Tanvi Bhatt

Repeated-Slip Training: An Emerging Paradigm for Prevention of Slip-Related Falls Among Older Adults

Falls frequently cause injury-related hospitalization or death among older adults. This article reviews a new conceptual framework on dynamic stability and weight support in reducing the risk for falls resulting from a forward slip, based on the principles of motor control and learning, in the context of adaptation and longer-term retention induced by repeated-slip training. Although an unexpected slip is severely destabilizing, a recovery step often is adequate for regaining stability, regardless of age. Consequently, poor weight support (quantified by reduction in hip height), rather than instability, is the major determinant of slip-related fall risk. Promisingly, a single session of repeated-slip training can enhance neuromechanical control of dynamic stability and weight support to prevent falls, which can be retained for several months or longer. These principles provide the theoretical basis for establishing task-specific adaptive training that facilitates the development of protective strategies to reduce falls among older adults.

Role of stability and limb support in recovery against a fall following a novel slip induced in different daily activities

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 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 recovery 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.

Effect of type of cognitive task and walking speed on cognitive motor interference during dual-task walking

OBJECTIVE We aimed to determine the effect of distinctly different cognitive tasks and walking speed on cognitive-motor interference of dual-task walking. METHODS Fifteen healthy adults performed four cognitive tasks: visuomotor reaction time (VMRT) task, word list generation (WLG) task, serial subtraction (SS) task, and the Stroop (STR) task while sitting and during walking at preferred-speed (dual-task normal walking) and slow-speed (dual-task slow-speed walking). Gait speed was recorded to determine effect on walking. Motor and cognitive costs were measured. RESULTS Dual-task walking had a significant effect on motor and cognitive parameters. At preferred-speed, the motor cost was lowest for the VMRT task and highest for the STR task. In contrast, the cognitive cost was highest for the VMRT task and lowest for the STR task. Dual-task slow walking resulted in increased motor cost and decreased cognitive cost only for the STR task. CONCLUSIONS Results show that the motor and cognitive cost of dual-task walking depends heavily on the type and perceived complexity of the cognitive task being performed. Cognitive cost for the STR task was low irrespective of walking speed, suggesting that at preferred-speed individuals prioritize complex cognitive tasks requiring higher attentional and processing resources over walking. While performing VMRT task, individuals preferred to prioritize more complex walking task over VMRT task resulting in lesser motor cost and increased cognitive cost for VMRT task. Furthermore, slow walking can assist in diverting greater attention towards complex cognitive tasks, improving its performance while walking.

Inoculation Against Falls: Rapid Adaptation by Young and Older Adults to Slips During Daily Activities

OBJECTIVE To determine whether aging diminishes ones ability to rapidly learn to resist falls on repeated-slip exposure across different activities of daily living. DESIGN Quasi-experimental controlled trial. SETTING Two university-based research laboratories. PARTICIPANTS Young (n=35) and older (n=38) adults underwent slips during walking. Young (n=60) and older (n=41) adults underwent slips during a sit-to-stand task. All (N=174) were healthy and community dwelling. INTERVENTION Low-friction platforms induced unannounced blocks of 2 to 8 repeated slips interspersed with blocks of 3 to 5 nonslip trials during the designated task. MAIN OUTCOME MEASURES The incidence of falls and balance loss. Dynamic stability (based on center of mass position and velocity) and limb support (based on hip height) 300 ms after slip onset. RESULTS Under strictly controlled, identical low-friction conditions, all participants experienced balance loss, but older adults were over twice as likely as young to fall on the first, unannounced, novel slip in both tasks. Independent of age or task, participants adapted to avoid falls and balance loss, with most adaptation occurring in early trials. By the fifth slip, the incidence of falls and balance loss was less than 5% and 15%, respectively, regardless of age or task. Reductions in falls and balance loss for each task were accomplished through improved control of stability and limb support in both age groups. A rapidly reversible age- and task-dependent waning of motor learning occurred after a block of nonslip trials. Adaptation to walk slips reached a steady state in the second slip block regardless of age. CONCLUSIONS The ability to rapidly acquire fall-resisting skills on repeated-slip exposure remains largely intact at older ages and across functional activities. Thus, repeated-slip exposure might be broadly effective in inoculating older adults against falls.

Dynamic gait stability, clinical correlates, and prognosis of falls among community-dwelling older adults

OBJECTIVE To establish an accurate measure for prognostic assessment of fall risk in community-dwelling older adults, this study examined the prediction accuracy of a dynamic gait stability measure and common clinical tests for slip-related falls among these adults. DESIGN Participants were tested for their fall-risk likelihood on a slip-test. SETTING Biomechanics research laboratory. PARTICIPANTS Community-dwelling older adults (N=119; ≥65y). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Participants performed a battery of clinical tests, including Berg Balance Scale, Timed Up & Go (TUG) test, static posturography, isometric muscle strength, and bone density. They were then exposed to an unannounced slip during gait. The dynamic stability during unperturbed gait was measured based on the center of mass position and velocity relative to the limits of stability against backward falling. Accuracy of each measure was examined for prediction of slip outcome (fall or recovery). RESULTS On the slip, 59 participants fell, 56 recovered their balance, and 4 were harness-assisted. Dynamic stability predicted fall outcome with 69% accuracy. Except for TUG and bone density, no other measure could differentiate fallers from nonfallers; TUG predicted 56% of fall outcomes. CONCLUSIONS Reproduction of actual falls provides a new benchmark for evaluating the prognostic power of different performance-based assessment tools. The TUG was able to better predict fall outcome than other clinical measures; however, the new dynamic gait stability measure was more sensitive than TUG in its prediction of falls. Ultrasound bone scan could be used to screen older adults for fall risk.

Generalization of Gait Adaptation for Fall Prevention: From Moveable Platform to Slippery Floor

A persons ability to transfer the acquired improvements in the control of center of mass (COM) state stability to slips induced in everyday conditions can have profound theoretical and practical implications for fall prevention. This study investigated the extent to which such generalization could take place. A training group (n=8) initially experienced 24 right-side slips in blocked-and-random order (from the 1st unannounced, novel slip, S-1 to the last, S-24) resulting from release of a low-friction moveable platform in walking. They then experienced a single unannounced slip while walking on an oil-lubricated vinyl floor surface (V-T). A control group (n=8) received only one unannounced slip on the same slippery floor (V-C). Results demonstrated that the incidence of balance loss and fall on V-T was comparable to that on S-24. In both trials, fall and balance-loss incidence was significantly reduced in comparison with that on S-1 or on V-C, resulting from significant improvements in the COM state stability. The observed generalization indicates that the control of COM stability can be optimally acquired to accommodate alterations in environmental constraints, and it may be broadly coded and easily modifiable within the CNS. Because of such mechanisms, it is possible that the locomotor-balance skills acquired with the aid of low-friction moveable platforms can translate into resisting falls encountered in daily living.

Immediate and latent interlimb transfer of gait stability adaptation following repeated exposure to slips

The authors trained 21 participants by using blocked-and-mixed exposure to right-side slips and then caused them to slip unexpectedly on the untrained left side. Authors retested participants with a right slip and a left slip at 1 week, 2 weeks, 1 month, and 4 months. The authors found that preslip stability on the first untrained left slip improved and was significantly greater than that on the first right slip, which probably contributed to the reduction in incidence of falls from ~30% to ~10%. Postslip stability and base of support (BOS) slip velocity were similar to those on the first right slip and much lower than those on the last right slip. Increases in pre- and postslip stabilities and BOS slip velocity during the left slip led to reductions in backward balance loss (BLOB) from ~95% on initial left slip to ~60% and to ~25% on the 1st and 3rd retest sessions, respectively. In contrast, BLOB remained at a constant ~40% level on the right slip of the same retest sessions. The results indicate a partial immediate transfer and a possible latent transfer.

ADAPTIVE CONTROL REDUCES TRIP-INDUCED FORWARD GAIT INSTABILITY AMONG YOUNG ADULTS

A vital functional plasticity of humans is their ability to adapt to threats to posture stability. The purpose of this study was to investigate adaptation to repeated trips in walking. Sixteen young adults were recruited and exposed to the sudden (electronic-mechanical) release of an obstacle, 11-cm in height, in the path of over ground walking during the mid-to-late left swing phase. Although none of the subjects fell on the first of eight unannounced, consecutive trips, all of them had to rely on compensatory step with a step length significantly longer than their regular to reduce their instability. In the subsequent trials, they were able to rapidly make adaptive adjustments in the control of their center-of-mass (COM) stability both proactively and reactively (i.e., before and after hitting or crossing the obstacle), such that the need for taking compensatory step was substantially diminished. The proactive adaptations included a reduced forward COM velocity that lessened forward instability in mid-to-late stance and an elevated toe clearance that reduced the likelihood of obstacle contact. The reactive adjustments were characterized by improved trunk control (by reducing its forward rotation) and limb support (by increasing hip height), and reduced forward instability (by both the posterior COM shift and the reduction in its forward velocity). These findings suggest that young adults can adapt appropriately to repeated trip perturbations and to reduce trip-induced excessive instability in both proactive and reactive manners.

Effects of yoga on brain waves and structural activation: A review

Previous research has shown the vast mental and physical health benefits associated with yoga. Yoga practice can be divided into subcategories that include posture-holding exercise (asana), breathing (pranayama, Kriya), and meditation (Sahaj) practice. Studies measuring mental health outcomes have shown decreases in anxiety, and increases in cognitive performance after yoga interventions. Similar studies have also shown cognitive advantages amongst yoga practitioners versus non-practitioners. The mental health and cognitive benefits of yoga are evident, but the physiological and structural changes in the brain that lead to this remain a topic that lacks consensus. Therefore, the purpose of this study was to examine and review existing literature on the effects of yoga on brain waves and structural changes and activation. After a narrowed search through a set of specific inclusion and exclusion criteria, 15 articles were used in this review. It was concluded that breathing, meditation, and posture-based yoga increased overall brain wave activity. Increases in graygray matter along with increases in amygdala and frontal cortex activation were evident after a yoga intervention. Yoga practice may be an effective adjunctive treatment for a clinical and healthy aging population. Further research can examine the effects of specific branches of yoga on a designated clinical population.

Prevention of Slip-Related Backward Balance Loss: The Effect of Session Intensity and Frequency on Long-Term Retention

OBJECTIVE To examine the effects of session intensity (number of slip exposures) and frequency on the retention of acquired adaptation for prevention of backward balance loss after repeated-slip training. DESIGN A 4-group, randomized, and controlled study. SETTING Biomechanics research laboratory. PARTICIPANTS Healthy young subjects (N=46; 21 men). INTERVENTIONS Twenty-four subjects experienced a high-intensity session of 24 repeated right-side slips; 12 received additional single-slip sessions at a frequency of 1 week, 2 weeks, and 1 month, whereas the rest got no ancillary training. Another 24 subjects received a low-intensity initial session of a single slip; 12 received the same high-frequency ancillary training, whereas the rest got none. All groups were retested with a single slip 4 months after the first session. MAIN OUTCOME MEASURES The incidence of backward balance loss, gait stability, and limb support. RESULTS The high-intensity groups, irrespective of ancillary training, displayed similar improvements in all 3 outcome measures. Remarkably, the low-intensity group receiving ancillary training also significantly improved in all measures, with retention comparable to that observed in the other 2 groups. A single-slip exposure without ancillary sessions was insufficient to yield a longer-term effect. CONCLUSIONS Frequent ancillary sessions may be unnecessary for slip-related fall prevention up to 4 months if the initial session intensity is sufficient. Furthermore, the minimum of a single slip may be as effective if the subject is exposed to frequent ancillary sessions.