Biomechanics of human quadriceps muscles during electrical stimulation

The quadriceps muscles of neurologically intact and spinal cord injured (SCI) human subjects were stimulated with constant current pulses. Up to three, separately adjustable stimulating electrodes over the motor points for vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) muscles were used to maximize torque generation while minimizing discomfort. The torque generated by stimulation increased as the knee was slowly flexed to about 1 rad (50-60 degrees) and decreased beyond that point (a 'negative slope' on a torque-angle curve). Despite this region of negative slope the force generated by small oscillations remained positively correlated to the angle changes. When the knee was slowly extended again from a flexed position, the torque continued to decline and therefore showed a large degree of 'hysteresis'. Of the three heads studied, only stimulation of RF muscle generally produced this behavior. VL and VM had torques that increased monotonically with knee flexion over the range studied. The torques generated with electrical stimulation of normal subjects represented up to about 30% of maximum voluntary contraction. When subjects generated similar torques voluntarily, the negative slope region and substantial hysteresis were not observed. Thus, SCI subjects may be adversely affected by hysteresis during electrically-induced transitions from sitting to standing and vice versa, while normal subjects are not.     

Attempts to optimise functional electrical stimulation of antagonistic muscles by mathematical modelling

The mathematical relationship between the kinetic data of joint motion and the functional electrical stimulation (FES) voltage of the corresponding antagonistic pair of muscles is given on the basis of a dynamic ankle joint model. The mathematical model is solved with the aid of state variables, while the resulting electrical stimulation voltage is found as a solution of the Volterra integral equation. The calculated stimulation voltage was applied to the plantar and dorsiflexors of the ankle joint of a hemiplegic patient. The measured ground reaction forces and goniograms during walking with and without electrical stimulation showed a significant improvement of the patient's gait. The problems of low saturation muscle force during FES, the need for individual determination of model parameters, nonlinearities of the system and the variability of gait are discussed.     

Modulation of the rate of force development in hip abductor muscles by neuromuscular electrical stimulation during gait

Abstract

Purpose/aim of the study: An increase of hip abductor muscle strength contributes to the increase in gait speed. It is known that the rate of force development (RFD), an indicator of muscle strength, is increased by the combined use of low-intensity neuromuscular electrical stimulation (NMES) to the glutaeus medius (GM) and low-load resistance training (RT). However, it is unclear whether low-intensity neuromuscular electrical stimulation of the glutaeus medius during walking also increases the rate of force development. The aim of this study was to clarify whether NMES to the GM during gait modulates the RFD of the hip abductor muscles in healthy adults.

Materials and methods: Twenty-two healthy adults randomly received both gait with sub-motor threshold NMES and gait with sham NMES conditions. The RFD was assessed at pre- and post-intervention. A two-way repeated measures analysis of variance was used to analyse the effects of time and intervention.

Results: Gait with sub-motor threshold NMES condition significantly increased the RFD in shorter time interval (0–50 and 0–100?ms) compared to gait with sham NMES condition.

Conclusions: These findings suggest that the adding low-intensity NMES of the GM to gait is effective in increasing the RFD of the hip abductor muscles.     

Repeatability of maximal voluntary force and of surface EMG variables during voluntary isometric contraction of quadriceps muscles in healthy subjects

The repeatability of initial values and rate of change of EMG signal mean spectral frequency (MNF), average rectified values (ARV), muscle fiber conduction velocity (CV) and maximal voluntary contraction (MVC) was investigated in the vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles of both legs of nine healthy male subjects during voluntary, isometric contractions sustained for 50 s at 50% MVC. The values of MVC were recorded for both legs three times on each day and for three subsequent days, while the EMG signals have been recorded twice a day for three subsequent days. The degree of repeatability was investigated using the Fisher test based upon the ANalysis Of VAriance (ANOVA), the Standard Error of the Mean (SEM) and the Intraclass Correlation Coefficient (ICC).

Data collected showed a high level of repeatability of MVC measurement (normalized SEM from 1.1% to 6.4% of the mean). MNF and ARV initial values also showed a high level of repeatability (ICC>70% for all muscles and legs except right VMO). At 50% MVC level no relevant pattern of fatigue was observed for the VMO and VL muscles, suggesting that other portions of the quadriceps might have contributed to the generated effort. These observations seem to suggest that in the investigation of muscles belonging to a multi-muscular group at submaximal level, the more selective electrically elicited contractions should be preferred to voluntary contractions.     

Alternating stimulation of synergistic muscles during functional electrical stimulation cycling improves endurance in persons with spinal cord injury

Therapeutic effects of functional electrical stimulation (FES) cycling for persons with spinal cord injury (SCI) are limited by high rates of muscular fatigue. FES-cycling performance limits and surface mechanomyography (MMG) of 12 persons with SCI were compared under two different stimulation protocols of the quadriceps muscles. One strategy used the standard “co-activation” protocol from the manufacturer of the FES cycle which involved intermittent simultaneous activation of the entire quadriceps muscle group for 400 ms. The other strategy was an “alternation” stimulation protocol which involved alternately stimulating the rectus femoris (RF) muscle for 100 ms and the vastus medialis (VM) and vastus lateralis (VL) muscles for 100 ms, with two sets with a 400 ms burst. Thus, during the alternation protocol, each of the muscle groups rested for two 100 ms “off” periods in each 400 ms burst. There was no difference in average cycling cadence (28 RPM) between the two protocols. The alternation stimulation protocol produced longer ride times and longer virtual distances traveled and used lower stimulation intensity levels with no differences in average MMG amplitudes compared to the co-activation protocol. These results demonstrate that FES-cycling performance can be enhanced by a synergistic muscle alternation stimulation strategy.     

Above- and below-lesion EMG pattern mapping for controlling electrical stimulation of paraplegics to facilitate unbraced walker-assisted walking

We describe and evaluate above- and below-lesion EMG control of functional electrical stimulation (FES) in upper motor neuron paraplegics, in order to provide them with a patient-responsive system for walking with a walker support. Control is considered in terms of a combination of above-lesion EMG control and below-lesion response-EMG control. The above-lesion EMG is used to control the activation of limb functions involved in standing up and walking with FES, control being accomplished by analysing raw surface-EMG time-series patterns to discriminate between upper-trunk muscle contraction patterns, which in turn, are correlated with intended lower-limb functions involved in walking, so that natural and instinctive balance changes in paraplegics are controlled by the patient from above the lesion. The below-lesion response-EMG is the EMG produced in response to the FES pulses at the stimulation sites, for adjusting stimulation levels as needed when contractions weaken due to muscle fatigue. Above-lesion EMG is a stochastic (random-like) signal, being a response to unsynchronized motor neuron firings, whereas the below-lesion EMG is a deterministic signal responding to synchronized firings that result solely from the FES pulses. We also discuss the merits and difficulties of EMG control, and evaluate patient performance under such control, noting that FES-activated walking without adequate and patient-responsive control is of very limited use to paraplegics.     

Chronic electrical stimulation of nongrafted and grafted skeletal muscles in rats

Our purpose was to determine the effects of chronic electrical stimulation on the structure and function of neve-intact grafts in rats. Fourteen days after grafting, extensor digitorum longus (EDL) grafts (n = 6) and nongrafted EDL muscles (n = 4) were stimulated 8 h/day at 10 Hz for 26 days. Measurements were made subsequently of cytochrome c concentration, capillary density, contraction and relaxation times, developed tension, and the resistance to fatigue. Compared with contralateral nonstimulated grafts, chronically stimulated grafts demonstrated a 65% greater cytochrome c concentration, 45% greater number of capillaries per millimeter squared, 30% greater resistance to fatigue, 35% longer contraction time, 30% longer relaxation time, and 30% lower maximum tetanic tension. The differences that resulted from the stimulation of nongrafted EDL muscles were significant but of less magnitude. Chronic stimulation of 8 h/day provided a mixed stimulus for adaptation that enhanced the metabolic and endurance characteristics of fibers in muscles and grafts, but decreased the total fiber cross-sectional area and development of force.     

Some biochemical and functional characteristics of macrophages activated by Tetrahymena pyriformis

Phagocytosis, enzyme activities and capacity to release hydrogen peroxide (H2O2) and superoxide anion (O2-) of peritoneal macrophages from mice inoculated with Tetrahymena pyriformis, a free-living ciliate, were examined in comparison with resident and BCG-activated macrophages. Fc receptor-mediated phagocytosis of sheep erythrocytes was markedly increased in Tetrahymena-activated macrophages to the same level as that seen in BCG-activated ones. Tetrahymena-activated macrophages showed an increased level of acid phosphatase (lysosomal enzyme) and a reduced level of alkaline phosphodiesterase I (plasma membrane ectoenzyme) as compared with resident macrophages. Similar changes in the activities of the two enzymes were also observed in BCG-activated macrophages. Both Tetrahymena- and BCG-activated macrophages exhibited more enhanced capacity to release H2O2 and O2- than resident macrophages when stimulated with phorbol myristate acetate. In the macrophages from mice inoculated with varying doses of Tetrahymena, a significant correlation was observed between the increased capacity of H2O2 and O2- release as observed in the present study, and the enhanced toxoplasmacidal activity as observed in a previous study, in a dose-dependent fashion.     

Assessing kinematics and kinetics of functional electrical stimulation rowing

Hybrid functional electrical stimulation (FES) rowing has positive effects on cardiovascular fitness, producing significantly greater aerobic power than either upper body or FES exercise alone. However, there is minimal information on the kinematics, kinetics, and mechanical efficiency of FES-rowing in the spinal cord injured (SCI) population. This study examined the biomechanics of FES-rowing to determine how motions, forces, and aerobic demand change with increasing intensity. Six individuals with SCI and six able-bodied subjects performed a progressive aerobic capacity rowing test. Differences in kinematics (motion profiles), kinetics (forces produced by the feet and arms), external mechanical work, and mechanical efficiency (work produced/volume of oxygen consumed) were compared in able-bodied rowing vs. SCI FES-rowing at three comparable subpeak workloads. With increasing exercise intensity (measured as wattage), able-bodied rowing increased stroke rate by decreasing recovery time, while FES-rowing maintained a constant stroke rate, with no change in drive or recovery times. While able-bodied rowers increased leg and arm forces with increasing intensity, FES-rowers used only their arms to achieve a higher intensity with a constant and relatively low contribution of the legs. Oxygen consumption increased in both groups, but more so in able-bodied rowers, resulting in able-bodied rowers having twice the mechanical efficiency of FES-rowers. Our results suggest that despite its ability to allow for whole body exercise, the total force output achievable with FES-rowing results in only modest loading of the legs that affects overall rowing performance and that may limit forces applied to bone.     

Ultrastructural features of supraspinal muscles in rabbits after long-term transcutaneous lateral electrical surface stimulation (LESS)

Lateral electrical surface stimulation is one of methods used in the therapy of the progressive form of idiopathic scoliosis (IS) in children and youth. However, there are data suggesting that this method may lead to serious adverse side effects, when used for a too long period of time per day. To clarify this issue, the present study was aimed at disclosing possible changes in the ultrastructural appearance of rabbit supraspinal muscles undergoing long-term stimulation (9 h per day, 3 months), an animal model successfully used to mimic the situation in humans. In comparison to the control animals, muscles of "overstimulated" rabbits exhibited clear signs of microscopical lesions, including depletion and disintegration of myofilaments, proliferation, dilatation and, sometimes, swelling of sarcoplasmic reticulum and/or mitochondria, as well as signs of destruction of the Z line. The above-mentioned abnormalities, especially the signs of degenerative processes associated with the Z line and the observed microlesions strongly suggest that the failure of the long-term LESS therapy of the IS may be attributable to these ultrastructural lesions.     

Effect of functional electrical stimulation on the effort and walking speed,surface electromyography activity,and metabolic responses in stroke subjects

ObjectiveTo investigate the effects of functional electrical stimulation (FES) combined with conventional rehabilitation program on the effort and speed of walking, the surface electromyographic (sEMG) activity and metabolic responses in the management of drop foot in stroke subjects.MethodsFifteen patients with a drop foot resulting from stroke at least 3 months prior to the start of the trial took part in this study. All subjects were treated 1 h a day, 5 days a week, for 12 weeks, including conventional stroke rehabilitation program and received 30 min of FES to the tibialis anterior (TA) muscle of the paretic leg in clinical settings. Baseline and post-treatment measurements were made for temporal and spectral EMG parameters of TA muscle, walking speed, the effort of walking as measured by physiological cost index (PCI) and metabolic responses.ResultsThe experimental results showed a significant improvement in mean-absolute-value (21.7%), root-mean-square (66.3%) and median frequency (10.6%) of TA muscle EMG signal, which reflects increased muscle strength. Mean increase in walking speed was 38.7%, and a reduction in PCI of 34.6% between the beginning and at end of the trial. Improvements were also found in cardiorespiratory responses with reduction in oxygen consumption (24.3%), carbon dioxide production (19.9%), heart rate (7.8%) and energy cost (22.5%) while walking with FES device.ConclusionsThe results indicate that the FES may be a useful therapeutic tool combined with conventional rehabilitation program to improve the muscle strength, walking ability and metabolic responses in the management of drop foot with stroke patients.     

Feedback controlled force enhancement and activation reduction of voluntarily activated quadriceps femoris during sub-maximal muscle action

Stretch of activated muscles leads to enhanced forces compared to isometric contractions at the same muscle length and the same level of activation. This so-called residual force enhancement (RFE) is thought to be a property of all muscles and preparations. However, observations concerning the existence, amount and duration of RFE are inconsistent, especially for voluntary activated large human muscles. Therefore, physiological relevance for daily activity is still questionable and the purpose of this study was to examine whether RFE is present in voluntary sub-maximal activated quadriceps femoris (QF). Seated in a rotational dynamometer with EMG attached to superficial parts of QF, 30 subjects performed isometric and isometric-eccentric-isometric contractions (20° stretch, ω = 60° s⁻¹) at 30% and 60% of maximum voluntary activation (MVA) and contraction (MVC). To account for the complexity of the multi-headed QF, a compensation model based on physiological cross-sectional area and individual EMG-torque relations was used to interpret EMG data. For both levels of intensity and both feedback control strategies, ANOVA identified significant RFE (at the same level of activation) and reduced activation (at the same level of torque). Against expectations, RFE was independent of the level of activation.     

Electromyogram and force during stimulated fatigue tests of muscles in dominant and non-dominant hands

Mechanical and electrical properties were studied for the first dorsal interosseous muscle of the dominant (d-FDI) and non-dominant hand (nd-FDI). Observations were made before, during and after a fatigue test, fatigue being evoked by percutaneous electrical stimulation of the ulnar nerve. The test consisted of 30 Hz bursts of ten supramaximal 0.1 ms pulses, repeated once a second for 5 min. The measurements included the amplitude of the first and fifth compound muscle action potentials (M-waves) within bursts, the peak burst force and the amplitude and time course of single twitches. At the end of the fatigue test, burst force had decreased to about the same extent in the FDI of both hands. The final decline in first M-wave amplitude was, however, significantly more pronounced for the nd-FDI than for the d-FDI. There were no longer any significant discrepancies between the two muscles after a subsequent recovery-period of 15 min. Comparisons among nd-FDI of various individuals demonstrated the presence of significant inter-individual differences in fatigue-related force-drop without any associated differences in M-wave decline. Intra-individual variability was similar for fatigue-related force-drop and M-wave decline.     

Locomotion induced by non-contingent intracranial electrical stimulation: Dopamine dependence and general characteristics

Intracranial self-stimulation (ICSS) is induced by delivery of electrical stimulation contingent upon a response such as bar pressing. This procedure has been widely used to investigate the brain reward system. Recent investigations, however, have noted that non-contingent electrical stimulation, also called experimenter applied stimulation (EAS), produces a unique set of locomotion behaviors that appear to be related to ICSS, and that these behaviors resemble locomotion similar to those elicited by dopamine enhancing drugs. However, little is known about the general characteristics of EAS-induced locomotion. While ICSS appears to be robust, long lasting, and highly rewarding in that the rat will invest vast amounts of time or energy to obtain the electrical stimulation, these parameters have not been explored for EAS. Moreover, the dopamine dependence of EAS-evoked locomotion is also not firmly established. Thus, the present study investigated dopamine dependence and general characteristics of the EAS-induced locomotion to determine its similarity to ICSS. Results suggested that motor and limbic systems were strongly activated by non-contingent EAS, and that the resulting locomotion was dopamine dependent, robust, continued across long time horizons, and was greater than that evoked by contingent electrical stimulation.     

Electrical stimulation of human forearm extensor muscles as an indicator of handgrip fatigue and recovery

A set-up for percutaneous electrical stimulation of the forearm extensor muscles and measurement of wrist extension force is described. The frequency-force relationship and pulse duration-force relationship are described together with an experimental protocol showing that brief electrical test stimulations do not produce fatigue. In another set of experiments carried out a few weeks later, the subjects performed handgrip contractions: protocol A at 25% of maximal voluntary contraction (MVC) continuously until exhaustion, protocol B at 25% MVC intermittent (contraction + relaxation = 10 + 2 s) until exhaustion, and protocol C at 25% MVC intermittent until half the time to exhaustion. In all experiments, brief electrical stimulations were used to test the degree of fatigue during and up to 24 h after the experiments. There were marked changes in the force during stimulation at 20 and 100 Hz and these changes did not correlate with the increase in intramuscular temperature. Low frequency fatigue persisted for at least 24 h after protocol A and 1 h after protocols B and C. The significance of this is discussed and it is suggested that low frequency fatigue could be used as a sensitive indicator of muscle dysfunction after low and medium intensity exercise.     

Acetylcholinesterase in chick embryo latissimus dorsii muscles: effects of curarization and electrical stimulation

The accumulation of acetylcholinesterase (AChE), the changes in AChE-specific activity and in AChE molecular form distribution were studied in slow-tonic anterior latissimus dorsi (ALD) and in fast-twitch posterior latissimus dorsi (PLD) muscles of the chick embryo. From stage 36 (day 11) to stage 42 (day 17) of Hamburger and Hamilton, the AChE-specific activity decreased, while the relative proportion of asymmetric A 12 and A 8 forms increased. Repetitive injection of curare resulted at stage 42 (day 17) in a decrease in AChE-specific activity, in the accumulation of the synaptic AChE and in the expression of AChE asymmetric forms. Electrical stimulation at a relatively high frequency (40 Hz) of curarized ALD and PLD muscles resulted in a normal increase in AChE asymmetric forms, whereas a lower frequency (5 Hz) resulted in a dominance of globular forms. Both patterns of stimulation partly prevented the loss in synaptic AChE accumulations. These results suggest that in chick embryo muscles, muscle activity and its rhythms are involved in the normal evolution of AChE.