Cardiorespiratory responses during functional electrical stimulation cycling and electrical stimulation isometric exercise.

STUDY DESIGN: Prospective experimental. OBJECTIVES: To compare the cardiorespiratory responses with electrical stimulation (ES) producing either dynamic leg cycling or intermittent isometric leg contractions using the same ES protocol. SETTING: Sydney, Australia. METHODS: Eight paraplegics (T4-T11) performed ES exercise sessions on two separate days. On day 1, cardiorespiratory responses were measured during 5 min of rest followed by 35 min of cycling, and finally 15 min of intermittent isometric exercise using the same ES parameters. On the second day, after 5 min of rest, 35 min of isometric exercise was performed followed by 15 min of cycling. RESULTS: There were no significant differences during the first 35 min of exercise on each day comparing the two modes of exercise for average rate of oxygen consumption (cycling, 534±128 ml min(-1); isometric 558±146 ml min(-1); P=0.451), the average heart rate (cycling, 93±15 b.p.m.; isometric 95±17 b.p.m.; P=0.264) or minute ventilation (cycling, 23.0±6.5 l min(-1); isometric 23.8±6.7 l min(-1); P=0.655). In addition, there were no significant differences between exercise modes for any peak cardiorespiratory values recorded during the initial 35 min of exercise or the following 15 min crossover exercise phase. CONCLUSION: The current data found that intermittent ES leg isometric exercise elicited a similar cardiorespiratory response compared with functional ES leg cycling, suggesting it should be investigated as a viable alternative intervention for increasing whole body metabolic rate during sustained exercise training sessions for individuals with paralyzed muscles.

Leg general muscle moment and power patterns in able-bodied subjects during recumbent cycle ergometry with ankle immobilization.

Rehabilitation of persons with pareses commonly uses recumbent pedalling and a rigid pedal boot that fixes the ankle joint from moving. This study was performed to provide general muscle moments (GMM) and joint power data from able-bodied subjects performing recumbent cycling at two workloads. Twenty-six able-bodied subjects pedalled a stationary recumbent tricycle at 60 rpm during passive cycling and at two workloads (low 15 W and high 40 W per leg) while leg kinematics and pedal forces were recorded. GMM and power were calculated using inverse dynamic equations. During the high workload, the hip and knee muscles produced extensor/flexor moments throughout the extensions/flexions phases of the joints. For low workload, a prolonged (crank angle 0-258°) hip extension moment and a shortened range (350-150°) of knee extension moment were observed compared to the corresponding extension phases of each joint. The knee and hip joints generated approximately equal power. At the high workload the hip and knee extensors generated increased power in the propulsion phase. For the first time, this study provides GMM and power patterns for able-bodied subjects performing recumbent cycling with an immobilized ankle. The patterns showed greater similarities to upright cycling with a free ankle, than previously supposed.

FES assisted standing in people with incomplete spinal cord injury: a single case design series.

STUDY DESIGN: Single case cross-over design with multiple baselines. OBJECTIVE: To compare two functional electrical stimulation (FES) training protocols to assist sit-to-stand in people with incomplete spinal cord injury (SCI). SETTING: The study was conducted in Sydney, Australia. METHODS: Four subjects with incomplete SCI undertook nine sessions of FES supported cycling at either 100 or 35 Hz stimulus frequency repeated. Ground reaction force and rate of generation of vertical ground reaction force during standing from sitting were measured before and after each training series. RESULTS: Subjects improved their ability to generate greater support through the feet after training with 35 Hz stimulus paradigm but increased the rate of force production after training with 100 Hz stimulation. CONCLUSIONS: Different FES training paradigms appear to produce different responses; however the ability to stand up seems more responsive to training with 35 Hz FES stimulation.

Comparison of the pedalling performance induced by magnetic and electrical stimulation cycle ergometry in able-bodied subjects.

The purpose of the study was to compare the mechanical power and work generated by able-bodied subjects during functional magnetic stimulation (FMS) vs. functional electrical stimulation (FES) induced ergometer training conditions. Both stimulation methods were applied at a 30 Hz frequency to the quadriceps muscles of 22 healthy able-bodied subjects to induce cycling for 4× four minutes or until exhaustion. FMS was performed via large surface, cooled coils, while FES was applied with a typical stimulation setup used for cycling. Significantly more (p<10(-3)) muscular power was generated by FMS (23.8 ± 9.1W [mean ± SD]) than by FES (11.3 ± 11.3 W). Additionally, significantly more (p<10(-6)) work was produced by FMS than by FES (4.413 ± 2.209 kJ vs. 0.974 ± 1.269 kJ). The increase in the work was paralleled by a significant prolongation of time to cycling failure (181.8 ± 33.4s vs. 87.0 ± 54.0 s, respectively, p<10(-5)). Compared to FES, FMS can produce more intense and longer cycling exercise in able-bodied subjects. The differing dynamic behaviour of FMS and FES in the presented measurement setup might be related to stimulation induced pain and fatigue mechanisms of the neuromuscular system.

Electrical stimulation plus progressive resistance training for leg strength in spinal cord injury: a randomized controlled trial.

STUDY DESIGN: A randomized controlled trial. OBJECTIVES: To determine the effectiveness of electrical stimulation (ES)-evoked muscle contractions superimposed on progressive resistance training (PRT) for increasing voluntary strength in the quadriceps muscles of people with spinal cord injuries (SCI). SETTING: Sydney, Australia. METHODS: A total of 20 people with established SCI and neurologically induced weakness of the quadriceps muscles participated in the trial. Participants were randomized between experimental and control groups. Volunteers in the experimental group received ES superimposed on PRT to the quadriceps muscles of one leg thrice weekly for 8 weeks. Participants in the control group received no intervention. Assessments occurred at the beginning and at the end of the 8-week period. The four primary outcomes were voluntary strength (Nm) and endurance (fatigue ratio) as well as the performance and satisfaction items of the Canadian Occupational Performance Measure (COPM; points). RESULTS: The between-group mean differences (95% confidence interval (CI)) for voluntary strength and endurance were 14 Nm (1-27; P=0.034) and 0.1 (-0.1 to 0.3; P=0.221), respectively. The between-group median differences (95% CI) for the performance and satisfaction items of the COPM were 1.7 points (-0.2 to 3.2; P=0.103) and 1.4 points (-0.1 to 4.6; P=0.058), respectively. CONCLUSION: ES superimposed on PRT improves voluntary strength, although there is uncertainty about whether the size of the treatment effect is clinically important. The relative effectiveness of ES and PRT is yet to be determined.

Mechanical design and driving mechanism of an isokinetic functional electrical stimulation-based leg stepping trainer.

The mechanical design of a constant velocity (isokinetic) leg stepping trainer driven by functional electrical stimulation-evoked muscle contractions was the focus of this paper. The system was conceived for training the leg muscles of neurologically-impaired patients. A commercially available slider crank mechanism for elliptical stepping exercise was adapted to a motorized isokinetic driving mechanism. The exercise system permits constant-velocity pedalling at cadences of 1-60 rev x min(-1). The variable-velocity feature allows low pedalling forces for individuals with very weak leg muscles, yet provides resistance to higher pedalling effort in stronger patients. In the future, the system will be integrated with a computer-controlled neuromuscular stimulator and a feedback control unit to monitor training responses of spinal cord-injured, stroke and head injury patients.

External power output changes during prolonged cycling with electrical stimulation.

This study analysed external power output and physiologic responses in 5 individuals with paraplegia during 40 minutes of electrical stimulation leg cycle exercise. Cycling was performed on a motor-driven isokinetic ergometer that enabled precise determinations of power output. Electrical stimulation was increased to 120-140 mA within the first 5 minutes and remained constant thereafter. Power output increased to 10.7 +/- 3.0 W after 2 minutes, dropped to 5.3 +/- 1.8 W after 6 minutes and subsequently recovered to 8.2 +/- 2.2 and 6.1 +/- 2.3 W after 19.5 and 40 minutes, respectively. Oxygen consumption increased to 0.47 +/- 0.09 l/min after 6 minutes and declined during the second half of the exercise bout. Gross mechanical efficiency after 19.5 minutes was elevated compared with the value after 6 minutes. Heart rate was significantly increased at the end of the trial. The time-dependent variability of power output and physiological responses question the concept of steady state for this form of exercise.