Injuries to the central nervous system result in a wide range of disabilities of which more than 60% show gait dysfunctions [
1].
As a consequence, these patients often demonstrate slow or abnormal
gait and impaired balance which result in a greatly increased risk of
falling with high probability of severe secondary injuries [
2].
At an advanced stage, gait dysfunctions and fear of falling can lead to
a loss of independence, social isolation and mobility restrictions [
2] - factors strongly related to a decreased quality of life [
3].
Therefore, a large proportion of modern rehabilitation programs focus
on gait and balance training in compliance with locomotor training
principles. These principles are known to maximize recovery and
restoration and state that weight-bearing through legs should be
maximized, appropriate sensory cues and task-specific, physiological
kinematics need to be provided while compensatory strategies should be
minimized [
4].
But locomotor training should not only focus on simple walking or
balance, but also on advanced activities like curb and stair negotiation
which are similarly indispensable for independent living. Paolucci et
al. however report that of initially non-ambulatory patients with
stroke, only 4.58% regain the ability to independently negotiate stairs
while 50.57% regain the ability to walk [
5]. One reason behind this is that negotiating stairs is much more challenging than overground walking [
6].
The greater complexity of stair negotiation and the increased risk of
falling compared to level ground walking originates from higher physical
demands such as the need for i) larger joint ranges of motion (ROMs),
ii) higher muscular strength, iii) better cardiovascular fitness [
7], iv) more precise foot placement which relies on accurate visual feedback [
8] and increased stability [
9].
In addition, stair negotiation is psychologically challenging due to
the increased probability of serious injury in case of a fall compared
to walking on level ground. To restore a high level of independence, it
is desirable to boost patients’ capabilities and confidence in safe
stair negotiation. Optimally, patients would start stair negotiation
training early in their rehabilitation process to maximally benefit from
the optimal time window during which the central nervous system might
show increased neuroplasticity [
10,
11].
Appropriate assistance and security are a requirement for early stair
climbing training, however this puts a large burden on therapists in
terms of support forces. One way to provide large supportive forces is
via robotic devices. Robotic rehabilitation technology that assists
training of stair negotiation from an early time point on is however
rare and limited to few devices such as end-effector-based gait
trainers, ceiling-mounted BWS systems, and wearable exoskeletons [
12,
13,
14,
15,
16,
17].
Compared to gait trainers, BWS systems and wearable exoskeletons have
the advantage that they allow training of real stair walking which helps
provide the appropriate afferent sensory input to relearn the task.
Wearable exoskeletons, the most recently emerged of these technologies,
are however still struggling with fall safety mechanisms and require
users to rely on crutches for balancing resulting in compensatory arm
activity [
18].
BWS systems on the other hand do not seem to substantially hinder or
compromise physiological movement execution which was at least shown for
able-bodied and patients with incomplete spinal cord injury during
overground walking with up to 30% of BWS [
19,
20,
21].
By changing BWS, the intensity of the training can be adapted to the
individual patient and his/her capabilities. Ceiling-mounted BWS systems
can therefore be a promising tool to support stair negotiation in
patients with remaining voluntary muscle control. However, the effect of
BWS on movement performance specifically during stair negotiation has
to our best knowledge not yet been investigated. It is therefore not
clear if BWS hinders physiological performance of stair ambulation,
something which must be first investigated in an able-bodied population.
Therefore,
this paper aims at providing insights into effects of different levels
of BWS on the biomechanics and myoelectric activity during stair
negotiation. We used the FLOAT (The FLOAT, RehaStim Medtech AG, Germany)
BWS system for our investigations. FLOAT can apply different levels of
unloading as well as horizontal assistance forces during a broad range
of training tasks including ground level walking, standing up/sitting
down, as well as stair negotiation [
15,
20,
21,
22,
23,
24,
25,
26].
From previous investigations of the FLOAT and other BWS systems during
overground walking in able-bodied subjects, it is known that with higher
levels of BWS temporal parameters change towards shorter stance
durations and lower limb joint ROMs are reduced apart from inconclusive
evidence for the ankle [
19,
20].
Kinetics and myoelectric activity show in most cases reductions with
some inconclusive evidence regarding compensatory activity. The general
consensus is however that deviations from physiological movement
patterns are small and negligible up to 30% BWS [
19,
20].
A similar understanding of alterations introduced by BWS in able-bodied
individuals during stair negotiation is important for validating the
task-specificity of BWS stair training, which optimally transfers to
daily life [
27].
We hypothesize that BWS, does not induce large deviations in lower limb
kinematic patterns while reducing neuromuscular demand without
introducing compensatory activity. If this holds true, BWS stair
training should be safe to apply for physiological training of stair
negotiation in patients with neurological diseases.
