Falls perceived as significant by lower limb prosthesis users are generally associated with fall consequences rather than circumstances.

PURPOSE: To determine if falls perceived as significant by lower limb prosthesis (LLP) users were associated with fall circumstances and/or consequences. MATERIALS AND METHODS: The circumstances and consequences of LLP users' most significant fall in the past 12-months were collected using the Lower Limb Prosthesis User Fall Event Survey. Participants rated fall significance from 0 (not significant) to 10 (extremely significant), which was then dichotomized into "low" and "high". Binary logistic regression was used to assess associations between fall significance and fall circumstances and consequences. RESULTS: Ninety-eight participants were included in the analysis. Five fall consequences were associated with greater significance: major injury (OR = 26.7, 95% CI: 1.6-459.6, p = 0.024), need to seek medical treatment (OR = 19.0, 95% CI: 1.1-329.8, p = 0.043), or allied-health treatment (OR = 18.2, 95% CI: 2.3-142.4, p = 0.006), decreased balance confidence (OR = 10.9, 95% CI: 2.4-49.3, p = 0.002), and increased fear of falling (OR = 7.5, 95% CI: 2.4-23.8, p = 0.001), compared to two fall circumstances: impact to the arm (OR = 5.0, 95% CI: 2.0-12.1, p = 0.001), and impact to the face, head, or neck (OR = 9.7, 95% CI: 1.2-77.4, p = 0.032). CONCLUSIONS: Significant falls were generally more associated with fall consequence than fall circumstances.

Falls remain common, injurious, costly, and socially isolating events for lower limb prosthesis (LLP) users.Falls perceived as most significant by LLP users were associated with injury, reduced balance confidence, and increased fear-of-falling.Studying falls perceived by LLP users as significant may help reduce falls that matter most to LLP users.

Age, Cognitive Task, and Arm Position Differently Affect Muscle Synergy Recruitment but have Similar Effects on Walking Balance.

Age modifies walking balance and neuromuscular control. Cognitive and postural constraints can increase walking balance difficulty and magnify age-related differences. However, how such challenges affect neuromuscular control remains unknown. We determined the effects of age, cognitive task, and arm position on neuromuscular control of walking balance. Young (YA) and older adults (OA) walked on a 6-cm wide beam with and without arm crossing and a cognitive task. Walking balance was quantified by the distance walked on the beam. We also computed step speed, margin of stability, and cognitive errors. Neuromuscular control was determined through muscle synergies extracted from 13 right leg and trunk muscles. We analyzed neuromuscular complexity by the number of synergies and the variance accounted for by the first synergy, coactivity by the number of significantly active muscles in each synergy, and efficiency by the sum of the activation of each significantly active muscle in each synergy. OA vs. YA walked a 14% shorter distance, made 12 times more cognitive errors, and showed less complex and efficient neuromuscular control. Cognitive task reduced walking balance mainly in OA. Decreases in step speed and margin of stability, along with increased muscle synergy coactivity and reduced efficiency were observed in both age groups. Arm-crossing also reduced walking balance mostly in OA, but step speed decreased mainly in YA, in whom the margin of stability increased. Arm-crossing reduced the complexity of synergies. Age, cognitive task, and arm position affect differently muscle synergy recruitment but have similar effects on walking balance.

After scaling to body size hip strength of the residual limb exceeds that of the intact limb among unilateral lower limb prosthesis users.

BACKGROUND: Hip muscles play a prominent role in compensating for the loss of ankle and/or knee muscle function after lower limb amputation. Despite contributions to walking and balance, there is no consensus regarding hip strength deficits in lower limb prosthesis (LLP) users. Identifying patterns of hip muscle weakness in LLP users may increase the specificity of physical therapy interventions (i.e., which muscle group(s) to target), and expedite the search for modifiable factors associated with deficits in hip muscle function among LLP users. The purpose of this study was to test whether hip strength, estimated by maximum voluntary isometric peak torque, differed between the residual and intact limbs of LLP users, and age- and gender-matched controls. METHODS: Twenty-eight LLP users (14 transtibial, 14 transfemoral, 7 dysvascular, 13.5 years since amputation), and 28 age- and gender-matched controls participated in a cross-sectional study. Maximum voluntary isometric hip extension, flexion, abduction, and adduction torque were measured with a motorized dynamometer. Participants completed 15 five-second trials with 10-s rest between trials. Peak isometric hip torque was normalized to body mass × thigh length. A 2-way mixed-ANOVA with a between-subject factor of leg (intact, residual, control) and a within-subject factor of muscle group (extensors, flexors, abductors, adductors) tested for differences in strength among combinations of leg and muscle group (α = 0.05). Multiple comparisons were adjusted using Tukey's Honest-Difference. RESULTS: A significant 2-way interaction between leg and muscle group indicated normalized peak torque differed among combinations of muscle group and leg (p < 0.001). A significant simple main effect of leg (p = 0.001) indicated peak torque differed between two or more legs per muscle group. Post-hoc comparisons revealed hip extensor, flexor, and abductor peak torque was not significantly different between the residual and control legs (p ≥ 0.067) but torques in both legs were significantly greater than in the intact leg (p < 0.001). Peak hip abductor torque was significantly greater in the control and residual legs than the intact leg (p < 0.001), and significantly greater in the residual than control leg (p < 0.001). CONCLUSIONS: Our results suggest that it is the intact, rather than the residual limb, that is weaker. These findings may be due to methodological choices (e.g., normalization), or biomechanical demands placed on residual limb hip muscles. Further research is warranted to both confirm, expand upon, and elucidate possible mechanisms for the present findings; and clarify contributions of intact and residual limb hip muscles to walking and balance in LLP users. CLINICAL TRIAL REGISTRATION: N/A.

The number of falls recalled in the past year and balance confidence predict the frequency of injurious falls by unilateral lower limb prosthesis users.

INTRODUCTION: Several personal characteristics have been associated with an increased risk of injurious falls by lower limb prosthesis (LLP) users. To date, however, none have been used to effectively predict the occurrence of injurious falls. OBJECTIVE: To develop a model that could predict the number of injurious falls over the next 6 months and identify fall-related circumstances that may increase the odds of a fall being injurious in unilateral LLP users. DESIGN: A secondary analysis of a prospective observational study. SETTING: Research laboratory. PARTICIPANTS: Sixty unilateral LLP users with a transtibial or transfemoral amputation. INTERVENTION: Not applicable. MAIN OUTCOME MEASURE(S): Participants' characteristics were recorded at baseline. Falls and their circumstances and consequences were collected prospectively over 6 months via monthly telephone calls. Multivariate negative binomial regression was used to predict the number of injurious falls over the next 6 months in LLP users. Incidence rate ratios (IRRs) were derived to determine the risk of an injurious fall. Bivariate logistic regression was used to identify the associations between injurious falls and fall-related circumstances. Odds ratios (ORs) were derived to characterize the odds that a fall would be injurious. RESULTS: The final multivariate model, which included the number of falls recalled in the past year (IRR = 1.31, 95% confidence interval [CI]: 1.01-1.71, p = .045) and balance confidence (p = .120), predicted the number of injurious falls in the next 6 months (χ2 (2) = 8.15, p = .017). Two fall-related circumstances were found to increase the odds that a fall would be injurious, fatigue due to activity (OR = 13.5, 95% CI: 3.50-52.3, p  = .001), and tiredness from a lack of sleep (OR = 5.36, 95% CI: 1.22-23.6, p = .026). CONCLUSION: The results suggest that the number of falls recalled in the past year and balance confidence scores predict the number of injurious falls an LLP user will experience in the next 6 months.

A survey for characterizing details of fall events experienced by lower limb prosthesis users.

Despite their importance to fall prevention research, little is known about the details of real-world fall events experienced by lower limb prosthesis users. This gap can be attributed to the lack of a structured, population-specific fall survey to document these adverse health events. The objective of this project was to develop a survey capable of characterizing the circumstances and consequences of fall events in lower limb prosthesis users. Best practices in survey development, including focus groups and cognitive interviews with diverse samples of lower limb prosthesis users, were used to solicit input and feedback from target respondents, so survey content would be meaningful, clear, and applicable to lower limb prosthesis users. Focus group data were used to develop fall event definitions and construct a conceptual fall framework that guided the creation of potential survey questions and response options. Survey questions focused on the activity, surroundings, situation, mechanics, and consequences of fall events. Cognitive interviews revealed that with minor revisions, survey definitions, questions, and response options were clear, comprehensive, and applicable to the experiences of lower limb prosthesis users. Administration of the fall survey to a national sample of 235 lower limb prosthesis users in a cross-sectional preliminary validation study, found survey questions to function as intended. Revisions to the survey were made at each stage of development based on analysis of participant feedback and data. The structured, 37-question lower limb prosthesis user fall event survey developed in this study offers clinicians and researchers the means to document, monitor, and compare fall details that are meaningful and relevant to lower limb prosthesis users in a standardized and consistent manner. Data that can be collected with the developed survey are essential to establishing specific goals for fall prevention initiatives in lower limb prosthesis users.

Direction of attentional focus in prosthetic training: Current practice and potential for improving motor learning in individuals with lower limb loss.

OBJECTIVE: Adopting an external focus of attention has been shown to benefit motor performance and learning. However, the potential of optimizing attentional focus for improving prosthetic motor skills in lower limb prosthesis (LLP) users has not been examined. In this study, we investigated the frequency and direction of attentional focus embedded in the verbal instructions in a clinical prosthetic training setting. METHODS: Twenty-one adult LLP users (8 female, 13 male; 85% at K3 level; mean age = 50.5) were recruited from prosthetic clinics in the Southern Nevada region. Verbal interactions between LLP users and their prosthetists (mean experience = 10 years, range = 4-21 years) during prosthetic training were recorded. Recordings were analyzed to categorize the direction of attentional focus embedded in the instructional and feedback statements as internal, external, mixed, or unfocused. We also explored whether LLP users' age, time since amputation, and perceived mobility were associated with the proportion of attentional focus statements they received. RESULTS: We recorded a total of 20 training sessions, yielding 904 statements of instruction from 338 minutes of training. Overall, one verbal interaction occurred every 22.1 seconds. Among the statements, 64% were internal, 9% external, 3% mixed, and 25% unfocused. Regression analysis revealed that female, older, and higher functioning LLP users were significantly more likely to receive internally-focused instructions (p = 0.006, 0.035, and 0.024, respectively). CONCLUSIONS: Our results demonstrated that verbal instructions and feedback are frequently provided to LLP users during prosthetic training. Most verbal interactions are focused internally on the LLP users' body movements and not externally on the movement effects. IMPACT STATEMENT: While more research is needed to explore how motor learning principles may be applied to improve LLP user outcomes, clinicians should consider adopting the best available scientific evidence during treatment. Overreliance on internally-focused instructions as observed in the current study may hinder prosthetic skill learning.

Normalization alters the interpretation of hip strength in established unilateral lower limb prosthesis users.

BACKGROUND: Valid comparisons of muscle strength between individuals or legs that differ in size requires normalization, often by simple anthropometric variables. Few studies of muscle strength in lower-limb prosthesis users have normalized strength data by any anthropometric variable, potentially confounding our understanding of strength deficits in lower-limb prosthesis users. The objective of this pilot study was to determine the need for as well as effectiveness and impact of normalizing hip strength in lower-limb prosthesis users. METHODS: Peak isometric hip extension and abduction torques were collected from 28 lower-limb prosthesis users. Allometric scaling was used to determine if hip torque values were significantly associated with, and therefore needed to be adjusted for, body mass, thigh length, or body mass x thigh length, and whether normalization was effective in reducing any associations. Between limb differences in peak hip torque, and correlations with balance ability, were inspected pre- and post-normalization. FINDINGS: Hip torques were consistently and significantly associated with body-mass x thigh length. Associations between peak hip torque and body-mass x thigh length were reduced by normalization. After normalization by body-mass x thigh length, between limb differences in hip extension torque, as well as the correlation between hip abduction torque and balance ability, changed from non-significant to significant. INTERPRETATION: In the absence of normalization, hip strength (i.e., peak torque) in lower-limb prosthesis users remains dependent on basic anthropometric variables, masking relationships between hip strength and balance ability, as well as between limb differences.

Beam width and arm position but not cognitive task affect walking balance in older adults.

Detection of changes in dynamic balance could help identify older adults at fall risk. Walking on a narrow beam with its width, cognitive load, and arm position manipulated could be an alternative to current tests. Therefore, we examined additive and interactive effects of beam width, cognitive task (CT), and arm position on dynamic balance during beam walking in older adults. Twenty older adults (69 ± 4y) walked on 6, 8, and 10-cm wide beams (2-cm high, 4-m-long), with and without CT, with three arm positions (free, crossed, akimbo). We determined cognitive errors, distance walked, step speed, root mean square (RMS) of center of mass (COM) displacement and trunk acceleration in the frontal plane. Beam width decrease progressively reduced distance walked and increased trunk acceleration RMS. Step speed decreased on the narrowest beam and with CT. Arm crossing decreased distance walked and step speed. COM displacement RMS and cognitive errors were not affected by any manipulation. In conclusion, distance walked indicated that beam width and arm position, but less so CT, affected dynamic balance, implying that beam walking has the potential to become a test of fall risk. Stability measurements suggested effective trunk adjustments to control COM position and keep dynamic balance during the task.

Performance-based balance tests, combined with the number of falls recalled in the past year, predicts the incidence of future falls in established unilateral transtibial prosthesis users.

BACKGROUND: Falls are common and consequential events for lower limb prosthesis (LLP) users. Currently, there are no models based on prospective falls data that clinicians can use to predict the incidence of future falls in LLP users. Assessing who is at risk for falls, and thus most likely to need and benefit from intervention, remains a challenge. OBJECTIVE: To determine whether select performance-based balance tests predict future falls in established, unilateral transtibial prosthesis users (TTPU). DESIGN: Multisite prospective observational study. SETTING: Research laboratory and prosthetics clinic. PARTICIPANTS: Forty-five established, unilateral TTPU. INTERVENTION: Not applicable. MAIN OUTCOME MEASURES: The number of falls reported over a prospective 6-month period. Timed Up-and-Go (TUG) and Four-Square Step Test (FSST) times, as well as Narrowing Beam Walking Test scores were recorded at baseline, along with the number of falls recalled over the past 12 months and additional potential fall-risk factors. RESULTS: The final negative binomial regression model, which included TUG (P = .044) and FSST (P = .159) times, as well as the number of recalled falls (P = .009), was significantly better than a null model at predicting the number of falls over the next 6 months (X2 [3] = 11.6, P = .009) and fit the observed fall count data (X2 [41] = 36.12, P = .20). The final model provided a significant improvement in fit to the prospective fall count data over a model with fall recall alone X2 (1) = 4.342, P < .05. CONCLUSION: No combination of performance-based balance tests alone predicted the incidence of future falls in our sample of established, unilateral TTPU. Rather, a combination of the number of falls recalled over the past 12 months, along with TUG and FSST times, but not NBWT scores, was required to predict the number of "all-cause" falls over the next 6 months. The resulting predictive model may serve as a suitable method for clinicians to predict the incidence of falls in established, unilateral TTPU.

Fall-related events in people who are lower limb prosthesis users: the lived experience.

PURPOSE: To explore lived experiences, and identify common themes as well as vocabulary associated with fall-related events in lower limb prosthesis (LLP) users. MATERIALS AND METHODS: Five focus groups of LLP users from across the United States were conducted remotely via video or tele-conferencing. Focus group transcripts were coded and analyzed using methods adapted from a grounded theory approach to identify themes. RESULTS: Focus group participants (n = 25) described experiences associated with fall-related events that resulted in the identification of six themes: (1) memories of fall-related events are shaped by time and context, (2) location and ground conditions influence whether falls occur, (3) some activities come with more risk, (4) fall-related situations are multi-faceted, and often involve the prosthesis, (5) how LLP users land, but not the way they go down, tends to vary, and (6) not all falls affect LLP users, but some near-falls do. CONCLUSION: Consideration for where LLP users fall, what they are doing when they fall, how they fall, what occurs as a result of a fall, and how well memory of a fall persists may enhance recording and reporting of falls, contribute to development of improved fall risk assessment tools, and inspire the design and function of prosthetic componentry for patient safety.Implications for rehabilitationFalls are a common problem in lower limb prosthesis (LLP) users that can lead to adverse health outcomes.Concerns over near falls, not just falls, may merit greater attention from rehabilitation professionals.Elements of the lived experience that appear unique to LLP users include the role of prosthetic fit, function, and comfort in losing and/or recovering balance; as well as the tendency of LLP users to modify rather than stop or avoid activities associated with falls.

Recalled Number of Falls in the Past Year-Combined With Perceived Mobility-Predicts the Incidence of Future Falls in Unilateral Lower Limb Prosthesis Users.

OBJECTIVE: Falls are a frequent and costly concern for lower limb prosthesis (LLP) users. At present, there are no models that clinicians can use to predict the incidence of future falls in LLP users. Assessing who is at risk for falls, therefore, remains a challenge. The purpose of this study was to test whether easily accessible clinical attributes and measurements predict the incidence of future falls in LLP users. METHODS: In this prospective observational study, a secondary analysis of data from 60 LLP users was conducted. LLP users reported the number of falls that they recalled over the past year before prospectively reporting falls over a 6-month observation period via monthly telephone calls. Additional candidate predictor variables were recorded at baseline. Negative binomial regression was used to develop a model intended to predict the incidence of future falls. RESULTS: The final model, which included the number of recalled falls (incidence rate ratio = 1.13; 95% CI = 1.01 to 1.28) and Prosthetic Limb Users Survey of Mobility T-scores (incidence rate ratio = 0.949; 95% CI = 0.90 to 1.01), was significantly better than a null model at predicting the number of falls over the next 6 months (χ22 = 9.76) and fit the observed prospective fall count data (χ256 = 54.78). CONCLUSION: The number of recalled falls and Prosthetic Limb Users Survey of Mobility T-scores predicted the incidence of falls over the next 6 months in established, unilateral LLP users. The success and simplicity of the final model suggests that it may serve as a screening tool for clinicians to use for assessing risk of falls. Additional research to validate the proposed model in an independent sample of LLP users is needed. IMPACT: Owing to its simplicity, the final model may serve as a suitable screening measure for clinicians to ascertain an initial evaluation of fall risk in established unilateral LLP users. Analyzing falls data as counts rather than as a categorical variable may be an important methodological consideration for falls prevention research.

Characterizing Practice Effects in Performance-Based Tests Administered to Users of Unilateral Lower Limb Prostheses: A Preliminary Study.

BACKGROUND: Performance-based tests are viewed as a gold standard for measuring physical capability. Practice effects, however, may threaten their predictive, discriminative, and evaluative applications. Despite these potential consequences, practice effects have received limited attention in users of lower limb prostheses (LLP). OBJECTIVE: To perform an initial characterization of the occurrence, time-course, and magnitude of practice effects in three performance-based tests administered to users of LLP. DESIGN: Secondary analysis of data from a multisite repeated-measures study. SETTING: Outpatient clinic and research laboratory. PARTICIPANTS: Convenience sample of established ambulatory users of unilateral transtibial and transfemoral prostheses (n = 60). INTERVENTION: Not applicable. MAIN OUTCOME MEASURES: Practice effects were identified as significant changes in slope of participants' cumulative trial-by-trial records. The occurrence, time-course, and magnitude of practice effects were computed for the Timed Up and Go (TUG), Four Square Step Test (FSST), and the 10-m Walk Test (10mWT). RESULTS: Across tests, practice effects were observed in 45% to 76% of participants. The proportion of participants with practice effects (ie, occurrence) was significantly greater for the FSST than the 10mWT (P = .008). The median number of trials (ie, time-course) required for participants to reach a consistent level of performance was not significantly different between tests (FSST: 4 trials, TUG: 4 trials; 10mWT: 3.5 trials; P = .481). Practice effect magnitude (ie, difference between the mean of trials during the plateau and best performance over the first two trials) was significantly greater than zero for the FSST (1.6 s; 16%) and TUG (1.4 s; 13%) (P < .05). CONCLUSION: Results indicate that the FSST, TUG, and 10mWT were susceptible to practice effects in this sample of users of LLP. Practice effects may obscure significant differences in walking and balance ability, and thereby, in the absence of modifications, limit the use of these tests for making individual patient clinical decisions and analyzing group-level data.

Generalization of motor module recruitment across standing reactive balance and walking is associated with beam walking performance in young adults.

BACKGROUND: Recent studies provide compelling evidence that recruiting a common pool of motor modules across behaviors (i.e., motor module generalization) may facilitate motor performance. In particular, motor module generalization across standing reactive balance and walking is associated with both walking speed and endurance in neurologically impaired populations (e.g., stroke survivors and individual's with Parkinson's disease). To test whether this phenomenon is a general neuromuscular strategy associated with well-coordinated walking and not limited to motor impairment, this relationship must be confirmed in neurologically intact adults. RESEARCH QUESTION: Is motor module generalization across standing reactive balance and walking related to walking performance in neurologically intact young adults? METHODS: Two populations of young adults were recruited to capture a wide range of walking performance: professionally-trained ballet dancers (i.e., experts, n = 12) and novices (n = 8). Motor modules (a.k.a. muscle synergies) were extracted from muscles spanning the trunk, hip, knee and ankle during walking and multidirectional perturbations to standing. Motor module generalization was calculated as the number of modules common to these behaviors. Walking performance was assessed using self-selected walking speed and beam-walking proficiency (i.e., distance walked on a narrow beam). Motor module generalization between experts and novices was compared using rank-sum tests and the association between generalization and walking performance was assessed using correlation analyses. RESULTS: Experts generalized more motor modules across standing reactive balance and walking than novices (p = 0.009). Across all subjects, motor module generalization was moderately associated with increased beam walking proficiency (r = 0.456, p = 0.022) but not walking speed (r = 0.092, p = 0.349). SIGNIFICANCE: Similar relationships between walking performance and motor module generalization exist in neurologically intact and impaired populations, suggesting that motor module generalization across standing reactive balance and walking may be a general neuromuscular mechanism contributing to the successful control of walking.

Reorganization of motor modules for standing reactive balance recovery following pyridoxine-induced large-fiber peripheral sensory neuropathy in cats.

Task-level goals such as maintaining standing balance are achieved through coordinated muscle activity. Consistent and individualized groupings of synchronously activated muscles can be estimated from muscle recordings in terms of motor modules or muscle synergies, independent of their temporal activation. The structure of motor modules can change with motor training, neurological disorders, and rehabilitation, but the central and peripheral mechanisms underlying motor module structure remain unclear. To assess the role of peripheral somatosensory input on motor module structure, we evaluated changes in the structure of motor modules for reactive balance recovery following pyridoxine-induced large-fiber peripheral somatosensory neuropathy in previously collected data in four adult cats. Somatosensory fiber loss, quantified by postmortem histology, varied from mild to severe across cats. Reactive balance recovery was assessed using multidirectional translational support-surface perturbations over days to weeks throughout initial impairment and subsequent recovery of balance ability. Motor modules within each cat were quantified by non-negative matrix factorization and compared in structure over time. All cats exhibited changes in the structure of motor modules for reactive balance recovery after somatosensory loss, providing evidence that somatosensory inputs influence motor module structure. The impact of the somatosensory disturbance on the structure of motor modules in well-trained adult cats indicates that somatosensory mechanisms contribute to motor module structure, and therefore may contribute to some of the pathological changes in motor module structure in neurological disorders. These results further suggest that somatosensory nerves could be targeted during rehabilitation to influence pathological motor modules for rehabilitation.NEW & NOTEWORTHY Stable motor modules for reactive balance recovery in well-trained adult cats were disrupted following pyridoxine-induced peripheral somatosensory neuropathy, suggesting somatosensory inputs contribute to motor module structure. Furthermore, the motor module structure continued to change as the animals regained the ability to maintain standing balance, but the modules generally did not recover pre-pyridoxine patterns. These results suggest changes in somatosensory input and subsequent learning may contribute to changes in motor module structure in pathological conditions.

Older adults reduce the complexity and efficiency of neuromuscular control to preserve walking balance.

Healthy aging modifies neuromuscular control of dynamic balance. Challenging tasks could amplify such modifications, providing clinical insights. We examined the effects of age and walking condition difficulty on neuromuscular control of walking balance. We analyzed whole-body kinematics and activity of 13 right leg and trunk muscles in 17 young (11 males and 6 females; age 24 ± 3 years) and 14 older adults (3 males and 11 females; age 69 ± 4 years) while walking on a taped line on the floor and a 6-cm wide beam. Spatiotemporal parameters of gait, margin of stability, motor performance, and muscle synergies were estimated. Regardless of age, maintaining walking balance was more difficult on the beam compared to the taped line as evidenced by a shorter distance walked (17.3%), a reduction in step length (5.8%) and speed (10.3%), as well as a 40.0% smaller margin of stability during beam vs. tape walking. The number of muscle synergies was also higher during beam vs. tape walking. Compared to younger adults, older adults had larger margin of stability during beam walking. Older adults also had higher muscle co-activity within each muscle synergy and greater variance accounted for by the first muscle synergy regardless of condition. Such age-effects may be interpreted as a safer, less efficient, and less complex neuromuscular modular control strategy. In conclusion, beam walking increased the difficulty of maintaining walking balance and induced adaptations in modular control. It seems that healthy older adults reduce the complexity and efficiency of neuromuscular control of walking to preserve walking balance.

Strength deficits in lower limb prosthesis users: A scoping review.

BACKGROUND: Strength deficits may play a central role in the severity of balance, mobility, and endurance impairments in lower limb prosthesis users. A body of literature detailing the scope and specifics of muscle weakness in lower limb prosthesis users is emerging, but has yet to be summarized. A synopsis of strength deficits, and their impact on functional abilities in lower limb prosthesis users, may inform rehabilitation and research needs. OBJECTIVES: Synthesize reported strength deficits in lower limb prosthesis users, and discuss possible causes, consequences, and solutions. STUDY DESIGN: Scoping review. METHODS: A search of biomedical databases was performed, and inclusion/exclusion criteria were applied to identify publications relevant to the purpose of the review. RESULTS: In all, 377 publications were identified, of which 12 met the inclusion/exclusion criteria. When compared with the controls and the intact limb, the primary strength outcome, peak torque, was lower in transtibial residual limb knee flexors and extensors, as well as transfemoral residual limb hip muscles. CONCLUSIONS: The reviewed studies provide evidence of strength deficits in lower limb prosthesis users. These deficits appear to be consequential, as they may contribute to balance, mobility, and endurance impairments. Additional research exploring alternative strength metrics, clinical tests, and causal links to functional impairments is required. CLINICAL RELEVANCE: Evidence of muscle weakness among lower limb prosthesis users, and its influence on balance, mobility, and endurance, suggests that greater clinical attention and scientific inquiry into physical conditioning of lower limb prosthesis users is merited and required.

Interrater and Test-Retest Reliability of Performance-Based Clinical Tests Administered to Established Users of Lower Limb Prostheses.

OBJECTIVE: A major barrier to reducing falls among users of lower limb prostheses (LLP) has been an absence of statistical indices required for clinicians to select and interpret scores from performance-based clinical tests. The study aimed to derive estimates of reliability, measurement error, and minimal detectable change values in performance-based clinical tests administered to unilateral LLP users. METHODS: A total of 60 unilateral LLP users were administered the Narrowing Beam Walking Test, Timed ``Up and Go'' (TUG), Four Square Step Test (FSST), and 10-Meter Walk Test on 2 occasions, 3 to 9 days apart. Intraclass correlation coefficients (ICCs) were calculated to assess interrater and test-retest reliability, while standard error of measurement (SEM) and minimal detectable change (MDC90) were derived to establish estimates of measurement error in individual scores or changes in score for each test. RESULTS: Interrater reliability ICCs (1,1) were high for all tests (ie, ≥0.98). Test-retest ICCs (2,1) varied by test, ranging from .88 for the TUG to .97 for the FSST. SEM and MDC90 varied between .39 and .96 and between .91 seconds and 2.2 seconds for the time-based tests (FSST, TUG, 10-Meter Walk Test). SEM and MDC90 for the Narrowing Beam Walking Test were .07 and .16, respectively. CONCLUSION: With the exception of the TUG, studied tests had test-retest ICCs (2,1) that exceeded the minimum required threshold to be considered suitable for group- and individual-level applications (ie, ICC ≥ 0.70 and ≥ 0.90, respectively). Future research on individuals with dysvascular and transfemoral amputations or in specific age categories is required. IMPACT: Along with published validity indices, these reliability, error, and change indices can help clinicians select balance tests suitable for LLP users. They can also help clinicians interpret test scores to make informed, evidence-based clinical decisions.

Using Clinical Balance Tests to Assess Fall Risk among Established Unilateral Lower Limb Prosthesis Users: Cutoff Scores and Associated Validity Indices.

BACKGROUND: Clinicians are routinely required to make decisions about fall risk among lower limb prosthesis (LLP) users. These decisions can be guided by standardized clinical balance tests but require population- and test-specific cutoff scores and validity indices to categorize individuals as probable fallers or nonfallers on the basis of test performance. Despite the importance of cutoff scores and validity indices to clinical interpretation of clinical balance test scores, they are rarely reported for LLP users. In their absence, clinicians cannot use results from clinical balance tests to assess the likelihood of a fall by any one patient. OBJECTIVE: Derive cutoff scores, and associated validity indices, for clinical balance tests administered to established unilateral LLP users. DESIGN: Cross-sectional study. SETTING: Outpatient clinic and research laboratory. PARTICIPANTS: Established ambulatory unilateral transtibial and transfemoral prosthesis users (n = 40). INTERVENTION: Not applicable. MAIN OUTCOME MEASURE(S): Optimal cutoff scores and related validity indices (ie, area under the curve, sensitivity, specificity, likelihood ratios) were computed for five balance tests, the activities-specific balance confidence scale (ABC), timed up and go (TUG), four square step test (FSST), Berg balance scale (BBS), and narrowing-beam walking test (NBWT). RESULTS: Cutoff scores were identified for the NBWT (≤.43/1.0), TUG (≥8.17 seconds], FSST (≥8.49 seconds), BBS (≤50.5/56), and ABC (≤80.2/100). Validity indices (ie, area under the curve, sensitivity, specificity, and likelihood ratios) for the NBWT, TUG, and FSST had greater diagnostic accuracy and provided more information about the probability of a fall than those for the BBS or ABC. CONCLUSION: Performance above or below identified cutoff scores for the NBWT, FSST, and TUG provides information about potentially important shifts in the probability of falling among established unilateral LLP users. These results can serve as initial benchmarks to reduce uncertainty surrounding fall risk assessment in established unilateral LLP users but require future prospective evaluation. LEVEL OF EVIDENCE: III.

Conventional administration and scoring procedures suppress the diagnostic accuracy of a performance-based test designed to assess balance ability in lower limb prosthesis users.

BACKGROUND: Practice effects have been observed among performance-based clinical tests administered to prosthesis-users. Their impact on test applications remains unknown. OBJECTIVE: To determine whether scoring a clinical balance test using conventional procedures that do not accommodate practice effects reduces its diagnostic accuracy relative to scoring it using recommended procedures that do accommodate practice effects. STUDY DESIGN: Cross-sectional study. METHODS: Narrowing Beam Walking Test data from 40 prosthesis users was scored using recommended methods (i.e. average of trials 3-5) and conventional methods applied to other tests (i.e. mean or best of trials 1-3). Area under the receiver operating characteristic curve for each method was compared to 0.50, to determine if it was better than chance at identifying prosthesis-users with a history of falls, and to 0.80, to determine if it surpassed a threshold recommended for diagnostic accuracy. RESULTS: Receiver operating characteristic curve area decreased when the Narrowing Beam Walking Test was scored using conventional rather than recommended procedures. Furthermore, when scored using conventional procedures, the NBWT no longer discriminated between prosthesis-users with and without a history of falls with a probability greater than chance, or exceeded recommended diagnostic thresholds. CONCLUSION: Scoring the Narrowing Beam Walking Test using conventional procedures that do not accommodate practice effects decreased its diagnostic accuracy among prosthesis-users relative to recommended procedures. Conventional scoring procedures may limit the effectiveness of performance-based tests used to screen for fall risk in prosthesis-users because they do not mitigate practice effects. The influence of practice effects on other tests, and test applications (e.g. clinical evaluation and prediction), is warranted. CLINICAL RELEVANCE: Scoring a clinical balance test using conventional procedures that do not mitigate practice effects reduced its diagnostic accuracy. Changing administration and scoring procedures to accommodate practice effects should be considered to improve the diagnostic accuracy of other performance-based balance tests.

Ensuring accurate estimates of step width variability during treadmill walking requires more than 400 consecutive steps.

Falls to the side are associated with significant morbidity, including increased risk of hip and radius fracture. Although step width variability, as measured by standard deviation, has been hypothesized to be associated with falls to the side, there is little supporting evidence. The extent to which such a relationship could be reliably established, however, is dependent on the accuracy with which step width, and thus step width variability, is measured. It has been reported that 400 consecutive steps are required to accurately estimate step width of young adults during treadmill walking. The degree to which this requirement generalizes to other populations has not been determined. Here, a secondary analysis of step width time series data from 19 middle-age women during treadmill walking revealed that 400 steps were insufficient to accurately estimate step width or step width variability for the majority of the women sampled. Patterns observed in the data suggest the potential influence of confounding factors including acclimatization to the task and fatigue during the protocol. The results suggest that the minimum number of steps previously reported as necessary to accurately assess step width and step width variability of young adults during treadmill walking is not valid for middle-age women. Furthermore, the results point to the potential value of reproducing and/or extending the original experiment that established 400 consecutive steps as necessary to accurately estimate step kinematics among young adults.