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Characterizing the limits of human stability during motion: perturbative experiment validates a model-based approach for the Sit-to-Stand task.

ABSTRACT: Falls affect a growing number of the population each year. Clinical methods to assess fall risk usually evaluate the performance of specific motions such as balancing or Sit-to-Stand. Unfortunately, these techniques have been shown to have poor predictive power, and are unable to identify the portions of motion that are most unstable. To this end, it may be useful to identify the set of body configurations that can accomplish a task under a specified control strategy. The resulting strategy-specific boundary between stable and unstable motion could be used to identify individuals at risk of falling. The recently proposed Stability Basin is defined as the set of configurations through time that do not lead to failure for an individual under their chosen control strategy. This paper presents a novel method to compute the Stability Basin and the first experimental validation of the Stability Basin with a perturbative Sit-to-Stand experiment involving forwards or backwards pulls from a motor-driven cable with 11 subjects. The individually-constructed Stability Basins are used to identify when a trial fails, i.e. when an individual must switch from their chosen control strategy (indicated by a step or sit) to recover from a perturbation. The constructed Stability Basins correctly predict the outcome of trials where failure was observed with over 90% accuracy, and correctly predict the outcome of successful trials with over 95% accuracy. The Stability Basin was compared to three other methods and was found to estimate the stable region with over 45% more accuracy in all cases. This study demonstrates that Stability Basins offer a novel model-based approach for quantifying stability during motion, which could be used in physical therapy for individuals at risk of falling.

SUBMITTER: Holmes PD

PROVIDER: S-EPMC7029948 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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Characterizing the limits of human stability during motion: perturbative experiment validates a model-based approach for the Sit-to-Stand task.

Holmes Patrick D PD Danforth Shannon M SM Fu Xiao-Yu XY Moore Talia Y TY Vasudevan Ram R

Royal Society open science 20200115 1

Falls affect a growing number of the population each year. Clinical methods to assess fall risk usually evaluate the performance of specific motions such as balancing or Sit-to-Stand. Unfortunately, these techniques have been shown to have poor predictive power, and are unable to identify the portions of motion that are most unstable. To this end, it may be useful to identify the set of body configurations that can accomplish a task under a specified control strategy. The resulting strategy-spec ...[more]

PMID: 32218959

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Project description:BackgroundPrevious studies have shown that people with Parkinson disease (PD) have difficulty performing the sit-to-stand task because of mobility and stability-related impairments. Despite its importance, literature on the quantification of dynamic stability control in people with PD during this task is limited.ObjectiveThe study objective was to examine differences in dynamic stability control between people with PD and people who were healthy and the extent to which externally cued training could improve such control during the sit-to-stand task in people with PD.DesignThis was a quasi-experimental controlled trial.MethodsThe performance of 21 people with PD was compared with that of 12 older adults who dwelled in the community. People with PD were randomly assigned to 2 groups: a group that did not receive training and a group that received audiovisually cued training (3 times per week for 4 weeks) for speeding up performance on the sit-to-stand task. Outcome measures recorded at baseline and after 4 weeks included center-of-mass position, center-of-mass velocity, and stability against either backward or forward balance loss (backward or forward stability) at seat-off and movement termination.ResultsCompared with people who were healthy, people with PD had greater backward stability resulting from a more anterior center-of-mass position at seat-off. This feature, combined with decreased forward stability at movement termination, increased their risk of forward balance loss at movement termination. After training, people with PD achieved greater backward stability through increased forward center-of-mass velocity at seat-off and reduced the likelihood of forward balance loss at movement termination through a posterior shift in the center-of-mass position.LimitationsThe study applied stability limits derived from adults who were healthy to people with PD, and the suggested impact on the risk of balance loss and falling is based on these theoretical stability limits.ConclusionsFor people with PD, postural stability against backward balance loss at task initiation was increased at the expense of possible forward balance loss at task termination. Task-specific training with preparatory audiovisual cues resulted in improved overall dynamic stability against both forward and backward balance loss.

Project description:Introduction: Inertial sensors generate objective and sensitive metrics of movement disability that may indicate fall risk in many clinical conditions including multiple sclerosis (MS). The Timed-Up-And-Go (TUG) task is used to assess patient mobility because it incorporates clinically-relevant submovements during standing. Most sensor-based TUG research has focused on the placement of sensors at the spine, hip or ankles; an examination of thigh activity in TUG in multiple sclerosis is wanting. Methods: We used validated sensors (x-IMU by x-io) to derive transparent metrics for the sit-to-stand (SI-ST) transition and the stand-to-sit (ST-SI) transition of TUG, and compared effect sizes for metrics from inertial sensors on the thighs to effect sizes for metrics from a sensor placed at the L3 level of the lumbar spine. Twenty-three healthy volunteers were compared to 17 ambulatory persons with MS (PwMS, HAI ? 2). Results: During the SI-ST transition, the metric with the largest effect size comparing healthy volunteers to PwMS was the Area Under the Curve of the thigh angular velocity in the pitch direction-representing both thigh and knee extension; the peak of the spine pitch angular velocity during SI-ST also had a large effect size, as did some temporal measures of duration of SI-ST, although less so. During the ST-SI transition the metric with the largest effect size in PwMS was the peak of the spine angular velocity curve in the roll direction. A regression was performed. Discussion: We propose for PwMS that the diminished peak angular velocity during SI-ST directly represents extensor weakness, while the increased roll during ST-SI represents diminished postural control. Conclusions: During the SI-ST transition of TUG, angular velocities can discriminate between healthy volunteers and ambulatory PwMS better than temporal features. Sensor placement on the thighs provides additional discrimination compared to sensor placement at the lumbar spine.

Project description:Background. In older patients, hospitalization is associated with a decline in functional performance and loss of muscle strength. Loss of muscle strength and functional performance can be prevented by systematic strength training, but details are lacking regarding the optimal exercise program and dose for older patients. Therefore, our aim was to test the feasibility of a progression model for loaded sit-to-stand training among older hospitalized patients. Methods. This is a prospective cohort study conducted as a feasibility study prior to a full-scale trial. We included twenty-four older patients (?65 yrs) acutely admitted from their own home to the medical services of the hospital. We developed an 8-level progression model for loaded sit-to-stands, which we named STAND. We used STAND as a model to describe how to perform the sit-to-stand exercise as a strength training exercise aimed at reaching a relative load of 8-12 repetitions maximum (RM) for 8-12 repetitions. Weight could be added by the use of a weight vest when needed. The ability of the patients to reach the intended relative load (8-12 RM), while performing sit-to-stands following the STAND model, was tested once during hospitalization and once following discharge in their own homes. A structured interview including assessment of possible modifiers (cognitive status by the Short Orientation Memory test and mobility by the De Morton Mobility Index) was administered both on admission to the hospital and in the home setting. The STAND model was considered feasible if: (1) 75% of the assessed patients could perform the exercise at a given level of the model reaching 8-12 repetitions at a relative load of 8-12 RM for one set of exercise in the hospital and two sets of exercise at home; (2) no ceiling or floor effect was seen; (3) no indication of adverse events were observed. The outcomes assessed were: level of STAND attained, the number of sets performed, perceived exertion (the Borg scale), and pain (the Verbal Ranking Scale). Results. Twenty-four patients consented to participate. Twenty-three of the patients were tested in the hospital and 19 patients were also tested in their home. All three criteria for feasibility were met: (1) in the hospital, 83% could perform the exercise at a given level of STAND, reaching 8-12 repetitions at 8-12 RM for one set, and 79% could do so for two sets in the home setting; (2) for all assessed patients, a possibility of progression or regression was possible-no ceiling or floor effect was observed; (3) no indication of adverse events (pain) was observed. Also, those that scored higher on the De Morton Mobility Index performed the exercise at higher levels of STAND, whereas performance was independent of cognitive status. Conclusions. We found a simple progression model for loaded sit-to-stands (STAND) feasible in acutely admitted older medical patients (?65 yrs), based on our pre-specified criteria for feasibility.

Dataset Information

Characterizing the limits of human stability during motion: perturbative experiment validates a model-based approach for the Sit-to-Stand task.

Publications

Characterizing the limits of human stability during motion: perturbative experiment validates a model-based approach for the Sit-to-Stand task.

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