Functional Electrical Stimulation (FES cycling)

Deutsche Version

Team members

• Design and examination: Dr. Dipl.-Ing. J. Szecsi
• Supervision: Prof. Dr. A. Straube, Prof. Dr. Dr. h.c. T. Brandt
• Doctorands: S. Kott, B. Kreuzpointner, T. Millian, M. Schiller
  
• Duration of the project: December 2006 until November 2008

Introduction

We report on the preliminary clinical and technical results of a preceding study whose aim is to identify suitable patients and to make appropriate adjustments to enable them to cycle by means of functional electrical stimulation (FES).

Sports and traffic accidents are daily events that can cause spinal cord injuries (SCI). Complete restitution of health is possible in only a few SCI patients. In most cases, the long-term treatment after initial surgery focuses on rehabilitation, and certain therapeutic methods will accompany many of these patients for the rest of their lives.

Functional electrical stimulation and cycling

To maintain the functionality of selected paralyzed muscles, the electrophysiologic method of functional electrical stimulation now plays an established role in rehabilitative medicine. In brief, electrical current is applied to the nerve endings through self-adhesive electrodes on the skin, causing a contraction of the corresponding muscle fibers. For instance, by stimulating certain muscles of the thigh in a specific order, the paralyzed limbs are moved and this facilitates pedaling.

Stationary (on an ergometer) or mobile (on a tricycle) FES cycling provides the patient with a high recreational value and at the same time several medical benefits such as muscle training, improvement of the cardiovascular system, and attenuation of secondary complications like deep vein thrombosis and osteoporosis. Various modifications of FES tricycles, e.g., addition of hand power or a motor, can achieve more general applicability in everyday life.

Targets and motivation of the study

To tap the full potential of FES cycling, the patients must regularly exercise on an ergometer. In other words, in addition to the laboratory setup, a home ergometer or tricycle has to be adapted to each particular patient. The adaptation of the device and the determination of an ideal stimulation pattern for the respective device and patient must be carried out once at the beginning of the training period.

Our aims were to standardize the criteria for identifying suitable patients and performing the first-line adjustments, to shorten the time needed for adjustment, and to provide independent training opportunities to a larger number of patients in their domestic surroundings.

Our new method for determining the patient-ergometer or patient-tricycle system, which we established during this study, accommodates both for a variety of cycling devices and for biological and mechanical properties of the individual patients. Our method can ensure smooth and sustained pedaling with different types of exercise devices, even after only a few measurement sessions.

According to current scientific opinion, we believe that tricycle or ergometer training needs to be continued for the patient’s lifetime. For this purpose home training is imperative, and patients need to be equipped with own stimulators and ergometers.

Patients

The study began on 13 August 2005 with 20 participants who have spinal cord injuries (SCI) and two who have multiple sclerosis.

Patients are required to regularly train with FES cycling at home (at least 30 min, three times a week). A training session always begins with a 5-minute passive warm-up carried out by the motor. Then electrical stimulation is started, and the mechanical resistance of the ergometer is continuously increased up to the highest possible gear that can be successfully used with a maximal intensity of stimulation. A gear is considered accomplished, if a speed of 40 – 50 rpm (resolutions per minute) can be maintained. If speed falls below 35 rpm, the patient must shift to a lower gear until the above-mentioned speed can be maintained. Participants are advised to keep a protocol of each training session, in which they note the duration of training and the highest achieved pedaling resistance, as shown on the ergometer.

Methods

The described standardized first-line adjustments for participants in FES cycling studies are based on both the classic medical indication for electrical stimulation and on our own biomechanical and physiological measurements made earlier to assess the physical condition of an individual patient.

Medical inclusion and exclusion criteria

The classic indication: FES cycling is possible for patients with complete spinal cord transsection (ASIA A) at the levels C5 – Th12, resulting in spastic paraplegia. Contraindications for FES (such as pacemaker, arrhythmias, wounds) need to be ruled out before the first stimulation. Most notably, patients with a level of lesion above Th4 are at an increased risk of autonomic dysregulation with pathologic flucuations of heart rate and blood pressure. Thus, repeated measurements of vital parameters are indispensable in the first sessions. Additionally, joint contractures or denervation of leg muscles are exclusion criteria for FES. Persons with distinct spasticity (Ashworth scale = 4-5) cannot cycle with FES. To rule out significant joint instabilities or severe arthroses, orthopedic examination of the lower limbs is necessary prior to stimulation.

The algorithm developed for estimating an individual’s ability to do FES cycling is shown in the figure below-mentioned.

Biomechanical inclusion and exclusion criteria

Isometric force measurement

To determine the torques that occur during cycling, a commercial tricycle was used. Its front wheel was removed and its fork fixed to a stationary frame. The muscle groups involved in cycling were stimulated every 20° along the circumference of 360°. The characteristics of the torque/angle ratio that were obtained in this manner enabled us to develop an individual stimulation profile.

Cycling ability

The ability to cycle can be defined by two criteria:

1. Short-term cycling ability

For short-term cycling ability (ability to pedal) the smoothness of the crank angular velocity is decisive. The inhomogeneity of pedaling should not exceed 7 – 10 rpm, because stagnancy of pedaling can be observed at a value of 15 rpm or higher. Then cycling is no longer possible.

2. Long-term cycling ability

The ability to cycle for a longer time makes FES cycling practical for everyday life. For example, the patient must be able to ride an FES bike for a certain minimum distance.

Spasticity and FES cycling

Patients with pronounced spasticity (Ashworth scale = 4 –5) cannot do FES cycling.

Overview of FES tricycles

Three tricycles were examined for their ergonomic features. By assessing their single advantages and uniting them in one model, we developed a novel concept for a tricycle, which at the moment only exists as computer simulation (see adjacent figure). The crank angle position, necessary for the control of muscle stimulation, is encoded with a relative shaft encoder (8 bit). The speed correction is calculated by differentiating and filtering the angle signal.

These signals are used to control the electrical stimulator (Krauth & Timmermann), which operates at a stimulation frequency of 20 Hz, a constant pulse width of 500 µsec, and a variable stimulation current up to 99 mA. The participant regulates the intensity of stimulation while training by using a throttle control mounted on the handlebar. Six muscle groups are stimulated: extensors and flexors of the thigh and the gluteal muscles. A typical stimulation pattern can be seen above (biomechanical criteria). This study shows, on the one hand, that individual patients can be characterized by actuation profiles and, on the other, individual cycles can be characterized by load profiles. Thus, the problems of adjustment are reduced to minimizing differences in phase and amplitude between actuation and load profiles. The picture above is a computer simulation of a technically optimized version, in which pedaling activates a generator, which in turn facilitates a steady pedal load via the attached motor.

Out-of-the-saddle FES-cycling

Reinforcing muscular and cardiovascular training as well as improving standing and walking are important goals of rehabilitation after SCI. While standard recumbent FES-cycling is considered a means to improve muscle condition. it is not adequate for achieving efficient balance control and intense cardiopulmonal training.

We present a new method of FES-propelled cycling, called upright or standing cycling, resembling of-out-the-saddle cycling of healthy cyclists climbing a hill.

Using a single subject with complete paraplegia Th9, this study investigated the technical feasibility and biomechanicaland physiological characteristics of training using an upright FES-cycle.

It could be shown that upright FES-cycling is technically straightforward to realize and combines the advantages of intense cardiovascular (power, peak O₂-uptake, PCI), orthostatic and balance training.

For demonstration video click here.

Results

After intensive training, several patients successfully strengthened their muscles, allowing them to also cycle for longer distances on the road. In June 2006, two of our patients participated in the 1st International FES Sports Day in Cardiff (see additional video). One won the race over 1000 m in 5:04 min and set the first world record in this discipline. The second participant from Munich came in fifth, an excellent achievement. The fundamental idea of this contest was to assess the present and future feasibility of FES.

Movie from Cardiff: mpg, 16 MB, silent

Ergometer Movie: Patient exercising with a therapy device (motorized dynamometer from Reck company). AVI, 1,7 MB.

Cycle Movie: A patient with complete spinal cord injury cycling on a FES tricycle. AVI, 8,3 MB

Upright FES-cycling: Paraplegic patient cycling FES-propelled in upright position. WMV, 16 MB

Conclusion

FES cycling is a promising technology for patients with palsies of the lower limb. Its potential benefits include various medical improvements. While the present applications focus on its use in sports, the goal of future investigations will be to achieve practical results in everyday life situations.

Contact

Dr. med. Dipl.-Ing. Johann Szecsi
Zentrum für Sensomotorik
Neurologische Klinik und Polklinik der LMU
Universitätsklinikum Großhadern
Marchioninistr. 23
81377 München
+49 89 7095 4818
e-mail: jszecsi(at)nefo.med.uni-muenchen.de

Acknowledgement

The authors would like to thank all patients participating in this project. Without them, it would not have been possible to realize this project. All interested parties and also patients with spinal cord injuries and other palsies of the legs are invited to contact us.

References

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