A single session of repeated-slip exposure could improve community-dwelling older adults' resilience to postural disturbances and, hence, significantly reduce their annual risk of falls.
Objectives To determine whether the fall-resisting skills acquired from a single perturbation training session can be retained for 6-months or enhanced by an intermediate ancillary session. Design A randomized controlled trial. Setting Biomechanics research laboratory. Participants Forty-eight community-dwelling elderly (>65 years). Intervention Initial perturbation training applied to all subjects using low-friction platforms to induce, unannounced blocks of repeated right-side slips, interspersed with non-slips. The single-session group retested with only one slip 6-months later. The dual-session group received an additional slip at 3-month, post initial session, followed by a retest slips at 6-months. Main Outcome Measures Slip outcome (incidence of falls and balance loss), dynamic stability (based on the center-of-mass position and velocity) and vertical limb support (based on hip height). Results Subjects in both groups significantly reduced fall and balance loss incidence from first to last training slips, which resulted from improved stability and limb support control. Both groups demonstrated significant retention in all outcome measures at 6-months compared to the first novel slip; although performance decay was evident in comparison to the last training slip. The ancillary slip at 3-months led to significantly better control of stability, and hence reduced balance loss outcome in the dual-session group at 6-months, than the single-session group. Conclusions Motor memory could be retained for 6-months or longer following a single-session of fall-resistance training, although a single “booster” slip could further impede its decay. Through the experience of slipping and falling, it may be possible to “inoculate” older adults against potentially life threatening falls.
With aging, individuals' gaits become slower and their steps shorter; both are thought to improve stability against balance threats. Recent studies have shown that shorter step lengths, which bring the center of mass (COM) closer to the leading foot, improve stability against slip-related falls. However, a slower gait, hence lower COM velocity, does the opposite. Due to the inherent coupling of step length and speed in spontaneous gait, the extent to which the benefit of shorter steps can offset the slower speed is unknown. The purpose of this study was to investigate, through decoupling, the independent effects of gait speed and step length on gait stability and the likelihood of slip-induced falls. Fifty-seven young adults walked at one of three target gait patterns, two of equal speed and two of equal step length; at a later trial, they encountered an unannounced slip. The results supported our hypotheses that faster gait as well as shorter steps each ameliorates fall risk when a slip is encountered. This appeared to be attributable to the maintenance of stability from slip initiation to liftoff of the recovery foot during the slip. Successful decoupling of gait speed from step length reveals for the first time that, although slow gait in itself leads to instability and falls (a one-standard-deviation decrease in gait speed increases the odds of fall by 4 fold), this effect is offset by the related decrease in step length (the same one-standard-deviation decrease in step length lowers fall risk by 6 times).
Falls in older adults are a major health and societal problem. It is thus imperative to develop highly effective training paradigms to reduce the likelihood of falls. Perturbation training is one such emerging paradigm known to induce shorter term fall reduction in healthy young as well as older adults. Its longer term benefits are not fully understood, however. The purpose of this study was to determine whether and to what degree older adults could retain their fall-resisting skills acquired from a single perturbation training session. Seventy-three community-dwelling older adults (≥65 years) received identical single-session perturbation training consisting of 24 slips. This was delivered through unannounced unlocking (and mixed with relocking) of low-friction movable sections of the walkway. A single retest was subsequently scheduled based on a three-stage sequential, pre-post-retest design. Outcome measurements, taken upon the first (novel) and the 24th (final) slips of the initial session and the retest slip, included fall-or-no-fall and stability (quantified by the shortest distance from relative motion state of the center-of-mass and the base-of-support to the limits of stability) at instants prior to (proactive) and after (reactive) the onset of the slip. The training boosted subjects' resilience against laboratory-induced falls demonstrated by a significant reduction from 42.5 % falls on the first slip to 0 % on the 24th slip. Rate of falls which occurred during the laboratory retest remained low in 6-month (0 %), 9-month (8.7 %), and 12-month retest (11.5 %), with no significant difference between the three time intervals. Such reduction of laboratory-induced falls and its retention were attributable to the significant training-induced improvement in the proactive and reactive control of stability. This unique pre-post-retest design enabled us to provide scientific basis for the feasibility of a single session of perturbation training to "inoculate" older adults and to reduce their annual risk of falls in everyday living.
Cycloplegia affected ACD and WTW but not AL or corneal curvature measurements. Generally, good agreement was found between the Lenstar and the IOLMaster, although not for WTW. Differences between these devices do not produce a clinically significant impact on IOL power.
The purpose of this study was to determine whether stability and limb support play a similar role in governing slip outcome in gait-slip as in sit-to-stand-slip, and whether such prediction could also be derived based on measures of these variables during regular, unperturbed movements. Fifty-three and forty-one young subjects all took one recovery step following an unannounced, novel, forward slip induced in gait-slip and in sit-to-stand, respectively. Logistic regression was used to predict recovery outcome based on preslip and reactive measures of stability and limb support across tasks. Following slip onset, all subjects in both tasks experienced rapid decay in stability and limb support (indicated by a hip descent), leading to some actual falls that could not have been predicted from regular, preslip walking. Immediately before recovery step touchdown, stability and limb support could together best predict 88.9% and 100% falls respectively for gait-slip and sit-to-stand-slip. Because of differences in the execution of the recovery step, stability became a better predictor of fallers in sit-to-stand-slip than in gait-slip after recovery limb touchdown. Recovery steps were highly effective in restoring stability, regardless of outcome and task. The predictive strength of stability diminished in gait-slip or reduced in sit-to-stand-slip after touchdown, while limb support remained able to differentiate fallers from those who recovered in both tasks. When slip-induced instability was combined with inadequate limb support, falls were nearly inevitable in both tasks.
Over-head-harness systems, equipped with load cell sensors, are essential to the participants’ safety and to the outcome assessment in perturbation training. The purpose of this study was to first develop an automatic outcome recognition criterion among young adults for gait-slip training and then verify such criterion among older adults. Each of 39 young and 71 older subjects, all protected by safety harness, experienced 8 unannounced, repeated slips, while walking on a 7-m walkway. Each trial was monitored with a motion capture system, bilateral ground reaction force (GRF), harness force and video recording. The fall trials were first unambiguously indentified with careful visual inspection of all video records. The recoveries without balance loss (in which subjects’ trailing foot landed anteriorly to the slipping foot) were also first fully recognized from motion and GRF analyses. These analyses then set the gold standard for the outcome recognition with load cell measurements. Logistic regression analyses based on young subjects’ data revealed that peak load cell force was the best predictor of falls (with 100% accuracy) at the threshold of 30% body weight. On the other hand, the peak moving average force of load cell across 1-s period, was the best predictor (with 100% accuracy) separating recoveries with backward balance loss (in which the recovery step landed posterior to slipping foot) from harness assistance at the threshold of 4.5% body weight. These threshold values were fully verified using the data from older adults (100% accuracy in recognizing falls). Because of the increasing popularity in the perturbation training coupling with the protective over-head-harness system, this new criterion could have far reaching implications in automatic outcome recognition during the movement therapy.
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