Kinematic and behavioral analyses of protective stepping strategies and risk for falls among community living older adults.

BACKGROUND: Protective stepping evoked by externally applied lateral perturbations reveals balance deficits underlying falls. However, a lack of comprehensive information about the control of different stepping strategies in relation to the magnitude of perturbation limits understanding of balance control in relation to age and fall status. The aim of this study was to investigate different protective stepping strategies and their kinematic and behavioral control characteristics in response to different magnitudes of lateral waist-pulls between older fallers and non-fallers. METHODS: Fifty-two community-dwelling older adults (16 fallers) reacted naturally to maintain balance in response to five magnitudes of lateral waist-pulls. The balance tolerance limit (BTL, waist-pull magnitude where protective steps transitioned from single to multiple steps), first step control characteristics (stepping frequency and counts, spatial-temporal kinematic, and trunk position at landing) of four naturally selected protective step types were compared between fallers and non-fallers at- and above-BTL. FINDINGS: Fallers took medial-steps most frequently while non-fallers most often took crossover-back-steps. Only non-fallers varied their step count and first step control parameters by step type at the instants of step initiation (onset time) and termination (trunk position), while both groups modulated step execution parameters (single stance duration and step length) by step type. Group differences were generally better demonstrated above-BTL. INTERPRETATION: Fallers primarily used a biomechanically less effective medial-stepping strategy that may be partially explained by reduced somato-sensation. Fallers did not modulate their step parameters by step type at first step initiation and termination, instances particularly vulnerable to instability, reflecting their limitations in balance control during protective stepping.

Hip but not thigh intramuscular adipose tissue is associated with poor balance and increased temporal gait variability in older adults.

BACKGROUND: Intramuscular adipose tissue (IMAT) of the lower extremity is a strong negative predictor of mobility function. Variability in temporal gait factors is another important predictor of mobility function. The purpose of this study was to examine the relationships between IMAT in the hip and thigh muscles, balance, and temporal gait variability in older adults. METHODS: Forty-eight healthy community dwelling older adults (74 +/- 1 year) underwent a CT scan to quantify IMAT in the gluteus maximus (Gmax), gluteus medius/minimus (Gmed/min), hamstrings, vastus lateralis, and adductor muscles. Temporal Gait measures were collected on a GAITRite walkway and gait variability was determined by calculating intraindividual standard deviations. Individuals were divided by tertiles of temporal gait variability into categories of high, medium, and low variability. Differences in the IMAT of the hip abductors were calculated for those with high and low gait variability and partial correlations for gait variability and all muscle composition measures were determined for all variables with normalized gait speed as a covariate. RESULTS: Gmed/min IMAT was greater in those with higher gait variability compared to those with lower gait variability (p<0.05). Gmed/min IMAT was related to stride width variability (r=0.30, p<0.05). Gmax IMAT was also related to time variability of swing (r=0.42), stance (r=0.26), double limb support (r=0.43), double support loading (r=0.44), and double support unloading (r=0.50) (all p<0.05). CONCLUSION: Increased IMAT in the proximal hip muscles, particularly the hip abductors, was associated with increased gait variability and poorer balance. These findings may have implications for the assessment and treatment of balance and falls such that interventions for enhancing balance and mobility among older individuals should take into account the importance of gluteal muscle composition.

Gluteal muscle composition differentiates fallers from non-fallers in community dwelling older adults.

BACKGROUND: Impaired balance, loss of mobility and falls are major problems associated with changes in muscle in older adults. However, the extent to which muscle composition and related performance measures for different lower limb muscles are associated with falls in older individuals is unclear. This study evaluated lower limb muscle attenuation, intramuscular adipose tissue (IMAT) infiltration and muscle performance in older fallers and non-fallers. METHODS: For this cross-sectional study, fifty-eight community dwelling older individuals (>65 years) were classified into fallers (n = 15) or non-fallers (n = 43). Computed tomography (CT) was used to determine muscle attenuation and intramuscular adipose tissue (IMAT) of multiple thigh and hip muscles. Muscle performance was assessed with isokinetic dynamometry. RESULTS: For both groups, Rectus Femoris showed the highest muscle attenuation and lowest IMAT infiltration, and Gluteus Maximus and Gluteus Medius/Minimus muscles had the lowest muscle attenuation and highest IMAT infiltration. Fallers exhibited lower muscle attenuation and higher IMAT infiltration than non-faller participants in most muscles, where the gluteal muscles were the most affected (p < 0.05). Fallers also showed a lower peak hip abduction torque (p < 0.05). There were significant associations (r = 0.31 to 0.53) between joint torques and muscle composition, with the strongest associations between Gluteus Medius/Minimus and hip abduction strength. CONCLUSIONS: While fallers were generally differentiated from non-fallers by muscle composition, the most affected muscles were the proximal gluteal muscles of the hip joint accompanied by lower hip abduction strength, which may contribute to impaired balance function and increased risk for falls.

Self-triggered assistive stimulus training improves step initiation in persons with Parkinson's disease.

BACKGROUND: Prior studies demonstrated that hesitation-prone persons with Parkinson's disease (PDs) acutely improve step initiation using a novel self-triggered stimulus that enhances lateral weight shift prior to step onset. PDs showed reduced anticipatory postural adjustment (APA) durations, earlier step onsets, and faster 1st step speed immediately following stimulus exposure. OBJECTIVE: This study investigated the effects of long-term stimulus exposure. METHODS: Two groups of hesitation-prone subjects with Parkinson's disease (PD) participated in a 6-week step-initiation training program involving one of two stimulus conditions: 1) Drop. The stance-side support surface was lowered quickly (1.5 cm); 2) Vibration. A short vibration (100 ms) was applied beneath the stance-side support surface. Stimuli were self-triggered by a 5% reduction in vertical force under the stance foot during the APA. Testing was at baseline, immediately post-training, and 6 weeks post-training. Measurements included timing and magnitude of ground reaction forces, and step speed and length. RESULTS: Both groups improved their APA force modulation after training. Contrary to previous results, neither group showed reduced APA durations or earlier step onset times. The vibration group showed 55% increase in step speed and a 39% increase in step length which were retained 6 weeks post-training. The drop group showed no stepping-performance improvements. CONCLUSIONS: The acute sensitivity to the quickness-enhancing effects of stimulus exposure demonstrated in previous studies was supplanted by improved force modulation following prolonged stimulus exposure. The results suggest a potential approach to reduce the severity of start hesitation in PDs, but further study is needed to understand the relationship between short- and long-term effects of stimulus exposure.

Arm training in standing also improves postural control in participants with chronic stroke.

PURPOSE: To prove the concept that postural control will improve without specific balance control training during arm training in standing with individuals with chronic stroke. METHODS: Nine participants (mean age 64±7) received training involving hand orthotic assisted grasp, reach and release in standing 1 h, 3×'s/week for 6 weeks. Training focused on task completion with no explicit instructions provided for postural alignment, weight shift or balance strategy. Testing consisted of quantified measures using NeuroCom™ Balance Master, Berg Balance Scale (BBS) and Activities-specific Balance Confidence Scale (ABC). RESULTS: Post training participants demonstrate increased (p<.05) composite stability scores for sensory organization testing (mean 71.55±12.7-75.55±11). Velocity and directional control of COP weight shift improved for all 9 subjects with 6/9 achieving 100% target acquisition. Directional control improved (p<.05) for medial/lateral movements for all speeds and composite score. Anterior/posterior rhythmic weight shifting increased significantly in COP velocity control at moderate and fast velocities and composite score. Increases in mean BBS (p<.01) from 41.33±10.1-46.88±8.03 exceeded the clinically important cutoff for the scale. Balance confidence improved with ABC mean scores 70.22±14.5-79.55±12.86 (p<.05). Seven participants demonstrated changes above the minimally important difference for this scale. CONCLUSIONS: Postural control improved following task oriented arm training in standing without explicit postural control goals, instruction or feedback challenging current training paradigms of isolated postural control training with conscious attention directed to center of pressure location and movement.

Posture and locomotion coupling: a target for rehabilitation interventions in persons with Parkinson's disease.

Disorders of posture, balance, and gait are debilitating motor manifestations of advancing Parkinson's disease requiring rehabilitation intervention. These problems often reflect difficulties with coupling or sequencing posture and locomotion during complex whole body movements linked with falls. Considerable progress has been made with demonstrating the effectiveness of exercise interventions for individuals with Parkinson's disease. However, gaps remain in the evidence base for specific interventions and the optimal content of exercise interventions. Using a conceptual theoretical framework and experimental findings, this perspective and review advances the viewpoint that rehabilitation interventions focused on separate or isolated components of posture, balance, or gait may limit the effectiveness of current clinical practices. It is argued that treatment effectiveness may be improved by directly targeting posture and locomotion coupling problems as causal factors contributing to balance and gait dysfunction. This approach may help advance current clinical practice and improve outcomes in rehabilitation for persons with Parkinson's disease.". . .postural activity should be regarded as a function in its own right and not merely as a component of movement. . ."James Purdon Martin.

Short-term changes in protective stepping for lateral balance recovery in older adults.

BACKGROUND: Fall prevention for older adults is dependent on the ability to maintain protective balance. This study measured the short-term changes of protective stepping following waist-pull perturbations in the medio-lateral direction, to identify what, if any, properties of protective stepping are improved with repeated perturbation exposures. METHODS: Sixty waist-pulls (2 directions × 5 intensities × 6 repetitions) from a single session were analyzed separately as early, middle, and late testing periods, for a comparison over time of typical responses. Outcome measures included the number of evoked steps, type of step, incidence of interlimb collisions, and kinematic and kinetic properties of the first step in frequently used crossover-type responses. FINDINGS: Improvements were evident as significantly reduced number of steps and collisions. However, these improvements could not be completely accounted for by significant changes in first step kinematic or kinetic properties. INTERPRETATION: We infer that older individuals experiencing repeated lateral waist-pull perturbations optimize the predictive or feed-forward motor control for balance recovery through stepping.

Six hours in the laboratory: a quantification of practice time during constraint-induced therapy (CIT).

OBJECTIVE: To quantify supervised in-laboratory time and practice intensity during the signature protocol specified as 6 hours/day over 10 days for the EXtremity Constraint-Induced Therapy Evaluation (EXCITE) randomized clinical trial. DESIGN: Retrospective analysis of constraint-induced movement therapy training documentation acquired at the University of Southern California site from EXCITE (n = 38). Training documentation was reviewed and analysed to determine average and between-subject variability of supervised in-laboratory time and actual task-specific practice time for concurrence with the specified constraint-induced movement therapy protocol. SETTING: Motor Behavior and Neurorehabilitation Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA. SUBJECTS: Data from 38 participants (35 met inclusion criteria) who, upon enrolment in the EXCITE trial, were between 3 and 10 months post stroke and between 47 and 81 years of age. RESULTS: The training records revealed an average of 64 hours (SD = 2.6) supervised in-laboratory time for 35 participants across 10 days of training. More importantly, the average time on task-specific practice was 3.95 hours per day (SD = 5.7) representing 62% of the in-laboratory time. Supervised in-laboratory time for10 training days was consistent across the sample as was total practice time for days 2-10, with a substantially lower practice time on the initial training day. CONCLUSIONS: Participants tolerated an intense task-specific practice schedule that consisted of approximately two-thirds of the specified minimum 6 hour in-laboratory time and was distributed evenly between adaptive task practice (shaping) and task practice components.

Lessons learned in participant recruitment and retention: the EXCITE trial.

Participant recruitment is considered the most difficult aspect of the research process. Despite the integral role of recruitment in randomized clinical trials, publication of data defining the recruitment effort is not routine in rehabilitation initiatives. The recruitment process for the Extremity Constraint-Induced Therapy Evaluation (EXCITE) trial illustrates obstacles to and strategies for participant accrual and retention that are inherent in rehabilitation clinical trials. The purpose of this article is to increase awareness of the multiple facets of recruitment necessary for successful clinical trials, thus supporting the continued development of evidence-based practice in physical therapy. The Recruitment Index is presented as a variable to measure recruitment efficacy. In addition, ethical aspects of recruitment are explored, including informed consent and the concept of therapeutic misconception.