1. Debbie Espy, PT, PhD Ann Reinthal, PT, PhD, NCS
Development of a Measure to Compare the Intensity of Balance Activities
Mireille Hamway, SPT James Flis, SPT
Debbie Espy, PT, PhD Ann Reinthal, PT, PhD, NCS
Department of Physical Therapy, College of Sciences and Health Professions, Cleveland State University, Cleveland, Ohio
Introduction
Proactive and reactive balance exercises are effective at reducing fall risk. Reactive may be more so, but proactive exercises are simpler clinically and often better tolerated. This is part of a larger study to determine if proactive exercises can match the intensity and effectiveness of reactive training. Measures of balance exercise intensity do not exist, however. This is the first step in creating a normalized measure to be used to compare the intensity of proactive to reactive balance tasks.
Results
The moment of the maximum displacement was more clear for the trials in which the subjects stepped. An observation made during review of the motion data suggested the vertical position of the COM tracked with the maximum AP displacements of the COM: COM was highest just before its most anterior and lowest just before its most posterior displacement. This alternative method was compared visually, frame by frame, to the initial method.
Figure 5. Graphs showing perceived LOS as a % of BOS in trials where the subjects were (5a,5c) and were not(5b,5d) permitted to take a step.
Figure 3. Screenshot from Cortex displaying the path of the COM during a trial in which a step was taken.
Purpose
The purpose of this study was to determine the feasibility of a measure of voluntary anterior and posterior (AP) limits of stability (LOS) relative to base of support (BOS) to be used to normalize an individual’s movement relative to their BOS during balance training tasks as a measure of the intensity of the task to that person 5b 5a 5d 5c 4a 4b 4c
Figure 4. Screenshot captured from Cortex demonstrating the path of the COM during a trial in which no step was taken. The COM path has been magnified in figure 4c.
Methods
Five adults
Mean age 64 years,
4 male, 1female
Independently mobile in their community, without impairments that would prevent safe participation
Subjects leaned forward or back until they had to take a step (Step) or until they could lean no further without a step (No Step)
Full body position data were captured using an eight camera motion capture system.
BOS was determined by a heel marker and a first toe marker
The most anterior/posterior displacement of the center of mass (COM) and the most anterior/posterior edge of the BOS were calculated at the instant just before the change in direction of lean (No Step) or just prior to the foot leaving the ground (Step)
The difference between the COM and BOS edge positions were calculated and taken as a percentage of full quiet standing BOS length
The most superior and inferior position of the COM and the time at which they occurred were also calculated. 1a 1b
Figure 1. Screenshot from Cortex of subject leaning forward during a trial in which no step was taken (1a) and during a trial in which a recovery step was taken(1b). The red arrow represents the subject’s COM.
Figure 6. Superior view of the COM moving anterior to the BOS in a trial where the subject was able to take a step
Conclusions/Clinical Relevance
The percentage of BOS remaining at the voluntary LOS appears to be a promising component of a balance exercise intensity measure. The same method would be used to analyze AP motions during balance activities, then compared to the voluntary value as a measure of how much more or less subjects moved relative to their LOS during the balance task than they did voluntarily. The vertical position of the COM appears to offer a simpler, and potentially low-tech option, to determine the time point of the maximum COM AP displacement. This would open a path to using low cost, wearable sensors for these measures, rather than lab-based systems. This should be further investigated. The measure being developed here will allow balance exercise intensity to be measured so that exercise programs can be more effectively prescribed and carried out. 2a 2b
Selected References
Figure 2. Screenshot from Cortex of subject leaning posteriorly in a trial in which no step was taken (2a) and in a trial in which a recovery step was taken (2b). The red arrow represents the subject’s COM.
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