Functional electrical stimulation to enhance reactive balance among people with hemiparetic stroke.

BACKGROUND: Individuals with stroke demonstrate a twofold higher fall incidence compared to healthy counterparts, potentially associated with deficits in reactive balance control, which is crucial for regaining balance from unpredictable perturbations to the body. Moreover, people with higher stroke-related motor impairment exhibit greater falls and cannot recover balance during higher perturbation intensities. Thus, they might need supplemental agents for fall prevention or even to be included in a perturbation-based protocol. Functional electrical stimulation is a widely used clinical modality for improving gait performance; however, it remains unknown whether it can enhance or interfere with reactive balance control. METHODS: We recruited twelve ambulatory participants with hemiparetic stroke (61.48 ± 6.77 years) and moderate-to-high motor impairment (Chedoke-McMaster Stroke Leg Assessment ≤ 4/7). Each participant experienced 4 unpredicted paretic gait-slips, with and without functional electrical stimulation (provided 50-500 ms after perturbation) in random order. The paretic quadriceps muscle group was chosen to receive electrical stimulation, considering the role of support limb knee extensors for preventing limb-collapse. Outcomes including primary (laboratory falls), secondary (reactive stability, vertical limb support) and tertiary (compensatory step length, step initiation, execution time) measures were compared between the two conditions. RESULTS: Participants demonstrated fewer falls, higher reactive stability, and higher vertical limb support (p < 0.05) following gait-slips with functional electrical stimulation compared to those without. This was accompanied by reduced step initiation time and a longer compensatory step (p < 0.05). CONCLUSION: The application of functional electrical stimulation to paretic quadriceps following gait-slips reduced laboratory fall incidence with enhanced reactive balance outcomes among people with higher stroke-related motor impairment. Our results lay the preliminary groundwork for understanding the instantaneous neuromodulatory effect of functional electrical stimulation in preventing gait-slip falls, future studies could test its therapeutic effect on reactive balance. Clinical registry number: NCT04957355.

Effect of Explicit Prioritization on Dual Tasks During Standing and Walking in People With Neurologic and Neurocognitive Disorders: A Systematic Review and Meta-analysis.

OBJECTIVES: To examine the effectiveness of explicit task (ie, equal, motor or cognitive) prioritization during dual tasking (DT) in adults with neurologic and neurocognitive disorders (stroke, Parkinson disease [PD], multiple sclerosis, dementia, Alzheimer disease, and mild cognitive impairment). DATA SOURCE: A systematic search in 4 databases (PubMed, Web of Science, Embase, and Cochrane Central) yielded 1138 unique studies published up to 2023. STUDY SELECTION: Forty-one experimental studies were selected that assessed the effect of explicit prioritization instructions on both motor and cognitive performance during dual-tasks related to standing and walking in selected populations. Primary outcome measures were walking speed and response accuracy. Availability of data allowed us to perform a meta-analysis on 27 of the 41 articles by using inverse variance with a random effects model. DATA EXTRACTION: The data including design, subject characteristics, motor and cognitive tasks, prioritization, motor and cognitive outcomes, instructions, and key findings were extracted. Two assessors rated the selected studies for risk of bias and quality using the Quality Assessment Tools of the National Institutes of Health. DATA SYNTHESIS: This study examined 1535 adults who were asked to perform motor-cognitive DT in standing or walking, including 381 adults with stroke, 526 with PD, 617 with multiple sclerosis, 10 with dementia, 9 with Alzheimer disease, and 8 with mild cognitive impairment. During all prioritization instructions, participants slowed down during DT (standardized mean difference (SMD)equal=0.43; SMDmotor=0.78; SMDcognitive=0.69, P<.03) while maintaining similar response accuracy (SMDequal=0.12; SMDmotor=0.23; SMDcognitive=-.01, P>.05). However, considerable between-group heterogeneity was observed resulting in different motor and cognitive responses between pathologies. CONCLUSION: Motor prioritization was achieved in adults with PD and stroke, unlike adults with neurocognitive disorders who were negatively affected by any type DT prioritizing. The reported within-group heterogeneity revealed that effects of explicit task prioritization are dependent on motor and cognitive task complexity, and the type of instructions. Recommendations are provided to ensure accurate use of instructions during DT paradigms.

Effects of mentally induced fatigue on balance control: a systematic review.

The relationship between cognitive demands and postural control is controversial. Mental fatigue paradigms investigate the attentional requirements of postural control by assessing balance after a prolonged cognitive task. However, a majority of mental fatigue research has focused on cognition and sports performance, leaving balance relatively underexamined. The purpose of this paper was to systematically review the existing literature on mental fatigue and balance control. We conducted a comprehensive search on PubMed and Web of Science databases for studies comparing balance performance pre- to post-mental fatigue or between a mental fatigue and control group. The literature search resulted in ten relevant studies including both volitional (n = 7) and reactive (n = 3) balance measures. Mental fatigue was induced by various cognitive tasks which were completed for 20-90 min prior to balance assessment. Mental fatigue affected both volitional and reactive balance, resulting in increased postural sway, decreased accuracy on volitional tasks, delayed responses to perturbations, and less effective balance recovery responses. These effects could have been mediated by the depletion of attentional resources or impaired sensorimotor perception which delayed appropriate balance-correcting responses. However, the current literature is limited by the number of studies and heterogeneous mental fatigue induction methods. Future studies are needed to confirm these postulations and examine the effects of mental fatigue on different populations and postural tasks. This line of research could be clinically relevant to improve safety in occupational settings where individuals complete extremely long durations of cognitive tasks and for the development of effective fall-assessment and fall-prevention paradigms.

Cognitive Task Domain Influences Cognitive-Motor Interference during Large-Magnitude Treadmill Stance Perturbations.

Reactive balance is postulated to be attentionally demanding, although it has been underexamined in dual-tasking (DT) conditions. Further, DT studies have mainly included only one cognitive task, leaving it unknown how different cognitive domains contribute to reactive balance. This study examined how DT affected reactive responses to large-magnitude perturbations and compared cognitive-motor interference (CMI) between cognitive tasks. A total of 20 young adults aged 18-35 (40% female; 25.6 ± 3.8 y) were exposed to treadmill support surface perturbations alone (single-task (ST)) and while completing four cognitive tasks: Target, Track, Auditory Clock Test (ACT), Letter Number Sequencing (LNS). Three perturbations were delivered over 30 s in each trial. Cognitive tasks were also performed while seated and standing (ST). Compared to ST, post-perturbation MOS was lower when performing Track, and cognitive performance was reduced on the Target task during DT (p < 0.05). There was a larger decline in overall (cognitive + motor) performance from ST for both of the visuomotor tasks compared to the ACT and LNS (p < 0.05). The highest CMI was observed for visuomotor tasks; real-life visuomotor tasks could increase fall risk during daily living, especially for individuals with difficulty attending to more than one task.

Trip-Related Fall Risk Prediction Based on Gait Pattern in Healthy Older Adults: A Machine-Learning Approach.

Trip perturbations are proposed to be a leading cause of falls in older adults. To prevent trip-falls, trip-related fall risk should be assessed and subsequent task-specific interventions improving recovery skills from forward balance loss should be provided to the individuals at risk of trip-fall. Therefore, this study aimed to develop trip-related fall risk prediction models from one's regular gait pattern using machine-learning approaches. A total of 298 older adults (≥60 years) who experienced a novel obstacle-induced trip perturbation in the laboratory were included in this study. Their trip outcomes were classified into three classes: no-falls (n = 192), falls with lowering strategy (L-fall, n = 84), and falls with elevating strategy (E-fall, n = 22). A total of 40 gait characteristics, which could potentially affect trip outcomes, were calculated in the regular walking trial before the trip trial. The top 50% of features (n = 20) were selected to train the prediction models using a relief-based feature selection algorithm, and an ensemble classification model was selected and trained with different numbers of features (1-20). A ten-times five-fold stratified method was utilized for cross-validation. Our results suggested that the trained models with different feature numbers showed an overall accuracy between 67% and 89% at the default cutoff and between 70% and 94% at the optimal cutoff. The prediction accuracy roughly increased along with the number of features. Among all the models, the one with 17 features could be considered the best model with the highest AUC of 0.96, and the model with 8 features could be considered the optimal model, which had a comparable AUC of 0.93 and fewer features. This study revealed that gait characteristics in regular walking could accurately predict the trip-related fall risk for healthy older adults, and the developed models could be a helpful assessment tool to identify the individuals at risk of trip-falls.

The Effect of Cognitive Task, Gait Speed, and Age on Cognitive-Motor Interference during Walking.

Dual-tasking can cause cognitive-motor interference (CMI) and affect task performance. This study investigated the effects of age, gait speed, and type of cognitive task on CMI during gait. Ten younger and 10 older adults walked on a pressure-sensitive GAITRite walkway which recorded gait speed and step length. Participants walked at a slow, preferred, or fast speed while simultaneously completing four cognitive tasks: visuomotor reaction time (VMRT), serial subtraction (SS), word list generation (WLG), and visual Stroop (VS). Each combination of task and speed was repeated for two trials. Tasks were also performed while standing. Motor and cognitive costs were calculated with the formula: ((single-dual)/single × 100). Higher costs indicate a larger reduction in performance from single to dual-task. Motor costs were higher for WLG and SS than VMRT and VS and higher in older adults (p < 0.05). Cognitive costs were higher for SS than WLG (p = 0.001). At faster speeds, dual-task costs increased for WLG and SS, although decreased for VMRT. CMI was highest for working memory, language, and problem-solving tasks, which was reduced by slow walking. Aging increased CMI, although both ages were affected similarly by task and speed. Dual-task assessments could include challenging CMI conditions to improve the prediction of motor and cognitive status.

Can prior exposure to repeated non-paretic slips improve reactive responses on novel paretic slips among people with chronic stroke?

This study examined if people with chronic stroke (PwCS) could adapt following non-paretic overground gait-slips and whether such prior exposure to non-paretic slips could improve reactive responses on novel paretic slip. Forty-nine PwCS were randomly assigned to either adaptation group, which received eight unexpected, overground, nonparetic-side gait-slips followed by two paretic-side slips or a control group, which received two paretic-side slips. Slip outcome, recovery strategies, center of mass (CoM) state stability, post-slip stride length and slipping kinematics were analyzed. The adaptation group demonstrated fall-reduction from first to eighth non-paretic slips, along with improved stability, stride length and slipping kinematics (p < 0.05). Within the adaptation group, on comparing novel slips, paretic-side demonstrated comparable pre-slip stability (p > 0.05); however, lower post-slip stability, increased slip velocity and falls was noted (p < 0.05). There was no difference in any variables between the novel paretic slips of adaptation and control group (p > 0.01). However, there was a rapid improvement on the 2nd slip such that adaptation group demonstrated improved performance from the first to second paretic slip compared to that in the control group (p < 0.01). PwCS demonstrated immediate proactive and reactive adaptation with overground, nonparetic-side gait-slips. However, PwCS did not demonstrate any inter-limb performance gain on the paretic-side after prior nonparetic-side adaptation when exposed to a novel paretic-side slip; but they did show significant positive gains with single slip priming on the paretic-side compared to controls without prior adaptation.Clinical registry number: NCT03205527.

Can a single session of treadmill-based slip training reduce daily life falls in community-dwelling older adults? A randomized controlled trial.

BACKGROUND: Task-specific training with single-session overground slip simulation has shown to reduce real-life falls in older adults. AIMS: The purpose of this study was to determine if fall-resisting behavior acquired from a single-session treadmill-based gait slip training could be retained to reduce older adults' falls in everyday living over a 6-month follow-up period. METHODS: 143 community-dwelling older adults (≥ 65 years old) were randomly assigned to either the treadmill-based gait slip training group (N = 73), in which participants were exposed to 40 unpredictable treadmill slips, or the control group (N = 70), in which participants walked on a treadmill at their comfortable speed. Participants reported their falls from the preceding year (through self-report history) and over the following 6 months (through fall diaries and monitored with phone calls). RESULTS: There was no main effect of time (retrospective vs. prospective fall) and training (treadmill training vs. control) on fall reduction (p > 0.05 for both). The survival distributions of event of all-cause falls or slip falls were comparable between groups (p > 0.05 for both). DISCUSSION: Unlike overground slip training where a single training session could significantly reduce everyday falls in a 6-month follow-up period, the results indicated that one treadmill-based gait slip training session by itself was unable to produce similar effects. CONCLUSION: Further modification of the training protocol by increasing training dosage (e.g., number of sessions or perturbation intensity) may be necessary to enhance transfer to daily living. This study (NCT02126488) was registered on April 30, 2014.

Near-Fall Detection in Unexpected Slips during Over-Ground Locomotion with Body-Worn Sensors among Older Adults.

Slip-induced falls are a growing health concern for older adults, and near-fall events are associated with an increased risk of falling. To detect older adults at a high risk of slip-related falls, this study aimed to develop models for near-fall event detection based on accelerometry data collected by body-fixed sensors. Thirty-four healthy older adults who experienced 24 laboratory-induced slips were included. The slip outcomes were first identified as loss of balance (LOB) and no LOB (NLOB), and then the kinematic measures were compared between these two outcomes. Next, all the slip trials were split into a training set (90%) and a test set (10%) at sample level. The training set was used to train both machine learning models (n = 2) and deep learning models (n = 2), and the test set was used to evaluate the performance of each model. Our results indicated that the deep learning models showed higher accuracy for both LOB (>64%) and NLOB (>90%) classifications than the machine learning models. Among all the models, the Inception model showed the highest classification accuracy (87.5%) and the largest area under the receiver operating characteristic curve (AUC), indicating that the model is an effective method for near-fall (LOB) detection. Our approach can be helpful in identifying individuals at the risk of slip-related falls before they experience an actual fall.

Gait Slip-Induced Fall-Type Assessment Based on Regular Gait Characteristics in Older Adults.

Older adults could experience split falls or feet-forward falls following an unexpected slip in gait due to different neuromuscular vulnerabilities, and different intervention strategies would be required for each type of faller. Thus, this study aimed to investigate the key factors affecting the fall types based on regular gait pattern. A total of 105 healthy older adults who experienced a laboratory-induced slip and fall were included. Their natural walking trial immediately prior to the novel slip trial was analyzed. To identify the factors related to fall type, gait characteristics and demographic factors were determined using univariate logistic regression, and then stepwise logistic regression was conducted to assess the slip-induced fall type based on these factors. The best fall-type prediction model involves gait speed and recovery foot angular velocity, which could predict 70.5% of feet-forward falls and 86.9% of split falls. Body mass index was also a crucial fall-type prediction with an overall prediction accuracy of 70.5%. Along with gait parameters, 84.1% of feet-forward falls and 78.7% of split falls could be predicted. The findings in this study revealed the determinators related to fall types, which enhances our knowledge of the mechanism associated to slip-induced fall and would be helpful for the development of tailored interventions for slip-induced fall prevention.

Reliability of Bluetooth inertial sensors for assessing lower limb segment angles and stride length during gait.

[Purpose] To assess the agreement between our custom Bluetooth IS system and the gold standard MOCAP system during gait. Bluetooth inertial movement sensors (IS) allow for real-time movement analysis with fewer restrictions than optoelectrical motion capture systems (MOCAP) and more accessibility than wireless IS systems. [Participants and Methods] We collected simultaneous Bluetooth IS and MOCAP data for 16 young participants walking at a self-selected speed. Sensors were placed on the right thigh and shank. Segment angles and stride length were calculated and compared between systems using Pearson's correlation coefficients (R), intra-class correlation coefficients (ICC), root mean square errors (RMSE), limits of agreement (LOA), and Bland-Altman plots. [Results] R values ranged from 0.371-0.715; ICC values ranged from 0.263-0.770. RMSE was 0.369 m for stride length and ranged from 6.85-13.07° in segment angles. Limits of agreement were -0.01-0.66 m for stride length and ranged from -27.71-20.53° in segment angles. [Conclusion] The Bluetooth IS system showed moderate agreement with MOCAP. Bluetooth IS could be used for reliable gait analysis with fewer space requirements and more portability than wireless IS or MOCAP systems. Bluetooth IS could be used outside of the clinic for real-time monitoring of gait during daily life.

Application of neuromuscular electrical stimulation on the support limb during reactive balance control in persons with stroke: a pilot study.

The aim of the present study was to investigate the effect of the application of neuromuscular electrical stimulation to the quadriceps muscle of the paretic limb during externally induced stance perturbations on reactive balance control and on fall outcomes in people with chronic stroke. Ten participants experienced 12 stance treadmill perturbation trails, 6 forward balance perturbation trials and 6 backward balance perturbation trials. For each perturbation condition, three perturbation trials were delivered synchronized with neuromuscular electrical stimulation applied to the quadriceps of the paretic limb and three perturbation trials were delivered without stimulation. Behavioral outcome measures, such as incidence of laboratory falls and number of compensatory steps, kinematic outcome measures, such as margin of stability and minimum hip high values after the perturbation, step initiation time, step execution time and step length of the stepping leg were analyzed. The application of neuromuscular electrical stimulation on the paretic quadriceps between the range of 50 and 500 ms after stance forward and backward perturbations reduced the laboratory falls incidence (p < 0.05), improved stability values (p < 0.05) and reduced the hip height descent (p < 0.05) compared to the experimental condition in which participants were exposed to stance perturbations without neuromuscular electrical stimulation. Additionally, step initiation time of the recovery step was lower in neuromuscular electrical stimulation condition during the forward balance perturbation protocol. Our results showed that the application of neuromuscular electrical stimulation on the knee extensor muscles of the paretic limb reduces the incidence of laboratory falls, enhances reactive stability control and reduces vertical limb collapse after stance forward and backward perturbations in people with chronic stroke.

Validity of Inertial Sensors for Assessing Balance Kinematics and Mobility during Treadmill-Based Perturbation and Dance Training.

Inertial sensors (IS) enable the kinematic analysis of human motion with fewer logistical limitations than the silver standard optoelectronic motion capture (MOCAP) system. However, there are no data on the validity of IS for perturbation training and during the performance of dance. The aim of this present study was to determine the concurrent validity of IS in the analysis of kinematic data during slip and trip-like perturbations and during the performance of dance. Seven IS and the MOCAP system were simultaneously used to capture the reactive response and dance movements of fifteen healthy young participants (Age: 18-35 years). Bland Altman (BA) plots, root mean square errors (RMSE), Pearson's correlation coefficients (R), and intraclass correlation coefficients (ICC) were used to compare kinematic variables of interest between the two systems for absolute equivalency and accuracy. Limits of agreements (LOA) of the BA plots ranged from -0.23 to 0.56 and -0.21 to 0.43 for slip and trip stability variables, respectively. The RMSE for slip and trip stabilities were from 0.11 to 0.20 and 0.11 to 0.16, respectively. For the joint mobility in dance, LOA varied from -6.98-18.54, while RMSE ranged from 1.90 to 13.06. Comparison of IS and optoelectronic MOCAP system for reactive balance and body segmental kinematics revealed that R varied from 0.59 to 0.81 and from 0.47 to 0.85 while ICC was from 0.50 to 0.72 and 0.45 to 0.84 respectively for slip-trip perturbations and dance. Results of moderate to high concurrent validity of IS and MOCAP systems. These results were consistent with results from similar studies. This suggests that IS are valid tools to quantitatively analyze reactive balance and mobility kinematics during slip-trip perturbation and the performance of dance at any location outside, including the laboratory, clinical and home settings.

Effect of an Exergaming-Based Dance Training Paradigm on Autonomic Nervous System Modulation in Healthy Older Adults: A Randomized Controlled Trial.

The purpose of this study was to determine if an exergaming-based dance training protocol can improve heart rate variability (HRV) in healthy older adults. A total of 20 healthy older adults (≥65 years old) were randomly assigned to two groups. The intervention group received an exergaming-based dance aerobic training for 6 weeks, while the control group received a 1-hr education on conventional physical exercises. Data obtained from HRV analysis pre- (Week 0) and postintervention (Week 7) consisted of high-frequency power, low- and high-frequency ratio, and root mean square of differences and percentage of adjacent RR intervals with a difference of duration greater than 50 ms values. HRV was assessed during rest and during a 6-min walk test. In addition, the YMCA submaximal cycle ergometer test was used to acquire estimated maximal O2 consumption pre- and postintervention. After the training, the intervention group showed significant improvement in HRV high-frequency power, root mean square of differences, and percentage of adjacent RR intervals with a difference of duration greater than 50 ms values in both rest and 6-min walk test conditions compared with the control group. Similarly, the intervention group showed higher maximal O2 consumption compared with the control group after the training. Our results support the effectiveness of an exergaming-based dance aerobic training on improving cardiac autonomic control in aging.

Mixed slip-trip perturbation training for improving reactive responses in people with chronic stroke.

This study determined the effect of mixed (slip- and trip-like stance perturbation) training on reactive responses in people with chronic stroke (PwCS) and examined modulation of their reactive responses on higher intensity perturbations posttraining (scaling). Twelve PwCS were exposed to consecutive blocks of treadmill-based slip-like and trip-like perturbations and mixed-stance perturbations. A higher intensity trial was provided postblock and postmixed training. Postural stability [center-of-mass position (CoMP) and velocity (CoMV)], compensatory step length, step count, and trunk angle were examined. PwCS demonstrated an anterior positioning of the CoM, increased step length, and reduced compensatory step count with slip-like block training (P < 0.05). Trip-like block training resulted in reductions in step count, step length, and trunk angle (P < 0.05); however, CoMP remained unchanged (P > 0.05). With mixed training, there was a decrease rather than an increase in step length for slip-like perturbations but a continued decrease in step length and trunk angle was seen on trip-like perturbations (P < 0.05); however, CoMP and step count remained unchanged for both. For both perturbations, the higher intensity trials demonstrated no change from the last block trial. Postmixed block, the higher intensity trial demonstrated an increase only in step count on trip-like perturbation. Between postblock and postmixed higher intensity trials, an increase in step count and decrease in step length was noted only for slip-like perturbations. Block training with slip- and trip-like stance perturbations can enhance reactive responses among PwCS. Although mixed perturbation training continued to improve trip-induced adaptation, prior slip-induced adaptive changes were not maintained and further slip-adaptation was not seen. PwCS demonstrated partial scaling of reactive responses postblock and postmixed training.NEW & NOTEWORTHY Block perturbation training led to development of favorable reactive responses to counteract treadmill-based, slip-like and trip-like stance perturbations among people with chronic stroke. During mixed block, previously acquired adaptive changes in reactive responses from slip-block training were not maintained, probably due to interference offered by trip block. Instead, on trip-like perturbations, trip block-induced adaptation was maintained and continued to show further improvement. Our findings might provide future direction for designing effective mixed perturbation training paradigms to counteract both opposing perturbation types.

Slip-Fall Predictors in Community-Dwelling, Ambulatory Stroke Survivors: A Cross-sectional Study.

BACKGROUND AND PURPOSE: Considering the multifactorial nature and the often-grave consequences of falls in people with chronic stroke (PwCS), determining measurements that best predict fall risk is essential for identifying those who are at high risk. We aimed to determine measures from the domains of the International Classification of Functioning, Disability and Health (ICF) that can predict laboratory-induced slip-related fall risk among PwCS. METHODS: Fifty-six PwCS participated in the experiment in which they were subjected to an unannounced slip of the paretic leg while walking on an overground walkway. Prior to the slip, they were given a battery of tests to assess fall risk factors. Balance was assessed using performance-based tests and instrumented measures. Other fall risk factors assessed were severity of sensorimotor impairment, muscle strength, physical activity level, and psychosocial factors. Logistic regression analysis was performed for all variables. The accuracy of each measure was examined based on its sensitivity and specificity for fall risk prediction. RESULTS: Of the 56 participants, 24 (43%) fell upon slipping while 32 (57%) recovered their balance. The multivariate logistic regression analysis model identified dynamic gait stability, hip extensor strength, and the Timed Up and Go (TUG) score as significant laboratory-induced slip-fall predictors with a combined sensitivity of 75%, a specificity of 79.2%, and an overall accuracy of 77.3%. DISCUSSION AND CONCLUSIONS: The results indicate that fall risk measures within the ICF domains-body, structure, and function (dynamic gait stability and hip extensor strength) and activity limitation (TUG)-could provide a sensitive laboratory-induced slip-fall prediction model in PwCS.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A323).

Effects of task-specific obstacle-induced trip-perturbation training: proactive and reactive adaptation to reduce fall-risk in community-dwelling older adults.

BACKGROUND: Trips account for over half of outdoor falls among community-dwelling older adults. AIMS: To investigate to what extent obstacle-induced trip-perturbation training could reduce fall-risk among older adults and to see whether training effects could be retained short term. METHODS: Forty community-dwelling older adults were exposed to 24 repeated trip-perturbations given in a "blocked-and-mixed" manner during over-ground gait. Another trip was given 30 min post-training. For each trip, recovery strategies and outcomes (fall versus no fall) were analyzed. Within-trial changes to proactive and reactive dynamic center of mass stability, pre-trip toe clearance and trunk angle, trunk angle at recovery completion, and recovery step length were analyzed. RESULTS: 48% of participants fell on their novel trip. The fall rate decreased significantly for subsequent trips, with no falls on the last trip. The decreased fall incidence resulted from improved feedforward and feedback adjustments for controlling center of mass stability and body kinematics. Proactive adaptations included reduced forward center of mass velocity, which lessened forward instability, and larger toe clearance, which increased the likelihood of obstacle avoidance. Reactive adjustments included reduced forward instability and improved trunk control (reduced forward rotation) at recovery step completion. Post-training, training effects were retained in terms of fall incidence, with slight decay in toe clearance and reactive stability. CONCLUSIONS: Older adults demonstrated appropriate locomotor-based proactive and reactive adaptations to repeated obstacle-induced trips with short-term retention similar to young adults, and thus could reduce their fall-risk through such training.

Which Are the Key Kinematic and Kinetic Components to Distinguish Recovery Strategies for Overground Slips Among Community-Dwelling Older Adults?

Slip outcomes are categorized as either a backward loss of balance (LOB) or a no loss of balance (no-LOB) in which an individual does not take a backward step to regain their stability. LOB includes falls and nonfalls, while no-LOB includes skate overs and walkovers. Researchers are uncertain about which factors determine slip outcomes and at which critical instants they do so. The purpose of the study was to investigate factors affecting slip outcomes in proactive and early reactive phases by analyzing 136 slip trials from 68 participants (age: 72.2 [5.3] y, female: 22). Segment angles and average joint moments in the sagittal plane of the slipping limb were compared for different slip outcomes. The results showed that knee flexor, hip extensor, and plantar flexor moments were significantly larger for no-LOB than for LOB in the midproactive phase, leading to smaller shank-ground and foot-ground angles at the slip onset, based on forward dynamics. In the early reactive phase, the hip extensor and plantar flexor moments were larger for no-LOB than for LOB, and all segment angles were smaller for no-LOB. Our findings indicate that the shank angle and knee moment were the major determinants of slip outcomes in both proactive and reactive phases.

Can Treadmill Slip-Perturbation Training Reduce Longer-Term Fall Risk Upon Overground Slip Exposure?

The purpose was to examine and compare the longer-term generalization between 2 different practice dosages for a single-session treadmill slip-perturbation training when reexposed to an overground slip 6 months later. A total of 45 older adults were conveniently assigned to either 24 or 40 slip-like treadmill perturbation trials or a third control group. Overground slips were given immediately after initial training, and at 6 months after initial training in order to examine immediate and longer-term effects. The performance (center of mass stability and vertical limb support) and fall percentage from the laboratory-induced overground slips (at initial posttraining and at 6 mo) were measured and compared between groups. Both treadmill slip-perturbation groups showed immediate generalization at the initial posttraining test and longer-term generalization at the 6-month retest. The higher-practice-dosage group performed significantly better than the control group (P < .05), with no difference between the lower-practice-dosage and the control groups at the 6-month retest (P > .05). A single session of treadmill slip-perturbation training showed a positive effect for reducing older adults' fall risk for laboratory-induced overground slips. A higher-practice dosage of treadmill slip perturbations could be more beneficial for further reducing fall risk.

Treadmill-gait slip training in community-dwelling older adults: mechanisms of immediate adaptation for a progressive ascending-mixed-intensity protocol.

The study purpose was to investigate whether older adults could improve their stability against a backward loss of balance (BLOB) after receiving repeated treadmill slips during walking and to see how such adaptive changes would be affected by practice dosage (combination of slip intensity and the number of slips at each intensity). Twenty-five healthy community-dwelling older adults received forty treadmill slips given over eleven blocks at five intensities (P1-P1-P2-P3-P4-P5-P4-P5-P5-P3-P1, larger number indicating higher intensity). Center of mass (COM) stability was calculated as the shortest distance of the instantaneous COM position and velocity relative to the base of support (BOS) from a theoretical threshold for BLOB (larger stability value indicated a better stability against BLOB). Stability, step length, and trunk angle were measured before and after slip onset to reflect proactive and reactive control, respectively. The first slips at each intensity block (i.e., P1, P3, P4, and P5) were compared with the first slips in the last blocks at those intensities to examine main effects of training dosage (intensity and repetition). Improvements in proactive and reactive stability were more pronounced for receiving more slips at larger intensities than fewer slips at smaller intensities. Older adults only demonstrated partial positive scaling effects to proactively, not reactively, establish a more stable initial COM state. The improved proactive stability was associated with an anterior shift of COM position relative to the BOS, resulting from a shorter pre-slip step length. The improved reactive stability was associated with an anterior shift of COM position, resulting from a larger compensatory step length and a faster COM velocity relative to the BOS. Our findings indicated that treadmill-gait slip perturbations elicited similar proactive and reactive control to that from over-ground slip perturbations, but greater slip intensity and repetition might yield more immediate adaptive improvements.