to the sensory experience for training. Second, an order effect cannot be ruled out because testing was always performed first in the overground walking environment. Third, we used self-selected walking speed in the BWSMAT environment, and training at faster and more normative speeds may have further decreased the H-reflex amplitude.58, 67, 68 Finally, there was high variability between subjects with incomplete SCI in duration postinjury (3−72mo), use of walking aids, and comfortable walking speeds (see table 1). The heterogeneity of subjects and a small sample size together may have contributed to low power to yield significant differences. Conclusions The soleus H-reflex amplitude decreased significantly during the swing phase, and there was a robust trend toward a decrease in the stance phase of walking in the BWSMAT environment compared with walking overground unassisted in persons with incomplete SCI. The contribution of specific variables of the training such as walking speed; walking kinematics, specifically the lower-limb joint excursion and stance and step times; trunk posture; and BWS on soleus H-reflex modulation need to be further investigated in the SCI population. This study showed a decrease in the soleus H-reflex amplitude in persons with incomplete SCI within a single training experience of manually assisted walking over treadmill when using BWS and trainers. The correlation between propulsion/foot clearance and H-reflex size post-SCI needs to be systematically investigated. Future studies also need to examine if the long-term benefit of locomotor training is correlated with normalization of soleus H-reflexes while walking over the treadmill and overground. Suppliers Acknowledgment We acknowledge the late Mark H. Trimble, PhD, for his contribution to the conceptualization of this study. References 1. 1Wernig A, Muller S. 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a Department of Physical Therapy, University of Florida, Gainesville, FL b McKnight Brain Institute, University of Florida, Gainesville, FL c Division of Biostatistics, College of Medicine, University of Florida, Gainesville, FL d VA Rehabilitation Outcomes Research Center, Malcolm Randall VAMC, Gainesville, FL e VA Brain Rehabilitation Research Center, Malcolm Randall VAMC, Gainesville, FL.  Reprint requests to Andrea L. Behrman, PhD, Dept of Physical Therapy, PO Box 100154, University of Florida, Gainesville, FL 32610-0154
Supported by the National Institutes of Health (grant no. KO1 HD01348) and VA Rehabilitation Research and Development Service (grant no. F2182C). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. PII: S0003-9993(07)01484-0 doi:10.1016/j.apmr.2007.07.031 © 2007 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved. | |
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