A DEVELOPMENT SYSTEM TO ENHANCE FES LEG CYCLE ERGOMETER TECHNOLOGY

Roger M. Glaser, William P. Couch, Thomas W.J. Janssen, José W. Almeyda, D. Drew Pringle, Steven R. Collins and Thomas Mathews Institute for Rehabilitation Research and Medicine, Wright State University School of Medicine; Rehabilitation Institute of Ohio, Miami Valley Hospital; and Dayton VA Medical Center, Dayton, OH

ABSTRACT

A development system was constructed to enhance performance of individuals with spinal cord injury (SCI) for functional electrical stimulation (FES) leg cycle ergometer (LCE) exercise. This development system readily permits changes in FES parameters to optimize recruitment of paralyzed muscle fibers and in pedal load resistance to enable use of various exercise testing and training protocols. For initial testing on the model ERGYS FES-LCE, max current limit was increased from 140 mA to as high as 300 mA, the shank muscles were added to the quadriceps, hamstring and gluteal muscle groups, and the FES firing angle ranges were increased by 55o. Eight subjects with SCI participated in stress testing with the original and the enhanced FES-LCE, using a continuous, progressive intensity protocol. The enhanced FES-LCE elicited significantly higher (p<.05) peak metabolic rate, pulmonary ventilation, heart rate, stroke volume, cardiac output and blood lactate concentration. Therefore, the enhanced FES-LCE may permit more effective muscular and cardiopulmonary training capability.

INTRODUCTION

The Therapeutic Alliances, Inc. model ERGYS FES-LCE was designed to promote cardiopulmonary fitness in individuals with paraplegia and quadriplegia due to SCI through leg pedaling via rhythmic induced contractions of the paralyzed quadriceps, hamstring and gluteal muscle groups. A ROM based computer-stimulator system controls both the FES parameters (i.e., waveform, firing angle ranges, current limit) to generate pedaling at 50 rpm and the flywheel resistive load for setting exercise intensity. Although this original FES-LCE technology, which became commercially available in 1984, has been shown to be efficacious (1,2), subsequent research indicated that higher magnitudes of metabolic and cardiopulmonary responses can be obtained via greater recruitment of muscle fibers by increasing maximal FES current (3), and by the addition of the tibialis anterior and gastroc-soleus muscles (4). In addition, a biomechanical modeling technique predicted that FES firing angle ranges could be substantially widened from those originally used to increase the contraction duty cycle for enhancing responses and providing for a smoother and more continuous propulsive action (5). Exercise testing and training responses may also be augmented by incorporating protocols that require the flywheel resistive load to be immediately adjustable in small increments without the need to discontinue exercise to reprogram the system.

Therefore, it would be desirable to have a development system to readily test the effects of altering FES parameters on metabolic and cardiopulmonary responses. In addition, the effectiveness of various exercise testing and training protocols could be evaluated by being able to immediately and continuously adjust flywheel resistive load. Therefore, the purpose of this project was to design and construct a development system that can be used in conjunction with an ERGYS FES-LCE..

METHODS

FES-LCE Development System. Fig. 1 illustrates the FES-LCE development system which can boost max FES current output from 140 mA up to 300 mA, utilize additional muscle groups, vary FES firing angle ranges (via ROM chips), and vary exercise load resistance in small increments before and during exercise. Also illustrated is the instrumentation for monitoring metabolic and cardiopulmonary responses of subjects during FES-LCE exercise.

Fig. 1. Illustration of the FES-LCE development system and instrumentation for physiologic data monitoring.

Fig. 2 provides a block diagram of the 10-channel current controller that retrofits to the ERGYS. This component essentially receives the 6 channels of FES output from the ERGYS and provides 10 channels of FES output. The additional 4 channels of FES are used to activate the right and left tibialis anterior and gastroc-soleus muscles. FES to these muscles is configured so that they will co-contract with the right and left quadriceps and hamstring muscles, respectively. The current controller can amplify the FES current to each muscle from a maximum limit of about 140 mA (monophasic pulses) to 300 mA (biphasic pulses). A separate front panel control permits setting of current limit for each muscle before and during exercise bouts. Data outputs are provided for FES current applied to each muscle and the pedaling RPM. Firing angle ranges are adjusted by means of custom ROM chips that plug directly into the ERGYS.

The retrofit load resistance controller for the ERGYS (Fig. 3) incorporates the original ERGYS load cell and particle brake to provide a continuous and immediate setting of flywheel braking force by the turn of a dial. This eliminated the need to discontinue exercise to reprogram the load setting. Load resistance can thus be varied at will during continuous or intermittent exercise protocols.

FES-LCE Exercise Performance. To evaluate the FES-LCE development system, 8 men with SCI volunteered to participate in stress testing on the original and enhanced ERGYS. Subjects were medically screened and signed an IRB-approved consent form prior to participation. ERGYS enhancements consisted of increasing FES current limit to 300 mA, adding the shank muscles, and increasing FES firing angle ranges by 55o. A continuous, progressive intensity exercise protocol was designed to determine peak metabolic and cardiopulmonary responses for both the original and the enhanced FES-LCE. For this, exercise was initiated at 0 kp load, and resistance was increased every 2 min by 1/16 kp (3.1 W at 50 rpm) increments until pedaling velocity dropped from 50 to below 35 rpm, at which time exercise was terminated.

During exercise, expired gases were collected by a metabolic cart, and maximal values for aerobic metabolic rate and pulmonary ventilation (VE) were determined. Heart rate (HR) was continuously monitored via ECG signals. Immediately after exercise cessation, cardiac output (Q) was non-invasively assessed by impedance cardiography. Five minutes after exercise a finger tip blood sample was analyzed for blood lactate concentration to estimate the anaerobic energy supplementation.

RESULTS AND DISCUSSION

When comparing exercise performance on the original vs enhanced ERGYS FES-LCE, we found that max PO achieved was similar (mean+SD = 8.6+8.5 W vs .8.2+5.3 W). Lack of greater PO for the enhanced ERGYS was probably due to the fatiguing effects of the longer contraction duty cycle with wider firing angle ranges. However, the enhanced ERGYS elicited higher (p<.05) peak aerobic metabolic rate (3.5+0.8 vs 4.4+0.7 METS), VE (26.7+10.8 vs 38.3+10.8 L/min), HR (76+19 vs 95+10 beats/min), Q (5.8+2.0 vs 7.9+2.8 L/min), and LA (4.4+2.1 vs 7.0+1.6 mmol/L). Greater peak metabolic and cardiopulmonary responses obtained with the incorporated modifications to the FES-LCE were most likely due to the recruitment of additional muscle fibers. This may provide greater "overload" to better elicit muscle and cardiopulmonary system training adaptations. In a practical sense, however, this recruitment should be gradually implemented during exercise training programs so as not to cause the early onset of fatigue and reduce potential training effects.

Conclusion.

The described retrofit ERGYS FES-LCE development system can permit study of various FES parameters to optimize exercise performance and metabolic and cardiopulmonary responses. The preliminary results obtained suggest that FES-LCE technology can be markedly improved to promote higher levels of health, fitness and rehabilitation potential in individuals with SCI.

REFERENCES

Ragnarsson KT. Physiologic effects of functional electrical stimulation-induced exercises in spinal cord-injured individuals. Clin Orthop Rel Res, 233:253-263, 1988.

Glaser RM. Functional neuromuscular stimulation: exercise conditioning of spinal cord injured patients. Int J Sports Med 15:142-8, 1994.

Glaser RM, SF Figoni, WP Couch, SR Collins, RA Shively. Effects of increased maximum current during electrical stimulation leg cycle ergometry. Med Sci Sports Exerc 26:S111, 1994.

Figoni SF, MM Rodgers, RM Glaser. Effects of electrical stimulation of shank musculature during ES-leg cycle ergometry. Med Sci Sports Exerc 26:S77, 1994.

Schutte LM, MM Rodgers, FE Zajac, RM Glaser. Improving the efficacy of electrical stimulation-induced leg cycle ergometry: an analysis based on a dynamic musculoskeletal model. IEEE Trans Rehabil Eng 1:109-25, 1993.

Acknowledgment.

This study was supported by the Rehabilitation Research and Development Service of the US Department of Veterans Affairs.

Roger M. Glaser, Ph.D., Director Institute for Rehabilitation Research and Medicine Wright State University School of Medicine Dayton, OH 45435, USA Tel: (513) 259-1326 Fax: (513) 259-1310 E-mail: rglaser@desire.wright.edu