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Biomedical subjects

D E Krebs

Publications and source records attributed to D E Krebs.

At least 19 recordsLinked to original sources
PubMed2002

The contribution of type of daily activity to loading across the hip and knee joints in the elderly.

OBJECTIVE: In the elderly, we evaluated loading across the hip or knee joints during different daily activities. METHODS: Elderly people drawn from the community entering an exercise study underwent a full kinetic and kinematics analysis of five different activities, standing, walking, arising from a chair, going downstairs and bending over. Inverse dynamic equations were used to compute forces and torques across the knees and hips during all of these activities. RESULTS: 132 elderly people, mean age 75, participated. Compressive forces across the knees and hips were, by far, the greatest vector forces and were highest during stair descent and, to a lesser extent, during walking. Compressive forces were lowest during standing. The highest moments were flexion and adduction moments, and these were maximal during stair descent. CONCLUSION: Of the five activities we studied, descending stairs was associated with the highest calculated forces and torques across the knees and hips, and that may account for its tendency to cause joint symptoms and for its possible association with osteoarthritis incidence.

Activities of Daily Living↗
PubMed2001

Kalman filter detection of blinks in video-oculography: applications for VVOR measurement during locomotion.

A Kalman filter algorithm was implemented for automatic detection of blink artifacts in video-oculography (VOG) data, and a cubic spline used to patch the eliminated data. The algorithm was tested by randomly introducing artificial blinks into eye movement data and computing the errors introduced by the patches. We also computed visual vestibulo-ocular reflex (VVOR) gain and phase in healthy and vestibulopathic subjects during a locomotor task, before and after blink removal, to demonstrate the interpretive importance of eliminating blink artifacts. The error introduced by the patched data was small (0.50+/-0.32 degrees ) and within the resolution of head angle measurements. Comparison of gain and phase shift before and after removing blinks revealed that even when calculated values are within expected limits, coherence of the VVOR signal was significantly (p=0.003) lower prior to blink removal (0.51+/-0.37) compared to that after blink removal (0.92+/-0.08). Comparison of VVOR calculations between healthy and vestibulopathic subjects (after removal of blinks) revealed that vestibulopathic subjects had significantly decreased gains (p=0.018) and increased phase shifts (p=0.009): these results agree with data reported in literature. We conclude that the Kalman filter detection and cubic spline patching algorithms are useful tools for VOG and should enable reliable VVOR measurements during unconstrained, ecologically meaningful locomotor activities.

Adult↗
PubMed2001

Lifting strategy and stability in strength-impaired elders.

STUDY DESIGN: Ninety-six subjects underwent biomechanical analysis of freestyle box lifting. OBJECTIVES: To relate lifting strategy to lower extremity muscle strength and postural stability in functionally limited elders. SUMMARY OF BACKGROUND DATA: Back pain and postural instability in elders is rampant and poorly understood. Much of the literature on lifting relates to young subjects. METHODS: Lifting strategy for 91 functionally limited elders was classified by timing of peak power in the back and knee joints. Isometric hip and knee extensor strength and postural stability were compared among strategy classifications. Postural stability was analyzed by measuring center of gravity (CG) displacement during lifting. RESULTS: Three lift strategy groups were established: back-lift, or back dominant strategy (BDS); leg-lift, or leg dominant strategy (LDS); and leg-dominant back-first mixed strategy (LDB). Subjects with relatively strong hip and knee extensors used leg dominant strategy; subjects with relatively strong knee, but weak hip, extensors used leg-dominant back-first mixed strategy; and subjects with weak hip and knee extensors used back dominant strategy. Leg dominant strategy and leg-dominant back-first mixed strategy engendered less center of gravity displacement and thus were posturally more stable than the back dominant strategy. CONCLUSION: Subjects apparently chose their lift strategy based on their hip and knee extensor strength. Weaker elders using a less stable back dominant strategy could be susceptible to falls and subsequent long bone and vertebral body fractures. Clinicians could identify at-risk elders by muscle testing. Beyond emphasizing strength and endurance exercise in elderly patients, weak elders should be taught to use a leg dominant lifting strategy, or if they are not physically able, to use a combined back/leg strategy.

Aged↗
PubMed2001

High curvature and jerk analyses of arm ataxia.

We investigated high curvature analysis (HCA) and integrated absolute jerk (IAJ) for differrentiating healthy and cerebellopathy (CB) patients performing pointing tasks. Seventeen CB patients and seventeen healthy controls were required to move a pointer at their preferred pace between two 50.8 cm laterally spaced targets while standing with theirarm extended in front of their body. HCA was used to quantify the frequency of sharp turns in the horizontal-plane (anterior-posterior and medio-lateral) velocity trajectory of the hand-held pointer. IAJ was assesssed by integration of absolute jerk (second time derivative of velocity) time histories in the anterior-posterior and medio-lateral directions. HCA scores and IAJ scores were then compared between CB patients and healthy controls; for both analyses, higher scores indicateless smooth movements. We hypothesized that CB patients would have less smooth movement trajectories than healthy controls due to upper extremity ataxia asssociated with cerebellar disease and degeneration. We found that CB patients had higher HCA scores than healthy controls (P = 0.014). Although CB patients had higher IAJ scores in both anterior-posterior (P = 0.060)and medio-lateral (P = 0.231) directions compared to the healthy controls, the differences were not significant. The difference in sensitivity between the HCA andthe IAJ analysis might be explained by primitive neural activation commands, ubiquitous though only evident with some cerebellar dysfunctions, which produce submovements which are themselves minimal jerk curves. We conclude that HCA may be a useful tool for quantifying upper extremity ataxia in CB patients performing a repeated pointing task.

Adult↗
PubMed2001

Mechanical energy analysis identifies compensatory strategies in disabled elders' gait.

Current concepts in disablement emphasize the importance of identifying mobility impairments in aging humans to enable timely intervention and, ultimately, prevent disability. Because mobility impairments are likely to result in compensatory movement strategies, recognizing and understanding those strategies may be critical in designing effective interventions for preventing disability. We sought to determine if mechanical energy methods are useful for identifying and understanding lower extremity compensatory movement strategies due to disabilities. Aleshinski's method was used to compute mechanical energy expenditure (MEE) and mechanical energy compensation (MEC) for the sagittal plane stance leg and low-back joints of healthy elders (HE) and disabled elders (DE) during preferred speed and paced (120 steps min(-1)) gait. DE subjects expended less ankle energy in late-stance and more low-back energy in mid-stance than did the HE subjects. When controlling for walking speed, the difference in ankle MEE disappeared, but mid-stance hip MEE was significantly higher for the DE subjects. Despite increased hip and low-back MEE, the DE subjects compensated hip and low-back muscles greater then HE subjects by increasing energy transferred into the pelvis, particularly when walking faster than their self-selected speed. Increased energy transfers into the pelvis during mid-stance may be a strategy used to assist in advancing and controlling the contralateral limb's swing phase. Increased trunk energy, however, may compromise dynamic stability and increase the risk of falling. We conclude that mechanical energy methods are useful for identifying and understanding compensatory movement strategies in elders with disabilities.

Adaptation, Physiological↗
PubMed2001

Mechanical energy transfer during gait in relation to strength impairment and pathology in elderly women.

OBJECTIVE: To examine the relationships among strength impairment, pathology and the mechanical energy transfers across the leg and low-back joints in a sample of frail elderly women with functional limitations. BACKGROUND: Past studies suggest mechanical energy analyses may be useful for identifying compensatory strategies used by elders during gait, but also suggest that age and strength are not the only factors that determine the extent of compensatory strategy use. METHODS: Gait data for 75 functionally limited women 60-90 years of age were analyzed. Subjects were categorized by strength and pathology diagnoses. Inverse dynamics was used to compute concentric (positive) and eccentric (negative) mechanical energy expenditures of the ankle, knee, hip and low-back during the stance phase of gait. Joint mechanical energy expenditures were compared between strength and diagnoses groups, and relationships among joint mechanical energy expenditures examined within groups. RESULTS: Weaker subjects demonstrated lower concentric ankle and eccentric knee mechanical energy expenditures, and higher eccentric low-back mechanical energy expenditures, than stronger subjects. Subjects with orthopaedic impairments demonstrated higher eccentric low-back mechanical energy expenditures than subjects with other impairments. Inverse correlations were found between ankle mechanical energy expenditures and hip and low-back mechanical energy expenditures for subjects with orthopaedic impairments. CONCLUSIONS: Elders with weak leg muscles and orthopaedic impairments increased hip and low-back mechanical energy expenditures, apparently to compensate for reduced ankle and knee mechanical energy expenditures. Further research is warranted to determine what long-term influences these compensatory strategies have on function and disability. Relevance. Mechanical energy methods could be useful for developing rehabilitative training programs to eliminate mobility impairments and avoid disablement in frail elders.fs

Adaptation, Physiological↗
PubMed2001

Vestibulopathy and age effects on head stability during chair rise.

It is unknown how vestibular dysfunction and age differentially affect balance control during functional activities. The objective of this study was to gain insight into the effects of age and vestibulopathy on head control when rising from a chair. Head relative to trunk (head-on-trunk) sagittal plane angular and linear control strategies were studied in patients with bilateral vestibular hypofunction (BVH) and in healthy subjects aged 30-80 years. A two-way analysis of variance was used to compare head-on-trunk kinematics by age (young vs elderly) and diagnosis (healthy vs BVH) at the time of liftoff from the seat. Angular control strategies differed with age but not diagnosis: young (healthy and BVH) subjects stabilized head rotations in space while elderly (healthy and BVH) subjects stabilized head rotations on the trunk. In contrast, linear control strategies differed by diagnosis but not age: BVH subjects (young and old) allowed a greater rate of head-on-trunk translation while healthy subjects (young and old) inhibited such translations. Young BVH subjects stabilized head-in-space rotations (as did young healthy subjects) without a functioning vestibular system, suggesting cervicocollic reflex and/or other sensory compensation for vestibular loss. Elderly BVH subjects stabilized head rotation with respect to the trunk, as did healthy elders, but did not stabilize head-on-trunk translations, suggesting a reliance on passive mechanical responses of the neck to sense head movements. We conclude that compensation strategies used by patients with vestibulopathy are age-dependent and appear to be more tractable in the younger BVH patient.

Adult↗
PubMed2001

Balance prosthesis based on micromechanical sensors using vibrotactile feedback of tilt.

A prototype balance prosthesis has been made using miniature, high-performance inertial sensors to measure lateral head tilt and vibrotactile elements mounted on the body to display head tilt to the user. The device has been used to study the feasibility of providing artificial feedback of head tilt to reduce postural sway during quiet standing using six healthy subjects. Two vibrotactile display schemes were used: one in which the individual vibrating elements, called tactors, were placed on the shoulders (shoulder tactors); another in which columns of tactors were placed on the right and left sides of the trunk (side tactors). Root-mean-square head-tilt angle (Tilt) and center of pressure displacement (Sway) were measured for normal subjects standing in a semi-tandem Romberg position with eyes closed, under four conditions: no balance aids; shoulder tactors; side tactors; and light touch. Compared with no balance aids, the side tactors significantly reduced Tilt (35%) and Sway (33%). Shoulder tactors also significantly reduced Tilt (44%) and Sway (17%). Compared with tactors, light touch resulted in less Sway, but more Tilt. The results suggest that healthy normal subjects can reduce their lateral postural sway using head tilt information as provided by a vibrotactile display. Thus, further testing with balance-impaired subjects is now warranted.

Adult↗
PubMed2001

Analysis of postural perturbation responses.

People with cerebellar ataxia lack lower limb coordination and dissipate sway motion slowly and inefficiently after a posture perturbation. We report a practical and low-cost "human resonance frequency test" for both laboratory and clinical use to quantify progress in balance and cerebellar rehabilitation. We assumed that the center-of-pressure (COP) oscillation rate of decay following a standing posture perturbation is directly related to resonance frequency; a more rapidly dissipating COP oscillation about the position of equilibrium indicates, by definition, more efficient postural control. We hypothesized that following successful physical rehabilitation, people with cerebellar degeneration will have a faster rate of decay of the COP response to an external perturbation. Because the COP is modulated by a synergy of trunk and lower limb motion strategies, COP decay rate may be a useful measure of lower limb coordination in people with cerebellar ataxia. The method was applied to three subjects with cerebellar ataxia before and after rehabilitation; there was good agreement between the calculated COP decay rate and conventionally used gait stability parameters providing pilot data for this simple approach.

Adaptation, Physiological↗
PubMed2001

Age-related changes in lower trunk coordination and energy transfer during gait.

The effects of aging on lower trunk (trunk-low-back joint-pelvis) coordination and energy transfer during locomotion has received little attention; consequently, there are scant biomechanical data available for comparison with patient populations whose upper body movements may be impaired by orthopaedic or neurologic disorders. To address this problem, we analyzed gait data from a cross-sectional sample of healthy adults (n = 93) between 20 and 90 yr old (n = 44 elderly, >50 yr old; n = 49 young, <50 yr old). Gait characteristics of elders were mostly typical: gait speed of elders (1.13 +/- 0.20 m/s) was significantly (P = 0.007) lower than gait speed of young subjects (1.20 +/- 0.18 m/s). Although elders had less low-back (trunk relative to pelvis) range of motion (ROM; P = 0.013) during gait than young subjects, no age-related differences were detected in absolute trunk and pelvis ROM or peak pitch angles during gait. Despite similar upper body postures, there was a strong association between age and pelvis-trunk angular velocity phase angle (r = 0.48, P < 0.001) with zero phase occurring at approximately 55 yr of age; young subjects lead with the pelvis while elderly subjects lead with the trunk. Age related changes in gait speed and low-back ROM were unable to explain the above findings. The trunk-leading strategy used by elders resulted in a sense reversal of the low-back joint power curve and increased (P = 0.013) the mechanical energy expenditure required for eccentric control of the lower trunk musculature during stance phase of gait. These data suggest an age-related change in the control of lower trunk movements during gait that preserves upper body posture and walking speed but requires a leading trunk and higher mechanical energy demands of lower trunk musculature-two factors that may reduce the ability to recover from dynamic instabilities. The behavioral and motor control aspects of these findings may be important for understanding locomotor impairment compensations in aging humans and in quantifying falls risk.

Abdominal Muscles↗
PubMed2000

Frontal plane dynamic stability and coordination in subjects with cerebellar degeneration.

Objective attempts to characterize postural control in subjects with cerebellar (Cb) pathology have focused primarily on sagittal plane responses to static standing, semi-dynamic standing, and platform perturbation. Repeated, dynamic, functional movement may provide a better opportunity to study the effects of ataxia on frontal plane postural stability. The purpose of this investigation was to quantify lateral stability using center of gravity (CG) and center of pressure (CP) movement analysis, and to examine motor responses necessary to complete a repetitive stepping task. Whole body kinematic and kinetic data were collected as patients with Cb degeneration and non-disabled volunteers repeatedly ascended forward and descended backward from a 7.6-cm step to the beat of a metronome. Cb subjects demonstrated significantly greater lateral CG instability, consistent with increased CG velocity and displacement variability in the frontal plane compared to non-disabled subjects. Significantly greater lateral CP displacement was found in subjects with Cb degeneration. Phase plot patterns from patients with Cb degeneration showed poor movement quality, indicated by abruptly changing CG phase plot patterns and abnormal CG acceleration and deceleration phases. Ataxic postural reactions were observed consistently during lateral weight shifting phases toward the stance limb. We hypothesized that lateral postural instability in Cb subjects stems from altered lower extremity intersegmental coordination and inadequate lateral CG velocity control. Frontal plane CG instability may necessitate a wide-based gait. Despite the varied neuroanatomic sites of degenerative Cb pathology, subjects with Cb pathology demonstrated similar CG movement patterns and altered motor strategies to avoid destabilization. Dynamic assessment provides important information regarding frontal plane instability not revealed by static assessment methods. These findings suggest that a dynamic, constrained stepping task effectively differentiates Cb and non-disabled volunteers, contributing to our knowledge of the effect of ataxic movement disturbances on frontal plane postural stability and lower limb coordination.

Adult↗
PubMed2000

Vestibular rehabilitation outcomes: velocity trajectory analysis of repeated bench stepping.

OBJECTIVES: To quantify vestibular rehabilitation (VR) outcomes in patients with vestibulospinal reflex pathology (VSP) using a new technique, high curvature analysis (HCA), that measures space trajectory stability. METHODS: Twelve patients with VSP and 10 healthy controls performed a repeated stepping task in a motion analysis laboratory. Patients with VSP were tested before and after a 12 week VR program. Three dimensional whole body center of gravity (CG) was captured during repeated bench stepping trials (step up forward/step down backward), and the resulting horizontal plane CG velocity trajectories were analyzed using HCA. RESULTS: VSP patients were significantly less stable than healthy subjects prior to VR (P=0.022), but these differences disappeared following VR (P=0.148). The stability of the VSP patients during the stepping task at 3 months increased significantly from baseline values (P=0.013). CONCLUSIONS: Evaluating the efficacy of VR requires analysis techniques that are sensitive to changes in stability. We conclude that HCA can be used for assessing improvements in CG stability of VSP patients while performing a repeated bench stepping activity.

Adult↗
PubMed2000

Vestibulopathy and the age effects on protective stepping during unperturbed standing.

This study examined the prevalence of protective stepping and accompanying preparatory postural responses associated with lateral weight transfer (WT) while subjects attempted to sustain stationary standing. The subjects were 92 healthy young and older adults and persons with vestibular hypofunction. Force platform and whole-body-motion recordings were used to evaluate the prevalence of stepping and WT responses during stationary standing (eyes open or closed) using a semi-tandem foot position. WT components were also evaluated for volitionally requested step initiation, and as a function of support base configuration and direction of stepping among younger subjects. Only 10% of trials by subjects with bilateral vestibular hypofunction (BVH) during semi-tandem standing with eyes closed were completed without a step, while 31% of subjects with UVH, 69% of healthy elders, and all young healthy subjects were able to stand for the entire 7-sec trials. WT responses always preceded volitional steps from a standard feet-parallel orientation but occurred in only 13% of the spontaneous steps. The prevalence of WT was influenced by the direction of volitional stepping from semi-tandem standing, but not by the initial standing width. Spontaneous stepping to maintain standing balance is a naturally occurring and prevalent behavior among older adults and persons with vestibular hypofunction during tests of quasi-static standing. Differences between volitional and spontaneous step initiation involving the prevalence of preparatory lateral WT are a complex function of motor planning, mechanical constraints, and functional context.

Adult↗
PubMed2000

Relationship among balance impairments, functional performance, and disability in people with peripheral vestibular hypofunction.

BACKGROUND AND PURPOSE: Physical therapy interventions are often based on assumed relationships among impairments, functional performance, and disability. The purposes of this study were (1) to describe balance impairments, functional performance, and disability in subjects with unilateral peripheral vestibular hypofunction (UVH) and bilateral peripheral vestibular hypofunction (BVH), (2) to examine the relationship among these factors, and (3) to determine whether disability can be explained by commonly used tests of balance and functional performance. SUBJECTS: Participants were 85 subjects (mean age=62.5 years, SD=16.5) with UVH (n=41) or BVH (n=44) diagnosed by vestibular function tests and clinical examination. METHODS: Each subject completed the Dizziness Handicap Inventory (DHI) to obtain a measure of disability. Functional performance was measured with a modified Timed Up & Go Test (TUG). Balance impairments were measured with computerized posturography and balance tests. Descriptive statistics, correlational analyses, and stepwise regressions were performed. RESULTS: Subjects with BVH had poorer balance but similar TUG scores and perceived levels of disability, as compared with subjects with UVH. Weak to moderate correlations existed among balance measurements, TUG scores, and DHI scores. Balance impairments and TUG scores together explained 78% of the variance in DHI scores of the subjects with BVH, whereas balance impairments alone explained 13% of the variance in DHI scores of the subjects with UVH. CONCLUSION AND DISCUSSION: Balance impairments and functional performance appear to be more closely related to disability in individuals with BVH as compared with those with UVH. Clinical tests of balance impairments and functional performance appear to be useful in explaining disability.

Adult↗
PubMed1999

Functional reach: does it really measure dynamic balance?

BACKGROUND: Functional reach (FR) is a new clinical measurement intended to assess dynamic balance. The purposes of this study were (1) to measure the mean FR distance in healthy elders compared with individuals with known balance impairments, (2) to analyze the extent to which FR measures dynamic balance, and (3) to describe movement strategies used during FR. METHODS: Thirteen healthy elders and 15 individuals with vestibular hypofunction (VH) were tested during FR and free gait. Whole body kinematic and kinetic data including the center of gravity (CG) and center of pressure (CP) using 11 body segments and two force plates, respectively, were collected. RESULTS: There was no difference in FR distance between healthy elders and individuals with VH. FR distance was not correlated to lateral stability measures, but was related to anterior-posterior postural control measures of FR (r = .69 to .84) in both groups. Although FR distance strongly correlated with maximum moment arm during FR in both groups, the correlations were not as strong when the subjects were then classified by movement strategy. The mean moment arm during FR was significantly less than that of free gait. CONCLUSIONS: These data suggest FR does not measure dynamic balance; healthy elders and balance-impaired individuals with vestibular dysfunction attained the same FR distance and did so without increasing the moment arm during or at the end of FR. Recording the strategy used during FR, however, may provide other valuable information necessary in addressing balance control. Clinical implications of assessing movement strategy are discussed.

Adult↗
PubMed1999

Dynamic balance control in elders: gait initiation assessment as a screening tool.

OBJECTIVE: To determine whether measurements of center of gravity-center of pressure separation (CG-CP moment arm) during gait initiation can differentiate healthy from disabled subjects with sufficient specificity and sensitivity to be useful as a screening test for dynamic balance in elderly patients. SUBJECTS: Three groups of elderly subjects (age, 74.97+/-6.56 yrs): healthy elders (HE, n = 21), disabled elders (DE, n = 20), and elders with vestibular hypofunction (VH, n = 18). DESIGN: Cross-sectional, intact-groups research design. Peak CG-CP moment arm measures how far the subject will tolerate the whole-body CG to deviate from the ground reaction force's CP; it represents dynamic balance control. Screening test cutoff points at 16 to 18 cm peak CG-CP moment arm predicted group membership. RESULTS: The magnitude of peak CG-CP moment arm was significantly greater in HE than in DE and VH subjects (p<.01) and was not different between the DE and VH groups. The peak CG-CP moment arm occurred at the end of single stance phase in all groups. As a screening test, the peak moment arm has greater than 50% sensitivity and specificity to discriminate the HE group from the DE and VH groups with peak CG-CP moment arm cutoff points between 16 and 18 cm. CONCLUSIONS: Examining dynamic balance through the use of the CG-CP moment arm during single stance in gait initiation discriminates between nondisabled and disabled older persons and warrants further investigation as a potential tool to identify people with balance dysfunction.

Aged↗
PubMed1999

Posturography does not test vestibulospinal function.

The clinical usefulness of posturography is unknown, despite its costing more than +500 per test in some areas of the United States, including Boston. We cross-sectionally and prospectively studied blinded vestibulo-ocular and vestibulospinal tests from 29 stable patients with chronic vestibular hypofunction; 22 patients were affected bilaterally (BVH), and 7 were affected unilaterally (UVH). Vestibulo-ocular function was assessed by electronystagmographic caloric stimulation and sinusoidal vertical axis rotation gains at 0.05 Hz. Vestibulospinal function was assessed by moving-platform and visualsurround posturography sensory organization tests (SOTs), paced and free gait in a gait laboratory, and clinical tests of timed gait and standing. Posturography SOT moving-platform tests 4 through 6, designed to assess vestibular function, correlated significantly (r < or = 0.72, P > or = 0.01) with vestibulo-ocular tests in 5 of 6 comparisons among BVH patients. Posturography SOT results, however, correlated poorly with other vestibulospinal measures: correlations were statistically significant for only 7 of 18 comparisons with clinical balance and gait function (r < or = 0.69, P > or = 0.01) and with 2 of 12 comparisons for gait laboratory dynamic stability measures (r < or = 0.55, P > or = 0.01) among the BVH patients. When both the platform and visual surround moved (SOT 6), however, correlations were statistically significant with static standing clinical measures (r = 0.51 to 0.69, P < 0.01) and with whole-body maximum moment arm during paced gait (r = 0.55, P < 0.01). Posturography scores for the UVH patients did not significantly correlate with any vestibulo-ocular or other vestibulospinal measures. These data indicate that among patients with BVH posturography SOT scores relate at best modestly with accepted measure of vestibulo-ocular function, less well with clinical measures of balance control, and poorly with dynamic gait-performance measures. We conclude that posturography SOT does not assess vestibulospinal function.

Adult↗