Predicting balance control in response to a trip: Does specificity matter?

Posted July 14, 2017

Tyler B. Weaver (PhD Candidate) & Andrew C. Laing (Associate Professor)
Injury Biomechanics and Aging Laboratory
https://uwaterloo.ca/injury-biomechanics-aging-lab/
Department of Kinesiology, University of Waterloo

It is no secret that falling is a concern for many older adults. Numerous scientific studies show that the ability to maintain balance is poorer in older adults compared to younger adults. Recently, studies have focused on a specific phase of balance recovery, which occurs when stepping to recover from a trip. The specific phase is referred to as the landing phase, or restabilisation phase, and occurs after foot-contact. It is necessary to study balance control during the landing phase, because successful foot-contact alone does not guarantee that one will not fall. One must also control their body movement after foot-contact.

Recent studies have shown that when recovering from a trip, older adults respond with larger body movement toward the foot that they stepped with (compared to young adults) (Singer et al., 2016). It is thought that this increased body movement in older adults could be a sign of reduced control, as too much movement toward the stepping foot could cause a secondary loss of balance. Therefore, it is important to determine which individual factors are predictive of balance control during this phase of reactive stepping. If certain factors are predictive of control during this phase, older adults (assisted by clinicians if necessary) could target such factors when trying to train improved balance recovery responses (for example, with strength training exercises for the legs).

To conduct our study, we recruited 40 young adults and 40 older adults (60 years of age and older) from the Kitchener-Waterloo community. All participants completed a series of 10 simulated-trips, where they were instructed to recover their balance by taking a single forward step. In response to each simulated-trip, we measured the participant’s body movement with a specialized set of cameras to track body movement. We also measured leg strength, leg flexibility and response time (stepping as fast as possible after an auditory tone) separately from the simulated-trip trials.

To determine which factors were predictive of body movement after a simulated-trip, we used multiple linear regressions. Two types of analyses were conducted. First, we conducted regressions using the general metrics of leg flexibility (hip flexion and hip abduction) and response time which were measured separately from the simulated-trip trials. Second, we conducted regressions incorporating specific metrics including step length, step width and response time, which were calculated directly from the simulated-trip responses. In both cases, we used the same measure of leg strength, which was hip extension strength. The balance measures we were interested in predicting were: 1) body movement at foot-contact, and 2) the maximum body movement after foot-contact (during the landing phase) (Figure 1).

Figure 1.

This image represents the points which were included in the statistical analyses. The solid black lack line represents an individual’s body movement after being released from the simulated-trip mechanism. The 'X' represents the point of foot-contact, while the maximum body position after foot-contact is shown graphically. After recovery, a stable region is typically observed.

Results revealed that the models consisting of specific metrics (compared to the metrics measured separate from the simulated-trip trials) were better predictors of body movement at foot-contact, as well as the maximum body movement after foot-contact. This was true in the young and older adults. The general models only significantly predicted body movement in the older adults, where hip extension strength was a significant predictor for both points in time (time-points depicted in Figure 1). Regarding the specific models, significance was driven by response time in the young adults, and step length in the older adults.

The findings from this study demonstrate the importance of specificity in predicting balance control during reactive stepping after a trip. Our results have potential implications for interventions targeted at improving landing phase balance control, particularly in older adults. By emphasizing within-task metrics (such as response time, step length, etc.), clinicians and researchers may be able to improve control during the landing phase of reactive stepping in older adults. In theory, the best way to emphasize task specificity would be to train the actual reactive stepping response using the simulated-trip (or similar) method. In addition, training hip strength may improve trip responses in older adults. Future studies should focus on an even larger sample size and older adults who are at an elevated risk of falling.

Reference:

Singer, J. C., Prentice, S. D., & McIlroy, W. E. (2016). Age-related challenges in reactive control of mediolateral stability during compensatory stepping: A focus on the dynamics of restabilisation. Journal of biomechanics, 49(5), 749-755.