Biomedical subjects

Marjorie E Johnson

Publications and source records attributed to Marjorie E Johnson.

7 recordsLinked to original sources

PubMed2006

A probabilistic model of glenohumeral external rotation strength for healthy normals and rotator cuff tear cases.

The reigning paradigm of musculoskeletal modeling is to construct deterministic models from parameters of an "average" subject and make predictions for muscle forces and joint torques with this model. This approach is limited because it does not perform well for outliers, and it does not model the effects of population parameter variability. The purpose of this study was to simulate variability in musculoskeletal parameters on glenohumeral external rotation strength in healthy normals, and in rotator cuff tear case using a Monte Carlo model. The goal was to determine if variability in musculoskeletal parameters could quantifiably explain variability in glenohumeral external rotation strength. Multivariate Gamma distributions for musculoskeletal architecture and moment arm were constructed from empirical data. Gamma distributions of measured joint strength were constructed. Parameters were sampled from the distributions and input to the model to predict muscle forces and joint torques. The model predicted measured joint torques for healthy normals, subjects with supraspinatus tears, and subjects with infraspinatus-supraspinatus tears with small error. Muscle forces for the three conditions were predicted and compared. Variability in measured torques can be explained by differences in parameter variability.

Computer Simulation↗

PubMed2006

Using support vector machines to optimally classify rotator cuff strength data and quantify post-operative strength in rotator cuff tear patients.

Shoulder strength data are important for post-operative assessment of shoulder function and have been used in diagnosis of rotator cuff pathology. Support vector machines (SVM) employ complex analysis techniques to solve classification and regression problems. A SVM, a machine learning technique, can be used for analysis and classification of shoulder strength data. The goals of this study were to determine the diagnostic competency of SVM based on shoulder strength data and to apply SVM analysis in efforts to derive a single representative shoulder strength score. Data were taken from fourteen isometric shoulder strength measurements of each shoulder (involved and uninvolved) in 45 rotator cuff tear patients. SVM diagnostic proficiency was found to be comparable to reported ultrasound values. Improvement of shoulder function was accurately represented by a single score in pairwise comparison of the pre-operative and the 12 month post-operative group (P < 0.004). Thus, the SVM-based score may be a promising metric for summarizing rotator cuff strength data.

Artificial Intelligence↗

PubMed2005

Age-dependent differences in lateral balance recovery through protective stepping.

BACKGROUND: Aging appears to present particular problems for lateral balance stability related to falls. Protective stepping is a common strategy for maintaining balance that may be impaired with aging due to changes in neuromusculoskeletal factors. This study assessed the response patterns, kinematics, and single support hip abduction torque during lateral protective stepping for balance recovery in healthy young and elderly adults. METHODS: Ten healthy elderly and 10 younger adults received stepper-motor driven waist-pulls of bipedal stance applied pseudorandomly to either side. Stepping response strategies were quantified with force platforms and motion analysis. FINDINGS: The young responded primarily using a single lateral sidestep with the limb that was initially loaded passively by the waist-pull, while older subjects favored crossover stepping using multiple steps with more inter-limb collisions. When the elderly did use loaded side steps, the steps were longer, slower, and higher and included greater and prolonged lateral trunk motion than in the young. Overall, older subjects produced greater and less rapid stabilizing hip abduction torque during the single support phase. INTERPRETATION: Age-associated differences in lateral balance control through stepping included using a riskier recovery strategy with increased collisions between the limbs, multiple steps, altered first step characteristics and lateral trunk motion during direct sidestepping, and a generally greater support hip torque. The difficulties with lateral balance control in aging may reflect factors such as impaired hip abduction torque-time capacity and lateral trunk mobility/control. Our findings contribute additional knowledge pertaining to the problem of balance dysfunction and falls among the elderly.

Accidental Falls↗

PubMed2004

Age-related changes in hip abductor and adductor joint torques.

OBJECTIVE: To test the hypothesis that older age significantly affects hip abduction and adduction joint torque-time generating capability in women. DESIGN: Cross-sectional study, wherein subjects were tested in a supported standing position. SETTING: University human performance laboratory. PARTICIPANTS: Seventy-six healthy, adult women (38 young; 38 old). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The dependent variables were peak isometric torque and its corresponding torque rate and average peak isokinetic torque. Age group differences were assessed by analysis of variance. RESULTS: Isometric peak torques were significantly lower in older women (P</=.001) for hip abduction (34%) and adduction (24%). Decreases with age were also significant for isometric rates of torque for both muscle groups (P</=.001). Average isokinetic peak torque of hip abduction and adduction showed even greater declines in older women versus the young (P</=.001) with losses of 44% and 56%, respectively. CONCLUSIONS: The hip abductor and adductor torques showed relatively marked age-related changes. To enhance balance assessment and treatment, and to reduce the risk of falls and related injuries in older women, greater focus should be placed on understanding the role of joint torque-time changes on frontal plane balance control.

Accidental Falls↗

PubMed2003

Triggering of protective stepping for the control of human balance: age and contextual dependence.

Human stepping is a commonly executed control strategy for maintaining standing balance in the natural environment. Aging changes in the initiation triggering of both voluntary (longer latency) and perturbation-induced (shorter latency) stepping are associated with falling, and are a complex function of altered sensorimotor, neuromuscular, and cognitive system factors. The aim of this study was to determine the effect of contextual uncertainty about balance stability on the triggering of protective stepping in young and older individuals. Subjects initiated forward stepping during simple reaction time and waist-pull perturbation conditions with and without contextual uncertainty about balance stability. The results showed that, regardless of age, the initiation timing for triggering both voluntary and induced stepping was delayed substantially (100-300 ms) by the presence of balance uncertainty, and that age-associated timing differences were exacerbated with contextual uncertainty. The initiation timing of the first step liftoff for perturbation-induced stepping did not reflect entirely an immediate necessity or last resort strategy to balance instability determined directly by specific sensory input, but rather a decision to step. Moreover, the time to liftoff onset for perturbation-induced stepping was similar for the old and young with contextual certainty, and occurred 130 ms earlier for the old than for the young when balance stability was uncertain. Overall, we concluded that older individuals can retain a residual capacity to sustain stationary standing stability as a function of the prevailing task conditions, and that the reduced timing threshold with age may involve a pre-selected strategy triggered earlier by non-specific event-related sensory input rather than specific movement-related information.

Acoustic Stimulation↗

PubMed2003

Step training improves the speed of voluntary step initiation in aging.

BACKGROUND: Falls related to balance dysfunction are among the major problems of older individuals. The timing characteristics of protective voluntary stepping are critically related to effective balance recovery and are often delayed and slowed with age. This study investigated the influence of step training on the timing characteristics of voluntary step initiation in younger and older adults. METHODS: Voluntary reaction time stepping was evaluated before and after training in 12 younger adults and 8 healthy community-dwelling older adults who performed a 3-week regimen of either twice weekly induced step training (destabilizing large waist pulls) or voluntary step practice to a somatosensory reaction stimulus cue (nondestabilizing small waist pulls). RESULTS: Overall, the first step initiation times were slower for the older than for the younger subjects for both the somatosensory reaction stimulus cue task and an auditory transfer cue task. Step completion time was completed earlier for the young posttraining subjects, and older subjects generally had a longer step length. Training resulted in significant reductions in step initiation timing for the old (17%) and young (15%) subjects. Across age groups, the induced training group showed greater reductions in step initiation time than the voluntary practice group for the auditory transfer cue task. CONCLUSIONS: A 3-week period of either voluntary or waist-pull-induced step training reduced step initiation time in older and younger adults. Moreover, compared with voluntary step practice, induced step training resulted in a significantly greater improvement in reaction time stepping for an auditory transfer cue task. At least in the short term, such step training has the potential to help older adults perform more like younger adults in their step initiation timing.

Accidental Falls↗

PubMed2002

Intelligent stretching of ankle joints with contracture/spasticity.

An intelligent stretching device was developed to treat the spastic/contractured ankle of neurologically impaired patients. The device stretched the ankle safely throughout the range of motion (ROM) to extreme dorsiflexion and plantarflexion until a specified peak resistance torque was reached with the stretching velocity controlled based on the resistance torque. The ankle was held at the extreme position for a period of time to let stress relaxation occur before it was rotated back to the other extreme position. Stretching was slow at the joint extreme positions, making it possible to reach a larger ROM safely and it was fast in the middle ROM so the majority of the treatment was spent in stretching the problematic extreme ROM. Furthermore, the device evaluated treatment outcome quantitatively in multiple aspects, including active and passive ROM, joint stiffness and viscous damping and reflex excitability. The stretching resulted in considerable changes in joint passive ROM, stiffness, viscous damping and reflex gain. The intelligent control and yet simple design of the device suggest that with appropriate simplification, the device can be made portable and low cost, making it available to patients and therapists for frequent use in clinics/home and allowing more effective treatment and long-term improvement.

Adult↗