Standing-up of a healthy subject and a paraplegic patient

Quadriceps mechanomyography reflects muscle fatigue during electrical stimulus-sustained standing in adults with spinal cord injury - a proof of concept

This study investigates whether mechanomyography (MMG) produced from contracting muscles as a measure of their performance could be a proxy of muscle fatigue during a sustained functional electrical stimulation (FES)-supported standing-to-failure task. Bilateral FES-evoked contractions of quadriceps and glutei muscles, of four adults with motor-complete spinal cord injury (SCI), were used to maintain upright stance using two different FES frequencies: high frequency (HF - 35 Hz) and low frequency (LF - 20 Hz). The time at 30° knee angle reduction was taken as the point of critical "fatigue failure", while the generated MMG characteristics were used to track the pattern of force development during stance. Quadriceps fatigue, which was primarily responsible for the knee buckle, was characterized using MMG-root mean square (RMS) amplitude. A double exponential decay model fitted the MMG fatigue data with good accuracy [R2 = 0.85-0.99; root mean square error (RMSE) = 2.12-8.10] implying changes in the mechanical activity performance of the muscle's motor units. Although the standing duration was generally longer for the LF strategy (31-246 s), except in one participant, when compared to the HF strategy, such differences were not significant (p > 0.05) but suggested a faster muscle fatigue onset during HF stimulation. As MMG could discriminate between different stimulation frequencies, we speculate that this signal can quantify muscle fatigue characteristics during prolonged FES applications.

Rising from Sitting in Elderly People, Part 1: Implications of Biomechanics and Physiology

Rising from a sitting position is arguably the most frequently performed component of activities of daily living and is a prerequisite to functional mobility and subsequent meaningful activity. A difficulty with rising, commonly observed in elderly people, may either be a nuisance factor or have a serious impact on independence and quality of life; thus the occupational therapist seeks to maintain and improve this function.

This literature review is in two parts. Part 1 discusses the functional implications and importance of rising from sitting and provides a biomechanical analysis of sit-to-stand that focuses on balance and momentum. It considers the dynamic relationship between the centre of mass and the centre of pressure, the phases of rising and the factors that affect ease of rising, such as initial body position, speed of rising and age-related physiological changes. Part 2 will offer movement, environmental and motivational strategies based on the findings presented in part 1. These strategies are designed to help elderly people to compensate for difficulties in rising. The analysis and strategies proposed are also applicable to younger clients with balance or muscle strength impairments.

Evoked EMG versus muscle torque during fatiguing functional electrical stimulation-evoked muscle contractions and short-term recovery in individuals with spinal cord injury

This study investigated whether the relationship between muscle torque and m-waves remained constant after short recovery periods, between repeated intervals of isometric muscle contractions induced by functional electrical stimulation (FES). Eight subjects with spinal cord injury (SCI) were recruited for the study. All subjects had their quadriceps muscles group stimulated during three sessions of isometric contractions separated by 5 min of recovery. The evoked-electromyographic (eEMG) signals, as well as the produced torque, were synchronously acquired during the contractions and during short FES bursts applied during the recovery intervals. All analysed m-wave variables changed progressively throughout the three contractions, even though the same muscle torque was generated. The peak to peak amplitude (PtpA), and the m-wave area (Area) were significantly increased, while the time between the stimulus artefact and the positive peak (PosT) were substantially reduced when the muscles became fatigued. In addition, all m-wave variables recovered faster and to a greater extent than did torque after the recovery intervals. We concluded that rapid recovery intervals between FES-evoked exercise sessions can radically interfere in the use of m-waves as a proxy for torque estimation in individuals with SCI. This needs to be further investigated, in addition to seeking a better understanding of the mechanisms of muscle fatigue and recovery.

Longitudinal performance of a surgically implanted neuroprosthesis for lower-extremity exercise, standing, and transfers after spinal cord injury

OBJECTIVE

To investigate the longitudinal performance of a surgically implanted neuroprosthesis for lower-extremity exercise, standing, and transfers after spinal cord injury.

DESIGN

Case series.

SETTING

Research or outpatient physical therapy departments of 4 academic hospitals.

PARTICIPANTS

Subjects (N=15) with thoracic or low cervical level spinal cord injuries who had received the 8-channel neuroprosthesis for exercise and standing.

INTERVENTION

After completing rehabilitation with the device, the subjects were discharged to unrestricted home use of the system. A series of assessments were performed before discharge and at a follow-up appointment approximately 1 year later.

MAIN OUTCOME MEASURES

Neuroprosthesis usage, maximum standing time, body weight support, knee strength, knee fatigue index, electrode stability, and component survivability.

RESULTS

Levels of maximum standing time, body weight support, knee strength, and knee fatigue index were not statistically different from discharge to follow-up (P>.05). Additionally, neuroprosthesis usage was consistent with subjects choosing to use the system on approximately half of the days during each monitoring period. Although the number of hours using the neuroprosthesis remained constant, subjects shifted their usage to more functional standing versus more maintenance exercise, suggesting that the subjects incorporated the neuroprosthesis into their lives. Safety and reliability of the system were demonstrated by electrode stability and a high component survivability rate (>90%).

CONCLUSIONS

This group of 15 subjects is the largest cohort of implanted lower-extremity neuroprosthetic exercise and standing system users. The safety and efficiency data from this group, and acceptance of the neuroprosthesis as demonstrated by continued usage, indicate that future efforts toward commercialization of a similar device may be warranted.

Improving valid and deficient body segment coordination to improve FES-assisted sit-to-stand in paraplegic subjects

We investigated dynamic optimization as a tool to improve functional electrical stimulation (FES) assisted sit to stand transfers of paraplegic subjects. The objective would be to find optimal strategy for voluntary trunk movement, which would minimize hip, knee and ankle torques and demand minimal upper limb participation during the motion. Motion of the knee and the ankle were constrained by electrical stimulation. Motion capture (MOCAP) data, and signals from handle force sensors were acquired during FES-assisted rising motion of one paraplegic subject. Based on a 3 DOF dynamic model, we used an optimization algorithm in order to determine optimal trajectories in terms of minimizing joint torques for various conditions of force level applied to handles. Motion computed using the optimization process is compared with the one recorded during the experiment. Our results suggest that in order to minimize the sum of joint torques and arm effort participation, paraplegic patients should bend their body forward in order to use linear momentum of the trunk in sit off phase. This information can be used to design controller for closed-loop FES-assisted standing-up. The controller could use trunk motion to trigger legs stimulation in order to optimize body segment coordination.

Evaluation of sit-to-stand motion using a pressure distribution measurement system--effect of differences in seat hardness on sit-to-stand motion

PURPOSE

This study examined differences between standing from an ordinary seat and standing from a low-repulsion mat using a pressure distribution measurement system (BIG-MAT) and identified parameters to determine sit-to-stand (STS) motion difficulty.

METHOD

Ten healthy male volunteers (aged 30-38 years) participated. During STS motion from an ordinary seat and from a low-repulsion urethane mat, plantar surface pressure changes of both feet and the centre of pressure (COP) trajectory were recorded for 7  s. This series of tests was performed four times in each subject. Left and right pressure changes and COP changes were evaluated. Differences in the measurements between the low-repulsion mat and the ordinary seat were compared using the paired t-test.

RESULTS

COP changes were similar to those previously reported. Time from hindfoot peak to forefoot peak was significantly shorter with the ordinary chair than with the mat (p < 0.05). Percent change in forefoot pressure at forefoot peak and hindfoot peak (p < 0.01) and percent change in forefoot pressure at forefoot peak and stabilisation (p < 0.05) were significantly different.

CONCLUSIONS

Time from hindfoot peak to forefoot peak and percent change in forefoot pressure at forefoot peak and hindfoot peak were the best indicators of STS motion difficulty.

Chronic stability and selectivity of four-contact spiral nerve-cuff electrodes in stimulating the human femoral nerve

This study describes the stability and selectivity of four-contact spiral nerve-cuff electrodes implanted bilaterally on distal branches of the femoral nerves of a human volunteer with spinal cord injury as part of a neuroprosthesis for standing and transfers. Stimulation charge threshold, the minimum charge required to elicit a visible muscle contraction, was consistent and low (mean threshold charge at 63 weeks post-implantation: 23.3 +/- 8.5 nC) for all nerve-cuff electrode contacts over 63 weeks after implantation, indicating a stable interface with the peripheral nervous system. The ability of individual nerve-cuff electrode contacts to selectively stimulate separate components of the femoral nerve to activate individual heads of the quadriceps was assessed with fine-wire intramuscular electromyography while measuring isometric twitch knee extension moment. Six of eight electrode contacts could selectively activate one head of the quadriceps while selectively excluding others to produce maximum twitch responses of between 3.8 and 8.1 N m. The relationship between isometric twitch and tetanic knee extension moment was quantified, and selective twitch muscle responses scaled to between 15 and 35 N m in tetanic response to pulse trains with similar stimulation parameters. These results suggest that this nerve-cuff electrode can be an effective and chronically stable tool for selectively stimulating distal nerve branches in the lower extremities for neuroprosthetic applications.

Standing-up robot: an assistive rehabilitative device for training and assessment

In this paper a robotic assistive device is presented, aimed at assisting physically impaired individuals when rising from a sitting to a standing position. The robotic device is designed as a three degrees of freedom (3-DOF) mechanism supporting the subject under the buttocks. The device is driven by an electrohydraulic servosystem capable of operating in multiple control modes. It is instrumented with a sensory system providing information about the standing-up parameters. Evaluation of the standing up assistive device was accomplished in robot-supported rising trials of a paraplegic subject. The experiments demonstrated that stable risings in different standing - up manoeuvres were achieved. The measurement results revealed the role of the arm support and the support of the artificially evoked moments in the paralysed lower extremities during rising. The results show that the device can be used efficiently for training and evaluation of standing up manoeuvres.

Gait training after stroke: a pilot study combining a gravity-balanced orthosis, functional electrical stimulation, and visual feedback

RATIONALE

This case report describes the application of a novel gait retraining approach to an individual with poststroke hemiparesis. The rehabilitation protocol combined a specially designed leg orthosis (the gravity-balanced orthosis), treadmill walking, and functional electrical stimulation to the ankle muscles with the application of motor learning principles.

CASE

The participant was a 58-year-old man who had a stroke more than three years before the intervention. He underwent gait retraining over a period of five weeks for a total of 15 sessions during which the gravity compensation provided by the gravity-balanced orthosis and visual feedback about walking performance was gradually reduced.

OUTCOMES

At the end of five weeks, he decreased the time required to complete the Timed Up and Go test; his gait speed increased during overground walking; gait was more symmetrical; stride length, hip and knee joint excursions on the affected side increased. Except for gait symmetry, all other improvements were maintained one month post-intervention.

CONCLUSIONS

This case report describes possible advantages of judiciously combining different treatment techniques in improving the gait of chronic stroke survivors. Further studies are planned to evaluate the effectiveness of different components of this training in both the subacute and chronic stages of stroke recovery.

Standing after spinal cord injury with four-contact nerve-cuff electrodes for quadriceps stimulation

This paper describes the performance of a 16-channel implanted neuroprosthesis for standing and transfers after spinal cord injury including four-contact nerve-cuff electrodes stimulating the femoral nerve for knee extension. Responses of the nerve-cuffs were stable and standing times increased by 600% over time-matched values with a similar eight-channel neuroprosthesis utilizing muscle-based electrodes on vastus lateralis for knee extension.

Human voluntary activity integration in the control of a standing-up rehabilitation robot: A simulation study

The paper presents a novel control approach for the robot-assisted motion augmentation of disabled subjects during the standing-up manoeuvre. The main goal of the proposal is to integrate the voluntary activity of a person in the control scheme of the rehabilitation robot. The algorithm determines the supportive force to be tracked by a robot force controller. The basic idea behind the calculation of supportive force is to quantify the deficit in the dynamic equilibrium of the trunk. The proposed algorithm was implemented as a Kalman filter procedure and evaluated in a simulation environment. The simulation results proved the adequate and robust performance of "patient-driven" robot-assisted standing-up training. In addition, the possibility of varying the training conditions with different degrees of the subject's initiative is demonstrated.

Effects of activation pattern on nonisometric human skeletal muscle performance

During volitional muscle activation, motor units often fire with varying discharge patterns that include brief, high-frequency bursts of activity. These variations in the activation rate allow the central nervous system to precisely control the forces produced by the muscle. The present study explores how varying the instantaneous frequency of stimulation pulses within a train affects nonisometric muscle performance. The peak excursion produced in response to each stimulation train was considered as the primary measure of muscle performance. The results showed that at each frequency tested between 10 and 50 Hz, variable-frequency trains that took advantage of the catchlike property of skeletal muscle produced greater excursions than constant-frequency trains. In addition, variable-frequency trains that could achieve targeted trajectories with fewer pulses than constant-frequency trains were identified. These findings suggest that similar to voluntary muscle activation patterns, varying the instantaneous frequency within a train of pulses can be used to improve muscle performance during functional electrical stimulation.

Neuromuscular electrical stimulation in neurorehabilitation

This review provides a comprehensive overview of the clinical uses of neuromuscular electrical stimulation (NMES) for functional and therapeutic applications in subjects with spinal cord injury or stroke. Functional applications refer to the use of NMES to activate paralyzed muscles in precise sequence and magnitude to directly accomplish functional tasks. In therapeutic applications, NMES may lead to a specific effect that enhances function, but does not directly provide function. The specific neuroprosthetic or "functional" applications reviewed in this article include upper- and lower-limb motor movement for self-care tasks and mobility, respectively, bladder function, and respiratory control. Specific therapeutic applications include motor relearning, reduction of hemiplegic shoulder pain, muscle strengthening, prevention of muscle atrophy, prophylaxis of deep venous thrombosis, improvement of tissue oxygenation and peripheral hemodynamic functioning, and cardiopulmonary conditioning. Perspectives on future developments and clinical applications of NMES are presented.

Transition from sitting to standing after trans-femoral amputation

Standing up is an important and common daily activity. It is essential for independence and a prerequisite for walking. Many elderly and many subjects with impairments have problems with transition from sitting to standing. The aim of the present study was to determine whether there was any difference between the characteristics of standing up in trans-femoral amputees and healthy subjects. Five young trans-femoral amputees and five healthy subjects were included in the study. They were asked to stand up. The body motion was recorded using an Optotrak contactless optical system. The force and moment vectors exerted on the seat were recorded by a JR3 six-axis robot wrist sensor. The force under the feet was recorded by two AMTI force plates. The trans-femoral amputees were found to stand up more slowly than the healthy subjects. The angles of the hip, knee, and ankle joints on the amputated side were different from the angles on the healthy side or in the healthy subjects. There was also a great difference in loading between the healthy and the prosthetic foot. It can be concluded that there are differences in standing up between the trans-femoral amputees and the healthy subjects. These differences may indicate a reason for problems many elderly trans-femoral amputees face when standing up.

Nonlinear modeling of FES-supported standing-up in paraplegia for selection of feedback sensors

This paper presents analysis of the standing-up manoeuvre in paraplegia considering the body supportive forces as a potential feedback source in functional electrical stimulation (FES)-assisted standing-up. The analysis investigates the significance of arm, feet, and seat reaction signals to the human body center-of-mass (COM) trajectory reconstruction. The standing-up behavior of eight paraplegic subjects was analyzed, measuring the motion kinematics and reaction forces to provide the data for modeling. Two nonlinear empirical modeling methods are implemented--Gaussian process (GP) priors and multilayer perceptron artificial neural networks (ANN)--and their performance in vertical and horizontal COM component reconstruction is compared. As the input, ten sensory configurations that incorporated different number of sensors were evaluated trading off the modeling performance for variables chosen and ease-of-use in everyday application. For the purpose of evaluation, the root-mean-square difference was calculated between the model output and the kinematics-based COM trajectory. Results show that the force feedback in COM assessment in FES assisted standing-up is comparable alternative to the kinematics measurement systems. It was demonstrated that the GP provided better modeling performance, at higher computational cost. Moreover, on the basis of averaged results, the use of a sensory system incorporating a six-dimensional handle force sensor and an instrumented foot insole is recommended. The configuration is practical for realization and with the GP model achieves an average accuracy of COM estimation 16+/-1.8 mm in horizontal and 39+/-3.7 mm in vertical direction. Some other configurations analyzed in the study exhibit better modeling accuracy, but are less practical for everyday usage.

Synthesis of standing-up trajectories using dynamic optimization

Dynamic optimization as a tool to compute standing-up trajectories was investigated. Sit-to-stand manoeuvres in five intact persons and five trans-femoral amputees were measured. Movements and ground reaction forces acting on the body were recorded. A five-segment 3D dynamic model of standing-up was developed. In each particular subject, the optimization criterion which yielded trajectories that best resemble the measured standing-up movement was determined. Since the intact persons used considerably different criteria in choosing the standing-up trajectories than the amputees, the optimal trajectories were computed by minimizing cost functionals (CF) with distinctive structures for each group of individuals. In intact persons, a unique cost functional was found which yielded realistic standing-up manoeuvres. In amputees, subject-specific sets of parameters indicating slightly different preferences in optimizing the effort of particular muscle groups were used.

Joint torques during sit-to-stand in healthy subjects and people with Parkinson's disease

OBJECTIVES

To compare lower limb joint torques during sit-to-stand in normal elderly subjects and people with Parkinson's disease, using a developed biomechanical model simulating all phases of sit-to-stand.Design. A cross-sectional study utilizing a Parkinsonian and a control group.

BACKGROUND

Subjects with Parkinson's disease were observed to experience difficulty in performing sit-to-stand. The developed model was used to calculate the lower limb joint torques in normal elderly subjects and subjects with Parkinson's disease, to delineate possible causes underlying difficulties in initiating sit-to-stand task.

METHODS

Six normal elderly subjects and seven age-matched subjects with Parkinson's disease performed five sit-to-stand trials at their self-selected speed. Anthropometric data, two-dimensional kinematic and foot-ground and thigh-chair reactive forces were used to calculate, via inverse dynamics, the joint torques during sit-to-stand in both before and after seat-off phases. The difference between the control and Parkinson's disease group was analysed using independent t-tests.

RESULTS

Both control and Parkinson's disease groups had a similar joint kinematic pattern, although the Parkinson's disease group demonstrated a slower angular displacement. The latter subjects produced significantly smaller normalized hip flexion torque and presented a slower torque build-up rate than the able-bodied subjects (P<0.05).

CONCLUSION

Slowness of sit-to-stand in people with Parkinson's disease could be due to a reduced hip flexion joint torque and a prolonged rate of torque production.

Standing-up exerciser based on functional electrical stimulation and body weight relief

The goal of the present work was to develop and test an innovative system for the training of paraplegic patients when they are standing up. The system consisted of a computer-controlled stimulator, surface electrodes for quadricep muscle stimulation, two knee angle sensors, a digital proportional-integrative-derivative (PID) controller and a mechanical device to support, partially, the body weight (weight reliever (WR)). A biomechanical model of the combined WR and patient was developed to find an optimum reference trajectory for the PID controller. The system was tested on three paraplegic patients and was shown to be reliable and safe. One patient completed a 30-session training period. Initially he was able to stand up only with 62% body weight relief, whereas, after the training period, he performed a series of 30 standing-up/sitting-down cycles with 45% body weight relief. The closed-loop controller was able to keep the patient standing upright with minimum stimulation current, to compensate automatically for muscle fatigue and to smooth the sitting-down movement. The limitations of the controller in connection with a highly non-linear system are considered.

Trunk movement in Parkinson's disease during rising from seated position

Parkinson's disease (PD) is associated with particular difficulties rising from a seated position. Little is known about the mechanisms of sit-to-stand in this condition. We sought to define trunk movement during sit-to-stand in a group of patients with PD. Six patients and seven normal volunteers were studied using a six camera ELITE motion analysis system (BTS, Milan, Italy), which permitted data collection in the coronal, sagittal, and transverse planes. Retroreflective markers were positioned along the spine at C7, T3, T6, T9, T12, L3, and the sacrum. Whole-trunk kinematics and the movement at the six different trunk markers were recorded during rising. PD patients have a significantly greater degree of trunk flexion than controls, showing a significant increase in angular velocity of the trunk in the sagittal plane. The total range of movement of trunk rotation was significantly smaller in the PD group, but lateral movement in the trunk was greater than normal. These data suggest that patients with early PD compensate for their difficulties rising from a chair by generating greater trunk flexion at higher angular velocity, thus developing greater forward momentum. This process results in a decrease in the duration of the unstable transitional phase of sit-to-stand, allowing PD patients to reach the upright position as easily and safely as possible. Small rotational movements are an effective way to maintain the centre of mass within the base of support during sit-to-stand. This mechanism appears to be denied to the PD patients who may use increased movements in the coronal plane as an alternative strategy.

The use of selective electrical stimulation of the quadriceps to improve standing function in paraplegia

Persons with spinal cord injury (SCI) can benefit significantly from functional neuromuscular stimulation (FNS) systems for standing if manual tasks can be performed while upright. Using FNS to sufficiently activate the knee extensors to rise from a sitting position often results in inadvertent activation of the rectus femoris and/or sartorius, which flex the hip. In this study, intramuscular electrodes implanted in the vastus lateralis and medialis of four subjects with SCI were used to activate these muscles individually and simultaneously to measure knee extension moment. Support forces applied to the arms and feet were measured while upright to quantify the effects of recruiting rectus femoris and/or sartorius. In three of the four subjects, vastus lateralis, by itself, generated adequate knee extension moment for rising from a chair and to maintain static standing. Simultaneous activation of the vastus lateralis and medialis using a bifurcated electrode generated adequate knee extension moment in one subject, and was within 10% of the required moment in another. While upright, activation of the rectus femoris resulted in arm support force increases of 4-11% body weight, while deactivation resulted in arm support force decreases of 6-9% body weight. The results indicate that selective activation of the vastus lateralis, individually or in combination with vastus medialis, can improve current FNS standing systems by reducing the arm support forces required to remain upright.

Patient-driven control of FES-supported standing up and sitting down: experimental results

A patient-driven control strategy for standing-up and sitting-down was experimentally tested on two paraplegic patients by applying functional electrical stimulation (FES) to the quadriceps muscle. The strategy--also known as "patient-driven motion reinforcement" (PDMR)--was developed by computer simulations reported in a former study. It is based on an inverse dynamic model (IDM) that predicts the stimulation pattern required to maintain the movement as it is initiated by the patient's voluntary effort. For reasons of safety and weight relief, the movement was supported by a seesaw construction. After some practice the patients were able to influence the stimulator output and to control the movement by their voluntary effort. Consequently, no pre-programmed reference trajectory was required. As a positive side effect, upper body effort could be minimized compared to trials without FES. To achieve a satisfactory performance of the PDMR controller a careful parameter identification of the inverse dynamic model was fundamental.

Activation of human quadriceps femoris muscle during dynamic contractions: effects of load on fatigue

Muscle fatigue is both multifactorial and task dependent. Electrical stimulation may assist individuals with paralysis to perform functional activities [functional electrical stimulation (FES), e.g., standing or walking], but muscle fatigue is a limiting factor. One method of optimizing force is to use stimulation patterns that exploit the catchlike property of skeletal muscle [catchlike-inducing trains (CITs)]. Although nonisometric (dynamic) contractions are important parts of both normal physiological activation of skeletal muscles and FES, no previous studies have attempted to identify the effect that the load being lifted by a muscle has on the fatigue produced. This study examined the effects of load on fatigue during dynamic contractions and the augmentation produced by CITs as a function of load. Knee extension in healthy subjects was electrically elicited against three different loads. The highest load produced the least excursion, work, and average power, but it produced the greatest fatigue. CIT augmentation was greatest at the highest load and increased with fatigue. Because CITs were effective during shortening contractions for a variety of loads, they may be of benefit during FES applications.

Effects of activation frequency on dynamic performance of human fresh and fatigued muscles

The force-frequency relationship for an individual muscle depends on the fatigue state, the length at which it is activated, and the muscle's activation history. The relationship among stimulation frequency and dynamic (nonisometric) muscle performance measurements (e.g., excursion, work, peak power, and average power) has not been reported. The purpose of this study was to identify the relationship between stimulation frequency and dynamic performance measurements for fresh and fatigued muscles. Constant-frequency and catchlike-inducing trains (CFT and CIT, respectively) were tested. When fresh, interpulse intervals of 40-50 ms [20-25 pulses/s (pps)] produced maximum performance for CFTs. For CITs, maximum performance occurred at interpulse intervals of 50-60 ms ( approximately 16-20 pps). Generally, CFTs produced slightly greater performance than did CITs. When fatigued, however, CITs produced greater performance than did CFTs. Maximum performance for CFTs occurred at interpulse intervals of 20-40 ms (25-50 pps) and at 30-50 ms (20-33 pps) for CITs. Enhancement of performance by CITs when fatigued may be due to less susceptibility to impairments in excitation-contraction coupling and greater ability to maintain rates of rise of force than CFTs.

Biomechanical analysis of sit-to-stand transfer in healthy and paraplegic subjects

OBJECTIVE

An experimental study of the sit-to-stand transfer in healthy adults with/without arm-support and in paraplegic patients with/without electrical stimulation of the quadriceps muscles was performed. The study was aimed to compare the joint torques, momentum transfer hypothesis, and stability of the sit-to-stand transfer in the healthy and paraplegic subjects.

METHODS

A planar 3-linkage rigid body model was used to compute the body-segmental linear momentum and the reaction forces and torques at the joints from measured data.

RESULTS

In healthy subjects the arm-support enlarged the support base of the body and thus, increased the postural stability. Strong arm-assistance reduced the maximum hip and knee joint torques by more than 50%. It was observed that the healthy participants rising with arm-support used momentum transfer to facilitate the transition from sitting to standing. The paraplegic participants did not apply the momentum transfer strategy and the sit-to-stand transfer was accomplished in a quasi-static manner. Stimulating the quadriceps, the legs could participate partly in the movement dynamics.

CONCLUSION

Our results indicate that some significant differences exist between the maneuver applied by the paraplegic patients to stand up and the strategies used by the healthy adults rising with arm-support.

RELEVANCE

Analysis of the biomechanical factors underlying the sit-to-stand activity is essential in the design of competent closed-loop neuroprosthesis controllers which assist paraplegic patients during rising.

Model-based development of neuroprosthesis for paraplegic patients

In paraplegic patients with upper motor neuron lesions the signal path from the central nervous system to the muscles is interrupted. Functional electrical stimulation applied to the lower motor neurons can replace the lacking signals. A so-called neuroprosthesis may be used to restore motor function in paraplegic patients on the basis of functional electrical stimulation. However, the control of multiple joints is difficult due to the complexity, nonlinearity, and time-variance of the system involved. Furthermore, effects such as muscle fatigue, spasticity, and limited force in the stimulated muscle further complicate the control task. Mathematical models of the human musculoskeletal system can support the development of neuroprosthesis. In this article a detailed overview of the existing work in the literature is given and two examples developed by the author are presented that give an insight into model-based development of neuroprosthesis for paraplegic patients. It is shown that modelling the musculoskeletal system can provide better understanding of muscular force production and movement coordination principles. Models can also be used to design and test stimulation patterns and feedback control strategies. Additionally, model components can be implemented in a controller to improve control performance. Eventually, the use of musculoskeletal models for neuroprosthesis design may help to avoid internal disturbances such as fatigue and optimize muscular force output. Furthermore, better controller quality can be obtained than in previous empirical approaches. In addition, the number of experimental tests to be performed with human subjects can be reduced. It is concluded that mathematical models play an increasing role in the development of reliable closed-loop controlled, lower extremity neuroprostheses.

Functional electrical stimulation and arm supported sit-to-stand transfer after paraplegia: a study of kinetic parameters

The sit-to-stand transfer of paraplegic patients using functional electrical stimulation (FES) of the knee extensors and arm support was analyzed in the study. In a group of 8 completely paralyzed subjects who were trained FES users, kinematic and dynamic parameters were recorded during standing up trials. A contactless optical system was used to assess the human body motion. The forces acting on the human body were measured by multi-axis force transducers. On the basis of recursive Newton-Euler inverse dynamic analysis, the forces and torques acting on the body joints were calculated. The joint moments in the lower and upper extremities during the sit-to stand task are presented in this paper. The influences of the patient's strength, FES training duration, and rising strategy on the joint loading are discussed.

Bone fracture during electrical stimulation of the quadriceps in a spinal cord injured subject

We report a fracture through the lateral femoral condyle of a paraplegic subject caused by electrical stimulation (ES). The subject was a 50-year-old man who 4 years earlier had sustained a complete spinal cord injury (SCI) at level T6. The fracture occurred during ES-induced measurement of maximal isometric torque of the quadriceps with the knee flexed at an angle of 90 degrees. ES was delivered through surface electrodes with biphasic square wave pulses from a constant current stimulator. The torque was calculated to be 93Nm, corresponding to 20.8kg at the ankle. The regional bone mineral density of the entire lower extremities was .83g/cm2, corresponding to 60% of sex- and age-matched able-bodied reference values. Several factors are suspected to have contributed to the fracture: maximal ES in combination with a muscle spasm, severe osteoporosis, increased muscular strength induced by regular ES cycling (twice a week), and testing position with the knee locked in 90 degrees flexion. The risk of fracture as well as various precautions are discussed and should be taken into consideration in future studies.

Patient-driven control of FES-supported standing up: a simulation study

To control movements aided by functional electrical stimulation (FES) in paraplegic patients, stimulation of the paralyzed lower limbs might be adjusted in response to voluntary upper body effort. Recently, Donaldson and Yu proposed a theoretical approach, called "control by handle reactions of leg muscle stimulation" (CHRELMS), in which stimulation of the lower limbs depends on upper body effort, i.e., body posture and recorded hand reactions, and is aimed to minimize arm forces during standing up and standing. An alternative strategy is presented in this paper, which accounts for voluntary upper body effort as well, but does not require estimation of hand reactions. The objective of this study is to test both strategies by applying them to a generic two-dimensional (2-D) neuromusculoskeletal model. The model takes into account the major properties of muscle and segmental dynamics during FES-supported standing-up movements of a paraplegic patient. In comparison to standing up without FES-support, both closed-loop strategies yield satisfying standing-up movements although no reference information (e.g., a desired trajectory) is required. Arm forces can be significantly reduced. Using the model to optimize the controller, time-consuming and strenuous trial-and-error experimentation could be avoided. However, final experimental studies are planned to verify the presented strategies.

Switching curve controller for FES-assisted standing up and sitting down

A low-level, closed-loop controller for FES-assisted standing up and sitting down is described. If, for able-bodied individuals, when standing up and sitting down, the knee angular velocity is plotted against knee angle, consistent phase-plane trajectories are produced. The bang-bang controller uses a model of this trajectory as a switching curve. The design rationale for the controller was the desire to avoid injuries that might occur if knee-locking on standing up and seat-contact on sitting down are not adequately controlled. This switching curve controller (SCC) was incorporated within a hierarchical, finite state control scheme, with electrical stimulation applied bilaterally to the knee extensors. The SCC was tested in a pilot study on a female volunteer with paraplegia (T5/6 ASIA A) and evaluated against an unramped, open-loop controller (OLC). The vertical hand forces and knee angles were measured. The subject was able to achieve standing up and sitting down safely using both controllers. For standing up, the SCC was not found to offer any quantifiable advantages over the OLC and was found to increase the hand force by 8.4%. In contrast, for sitting down the SCC was found to reduce the knee angular velocities as the subject approached the seat by 27%, demonstrating a safer, softer landing.

A perspective on the control of FES-supported standing

This special section is about the control of electrical stimulators to restore standing functions to paraplegics. It addresses several important topics regarding the interactions of the intact central nervous systems (CNS) with the artificial control system. The topics are as follows: how paraplegics use their arms to help themselves stand up with functional electrical stimulation (FES); the user-driven artificial control of FES-supported standing up; a controller which is promising for the control of sitting down; the application of reinforcement machine learning for the controllers of standing up; arms-free standing with voluntary upper body balancing and artificially controlled ankle stiffness; and cognitive feedback in balancing. This Commentary introduces the papers in this section and relates them to earlier research.

New look at force-frequency relationship of human skeletal muscle: effects of fatigue

A muscle does not have a unique force-frequency relationship; rather, it is dynamic and depends on the activation history of muscle. The purpose of this study was to investigate the force-frequency relationship of nonfatigued and fatigued skeletal muscle with the use of both catchlike-inducing trains (CITs) that exploited the catchlike property of skeletal muscle and constant-frequency trains (CFTs). Quadriceps femoris muscles were studied during isometric contractions in twelve healthy subjects (5 females, 7 males). Both the peak force and force-time integrals produced in response to each stimulation train were analyzed. Compared with nonfatigued muscles, higher frequencies of activation were needed to produce comparable normalized peak forces when the muscles were fatigued (i.e., a "rightward" shift in the force-frequency relationship) for both the CFTs and the CITs. When using the normalized force-time integral to measure muscle performance, the CFTs required slightly higher frequencies to produce comparable normalized forces from fatigued muscles, but the CITs did not. Furthermore, when the muscles were fatigued, the CITs produced greater peak forces and force-time integrals than all comparable CFTs with frequencies </=20 pps. In general, the lower the frequency the greater the augmentation produced by the CITs. In addition, the CIT that elicited the greatest force-time integral produced a 25% greater force-time integral than the best CFT. Because the CITs augmented forces across a wide range of physiological relevant activation rates, these results may have important clinical implications when using electrical stimulation to aid patients with paralysis. The results of this study contribute to our understanding of the relationship between the activation pattern of a muscle and the force output produced.

New quantitative and qualitative measures on functional mobility prediction for stroke patients

The purpose of this study was to explore whether we could provide supportive laboratory evidence for clinical observations that a stroke patient has lost functional mobility/locomotion capability based on dynamic balance responses (centre of pressure, COP sway patterns) and motor control activities (EMG patterns) during the motor task of sit-to-stand. A computerized controlled dynamic postural control assessment system was developed and used in this study. Various dynamic balance indices were introduced and derived from COP sway patterns expressed in four domains (i.e. space, time, force, and frequency). Motor control was assessed by multi-channel surface electromyography of each side of the lower limb during the same motor task. The functional mobility capability was evaluated using a traditional FIM method. Fourteen stroke patients with right hemiplegia and nine healthy elderly were recruited as the experimental and control groups respectively. Muscle activity was recorded for quadriceps, hamstrings, anterior tibialis, and triceps surae muscles and used for analysis. Centre of pressure sway patterns and ground reaction forces were registered. All signals were synchronized at 'seat-off'. Surface electromyographic patterns of activities recorded during sit-to-stand and dynamic balance indices computed from centre of pressure sway patterns were categorized and compared with the functional mobility scores. The results show that both the motor control patterns and dynamic balance indices correlated well to the extent of mobility impairment evaluated using the traditional FIM method. An important conclusion for rehabilitation medicine is that the functional mobility capability of stroke patients may be quantified analytically using dynamic balance indices and visualized graphically through EMG motor patterns.

Reduction of the fatigue-induced force decline in human skeletal muscle by optimized stimulation trains

OBJECTIVE

To identify the stimulation pattern that optimizes the force-time integral produced during isometric contractions of fatigued human skeletal muscle.

DESIGN

Twelve healthy subjects with no history of lower extremity orthopedic problems voluntarily participated.

RESULTS

The primary findings were that (1) the optimized trains showed augmentation only from fatigued muscles and (2) a simple stimulation pattern, containing one brief (5msec) initial interpulse interval, produced the greatest force-time integrals and rates of rise of force. With muscle fatigue, the rate of rise of force of the constant-frequency train slowed, whereas the rate of rise of force of the optimized trains remained unchanged. This difference in the rate of rise of force may explain why the optimized trains, which take advantage of the catchlike property of skeletal muscle, are able to augment forces from fatigued muscles when compared with the constant-frequency train.

CONCLUSIONS

These results may have important clinical implications when using brief trains of electric stimulation to aid patients in performing functional movements and contribute to our understanding of the relationship between the activation pattern of a muscle and the force output produced.

Comparison of balance responses and motor patterns during sit-to-stand task with functional mobility in stroke patients

This study was undertaken to explore whether we could provide supportive laboratory evidence for the clinical observations that a stroke patient has lost functional mobility/locomotion capability based on dynamic balance responses (center of force sway patterns) and motor control activities (electromyography patterns) during the motor task of sit-to-stand. A computerized controlled dynamic postural control assessment system was developed and used in this study. Various dynamic balance indexes were introduced and derived from center of force sway patterns expressed in four domains (space, time, force, and frequency). Motor control was assessed by multichannel surface electromyography of each side of the lower limb during the same motor task. The functional mobility capability was evaluated using the traditional FIM method. Fourteen stroke patients with right hemiplegia and nine healthy elderly individuals were recruited as the experimental and control groups, respectively. Muscle activity was recorded for quadriceps, hamstrings, anterior tibialis, and triceps surae muscles and was used for analysis. Center of force sway patterns and ground reaction forces were registered. All signals were synchronized at "seat-off." Surface electromyographic patterns of activities recorded during sit-to-stand and dynamic balance indexes computed from center of force sway patterns were categorized and compared with the functional mobility scores. Results show that both the motor control patterns and dynamic balance indexes correlated well to the extent of mobility impairment evaluated using the traditional FIM method. An important conclusion for rehabilitation medicine is that the functional mobility capability of stroke patients may be expressed numerically using dynamic balance indexes and visualized graphically through electromyographic motor patterns.

Analysis of the sit-stand-sit movement cycle in normal subjects

OBJECTIVE: This study aimed to establish a basis of descriptive data for the sit-stand-sit movement cycle in 50 normal subjects, 25 male and 25 female, aged between 20.1 and 78.3 years (mean age 46.8 years). DESIGN: A descriptive design was employed to establish the characteristics of the activity in normal subjects. BACKGROUND: Research has been carried out into kinetic and kinematic characteristics of the sit-to-stand movement, but few researchers have considered stand-to-sit. Most studies have involved small samples, subjects with pathology, or elderly subjects, so a baseline of data from normal subjects has not yet been established. METHOD: Linear displacement and acceleration of the trunk and angular displacement of the knee were recorded simultaneously within the same temporal framework. The measurement system consisted of a vector stereograph, and triaxial accelerometers located at the level of C(7), and an electrogoniometer located at the lateral aspect of the knee. Subjects rose from and descended to the seated position a total of six times at their own self-selected speed. Numerical data were subjected to descriptive analysis, matched-pairs t tests and Pearson's rho correlations. RESULTS: Mean values for the time to rise was 1.91 s and to descend was 1.97 s. Forward lean velocity was greater during rising than descending (P < 0.001), and recovery velocity was greater during descending than rising (P < 0.001). Temporal contributions of forward lean and vertical displacement and the period of overlap between them were identified, and relationships between acceleration and temporal events and components were established. Differences existed among groups, involving primarily the elderly groups and occurring during the rising phase. CONCLUSIONS: This study has proposed a baseline of descriptive data in normal subjects for the sit-stand-sit movement cycle. RELEVANCE: In practical and clinical applications of information gained from analysis of functional activities, establishment of what is accepted as 'normal' is necessary before abnormalities can be identified and analysed, and intervention implemented and evaluated. This study provides that basis.

Femoral neck fractures in the elderly patient: a preventable injury

There is growing evidence that many fractures of the femoral neck in the elderly occur spontaneously because of stresses imposed on osteoporotic bone, rather than because of the trauma of the fall. A case of a spontaneous femoral neck fracture (Garden type IV) in an elderly woman with osteoporosis is presented. Early detection and medical management of osteoporosis complemented with assistive technology could have prevented this common injury.

Restoration and analysis of standing-up in complete paraplegia utilizing functional electrical stimulation

OBJECTIVE

Restoration of stand-up motion in patients with complete paraplegia utilizing multichannel functional electrical stimulation, and analysis of the restored motion.

DESIGN

Nonrandomized control trial.

SETTING

General community, a referral center, institutional practice, and ambulatory care:

PATIENTS

Twelve volunteer samples were used for the collection of normal data. Two complete paraplegics received treatment for the restoration of stand-up motion.

MAIN OUTCOME MEASURES

The electromyogram, joint angle, and floor reaction force were investigated during standing-up with arms crossed in front of the chest, and hands-assisted standing-up using parallel bars. The maximum knee joint torque during standing-up without hands-assists was calculated using a three-segment link model. Standing-up motion in complete paraplegics was restored, and then analyzed using the three-dimensional floor reaction force and the hip, knee, and ankle angles.

RESULTS

Main muscles used to stand up were the quadriceps, tibialis anterior, and paraspinal muscles. Hands-assists reduced the muscle activity and the vertical floor reaction force. Peak muscle activity was less during hands-assisted standing-up, except for the rectus femoris and the iliopsoas muscle. The maximum knee joint torque during standing-up was 1.6Nm/kg for both knees. Two complete paraplegics were able to stand up smoothly from a wheelchair based on stimulation data obtained from normal subjects. The characteristic pattern during standing-up was knee flexion preceding extension.

CONCLUSION

Stand-up motion was restored utilizing electromyogram data and knee joint torque data from normal subjects.

Two strategies of transferring from sit-to-stand; the activation of monoarticular and biarticular muscles

In this study, two different strategies of rising from a chair were compared, using integrated biomechanical and electromyographic analyses. Nine healthy subjects were instructed to rise using two different strategies: natural sit-to-stand transfer (NSTS) and a sit-to-stand transfer with full flexion of the trunk (FSTS). Sagittal kinematics and ground reaction forces were registered. Muscle activity of nine muscles of the right leg were recorded by means of surface EMG. All signals were synchronized at seat-off. The results show that no differences occur between the kinematics of knee and ankle, whereas the hip flexion is, as expected, higher during FSTS. The higher moment about the knee during NSTS is shifted to proportionally higher moments about the hip and ankle during FSTS. It is mainly the differences in the EMG-levels of the biarticular hip and knee muscles which might explain the differences in net moment. These results are in accordance with a theory about a particular role of biarticular muscles. On the other hand, the shift from knee to ankle cannot be associated with a particular increase in activity of the biarticular m.gastrocnemius. It is hypothesized that about the ankle, control of stability is preferred over movement control. An important conclusion for rehabilitation medicine is that a lower net moment about the knee in FSTS does not automatically imply that this reduces the load on the knee extensors.

Transfer strategies used to rise from a chair in normal and low back pain subjects

The mechanics of rising from a chair are analysed in two groups of male subjects including five normal subjects and five chronic non-specific, low back pain subjects. Chair height, foot placement and arm position were controlled while force plate, video and electromyographic data were collected. The task was broken into three phases: initiation, chair unloading, and ascending. Moment and power analyses of the ascending phase showed two different strategies were used among the normal subjects. A 'knee strategy', comprising higher knee muscle moments, propelled the body into the standing posture while keeping the trunk relatively vertical; a 'hip-trunk strategy' flexed the trunk farther forward, decreasing the knee moments, but at the same time increasing the moments at the hip and low back. The low back pain subjects used a modified strategy that distributed the moments and power more evenly throughout the lower limb and low back.

An analysis of sit-to-stand movements

We analyzed the movements involved in rising from a knee-high chair in 12 healthy men weighing within +/- 10% of standard body weight. A regular series of transition points was observed in the angles of the hip, knee, and ankle joints throughout the sit-to-stand movement, which was classified into six stages. As the duration of sit-to-stand movements increased, the duration of Stage 2 decreased, whereas Stage 3 grew longer. The durations of stages 4 and 5 remained constant. We also calculated the minimum unilateral hip and knee extension torque per weight in kilograms required for natural sit-to-stand movements, or N-Stand (1.7-2.3 seconds), and found that minimum hip extension torque was 0.7Nm and minimum knee extension torque was 0.9Nm. The minimum hip and knee extension torque required for N-Stand corresponds to a mean 27% and 30%, respectively, of the actual maximum hip and knee extension torque.

Biomechanical analyses of rising from a chair

Quantification of the biomechanical factors that underlie the inability to rise from a chair can help explain why this disability occurs and can aid in the design of chairs and of therapeutic intervention programs. Experimental data collected earlier from 17 young adult and two groups of elderly subjects, 23 healthy and 11 impaired, rising from a standard chair under controlled conditions were analyzed using a planar biomechanical model. The joint torque strength requirements and the location of the floor reaction force at liftoff from the seat in the different groups and under several conditions were calculated. Analyses were also made of how body configurations and the use of hand force affect these joint torques and reaction locations. In all three groups, the required torques at liftoff were modest compared to literature data on voluntary strengths. Among the three groups rising with the use of hands, at the time of liftoff from the seat, the impaired old subjects, on an average, placed the reaction force the most anterior, the healthy old subjects placed it intermediately and the young subjects placed it the least anterior, within the foot support area. Moreover, the results suggest that, at liftoff, all subjects placed more importance on locating the floor reaction force to achieve acceptable postural stability than on diminishing the magnitudes of the needed joint muscle strengths.

On/off control in FES-induced standing up: a model study and experiments

Control of paraplegic standing up was studied with respect to the limitation of the end-velocity of the knee joint when the patient reaches the upright position. Closed-loop on/off control of knee extensor muscle was compared with open-loop controlled standing up both in a model study and in paraplegic patients in a controlled model situation. Criteria were knee-end-velocity and knee extensor muscle activation time. Sensitivity of the system to additional arm support and (in the model study) to the dynamics of knee extensor muscle was studied. It is concluded that the control scheme may reduce knee-end velocity to about 40 per cent and knee extensor activation time to near 70 per cent of the respective open-loop values.

Speed variation and resultant joint torques during sit-to-stand

The purpose of this study was to test the hypothesis that a progressively faster speed of ascent requires significantly greater peak resultant joint torque (RJT) at major load-bearing joints of the lower limb during the sit-to-stand (STS) transfer. Eight healthy adults performed the STS at slow, natural, and fast speeds. A motion analysis system and two force platforms were employed to record kinetic data, and equations of motion were applied to compute the RJT for the ankle, knee, and hip. The results of the study supported the hypothesis that when the speed of ascent increased progressively, the peak hip flexion, knee extension, and ankle dorsiflexion RJTs increased disproportionately. However, the peak hip extension and ankle plantar flexion RJTs remained relatively constant across the range of the speeds. Implications for clinical practice pertaining to the timing and magnitude of RJT, as well as for interventions that emphasize the adaptive characteristics of movements, are suggested.

Properties of implanted electrodes for functional electrical stimulation

Implanted wire electrodes are increasingly being used for the functional electrical stimulation of muscles in partially paralysed patients, yet many of their basic characteristics are poorly understood. In this study we investigated the selectivity, recruitment characteristics and range of control of several types of electrode in triceps surae and plantaris muscles of anaesthetized cats. We found that nerve cuffs are more efficient and selective (i.e., cause less stimulus spread to surrounding muscles) than intramuscular electrodes. Bipolar intramuscular stimulation was more efficient and selective than monopolar stimulation, but only if the nerve entry point was between the electrodes. Monopolar electrodes are efficient and selective if located close to the nerve entry point, but their performance declines with distance from it. Nonetheless, for a variety of reasons monopolar stimulation provides the best compromise in many current applications. Short duration pulses offer the best efficiency (least charge per pulse to elicit force) but high peak currents, increasing the risk of electrode corrosion and tissue damage. Electrode size has little effect on recruitment and should therefore be maximised because this minimises current density.