33 research outputs found
Cooperative ankle-exoskeleton control can reduce effort to recover balance after unexpected disturbances during walking
No full textBACKGROUND: In the last two decades, lower-limb exoskeletons have been developed to assist human standing and locomotion. One of the ongoing challenges is the cooperation between the exoskeleton balance support and the wearer control. Here we present a cooperative ankle-exoskeleton control strategy to assist in balance recovery after unexpected disturbances during walking, which is inspired on human balance responses. METHODS: We evaluated the novel controller in ten able-bodied participants wearing the ankle modules of the Symbitron exoskeleton. During walking, participants received unexpected forward pushes with different timing and magnitude at the pelvis level, while being supported (Exo-Assistance) or not (Exo-NoAssistance) by the robotic assistance provided by the controller. The effectiveness of the assistive strategy was assessed in terms of (1) controller performance (Detection Delay, Joint Angles, and Exerted Ankle Torques), (2) analysis of effort (integral of normalized Muscle Activity after perturbation onset); and (3) Analysis of center of mass COM kinematics (relative maximum COM Motion, Recovery Time and Margin of Stability) and spatio-temporal parameters (Step Length and Swing Time). RESULTS: In general, the results show that when the controller was active, it was able to reduce participants' effort while keeping similar ability to counteract and withstand the balance disturbances. Significant reductions were found for soleus and gastrocnemius medialis activity of the stance leg when comparing Exo-Assistance and Exo-NoAssistance walking conditions. CONCLUSIONS: The proposed controller was able to cooperate with the able-bodied participants in counteracting perturbations, contributing to the state-of-the-art of bio-inspired cooperative ankle exoskeleton controllers for supporting dynamic balance. In the future, this control strategy may be used in exoskeletons to support and improve balance control in users with motor disabilities.Biomechatronics & Human-Machine Contro
Recovering linear and angular momentum during walking
No full textFor most individuals maintaining balance during walking goes natural. We are not continuously thinking of how to maintain balance, and still we usually do not fall. However, maintaining balance is not a given for everyone. Both aging and various neuromuscular disorders affect the ability to maintain balance, resulting in an increased incidence of falls and the associated consequences. Also, in the situation of someone walking with an assistive device such as a powered lower-limb exoskeleton, for example due to a spinal cord injury (SCI), maintaining balance may be challenging. To provide better care and training programs and to improve balance support with assistive devices, a better understanding is needed of human balance recovery. Previous research often focused on the recovery of linear perturbations disturbing the body's linear momentum. However, in daily life we also encounter perturbations resulting in a rotational effect, disturbing the body's angular momentum. The aim of this work was to gain insights in the use of human balance strategies to recover whole-body linear and angular momentum. To provoke balance recovery responses we performed experiments in which perturbations were applied during standing and treadmill walking. These studies were performed with healthy participants, since they can serve as a source of inspiration for how balance recovery strategies are being used successfully. Perturbations of the linear and/or angular momentum were induced by the application of forces to the body at shoulder and/or pelvis height, provided by a haptic robot. This allowed for a controlled duration, magnitude and onset of the perturbations. Thereafter we analyzed how modulations of the ground reaction force and its point of application were used in order to maintain balance. We studied this in 1) situations that are relevant for SCI individuals walking with a powered lower limb exoskeleton and 2) situations that have not extensively been studied before, and therefore fill a gap in the current knowledge on human balance recovery. In several chapters we address the topic of balance recovery during very slow walking, since this is a relevant speed for walking with a lower limb exoskeleton. Walking very slowly increases the time spent in the double support phase. Studying the responses to perturbations of the whole-body linear momentum (WBLM) while standing in a static double support phase, also called a staggered stance posture, provided insights in the coupling between the frontal- and sagittal-plane. A large base of support (BoS) enables opportunities for centre of pressure (CoP) modulation. Therefore, the large dimension of the BoS in the anteroposterior direction during staggered stance could also be used in the recovery from perturbations that were perpendicular to this direction. Focusing on the double support phase, with simulations based on a simple linear inverted pendulum model, we showed the effects of modulations of the CoP trajectory on the control of the centre of mass position and velocity. Comparing the simulated opportunities with the strategies that healthy individuals used, it turned out that we do not fully exploit the available options for a quick balance recovery. A specific type of perturbation that we used for several studies is a perturbation of the whole-body angular momentum (WBAM). This was obtained by applying two perturbations at the same time in opposite direction on the pelvis and upper body respectively. The responses to these perturbations revealed a high priority in recovery of the WBAM. This was done even at the expense of the WBLM. The WBAM recovery comprised a modulation of the horizontal ground reaction force, affecting the WBLM while this was not perturbed initially. This effect was independent of the instant of the gait cycle at which the perturbation was given and holds for very slow and normal walking speeds. The results emphasize the importance and prioritization of WBAM regulation in balance recovery. To conclude, the studies presented in this thesis provide insights into the human balance strategies used to recover from perturbations of the WBLM and WBAM during walking at very low and normal speeds. These insights can be considered in the development of controllers to assist balance or to improve balance training for those experiencing difficulties with balance control. Finally, the recorded data itself is valuable for validating whether proposed recovery strategies are human-like
Balance recovery following pelvis perturbations during very slow walking
No full textBACKGROUND AND AIM: Healthy humans have the ability to handle balance perturbations during walking very well. The ankle moment, as well as the foot placement location and timing are altered to counteract the perturbations and maintain balance.[1] Previously, healthy subjects have shown a strong linear relation between the body´s centre of mass (COM) velocity at heel contact (HC), and both the foot placement location and centre of pressure (COP) at subsequent toe off (TO) during laterally perturbed walking.[2] The walking speeds were 0.63 and 1.25 m/s.[2] In this study, it is questioned whether this relation also exist during very slow walking, because there will be more time during the double support phase to alter the balance recovery strategy. Therefore, we investigated the relation between the body´s COM velocity, and both the foot placement location and COP during a very slow walking speed. METHODS: Mediolateral (ML) pelvis perturbations were applied to 10 healthy subjects, during very slow (0.36 m/s) and normal (1.25 m/s) treadmill walking at TO of the right foot. An active optical motion capture system was used to record the body kinematics. Ground reaction forces were measured with the built-in force plates in the treadmill. The data was analysed to obtain COM velocities at HC right, foot placement location at HC right, COP locations at TO left and phase durations. RESULTS: Figure 1 presents the durations of the double and single support phases for the different perturbation magnitudes. The ML perturbations significantly affected the double and single support durations during very slow walking, while these durations were not affected during normal walking. Additionally, the COM velocity at HC right showed to have a high predictive value for the foot placement of the leading foot during the normal walking speed, whereas this was considerable lower during the very slow walking speed. The predictive value of the COM velocity was present for the COP location at the subsequent TO for both the normal and very slow walking speed. CONCLUSIONS: The results showed altered recovery strategies in the frontal plane during very slow walking compared to the normal walking speed. These differences were potentially caused by the longer double support phase duration, in which subjects used other strategies to control the distance between the COM and COP. REFERENCES:[1] A. L. Hof, R. M. van Bockel, T. Schoppen, and K. Postema, "Control of lateral balance in walking. Experimental findings in normal subjects and above-knee amputees," Gait Posture, vol. 25, no. 2, pp. 250-258, 2007. [2] M. Vlutters, E. H. F. van Asseldonk, and H. van der Kooij, "Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking," J. Exp. Biol., vol. 219, no. 10, pp. 1514-1523,2016
sj-pdf-1-jcb-10.1177_0271678X231169579 - Supplemental material for Hemoglobin and cerebral hypoxic vasodilation in humans: Evidence for nitric oxide-dependent and <i>S</i>-nitrosothiol mediated signal transduction
No full textSupplemental material, sj-pdf-1-jcb-10.1177_0271678X231169579 for Hemoglobin and cerebral hypoxic vasodilation in humans: Evidence for nitric oxide-dependent and S-nitrosothiol mediated signal transduction by Ryan L Hoiland, David B MacLeod, Benjamin S Stacey, Hannah G Caldwell, Connor A Howe, Daniela Nowak-Flück, Jay MJR Carr, Michael M Tymko, Geoff B Coombs, Alexander Patrician, Joshua C Tremblay, Michelle Van Mierlo, Chris Gasho, Mike Stembridge, Mypinder S Sekhon, Damian M Bailey and Philip N Ainslie in Journal of Cerebral Blood Flow & Metabolism</p
Balance recovery in the double support during perturbed walking
No full textI. INTRODUCTION Exoskeleton walking increases the relative time spent in the double support phase (DSP). It is therefore crucial to control balance when both feet are on the ground. Healthy humans have excellent balance capabilities to avoid falling. The centre of pressure (CoP) describes the control of the centre of mass (CoM) movement [1]. The range of possible CoP locations in the DSP is determined by the foot placement at the end of the preceding single support phase. This study focuses on the CoP modulation during the DSP in the control of the CoM state. II. METHODS CoP trajectories in response to pelvis perturbations were extracted from an existing data set by Vlutters et al [2]. Anteroposterior and mediolateral perturbations with magnitudes up to 16% of the body weight were given at the moment of toe off. Parameterized CoP trajectories were generated with a spline function based on the experimental CoP trajectories, examples are shown in figure 1. Parameterization was done as a function of 1) the duration of the DSP, 2) the amplitude of the CoP, and 3) percentage of the amplitude reached halfway the DSP (= midpoint). The parameters were varied within a range equal to the standard deviation around the mean value obtained from the experimental data. The generated trajectories were used in model simulations of the CoM during the first DSP following the perturbation. A simple inverted pendulum model, relating the horizontal distance between the CoP and CoM to CoM acceleration, was used to assess the effectiveness of the CoP modulation in counteracting perturbation induced CoM velocity changes [3]. III. RESULTS The model outcome corresponds with the experimental data, figure 1. All the three CoP parameters are linearly related to the change in CoM velocity over the DSP, in both the experimental and modelled data. Changes of the midpoint resulted in larger variations in the modelled Δ CoM velocity, compared to those resulting from changes in the duration or amplitude, see figure 2. IV. DISCUSSION A simple inverted pendulum model was able to model representative CoM trajectories from the generated CoP trajectories as input. To control the CoM velocity after a perturbation, subjects used all CoP parameters. However, in the experimental data these parameters were also related with each other. When uncoupling the effect of these parameters in the model, the shape of the CoP trajectory, represented by the CoP shift that is reached halfway the DSP, had the largest influence on the changes of the CoM velocity during the DSP. Shifting the load earlier or later to the leading leg helps in increasing or decreasing the CoM velocity. This will help in counteracting the effect of the perturbation and returning to the baseline CoM velocity. REFERENCES [1] H. Reimann, T. D. Fettrow, E. D. Thompson, P. Agada, B. J. McFadyen, and J. J. Jeka, “Complementary mechanisms for upright balance during walking,” PLoS One, vol. 12, no. 2, pp. 1–16, 2017. [2] M. Vlutters, E. H. F. van Asseldonk, and H. van der Kooij, “Center of mass velocity-based predictions in balance recovery following pelvis perturbations during human walking,” J. Exp. Biol., vol. 219, no. 10, pp. 1514–1523, 2016. [3] Y. Jian, D. Winter, M. Ishac, and L. Gilchrist, “Trajectory of the body COG and COP during initiation and termination of gait,” Gait Posture, vol. 1, no. 1, pp. 9–2
Pelvis perturbations in various directions while standing in staggered stance elicit concurrent responses in both the sagittal and frontal plane
No full textIncreasing knowledge on human balance recovery strategies is important for the development of balance assistance strategies using assistive devices like a powered lower-limb exoskeleton. One of the postures which is relevant for this scenario, but underexposed in research, is staggered stance, a posture with one foot in front. We therefore aimed to gain a better understanding of balance recovery in staggered stance. We studied balance responses at joint- and muscle levels to pelvis perturbations in various directions while standing in this posture. Ten healthy individuals participated in this study. We used one actuator beside and one behind the participant to apply 150 ms perturbations in mediolateral (ML), anteroposterior (AP) and diagonal directions, with a magnitude of 3, 6, 9 and 12% of the participant’s body weight (BW). Meanwhile, motion capture, ground reaction forces and moments, and electromyography of the muscles around the ankles and hips were recorded. The perturbations caused movements of the centre of mass (CoM) and centre of pressure (CoP) in the direction of the perturbation. These were often accompanied by motions in a direction different from the perturbation direction. After perturbations perpendicular to the line between both feet, large and significant AP deviations were present of the CoM (-0.27 till 0.40 cm/%BW, p < 0.029) and CoP (-0.99 till 0.80 cm/%BW, p < 0.001). Also, stronger responses on joint and muscle level were present after these perturbations, compared to AP and diagonal perturbations collinear with the line between both feet. The hip, knee and ankle joints contributed differently to the balance responses after the different perturbation directions. To conclude, standing in a staggered stance posture makes individuals more vulnerable to perturbations perpendicular to the line between both feet, requiring larger responses on joint level as well as contributions in the sagittal plan
Sagittal-plane balance perturbations during very slow walking: Strategies for recovering linear and angular momentum
No full textSpatiotemporal gait characteristics change during very slow walking, a relevant speed considering individuals with movement disorders or using assistive devices. However, we lack insights in how very slow walking affects human balance control. Therefore, we aimed to identify how healthy individuals use balance strategies while walking very slow. Ten healthy participants walked on a treadmill at an average speed of 0.43 m s−1, while being perturbed at toe off right by either perturbations of the whole-body linear momentum (WBLM) or angular momentum (WBAM). WBLM perturbations were given by a perturbation on the pelvis in forward or backward direction. The WBAM was perturbed by two simultaneous perturbations in opposite directions on the pelvis and upper body. The given perturbations had magnitudes of 4, 8, 12 and 16 % of the participant’s body weight, and lasted for 150 ms. After perturbations of the WBLM the centre of pressure placement was modulated using the ankle joint, while keeping the moment arm of the ground reaction force (GRF) with respect to the centre of mass (CoM) small. After the perturbations of the WBAM a quick recovery was initiated, using the hip joint and adjusting the horizontal GRF to create a moment arm with respect to the CoM. These findings suggest no fundamental differences in the use of balance strategies at very slow walking compared to normal speeds. Still as the gait phases last longer, this time was exploited to counteract perturbations in the ongoing gait phase
Recovery from sagittal-plane whole body angular momentum perturbations during walking
No full textHealthy individuals highly regulate their whole body angular momentum (WBAM) during walking. Since WBAM regulation is essential in maintaining balance, a better understanding is required on how healthy individuals recover from WBAM perturbations. We therefore studied how healthy individuals recover WBAM in the sagittal plane. WBAM can be regulated by adjusting the moment arm of the ground reaction force (GRF) vector with respect to the whole-body centre of mass (CoM). In principle this can be done by centre of pressure (CoP) modulation and/or adjustments of the GRF direction. Two simultaneous perturbations of the same magnitude were applied in opposite direction to the pelvis and upper body (0.34m apart) to perturb WBAM but not the whole body linear momentum (WBLM), while participants walked on a treadmill. The perturbations were given at toe off right, had a magnitude of 4, 8, 12 and 16% of the participant's body weight, and lasted for 150ms. A recovery of the WBAM was seen directly after the perturbations, induced by adapting the moment arm of the GRF with respect to the CoM. The hip joint of the stance leg played an important role in achieving the WBAM recovery. A change in the direction of the GRF vector and not a contributing CoP modulation, caused the change in moment arm. However, the change in GRF direction came from a change in the horizontal GRF, which also affects the WBLM. This suggest that regulating WBAM may take precedence over the WBLM in early recovery.Biomechatronics & Human-Machine Contro
Pelvis perturbations in various directions while standing in staggered stance elicit concurrent responses in both the sagittal and frontal plane.
No full textIncreasing knowledge on human balance recovery strategies is important for the development of balance assistance strategies using assistive devices like a powered lower-limb exoskeleton. One of the postures which is relevant for this scenario, but underexposed in research, is staggered stance, a posture with one foot in front. We therefore aimed to gain a better understanding of balance recovery in staggered stance. We studied balance responses at joint- and muscle levels to pelvis perturbations in various directions while standing in this posture. Ten healthy individuals participated in this study. We used one actuator beside and one behind the participant to apply 150 ms perturbations in mediolateral (ML), anteroposterior (AP) and diagonal directions, with a magnitude of 3, 6, 9 and 12% of the participant's body weight (BW). Meanwhile, motion capture, ground reaction forces and moments, and electromyography of the muscles around the ankles and hips were recorded. The perturbations caused movements of the centre of mass (CoM) and centre of pressure (CoP) in the direction of the perturbation. These were often accompanied by motions in a direction different from the perturbation direction. After perturbations perpendicular to the line between both feet, large and significant AP deviations were present of the CoM (-0.27 till 0.40 cm/%BW, p < 0.029) and CoP (-0.99 till 0.80 cm/%BW, p < 0.001). Also, stronger responses on joint and muscle level were present after these perturbations, compared to AP and diagonal perturbations collinear with the line between both feet. The hip, knee and ankle joints contributed differently to the balance responses after the different perturbation directions. To conclude, standing in a staggered stance posture makes individuals more vulnerable to perturbations perpendicular to the line between both feet, requiring larger responses on joint level as well as contributions in the sagittal plane
Minimal centre of pressure adjustments for recovering whole body angular momentum in gait
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