[The influence of movement's observation on recuperation after physical fatigue].

The study aim was to investigate effects of mental activity, accompanied by mu-rhythm depression, on recuperation after physical fatigue. In a study participants performed 11 one minute bouts of static hand grip intermitted by 2 minutes restpauses. During pauses participants watched video with either dynamic hand grips (biological movements) or deformation of geometric figure (control). Obtained data showed there was a significant depression of mu-rhythm during biological movement's observation. There was significant fatigue of subjects in an exercise with physical activity, but there was no reliable influence of performed mental activity on recovery after fatigue.

Temporal strategy and performance during a fatiguing short-cycle repetitive task.

This study investigated temporal changes in movement strategy and performance during fatiguing short-cycle work. Eighteen participants performed six 7-min work blocks with repetitive reaching movements at 0.5 Hz, each followed by a 5.5-min rest break for a total duration of 1 h. Electromyography (EMG) was collected continuously from the upper trapezius muscle, the temporal movement strategy and timing errors were obtained on a cycle-to-cycle basis, and perceived fatigue was rated before and after each work block. Clear signs of fatigue according to subjective ratings and EMG manifestations developed within each work block, as well as during the entire hour. For most participants, timing errors gradually increased, as did the waiting time at the near target. Changes in temporal movement strategy were negatively correlated with changes in the level and variability of EMG, suggesting that an adaptive temporal strategy offset the development of unstable motor solutions in this fatiguing, short-cycle work. PRACTITIONER SUMMARY: Sustained performance of operators is essential to maintain competitiveness. In this study of repetitive work, participants gradually changed their temporal movement strategy, for possibly alleviating the effects of fatigue. This suggests that in order to effectively counteract fatigue and sustain performance, industrial production should allow extensive spatial and temporal flexibility.

Characterization of a laboratory model of computer mouse use - applications for studying risk factors for musculoskeletal disorders.

In the present study, we assessed the wrist kinetics (range of motion, mean position, velocity and mean power frequency in radial/ulnar deviation, flexion/extension, and pronation/supination) associated with performing a mouse-operated computerized task involving painting rectangles on a computer screen. Furthermore, we evaluated the effects of the painting task on subjective perception of fatigue and wrist position sense. The results showed that the painting task required constrained wrist movements, and repetitive movements of about the same magnitude as those performed in mouse-operated design tasks. In addition, the painting task induced a perception of muscle fatigue in the upper extremity (Borg CR-scale: 3.5, p<0.001) and caused a reduction in the position sense accuracy of the wrist (error before: 4.6 degrees , error after: 5.6 degrees , p<0.05). This standardized painting task appears suitable for studying relevant risk factors, and therefore it offers a potential for investigating the pathophysiological mechanisms behind musculoskeletal disorders related to computer mouse use.

Correlates of measures of voluntary force with the functional state of the motor system.

Oscillation spectra were analyzed for prolonged isometric force recorded in healthy subjects of three age groups. Changes in the distributions of spectral components of the oscillations in force were noted, along with differences in the distributions of spectral density as exhaustion developed in the age groups. The amplitude-frequency ranges of changes in the spectral densities of oscillations in force characterized the activity at the suprasegmental and segmental levels of the motor system which support the voluntary control and automatic regulation of posture during the performance of movements. Correlates of the functional state of the motor system are discussed in terms of the voluntary and involuntary components of control. A significant increase in activity in the central structures of the movement control system was seen with the development of exhaustion, along with decreases in the frequency range of the activity of subcortical structures with age.

[Parameters of voluntary effort correlates with functional state of the motor control system].

The spectrum oscillations of a prolonged supported effort that was registered at isometric regimen in 3 age groups of healthy volunteers, were analyzed. Changes in distribution of spectral density of effort oscillations and distinction in distribution of spectral density as a reaction to fatigue in age groups, were shown. The revealed amplitude-frequency ranges of changes of spectral density of effort oscillations characterize activity of suprasegmental and segmental levels of motor control system fulfilling the voluntary movement control and the automatic regulation of posture. The correlates with functional state of motor control system are considered in the terms of voluntary and involuntary components of regulation. The substantial growth of activity in the central structures of motor control system in process of development of fatigue and the narrowing of the frequency range of activity of sub-cortical structures with age, were revealed.

Short-term effects of repetitive arm work and dynamic exercise on glucose metabolism and insulin sensitivity.

AIM: To determine whether repetitive arm work, with a large component of static muscle contraction alters glucose metabolism and insulin sensitivity. METHOD: Euglycemic clamps (2 h) were started in ten healthy individuals 15 min after 37 min periods of: (1) repetitive arm work in a simulated occupational setting; (2) dynamic concentric exercise on a cycle ergometer at 60% of VO(2max) and (3) a resting regime as a control. During the experimental periods, blood samples were collected, blood pressure was measured repeatedly and electrocardiogram (ECG) was recorded continuously. During the clamps, euglycemia was maintained at 5 mmol l(-1) and insulin was infused at 56 mU m(-2) min(-1) for 120 min. RESULTS: The insulin-mediated glucose disposal rate (M-value) for the steady-state period (60-120 min) of the clamp, tended to be lower following arm work than for both cycling and resting regimes. When dividing the steady-state period into 20-min intervals, the insulin sensitivity index (ISI) was significantly lower for arm work compared with the resting control situation between 60-80 min (P = 0.04) and 80-100 min (P = 0.01), respectively. Catecholamines increased significantly for arm work and cycling compared with resting regime. Data from heart rate variability (HRV) measurements indicated significant sympathetic activation during repetitive arm work. CONCLUSION: The results indicate that repetitive arm work might acutely promote insulin resistance, whereas no such effect on insulin resistance was produced by dynamic concentric exercise.

Effects of time pressure and precision demands during computer mouse work on muscle oxygenation and position sense.

The present study investigated the effects of time pressure and precision demands during computer mouse work on muscle oxygenation and position sense in the upper extremity. Twenty-four healthy subjects (12 males and 12 females) performed a 45-min standardized mouse-operated computer task on two occasions. The task consisted of painting rectangles that were presented on the screen. On one occasion, time pressure and precision demands were imposed (more demanding task, MDT), whereas, on the other occasion, no such restraints were added (less demanding task, LDT). The order of the two task versions was randomized. Tissue oxygen saturation in the trapezius and extensor carpi radialis muscles was recorded throughout, and the position-matching ability of the wrist was measured before and after the tasks. In addition, measurements of autonomic nervous system reactivity and subjective ratings of tenseness and physical fatigue were obtained. Performance was measured in terms of the number of rectangles that were painted during the task. During MDT, oxygen saturation in extensor carpi radialis decreased (P < 0.05) compared to LDT. These data were paralleled by increased electrodermal activity (P < 0.05), skin blood flow (P < 0.05), ratings of tenseness and fatigue (P < 0.01), and increased performance (P < 0.01) during MDT. Females exhibited lower oxygen saturation than males, during rest as well as during the computer tasks (P < 0.01). Wrist repositioning error increased following LDT as compared to MDT (P < 0.05). In conclusion, computer mouse work under time pressure and precision demands caused a decrease in forearm muscle oxygenation, but did not affect wrist position sense accuracy. We attribute our changes in oxygenation more to increased oxygen consumption as a result of enhanced performance, than to vasoconstriction.

Provocation study of persons with perceived electrical hypersensitivity and controls using magnetic field exposure and recording of electrophysiological characteristics.

The aim of the present study was to investigate possible neurophysiological effects of intermittent 15 sec on/off cycle, 60 Hz, 10 microT magnetic field exposure on patients with perceived "electromagnetic hypersensitivity" (EHS), and control subjects during rest and performance of a mental arithmetic task. Twenty participants (15 female, 5 male, 31-60 years old, mean 45.8 +/- 0.7 years) were invited from the group of EHS patients. Twenty volunteers (15 female, 5 male, 31-59 years old, mean 45.0 +/- 0.7 years?) served as a control group. The test protocol consisted of a set of examinations: EEG, visual evoked potentials, electrodermal activity, ECG, and blood pressure. The total duration of the test was 40 min, divided into two 10 min rest periods and two 10 min periods of mathematical performance. Magnetic field and sham exposures were presented randomly during these periods, resulting in four different conditions: Field-Rest, Sham-Rest, Field-Math, and Sham-Math. The data showed significant main effects of the Group factor (EHS vs. control subjects) on heart rate (F(1,80) = 20.6; P < 0.01), heart rate spectrum ratio (F(1,80) = 9.5; P = 0.02), and electrodermal activity (F(1,76) = 4.2; P = 0.04), whereas EEG characteristics did not differ between groups. The Condition factor (mathematical task vs. relaxed) showed main effects for heart rate (F(1,80) = 14.8; P < 0.01), heart rate spectrum ratio (F(1,80) = 7.8; P = 0.06), electrodermal activity (F(1,76) = 56.8; P < 0.01), and alpha and theta spectral bands of EEG. Magnetic field exposure did not affect autonomous system or electroencephalographic variables of either group. These data do not indicate that EHS patients or control are affected by low-level 60 Hz magnetic field exposure. However, persons reporting EHS differed from the control subjects in baseline values of investigated physiological characteristics. Perhaps EHS patients have a rather distinctive physiological predisposition to sensitivity to physical and psychosocial environmental stressors.

Neurophysiological study of patients with perceived 'electrical hypersensitivity'.

The aim of the present study was to investigate baseline neurophysiological characteristics of the central and autonomous regulation and their reactivity to different tests in a group of persons with so-called 'electrical hypersensitivity', which is often considered as a form of psychosomatic disorders. Twenty patients with combinations of neuroasthenic symptoms (general fatigue, weakness, dizziness, headache) and facial skin (itching, tingling, redness) have been investigated. An equal number of symptom-free persons served as a control group. The examination comprised self-reported measures, testing of visual functions, measurements of blood pressure, heart rate and its variability, electrodermal activity, respiration, EEG and visual evoked potentials (VEP). Several variables were found to differ between the patient and the control groups. The mean value of heart rate in rest condition was higher in the patient group compared to the controls (mean value of inter-beat intervals were 0.80 and 0.90 s, respectively). Heart rate variability and response to standing test were decreased in the patient group compared to the controls. Patients had faster onset, higher amplitudes, and left-right hand asymmetry of the sympathetic skin responses. They had a higher critical fusion frequency (43 vs. 40 Hz), and a trend to increased amplitude of steady-state VEPs at stimulation frequencies of 30-70 Hz. The data indicated that the observed group of patients had a trend to hyper sympathotone, hyperresponsiveness to sensor stimulation and heightened arousal.

[Transcranial magnetic stimulation in neurotic depression]. / Transkranial'naia magnitnaia stimuliatsiia pri nevroticheskoi depressii.

Transcranial magnetic stimulation (TMS) was applied in combination with psychotherapy in patients with neurotic depression, including 15 patients of the experimental group and 14 patients of the control one. 10 sessions of daily TMS for the patients from the experimental group (0.015 T, 40 pulses per sec) were performed at the same time for 20 min (twice for 10 min with 5-min interval) in a room which excluded any external stimulation. TMS was performed by contact method: 5 cm coil was applied to the left prefrontal area. The control group received the imitation of TMS-procedure stimulation. The improvement of mental state was in 13 patients of experimental group and in 3 of control one. The course of TMS resulted in a significant attenuation of depression by the Hamilton Depression Rating scale (from 22.9 to 8.6) and the Anxiety Inventory (from 39.4 to 26.6), that was significantly higher in comparison with the control. There weren't found any TMS-related changes in blood pressure and pulse rate as well as any pathological EEG symptoms.

Steady-state visual evoked potentials to computer monitor flicker.

In the present study, steady-state visual evoked potentials (S-VEP) in response to amplitude-modulated light from a computer monitor (colour sVGA, 15-inch tube) have been examined. S-VEPs to computer monitors with different refresh rates (60 Hz or 72 Hz) and screen brightness (65 cd/m2 or 6 cd/m2) were recorded in 13 subjects with normal or corrected-to-normal vision. EEG samples were amplified, averaged and stored using Cadwell Excel EMG-EP recorder and a regression model was applied for the amplitude analysis. The mean values of S-VEP amplitude at 60 Hz were found to be significantly higher at 60 Hz refresh rate vs. 72 Hz (F1,12 = 14.1; P = 0.003). Effect of screen brightness (F2,24 = 6.5; e = 0.62; P = 0.00075) as well as the interaction effect of refresh rate and screen brightness (F2,24 = 11.6; P = 0.0003) were also found to be significant. Data obtained show that the characteristics of amplitude-modulated light from a computer monitor (frequency, brightness, waveform) are sufficient to elicit S-VEP, and the influence is not only restricted to the peripheral divisions of the visual system as it was shown earlier, but also extends to the central brain structures.

Neurophysiological effects of flickering light in patients with perceived electrical hypersensitivity.

An increasing number of people in Sweden are claiming that they are hypersensitive to electricity. These patients suffer from skin as well as neurological symptoms when they are near computer monitors, fluorescent tubes, or other electrical appliances. Provocation studies with electromagnetic fields emitted from these appliances have, with only one exception, all been negative, indicating that there are other factors in the office environment that can effect the autonomic and/or central nervous system, resulting in the symptoms reported. Flickering light is one such factor and was therefore chosen as the exposure parameter in this study. Ten patients complaining of electrical hypersensitivity and the same number of healthy voluntary control subjects were exposed to amplitude-modulated light. The sensitivity of the brain to this type of visual stimulation was tested by means of objective electrophysiological methods such as electroretinography and visual evoked potential. A higher amplitude of brain cortical responses at all frequencies of stimulation was found when comparing patients with the control subjects, whereas no differences in retinal responses were revealed.

[Effect of a 50 Hz magnetic field on rat behavior depends on the direct current component]. / Vliianie magnitnogo polia chastotoi 50 Gts na povedenie krys zavisit ot znacheniia postoiannogo magnitnogo polia.

The influence of extremely low frequency magnetic field on rats behavior (working memory, learning, social activity) was examined. Rats were exposed to magnetic fields at three different conditions: exposure 1-50 Hz, 46 mT; DC 65 mTl; exposure II-50 Hz, 46 mTl; DC 14-17 mTl; Exposure III-sham. Field related changes were observed after exposure I: the increase of error rate in Y-maze performance, shorter adaptation time in instrumental performance, the decrease of aggression and sociability, enhancement of the defence reactions. Data obtained show that influence of 50-Hz magnetic field depends on the level of DC field. The combination presumably considered as resonant to Ca++ was more effective.