PHYS THER
Vol. 87, No. 11, November 2007, pp. 1493-1494
DOI: 10.2522/ptj.20060326.ar
Author Response
Yi-Chung Pai and
Tanvi S Bhatt
We are grateful for Said's insightful appraisal of our work,1 and we would like to respond to her thought-provoking comments, as follows.
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An Early Predictor of "Fallers"?
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In concurrence with Said, we believe that prospective exploration of the relationship between the laboratory and the "real world" could provide essential verification of current hypotheses. We have recently examined the relationship between scores on one of the commonly used volitional-based performance measures (the Timed "Up & Go" Test [TUG]) and slip recovery outcomes, along with self-reported falls experienced in the "real world" during the past 12 months, among the same group of older adults (>65 years of age). We found in this prospective study that 4 (31%) of the 13 respondents reported at least one fall. The recovery response and, most notably, variables indicative of a person's adaptability to slips were better predictors of future falls than the TUG scores after controlling for the confounding variables of sex and age. We noted that the number of subjects in the follow-up portion of this study was relatively small because of the long interval between the initial laboratory testing and the follow-up interview (
30 months). This observation, at the very least, however, provided a sound rationale and justification for a full-scale investigation.
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A Novel Method of Fall Prevention
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It is indeed still unknown to what extent this training paradigm is applicable to typical clients receiving physical therapy intervention for a balance-related problem or other sensory, motor, or cognitive impairment predisposing them to an elevated risk for falls. It remains likely, nevertheless, that these individuals will benefit from a repeated perturbation training paradigm such as this one because of the promising adaptation capabilities of the central nervous system, clearly demonstrated even in the presence of existing neurological insults.2–4 Examination of the extent and the length of training required to enable these individuals to adapt to such a training paradigm and retain the benefits over a meaningful period may shed light on the specific role of sensorimotor systems in the adaptation and retention processes.
We agree with Said that it remains to be established whether training using both proactive and reactive strategies in the laboratory or clinical environment can be transferred to the "real world." As a first step, an answer to this question can be found through a prospective study of falls experienced in "real world" by the same people who participated in the initial training session. Those subjects who have received training are expected to experience fewer falls (ie, lower reported incidence) than the controls. With this kind of firsthand knowledge, investigation then can focus on how to improve transfer, which is indeed possible, at least in theory. Recent findings among young adults suggest an interlimb transfer of the repeated-slip training effects.5 These results showed measurable generalization of the training effects to the contralateral, untrained side, leading to a significant reduction in falls incidence from 30% on the first unexpected slip to 10% on the first untrained side slip in gait. Our preliminary results indicated a similar, if not an even better, efficiency of transfer among older adults than young adults. Investigation also is under way focusing on intertask transfer. Although transfer theoretically can be improved when practice is carried out under variable conditions, future studies need to determine how variable these conditions must be in order to augment the transfer of the intended effects, obtained from the laboratory and clinical settings, to the real-life conditions.
Logistically, demonstrating that the benefits acquired in a single training session can be retained for months and beyond is a necessary prerequisite for further consideration of the related transfer issues. One of the unique properties of this paradigm is this suspected outstandingly long sustainability of the training effects, and this opens up the attractive prospect of developing a vaccination-like intervention against falls incidence among older adults. As of now, we still need to demonstrate that the benefits from this single-session slip exposure can be retained in older adults for very long intervals (eg, 6 months to a year). Without this retention capability, multisession weekly or monthly clinic costs may render this approach unpromising. The need for investigation and solution of related transfer issues, thus, would be correspondingly diminished.
Finally, we again agree with Said that many practical issues pertaining to implementation and perhaps even reimbursement for services will have to be resolved before it will be possible to carry out training of the proactive and reactive strategies with systematically induced, unannounced perturbation in the clinical environment. The safety issue is indeed a paramount concern. The risk of injury can be minimized by a proper reduction of slip distance and by application of protective harnesses, which we believe can be made available in the clinical setting at an affordable cost. It is possible to envision multipurpose, low-cost harness systems that can be as common as the standard parallel bars used in rehabilitation settings. With the safety issue finally resolved, these evidence-based prospects, which incorporate principles of prophylactic practice, could well have far-reaching benefits, even for populations beyond those encountered in the current clinical settings.
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Conclusion
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From laboratory to clinic, we are embarking on a road that has yet to be clearly mapped. Hopefully, we have succeeded in making the case that this road is well worth traveling.
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Footnotes
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The authors thank Dr James M Girsch and Dr Mary Keehn for reading and commenting on this author response.
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References
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- Pai YC, Bhatt TS. Repeated-slip training: an emerging paradigm for prevention of slip-related falls among older adults.
Phys Ther. 2007;87:1482–1495.
- Di Fabio RP, Badke MB, Duncan PW. Adapting human postural reflexes following localized cerebrovascular lesion: analysis of bilateral long latency responses.
Brain Res. 1986;363:257–264.[CrossRef][Web of Science][Medline]
- Mummel P, Timmann D, Krause UW, et al. Postural responses to changing task conditions in patients with cerebellar lesions.
J Neurol Neurosurg Psychiatry. 1998;65:734–742.[Abstract/Free Full Text]
- Reisman DS, Wityk R, Silver K, Bastian AJ. Locomotor adaptation on a split-belt treadmill can improve walking symmetry post-stroke.
Brain. 2007;130(pt 7):1861–1872.
- Bhatt TS, Pai YC. Immediate and latent interlimb transfer of gait stability adaptation following repeated exposure to slips.
J Mot Behav. In press.
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Copyright © 2007 by the American Physical Therapy Association.
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A Novel Method of...
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