Biomedical subjects

Eli Isakov

Publications and source records attributed to Eli Isakov.

6 recordsLinked to original sources

PubMed2006

Evaluation of methods for extraction of the volitional EMG in dynamic hybrid muscle activation.

BACKGROUND: Hybrid muscle activation is a modality used for muscle force enhancement, in which muscle contraction is generated from two different excitation sources: volitional and external, by means of electrical stimulation (ES). Under hybrid activation, the overall EMG signal is the combination of the volitional and ES-induced components. In this study, we developed a computational scheme to extract the volitional EMG envelope from the overall dynamic EMG signal, to serve as an input signal for control purposes, and for evaluation of muscle forces. METHODS: A "synthetic" database was created from in-vivo experiments on the Tibialis Anterior of the right foot to emulate hybrid EMG signals, including the volitional and induced components. The database was used to evaluate the results obtained from six signal processing schemes, including seven different modules for filtration, rectification and ES component removal. The schemes differed from each other by their module combinations, as follows: blocking window only, comb filter only, blocking window and comb filter, blocking window and peak envelope, comb filter and peak envelope and, finally, blocking window, comb filter and peak envelope. RESULTS AND CONCLUSION: The results showed that the scheme including all the modules led to an excellent approximation of the volitional EMG envelope, as extracted from the hybrid signal, and underlined the importance of the artifact blocking window module in the process. The results of this work have direct implications on the development of hybrid muscle activation rehabilitation systems for the enhancement of weakened muscles.

Journal Article↗

PubMed2006

Partition between volitional and induced forces in electrically augmented dynamic isometric muscle contractions.

Augmentation of force in partially deficient muscles can be achieved by combining electrical stimulation (ES) with their volitional activation (hybrid activation). However, while the overall torque results from the combination of the volitional and the electrically-induced torque components, the exact share between these components is not known. In a previous work, we described a method to resolve the share between the torque components under isometric static contractions. In this work, we extend our analysis to the case of isometric dynamic contractions. Five healthy subjects were instructed to contract their Tibialis Anterior (TA) muscles according to a typical gait-like dynamic torque pattern, that was visually displayed to them, while monitoring their actual ankle torque and TA electromyography (EMG). These experiments were done with and without augmented activation by means of ES. A computational algorithm was developed to dissociate the volitional from the overall torque, based on EMG signal processing and on precalibration of the dynamic system of the volitional torque versus EMG. The results indicated the quantitative relations between decrease in the volitional torque and the required increase in ES enhancement. The developed method also demonstrated what ES intensity profile is necessary to produce a desired overall torque output. This provides the means for designing an adaptive rehabilitation device for the hybrid activation of deficient muscles.

Adult↗

PubMed2004

Physical fitness and functional ability of children with intellectual disability: effects of a short-term daily treadmill intervention.

Persons with intellectual disability (ID) and associated multiple disabilities have been found by many researchers to be a population with deficient physical fitness measures, which can be explained by an inactive lifestyle, a result of lack of awareness of the positive physical effects of physical exercise, or lack of motivation for any motor activity. Various plans for physical exercise have been put forward, but many are found impractical in nonresearch-based intervention. In this study, 15 children with ID on a motor functioning level of 7-14 months used a treadmill daily for 2 months. Our findings indicated a most significant improvement in the level of physical fitness of the participants (p < 0.005), as measured by pulse at rest and during effort. The improvement in physical fitness modestly (r = 0.5), but significantly (p < 0.05), correlated with a significant (p < 0.0007) improvement in functional ability of the participating children. Further examination a year after intervention terminated showed a return to preintervention pulse-at-rest values. The research examined the treadmill training method and found that it can be operated with the support of an unskilled staff person under the supervision of a physiotherapist. The research was performed under real-life conditions, enabling relatively easy implementation in the existing conditions of special education centers. This method is a type of exercise that is easy to operate without entailing long-term budgetary expenses and might improve the health status of children with ID, who are a population at risk for developing heart-related diseases at a young age.

Child↗

PubMed2003

Constant and variable stiffness and damping of the leg joints in human hopping.

The present study deals with the stiffness and damping profiles of the leg joints during the ground-contact phase of hopping. A two-dimensional (sagittal plane) jumping model, consisting of four linked rigid segments and including the paired feet, shanks, thighs, and the head-arms-trunk segment, was developed. The segments were interconnected by damped torsional springs, representing the action of the muscles, tendons and ligaments across the joint and of the other joint tissues. A regressive function was used to express stiffness and damping, and included second-order dependence on angle and first-order dependence on angular velocity. By eliminating redundancies in the numerical solution using multicollinearity diagnostic algorithms, the model results revealed that the correct and sufficient nonlinearity for the joint stiffness is of the first order. Damping was found negligible. The stiffness profiles obtained were bell-shaped with a maximum near midstance and nonzero edge values. In predicting the joint moments, the obtained variable joint stiffnesses provided a closer agreement compared to a constant stiffness model. The maximal stiffness was found to be in linear correlation with the initial stiffness in each joint, providing support to the of muscles' preactivation strategy during the flight phase of hopping. All stiffnesses increased with increasing hopping frequency. The model presented provides an effective tool for future designing of artificial legs and robots and for the development of more accurate control strategies.

Adult↗

PubMed2003

Lower extremity amputations in chronically dialysed patients: a 10 year study.

BACKGROUND: Lower limb critical ischemia is a major problem in dialysed patients. OBJECTIVE: To evaluate the results of revascularization procedures, amputations and prosthetic rehabilitation in dialysed amputees. METHODS: In this retrospective study we examined the charts of selected dialysis patients. Forty-eight patients had undergone major amputation (4.5% of the dialysis population), and 24 patients entered the rehabilitation program. Widespread arterial calcification was common and led to falsely elevated ankle-brachial pressure indices in 9 of 14 limbs. Eight patients underwent revascularization. Subsequent major amputation was carried out 4 +/- 4.5 months after the revascularization (above knee in 5 patients and below knee in 3). Of the 16 patients who underwent primary amputation, only 2 were above-knee amputees. Seven patients with toe or metatarsal amputation went on to a major amputation 1.8 +/- 1.2 months after the distal amputation. RESULTS: No differences were found between diabetic and non-diabetic patients regarding the number of revascularization operations performed, the level of major amputation, or overall survival. Prosthetic rehabilitation was considered successful in 12 patients, partially successful in 8, and failed in 4 patients. Patient survival time was shortest in those patients with failed rehabilitation. A younger age confirmed favorable rehabilitation results, while long-standing diabetics and bilateral amputees were poor rehabilitation candidates. Patients who underwent primary amputation had more successful rehabilitation. A comparison between 24 dialysed amputees and 138 non-uremic amputees revealed similar rehabilitation results, although hospitalization time was longer in the dialysed patients. CONCLUSIONS: Early definitive therapy is essential when dealing with critical ischemia. After diagnostic angiography, proximal revascularization should be performed where feasible. Primary amputation is indicated in patients with extensive foot infection or gangrene. Prosthetic rehabilitation is warranted in most dialysed amputees.

Adult↗

PubMed1998

Dynamic loading on the human musculoskeletal system -- effect of fatigue.

OBJECTIVE: A study was conducted to investigate the effects of fatigue on the ability of human musculoskeletal system to deal with the onslaught of the heel strike initiated shock waves. DESIGN: Running on a treadmill at the anaerobic threshold level for 30 min was used to acquire the experimental data on the foot strike initiated shock waves. BACKGROUND: Muscles act to lower the bending stress on bone and to attenuate the dynamic load on human musculoskeletal system. Fatigue may diminish their ability to dissipate and attenuate loading on the system. Knowledge of the effects of fatigue on the ability of the human musculoskeletal system to attenuate the shock waves may help in design of the training procedures and exercises. METHODS: Twenty-two young healthy males participated in this study. Each one was running on the treadmill at the speed corresponding to his anaerobic threshold for 30 min. The heel strike induced shock waves were recorded every 5 min on the tibial tuberosity and sacrum. The data obtained were analyzed in both temporal and frequency domains. RESULTS: The results reveal significant increase in the dynamic loading experienced by the human musculoskeletal system with fatigue. This may be attributed to the inability of the fatigued system to provide an efficient way to attenuate shock waves. CONCLUSIONS: The analysis of the recorded signals suggests that fatigue contributes to the reduction of the human musculoskeletal system's capacity to attenuate and dissipate those shock waves. This capacity appears to be a function not only of the fatigue level, but also of the vertical location along the skeleton. RELEVANCE: Fatigue during running may affect the ability of the human musculoskeletal system to attenuate and dissipate the heel strike induced shock waves. The study of the fatigue effect on shock wave attenuation provides information that may benefit the runner.

Journal Article↗