Gait training early after stroke with a new exoskeleton – the hybrid assistive limb: a study of safety and feasibility
Journal of NeuroEngineering and Rehabilitation
Anneli Nilsson 2
Katarina Skough Vreede 1 2
Vera Hglund 2
Hiroaki Kawamoto 0
Yoshiyuki Sankai 0
Jrgen Borg 1 2
0 Faculty of Systems and Information Engineering, University of Tsukuba , Tsukuba , Japan
1 Department of Clinical Sciences Karolinska Institute , Stockholm , Sweden
2 Department of Rehabilitation Medicine, Danderyd University Hospital , Building 39, floor 3, SE- 182 88 Stockholm , Sweden
Gait training early after stroke with a new
exoskeleton the hybrid assistive limb: a study of
safety and feasibility
Nilsson et al.
Gait training early after stroke with a new
exoskeleton the hybrid assistive limb: a study of
safety and feasibility
Background: Intensive task specific training early after stroke may enhance beneficial neuroplasticity and functional
recovery. Impaired gait after hemiparetic stroke remains a challenge that may be approached early after stroke by
use of novel technology. The aim of the study was to investigate the safety and feasibility of the exoskeleton
Hybrid Assistive Limb (HAL) for intensive gait training as part of a regular inpatient rehabilitation program for
hemiparetic patients with severely impaired gait early after stroke.
Methods: Eligible were patients until 7 weeks after hemiparetic stroke. Training with HAL was performed 5 days
per week by the autonomous and/or the voluntary control mode offered by the system. The study protocol
covered safety and feasibility issues and aspects on motor function, gait performance according to the 10 Meter
Walking Test (10MWT) and Functional Ambulation Categories (FAC), and activity performance.
Results: Eight patients completed the study. Median time from stroke to inclusion was 35 days (range 6 to 46).
Training started by use of the autonomous HAL mode in all and later switched to the voluntary mode in all but
one and required one or two physiotherapists. Number of training sessions ranged from 6 to 31 (median 17) and
walking time per session was around 25 minutes. The training was well tolerated and no serious adverse events
occurred. All patients improved their walking ability during the training period, as reflected by the 10MWT
(from 111.5 to 40 seconds in median) and the FAC (from 0 to 1.5 score in median).
Conclusions: The HAL system enables intensive training of gait in hemiparetic patients with severely impaired gait
function early after stroke. The system is safe when used as part of an inpatient rehabilitation program for these
patients by experienced physiotherapists.
Stroke is a global health problem and one major cause of
acquired disability in adults . Hemiparesis is the most
common acute manifestation of stroke and often impacts
on gait function [2,3]. Although performance is improved
in most stroke survivors during the first months post
stroke, one third or more will need assistance in walking
and remains limited in community ambulation [3,4]. Thus,
independent gait remains a challenge in the rehabilitation
after stroke .
1Department of Rehabilitation Medicine, Danderyd University Hospital,
Building 39, floor 3, SE- 182 88 Stockholm, Sweden
Full list of author information is available at the end of the article
Normal gait requires postural control, weight shifting
and rhythmic and correct timing of muscle activity during
repeated gait cycles and depends on the integrity of a
complex interaction in sensory-motor neural networks at
both spinal and supraspinal levels . Depending on
location and extent of the lesion and of restorative
and compensatory mechanisms , gait characteristics may
vary between and within patients over time after stroke.
Accumulating evidence indicates that early onset,
intensive, repetitive task specific training may accelerate
functional restitution after stroke and improve final motor
outcomes , including gait function [9,10] although most
motor rehabilitation trials have been performed in the
chronic stage post stroke . Even though early onset
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unless otherwise stated.
and intensive training of motor functions after stroke may
enhance recovery by driving beneficial neuroplasticity a
better understanding and prediction of the individual
capacity and response to specific training paradigms remains
a challenge [12,13].
Devices used to support gait training after stroke include
treadmill training with or without body weight support
(BWS). A recent Cochrane review found no overall
statistically significant effect on gait function after treadmill
training with BWS as compared with training without BWS
 but this may differ between subgroups of patients with
various severities and gait velocity during training may also
have an impact . These devices may be combined with
electromechanical gait machines, which can allow more
reproducible gait movements when compared to when a
therapist move the patients legs. Gait machines are often
categorized as machines using an end-effector principle
and machines that function as exoskeletons . Machines
based on the end-effector principle use foot plates that
move the feet in a controlled gait pattern and allow the
operator to adjust many aspects of locomotion, such as speed,
stride length and step height. In contrast, exoskeletons
such as Lokomat  are attached to the patient and
function as an external skeleton. Exoskeletons for lower
extremities have joints matching the patients lower limb
joints and motors that drive movements over these joints
to assist leg movements. A recent Cochrane review
concluded that electromechanical-assisted gait training in
combination with physiotherapy after stroke increased the
odds of participants becoming independent in walking and
most so when this is applied in the first three months after
stroke in patients, who are not able to walk . However,
further studies are needed with regard to the role of
current types of electromechanical device [18,19] as well as
to new concepts and devices and their evaluation in clinical
trials [20,21]. One conceptual issue relates to the
importance of incorporating active participation in the training.
This has been approached in several studies by comparing
training by use of gait machines such as Lokomat or Gait
Trainer only, with regular therapist training that allows
more variation, or combinations of these [22-28]. One new
approach was taken by Krishnan et al. , who used a
Lokomat device designed to allow patient cooperation and
a target tracking task for matching of the ankle position to
a movement template provided on a screen. A multilevel
outcome analyses indicates that such active robotic
training may be a potentially effective training model.
Recently, an exoskeleton with a hybrid system that
allows both an automatic and a voluntary mode of action
to support training of gait, the Hybrid Assistive Limb
system (HAL) has been developed [30-32] and introduced in
clinical trials [33-35]. This exoskeleton provides support
according to the patients condition by a control algorithm
and supporting devices, where each joint (left and right
hip and left and right knee) can be controlled separately.
The key features of the HAL system has been reported in
detail previously [30-32] and is briefly outlined here.
The HAL system comprises two subsystems for (cybernic)
voluntary control (CVC) and (cybernic) autonomous
control (CAC) respectively. Both modes of action depend on
the users intention in different ways. The CAC mode
utilizes voluntary weight shift to initiate gait cycles and then
provides predefined movements while gait in the CVC
mode continuously use input from voluntarily activated
gait muscles to provide support by the exoskeleton. This
is achieved by recordings of the bioelectrical signals
generated during muscle activation, as described by Kawamoto
et al. 2002 . Surface electrodes are placed over lower
extremity extensor and flexor muscles and the recorded
signals are incorporated in the control algorithm. The
technology enables even weak muscle activity to be used
to initiate and adjust the assistive torque, which may then
be modified by a therapist . Output is magnified and
adjusted to the level of assistance needed over each hip
and knee joint. A main controller of the system is used to
control the power units, monitor the batteries,
communicate with the system operator and modulate the assisting
torque of each power unit. HAL is equipped with a
sensing system receiving input also from potentiometers that
are mounted on each joint and used as angular sensors to
measure the joint angles, from force-pressure sensors in
the shoes and from a gyro sensor and an acceleration
sensor, which are mounted on the HAL body trunk, to
measure posture .
The CVC mode allows the operator to adjust the
degree of physical support for each joint and gradually
reduce support as training progress. The EMG input,
the adjusted torque limit and torque tuner for each joint
and the adjusted assistance level for the flexor and
extensor muscle groups respectively all together determine
the power output . These settings can not be
standardized but are individually adapted over time. Settings
are modified by the therapist during the training session
depending on the patients performance in order to
achieve a gait pattern that is as close as possible to normal
gait. If the subject is paralytic, as may be the case early after
stroke, the CAC mode may be used. Gait is then initiated
and sustained by the voluntary locomotor intention, based
on output from force-pressure sensors in the shoes. In this
mode, the exoskeleton will e.g. swing the left leg when
enough weight is put on the right leg in stance phase.
Gait training with HAL may be performed with or
without BWS. Recently, aspects on feasibility and safety
of HAL have been reported for early mobilization of
patients in a neurosurgical ward by use of a prior
version of the HAL system  and for gait training
in patients with chronic impairment after a variety of
conditions including stroke [33,34].
The aim of the present study was to explore the safety
and feasibility of the HAL system when used for early
onset, intensive gait training as part of an inpatient
rehabilitation program for patients with hemiparetic stroke.
Specifically, we wanted to explore the applicability of the
system in patients with severely impaired gait function.
The trial was conducted at the Department of
Rehabilitation Medicine, at Danderyd University Hospital and
integrated in the individualized, team based, regular
inpatient program. Eligible were patients living in the
Stockholm region and who were admitted to the
department for post-acute, inpatient rehabilitation after stroke
between June 2012 and August 2013. Inclusion criteria
were: less than seven weeks since stroke; able to sit on a
bench with/without supervision at least five minutes;
unable to walk independently due to lower extremity
paresis with/without somato-sensory impairment and with/
without spasticity; sufficient postural control to allow
upright position in standing with aids and/or manual support;
ability to understand training instructions as well as written
and oral study information and to express informed
consent; body size compatible with the HAL suit. Exclusion
criteria were: contracture restricting gait movements at any
lower limb joint (hip, knee, ankle); cardiovascular or other
somatic condition incompatible with intensive gait training;
severe, contagious infections (e.g. with Methicillin Resistant
Staphylococcus Aureus (MRSA) or Extended Spectrum
Beta-Lactamase (ESBL) bacteria). Eight consecutive patients
fulfilled these criteria and completed the study protocol.
Training with HAL was performed during daily sessions
on Monday to Friday. The patient was encouraged to
walk as long time as he/she was able to including pauses,
without exceeding 60 minutes (net walking time). In all
patients, training with HAL was used in combination with
BWS and treadmill for safety reasons and to allow
adjustments of speed. The degree of BWS was individualized
but never less than the weight of the HAL-suit, i.e. 14 kilos.
Support from handrail of the treadmill was allowed.
Training was performed by one or two physiotherapists
(PTs), who had learned and trained to use the HAL
system (HAL-ML05). The double leg version was used and
the suit was attached to the patients when standing or
sitting. For an illustration of HAL training see Figure 1.
The physiotherapist provided verbal instructions,
encouragement and feedback to the patient. A mirror placed in
front of the patient allowed visual feedback. Training
started with the CAC and/or CVC mode for hip and knee
joint on the affected side and aimed to use the CVC mode
as soon as possible. HAL assistance was successively
decreased as convenient according to the PTs evaluation.
Initial walking speed was 0.4 km/h, increased as tolerated
and set at the highest speed possible to be compatible with
the necessary HAL assist level. The degree of BWS was
then successively reduced but adapted not to hamper
optimal speed. All settings were individualized and
adjusted to optimize normal gait pattern, which was evaluated
through continuous observational gait analysis during
training, according to the ten-point-checklist suggested by
Kirtley . The duration of the total treatment period was
individualized. Training with HAL was stopped when HAL
was no longer considered useful by the PT or when three
months had elapsed since the stroke. Training with HAL
was integrated in each participants individualized program
according to current practice. This included goal oriented
individualized and/or group training at the discretion of
the rehabilitation team.
The study protocol addressed: (1) time to arrange the
equipment and initiate a training session with HAL, (2)
gait speed and quality at baseline and immediately after
the training period, (3) utilization of BWS and of
conventional aids such as orthoses during HAL training, (4)
adverse events (such as falls, skin impact, pain etc.) related
to use of HAL, technical risk factors and prevention of
these, (5) patients attitudes towards training with HAL. In
addition, training data (e.g. gait speed and distance) and
HAL settings were registered at each training session.
Assessments at baseline and at endpoint comprised: the
NIH Stroke Scale (NIHSS) ; the Fugl-Meyer Scale for
the lower extremities (FM-LE) ; Bergs Balance scale
(BBS) [39,40]; Timed Up and Go (TUG) ; 10 Meter
Walking Test (10MWT)  self-selected and maximum
speed; the Clinical Outcome Variable Scale, Swedish
version (S-COVS) Section 58 ; Functional Ambulation
Categories (FAC) ; Falls-efficacy Scale Swedish version
(FES(S)) ; Barthel Index (BI) ; Functional
Independence Measure (FIM) ; EQ-5D and EQ-5D VAS
. In addition, patients attitudes towards HAL training
were captured by use of a visual analogue scale (VAS)
ranging from 0 (negative) to 10 (positive). Further, relevant
comments were documented during the training sessions.
All assessments were conducted by the same
physiotherapist who was not blinded to the intervention.
The study was approved by the Stockholm Ethical
Review Board (Dnr: 2012/696-31/1).
Clinical trial registration
The study was approved and registered as a clinical
trial by the Swedish Medical Products Agency (Dnr:
Figure 1 Illustration of training.
Patients and injury characteristics
None of the patients who fulfilled study criteria declined
participation and there were no drop-outs. All eight
patients included were men. Median age was 56 years
(range 39 to 64), median time from stroke to inclusion
was 35 days (range 6 to 46). At baseline, Barthel Index
ranged from 10 to 60 (median 30), FIM scores ranged
from 26 to 96 (median 60). Demographic and injury
characteristics are presented in Table 1.
Data from assessments at baseline and immediately
after finishing the training are presented in Tables 1 and 2.
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Table 2 Baseline and endpoint data, median (range)
Fugl-Meyer, LE (086)
Bergs balance scale (056)
Timed up and go (s)
10 meter walking test, self selected speed (s)
10 meter walking test, maximal speed (s)
S-COVS, item 58 (428)
Functional ambulation categories (05)
Falls efficacy scale (0130)
Barthel index (0100)
Functional independence measure (18126)
EQ-5D VAS (0100)
At baseline, FM-LE scores ranged from 41 to 63 (median
49) and gait was severely impaired as reflected by the TUG,
10MWT and FAC data (Table 2). Only one patient could
perform the TUG test at baseline, 4 could perform the
10MWT and then needed on average 2 minutes, and the
median FAC sore was 0 (Table 2). EQ5D and FES data are
incomplete due to communication problems.
Practical aspects on the use of HAL
HAL training was conducted by one or two PTs,
depending on the severity of the patients impairments. However,
two therapists were present during donning and initial
sessions for all patients and during the whole training
period for 3 patients. A typical training session lasted
around 90105 minutes, including time for preparation of
electrodes, putting on the harness and the suit and
transfer to the treadmill. Time to arrange the equipment for
training varied slightly depending on the patient's motor
and cognitive skills. In general 1520 minutes was needed
from the patient arrived to the training session until gait
training with HAL could start. Favorable factors were:
ability to independently move between wheelchair and
bench; ability to stand with the support of aids and
moderate support of therapist when putting on for example
electrodes, harness and HAL; ease to understand verbal
instructions. Factors that increased the time for
preparation were need for shaving the skin before
attaching electrodes and need of great support in standing to
maintain postural control. Time needed after finished
HAL training (i.e. to remove the suit, harness and
electrodes) was in general less than preparation time
(around ten minutes). No patient needed a foot
orthosis in addition to the support provided by the HAL
suit and its connected shoe. All patients used the handrail
unilateral (non paretic side) for support.
Training program and clinical course
Training data are presented in Table 1. Total, number of
training sessions varied from 6 to 31 (median 16)
depending on the clinical progress i.e. until HAL was no longer
considered useful by the PT, or until three months after
the stroke. The net walking time per session was around
25 minutes. The average individual walking distance per
session ranged from 155 to 797 meters. The maximal
walking distance observed during one session was 1188 meters
in one patient (Case nr 3). Walking distances during HAL
training for each study patient are presented in Figure 2.
All patients started with the CAC mode and all except one
later switched to use the CVC mode. On average, for these
7 patients, the initial 6 sessions out of 16 were with the
CAC mode. The switch was performed as soon as the
voluntarily induced EMG activity was sufficient to elicit a
command signal. The amount of BWS provided was in
median 27 (range 2336) percent of the patients' body weight.
Measures of motor function, gait and of activity
performance improved from baseline to the end of the
training period in all patients (Table 2). Improvements in gait
function in terms of FAC, increased by 1.5 units and time
to walk 10 meters decreased by around 65% (n = 4). For
further details see Table 2.
Patients attitudes to use of the HAL system
All patients except one (with moderate communication
problems) responded to the visual analogue scale.
Overall, patients attitudes were positive. The average VAS
rating of the over all attitude to continue training with
HAL, was 7/10 (range 0.5-10).
No serious adverse events occurred. Minor and temporary
side effects comprised pain due to pressure from the cuff
Figure 2 Walking distance by HAL training session.
over the knee (n = 1; managed by changing the height of
the cuff ) and over the malleolus (n = 1; managed by
changing the angle of the lower leg and foot joint); moderate
discomfort of tight straps and the feeling of being trapped
(n = 1), discomfort from shoulder straps (n = 2); sense of
the suit being heavy over the lower back (n = 1);
temporary skin irritation/redness from electrodes (n = 2;
disappeared after finishing HAL training); moderate pain in the
groin after a HAL training session (n = 1) (related to
chafing from the harness); chafed feet due to wrong shoe size
(n = 1) (manage by change of shoes); slight risk of
stumbling due to impaired weight shifting occurred from time
to time (support by two therapists was needed). One
patient reported pain in the paretic arm during training.
However, similar pain did also occur during other training
sessions and thus was not specific for training with HAL.
Issues related to technical problems were few and did not
affect patient safety.
The main findings of this study are that the HAL system
enables intensive, repetitive gait training in hemiparetic
patients with severely impaired gait function early after
stroke and that the system is feasible and safe when used
as part of an inpatient rehabilitation program for these
patients by experienced physiotherapists. Although this
study does not allow any conclusions on the additional
value of training with HAL with regard to recovery
rate or final outcome as compared to other gait training
programs, the findings may guide further studies in this
This is the first application of the new Hybrid Assistive
Limb system that allows both training of gait induced
by weight shift (autonomous mode) and a gait pattern
induced by the voluntary drive to walk, in contrast to
other gait machines such as Lokomat , in patients
with a hemiparesis early after stroke. It is to the best
of our knowledge the first study of early onset of intensive
gait training after stroke that utilizes this type and model
of exoskeleton (HAL-ML05). Patients included in the
study represented the more severe spectrum of patients
with hemiparetic impairments after stroke. Accordingly,
all eight patients initiated the training period by use of the
autonomous HAL mode, which allowed the training to
start earlier than otherwise possible. All except one patient
later switched to training by use of the voluntary HAL
mode. It should be pointed out that the voluntary
activation pattern, as reflected by electromyography and
translated to assisted movements, is by definition disturbed in
the condition at study and thus requires corrections,
which are part of the HAL system, and that the HAL
settings are individually adapted by an experienced
physiotherapist to achieve a gait pattern as close to
normal as possible.
A typical training session lasted for about 100 minutes.
The length of the training sessions, set to maximally
60 minutes net walking time, was predetermined based
on clinical experience of what may be feasible and with
regard to integration with the regular rehabilitation
program. This time frame turned out to correspond well
with what participants could manage, general fatigue
being the most common limiting factor. Interestingly, the
study patients walked in average approximately 444 m/
session. The walking distance during HAL training
sessions did not increase linearly over time but exhibited
considerable intra-individual variation, which probably
reflects increasing demands when the degree of
assistance was reduced, fluctuations of the patients medical
condition, mood and vitality as well as the learning
Even though the study does not allow any conclusion,
it was a consistent clinical impression that use of HAL
enabled patients to achieve longer walking distances
than would have been possible by regular gait training
with or without BWS. Comparison in this respect with
results from other studies using other training devices
are hampered by differences with regard to inclusion
criteria, time since stroke, training program and study
The test protocol captured a broad range of functional
aspects. As expected, all patients exhibited
improvements from baseline to endpoint assessments. These
probably reflect time dependent, spontaneous recovery,
which is mainly completed within the first ten weeks
after stroke [49,50] as well as beneficial effects of the
regular rehabilitation program, while an additional effect
of the specific training with HAL cannot be disentangled
and obviously was beyond the scope of this study. It may
be noted that the observed improvement of functional
gait as assessed by FAC, seemed more pronounced than
may be explained only by time. FAC units increased by
more than 1 unit (from a median value of 0 to 1.5, in
mean by 1.25) in our small study sample of patients who
started the HAL training around five weeks after stroke
onset. In a longitudinal study by Kwakkel et al.  of
101 patients the corresponding figure for change of FAC
was 1.1 units (in mean) over a 16 weeks period from
stroke onset and this time dependent increase was most
pronounced during the initial six weeks. Thus, even if
our data do not allow any conclusion the observations
lend some support to the interpretation that the
improvements observed do not only reflect spontaneous
recovery over time. Most previous gait training studies
that report improvements of FAC differ considerably
from our study with regard to study samples, baseline
levels and study design [22,24-27]. One study by van
Nunen et al.  offer data that may be used for a
cautious comparison. That study compared the recovery of
walking in non-ambulatory patients in the subacute
phase after stroke. At baseline, in mean 62 days for 16
patients performing Lokomat + conventional training,
and in mean 67 days for 14 patients performing
conventional training, FAC was 1.50 and 1.00 respectively. At
week 10, FAC had increased by 1.25 in the combined
therapy group and by 1.29 in the other group. This is
similar to the observations in our study. However, the
FAC score baseline level was lower and training onset
was earlier (median 35 days) in our study.
Training with HAL was performed by use of BWS and
treadmill in all patients, which offered better control of
safety and of gait speed. The combined use of BWS and
HAL worked smoothly and no obstacles for such combined
use were observed. The treadmill enabled accurate
recording of walking speed and distance for each patient and
training session. Although the width of the treadmill
occasionally limited weight shifting, it never stopped a training
session. The use of a harness seems essential to allow the
HAL training to be safe and feasible for patients with
severe paresis in the early stage after stroke.
Regular gait training for the study patients had
likely been by use of treadmill and BWS and then
most patients would probably have needed manual
assistance by two or more physiotherapists to move the
paretic leg and to assist weight shifting. However the
potential benefits with regard to therapist time as
compared to conventional gait training remains to be
investigated and time spent to put on the suit and adjust
settings must also be considered. This time was dependent
on the patients general physical condition but seemed not
related to spasticity, sensory impairments or motor
performance of the upper extremity and diminished
No serious adverse events occurred during training
with HAL. Minor and temporary side effects comprised
e.g. local pain, skin irritation and sense of heaviness of
the lower back by the suit. It should be pointed out that
even though participating patients had severe motor
impairments all had regained sitting balance and were
able to communicate with the therapist. In addition, the
physiotherapists who conducted the training were
experienced in rehabilitation after hemiparetic stroke and
had been trained to use the HAL system. Minor
technical issues occurred but did never impact on safety or
the training schedule.
According to the questionnaire as well as face to face
contacts, patients attitudes were generally positive to
training with HAL. Regaining independent gait function
is often considered a primary goal in stroke
rehabilitation and it is reasonable to assume that the option to
start training early by use of HAL may serve as a
This prospective study is based on a small study sample
at one study site and used no blinding or control group.
The study included a selected subgroup of patients, who
are not representative for the whole stroke population
with regard to age, gender or neurological impairments.
Notably, all study patients were men in spite of
consecutive inclusion according to the study criteria. This
probably is a random effect even though an uneven gender
distribution (with around twice as many men) among
patients, who are referred to the study clinic, may also
have played a role. Thus, the findings are only relevant
for the subgroup at study and cannot be generalized to
the whole stroke population.
This study of the Hybrid Assistive Limb system for
intensive gait training early after stroke demonstrates
that such training can be performed also by hemiparetic
patients with severely impaired gait function and that
the system is safe when used as part of an inpatient
rehabilitation program for these patients by experienced
physiotherapists. The observations should be useful for
the design of further studies comparing training with the
HAL system with other models for training of gait early
Anneli Nilsson, Katarina Skough Vreede, Vera Hglund and Jrgen Borg have no
competing interests to declare. Hiroaki Kawamoto is a founder, shareholder,
and an external director of CYBERDYNE Inc. which produces the HAL. Yoshiyuki
Sankai is a founder, shareholder, and the CEO of CYBERDYNE Inc.
AN and KSV participated in the design of the study, carried out the HAL
training and assessments, performed the statistical analysis and drafted the
manuscript. VH included patients for participation in the study and collected
their informed consent. HK and YS participated in the design of the study
and provided the HAL suits and technical support. JB participated in the
coordination and design of the study, in the statistical analysis and in
drafting and finalizing the manuscript. All authors approved the manuscript.
This study was supported by Cyberdyne Inc Japan and by Stockholm County
Council. We thank Sofie Nybom at Stockholm County Council Innovation for
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