Time filter

Source Type

Hak L.,VU University Amsterdam | Van Dieen J.H.,VU University Amsterdam | Van Der Wurff P.,Center for Augmented Motor Learning and Training | Van Der Wurff P.,University of Groningen | And 6 more authors.
Archives of Physical Medicine and Rehabilitation | Year: 2013

Objective: To investigate which strategies transtibial amputees use to cope with challenges of gait stability and gait adaptability, and how these strategies differ from strategies used by able-bodied controls. Design: Cross-sectional study. Setting: An instrumented treadmill mounted onto a 6°-of-freedom motion platform in combination with a virtual environment. Participants: Transtibial amputees (n=10) and able-bodied controls (n=9). Interventions: Mediolateral (ML) translations of the walking surface were imposed to manipulate gait stability. To provoke an adaptive gait pattern, a gait adaptability task was used in which subjects had to hit virtual targets with markers guided by their knees. Main Outcome Measures: Walking speed, step length, step frequency, step width, and selected measures of gait stability (short-term Lyapunov exponents and backward and ML margins of stability [MoS]). Results: Amputees walked slower than able-bodied people, with a lower step frequency and wider steps. This resulted in a larger ML MoS but a smaller backward MoS for amputees. In response to the balance perturbation, both groups decreased step length and increased step frequency and step width. Walking speed did not change significantly in response to the perturbation. These adaptations induced an increase in ML and backward MoS. To perform the gait adaptability task, both groups decreased step length and increased step width, but did not change step frequency and walking speed. ML and backward MoS were maintained in both groups. Conclusions: Transtibial amputees have the capacity to use the same strategies to deal with challenges of gait stability and adaptability, to the same extent as able-bodied people. © 2013 by the American Congress of Rehabilitation Medicine.


Hak L.,VU University Amsterdam | Houdijk H.,VU University Amsterdam | Houdijk H.,Heliomare Rehabilitation Center | Steenbrink F.,Motek Medical b.v. | And 5 more authors.
Journal of Biomechanics | Year: 2013

Besides a stable gait pattern, gait in daily life requires the capability to adapt this pattern in response to environmental conditions. The purpose of this study was to elucidate the anticipatory strategies used by able-bodied people to attain an adaptive gait pattern, and how these strategies interact with strategies used to maintain gait stability. Ten healthy subjects walked in a Computer Assisted Rehabilitation ENvironment (CAREN). To provoke an adaptive gait pattern, subjects had to hit virtual targets, with markers guided by their knees, while walking on a self-paced treadmill. The effects of walking with and without this task on walking speed, step length, step frequency, step width and the margins of stability (MoS) were assessed. Furthermore, these trials were performed with and without additional continuous ML platform translations. When an adaptive gait pattern was required, subjects decreased step length (p<0.01), tended to increase step width (p=0.074), and decreased walking speed while maintaining similar step frequency compared to unconstrained walking. These adaptations resulted in the preservation of equal MoS between trials, despite the disturbing influence of the gait adaptability task. When the gait adaptability task was combined with the balance perturbation subjects further decreased step length, as evidenced by a significant interaction between both manipulations (p=0.012).In conclusion, able-bodied people reduce step length and increase step width during walking conditions requiring a high level of both stability and adaptability. Although an increase in step frequency has previously been found to enhance stability, a faster movement, which would coincide with a higher step frequency, hampers accuracy and may consequently limit gait adaptability. © 2012 Elsevier Ltd.


Hak L.,VU University Amsterdam | Houdijk H.,VU University Amsterdam | Houdijk H.,Heliomare Rehabilitation Center | Steenbrink F.,Motek Medical b.v. | And 4 more authors.
Gait and Posture | Year: 2012

It has frequently been proposed that lowering walking speed is a strategy to enhance gait stability and to decrease the probability of falling. However, previous studies have not been able to establish a clear relation between walking speed and gait stability. We investigated whether people do indeed lower walking speed when gait stability is challenged, and whether this reduces the probability of falling.Nine healthy subjects walked on the Computer Assisted Rehabilitation ENvironment (CAREN) system, while quasi-random medio-lateral translations of the walking surface were imposed at four different intensities. A self-paced treadmill setting allowed subjects to regulate their walking speed throughout the trials. Walking speed, step length, step frequency, step width, local dynamic stability (LDS), and margins of stability (MoS) were measured.Subjects did not change walking speed in response to the balance perturbations (. p=. 0.118), but made shorter, faster, and wider steps (. p<. 0.01) with increasing perturbation intensity. Subjects became locally less stable in response to the perturbations (. p<. 0.01), but increased their MoS in medio-lateral (. p<. 0.01) and backward (. p<. 0.01) direction.In conclusion, not a lower walking speed, but a combination of decreased step length and increased step frequency and step width seems to be the strategy of choice to cope with medio-lateral balance perturbations, which increases MoS and thus decreases the risk of falling. © 2012 Elsevier B.V.


Mert A.,Center for Augmented Motor Learning and Training | Hak L.,VU University Amsterdam | Bles W.,TNO
2011 International Conference on Virtual Rehabilitation, ICVR 2011 | Year: 2011

Introduction: Balance is negatively influenced by optokinetic stimuli. Fall research with these stimuli has been done with standing subjects. Less is known of the influence these stimuli have on risk of falling while walking. The objective of this study was to qualitatively investigate the influence of optokinetic roll stimuli on balance during walking. © 2011 IEEE.


Hak L.,VU University Amsterdam | Van Dieen J.H.,VU University Amsterdam | Van Der Wurff P.,Center for Augmented Motor Learning and Training | Houdijk H.,Heliomare Rehabilitation Center
Physical Therapy | Year: 2014

Objective. The purpose of this study was to characterize differences in step length, FFP, and the concomitant difference in BW MoS between steps of the prosthetic and nonprosthetic legs (referred to as prosthetic and nonprosthetic steps, respectively) of people after transtibial amputation.Background. The asymmetry in step length in prosthetic gait is often seen as a detrimental effect of the impairment; however, this asymmetry also might be a functional compensation. An advantage of a smaller step length of the nonprosthetic leg, and specifically foot forward placement (FFP), might be that it will bring the center of mass closer to the base of support of the leading foot and thus increase the backward margin of stability (BW MoS).Design. This was an observational and cross-sectional study.Methods. Ten people after transtibial amputation walked for 4 minutes on a self-paced treadmill. Step length and FFP were calculated at initial contact. The size of the BW MoS was calculated for the moment of initial contact and at the end of the double-support phase of gait.Results. Step length (5.4%) and FFP (7.9%) were shorter for the nonprosthetic step than for the prosthetic step. The BW MoS at initial contact was larger for the nonprosthetic step, but because of a significant leg _ gait event interaction effect, BW MoS did not differ significantly at the end of the double-support phase.Limitations. All participants were relatively good walkers (score of E on the Special Interest Group in Amputee Medicine [SIGAM] scale).Conclusions. The smaller step length and FFP of the nonprosthetic step help to create a larger BW MoS at initial contact for the nonprosthetic step compared with the prosthetic step. Hence, step length asymmetry in people after transtibial amputation might be seen as a functional compensation to preserve BW MoS during the double-support phase to cope with the limited push-off power of the prosthetic ankle. © 2014 American Physical Therapy Association.


Hak L.,VU University Amsterdam | Houdijk H.,VU University Amsterdam | Houdijk H.,Heliomare Rehabilitation Center | Van Der Wurff P.,Center for Augmented Motor Learning and Training | And 5 more authors.
Clinical Biomechanics | Year: 2013

Background People recovering from a stroke are less stable during walking compared to able-bodied controls. The purpose of this study was to examine whether and how post-stroke individuals adapt their steady-state gait pattern to maintain or increase their margins of stability during walking, and to examine how these strategies differ from strategies employed by able-bodied people. Methods Ten post-stroke individuals and 9 age-matched able-bodied individuals walked on the Computer Assisted Rehabilitation Environment. Medio-lateral translations of the walking surface were imposed to manipulate gait stability. To provoke gait adaptations, a gait adaptability task was used, in which subjects occasionally had to hit a virtual target with their knees. We measured medio-lateral and backward margins of stability, and the associated gait parameters walking speed, step length, step frequency, and step width. Findings Post-stroke participants showed similar medio-lateral margins of stability as able-bodied people in all conditions. This was accomplished by a larger step width and a relatively high step frequency. Post-stroke participants walked overall slower and decreased walking speed and step length even further in response to both manipulations compared to able-bodied participants, resulting in a tendency towards an overall smaller backward margins of stability, and a significantly smaller backward margin of stability during the gait adaptability task. Interpretation Post-stroke individuals have more difficulties regulating their walking speed, and the underlying parameters step frequency and step length, compared to able-bodied controls. These quantities are important in regulating the size of the backward margin of stability when walking in complex environments. © 2013 Elsevier Ltd.


Hak L.,VU University Amsterdam | Houdijk H.,VU University Amsterdam | Houdijk H.,Heliomare Rehabilitation Center | Van Der Wurff P.,Center for Augmented Motor Learning and Training | And 6 more authors.
Journal of Rehabilitation Medicine | Year: 2015

Objective: To investigate whether post-stroke participants can walk at different combinations of stride frequency and stride length and how these adaptations affect the backward and medio-lateral margins of stability. Setting: Computer Assisted Rehabilitation Environment (CAREN). Participants: Ten post-stroke individuals. Intervention: Six trials of 2 min walking on a treadmill at different combinations of stride frequency and stride length. Treadmill speed was set at the corresponding speed, and subjects received visual feedback about the required and actual stride length. Outcome measures: Mean stride length and frequency and backward and medio-lateral margins of stability for each trial. Results and conclusion: Stroke patients were able to adjust step length when required, but had difficulty adjusting step frequency. When a stride frequency higher than self-selected stride frequency was imposed patients additionally needed to increase stride length in order to match the imposed treadmill speed. For trials at a high stride frequency, in particular, the increase in the backward and medio-lateral margins of stability was limited. In conclusion, training post-stroke individuals to increase stride frequency during walking might give them more opportunities to increase the margins of stability and consequently reduce fall risk. © 2015 The Authors. © 2015 Foundation of Rehabilitation Information.

Loading Center for Augmented Motor Learning and Training collaborators
Loading Center for Augmented Motor Learning and Training collaborators