Walking through a narrow aperture requires unique postural configurations, i.e., body rotation in the yaw dimension. Stroke individuals may have difficulty performing the body rotations due to motor paralysis on one side of their body. The present study was therefore designed to investigate how successfully such individuals walk through apertures and how they perform body rotation behavior.
Stroke fallers (n = 10), stroke non-fallers (n = 13), and healthy controls (n = 23) participated. In the main task, participants walked for 4 m and passed through apertures of various widths (0.9–1.3 times the participant’s shoulder width). Accidental contact with the frame of an aperture and kinematic characteristics at the moment of aperture crossing were measured. Participants also performed a perceptual judgment task to measure the accuracy of their perceived aperture passability.
Results and Discussion
Stroke fallers made frequent contacts on their paretic side; however, the contacts were not frequent when they penetrated apertures from their paretic side. Stroke fallers and non-fallers rotated their body with multiple steps, rather than a single step, to deal with their motor paralysis. Although the minimum passable width was greater for stroke fallers, the body rotation angle was comparable among groups. This suggests that frequent contact in stroke fallers was due to insufficient body rotation. The fact that there was no significant group difference in the perceived aperture passability suggested that contact occurred mainly due to locomotor factors rather than perceptual factors. Two possible explanations (availability of vision and/or attention) were provided as to why accidental contact on the paretic side did not occur frequently when stroke fallers penetrated the apertures from their paretic side.
Stroke is a disease caused by infarction, or hemorrhages of the blood vessels in the brain. Stroke is the major cause of neurological disabilities that affect many aspects of daily living. As one such issue, individuals with stroke often exhibit impaired walking, primarily due to motor paralysis on one side (typically the contralateral side of the affected side of the brain) of their body. A typical symptom indicating impaired walking is gait asymmetry. Gait asymmetry is the irregular coordination between the lower limbs and is produced mainly by differences in the magnitude of force displayed between the paretic and non-paretic limbs . Walking with gait asymmetry is biomechanically inefficient for achieving forward progression and makes maintaining balance more challenging
A particularly challenging aspect of maintaining balance becomes much more evident during adaptive locomotion, i.e., when basic movement patterns need to be modified adaptively in response to environmental constraints. Previous studies have shown that, as compared to control individuals, stroke individuals had difficulty stepping over an obstacle , walking fast while performing a cognitive task concurrently , changing their walking speed in response to changes in the optic flow , changing direction while walking [7–9], and turning [10,11]. In fact, the risk of falling is likely to increase when stroke individuals turn [12–14].
In line with these studies, the present study was designed to uncover challenging aspect of maintaining during adaptive locomotion in stroke individuals. The uniqueness of this study was to test their ability to safely walk through apertures. Adaptive modification of walking through a narrow aperture includes fine-tuning the walking direction toward the center of the aperture [15,16], decrease in movement speed [17,18], and changes in body configuration such as (upper-) body rotation in the yaw dimension [17–26]. The most powerful means to avoid accidental contact is the body rotation because it effectively reduces horizontal space required for crossing. Testing the ability to safely walk through an aperture has helped not only to understand perceptual-motor control of adaptive locomotion for obstacle avoidance [17,25–27] but also to describe the reason that controlling adaptive locomotion is difficult for some types of participants. Older adults had more variability in their body rotations at various aperture widths [28,29]. Patients with Parkinson’s disease (PD) showed sharply decreased walking speeds in front of an aperture, which could be caused by episodes of freezing . When young adults used a manual wheelchair for the first time, contact with the frame of an aperture occurred more frequently with dramatically different spatial-temporal patterns of fixation [30,31]. To our knowledge, there has been no study testing the ability of stroke individuals to safely walk through an aperture.
Measuring the behavior of walking through an aperture potentially provides some new insights into the increased risk of instability during adaptive locomotion in stroke individuals. This is particularly because stroke individuals could show difficulty performing the body rotations due to their motor paralysis on one side of their body and, as a result, they could have difficulty avoiding accidental contact with the frame of apertures. Walking through a narrow aperture with body rotation results in unique postural configurations, i.e., the body is rotated in the yaw dimension while the walking direction is maintained toward the center of the aperture. The uniqueness of the body rotation behavior becomes clear when it is compared with the turning behavior, which also involves individuals rotating their bodies, while its purpose is to change the direction of walking. Rotating the body to walk through an aperture usually involves a pivot-like turn, in which the body rotates about its vertical axis on the trailing limb at the moment it crosses the aperture. If stroke individuals penetrate an aperture from the paretic side (i.e., the trailing limb is non-paretic), then they would be able to perform a pivot-like turn. However, they would have difficulty maintaining their balance after the turn because they need to shift their body weight to the leading, or paretic, limb to progress forward. In contrast, if stroke individuals penetrate an aperture from the non-paretic side (i.e., the trailing limb is paretic), then an alternate strategy, rather than a pivot-like turn, would be selected for rotating their bodies. In both cases, taking multiple steps to rotate the body, which has been observed in the turning behavior performed of older adults [32,33], was expected to occur. This was because it was effective, at least for stroke individuals, to avoid shifting their body weight onto the paretic limb for a relatively long time. However, because there has been no study, it remains unknown as to which strategy would be more preferable for strong individuals and which strategy would lead to safe walking through apertures without making any contact with the frame of an aperture. The rationale for conducting the present study was to clarify these issues.
In the present study, two groups of stroke individuals were recruited: stroke fallers and stroke non-fallers. Stroke fallers were identified as those having a history of falling history in the past year. A systematic review of the literature showed that a history of falling in the past year most strongly predicts the likelihood of future falls among community-living older adults . Several previous studies have shown that significant gait characteristics of stroke individuals were more evident in those at high risk of falling [11,35]. Moreover, Takatori et al.(2009) reported that stroke individuals with a history of falls showed a large gap between the visual estimation of a reachable distance and the actual distance reachable . If such a large gap between perception and action exists in various types of behavior, then stroke fallers would show inaccurate judgment of the passability of an aperture, which could lead to accidental contact with the frame of an aperture. To examine whether accidental contact was related to the inaccurate judgment of the passability of the aperture, participants in the present study performed both the behavioral task of walking through apertures and the perceptual judgment task of aperture passability.
Twenty-three individuals with stroke (eleven females) participated. The mean age was 60.7 years (SD = 10.1). Twenty-three age-, gender-, and height-matched healthy individuals also participated as control participants. This study was approved by the ethics committee of the Kameda Medical Center. The tenets of the Declaration of Helsinki were followed. All participants gave their written informed consent prior to participation. Notably, the individual shown in Fig 1 has given written informed consent (as outlined in PLOS consent form) to publish an image of the participant.