[Influence of low frequency magnetic field on chosen parameters of oxidative stress in rat's muscles]

Free radicals are atoms, molecules or their fragments, which excess leads to the development of the oxidative stress, which is caused of many neoplasmic, neurodegenerative, inflammatory diseases and aging the organism. The main of exogenous sources of free radicals are among others: industrial pollution, tobacco smoke, ionizing radiation, ultrasound and magnetic field. The low magnetic field is applied in the physician therapy. The aim of this study was to evaluate the influence of low magnetic field on the parameters of oxidative stress in rat's muscles.

MATERIALS AND METHODS

Thirty male rats, weight of 280-300 g were randomly divided into three experimental groups: control I and treatment II and III (ELFMF-exposed), each containing seven animals. Animals in treat group II were exposed to 40 Hz, 7 mT for 0.5 h/day for 14 days (this kind of the ELFMF is mostly use in magnetotherapy) while, group III was exposed to 40 Hz, 7 mT for 1 h/day for 14 days. Control rats were in separate room without exposing to ELFMF. Immediately after the last exposure, the part of muscles was taken under pentobarbital anaesthesia. The effects of exposure to ELFMF on oxidative states were assessed on the measurements of concentration of -SH group, H2O2, and the concentration of proteins in muscles homogenates.

RESULTS

Exposure to ELFMF: 40 Hz, 7 mT, 30 and 60 min/day used for 2 weeks caused significant increase in -SH group concentration and decrease of the protein concentration in the muscles homogenates.

CONCLUSION

Low magnetic field used in magnetotherapy causes the significant changes of the generating the reactive forms of oxygen in the muscles which depend on the parameters of low magnetic field.

Rat muscle opacity decrease due to the osmosis of a simple mixture

It is known that the fibrous structure of muscle causes light scattering. This phenomenon occurs due to the refractive index discontinuities located between muscle fibers and interstitial fluid. To study the possibility of reducing light scattering inside muscle, we consider its spectral transmittance evolution during an immersion treatment with an optical clearing solution containing ethanol, glycerol, and distilled water. Our methodology consists of registering spectral transmittance of muscle samples while immersed in that solution. With the spectral data collected, we represent the transmittance evolution for some wavelengths during the treatment applied. Additionally, we study the variations that the treatment has caused on the samples regarding tissue refractive index and mass. By analyzing microscopic photographs of tissue cross section, we can also verify changes in the internal arrangement of muscle fibers caused by the immersion treatment. Due to a mathematical model that we develop, we can explain the variations observed in the studied parameters and estimate the amount of optical clearing agent that has diffused into the tissue samples during the immersion treatment. At the end of the study, we observe and explain the improvement in tissue spectral transmittance, which is approximately 65% after 20 min.

[Muscle regeneration and the state of the thymus in adult rats under laser irradiation and alloplasty of the gastrocnemius muscles and diaphragm of newborn rats]

The regeneration of gastrocnemius muscles of adult rats under implantation conditions in areas of muscle tissue damage in newborn rats has been studied. Alloplasty was performed using minced gastrocnemius and diaphragm muscles, which differs at birth in animals by degree of differentiation. The rat-recipient area of alloplasty was subjected to He-Ne laser radiation before operation, with the aim of reducing the immune response to allogenic muscle tissue. It has been shown that the number of regenerating myofibers produced in implanted gastrocnemius muscles is more than in alloplants from diaphragms. However, the formation of cartilage, bone, and adipose tissue foci were observed in the alloplastic region throughout the whole regeneration period. After implantation of minced diaphragm muscles, cartilage nodes were observed only in 7-day regenerates. At the end of observation, in the first instance, the area of muscle trauma in adult rat muscles was replaced by adipose tissue, even in the case of initial laser irradiation. During the implantation of diaphragm muscles, the area of trauma was filled with regenerating muscle tissue.

Evaluation of transfection efficiency in skeletal muscle using nano/microbubbles and ultrasound

Recent studies have revealed that ultrasound contrast agents with low-intensity ultrasound, namely, sonoporation, can noninvasively deliver therapeutic molecules into target sites. However, the efficiency of molecular delivery is relatively low and the methodology requires optimization. Here, we investigated three types of nano/microbubbles (NMBs)-human albumin shell bubbles, lipid bubbles and acoustic liposomes-to evaluate the efficiency of gene expression in skeletal muscle as a function of their physicochemical properties and the number of bubbles in solution. We found that acoustic liposomes showed the highest transfection and gene expression efficiency among the three types of NMBs under ultrasound-optimized conditions. Liposome transfection efficiency increased with bubble volume concentration; however, neither bubble volume concentration nor their physicochemical properties were related to the tissue damage detected in the skeletal muscle, which was primarily caused by needle injection.

Mirror movements and ipsilateral motor evoked potentials in ALS

It can be difficult to detect upper motor neuron (UMN) involvement in early amyotrophic lateral sclerosis (ALS). The present study tested the usefulness of mirror movements (MMs), i.e., contralateral coactivation of hand muscles, as a UMN sign in ALS. Thirty-seven patients with possible, probable or definite ALS and 19 patients with suspected ALS without clinical signs of UMN involvement, 21 disease controls and 15 healthy volunteers were included. MMs were studied clinically, electromyographically and by transcranial magnetic stimulation (TMS), looking for ipsilateral motor evoked potentials (IMEPs). MMs were observed clinically in 15 ALS patients (27%) and electromyographically in 28 (50%). IMEPs in the abductor pollicis brevis muscle following TMS were recorded in 34 (61%) of all ALS patients and in nine (47%) out of 19 patients with suspected ALS, but not in healthy controls. Central motor conduction times were prolonged in 15 ALS patients (27%). It is concluded that MMs, especially if studied by EMG and TMS (IMEPs) can essentially improve detection of UMN involvement, especially in early stages of ALS.

Regeneration of skeletal muscles and state of thymus in γ‐irradiated rats under laser therapy of the area of muscle trauma

The gamma-irradiation of adult rats with a semi-lethal dose (6 Gy) suppressed the posttraumatic regeneration of skeletal muscles and brought about considerable destructive changes in the thymus. The effect of He-Ne laser radiation at a total dose 4.5-5.4 J/cm2 at each operated leg in irradiated rats stimulated the regenerative capacity of skeletal muscle tissue, the healing of skin-muscle wound, and the processes of postradiation recovery in thymus cells (a decrease of chromosome aberrations). The histological structure of regenerates had more muscle pattern. At the same time, the positive dynamics of regenerative processes in muscles was achieved by an increased functional load on the thymus. To stimulate the regeneration of irradiated muscles on the background of a more moderate load on the thymus, the prolonged period of laser therapy and fragmentary distribution of laser exposures during muscle regeneration were preferable. Wound healing improved visibly. Nor formation of chronic radiation ulcers on operated shins was observed.

EFFECTS OF VITAMIN E AND ELECTRICAL STIMULATION ON THE DENERVATED RAT GASTROCNEMIUS MUSCLE MALONDIALDEHYDE AND GLUTATHIONE LEVELS

Effects of vitamin E treatment and local electrical stimulation on progression of atrophy in the denervated rat gastrocnemius muscle were studied. Denervation was performed by right leg sciatic nerve axotomy. Electrical stimulation (3-10 mA ms(-1), 10 min per day for 7 days) was applied to the right gastrocnemius muscle starting from day 1 of denervation. The muscle samples were assayed for malondialdehyde (MDA) and glutathione levels, as well as the histological appearance after 8 days of denervation. MDA levels were markedly increased following denervation. However, electrical stimulation, vitamin E treatment (30 mg kg(-1), i.m., everyday for 7 days), and combination of electrical stimulation and vitamin E treatment markedly reduced MDA levels. Glutathione levels were significantly decreased in the denervation group. Electrical stimulation, vitamin E treatment, and electrical stimulation plus vitamin E treatment prevented these reductions in glutathione levels. In the vitamin E treatment group, glutathione levels were markedly higher than in the control group. These results indicate that electrical stimulation and vitamin E treatment alone, or in combination, were able to prevent the effects of denervation on muscle atrophy.

[Morphofunctional characteristics of the thymus and the muscle regenerating under laser irradiation and alloplasty of the adult muscle tissue in the trauma region]

The effect of muscle tissue alloplasty and He-Ne laser radiation on the skeletal muscle regeneration and thymus function was studied. Allogenic muscle tissue was implanted from an adult rat. Without laser irradiation (the first series of experiments), initial enhancement of thymus recovery observed on day 7 after alloplasty (a characteristic stress response to operation) was followed by gradual destructive changes in the thymus tissue. On day 30 after alloplasty, connective tissue developed in the implantation area in muscle regenerates, and the muscle tissue accounted for 64 +/- 2%. Implantation of unirradiated allografts into the muscles of recipient rats preirradiated with a He-Ne laser (the second series of experiments) resulted in a nearly complete destruction of the thymus and suppression of its function; the mitotic index of thymocytes was low. These changes were observed throughout the experiment starting immediately after the operation. In this case, the allogenic transplant retained the ability to develop: the 30-day repairing muscles consisted of 71 +/- 2% of muscle tissue. When an allograft preirradiated with a He-Ne laser was implanted into unirradiated rats (the third series of experiments), thymus destruction at the beginning of the postoperative period was much less significant than in the second series of experiments but more pronounced than in the first series. Then, thymus recovered more rapidly, the allogenic transplant was resorbed, and the muscle tissue in the regenerates accounted for 62 +/- 3%.

Anti-inflammatory effects of electronic signal treatment

Inflammation often plays a key role in the perpetuation of pain. Chronic inflammatory conditions (e.g. osteoarthritis, immune system dysfunction, micro-circulatory disease, painful neuritis, and even heart disease) have increased as baby boomers age. Medicine's current anti-inflammatory choices are NSAIDs and steroids; the value in promoting cure and side effect risks of these medications are unclear and controversial, especially considering individual patient variations. Electricity has continuously been a powerful tool in medicine for thousands of years. All medical professionals are, to some degree, aware of electrotherapy; those who directly use electricity for treatment know of its anti-inflammatory effects. Electronic signal treatment (EST), as an extension of presently available technology, may reasonably have even more anti-inflammatory effects. EST is a digitally produced alternating current sinusoidal electronic signal with associated harmonics to produce theoretically reasonable and/or scientifically documented physiological effects when applied to the human body. These signals are produced by advanced electronics not possible even 10 to 15 years ago. The potential long-lasting anti-inflammatory effects of some electrical currents are based on basic physical and biochemical facts listed in the text below, namely that of stimulating and signaling effective and long-lasting anti-inflammatory effects in nerve and muscle cells. The safety of electrotherapeutic treatments in general and EST in particular has been established through extensive clinical use. The principles of physics have been largely de-emphasized in modern medicine in favor of chemistry. These electrical treatments, a familiar application of physics, thus represent powerful and appropriate elements of physicians' pain care armamentaria in the clinic and possibly for prescription for use at home to improve overall patient care and maintenance of quality of life via low-risk and potentially curative treatments.

Low level lasers in dentistry

Low level laser therapy (LLLT) uses light energy, in the form of adenosine triphosphate (ATP), to elicit biological responses in the body. The increased cellular energy and changes in the cell membrane permeability result in pain relief, wound healing, muscle relaxation, immune system modulation, and nerve regeneration. This article investigates the clinical effects of LLLT and explains how it can be applied in the dental field.

Reduction of photobleaching and photodamage in single molecule detection: observing single actin monomer in skeletal myofibrils

Recent advances in detector technology make it possible to achieve single molecule detection (SMD) in a cell. SMD avoids complications associated with averaging signals from large assemblies and with diluting and disorganizing proteins. However, it requires that cells be illuminated with an intense laser beam, which causes photobleaching and cell damage. To reduce these effects, we study cells on coverslips coated with silver nanoparticle monolayers (NML). Muscle is used as an example. Actin is labeled with a low concentration of fluorescent phalloidin to assure that less than a single molecule in a sarcomere is fluorescent. On a glass substrate, the fluorescence of actin decays in a step-wise fashion, establishing a single molecule detection regime. Single molecules of actin in living muscle are visualized for the first time. NML coating decreases the fluorescence lifetime 17 times and enhances intensity ten times. As a result, fluorescence of muscle bleaches four to five times slower than on glass. Monolayers decrease photobleaching because they shorten the fluorescence lifetime, thus decreasing the time that a fluorophore spends in the excited state when it is vulnerable to oxygen attack. They decrease damage to cells because they enhance the electric field near the fluorophore, making it possible to illuminate samples with weaker light.

The effect of cutaneous input on intracortical inhibition in focal task-specific dystonia

In normal subjects short interval intracortical inhibition (SICI) is topographically modulated by cutaneous input, which may be important for focusing muscle activation during tasks. In patients with writer's cramp, a task-specific focal dystonia characterized by inappropriate and excessive muscle activation of the upper limb during certain motor tasks, intracortical inhibition is reduced at rest and lacks the normal topographically-specific modulation during motor tasks. In the present study we investigated whether cutaneous input modulated SICI in a group of patients with writer's cramp and a control group of subjects. Electromyographic recordings were made from the right first dorsal interosseous (FDI), abductor pollicis brevis (APB), and abductor digiti minimi (ADM) muscles. Brief electrical stimuli were applied to either digit II or digit V with ring electrodes. SICI was investigated using a paired transcranial magnetic stimulation paradigm employing interstimulus intervals of 1-15 ms. Cutaneous input from both digit II and digit V modulated motor evoked potentials and SICI in a topographically-specific manner in control subjects. In contrast, cutaneous input failed to modulate motor evoked potentials or SICI in the focal hand dystonia patients. These results provide further evidence of abnormal sensorimotor integration in focal hand dystonia.

Ultrasound imaging to monitor photothermal therapy - feasibility study

This study investigates the feasibility of ultrasound imaging to monitor temperature changes during photothermal treatment. Experiments were performed on tissue-mimicking phantoms and ex-vivo animal tissue samples. Gold nanoparticles were utilized as photoabsorbers. Prior to laser irradiation, structural features of the phantoms and tissue were visualized by ultrasound imaging. Ultrasound thermal imaging, performed during laser heating, showed that the temperature elevation was localized to the region of embedded or injected nanoparticles. The results of our study suggest that ultrasound imaging is a candidate approach to remotely guide photothermal therapy.

Comparative efficacy of repetitive nerve stimulation, exercise, and cold in differentiating myotonic disorders

The decremental response of the compound muscle action potential (CMAP) to provocative tests is not characterized in genetically verified myotonic disorders. We therefore studied the relationship between decremental responses and mutation type in 10 patients with recessive myotonia congenita (rMC), two with paramyotonia congenita (PMC), nine with myotonic dystrophy type 1 (DM1), four with DM2, and 14 healthy people. CMAPs were measured at rest, just after a short exercise test (SET), and during short, 5- and 10-HZ, repetitive nerve stimulation (RNS) trains at 32 degrees C and at 20 degrees C. The degree of decrement was not related to the severity of clinical myotonia. Controls and PMC patients had similar responses when warm, but with cooling PMC patients had a persistent decrement of CMAPs. In the rMC patients the decremental responses were related to the type of mutation of the CLCN1 gene, as a decrement was encountered in the T268M, R894X, IVS17+1 G>T, K248X, and 2149 del G, but not with the IVS1+3 A>T, F167L, or dominant A313T mutations. In DM1 patients there was no relationship between decrement and CTG repeats. The degree of partial inexcitability in myotonic muscle membrane therefore depends on the mutation type rather than degree of clinical myotonia. RNS at 10 HZ is more sensitive than SET for demonstrating abnormalities in rMC patients when warm; differences are less marked when cold, which is useful to diagnose PMC. Provocative tests are therefore useful in myotonias to demonstrate muscle inexcitability, which depends on the chloride or sodium channelopathy.

Synapse formation and elimination: role of activity studied in different models of adult muscle reinnervation

Synapse competition and elimination are a general developmental process both in central and in peripheral nervous systems that is strongly activity dependent. Some common features regulate synapse competition, and one of these is an application to development of the Hebb's postulate of learning: repeated coincident spike activity in competing presynaptic inputs on the same target cell inhibits competition, whereas noncoincident activity promotes weakening of some of the inputs and ultimately their elimination. Here we report experiments that indicate that the development of muscle innervation (initial polyneuronal innervation and subsequent synapse elimination) follows the Hebb's paradigm. We utilized two different models of muscle reinnervation in the adult rat: 1) we crushed nerves going to soleus or extensor digitorum longus muscles, to activate regeneration of the presynaptic component of the neuromuscular junctions (NMJ), or 2) we injected the soleus muscle with Marcaine (a myotoxic agent) to activate regeneration of the postsynaptic component, the muscle fiber. A condition of transient polyneuronal innervation occurs during NMJ regeneration in both cases, although the two models differ insofar as the relative strength of the competing inputs is concerned. During the period of competition (a few days or weeks, in Marcaine or crush experiments, respectively), we imposed a synchronous firing pattern on the competing inputs by stimulating motor axons distal to a chronic conduction block and demonstrated that this procedure strongly inhibits synapse elimination, with respect to control muscles in which regeneration occurs under natural impulse activity of motoneurons.

[Superficial microwaves hyperthermia tumoral temperature distribution by using finite element analysis]

The main aim of this study is to present a virtual method for tumor temperature distribution by using finite element analysis.

MATERIAL AND METHODS

First step is geometrical synthesis that means tumor and neighbor structures three-dimensional reconstruction using CT sections; the second represent temperature and material synthesis: temperature values application and tissues density, thermal conductivity, specific heat values application, then finite element analysis.

RESULTS

Finite element analysis indicate tumor temperature distribution with maximum and minimum values as a result of microwave hyperthermia treatment.

Nociceptive contribution to the evoked potentials after painful intramuscular electrical stimulation

Our study aimed at investigating the nociceptive contribution to the somatosensory evoked potentials after electrical intramuscular stimulation (mSEPs) at painful intensity. Scalp mSEPs were recorded in 10 healthy subjects after electrical stimulation of the left brachioradialis muscle at three intensities: non-painful (I2), slightly painful (I4) and moderately painful (I6). For each intensity, mSEPs were recorded in a neutral condition (NC) in which subjects did not have any task, and in an attention condition (AC) in which subjects were asked to count the number of stimuli. In both NC and AC, the N120 and P220 amplitudes were significantly higher at I6 than at I2. While the N120 amplitude did not vary between NC and AC, the P220 amplitude was significantly higher in AC than in NC at all stimulus intensities. Our results suggest that nociceptive inputs contribute to the N120 amplitude increase at painful stimulus intensity, while the P220 amplitude is more sensitive to changes of subjects' attention level. Therefore, the N120 amplitude increase to moderately painful stimuli, as compared to non-painful stimuli, may represent a marker of the activation of the muscular thin myelinated afferents.

Intensity modulated neutron radiotherapy for the treatment of adenocarcinoma of the prostate

PURPOSE

This study investigates the enhanced conformality of neutron dose distributions obtainable through the application of intensity modulated neutron radiotherapy (IMNRT) to the treatment of prostate adenocarcinoma.

METHODS AND MATERIALS

An in-house algorithm was used to optimize individual segments for IMNRT generated using an organ-at-risk (OAR) avoidance approach. A number of beam orientation schemes were investigated in an attempt to approach an optimum solution. The IMNRT plans were created retrospectively for 5 patients previously treated for prostate adenocarcinoma using fast neutron therapy (FNT), and a comparison of these plans is presented. Dose distributions and dose-volume histograms (DVHs) were analyzed and plans were evaluated based on percentage volumes of rectum and bladder receiving 95%, 80%, and 50% (V(95), V(80), V(50)) of the prescription dose, and on V(60) for both the femoral heads and GM(muscle) group.

RESULTS

Plans were normalized such that the IMNRT DVHs for prostate and seminal vesicles were nearly identical to those for conventional FNT plans. Use of IMNRT provided reductions in rectum V(95) and V(80) of 10% (2-27%) and 13% (5-28%), respectively, and reductions in bladder V(95) and V(80) of 12% (3-26%) and 4% (7-10%), respectively. The average decrease in V(60) for the femoral heads was 4.5% (1-18%), with no significant change in V(60) for the GM(muscle) group.

CONCLUSIONS

This study provides the first analysis of the application of intensity modulation to neutron radiotherapy. The IMNRT technique provides a substantial reduction in normal tissue dose in the treatment of prostate cancer. This reduction should result in a significant clinical advantage for this and other treatment sites.

The electrophysiological muscle scan

This study aims to assess the potential of the electrophysiological muscle scan or stimulus-response curve as a diagnostic instrument. If stimulus intensity is gradually increased from subthreshold to supramaximal values, all motor units in a muscle are successively activated. Thus, by plotting response size versus stimulus intensity, an impression (scan) of the entire muscle can be obtained. We recorded 54 detailed scans from 34 patients and 11 healthy subjects, and analyzed them visually and quantitatively. The scan summarized much diagnostic information in a single picture. Specific patterns in or properties of the scan (steps, maximum, variability, decrements, stimulus intensities used) provide clinically relevant information regarding motor unit number, size, and stability, and neuromuscular transmission and axonal excitability. The scan can be recorded noninvasively in about 5 minutes and is fairly easy to interpret. Because it is built up from contributions of all functioning motor units, the scan shows if and how many large motor units are present. There is no sample bias. For these reasons, further exploration and exploitation of this tool in the clinical setting are warranted.

Mathematical model that predicts the force-intensity and force-frequency relationships after spinal cord injuries

We have previously developed and tested a muscle model that predicts the effect of stimulation frequency on muscle force responses. The aim of this study was to enhance our isometric mathematical model to predict muscle forces in response to stimulation trains with a wide range of frequencies and intensities for the quadriceps femoris muscles of individuals with spinal cord injuries. Isometric forces were obtained experimentally from 10 individuals with spinal cord injuries (time after injury, 1.5-8 years) and then compared to forces predicted by the model. Our model predicted accurately the force-time integrals (FTI) and peak forces (PF) for stimulation trains of a wide range of frequencies (12.5-80 HZ) and intensities (150-600-mus pulse duration), and two different stimulation patterns (constant-frequency trains and doublet-frequency trains). The accurate predictions of our model indicate that our model, which now incorporates the effects of stimulation frequency, intensity, and pattern on muscle forces, can be used to design optimal customized stimulation strategies for spinal cord-injured patients.

Respiratory and cardiovascular responses evoked by tibialis anterior muscle afferent fibers in rats

The muscle metaboreflex is thought to be one of the neural mechanisms involved in the cardiovascular and respiratory adjustments to muscular activity. The afferent arm of the reflex is composed of thinly myelinated group III and unmyelinated group IV sensitive fibers. Such reflex arc had been extensively described in cats, dogs, rabbits and humans. However, results obtained in rats are controversial and the role of the afferent fibers from the tibialis anterior skeletal muscle has never been shown. The purpose of the present experiments was to study the responses of both respiratory and cardiovascular systems following activation of the metabosensitive fibers originating from tibialis anterior muscle in non decerebrated and non vagotomized barbituric anesthetized adult rats. Mean arterial blood pressure, mean arterial blood flow, heart rate and phrenic nerve activity (frequency and amplitude) were monitored during electrically induced fatigue or after intramuscular injection of potassium chloride or lactic acid (specific stimuli of the group III and IV afferent fibers). The experiments were performed under normal condition, then after regional circulatory occlusion, which isolated and maintained the neural drive and abolished humoral communication and after section of the peroneal nerve innervating the tibialis anterior muscle. We showed that cardiorespiratory parameters were increased significantly in response to stimuli under normal conditions and after venous outflow occlusion excluding any participation of central chemoception. No change was observed after nerve section. Our data indicate that changes occurring in rat hindlimb muscle such as the tibialis anterior are sufficient to regulate the cardiorespiratory function via metabosensitive fiber activation.

Modulation of long-interval intracortical inhibition and the silent period by voluntary contraction

Transcranial magnetic stimulation was used to examine the effect of voluntary contraction on the magnitude of long-interval intracortical inhibition (LICI) and the duration of the silent period in intrinsic hand muscles. The magnitude of LICI acting on the first dorsal interosseus (FDI) measured with a paired-pulse protocol with an inter-pulse interval of 100 ms decreased with increasing tonic level of voluntary abduction force generated by the index finger. LICI in abductor pollicis brevis (APB) decreased from the condition in which the index finger was at rest to the conditions in which it was abducted, whereas LICI in abductor digiti minimi (ADM) was unaffected by the level of index finger abduction. During voluntary abduction of the index finger, the magnitude of LICI was least in FDI, intermediate in ADM, and greatest in APB, suggesting that it may be a mechanism by which tonic activation of hand muscles is fractionated. The magnitude of LICI increased with conditioning stimulus intensity, but intensity did not interact with abduction force. The duration of the silent period (SP) in FDI decreased with the level of voluntary index finger abduction and increased with eliciting stimulus intensity. Within-subject correlations showed that the effects of voluntary drive on SP duration and motor-evoked potential amplitude did not covary, implying an indirect effect of voluntary drive on SP duration. It is proposed that whereas voluntary drive directly reduces the magnitude of slow-acting inhibition acting on the active movement representations and near neighbors, sensory feedback from the contracting muscle acts to limit its time course.

A comparison of voluntary and involuntary measures of electromechanical delay

Electromechanical delay (EMD) is a measurement used to assess the mechanical lag between muscle activation onset and force production. EMD measurements may be performed by voluntary or electrically evoked muscle activation. This study compared gastrocnemius EMD during voluntary and involuntary contractions and assessd the intrasession reliability of each set of measurements. Subjects were 15 volunteers (age 21 +/- 2 years, ht 171.8 +/- 10.0 cm, mass 76.1 +/- 13.4 kg). EMD measurements were recorded from the medial head of the gastrocnemius of each subject during voluntary and involuntary contractions. Order was counterbalanced between subjects. Subjects stood with the dominant leg on a force plate, the nondominant next to the force plate, and with their hands in contact with a bar in front of them. A supramaximal percutaneous stimulus was applied to the tibial nerve in the popliteal fossa for involuntary (electrically evoked) contractions. For voluntary contractions, subjects were instructed to rise up on the toes as quickly as possible. Four trials were collected for each condition with 30 s of rest between each. Repeated measures ANOVAs were performed for each condition to calculate an ICC (2,1). Means of the 4 trials for each condition were used to detect differences between groups. EMD was greater in the voluntary condition (22.8 +/- 8.2 ms) compared to the involuntary condition (9.7 +/- 3.1 ms; p < .001). Intrasession reliability for each condition was very strong (involuntary ICC (2,1) = .977; voluntary ICC (2,1) = .972). EMD measured during a single leg stance is much shorter when measured during an electrically evoked (voluntary) contraction. The difference in EMD between conditions is likely the result of differences in recruitment during the two types of contractions. Reliability within a measurement session was very strong for each of the conditions.

Postpartum glycemic homeostasis in early lactating rats is accompanied by transient and specific increase of soleus insulin response through IRS2/AKT pathway

It is known that at the moment of delivery immediate lost of conceptus (main site of glucose disposal in late pregnancy) is not able to disturb glucose homeostasis in early lactating mothers. However, the mechanism by which this adaptation takes place in early lactation is still unknown. Most studies concerning insulin sensitivity in lactating rats were carried out at 11–13 days postpartum and did not describe functional changes in insulin response in early lactation. Here we show that lactation hypersensitivity to insulin is observed as early as 3 days after delivery (L3). We show that the oxidative soleus muscle displays a transient increased maximal insulin-induced glucose uptake and CO2production, which is temporally limited to L3. Response of soleus muscle was accompanied by an increase in glucose transporter 4 (GLUT4) content at L3. This adaptive response was not detected in the glycolytic plantaris muscle, which displayed lower content of GLUT4. We also found that soleus muscle from early lactating rats have higher insulin receptor expression and tyrosine phosphorylation. Downstream steps of insulin signaling pathway; e.g., insulin receptor substrate 2 tyrosine phosphorylation and its association with phosphatidylinositol 3-kinase were also upregulated in soleus muscle. In parallel, protein tyrosine phosphatase 1B expression, a negative regulator of insulin signal, was reduced. Importantly, all of these molecular alterations were time limited to L3 and were not observed in plantaris muscle. These results suggest that improved insulin action in oxidative, but not in glycolytic muscle might contribute to achievement of glucose homeostasis postpartum.