818

Combined Use of Body Weight Support, Functional Electric
Stimulation, and Treadmill Training to Improve Walking
Ability in Individuals With Chronic Incomplete
Spinal Cord Injury
Edelle C. Field-Fote, PhD, PT
ABSTRACT. Field-Fote EC. Combined use of body weightsupport, functional electric stimulation, and treadmill training to
improve walking ability in individuals with chronic incomplete
spinal cord injury. Arch Phys Med Rehabil 2001;82:818-24.
Objective: To assess the effect of an intervention combining
body weight support (BWS), functional electric stimulation(FES), and treadmill training on overground walking speed(OGWS), treadmill walking speed, speed and distance, andlower extremity motor scores (LEMS).
Design: Before and after comparison.
Setting: Miami Project to Cure Paralysis.
Participants: Nineteen subjects with American Spinal Injury Association class C injury who were at least 1 year
postinjury and had asymmetrical lower extremity function.
Intervention: Subjects trained 1.5 hours per day, 3 days per
week, for 3 months. The training consisted of body weight–
supported treadmill walking assisted by electric stimulation.
Stimulation was applied to common peroneal nerve of theweaker lower extremity (LE) and timed to assist with the swing
phase of the step cycle.
Main Outcome Measures: OGWS in the absence of both
BWS and FES; LEMS, and treadmill training parameters of
speed and distance.
Results: Over the course of training, there was a significant
increase in OGWS (from .12 ⫾ 0.8m/s to .21 ⫾ .15m/s, p ⫽.0008), treadmill walking speed (from .23 ⫾ .12m/s to .49 ⫾.20m/s, p ⫽ .00003), and treadmill walking distance (from93 ⫾ 84m to 243 ⫾ 139m, p ⫽ .000001). The median LEMS
increased significantly for both the stimulated and nonstimulated leg (from 8 to 11 in the FES-assisted leg, from 15 to 18
in the nonassisted leg, p ⬍ .005 for each).
Conclusions: All subjects showed improvement in OGWS
and overall LE strength. Further research is required to delineate
the essential elements of these particular training strategies.
Key Words: Electric stimulation; Exercise test; Gait; Rehabilitation; Spinal cord injuries; Walking.
© 2001 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine andRehabilitation

From the Division of Physical Therapy and the Miami Project to Cure Paralysis,
University of Miami School of Medicine, Miami, FL.
Accepted in revised form August 31, 2000.
Supported in part by the National Institutes of Health (grant no. HD01193-03) andby the Miami Project to Cure Paralysis.
No commercial party having a direct financial interest in the results of the researchsupporting this article has or will confer a benefit upon the author(s) or upon any
organization with which the author(s) is/are associated.
Reprint requests to Edelle C. Field-Fote, PhD, PT, c/o University of Miami,
Division of Physical Therapy, 5915 Ponce de Leon Blvd, Ste 500, Coral Gables, FL
33146, e-mail: edee@miami.edu.
0003-9993/01/8206-6386$35.00/0
doi:10.1053/apmr.2001.23752

Arch Phys Med Rehabil Vol 82, June 2001

ANY INDIVIDUALS with incomplete spinal cord injury
M(SCI) have the potential to walk. In recent years,
numerous studies have investigated the effect of gait training in
1-6

individuals with incomplete SCI to improve walking function.
The experimental interventions have mainly been of 2 types:
functional electric stimulation (FES)7-13 or body weight support(BWS),14-20 the latter at times in conjunction with pharmacologic agents.21-23 Results of these studies, with regard to improvement in walking ability, have been promising.
BWS assists the stance cycle of gait, allowing lower extremity (LE) loading to vary according to the capabilities of theparticipant and providing assistance to balance by stabilizationof the trunk. Previous investigations have assessed the effects
of different levels of BWS on various treadmill gait parameters
including hip and knee angle displacements, mean muscle burst
amplitude, and temporal gait measures. Of the BWS conditions
studied, the 30% BWS condition produced the gait parametersmost closely resembling those measured at 0% (full weightbearing).24 In addition, during overground walking with levelsof BWS greater than 30%, subjects are unable to generate theground reaction forces necessary to propel themselves forward(personal unpublished observation). The motorized treadmill
provides rhythmic timing cues and assists with retropulsion of
the stance limb, which promotes hip extension. This hip extension may be critical to the initiation of the swing phase.25,26
The swing phase of gait can be assisted with FES by using theflexion withdrawal response evoked with electric stimulation to
the common peroneal nerve. This use of FES eliminates theneed for manual assistance, the provision of which may impose
strenuous physical demands on the therapist or trainer.
Although there have been no reports of prior investigationsof the combined use of these interventions in individuals withincomplete SCI, this combined approach has considerable theoretical support,27 and as been used successfully in individuals
with hemiplegia. Hesse et al28 investigated the use of multichannel electric stimulation in combination with treadmill
training and BWS in 11 nonambulatory individuals with hemiparesis (9 due to cerebrovascular accident [CVA:5 hemorrhagic, 4 ischemic], 1 each to trauma and tumor). After the
program, improvements were seen across all subjects in gaitparameters such as velocity, stride length, and cadence. Although this study has interesting implications for walking inindividuals with chronic incomplete SCI, there are limitations
that prevent the findings from being fully applicable to that
population. In addition to difference in neurologic etiology, 5of the subjects with CVA were within 5 months postinsult, atime during which spontaneous recovery of function is to be
expected.29
This investigation sought to assess changes in walking function and voluntary limb control, as well as the relationships
among these variables, in individuals with chronic (defined as
at least 1 year postinjury16) incomplete SCI who are classified
as American Spinal Injury Association (ASIA) class C.30 My

IMPROVING WALKING ABILITY IN CHRONIC INCOMPLETE SCI, Field-Fote

819

Table 1: Walking Mobility Criteria for Levels of Ambulation
Criterion

Description

1. Physiologic ambulator

Endurance, strength, or level of assistance required make the ambulation not functional. May requireassistance to stand. (Walks for exercise only.)
Walks in the home but limited by endurance, strength, or safety. (Walks rarely in the home/never incommunity.)
Walks continuously for distances that are considered reasonable for inside the home. May requireassistance with stairs inside and curbs, ramps outside the home. A wheelchair may be used
outdoors. (Walks occasionally in home/rarely in community.)
Walks outside the home and can manage, doors, low curbs, and ramps. A wheelchair may be used
for long distances. (Walks regularly in the home/occasionally in community.)
Walks for distances of approximately 400 meters (1⁄4 mile) at a speed at least 50% of normal. Can
manage all aspects of walking safely, including curbs, stairs, and doors. (Walks regularly in thecommunity [rarely/never uses wheelchair].)

2. Limited household
ambulator
3. Independent household
ambulator
4. Limited community
ambulator
5. Independent community
ambulator

NOTE. Data from Perry et al.32

selection of individuals who were at least 1 year postinjury was
based on literature indicating that gains in walking ability
plateau by the first postinjury year.6,31 I hypothesized that withtraining, subjects would show an improvement in walking
speed, both on the treadmill and overground, an increase intreadmill walking endurance, and an increase in LE strength.
METHODS
Subjects
Nineteen individuals (13 men, 6 women; mean age, 31.7 ⫾9.4yr) participated in this study. Thirteen subjects presented
with tetraplegia, 6 with paraplegia. All subjects had ASIA class
C injuries (sensory and motor function are preserved below thelevel of the lesion, but at least half of the muscles below thelevel of the lesion have a grade ⬍ 3). Median time postinjury
was 56 months (range, 12–171mo). All subjects signed an
informed consent consistent with University of Miami regulations for protection of human subjects.
Inclusion criteria included asymmetric LE strength with theability: (1) to rise from sit to stand, using upper extremity
assistance, and no more than moderate assistance from anotherperson; (2) to stand upright on both legs with no more than
30% BWS; (3) with 30% BWS, to advance the stronger leg
independently with the treadmill speed at 0.1 miles per hour;and (4) in the weaker leg, to display a robust flexion withdrawal reflex at tolerable levels of electric stimulation. One
subject (S9) was unable to complete the final 2 weeks of the
training program owing to a family emergency that arose in the10th week of training.
Testing
Subjects were tested prior to and following participation in
the training program. The primary measure of interest was
overground walking speed (OGWS) in the absence of BWS
and FES, which was assessed based on distance traversed in a
2-minute timed walk along an 80-foot oblong track. Subjects
were allowed to use their preferred assistive device and anynecessary orthotic devices, and walked at their fastest comfortable walking speed (instructed as “you will be walking for 2
minutes, walk at a quick pace, but not so fast that you will be
exhausted at the end”). Subjects were also tested while walking
at their fastest comfortable walking speed on a motorized
treadmill during which time they were videotaped from thesagittal view (on the side of the weaker limb) for later kinematic analysis. The level of BWS and the timing of FES during

the initial and final treadmill testing were adjusted to allow thesubject to walking with optimal gait quality. Voluntary motor
control in the LEs was assessed according to ASIA standards,30
with the combined score of the hip flexor, knee extensor, ankle
plantarflexor, ankle dorsiflexor, and great toe extensor comprising the lower extremity motor score (LEMS).6,31 A pretraining walking mobility score was established for each subject by asking subjects to rate their typical walking practicebased on a modified version of the scale developed by Perry etal32 (table 1).
For the overground walking tests, subjects were strapped
into a safety harnessa that was suspended from a ceilingmounted track-and-trolley assembly. This was only for safety
and no weight support was provided during the overgroundtesting. If the subject required manual assistance to advance theweaker leg during overground walking, this assistance wasprovided and noted. Subjects were allowed 3 sessions to become accustomed to walking on the treadmill with the BWS
and FES prior to the onset of the initial testing session.
Training
Subjects participated in a 36-session (3d/wk for 12wk) training program of BWS and FES-assisted treadmill walking.
Subjects were allotted a 1.5-hour block of time during which
they were permitted to determine their own walk/rest bouts.
BWS was provided by a harness suspended from an overhead
support. The level of BWS provided to each subject could be
increased or decreased via a motorized winch and could bemonitored via an light-emitting diode display. Electric stimulation (Grass S88 stimulator coupled to an SIU5 stimulus
isolation unitb) to the common peroneal nerve was triggered attime of terminal stance to elicit a flexion withdrawal response
to assist with stepping in the weaker limb. Stimulation parameters were: 500ms train, 50 pulses/s, 1ms pulse duration, andbetween 60 to 100 volts depending on subject tolerance and thelevel of stimulation necessary to elicit a robust flexion withdrawal reflex. Within each training session, the treadmill speed
and amount of support (up to 30% BWS) provided was adjusted to allow the subject to walk optimally on the treadmill.
Subjects were encouraged to walk as fast as they could while
preserving good gait kinematics and were told that walking
distance (time) was not important. For each walking bout, thetime and distance of the walk were recorded. No attempts weremade to wean the subject from use of BWS or FES over thecourse of training.
Arch Phys Med Rehabil Vol 82, June 2001

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IMPROVING WALKING ABILITY IN CHRONIC INCOMPLETE SCI, Field-Fote

Data Analysis
Data were analyzed using Microsoft Excel 97 SR-2 Statistical Tool Pacc and customized programs. The required level ofsignificance for all tests was p equal to .01. Both parametricand nonparametric statistical methods were used to comparechanges in walking parameters and LEMS pre- and posttraining. One-tailed, paired t tests were used to test the hypothesisthat OGWS, treadmill walking speed (TWS), and treadmill
walking distance increased with training. Effect size and power
calculations for changes in OGWS were calculated and adjusted for repeated measures according to the technique recommended by Portney and Watkins.33 Wilcoxon’s test, amatched-pairs, signed-rank test for ordinal data,34 was used tocompare LEMS within and between legs pre- and posttraining.
Pearson’s product-moment correlation (r) was used to test therelationships among OGWS and TWS. Spearman’s rank correlation coefficient (rs), a nonparametric equivalent to the Pearson r, for correlations among ordinal data,33 was used to assess
the relationship between LEMS and the subject’s initial walking mobility scores as well as to test the relationship between
these 2 variables and OGWS.
RESULTS
Walking Parameters
Individual subject data for OGWS (tested pre-, posttraining)
and TWS and treadmill distance per session are given in figure
1. The OGWS reflects the speed the subjects were able to walk
independently (no BWS, no stimulation) using whatever assistive device they typically used. At the time of the initial test, 6
subjects (S1, S2, S6, S10, S12, S18) required manual assistanceto advance their weaker leg; by the final test only 2 subjects
continued to require this assistance (S6, S12). Treadmill speed
and distance reflect subject performance under the training
condition (assisted by both BWS and stimulation).
Mean OGWS (m/s) improved over the course of training(initial ⫽ .12 ⫾ 0.8m/s; final ⫽ .21 ⫾ .15m/s; fig 1A), as didmean TWS (initial ⫽ .23 ⫾ .12m/s; final ⫽ .49 ⫾ .20m/s; fig
1B). The OGWS and TWS increases were seen in all subjects(median change, 77% and 106%, respectively; fig 2), thesechanges were statistically significant (OGWS: p ⫽ .0008;
TWS: p ⫽ .00003) and the effect size for OGWS was large(r ⫽ .77), yielding a statistical power of 65%. There was agood correlation between OGWS and TWS, at both the beginning (r ⫽ .71) and end (r ⫽ .82) of training, but there was no
relationship between pre-post change in walking speed overground versus that on the treadmill (r ⫽ ⫺.07).
Mean treadmill distance/session (initial ⫽ 93 ⫾ 84m; final ⫽ 243 ⫾ 139m; fig 1C) increased significantly (p ⫽.000001). Most subjects experienced an increase in treadmill
walking distance (median change, 253%); however, there were
2 subjects (S6, S14), who walked a shorter distance as thetreadmill speed increased (⫺17% and ⫺63%, respectively). In
these subjects, walking distance was sacrificed to attain faster
speeds.
Prior to the onset of training, a walking mobility score wasestablished for each subject based on his/her typical walking
practice. There was a good correlation (rs ⫽ .74) between
initial OGWS and mobility scores.
Lower Extremity Motor Scores
LE strength, as indicated by LEMS, increased over thecourse of training (fig 3). There was a median increase of 3
points in each leg (from score of 8 to score of 11 in the
FES-assisted leg, from 15 to 18 in the nonassisted leg); thisArch Phys Med Rehabil Vol 82, June 2001

increase was statistically significant in each case (p ⬍ .005 foreach). The difference between the FES-assisted and nonassisted leg was statistically significant (p ⬍ .005) both pre- andposttraining; this was expected given the inclusion criteria of
marked asymmetry in leg strength. In 4 individuals, LEMS for
1 leg were lower after than before training, and in 3 individuals
1 leg showed no change.
A relationship was found between walking speed andstrength as indicated by a moderate correlation (rs ⫽ .64)
between pretraining OGWS and LEMS; posttraining OGWS
and LEMS showed a fair correlation (rs ⫽ .39). There was little
or no correlation between the change in OGWS and the change
in LEMS (rs ⫽ ⫺.16). There was a moderate correlation (rs ⫽.60) between pretraining LEMS and mobility scores (as established prior to training).
Follow-Up
Because most subjects did not live locally, we were able to
do only limited follow-up after posttraining assessment. Fourstudy participants (S1, S2, S5, S11) were available for reevaluation at posttraining time intervals of 2 months to 1 year.
Three of these individuals (S1, S2, S5) demonstrated OGWSs
that were as good or better than that of their final evaluation.
One subject (S11) did not retain the gains made during participation in the training program. However, this individual had
undergone surgery (revision of cervical decompression andfusion, unrelated to participation in the study) during the poststudy year and had subsequently had a prolonged period during
which she was unable to ambulate. This may account for theloss of the gains made during the training program. Thesefindings agree with those of Wernig et al35 who evaluatedsubjects between 6 months and 6.5 years after participation ina training program of BWS and treadmill training, and foundthat the vast majority maintained the gains achieved withtraining.
DISCUSSION
All of the subjects who participated in this study demonstrated an improvement in OGWS. All subjects had SCI of atleast 1 year’s duration, and therefore I attribute the increase inwalking speed to participation in the study. Walking speed has
been suggested to be the criterion standard of walking ability inneurologically compromised individuals.36-38 The finding ofstatistical significance, together with the effect size, suggeststhat these are meaningful changes in OGWS. The good correlation between OGWS and TWS supports the notion that those
who are able to walk fastest on the treadmill are also able towalk fastest overground. However, the lack of correlation
between change in OGWS and change in TWS suggests that
there is little relationship between the amount of improvementin OGWS and improvement in treadmill training speed.
The finding that LEMS correlated with walking speed agrees
with prior studies by Waters et al.6,31,39 The change in LEMS
was statistically significant, but whether this change (a medianof 3 points) is functionally significant is debatable. The findingthat there is a moderate correlation between OGWS and mobility score and between LEMS and mobility score demonstrates that, in addition to individuals with stroke,32 mobility
scores may be applicable to ambulatory individuals with SCI.
No relationship, however, was found between the change in
LEMS and the change in OGWS.
The use of time-delimited walk tests is increasingly common
in the rehabilitation literature40-45 because they inherently include a reproducible measure of exercise tolerance as well as
speed. The decision to use the 2-minute walk test (rather thantests of other time durations) is based on evidence that this isIMPROVING WALKING ABILITY IN CHRONIC INCOMPLETE SCI, Field-Fote821

Fig 1. Initial and final valuesfor (A) OGWS (independent:
no BWS, no stimulation); (B)TWS (assisted by BWS andstimulation); and (C) TWS (assisted by BWS and stimulation). Changes in speed werein the positive direction, 2
subjects (S8, S15) had lower
treadmill walking distances in
the final test compared withinitial values (see text).

a reliable test that compares favorably with time-delimited testsof longer durations.46 Also, in addition to providing a functional time period over which to calculate walking speed,
preliminary work suggests that 2 minutes is the minimum timerequired for an individual with SCI to reach a metabolic steadystate during ambulation (Patrick L. Jacobs, PhD, exercise physiologist, written communication, Sept 1999).

Recent evidence40,47 suggests that, to maximize locomotor
performance in individuals with central nervous system pathology, subjects must train at a pace that approximates normal
walking speeds. None of the subjects approached normal
OGWSs in their independent walking by the end of the study,
but 7 of the 19 subjects (37%) effectively doubled their
OGWS. Cerny et al48 suggest that individuals with SCI who
Arch Phys Med Rehabil Vol 82, June 2001

822

IMPROVING WALKING ABILITY IN CHRONIC INCOMPLETE SCI, Field-FoteFig 2. Median (thick bar), lower quartile (lower border of box),
upper quartile (upper border of box), and range (vertical bar) for
changes in over-ground and treadmill walking speeds. One outlier
for treadmill speed is noted by (*) and the value is given.

walk at speeds of less than 0.9m/s (54m/min or 2.0 miles/hr)
are unlikely to use walking as their primary mode of locomotion. However, this conclusion was based on a study of 10
individuals with paraplegia, all of whom required bilateralknee-ankle-foot orthoses (KAFOs), and only 2 of whom used
walking as their primary means of locomotion. In the present
study, the 2 individuals (S9, S14) who walked as their primarymeans of locomotion did not use orthoses (although this might
have been recommended to them), had a LEMS of 31 and 28,
respectively, and had 1 leg that was appreciably stronger. Partof this difference may be because the swing-through gait usedwith bilateral KAFOs in individuals with low-level spinal
injury is faster than that which may be accomplished with areciprocal gait pattern in an individual with incomplete injuries
at higher spinal levels. I think that, despite the fact that subjects
in this study may not have become community ambulators by
the end of the training period, the improvements in walking
function obtained as a result of training will have positive
benefits in many other aspects of their daily lives.
I was especially interested in individuals with asymmetriclower extremity involvement, because these individuals would
most closely resemble the subjects with hemiplegia studied
previously. Although significant changes in walking speed andlower extremity strength were found, as was seen in individuals
with hemiplegia, these outcome measures were more variablein our sample of individuals with incomplete SCI than they
were in the prior sample of individuals with hemiplegia.28 This
study included only subjects who had ASIA class C injuries;
this category is broadest of all the ASIA categories. From amaximum possible score of 50 (5 muscle groups in each leg
with a maximum possible score of 5 for each group), thiscategory includes individuals whose LEMS range from a lowof 1 to a high of 32. It is suggested that this variability in theincomplete SCI subject population likely accounts for a great
degree of the variability in outcomes.
In addition to the differences in subject population, a minimalist approach was taken to the amount of assistance provided. Instead of a multichannel stimulation protocol, a simplified approach was employed using only a single channel ofArch Phys Med Rehabil Vol 82, June 2001

stimulation to evoke a flexion reflex to assist with the swing
phase of gait. Use of a spinal reflex to facilitate stepping has
clear advantages over either multichannel stimulation or manual assistance. In addition to providing direct motor excitation
to the ankle dorsiflexors, such stimulation has reduced antagonist (extensor) muscle spasticity49 (defined as a velocitydependent increase in resistance to passive stretch)50 and modulated spinal reflex activity in a way that may be functionallybeneficial.51 Although it is well recognized that sensory input isimportant for the modulation of the output of the locomotor
generator,26 evidence also suggests that sensory input may
facilitate locomotor recovery following a spinal lesion.52
Locomotor function is affected by an individual’s muscularstrength, cardiovascular endurance, and the ability of the nervous system to recruit effectively and efficiently the appropriate motoneurons. Evidence suggests that the human spinal cord
contains circuitry that is capable of producing locomotor-like
output.14,19,53-55 The present intervention takes advantage ofspinal circuitry to assist with production of stepping (throughthe use of the flexion withdrawal reflex) and uses the conceptsof task-oriented training. This study indicates that such a training regimen can affect important functional measures such as
OGWS and LE strength in individuals with chronic SCI.
Limitations
Subjects who participated in this study demonstrated asymmetrical LE function with severe strength deficits in at least 1
leg; because of this, these results may not be generalizable toall subjects with chronic incomplete SCI. In addition, no comparison group was used, therefore, it is possible that similar
results may be obtained with only 1 form of intervention (BWSor FES) or with more conventional types of training.
Further Development
A number of subjects reported that, in addition to improvements in OGWS and LE strength, they had experienced otherbenefits to the training. The most commonly cited secondary
benefits were improved ability to perform transfers and stairclimbing tasks, and improved standing balance. Two subjects
also reported improved bowel and bladder function. Futurestudies should attempt to assess these functions in a standardized way before and after the subjects’ participation in the
study. No adverse effects were reported.

Fig 3. Change in LEMS over the course of training. Stippled andsolid bars indicate scores for the FES and no-FES leg, respectively.
Absent bar indicates no change in score.

IMPROVING WALKING ABILITY IN CHRONIC INCOMPLETE SCI, Field-Fote

CONCLUSIONS
Subjects with incomplete SCI, who retain some capacity forambulation, would likely benefit from a walking program thatcombines BWS, FES, and treadmill training. Although theamount of improvement in walking speed (as measured byincreased OGWS) varies with individual participant characteristics, this training clearly has positive effects on function. Useof FES for assistance with limb advancement offers advantages
over other forms of assistance. This training regimen employs
the principles of task-oriented training and uses the purported
locomotor-generating circuitry of the spinal cord.
Acknowledgments: The author thanks Blair Calancie, PhD, for
input during design of this study and for review of the manuscript.
Thanks also to Carol Vandenakker, MD, for providing medical clearance for the subject’s participation, and to Monica Perez, PT, for her
assistance with training the subjects.
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