Biomedical subjects

Neil B Alexander

Publications and source records attributed to Neil B Alexander.

16 recordsLinked to original sources

PubMed2025

LIVE-SMART: A sequential, multiple assignment randomized trial to reduce falls in cirrhosis.

INTRODUCTION: Falls are a major threat to the well-being of patients with cirrhosis. We are performing a clinical trial to determine whether lactulose, TeleTai-Chi, or their combination will reduce falls in HE and improve health-related quality of life (HRQOL) among patients with cirrhosis. METHODS AND ANALYSIS: Patients with cirrhosis and portal hypertension without HE will be enrolled in 3 US states and followed participants for 24 weeks. In stage 1 (12 wk), participants will be randomized to receive either lactulose therapy or enhanced usual care. In stage 2 (12 wk), participants will be randomized to either TeleTai-Chi or usual care. The primary outcome is a hierarchical composite: Injurious falls, noninjurious falls, incident HE, and death/transplantation. Secondary outcomes include cognitive function, days-alive and out-of-hospital, and HRQOL. After completion of the interventions, participants will be followed for 48 weeks for health and financial outcomes. ETHICS AND DISSEMINATION: Our study has a central institutional review board with individual site IRB review. Dissemination includes the publication of study findings and patient-focused educational webinars.

Female↗

PubMed2006

A kinematic analysis of the rapid step test in balance-impaired and unimpaired older women.

Little is known about the kinematic and kinetic determinants that might explain age and balance-impairment alterations in the results of volitional stepping performance tests. Maximal unipedal stance time (UST) was used to distinguish "balance-impaired" old (BI, UST<10s, N=15, mean age=76 years) from unimpaired old (O, UST>30s, N=12, mean age=71 years) before they and healthy young females (Y, UST>30s, N=13, mean age=23 years) performed the rapid step test (RST). The RST evaluates the time required to take volitional front, side, and back steps of at least 80% maximum step length in response to verbal commands. Kinematic and kinetic data were recorded during the RST. The results indicate that the initiation phase of the step was the major source of age- and balance impairment-related delays. The delays in BI were primarily caused by increased postural adjustments prior to step initiation, as measured by center-of-pressure (COP) path length (p<0.003). The Step landing phase showed similar, but non-significant, temporal trends. Step length and peak center-of-mass (COM) deceleration during the Step-Out landing decreased in O by 18% (p=0.0002) and 24% (p=0.001), respectively, and a further 12% (p=0.04) and 18% (p=0.08) in BI. We conclude that the delay in BI step initiation was due to the increase in their postural adjustments prior to step initiation.

Adult↗

PubMed2006

Bath transfers in older adult congregate housing residents: assessing the person-environment interaction.

OBJECTIVES: To examine environmental feature utilization (EFU) and the types and prevalence of performance difficulties during a videotaped bath transfer and to determine the personal characteristics associated with total EFU and performance difficulties. DESIGN: Cross-sectional analysis. SETTING: Two congregate housing facilities in southeastern Michigan. PARTICIPANTS: Eighty-nine older adults who reported independence in bathing. MEASUREMENTS: Trained video coders recorded EFU (defined as upper extremity contact with features in the environment) and rated performance difficulties (defined as lack of fluid movement or difficulty negotiating the environment). EFU was measured by determining whether features used were safe (i.e., designed for use as a transfer support) or unsafe and by total EFU (i.e., number of environmental features used during the transfer). Personal characteristics included self-reported medical conditions, bath transfer difficulty, functional mobility, lower extremity strength, range of motion functional impairment, and falls efficacy. RESULTS: For participants with a tub-shower, safe EFU was higher than unsafe EFU (85% vs 19%; P<.001). Participants with shower stalls had the same rate of safe and unsafe EFU (71%). In multiple regression analysis, self-reported bath transfer difficulty was associated with total EFU (P=.01). One-third of the sample had performance difficulties. In multivariate analysis, range of motion functional impairment (odds ratio (OR)=13.49, 95% confidence interval (CI)=1.11-163.53) and lowest quartile in falls efficacy scores (OR=5.81, 95% CI=1.24-27.41) were associated with performance difficulties. CONCLUSION: Unsafe EFU and performance difficulties were common in independently bathing older adults. Self-reported bath transfer difficulty appears to be a good indicator of high total EFU and may be used as a screening question for clinicians. Important strategies to reduce unsafe EFU and to increase falls efficacy include removing shower sliding glass doors and training older adults in safe transfer techniques.

Activities of Daily Living↗

PubMed2006

Dynamic balance and stepping versus tai chi training to improve balance and stepping in at-risk older adults.

OBJECTIVES: To compare the effect of two 10-week balance training programs, Combined Balance and Step Training (CBST) versus tai chi (TC), on balance and stepping measures. DESIGN: Prospective intervention trial. SETTING: Local senior centers and congregate housing facilities. PARTICIPANTS: Aged 65 and older with at least mild impairment in the ability to perform unipedal stance and tandem walk. INTERVENTION: Participants were allocated to TC (n = 107, mean age 78) or CBST, an intervention focused on improving dynamic balance and stepping (n = 106, mean age 78). MEASUREMENTS: At baseline and 10 weeks, participants were tested in their static balance (Unipedal Stance and Tandem Stance (TS)), stepping (Maximum Step Length, Rapid Step Test), and Timed Up and Go (TUG). RESULTS: Performance improved more with CBST than TC, ranging from 5% to 10% for the stepping tests (Maximum Step Length and Rapid Step Test) and 9% for TUG. The improvement in TUG represented an improvement of more than 1 second. Greater improvements were also seen in static balance ability (in TS) with CBST than TC. CONCLUSION: Of the two training programs, in which variants of each program have been proven to reduce falls, CBST results in modest improvements in balance, stepping, and functional mobility versus TC over a 10-week period. Future research should include a prospective comparison of fall rates in response to these two balance training programs.

Aged↗

PubMed2005

Can initial and additional compensatory steps be predicted in young, older, and balance-impaired older females in response to anterior and posterior waist pulls while standing?

The initiation of a single compensatory step in response to balance perturbations has been predicted with accuracies of up to 71%. We sought to determine whether similar methods also could be used to predict the onset of additional compensatory steps in both healthy and balance-impaired older females. Anterior and posterior waist pulls of five different magnitudes were applied to 13 unimpaired young (mean age 23 years), 12 unimpaired older (mean age 71 years), and 15 balance-impaired older (mean age 76 years) women. Body segment kinematic data were recorded at 100 Hz. A step was predicted when the time for the center-of-mass to reach the vertical projection of the boundary of the base-of-support fell below a certain threshold. The results show that 83% of all steps and non-steps were correctly predicted at an optimal time-to-boundary threshold (tau(opt)) of 0.78 s. Step prediction accuracy did not differ significantly by group: 86% of steps and non-steps by young, 84% by unimpaired old, and 82% by balance-impaired old women were correctly predicted at tau(opt) of 0.58, 0.67, and 0.78 s, respectively. Anterior steps and non-steps were predicted more accurately than posterior ones (94% vs. 79% correct at tau(opt) of 0.52 and 0.84 s, respectively) and initial steps were better predicted than additional ones (87% vs. 81% correct at tau(opt) of 0.77 and 0.34 s, respectively). We conclude that this step prediction method reasonably predicts initial and additional steps in the anterior and posterior direction by all three subject cohorts.

Accidental Falls↗

PubMed2005

Trunk repositioning errors are increased in balance-impaired older adults.

BACKGROUND: Controlling the flexing trunk is critical in recovering from a loss of balance and avoiding a fall. To investigate the relationship between trunk control and balance in older adults, we measured trunk repositioning accuracy in young and balance-impaired and unimpaired older adults. METHODS: Young adults (N = 8, mean age 24.3 years) and two groups of community-dwelling older adults defined by unipedal stance time (UST)-a balance-unimpaired group (UST > 30 seconds, N = 7, mean age 73.9 years) and a balance-impaired group (UST < 5 seconds, N = 8, mean age 79.6 years)-were tested in standing trunk control ability by reproducing a approximately 30 degrees trunk flexion angle under three visual-surface conditions: eyes opened and closed on the floor, and eyes opened on foam. Errors in reproducing the angle were defined as trunk repositioning errors (TREs). Clinical measures related to balance, trunk extensor strength, and self-reported disability were obtained. RESULTS: TREs were significantly greater in the balance-impaired group than in the other groups, even when controlling for trunk extensor strength and body mass. In older adults, there were significant correlations between TREs and three clinical measures of balance and fall risk, UST and maximum step length (-0.65 to -0.75), and Timed Up & Go score (0.55), and between TREs and age (0.63-0.76). In each group TREs were similar under the three visual-surface conditions. Test-retest reliability for TREs was good to excellent (intraclass correlation coefficients > or =0.74). CONCLUSIONS: Older balance-impaired adults have larger TREs, and thus poorer trunk control, than do balance-unimpaired older individuals. TREs are reliable and valid measures of underlying balance impairment in older adults, and may eventually prove to be useful in predicting the ability to recover from losses of balance and to avoid falls.

Adolescent↗

PubMed2005

Age differences in timed accurate stepping with increasing cognitive and visual demand: a walking trail making test.

BACKGROUND: Impaired vision, cognition, and divided attention performance predict falls. Requiring both visual and cognitive input, the ability to step accurately is necessary to safely traverse challenging terrain conditions such as uneven or slippery surfaces. We compared healthy young and older adults in the time taken to step accurately under conditions of increasing cognitive and visual demand. METHODS: Healthy Young (n = 42, mean age 21) and Older (n = 37, mean age 70) participants were required to step accurately on an instrumented walkway under conditions of increasing visual and cognitive demand. Based on the paper-and-pencil neuropsychological test, the Trail Making Test (P-TMT) A and B, participants stepped on instrumented targets with increasing sequential numbers (Walking Trail Making Test A [W-TMT A]) and increasing sequential numbers and letters (Walking Trail Making Test B [W-TMT B]), under conditions of Low as well as Normal lighting. RESULTS: W-TMT performance time increased with increased age (Older vs Young), decreased light (Low vs Normal), and increased cognitive demand (Trails B vs Trails A). W-TMT performance time was disproportionately increased in Low light and in the Older group under the highest cognitive demand (W-TMT B) conditions. Paired W-TMT A-B differences were three times higher in the Older group than in the Young group. In the Older group, the correlation between W-TMT results and P-TMT B was particularly strong (p <.001). CONCLUSIONS: The time to perform a stepping accuracy task, such as may be required to avoid environmental hazards, increases under reduced lighting and with increased cognitive demand, the latter disproportionately so in older adults.

Adolescent↗

PubMed2005

Gait disorders: search for multiple causes.

Gait disorders predict functional decline in older adults. They are often the result of multiple causes, so a full assessment should consider different sensorimotor levels and should include a focused physical examination and evaluation of functional performance. Exercise and medical and surgical interventions are effective and can reduce the degree of gait disorder, but usually not without some residual impairment. Orthoses and mobility aids are also important interventions to consider.

Age Factors↗

PubMed2005

Assessing falls in older adults: a comprehensive fall evaluation to reduce fall risk in older adults.

Falls account for significant morbidity and mortality in the older adult population. A comprehensive fall evaluation (CFE) is proposed, particularly for use in recurrent fallers, those who seek medical attention for a fall, and those with a gait and/or balance disorder. The CFE focuses on key factors in the medical and fall history, review of systems, and physical examination. Interventions utilize a multifactorial model, although balance exercise may be the most critical component. While some components may be marginally successful when presented individually as an intervention (such as correction of vision impairment or environmental hazard reduction), when presented together, fall risk can be significantly reduced.

Accidental Falls↗

PubMed2004

Compensatory stepping in response to waist pulls in balance-impaired and unimpaired women.

An effective stepping response is often critical in avoiding a fall. Our objective was to study the effects of age and balance impairment on anterior and posterior compensatory stepping strategies in response to waist pull perturbations of 1-5% body weight (BW). Based on maximal unipedal stance time (UST), we tested 15 balance-impaired old (BI, UST < 10s, mean age = 76 years), 12 healthy old (O, UST>30s, mean age = 71 years), and 13 healthy young women (Y, UST >30s, mean age=23 years). Randomized anterior and posterior pulls of 1-5% body weight (BW) were applied to the waist while kinematic and kinetic recovery responses were recorded. Results show that O and BI required 0.5 more steps than Y to recover balance for posterior pulls of 4-5% BW (P < 0.01). For anterior pulls of 4-5% BW, only BI had a greater probability of step initiation (P<or=0.05 or <0.02) and mean number of steps required to recover balance (P < 0.03). The Y used 93% greater torso extension and 24% greater torso flexion in responding to anterior and posterior pulls, respectively. In the posterior, but not anterior direction, O employed smaller (P < 0.007), but more laterally-directed (P < 0.03) steps than the Y. The BI were less able to attenuate their momentum during the step landing in both directions. We conclude that the additional steps required by the BI in both directions occurred because their initial step failed to properly arrest their momentum. Controlling torso inclination before step liftoff and linear momentum after step landing are critical components of successful compensatory stepping.

Accidental Falls↗

PubMed2004

Age-related changes in maximal hip strength and movement speed.

BACKGROUND: We quantified age-related decreases in the ability of female participants to generate whole leg movements about the hip. METHODS: We measured maximum hip strength and hip velocity in 12 young and 12 older healthy women. Both capabilities could help fall prevention by contributing to fast leg movements. We also measured maximum velocities as a function of isotonic load. RESULTS: Young participants produced 107.6 +/- 25.4 N-m (mean +/- SD) isometric torque in flexion and 109.3 +/- 22.3 N-m in extension. Older participants produced 22% and 31% lower torques, respectively (p<.001). Young participants generated maximum velocities of 362.8 +/- 51.5 degrees/s in flexion and 371.5 +/- 54.2 degrees/s in extension. Older participants produced 16% lower velocities in both directions (p<.001). Older participants also produced lower velocities as a function of load (p<.001), and lower maximum power (p<.001). CONCLUSION: Both maximum strength and velocity contribute to reduced ability to move the leg quickly with age.

Adult↗

PubMed2004

Tests of stepping as indicators of mobility, balance, and fall risk in balance-impaired older adults.

OBJECTIVES: To determine the relationships between two tests of stepping ability (the maximal step length (MSL) and rapid step test (RST)) and standard tests of standing balance, gait, mobility, and functional impairment in a group of at-risk older adults. DESIGN: Cross-sectional study. SETTING: University-based laboratory. PARTICIPANTS: One hundred sixty-seven mildly balance-impaired older adults recruited for a balance-training and fall-reduction program (mean age 78, range 65-90). MEASUREMENTS: Measures of stepping maximally (MSL, the ability to maximally step out and return to the initial position) and rapidly (RST, the time taken to step out and return in multiple directions as fast as possible); standard measures of balance, gait, and mobility including timed tandem stance (TS), tandem walk (TW, both timing and errors), timed unipedal stance (US), timed up and go (TUG), performance oriented mobility assessment (POMA), and 6-minute walk (SMW); measures of leg strength (peak knee and ankle torque and power at slow and fast speeds); self-report measures of frequent falls (>2 per 12 months), disability (Established Population for Epidemiologic Studies of the Elderly (EPESE) physical function), and confidence to avoid falls (Activity-specific Balance Confidence (ABC) Scale). Spearman and Pearson correlation, intraclass correlation coefficient, logistic regression, and linear regression were used for data analysis. RESULTS: MSL consistently predicted a number of self-report and performance measures at least as well as other standard balance measures. MSL correlations with EPESE physical function, ABC, TUG, and POMA scores; SMW; and peak maximum knee and ankle torque and power were at least as high as those correlations seen with TS, TW, or US. MSL score was associated with the risk of being a frequent faller. In addition, the six MSL directions were highly correlated (up to 0.96), and any one of the leg directions yielded similar relationships with functional measures and a history of falls. Relationships between RST and these measures were relatively modest. CONCLUSION: MSL is as good a predictor of mobility performance, frequent falls, self-reported function, and balance confidence as standard stance tests such as US. MSL simplified to one direction may be a useful clinical indicator of mobility, balance, and fall risk in older adults.

Accidental Falls↗

PubMed2003

Oxygen-uptake (VO2) kinetics and functional mobility performance in impaired older adults.

BACKGROUND: Measures of maximal oxygen uptake (VO(2max)) are limited in disabled older adults, and measures of submaximal oxygen uptake (VO(2)) may better predict functional mobility limitations. These measures may include oxygen-uptake kinetics at the onset of submaximal exercise or during recovery. We sought to determine whether the lag in oxygen uptake at the beginning of exercise (oxygen deficit) and excess oxygen uptake above rest following exercise (excess postexercise oxygen consumption) (a) predict physical performance in impaired older adults with decreased aerobic function, and (b) predict physical performance better than peak VO(2). METHODS: Two groups of community-dwelling volunteers aged 65 or older were recruited according to their performance on a maximal graded exercise test. Using the Social Security Administration criterion of disability of a peak VO(2) 18 (Unimpaired, n = 21, mean +/- SEM age 76 +/- 1 years). RESULTS: The mean +/- SEM peak VO(2) was 58% lower in the Impaired (14 +/- 1 ml/kg/min) than the Unimpaired (24 +/- 1 ml/kg/min) adults. The time constant for oxygen deficit, tc(deficit), was more than twice as high in the Impaired than the Unimpaired (p <.05), and the time constant for excess postexercise oxygen consumption, tc(EPOC), tended to be higher in the Impaired than the Unimpaired (by 43%, p =.09). Measures of submaximal oxygen-uptake kinetics were as strong or more strongly predictive of functional mobility performance than peak VO(2) in both Unimpaired and Impaired older adults. The major predictor of functional performance for the Unimpaired was a measure of oxygen deficit accruing during exercise (tc(deficit)), and for the Impaired, it was a measure of oxygen debt during recovery, tc(EPOC). CONCLUSIONS: Measurement of submaximal oxygen-uptake kinetics may provide a more practical and relevant assessment of deconditioning in frail older adults, and may eventually supplant maximal (peak) oxygen uptake as a predictor of functional disability in older adults.

Aged↗

PubMed2002

Floor-rise strategy training in older adults.

OBJECTIVES: To determine the effect of a 2-week (six-session) training intervention to improve the ability of disabled older adults to rise from the floor. DESIGN: Prospective intervention trial. SETTING: Congregate housing in Michigan. PARTICIPANTS: Subjects aged 65 and older who admitted to requiring assistance (such as from a person, equipment, or device) in performing at least one of the following mobility-related activities of daily living: transferring, walking, bathing, and toileting. INTERVENTION: Participants were randomly allocated to individual training (n = 17, mean age 81) in strategies to rise from the floor (using for example, certain key intermediate body positions) or a control chair-based flexibility intervention (n = 18, mean age 80). MEASUREMENTS: At baseline and postintervention, residents were queried regarding their rise difficulty (difficulty scale) and symptoms (symptoms scale) associated with the rise and were tested in their ability to perform timed floor-rise tasks. These tasks varied in starting position (supine vs all fours) and in use of a support to assist in rising (no support, use of an end table, use of a chair). RESULTS: Using baseline performance as the covariate, by analysis of covariance (ANCOVA), the training group showed a significant (P <.05) improvement in mean number of rise tasks completed (baseline mean 6.6, postintervention mean 7.3) versus essentially no improvement in the controls. Similarly, by ANCOVA, the training group (compared with controls) showed a significant (P <.05) improvement on the difficulty and symptoms scales. There was no intervention effect for rise time. CONCLUSIONS: A short-term, strategy-based intervention improved floor-rise ability and perceived difficulty and symptoms associated with the rise. This approach, focusing on key intermediate body positions, may be useful in training floor-rise skills, particularly in older adults at risk for falls.

Activities of Daily Living↗

PubMed2002

Effects of age and gender on toe flexor muscle strength.

BACKGROUND: Toe flexor muscle strength determines the anterior limit of the functional base of support, thereby affecting a standing individual's maximum forward reach or lean capacity. We developed a method for measuring toe flexor muscle strength in order to test the null hypotheses that it is neither affected by age nor gender. METHODS: Gender-balanced groups of 20 healthy young adults (YA) (average age 22.8 years) and 20 healthy older adults (OA) (average age 73.2 years) participated in the study. Toe flexor isometric muscle strength, calculated as the maximum volitional moment developed simultaneously in the sagittal plane by the toe flexor muscles about a reference axis through the first metatarsophalangeal joint, was measured in three trials while subjects reached forward as far as possible while standing on a force plate. RESULTS: Significant age (p <.005) and gender (p <.0005) differences were found in maximum toe flexor muscle strength. OA were 28.9% less strong than the YA [mean (SD) 13.5 (5.7) Nm and 19.0 (6.8) Nm, respectively]. The men developed 39.1% greater strength than the women [20.2 (7.1) Nm and 12.3 (3.7) Nm, respectively]. However, when normalized by body size (body weight x height), the gender difference in strength no longer reached statistical significance. Across all subjects, the anterior limit of the functional base of support was significantly correlated with toe flexor strength (coefficient of determination: 0.84). CONCLUSIONS: Toe flexor muscle strength decreased significantly with age. This decrement underlies the known age-related reduction in the functional base of support.

Adult↗

PubMed2002

Biomechanical factors affecting the peak hand reaction force during the bimanual arrest of a moving mass.

Fall-related wrist fractures are among the most common fractures at any age. In order to learn more about the biomechanical factors influencing the impact response of the upper extremities, we studied peak hand reaction force during the bimanual arrest of a 3.4 kg ballistic pendulum moving toward the subject in the sagittal plane at shoulder height. Twenty healthy young and 20 older adults, with equal gender representation, arrested the pendulum after impact at one of three initial speeds: 1.8, 2.3, or 3.0 m/sec. Subjects were asked to employ one of three initial elbow angles: 130, 150, or 170 deg. An analysis of variance showed that hand impact force decreased significantly as impact velocity decreased (50 percent/m/s) and as elbow angle decreased (0.9 percent/degree). A two segment sagittally-symmetric biomechanical model demonstrated that two additional factors affected impact forces: hand-impactor surface stiffness and damping properties, and arm segment mass. We conclude that hand impact force can be reduced by more than 40 percent by decreasing the amount of initial elbow extension and by decreasing the velocity of the hands and arms relative to the impacting surface.

Accidental Falls↗