Electrically-induced Contractions Research Articles

Optimal Motor Point Search Using Mm-Order Electrode Arrays

Human-machine integration has been widely implemented in various fields, such as entertainment, human movement assistance, and rehabilitation. This study focuses on electrically-induced muscle contractions. In this technology, it is important to stimulate the optimal position, called the motor point (MP), on the muscle belly to induce the contraction with the lowest current injection. Because the positional relationship between the skin surface and muscles varies according to muscle contraction and body posture, it is difficult to achieve constant and accurate stimulation. Therefore, targeted motor intervention is not possible in several instances. We propose an approach that automatically identifies and stimulates a single precise MP in response to individual differences and postural changes using mm-order electrode arrays in two dimensions (2D). In this study, we develop a system to search for MPs by arranging 2-mm diameter electrodes in a 2D array. Our experiments successfully visualized the MPs in a 2D skin surface, which shifts according to the elbow joint angle change and twisting movement. The results demonstrated the feasibility of 2D electrode arrays. These findings contribute to the design of future devices and an algorithm for electrical muscle stimulation that enables effective muscle contraction.

Comparing preference related to comfort in torque-matched muscle contractions between two different types of functional electrical stimulation pulses in able-bodied participants

Context/Objective Functional electrical stimulation (FES) is commonly used in rehabilitation to generate electrically-induced muscle contractions. FES has been shown to assist in the recovery of voluntary motor functions after stroke or spinal cord injury. However, discomfort associated with FES can motivate patients to withdraw their participation from FES therapy despite its benefits. To address this issue, a functional electrical stimulator, called MyndMove™ (MyndTec Inc., Canada), has been developed to generate more comfortable contractions than conventional stimulators. Design Cross-sectional, interventional, with two treatment arms. Setting A laboratory within a rehabilitation center. Participants Twelve able-bodied participants. Intervention FES delivered with two different stimulators, MyndMove™ and Compex Motion (Compex, Switzerland), during muscle contractions of high, moderate and low stimulation intensity. Outcome Measures Comfort-related preference to a given stimulator and the discomfort score rated through a Numeric Rating Scale (NRS-101) for both stimulators. Results Participants perceived a reduction in discomfort during high-intensity stimulation generated using MyndMove™. In addition, MyndMove™ stimulations were preferred in 60% of all contractions. The reduction in discomfort associated with MyndMove™ might be due the fact that MyndMove™ delivers less charge to generate contractions of equivalent intensity, compared to Compex Motion. Conclusion Reducing discomfort during FES may help in generating stronger and more clinically useful contractions, increasing accessibility of FES therapy to include individuals with low tolerance to FES.

Measurement of Insulin- and Contraction-Stimulated Glucose Uptake in Isolated and Incubated Mature Skeletal Muscle from Mice.

Skeletal muscle is an insulin-responsive tissue and typically takes up most of the glucose that enters the blood after a meal. Moreover, it has been reported that skeletal muscle may increase the extraction of glucose from the blood by up to 50-fold during exercise compared to resting conditions. The increase in muscle glucose uptake during exercise and insulin stimulation is dependent on the translocation of glucose transporter 4 (GLUT4) from intracellular compartments to the muscle cell surface membrane, as well as phosphorylation of glucose to glucose-6-phosphate by hexokinase II. Isolation and incubation of mouse muscles such as m. soleus and m. extensor digitorum longus (EDL) is an appropriate ex vivo model to study the effects of insulin and electrically-induced contraction (a model for exercise) on glucose uptake in mature skeletal muscle. Thus, the ex vivo model permits evaluation of muscle insulin sensitivity and makes it possible to match muscle force production during contraction ensuring uniform recruitment of muscle fibers during measurements of muscle glucose uptake. Moreover, the described model is suitable for pharmacological compound testing that may have an impact on muscle insulin sensitivity or may be of help when trying to delineate the regulatory complexity of skeletal muscle glucose uptake. Here we describe and provide a detailed protocol on how to measure insulin- and contraction-stimulated glucose uptake in isolated and incubated soleus and EDL muscle preparations from mice using radiolabeled [3H]2-deoxy-D-glucose and [14C]mannitol as an extracellular marker. This allows accurate assessment of glucose uptake in mature skeletal muscle in the absence of confounding factors that may interfere in the intact animal model. In addition, we provide information on metabolic viability of incubated mouse skeletal muscle suggesting that the methodapplied possesses some caveats under certain conditions when studying muscle energy metabolism.

Architectural Changes in Superficial and Deep Compartments of the Tibialis Anterior During Electrical Stimulation Over Different Sites

Electrical stimulation is widely used in rehabilitation to prevent muscle weakness and to assist the functional recovery of neural deficits. Its application is however limited by the rapid development of muscle fatigue due to the non-physiological motor unit (MU) recruitment. This issue can be mitigated by interleaving muscle belly (mStim) and nerve stimulation (nStim) to distribute the temporal recruitment among different MU groups. To be effective, this approach requires the two stimulation modalities to activate minimally-overlapped groups of MUs. In this manuscript, we investigated spatial differences between mStim and nStim MU recruitment through the study of architectural changes of superficial and deep compartments of tibialis anterior (TA). We used ultrasound imaging to measure variations in muscle thickness, pennation angle, and fiber length during mStim, nStim, and voluntary (Vol) contractions at 15% and 25% of the maximal force. For both contraction levels, architectural changes induced by nStim in the deep and superficial compartments were similar to those observed during Vol. Instead, during mStim superficial fascicles underwent a greater change compared to those observed during nStim and Vol, both in absolute magnitude and in their relative differences between compartments. These observations suggest that nStim results in a distributed MU recruitment over the entire muscle volume, similarly to Vol, whereas mStim preferentially activates the superficial muscle layer. The diversity between spatial recruitment of nStim and mStim suggests the involvement of different MU populations, which justifies strategies based on interleaved nerve/muscle stimulation to reduce muscle fatigue during electrically-induced contractions of TA.

Cessation of electrically-induced muscle contraction activates autophagy in cultured myotubes

Exercise is known to improve skeletal muscle function. The mechanism involves muscle contraction-induced activation of the mTOR pathway, which plays a central role in protein synthesis. However, mTOR activation blocks autophagy, a recycling mechanism with a critical role in cellular maintenance/homeostasis. These two responses to muscle contraction look contradictory to the functional improvement of exercise. Herein, we investigate these paradoxical muscle responses in a series of active–inactive phases in a cultured myotube model receiving electrical stimulation to induce intermittent muscle contraction. Our model shows that (1) contractile activity induces mTOR activation and muscle hypertrophy but blocks autophagy, resulting in the accumulation of damaged proteins, while (2) cessation of muscle contraction rapidly activates autophagy, removing damaged protein, yet a prolonged inactive state results in muscle atrophy. Our findings provide new insights into muscle biology and suggest that not only muscle contraction, but also the subsequent cessation of contraction plays a substantial role for the improvement of skeletal muscle function.

Sex And Fiber-type Differences: Vascular ATP-sensitive K + (K ATP ) Channels Support Critical Speed And Interstitial PO 2

Glibenclamide (GLI), prescribed to Type II diabetes patients, enhances insulin release by inhibiting pancreatic KATP channels. KATP channels support maximal aerobic capacity (V̇O2max) and blood flow during treadmill running in male rats. Whether high-intensity exercise tolerance (i.e. critical speed, CS) and muscle O2 delivery-utilization matching (interstitial PO2, PO2is) is impaired, and whether sex differences exist in KATP function, are unknown. PURPOSE We hypothesized that systemic inhibition of KATP channels via GLI would decrease V̇O2max and CS, while local inhibition would decrease contracting PO2is and blood flow within fast-twitch oxidative (mixed gastrocnemius (MG)) and slow-twitch oxidative (soleus (SOL)) muscles with females (F and F+OVX) expressing the greatest reduction. METHODS: Male (n=12), female (n=10, proestrus) and ovariectomized female (F+OVX; n=12) Sprague-Dawley rats with and without GLI (10 mg kg-1 in DMSO i.p.). V̇O2max and CS were assessed using state-of-the art techniques on a motorized treadmill. PO2is was determined, before and after GLI superfusion (5 mg kg-1), via phosphorescence quenching (G4) in the exposed MG and SOL muscles during electrically-induced contractions and blood flow by fluorescent-labeled microspheres (15 μm). RESULTS: GLI decreased V̇O2max in female (71.5 ± 1.0 vs 67.9 ± 1.5) and F+OVX (76.8 ± 1.4 vs 74.4 ± 1.4; p<0.05 for both) but not males (81.5 ± 2.0 vs 80.8 ± 2.0 mL O2 min-1 kg-1; p>0.05). CS was reduced equivalently in all groups (8-11%; p<0.05). GLI reduced MG blood flow (female: 49 ± 9 vs 34 ± 5; male: 50 ± 5 vs 35 ± 4) and PO2is (female: 7.3 ± 0.5 vs 6.1 ± 0.5; male: 8.9 ± 1.1 vs 7.2 ± 0.5), but not SOL, of female and male rats (p<0.05). Conversely, in F+OVX, PO2is was reduced in the SOL (14.5 ± 1.5 vs 10.2 ± 1.1; p<0.05), but not MG. CONCLUSION: These data support the role of vascular KATP channels in exercise tolerance (i.e. CS) by matching O2 delivery-utilization with ovariectomy shifting KATP channel effects from fast- to slow-twitch muscles. Supported by NIH Grants: HL108328 and F31HL145981

Optimizing neuromuscular electrical stimulation for hand opening

Aim: To investigate the effect of introducing an interphase interval to a biphasic pulse on force production and muscle fatigue, during stimulation of the wrist and finger extensors and to determine whether the IPI effect on force is dependent on electrode position.Methods: Electrically-induced contraction forces of the wrist and finger extensors were measured in 15 healthy subjects undergoing stimulation. These forces were assessed with interphase interval settings at 0, 100, and 200μs, with both electrodes located just distal to common extensor origin (proximal placement) or with the distal electrode placed over the extensor and abductor policies longus muscles (distal placement). The degree of discomfort related to stimulation sensation was evaluated using a numeric rating scale. Muscle fatigue was measured during proximal placement.Results: Under both electrode locations, introduction of 100 or 200 μs interphase interval enhanced force production; yet, only the 100μs interphase interval increased force without increasing discomfort. Additionally, stimulation sensation was more comfortable with proximal placement. Introducing interphase interval significantly increased the muscle force output during a repetitive stimulation fatigue protocol.Conclusions: When using neuromuscular electrical stimulation to activate the wrist and finger extensors, clinicians should consider locating both stimulating electrodes proximally over the extensor surface of the forearm and apply a 100 µs interphase interval to a biphasic pulse. Future research that should establish these findings in individuals with various pathologies, especially in patients with residual hand spasticity.

Effects of amplitude and phase-duration modification on electrically induced contraction force and discomfort.

Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation. However, the optimal combination of phase-duration and amplitude for enhancing motor output is not yet resolved. To test the effects of increasing phase-duration and amplitude on isometric knee extension force and discomfort, while controlling the effects of electrode-skin resistance and body mass index (BMI). Twenty-one healthy volunteers participated in the study. Stimulation was set at 250 μsec phase-duration and 45Hz to evoke 10% of maximal voluntary isometric contraction of the quadriceps. Electrode-skin resistance was measured. Then, electrically induced contraction (EIC) forces and discomfort level were measured under four conditions: Moderate (25%) or substantial increase (50%) from baseline amplitude with constant phase-duration and moderate (25%) or substantial increase (50%) in phase-duration with amplitude constant. Compared with baseline, EIC force was significantly higher in all intensification conditions, while discomfort was significantly greater in all conditions except for moderate increase in phase-duration (p= 0.44). Amplitude intensification produced significantly higher force and greater discomfort than phase-duration. Electrode-skin resistance and BMI were not significant covariates. Greater force is elicited by increasing amplitude than by similar increase in phase-duration; however, the associated discomfort is also higher. Clinicians may use phase-duration while conditioning for NMES.

Effects of Duchenne muscular dystrophy on muscle stiffness and response to electrically-induced muscle contraction: A 12-month follow-up

The present study aimed to assess the ability of muscle stiffness (shear modulus) and response to electrically-induced muscle contraction to detect changes in muscle properties over a 12-month period in children with Duchenne muscular dystrophy (DMD). Ten children with DMD and nine age-matched healthy male controls participated in two experimental sessions (T0 and T+12months) separated by 12.4 ± 0.9 months. Two contractions of the biceps brachii were electrically-induced during which an ultrasound probe was placed over the muscle. The resting shear modulus was measured using elastography from six muscles. Evoked maximal torque was increased at T+12months in controls (+11.2 ± 7.6%, P < 0.001) but was not modified in children with DMD (P = 0.222). Electromechanical delay (+12.9 ± 11.3%, P < 0.001) and its force transmission component (+10.1 ± 21.6%, P = 0.003) were significantly longer at T+12months than T0 for children with DMD. The results revealed an increase in muscle stiffness at T+12months in children with DMD for tibialis anterior (+75.1 ± 93.5%, P = 0.043), gastrocnemius medialis (+144.8 ± 180.6%, P = 0.050) and triceps brachii (+35.5 ± 32.2%, P = 0.005). This 12-month follow-up study demonstrates that electromechanical delay and elastography may help detect subtle muscle impairments in patients with DMD. These sensitive outcomes may improve the follow-up of innovative therapeutic interventions within the field of DMD.

Muscle Fatigue Affects the Interpolated Twitch Technique When Assessed Using Electrically-Induced Contractions in Human and Rat Muscles.

The interpolated twitch technique (ITT) is the gold standard to assess voluntary activation and central fatigue. Yet, its validity has been questioned. Here we studied how peripheral fatigue can affect the ITT. Repeated contractions at submaximal frequencies were produced by supramaximal electrical stimulations of the human adductor pollicis muscle in vivo and of isolated rat soleus fiber bundles; an extra stimulation pulse was given during contractions to induce a superimposed twitch. Human muscles fatigued by repeated 30-Hz stimulation trains (3 s on–1 s off) showed an ~80% reduction in the superimposed twitch force accompanied by a severely reduced EMG response (M-wave amplitude), which implies action potential failure. Subsequent experiments combined a less intense stimulation protocol (1.5 s on–3 s off) with ischemia to cause muscle fatigue, but which preserved M-wave amplitude. However, the superimposed twitch force still decreased markedly more than the potentiated twitch force; with ITT this would reflect increased “voluntary activation.” In contrast, the superimposed twitch force was relatively spared when a similar protocol was performed in rat soleus bundles. Force relaxation was slowed by >150% in fatigued human muscles, whereas it was unchanged in rat soleus bundles. Accordingly, results similar to those in the human muscle were obtained when relaxation was slowed by cooling the rat soleus muscles. In conclusion, our data demonstrate that muscle fatigue can confound the quantification of central fatigue using the ITT.

The Effect of an Interphase Interval on Electrically Induced Dorsiflexion Force and Fatigue in Subjects With an Upper Motor Neuron Lesion.

The study objective was to investigate the effects of an interphase interval (IPI) interposed between the two phases of a biphasic symmetric pulse, on electrically induced contraction (EIC) forces and fatigue during stimulation of the ankle dorsiflexors in individuals with an upper motor neuron lesion (UMNL). The dorsiflexor muscles of 20 subjects with UMNL routinely using functional electrical stimulation to correct a foot drop during ambulation, were electrically stimulated with biphasic pulses (250 µs phase duration and 35 Hz pulse frequency) using nine IPI durations (ranging from 0 to 400 µs). The induced muscle force and fatigue were measured. A significant positive correlation was found between IPI duration and induced muscle force. Introducing a 250 µs IPI significantly decreased rate of muscle fatigue compared to stimulation with no IPI (P < 0.05). Thus, the introduction of an IPI may reduce the current intensity required to achieve a specific force during functional electrical stimulation in individuals with UMNL. Reduction in muscle fatigue may shorten the conditioning period necessary for first time users of functional electrical stimulation.

Characterization of V0162, a new long-acting antagonist at human M3 muscarinic acetylcholine receptors

The anticholinergic properties of the mequitazine enantiomer V0162 make it a drug candidate for the treatment of chronic obstructive airway diseases. Here, we compared V0162’s in vitro pharmacological activity at recombinant human M3 muscarinic acetylcholine receptors (hM3Rs) with that of other anticholinergics, using (i) a radioligand binding assay, (ii) a functional reporter gene assay and (iii) a bronchoconstriction inhibition assay on human bronchial preparations. V0162 had high affinity for hM3Rs, with a pKi varying from 9.01 after a 2h incubation to 9.21 after 23h. The other mequitazine enantiomer (V0114) was less potent. V0162 displayed rapid off-kinetics and a biphasic time course of binding. V0162 was found to be an antagonist behaving as an inverse agonist for hM3R-mediated reporter gene activation, with much the same efficacy as atropine, ipratropium and tiotropium. However, in contrast to ipratropium and atropine, V0162’s inhibitory potency was only slightly affected by compound washout. V0162 antagonized acetylcholine-mediated contractions in a human bronchial preparation; the pA2 values increased with the incubation time (up to 2h). Moreover, there was a progressive increase in V0162’s ability to inhibit electrically-induced contractions, which persisted after compound washout. In conclusion, V0162 is the most active mequitazine enantiomer at hM3Rs and shows a complex pattern of binding to the membrane compartment. These particular features may be of therapeutic value when persistent antagonism at hM3Rs is required.

Effects of interphase interval and stimulation form on dorsiflexors contraction force

Neuromuscular electrical stimulation (NMES) is commonly used in rehabilitation to restore movement to patients following orthopedic and neurological injuries. When applying NMES the goal is to induce the strongest contractions with minimal discomfort. This study aimed to determine whether introducing an interphase interval (IPI) to 400 μ sec biphasic pulses during stimulation of the dorsiflexor muscles would have the same effect on force production and stimulation discomfort when stimulation was controlled by constant current (CC) or constant voltage (CV). Eighteen healthy volunteers participated in the study. Each subject participated in one session. Electrically induced contraction (EIC) forces and degree of discomfort were measured during stimulation of the ankle dorsiflexors with 0, 100 and 200 μ sec IPI settings with CC or CV. Compared to IPI = 0 μ sec, introduction of a 200 μ sec IPI increased force production with CC stimulation without increasing discomfort. No other enhancements in the EIC force compared to IPI = 0 μ sec were found between the IPIs with CC or CV. IPI may increase the effectiveness of biphasic pulse with CC, but not with CV stimulation.

Effect of kidsolone on isolated rat′s tracheal smooth muscle

Purpose: Prednisolone (Kidsolone) is an anti-inflammatory drug that is mainly used for patients with chronic obstructive airway diseases (COAD), such as asthma and chronic obstructive pulmonary diseases (COPD). The objective of this study was to determine the effects of Kidsolone on the trachea of rats in vitro . Materials and Methods: We tested the effectiveness of Kidsolone on isolated rat trachea submersed in Krebs solution in a muscle bath. Changes in tracheal contractility in response to the application of parasympathetic mimetic agents were measured. The following assessments of Kidsolone were performed: (1) Effect on tracheal smooth muscle resting tension; (2) effect on contraction caused by 10-6 M methacholine; (3) effect of the drug on electrically-induced tracheal smooth muscle contractions. Result: Our results demonstrated that no significant effects were induced by the addition of 10-8-10-5 M Kidsolone on tracheal tension after methacholine treatment, indicating that Kidsolone had no anti-cholinergic effect. It alone had a minimal effect on the basal tension of the trachea as the concentration increased. Furthermore, Kidsolone did not affect electrical field stimulation-induced spike contraction, which represent the Kidsolone could not antagonize the parasympathetic innervation responsible for trachea smooth muscle contraction. Conclusion: The immediate effect of Kidsolone on COAD may be indirectly. Therefore, sorely use of inhalation Kidsolone without β2-agonist in treating acute asthma or COPD attack may be more suboptimal than co-administration of them.

Involvement of the P2X7 purinergic receptor in colonic motor dysfunction associated with bowel inflammation in rats.

Background and PurposeRecent evidence indicates an involvement of P2X7 purinergic receptor (P2X7R) in the fine tuning of immune functions, as well as in driving enteric neuron apoptosis under intestinal inflammation. However, the participation of this receptor in the regulation of enteric neuromuscular functions remains undetermined. This study was aimed at investigating the role of P2X7Rs in the control of colonic motility in experimental colitis.Experimental ApproachColitis was induced in rats by 2,4-dinitrobenzenesulfonic acid. P2X7R distribution was examined by immunofluorescence analysis. The effects of A804598 (selective P2X7R antagonist) and BzATP (P2X7R agonist) were tested on contractions of longitudinal smooth muscle evoked by electrical stimulation or by carbachol in the presence of tetrodotoxin.Key ResultsP2X7Rs were predominantly located in myenteric neurons, but, in the presence of colitis, their expression increased in the neuromuscular layer. In normal preparations, A804598 elicited a negligible increase in electrically induced contractions, while a significant enhancement was recorded in inflamed tissues. In the presence of Nω-propyl-L-arginine (NPA, neuronal nitric oxide synthase inhibitor) the A804598 effects were lost. P2X7R stimulation with BzATP did not significantly affect electrical-induced contractions in normal colon, while a marked reduction was recorded under inflammation. The inhibitory effect of BzATP was antagonized by A804598, and it was also markedly blunted by NPA. Both P2X7R ligands did not affect carbachol-induced contractions.Conclusions and ImplicationsThe purinergic system contributes to functional neuromuscular changes associated with bowel inflammation via P2X7Rs, which modulate the activity of excitatory cholinergic nerves through a facilitatory control on inhibitory nitrergic pathways.

Silodosin and tadalafil have synergistic inhibitory effects on nerve-mediated contractions of human and rat isolated prostates

Lower urinary tract symptoms (LUTS) in men with benign prostatic hyperplasia (BPH) are associated with erectile dysfunction. Alpha-1-adrenoceptor antagonists are effective drugs for treating symptomatic BPH. Clinical data show improvements in LUTS by phosphodiesterase 5 inhibitors. This study aimed to evaluate effects of silodosin, a highly selective α1A-adrenoceptor antagonist, alone or in combination with the phosphodiesterase 5 inhibitor tadalafil on contractions of isolated human and rat prostates. In organbath studies, effects of increasing concentrations of silodosin (1nM–1µM) and tadalafil (100nM–100µM) on contractions by electrical field stimulation or phenylephrine of human and rat prostate strip preparations were investigated. The combination silodosin and tadalafil reduced electrically-induced contractions of human prostate preparations better than single drugs alone. At any frequencies (1–32Hz), inhibitory effects of combined therapy (P-values vs single drug) in human tissue were 26–42% (1nM silodosin+100nM tadalafil; P<0.05), 40–58% (10nM silodosin+1µM tadalafil; P<0.001–0.05), 56–67% (100nM silodosin+10µM tadalafil; P<0.01–0.05), and 33–55% (1µM silodosin+100µM tadalafil P<0.01–0.05). Similar findings were obtained in rat prostate preparations. In human and rat prostate tissue, the drug combination exerted similar inhibitory effect on phenylephrine contractions as silodosin alone. Silodosin plus tadalafil had greater potency than each drug alone to inhibit prostate contractions to electrical field stimulation but not to phenylephrine. This study supports the clinical application of a combination of an α1A-adrenoceptor antagonist and a phosphodiesterase 5 inhibitor for symptomatic BPH and suggests that the drug combination requires endogenous nerve-activity for optimal effect.

A pilot spectroscopy study on time-varying bioimpedance during electrically-induced muscle contraction.

Alterations in the health of muscles can be evaluated through the use of electrical impedance myography (EIM). To date, however, nearly all work has relied upon single-frequency/spectroscopy stepped-sine measurements of static muscle (contracted or relaxed). In this work, we assessed the temporal alterations in the impedance spectrum (1 kHz to 1 MHz) behavior of gastrocnemius during the active process of muscle contraction. The approach is based on the multisine impedance spectroscopy technique. The gastrocnemii of a wild type mouse was measured during electrically-induced muscle contraction via direct current stimulation of the sciatic nerve. The processes of contraction and relaxation were clearly identified in the time-frequency impedance spectrum likely corresponding to an increase muscle fiber diameter. The technique of dynamic multisine EIM has the potential of providing useful insights into contractile mechanisms of muscle in health and disease.

The effect of electrode placement and interphase interval on force production during stimulation of the dorsiflexor muscles.

The aims of this study were to investigate whether introducing an interphase interval (IPI) to biphasic pulses during stimulation of the dorsiflexor muscles would affect force production and to determine whether the IPI effect is dependent on electrode position. Twelve healthy volunteers participated in the study. Each subject participated in one session during which electrically induced contraction (EIC) forces of the ankle dorsiflexors were measured with five different IPI settings ranging from 0 to 400 μs. Forces of EICs were assessed with the electrodes placed either with the proximal electrode positioned over the common peroneal nerve and the second electrode over the dorsiflexor muscles or with both electrodes located over the dorsiflexor muscles. The order of electrode placements and of the different IPI settings was randomized across subjects. The results indicated that the introduction of a 100-μs-long IPI may enhance force production when one electrode is located over the common peroneal nerve. However, increasing the duration of the IPI beyond 100 μs did not result in further increase in force production. In contrast, the introduction of an IPI did not increase force production when both electrodes were located over the dorsiflexor muscles. These findings may help to optimize stimulation settings during functional electrical stimulation to prevent foot-drop.

Hydrogel-based bioassay sheets for in vitro evaluation of contraction-dependent metabolic regulation in skeletal muscle cells.

Two types of hydrogel-based bioassay sheets were developed for in vitro evaluation of contraction-dependent metabolic regulation in skeletal muscle cells: one is an oxygen sensor sheet and the other is an immunocapture sheet for a myokine, interleukin-6 (IL-6). These soft, molecularly permeable hydrogel-based bioassay sheets were directly laminated to another hydrogel on which myotubes were micropatterned, and displayed usefully measurable changes in local oxygen consumption and IL-6 secretion of myotubes upon electrically-induced contraction.

A brief interphase interval interposed within biphasic pulses enhances the contraction force of the quadriceps femoris muscle

There is still unsettled controversy regarding the optimal neuromuscular electrical stimulation (NMES) parameters that will induce the strongest contractions with minimal discomfort. The purpose of this study was to determine whether the introduction of an interphase interval (IPI) interposed within the two phases of biphasic pulses will affect sensory and motor thresholds, the force of the electrically induced contractions (EIC), and the degree of discomfort associated with these contractions. Within subjects, repeated measures design was employed with 29 healthy young volunteers. Sensory and motor thresholds and the force of the EIC were determined with biphasic pulses. Five different settings were tested in random order with IPIs ranging between 0 and 250 μ sec. Introducing IPIs during stimulation with biphasic pulses enhanced force production, with the increase related to the duration of the IPI. The sensory and motor thresholds, as well as the degree of discomfort associated with the induced contractions, were not affected by the IPIs. Biphasic pulses that incorporate IPIs may increase the effectiveness of NMES in terms of force production.