A biomechanical cause of low power production during FES cycling of subjects with SCI.

BACKGROUND: The goal of Functional Electrical Stimulation (FES) cycling is to provide the health benefits of exercise to persons with paralysis. To achieve the greatest health advantages, patients should produce the highest possible mechanical power. However, the mechanical power output (PO) produced during FES cycling is very low. Unfavorable biomechanics is one of the important factors reducing PO. The purpose of this study was to investigate the primary joints and muscles responsible for power generation and the role of antagonistic co-contraction in FES cycling. METHODS: Sixteen subjects with complete spinal cord injury (SCI) pedaled a stationary recumbent FES tricycle at 60 rpm and a workload of 15 W per leg, while pedal forces and crank angle were recorded. The joint muscle moments, power and work were calculated using inverse dynamics equations. RESULTS: Two characteristic patterns were found; in 12 subjects most work was generated by the knee extensors in the propulsion phase (83% of total work), while in 4 subjects most work was shared between by the knee extensors (42%) and flexors (44%), respectively during propulsive and recovery phases. Hip extensors produced only low net work (12 & 7%). For both patterns, extra concentric work was necessary to overcome considerable eccentric work (-82 & -96%). CONCLUSIONS: The primary power sources were the knee extensors of the quadriceps and the knee flexors of the hamstrings. The antagonistic activity was generally low in subjects with SCI because of the weakness of the hamstrings (compared to quadriceps) and the superficial and insufficient hamstring mass activation with FES.

Comparison of torque and discomfort produced by sinusoidal and rectangular alternating current electrical stimulation in the quadriceps muscle at variable burst duty cycles.

OBJECTIVE: The aim of this study was to investigate the effect of neuromuscular electrical stimulation burst duty cycle (BDC) and current type (sinusoidal alternating current [sAC] vs. rectangular alternating current [rAC]) on the electrically induced isometric torque (EIT) and discomfort. Pulsed current (PC) stimulation, which corresponds to one pulse rAC, was included in testing. DESIGN: A repeated-measures design was used. The left quadriceps of 22 healthy subjects (mean ± SD age, 33 ± 8 yrs) were stimulated alternately with sAC and rAC current bursts (4-kHz carrier frequency; 71 bursts per second burst frequency) to produce isometric contractions. A range of BDCs were tested for sAC (7%-50%) and rAC (2%-18%) stimulation at fixed intensities while EIT and discomfort were recorded. BDC presentation order was randomized. RESULTS: Overall, both current types elicited peak EIT at ∼14% BDC (range, 7%-21%). Significantly more EIT was produced by rAC than by sAC stimulation (P < 0.005). Discomfort increased with BDC and was similar for both current types. CONCLUSIONS: The study confirmed previous findings that conventional sAC stimulation (50% BDC) and pulsed current stimulation (rAC with 2% BDC) used in sports and rehabilitation produce similar EIT levels. However, rAC stimulation at low BDC (7%-18%) was more effective (+35% torque produced with similar discomfort) than pulsed current or conventional sAC.

Functional electrical stimulation-assisted cycling of patients with multiple sclerosis: biomechanical and functional outcome--a pilot study.

OBJECTIVE: To determine whether functional electrical stimulation-supported ergometric training of patients with multiple sclerosis has a prosthetic or therapeutic effect on biomechanical (power, smoothness of cycling) and functional outcomes (walking capability, strength of muscle, spasticity). DESIGN: Twelve subjects with multiple sclerosis participated in an electrical stimulation-supported ergometric training (3 sessions/week for 2 weeks). Measurements were made in a cross-over design to study prosthetic (with and without stimulation) and therapeutic effects (before and after training). METHODS: Power and smoothness were calculated by cadence and torque recordings of cycling and spasticity; strength and walking capability were measured by the Modified Ashworth Scale, Manual Muscle Test, and 10-Metre Walk Test. RESULTS: The power and smoothness of pedalling significantly improved prosthetically with electrical stimulation (p=0.02), but did not show significant improvement over the 2 weeks of training. Significant short-term reductions in spasticity (before vs after training session; p<0.05) were found. Isometric strength did not increase significantly during the 2-week training period and there was no improvement in walking ability. CONCLUSION: Patients with multiple sclerosis are able to improve their cycling power and smoothness by pedalling with stimulation. We suggest that severely affected patients benefit more from functional electric stimulation-cycling therapy than do slightly affected patients.

A comparison of functional electrical and magnetic stimulation for propelled cycling of paretic patients.

OBJECTIVE: To compare isometric torque and cycling power, smoothness and symmetry using repetitive functional magnetic stimulation (FMS) and functional electrical stimulation (FES) in patients with paretic legs with preserved sensibility and in patients without sensibility. DESIGN: Repeated-measures design. SETTING: Laboratory setting. PARTICIPANTS: Eleven subjects with complete spinal cord injury (SCI) and 29 subjects with chronic hemiparesis (16.6+/-5.5mo poststroke) volunteered. INTERVENTIONS: Using a tricycle testbed, participants were exposed to isometric measurements and ergometric cycling experiments, performed during both 20Hz FMS and FES stimulation. Subjects with hemiparesis and with complete SCI were stimulated at maximally tolerable level and maximal intensity, respectively. MAIN OUTCOME MEASURES: Maximal isometric pedaling torque and mean ergometric power, smoothness, and symmetry were recorded for voluntary, FES, and FMS conditions. RESULTS: Two different patterns of the efficacy of FMS were identified. (1) Patients with complete SCI did not benefit (less torque and power was evoked with FMS than with FES, P<.003 and 10(-4) respectively). (2) Patients with hemiplegia and preserved sensibility could improve their torque output (P<.05), smoothness, and symmetry of pedaling (P<.05) with FMS more than with FES. CONCLUSIONS: FMS is a potential alternative to surface FES of the large thigh musculature in stimulation-supported cycling of patients with partially or completely preserved sensibility.

Changes in spastic muscle tone increase in patients with spinal cord injury using functional electrical stimulation and passive leg movements.

OBJECTIVE: Comparison of cycling interventions to reduce spastic muscle tone increase in patients with spinal cord injury. SETTING: Neuroprosthetic outpatient clinic in a university hospital. METHODS: Five patients with spinal cord injury took part in a crossover study in which the lower limbs (1) were stimulated by functional neuromuscular electrical stimulation (FES) to induce leg cycling movements and (2) were passively moved by an ergometer machine. Patients sat in a comfortable chair fastened to the ergometer while FES was done to induce leg cycling (active session). During the passive leg movement session the ergometer moved their legs for the same period of time at the same velocity and frequency. MAIN OUTCOME MEASURES: The change in spastic muscle tone increase before and after each training session was tested with the modified Ashworth Scale and the pendulum test of spasticity (relaxation index and peak velocity). RESULTS: The averaged data of the relaxation index increased after FES by about 68%. Compared with the slight increase after the passive movement training of 12%, this is statistically significant (P = 0.01). Peak velocity increased after FES by around 50%, while it was nearly unchanged after the passive intervention (1%); this is also significant (P = 0.01). This was similar with the peak velocity and the modified Ashworth Scale. CONCLUSION: The study presents further interesting aspects of the usefulness of FES in patients with spinal cord injury to reduce spastic muscle tone.

Improving functional electrical stimulation driven cycling by proper synchronization of the muscles.

Our aim is to define optimal stimulation patterns for controlling lower limb movements of spinal cord injured patients. Here we report on a study about cycling movements of healthy subjects under regular conditions and spinal cord injured patients whose cycling movement was generated by functional electrical stimulation. The stimulation pattern required for coordinated activities of lower limb muscles of spinal cord injured patients was improved by using the observations what we gained from measuring and analyzing cycling movements of 42 young healthy subjects. Kinematical parameters (joint angles) and muscle activities (EMG) were recorded simultaneously by an ultrasound based movement analyzing system. We replaced the cycling program of the commercially available stimulator with a new one that we developed on the basis of the measured healthy cycling movements. We present that our new stimulation patterns provided a great increase in the performance of our spinal cord injured patients.

FES cycling reduces spastic muscle tone in a patient with multiple sclerosis.

We report on a multiple sclerosis patient who received functional electrical stimulation to reduce spastic muscle tone of the lower limbs. Stimulation by means of surface electrodes applied to the thigh muscles induced cycling leg movements. Spastic muscle tone was measured clinically using the modified Ashworth scale and semiautomatically by pendulum testing of spasticity. This was done before and directly after stimulation. The patient was able to endure the stimulation for ca. 30 minutes; there was a significant reduction of spasticity after each stimulation session. We conclude, that this type of stimulation could be another potential treatment modality for multiple sclerosis patients, especially those with a high score in the expanded disability Status scale.

Functional output improvement in FES cycling by means of forced smooth pedaling.

PURPOSE: Investigation of the influence of forced smooth and normal (nonsmooth) pedaling on the functional output of outdoor functional neuromuscular electrical stimulation (FES)-propelled cycling of spinal cord-injured subjects. SUBJECTS: Twelve subjects with complete spinal cord injury (T4-T12) and limited previous FES training. METHOD: Each subject participated in two separate outdoor sessions: once while pedaling a tricycle in a fixed gear, and a second time while free pedaling the same tricycle; both times with FES. Data on distance covered until exhaustion, cadence, and pedal forces were collected. Energy balance calculations led to evaluations of jerk loss and joint-related concentric/eccentric work. RESULTS: First-trial and total session distances were 68 and 103% longer, respectively, in the forced smooth cycling session than in the free cycling session (P < 0.001). Significantly more additional crank work (accompanied by increased concentric work production) was generated in nonsteady cycling phases to overcome increased jerk losses during free than during fixed-gear pedaling. During fixed-gear pedaling, timing and joint location of muscle work generation were more similar to the cycling of able-bodied subjects than during freewheel pedaling, because most work was generated by knee extensors in the power phase during the former pedaling mode. CONCLUSIONS: The superiority of forced smooth cycling to free cycling, as regards functional output distance, is based on less energy expenditure (less jerk loss and muscle tension) and on more efficient production of energy (more efficient timing and joint location of work production). Some energetic mechanisms that are advantageous for fixed-gear cycling act predominantly in unsteady phases; others work continuously during all phases of cycling.

Low-frequency rectangular pulse is superior to middle frequency alternating current stimulation in cycling of people with spinal cord injury.

OBJECTIVE: To determine the efficacy of using modulated middle frequency alternating current (MFAC) muscle stimulation for functional electric stimulation-propelled cycling by people with spinal cord injury (SCI) compared with the conventional method of using standard low-frequency rectangular pulses (LFRP). DESIGN: Repeated-measures. SETTING: Laboratory setting. PARTICIPANTS: Eleven otherwise healthy volunteer subjects with SCI (8 with American Spinal Injury Association [ASIA] grade A, 3 with ASIA grade B). INTERVENTIONS: To evaluate cycling-relevant differences between LFRP and modulated MFAC stimulation, we exposed participants to isometric measurements and cycling experiments performed during both 20 Hz LFRP and 4 KHz modulated with 50 Hz MFAC. MAIN OUTCOME MEASURES: We recorded maximal isometric torque, maximal dynamic work during 20 minutes of ergometer cycling, and perceived discomfort for each of the 2 stimulation patterns. RESULTS: Both the isometric torque (P<.02) and work generated (P<.001) during MFAC stimulation were significantly lower than during standard LFRP stimulation. Four participants reported discomfort and 1 of them also developed skin burns during MFAC stimulation. CONCLUSIONS: Our findings suggest that in SCI subjects, stimulated cycling with low frequency is generally more effective than cycling with modulated MFAC in terms of torque, work, and pain sensation.