Investigation of the Hammerstein hypothesis in the modeling of electrically stimulated muscle

To restore functional use of paralyzed muscles by automatically controlled stimulation, an accurate quantitative model of the stimulated muscles is desirable. The most commonly used model for isometric muscle has had a Hammerstein structure, in which a linear dynamic block is preceded by a static nonlinear function, To investigate the accuracy of the Hammerstein model, the responses to a pseudo-random binary sequence (PRBS) excitation of normal human plantarflexors, stimulated with surface electrodes, were used to identify a Hammerstein model but also four local models which describe the responses to small signals at different mean levels of activation. Comparison of the local models with the Linearized Hammerstein model showed that the Hammerstein model concealed a fivefold variation in the speed of response. Also, the small-signal gain of the Hammerstein model was in error by factors up to three. We conclude that, despite the past widespread use of the Hammerstein model, it is not an accurate representation of isometric muscle. On the other hand, local models, which are more accurate predictors, can be identified from the responses to short PRBS sequences. The utility of local models for controller design is discussed

A human body model for dynamic response analysis of an integrated human-seat-controller-high speed marine craft interaction system

Small boats are increasingly being operated at high speed in rough weather by organisations carrying out essential missions such as the military and rescue services. Crew and passengers on these boats are exposed to continuous vibration and impacts leading to reduced crew effectiveness, fatigue and the possibility of injury. In addition to this marine craft will soon fall under the jurisdiction of the European Union Directive 2002/44/EC on the protection of workers from vibration.To assess the possibility of injury and mitigate it at the design stage of a vessel a design tool is needed to assess the vibration levels on/in the human body while the boat operates in dynamic environments. A review of current human body models is presented and a new human body model, which allows for estimates of muscle activity, is proposed. This model is supplemented by a numerical approach using finite element methods to assess the dynamic response of the integrated human-seat-controller-boat interaction system excited by wave loads or boat motions measured in full scale boat operation tests. The vibration control actuators are arranged between the seat and boat to reduce vibrations transmitted to the human body from the boat to obtain a comfortable ride condition

A human body model for dynamic response analysis of an integrated human-seat-controller-high speed marine craft interaction system

Small boats are increasingly being operated at high speed in rough weather by organisations carrying out essential missions such as the military and rescue services. Crew and passengers on these boats are exposed to continuous vibration and impacts leading to reduced crew effectiveness, fatigue and the possibility of injury. In addition to this marine craft will soon fall under the jurisdiction of the European Union Directive 2002/44/EC on the protection of workers from vibration.To assess the possibility of injury and mitigate it at the design stage of a vessel a design tool is needed to assess the vibration levels on/in the human body while the boat operates in dynamic environments. A review of current human body models is presented and a new human body model, which allows for estimates of muscle activity, is proposed. This model is supplemented by a numerical approach using finite element methods to assess the dynamic response of the integrated human-seat-controller-boat interaction system excited by wave loads or boat motions measured in full scale boat operation tests. The vibration control actuators are arranged between the seat and boat to reduce vibrations transmitted to the human body from the boat to obtain a comfortable ride condition

Control strategies for integration of electric motor assist and functional electrical stimulation in paraplegic cycling: Utility for exercise testing and mobile cycling

AIM: The aim of this study was to investigate feedback control strategies for integration of electric motor assist and functional electrical stimulation (FES) for paraplegic cycling, with particular focus on development of a testbed for exercise testing in FES cycling, in which both cycling cadence and workrate are simultaneously well controlled and contemporary physiological measures of exercise performance derived. A second aim was to investigate the possible benefits of the approach for mobile, recreational cycling. METHODS: A recumbent tricycle with an auxiliary electric motor is used, which is adapted for paraplegic users, and instrumented for stimulation control. We propose a novel integrated control strategy which simultaneously provides feedback control of leg power output (via automatic adjustment of stimulation intensity) and cycling cadence (via electric motor control). Both loops are designed using system identification and analytical (model-based) feedback design methods. Ventilatory and pulmonary gas exchange response profiles are derived using a portable system for real-time breath-by-breath acquisition. RESULTS:We provide indicative results from one paraplegic subject in which a series of feedback-control tests illustrate accurate control of cycling cadence, leg power control, and external disturbance rejection. We also provide physiological response profiles from a submaximal exercise step test and a maximal incremental exercise test, as facilitated by the control strategy. CONCLUSION: The integrated control strategy is effective in facilitating exercise testing under conditions of well-controlled cadence and power output. Our control approach significantly extends the achievable workrate range and enhances exercise-test sensitivity for FES cycling, thus allowing a more stringent characterization of physiological response profiles and estimation of key parameters of aerobic function.We further conclude that the control approach can significantly improve the overall performance of mobile recreational cycling

An isovelocity dynamometer method to determine monoarticular and biarticular muscle parameters

This study aimed to determine whether subject-specific individual muscle models for the ankle plantar flexors could be obtained from single joint isometric and isovelocity maximum torque measurements in combination with a model of plantar flexion. Maximum plantar flexion torque measurements were taken on one subject at six knee angles spanning full flexion to full extension. A planar three-segment (foot, shank and thigh), two muscle (soleus and gastrocnemius) model of plantar flexion was developed. Seven parameters per muscle were determined by minimizing a weighted root mean square difference (wRMSD) between the model output and the experimental torque data. Valid individual muscle models were obtained using experimental data from only two knee angles giving a wRMSD score of 16 N m, with values ranging from 11 to 17 N m for each of the six knee angles. The robustness of the methodology was confirmed through repeating the optimization with perturbed experimental torques (±20%) and segment lengths (±10%) resulting in wRMSD scores of between 13 and 20 N m. Hence, good representations of maximum torque can be achieved from subject-specific individual muscle models determined from single joint maximum torque measurements. The proposed methodology could be applied to muscle-driven models of human movement with the potential to improve their validity

The effects of a 12-week leisure centre-based, group exercise intervention for people moderately affected with multiple sclerosis: a randomized controlled pilot study

<b>Objective:</b> To establish the effects of a 12-week, community-based group exercise intervention for people moderately affected with multiple sclerosis. <b>Design:</b> Randomised controlled pilot trial. <b>Setting:</b> Two community leisure centres. <b>Participants:</b> Thirty-two participants with multiple sclerosis randomised into intervention or control groups. <b>Intervention:</b> The intervention group received 12 weeks of twice weekly, 60-minute group exercise sessions, including mobility, balance and resistance exercises. The control group received usual care. <b>Main outcome measures:</b> An assessor blinded to group allocation assessed participants at baseline, after eight weeks and after 12 weeks. The primary outcome measure was 25-foot (7.6 m) walk time, secondary outcomes assessed walking endurance, balance, physical function, leg strength, body mass index, activity levels, fatigue, anxiety and depression, quality of life and goal attainment. <b>Results:</b> The intervention made no statistically significant difference to the results of participants’ 25-foot walk time. However the intervention led to many improvements. In the intervention group levels of physical activity improved statistically between baseline and week 8 (P < 0.001) and baseline and week 12 (P = 0.005). Balance confidence results showed a significant difference between baseline and week 12 (P = 0.013). Good effect sizes were found for dynamic balance (d = 0.80), leg strength (d = 1.33), activity levels (d = 1.05) and perceived balance (d = 0.94). <b>Conclusion:</b> The results of the study suggest that community-based group exercise classes are a feasible option for people moderately affected with multiple sclerosis, and offer benefits such as improved physical activity levels, balance and leg strength