Age-Related Changes in Turn–Amplitude Characteristics of the EMG Recorded during Graded Isometric Contraction

The number of turns, the mean amplitude, and the peak ratio of the electromyogram (EMG) recorded in m. biceps brachii at different levels of isometric contraction were analyzed in nine age groups (from 1 month to 72 years, N = 192). Regression equations describing the age-related changes in number of EMG turns and mean EMG amplitude were respectively y = –A(2.48 ± 0.14) – M(1.32 ± 0.17) + B(11.02 ± 0.68) + (194.71 ± 7.81) (P < 0.001) and y = –A(2.47 ± 0.19) – M(1.87 ± 0.23) + B(10.03 ± 0.88) + (321.57 ± 11.05) (P < 0.001), where A is the age, years; M is the body mass, kg; and B is the load, kg. With increasing age, the interference EMG tended to assume a so-called neurogenic form as a result of age-specific organization of motor functions at the segmental level.     

Effects of Local and Remote Muscle Pain on Stretch ReflexActivities in the Elbow Joint Flexors and Extensors of Unanesthetized Cats

In experiments on unanesthetized cats, we compared the effects of experimentally induced pain in the m. biceps brachii or in the neck muscles on EMG activity of the flexors and extensors of the elbow joint (mm. biceps et triceps brachii, respectively) evoked by a passive extension-flexion of the above joint. Muscle pain was induced by injections of 0.5 ml of a hypertonic (7%) NaCl solution into the above-mentioned muscles. In the case of pain in the biceps, i.e., in the muscle directly involved in realization of the reflex, we observed an increase in the amplitude and significant shortening of the latency of EMG responses of this muscle. The amplitude of a short-latency (supposedly monosynaptic) component of the biceps reflex (М1 response) increased by 65%, while an increment of the latter (supposedly polysynaptic) М2 component was 117%. When pain was induced in anatomically remote neck muscles, the stretch reflex in the biceps was considerably suppressed. The maximum amplitudes of the М1 and М2 components decreased by 25 and 30%, respectively, but the latencies of these components decreased significantly, similarly to what was observed in the case of induction of experimental pain in the biceps. Under both conditions of experimental pain, changes in the parameters of EMG responses of the forearm extensor (m. triceps brachii) demonstrated similarity with those of the biceps responses. The maximum effect of pain induction was observed within the first 5 min after injections of the hypertonic solution; full recovery of the stretch reflex parameters was observed on the 20th to 30th min. We conclude that the effects of pain induction on the reflex under study are not generalized. They depend on the site of such induction with respect to the muscle where the stretch reflex is elicited. Unidirectional effects of both types of pain on the antagonist muscles allow us to suppose that modulation of the reflex reactions upon pain induction is mediated by influences from the supraspinal CNS structures. Induction of pain in the biceps increased the amplitude of EMG manifestations of the stretch reflex, while such induction in the neck muscles decreased such responses; nonetheless, in both cases the latency of the reflexes decreased. This fact allows us to believe that the sensitivity of muscle spindles increased under both conditions of the pain influence.     

Peculiarities of Activation of the Upper Limb Muscles in Realization of Two-Joint Movements in Humans

In tests on humans, we recorded EMG activity from the muscles flexing and extending the forearm and shoulder in the course of realization of sequential single-joint and simultaneous two-joint movements of the upper limb. As was shown, the shoulder muscles m. biceps brachii and m. triceps brachii are involved in flexion/extension of both elbow and shoulder joints. Central commands sent to the above muscles in the course of a two-joint movement could be considered a superposition of the central commands coming to the same muscles in realization of the corresponding sequential single-joint movements with the same changes in the angles of the elbow and shoulder joints. External loadings applied in the direction of extension of the elbow and shoulder joints induced, in general, similar changes in coordination of the activity of muscles moving the forearm and shoulder under conditions of both single-joint and two-joint movements. These facts allow us to suppose that coordination of the muscle activity in two-joint movements depends to a greater extent on the forces influencing limb links than on the mode of realization of the movements (two sequential single-joint movements vs a two-joint movement corresponding to the above motor events).     

Control of the Elbow Extensor Muscles in Slow Targeted Extensions of the Arm in Humans

Relations between the kinematic parameters of slow (non-ballistic) targeted extension movements in the elbow joint of humans and characteristics of the movement-related EMG activity in the two heads of the m. triceps brachii were analyzed. Test movements were performed under conditions of application of non-inertional external loadings directed toward flexion. It was shown that the movement-related EMG activity of the elbow extensors, similarly to what was observed in the flexors at flexion movements with the same parameters, demonstrates a complex structure and includes dynamic and stationary phases. In the former phase, in turn, initial and main components can be differentiated. The rising edge and decay of the main component of the dynamic extensor EMG phase could be approximated by exponential functions; this component was never split into a few subcomponents. Dependences between the amplitudes of m. triceps brachii EMG phases and the amplitude of the movement (or external loading) were, as a rule, nonlinear but monotonic. An increase in the test movement velocity led to an increase in the rate of rise of the rising edge of the dynamic EMG phase, while an increment in the amplitude was less significant. Under the used test conditions, the activity of the elbow extensors was usually accompanied by some coactivation of the antagonists (m. biceps brachii). It is concluded that motor commands coming to the elbow extensors at performance of the extension test movements differ from motor commands to the flexors at analogous flexion test movements by a simpler structure and more tonic pattern. Biomechanical specificities of fixation of the mentioned muscle groups to the arm bones (stability of the moment for application of the extensor force under conditions of changing the joint angle vs variable moment of the flexor force) are considered one of the main reasons for such specificity of the patterns of the extensor and flexor motor commands.     

Changes in kinematic and EMG variability while practicing a maximal performance task.

This paper examines changes in the variability of electromyographic (EMG) activity and kinematics as a result of practicing a maximal performance task. Eight subjects performed rapid elbow flexion to a target in the horizontal plane. Four hundred trials were distributed equally over four practice sessions. A potentiometer at the elbow axis of rotation of a manipulandum recorded the angular displacement. The EMG activity of the biceps and the triceps brachii was monitored using Beckman surface electrodes. Limb speed increased while both target error and trajectory (velocity versus position) variability decreased. There was an increase in the absolute measure of total EMG variability (the first standard deviation at each point of the biceps and triceps waveform multiplied together). However, the coefficient of variation (the first standard deviation divided by the mean and the result multiplied by 100) of the mean amplitude value of the individual EMG bursts decreased. The variability of triceps motor time also decreased while the variability biceps motor time remained unchanged. The results demonstrated a clear relationship between kinematic and EMG variability. The EMG and the trajectory data suggest that practice resulted in greater central nervous system control over both the spatial-temporal aspects of movement and the magnitude of the biceps and triceps muscle force-impulses.     

Positioning Errors in Simple Targeted Movements of the Forearm Realized in the Absence of Visual Control: Effects of Vibrational Stimulation of Antagonist Muscles

In 17 healthy subjects, we examined the characteristics of targeted movements of the forearm, flexion from the initial position of full extension taken as 0 deg to a 50 deg target angle in the elbow joint (flexor tests, FTs) and extension from the initial angle of 100 deg to the same target angle (extensor tests, ETs) with return to the initial positions. A standard movement (its trajectory corresponded to a simple trapezium) was performed under conditions of visual feedback (the value of the target angle and trajectory of the movement were visualized on the screen of a monitor); then, this movement should be reproduced by the subject (according to an acoustic signal) in the absence of visual control. Target-reaching test movements in the absence of visual feedback differed from the standard ones in a higher velocity. Blindfold reproduction of standard movements realized under kinesthetic control was accompanied in all subjects by noticeable positive systematic errors of targeted positioning (in the group, on average, 5.16 ± 0.55 and 4.83 ± 0.58 deg under FT and ET conditions, respectively). Vibrational stimulation of the muscles whose activity mainly provided the movement and positioning (m. biceps brachii in the FT cases and m. triceps brachii in the case of ETs) resulted in decreases of the errors of kinesthetic positioning; intragroup means of these errors were 2.55 ± 0.36 deg (FTs) and 2.26 ± 0.40 deg (ETs). The positioning errors demonstrated even greater decreases upon vibrational stimulation of the muscles, which were relatively inactive under conditions of the tests and underwent passive stretching in the course of the movements (m. triceps in FTs and m. biceps in ETs). Mean intragroup values of the errors in these cases were 0.46 ± 0.25 and 0.52 ± 0.31 deg, respectively. The nature of systematic positioning errors in the reproduction of targeted movements in the absence of visual control and the mechanisms underlying the influence of vibrational stimulation of the muscles involved in realization of these movements on the positioning errors under kinesthetic control are discussed.     

Effects of mechanical assistance on muscle activity and motor performance during isometric elbow flexion

Mechanical assistance on joint movement is generally beneficial; however, its effects on cooperative performance and muscle activity needs to be further explored. This study examined how motor performance and muscle activity are altered when mechanical assistance is provided during isometric force control of ramp-down and hold phases. Thirteen right-handed participants (age: 24.7 ± 1.8 years) performed trajectory tracking tasks. Participants were asked to maintain the reference magnitude of 47 N (REF) during isometric elbow flexion. The force was released to a step-down magnitude of either 75% REF or 50% REF and maintained, with and without mechanical assistance. The ramp-down durations of force release were set to 0.5, 2.5, or 5.0 s. Throughout the experiment, we measured the following: (1) the force output using load cells to compute force variability and overshoot ratio; (2) peak perturbation on the elbow movement using an accelerometer; (3) the surface electromyography (sEMG) from biceps brachii and triceps brachii muscles; and (4) EMG oscillation from the biceps brachii muscle in the bandwidth of 15–45 Hz. Our results indicated that mechanical assistance, which involved greater peak perturbation, demonstrated lower force variability than non-assistance (p < 0.01), while EMG oscillation in the biceps brachii muscle from 15 to 45 Hz was increased (p < 0.05). These findings imply that if assistive force is provided during isometric force control, the central nervous system actively tries to stabilize motor performance by controlling specific motor unit activity in the agonist muscle.     

Effect of T3 administration on electrophysiological properties of lizard ventricular muscle fibres

We investigated the effects on the electrophysiological properties of ventricular muscle fibres from lizards kept at 20 °C of mild and severe hyperthyroidism. The hyperthyroidism was induced by a 4-day treatment with either 0.025 or 1.0 g triiodothyronine g^-1 body weight, documented by increased serum levels of thyroid hormone. Triiodothyronine treatment did not modify the duration of the action potential recorded in vitro at 25 °C from ventricular muscles stimulated at 1 Hz. Recordings at higher temperatures were associated with a faster repolarization phase and a decrease of action potential duration in both euthyroid and hyperthyroid animals. However, in lizards treated with 1.0 g triiodothyronine · g^-1 body weight, the 90% repolarization recovery times at 30 and 35 °C (95.6±14.9 ms and 53.0±6.0 ms, respectively), were significantly shorter than normal (177.6±29.2 and 107.2±18.1 ms, respectively). Action potential duration was also dependent on stimulation frequency of the preparations. Increased frequency led to significant decrease of the duration of action potentials recorded at 25 °C. In euthyroid preparations the reductions in 90% repolarization recovery time, owing to increases in stimulation frequency to 2.5 and 5 Hz, were 19.3±1.7 and 35.6±2.0 ms, respectively. In hyperthyroid preparations, the reductions in the 90% recovery time due to stimulus frequency increases varied from 35.4±1.9 and 58.1±2.1 ms at low hormone doses to 38.9±2.0 and 58.2±2.1 ms at high hormone doses. As a result of these differences, the action potential durations recorded from the two hyperthyroid preparations at high stimulation rates were shorter than from euthyroid preparations. The results obtained suggest that lizard cardiac tissue is responsive to hormone action at low environmental temperature, but the effects of such action become evident when the temperature and heart rate increase.Abbreviations A _20% integrated area above 20% depolarization - bw body weight - hw heart weight - FT ₃ free triiodothyronine - RT ₄₀ RT ₅₀ RT ₇₀ and RT ₉₀ recovery time at 40, 50, 70, and 90% of repolarization, respectively - T ₃ triiodothyronine - TT ₃ Total triiodothyronine     

Spectral properties of electromyographic and mechanomyographic signals during dynamic concentric and eccentric contractions of the human biceps brachii muscle

The purpose of this study was to describe and examine the variations in recruitment patterns of motor units (MUs) in biceps brachii (BB) through a range of joint motion during dynamic eccentric and concentric contractions. Twelve healthy participants (6 females, 6 males, age = 30 ± 8.5 years) performed concentric and eccentric contractions with constant external loading at different levels. Surface electromyography (EMG) and mechanomyography (MMG) were recorded from BB. The EMGs and MMGs were decomposed into their intensities in time–frequency space using a wavelet technique. The EMG and MMG spectra were then compared using principal component analysis. Variations in total intensity, first principal component (PCI), and the angle θ formed by first component (PCI) and second component (PCII) loading scores were explained in terms of MU recruitment patterns and elbow angles. Elbow angle had a significant effect on dynamic concentric and eccentric contractions. The EMG total intensity was greater for concentric than for eccentric contractions in the present study. MMG total intensity, however, was lower during concentric than during eccentric contractions. In addition, there was no significant difference in θ between concentric and eccentric contractions for both EMG and MMG. Selective recruitment of fast MUs from BB muscle during eccentric muscle contractions was not found in the present study.     

Histamine and tele-methylhistamine quantification in cerebrospinal fluid from narcoleptic subjects by liquid chromatography tandem mass spectrometry with precolumn derivatization

An ultra-performance liquid chromatography tandem mass spectrometry (UPLC™–MS/MS) assay was developed for the simultaneous analysis of histamine, its major metabolite tele-methylhistamine, and an internal standard (N-tele-(R)-α-dimethylhistamine) from human cerebrospinal fluid (CSF) samples. The method involves derivatization of primary amines with 4-bromobenzenesulfonyl chloride and subsequent analysis by reversed phase liquid chromatography with mass spectrometry detection and positive electrospray ionization. The separation of derivatized biogenic amines was achieved within 3.5 min on an Acquity® BEH C₁₈ column by elution with a linear gradient of acetonitrile/water/formic acid (0.1%). The assay was linear in the concentration range of 50–5000 pM for each amine (5.5–555 pg/ml for histamine and 6.25–625 pg/ml for tele-methylhistamine). For repeatability and precision determination, coefficients of variation (CVs) were less than 11.0% over the tested concentration ranges, within acceptance criteria. Thus, the developed method provides the rapid, easy, highly sensitive, and selective requirement to quantify these amines in human CSF. No significant difference was found in the mean ± standard error levels of these amines between a group of narcoleptic patients (histamine = 392 ± 64 pM, tele-methylhistamine = 2431 ± 461 pM, n = 7) and of neurological control subjects (histamine = 402 ± 72 pM, tele-methylhistamine = 2209 ± 463 pM, n = 32).     

Intra-Individual Reaction Time Variability in Mild Cognitive Impairment and Alzheimer’s Disease: Gender,Processing Load and Speed Factors

Compared to cognitively healthy ageing (CH), intra-individual variability in reaction time (IIV_RT), a behavioural marker of neurological integrity, is commonly reported to increase in both Alzheimer’s disease (AD) and mild cognitive impairment (MCI). It varies in MCI with respect to whether it represents the pro-dromal stages of dementia or not; being greatest in those most likely to convert. Abnormal IIV_RT in MCI therefore represents a potential measure of underlying functional integrity that may serve to differentiate MCI from CH and to help identify those patients for whom MCI is the result of a progressive pathological process. As the clinical approach to MCI is increasingly stratified with respect to gender, we investigated whether this factor could influence study outcome. The influence of RT_SPEED and processing load upon IIV_RT was also examined. Under low processing load conditions, IIV_RT was significantly increased in both MCI and AD compared to CH. However, correcting for an individual’s processing speed abolished this effect in MCI but not in AD, indicating that the increased IIV_RT in MCI and AD may result from different factors. In MCI but not in CH, IIV_RT was significantly greater for females. Increasing task processing load by adding distracting information, although increasing overall IIV_RT, failed to improve the differentiation between CH and both MCI and AD, and in MCI resulted in a reduction in the influence of gender upon study outcome. The outcome of studies investigating IIV_RT in MCI and AD compared to CH therefore appear influenced by the gender of the participants, by task-related processing load and processing speed.     

The role of biceps brachii and brachioradialis for the control of elbow flexion and extension movements

How do synergistic muscles interact, when their contraction aims at stabilizing and fine-tuning a movement, which is induced by the antagonistic muscle? The aim of the study was to analyze the interaction of biceps and brachioradialis during fine-tuning control tasks in comparison to load bearing ones. The surface electromyogram of biceps, brachioradialis and triceps were examined in 15 healthy subjects in dynamic flexion and extension movements with different combinations of contraction levels, joint angles and angular velocities. The measurements were conducted in two configurations, where the torque due to an external load opposes the rotational direction of the elbow flexion (load bearing tasks) or the elbow extension (fine-tuning tasks).Whereas during load bearing control tasks, similar muscular activation of biceps and brachioradialis was observed for all joint angles, angular velocities and external loads, during fine-tuning control tasks a significant difference of the muscular activation of both flexors was observed for 1 kg, F(3.639, 47.305) = 2.864, p = 0.037, and 5 kg of external load, F(1.570, 21.976) = 6.834, p = 0.008.The results confirm the synergistic muscular activation of both flexors during load bearing tasks, but suggest different control strategies for both flexors when they comprise a fine-tuning control task.     

Glycine-induced currents are insensitive to the glycine receptor α1 subunit-specific blocker, cyanotriphenylborate, in older circling mice

The pharmacologic characteristics of glycine receptors (GlyRs) in the lateral superior olive (LSO) of circling mice, animal model for inherited deafness, were investigated using a GlyR α₁ subunit-specific receptor blocker (cyanotriphenylborate [CTB]). There was a statistically significant age-dependent increase in the antagonistic effect of CTB in heterozygous (+/cir) mice. In postnatal (P)0–P3 heterozygous (+/cir) mice, glycine currents evoked by glycine puffs were reduced to 20.4 ± 2.6, 37.1 ± 3.1, and 63.9 ± 2.5% at 0.1, 1, and 10 μM CTB (n = 13) compared to controls, while the glycine currents were reduced to 22.3 ± 3.5, 52.9 ± 4.1, and 78.3 ± 3.5% at 0.1, 1, and 10 μM CTB (n = 7) in P8–P12 heterozygous (+/cir) mice. In contrast, the antagonistic effect of CTB was not strong and even less than that of younger animals in older homozygous (cir/cir) mice. In P0–P3 homozygous (cir/cir) mice, the extent of inhibition was 20.2 ± 3.7, 37.8 ± 4.3, and 66.8 ± 4.2% at 0.1, 1, and 10 μM CTB (n = 6) compared to controls, while the extent of inhibition was 18.7 ± 2.4, 28.1 ± 3.9, and 39.1 ± 8.2% (n = 6) in P8–P12 homozygous (cir/cir) mice. The age-dependent decrease in the antagonistic effect of CTB indicates the abnormal development of the α₁ subunit-containing GlyRs in homozygous (cir/cir) mice.     

Trainability of Muscular Activity Level during Maximal Voluntary Co-Contraction: Comparison between Bodybuilders and Nonathletes

Antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE). Whether the muscular activity level during the task has trainability remains unclear. The present study examined this issue by comparing the muscular activity level during maximal voluntary co-contraction for highly experienced bodybuilders, who frequently perform voluntary co-contraction in their training programs, with that for untrained individuals (nonathletes). The electromyograms (EMGs) of biceps brachii and triceps brachii muscles during maximal voluntary co-contraction of elbow flexors and extensors were recorded in 11 male bodybuilders and 10 nonathletes, and normalized to the values obtained during the MVE of agonist contraction for each of the corresponding muscles (% EMG_MVE). The involuntary coactivation level in antagonist muscle during the MVE of agonist contraction was also calculated. In both muscles, % EMG_MVE values during the co-contraction task for bodybuilders were significantly higher (P<0.01) than those for nonathletes (biceps brachii: 66±14% in bodybuilders vs. 46±13% in nonathletes, triceps brachii: 74±16% vs. 57±9%). There was a significant positive correlation between a length of bodybuilding experience and muscular activity level during the co-contraction task (r = 0.653, P = 0.03). Involuntary antagonist coactivation level during MVE of agonist contraction was not different between the two groups. The current result indicates that long-term participation in voluntary co-contraction training progressively enhances muscular activity during maximal voluntary co-contraction.     

Time course of stretching-induced changes in mechanomyogram and force characteristics

To evaluate the time-course of stretching-induced changes in mechanical properties of the muscle-tendon unit (MTU), 11 participants (age 22 ± 1 yr; body mass 77 ± 5 kg; stature 1.78 ± 0.05 m; mean ± SD) underwent tetanic electrical stimulations of the medial gastrocnemius muscle before and after (up to 2 h) stretching administration. During contractions, surface electromyogram (EMG), mechanomyogram (MMG) and force were recorded simultaneously. From MMG, peak-to-peak (p–p) and root mean square (RMS) were calculated during the on-phase and plateau phase of tetanic contraction, respectively. After stretching: (i) no differences were found in EMG parameters; (ii) MMG p–p and slope decreased (−16% and −10%, respectively; P < 0.05) and remained depressed for the entire recovery period; (iii) MMG RMS increased (+20%; P < 0.05), returning to pre-stretching values within 15 min; and (iv) peak force (pF), with its first (dF/dt) and second (d²F/dt²) derivative, decreased significantly by 32%, 35% and 54%, respectively, and remained depressed for the entire recovery period. The lack of MMG p–p and pF recovery could be ascribable to a reduced muscle force generating capacity due to persisting changes in viscoelastic characteristics of series elastic components. The early return of MMG RMS to pre-stretching values suggests that changes in viscoelastic parallel components recovered after few minutes.     

Facilitation and Inhibition of the <Emphasis Type="Italic">Soleus</Emphasis> H Reflex Related to Movements of the Upper Limb in Humans

In studies on healthy volunteers, we recorded an EMG discharge from the m. soleus corresponding to the H reflex evoked by transcutaneous stimulation of the n. tibialis comm. Changes in the magnitude of this reflex related to realization of brief voluntary movements of the ipsilateral upper limb were examined. The subjects were in a prone position. Fast flexion-extension of the forearm resulted first in 100- to 200-msec-long facilitation of the H reflex begun 30–40 msec before the appearance of EMG activity in the m. biceps brachii; this feature is indicative of the central nature of this effect related to the action of motor programs initiating the forearm movement. Facilitation of the H reflex was followed by its inhibition lasting several seconds. Within an interval corresponding to the maximum suppression of the H response, we tested the effect of additional conditioning stimulation of the n. peroneus comm. Occlusion of the inhibitory effects indicates that the same inhibitory neurons mediate the influences from both the peroneal input and the pathways transmitting inhibitory influences from the neuronal systems controlling upper limb muscles. Contractions of the ipsilateral m. biceps brachii evoked by direct electrical stimulation of the latter also resulted in inhibition of the soleus H reflex, which was rather similar in its time course to the above-mentioned inhibitory effects. There was no inhibition of the reflex after stimulations of the cutaneous receptors and n. medianus. These findings allow us to suppose that long-lasting inhibition of the H reflex induced by voluntary movements of the upper limb results from afferent influences from the receptors of contracting muscles. Such effects can be realized via the propriospinal pathways or long reflex arcs.     

Neuromuscular efficiency during sit to stand movement in women with knee osteoarthritis

The purpose of this study was to investigate the neuromuscular efficiency of women with knee osteoarthritis (OA) when performing a sit-to-stand movement and during maximum strength efforts. Twelve women with unilateral knee OA (age 60.33 ± 6.66 years, height 1.61 ± 0.05 m, mass 77.08 ± 9.2 kg) and 11 controls (age 56.54 ± 5.46 years, height 1.64 ± 0.05 m, mass 77.36 ± 13.34 kg) participated in this study. Subjects performed a sit-to-stand movement from a chair while position of center of pressure and knee angular speed were recorded. Furthermore, maximal isokinetic knee extension and flexion strength at 60°/s, 120°/s and 150°/s was measured. Surface, electromyography (EMG) from the biceps femoris (BF), vastus lateralis (VL) and vastus medialis (VM) was recorded during all tests. Analysis of variance (ANOVA) showed that during the sit-to-stand OA group demonstrated significantly lower knee angular speed (44.49 ± 9.61°/s vs. 71.68 ± 19.86°/s), a more posterior position of the center of pressure (39.20 ± 7.02% vs. 41.95 ± 2.49%) and a higher antagonist BF activation (57.13 ± 20.55% vs. 32.01 ± 19.5%) compared with controls (p < 0.05). Further, women with knee OA demonstrated a lower Moment-to-EMG ratio than controls in extension and eccentric flexion at 60°/s and 150°/s, while the opposite was found for concentric flexion at 60°/s (p < 0.05). Among other factors, the slower performance of the sit-to-stand movement in women with OA is due to a less efficient use of the knee extensor muscles (less force per unit of EMG) and, perhaps, a higher BF antagonist co-activation. This may lead subjects with OA to adopt a different movement strategy compared with controls.     

Isolation and measurement of urinary 8-iso-prostaglandin F2α by high-performance liquid chromatography and gas chromatography–mass spectrometry

8-iso-Prostaglandin F_2α (8-iso-PGF_2α) is a product of free radical-catalyzed peroxidation of arachidonic acid. Measurement of its urinary excretion has been proposed as an index of oxidative status in vivo. A stable isotope dilution method for its quantification by gas chromatography–electron capture chemical ionization mass spectrometry is described. Sample cleanup required the combined use of high-performance liquid chromatography and thin-layer chromatography. The inter-assay R.S.D. in two separate determinations was 1.6 (n=4) and 2.3% (n=4). The accuracy of the assay was evaluated through recovery experiments. The equation of the regression plot correlating the amounts added and recovered was y=0.91x−0.31, r=0.9916 (n=12). The pair of fragment ions ([M−181]⁻) at m/z 569 and m/z 573 was monitored for quantification. The mean 8-iso-PGF_2α excretion rate was 528±127 (S.D.) ng per day in five male volunteers and 730±305 ng per day in six females. Intake of 80 mg of lycopene per day by eleven volunteers for four weeks resulted in a non-significant reduction of 8-iso-PGF_2α excretion.     

Accuracy and precision of a wrist movement when vibrotactile prompts inform movement speed

Abstract

Purpose: This study investigated the effect of movement speed on task accuracy and precision when participants were provided temporally oriented vibrotactile prompts. Materials and methods: Participants recreated a simple wrist flexion/extension movement at fast and slow speeds based on target patterns conveyed via vibrating motors affixed to the forearm. Each participant was given five performance-blinded trials to complete the task at each speed. Movement accuracy (root mean square error) and precision (standard deviation) were calculated for each trial in both the spatial and temporal domains. Results: 28 participants completed the study. Results showed temporal accuracy and precision improved with movement speed (both: fast?>?slow, p?<?0.01), while all measures improved across trials (temporal accuracy and precision: trial 1?<?all other trials, p?<?0.05; spatial accuracy: trial 1 and 2?<?all other trials, p?<?0.05; spatial precision: trial 1?<?all other trials, p?<?0.05). Conclusions: Overall, temporal and spatial results indicate participants quickly recreated and maintained the desired pattern regardless of speed. Additionally, movement speed seems to influence movement accuracy and precision, particularly within the temporal domain. These results highlight the potential of vibrotactile prompts in rehabilitation paradigms aimed at motor re-education.     

Differential effect of ethanol on muscarinic cholinergic binding to rat and locust neural membranes

We have compared the effect of ethanol, a membrane perturbant, on the muscarinic binding sites in neural membranes from a vertebrate (rat) and an insect (locust). The binding of the muscarinic antagonist [³H]quinuclidinyl benzilate ([³H]QNB) to both rat and locust neural membranes was inhibited by ethanol at 10–500 mM concentrations; but this inhibition was greater in the locust. Ethanol (500 mM) increased the apparent dissociation constant (K d) of [³H]QNB binding to rat membranes from 0.13±0.01 nM in control to 0.20±0.02 nM; there was also an small but significant reduction in the number of binding sitesB _max. In locust, 500 mM ethanol reduced theB _max of [³H]QNB binding from 590±30 in control to 320±40 pmol/g protein; no significant alteration in theK _D was detected. The dissociation rate constant (k _off) of [³H]QNB increased from 0.020±0.003 in controls to 0.031±0.004 (min^–1) in the presence of 500mM ethanol, the association rate constant (k _on) did not change significantly. In locust, 500 mM ethanol did not affect eitherk _on ork _off. Competition experiments revealed that the binding affinities of both the agonist carbamylcholine and the antagonist atropine to the rat membranes were reduced in the presence of ethanol. In contrast, ethanol caused no alteration in the binding affinities of these ligands to the locust membranes. This differential effect of ethanol on rat and locust muscarinic binding suggests a difference in the hydrophobic domains and/or the membrane interactions of the muscarinic receptors in the two species.