Thresholds for Inducing Protective Stepping Responses to External  Perturbations of Human Standing

Mille, Marie-Laure; Rogers, Mark W.; Martinez, Katherine M.; Hedman, Lois Deming; Johnson, Matthew L.; Lord, Stephen R.; Fitzpatrick, Richard C.

doi:10.1152/jn.00974.2002

Cited by 87 publications

(64 citation statements)

References 41 publications

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“…Significant sensory and/or motor deficits, frailty, anxiety, or personal preference can contribute to and accentuate this mismatch. It is possible that a person takes an "unnecessary" step because of a lack of physical strength or quickness, although such a scenario seems to be less likely among more active and healthy individuals (McIlroy and Maki, 1996;Mille et al, 2003;Pai et al, 2006;Pavol et al, 1999;Thelen et al, 1997). In reality, taking a recovery step, even if it is unnecessary, is a very desirable and prudent protective strategy commonly adopted by older adults (Maki and McIlroy, 1997;Pai, 2003).…”

Section: Discussionmentioning

confidence: 99%

Predicted threshold against backward balance loss following a slip in gait

Yang

Anderson

Pai

2008

Journal of Biomechanics

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The purpose of this study was to use a 7-link, moment-actuated human model to predict, at liftoff of the trailing foot in gait, the threshold of the center of mass (COM) velocity relative to the base of support (BOS) required to prevent backward balance loss during single stance recovery from a slip. Five dynamic optimization problems were solved to find the minimum COM velocities that would allow the simulation to terminate with the COM above the BOS when the COM started 0.25, 0.5, 0.75, 1.0, and 1.25 foot lengths behind the heel of the stance foot (i.e., behind the BOS). The initial joint angles of the model were based on averaged data from experimental trials. Foot-ground contact was modeled using 16 visco-elastic springs distributed under the stance foot. Slipping was modeled by setting the sliding coefficient of friction of these springs to 0.02. The forward velocity of the COM necessary to avoid a backward balance loss is nearly two times larger under slip conditions than under non-slip conditions. The predicted threshold for backward balance loss following a slip agreed well with experimental data collected from 99 young adults in response to 927 slips during walking. In all trials in which a subject's COM had a velocity below the predicted threshold, the subject's recovery foot landed posterior to the slipping foot as predicted. Finally, combining experimental data with optimization, we verified that the 7-link model could more accurately predict gait stability than a 2-link model.

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Section: Discussionmentioning

confidence: 99%

Predicted threshold against backward balance loss following a slip in gait

Yang

Anderson

Pai

2008

Journal of Biomechanics

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“…Failed compensatory steps have been observed in 45% of older adult falls in the free-living environment [17]. Although compensatory stepping is impaired with older age [13,24,26,33,39], it is a modifiable skill that improves with practice [4,11,40,46]. A task-specific fall prevention training program has been developed based on compensatory step training that has successfully reduced trip-related falls by the elderly after laboratory-induced trips [11] and prospectively reported trip-related falls that occur in the community [41].…”

Section: Introductionmentioning

confidence: 99%

Task-specific Fall Prevention Training Is Effective for Warfighters With Transtibial Amputations

Kaufman

Wyatt

Sessoms

et al. 2014

Clinical Orthopaedics &Amp; Related Research

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Background Key factors limiting patients with lower extremity amputations to achieve maximal functional capabilities are falls and fear of falling. A task-specific fall prevention training program has successfully reduced prospectively recorded trip-related falls that occur in the community by the elderly. However, this program has not been tested in amputees. Questions/purposes In a cohort of unilateral transtibial amputees, we aimed to assess effectiveness of a falls prevention training program by (1) quantifying improvements in trunk control; (2) measuring responses to a standardized perturbation; and (3) demonstrating retention at 3 and 6 months after training. Second, we collected patientreported outcomes for balance confidence and falls control. Methods Fourteen male military service members (26 ± 3 years) with unilateral transtibial amputations and who had been walking without an assistive device for a median of 10 months (range, 2-106 months) were recruited to participate in this prospective cohort study. The training program used a microprocessor-controlled treadmill designed to deliver task-specific postural perturbations that simulated a trip. The training consisted of six 30-minute sessions delivered over a 2-week period, during which task difficulty, including perturbation magnitude, increased as the patient's ability progressed. Training effectiveness was assessed using a perturbation test in an This study was funded by the Department of Defense Grant Number W81X-WH-11-2-0058 (Log No. DM090896) and the Navy Bureau of Medicine and Surgery, Wounded, Ill, and Injured Program. Approved for public release; distribution is unlimited. This research was conducted in compliance with all applicable federal regulations governing the protection of human subjects (protocol NMCSD.2001.003 and Protocol NHRC.2001.0031). The institution of one or more of the authors (MDG) has a patent on technology (ActiveStep TM ; Symbex, Lebanon, NH, USA) noted in this manuscript. One of the authors (MDG) is an inventor of the ActiveStep TM system but has no conflicts of interest to declare with regard to the present study. The views expressed are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defense, or the US Government. Clinical Orthopaedics and Related Research ®A Publication of The Association of Bone and Joint Surgeons® immersive virtual environment. The key outcome variables were peak trunk flexion and velocity, because trunk kinematics at the recovery step have been shown to be a determinant of fall likelihood. The patient-reported outcomes were also collected using questionnaires. The effectiveness of the rehabilitation program was also assessed by collecting data before perturbation training and comparing the key outcome parameters with those measured immediately after perturbation training (0 months) as well as both 3 and 6 months posttraining. Results Mean trunk flexion angle and velocity significantly improved after participating in the ...

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“…Most studies evaluating stepping strategies use randomized platform (McIlroy and Maki 1996;Pai et al 2000;Schulz et al 2005) or waist-pull (Luchies et al 1994;Pai et al 1998;Mille et al 2003) perturbations. Schulz et al (2006) investigated the CoM TtC under such dynamic conditions, using the velocity-only TtC computation.…”

Section: Introductionmentioning

confidence: 99%

Predicting dynamic postural instability using center of mass time-to-contact information

Hasson

Emmerik

Caldwell

2008

Journal of Biomechanics

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Our purpose was to determine whether spatiotemporal measures of center of mass motion relative to the base of support boundary could predict stepping strategies after upper-body postural perturbations in humans. We expected that inclusion of center of mass acceleration in such time-tocontact (TtC) calculations would give better predictions and more advanced warning of perturbation severity. TtC measures were compared with traditional postural variables, which don't consider support boundaries, and with an inverted pendulum model of dynamic stability developed by Hof et al. (2005). A pendulum was used to deliver sequentially increasing perturbations to 10 young adults, who were strapped to a wooden backboard that constrained motion to sagittal plane rotation about the ankle joint. Subjects were instructed to resist the perturbations, stepping only if necessary to prevent a fall. Peak center of mass and center of pressure velocity and acceleration demonstrated linear increases with postural challenge. In contrast, boundary relevant minimum TtC values decreased nonlinearly with postural challenge, enabling prediction of stepping responses using quadratic equations. When TtC calculations incorporated center of mass acceleration, the quadratic fits were better and gave more accurate predictions of the TtC values that would trigger stepping responses. In addition, TtC minima occurred earlier with acceleration inclusion, giving more advanced warning of perturbation severity. Our results were in agreement with TtC predictions based on Hof's model, and suggest that TtC may function as a control parameter, influencing the postural control system's decision to transition from a stationary base of support to a stepping strategy.

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Thresholds for Inducing Protective Stepping Responses to External Perturbations of Human Standing

Cited by 87 publications

References 41 publications

Predicted threshold against backward balance loss following a slip in gait

Predicted threshold against backward balance loss following a slip in gait

Task-specific Fall Prevention Training Is Effective for Warfighters With Transtibial Amputations

Predicting dynamic postural instability using center of mass time-to-contact information

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