A Pilot Study Evaluating the Feasibility of Testing for an Acute Impact of Human Exposure to a Power-line Frequency Magnetic Field on Blood Cortisol and Thyroid-Stimulating Hormone.

Numerous studies have been carried out on the potential effects of an extremely low frequency (ELF-0-300 Hz) magnetic field (MF) on human health. However, there is limited data on the effect of a high exposure level to ELF MFs for a prolonged period. Therefore, the objective of this pilot work was to demonstrate the feasibility of a study evaluating the stress hormone concentrations resulting from a 10-min exposure to a 60 Hz MF of several tens of thousands of µT. In this pilot study, human volunteers were thus exposed for the first time to a 60 Hz, 50 mT MF for a duration of 10 min. Stress hormone levels were measured before (once), during (twice) and after (once) this 10-min exposure period. The small sample size (n = 5) did not allow to conduct standard inferential statistical tests and no conclusion regarding the exposure effects can be drawn. However, this study demonstrates the feasibility of using a simple blood testing material in a protocol testing for the effect of a 10-min exposure to a high MF level in healthy human volunteers. © 2022 Bioelectromagnetics Society.

Vestibular Extremely Low-Frequency Magnetic and Electric Stimulation Effects on Human Subjective Visual Vertical Perception.

Electric fields from both extremely low-frequency magnetic fields (ELF-MF) and alternating current (AC) stimulations impact human neurophysiology. As the retinal photoreceptors, vestibular hair cells are graded potential cells and are sensitive to electric fields. Electrophosphene and magnetophosphene literature suggests different impacts of AC and ELF-MF on the vestibular hair cells. Furthermore, while AC modulates the vestibular system more globally, lateral ELF-MF stimulations could be more utricular specific. Therefore, to further address the impact of ELF-MF-induced electric fields on the human vestibular system and the potential differences with AC stimulations, we investigated the effects of both stimulation modalities on the perception of verticality using a subjective visual vertical (SVV) paradigm. For similar levels of SVV precision, the ELF-MF condition required more time to adjust SVV, and SVV variability was higher with ELF-MF than with AC vestibular-specific stimulations. Yet, the differences between AC and ELF-MF stimulations were small. Overall, this study highlights small differences between AC and ELF-MF vestibular stimulations, underlines a potential utricular contribution, and has implications for international exposure guidelines and standards. © 2022 Bioelectromagnetics Society.

Impact of extremely low-frequency magnetic fields on human postural control.

Studies have found that extremely low-frequency (ELF, < 300 Hz) magnetic fields (MF) can modulate standing balance; however, the acute balance effects of high flux densities in this frequency range have not been systematically investigated yet. This study explores acute human standing balance responses of 22 participants exposed to magnetic induction at 50 and 100 mTrms (MF), and to 1.5 mA alternating currents (AC). The center of pressure displacement (COP) was collected and analyzed to investigate postural modulation. The path length, the area, the velocity, the power spectrum in low (< 0.5 Hz) and medium (0.5-2 Hz) bands have computed and showed the expected effect of the positive control direct current (DC) electric stimulation but failed to show any significant effect of the time-varying stimulations (AC and MF). However, we showed a significant biased stabilization effect on postural data from the custom experimental apparatus employed in this work, which might have neutralized the hypothesized results.

Effects of A 60 Hz Magnetic Field of Up to 50 milliTesla on Human Tremor and EEG: A Pilot Study.

Humans are surrounded by sources of daily exposure to power-frequency (60 Hz in North America) magnetic fields (MFs). Such time-varying MFs induce electric fields and currents in living structures which possibly lead to biological effects. The present pilot study examined possible extremely low frequency (ELF) MF effects on human neuromotor control in general, and physiological postural tremor and electroencephalography (EEG) in particular. Since the EEG cortical mu-rhythm (8-12 Hz) from the primary motor cortex and physiological tremor are related, it was hypothesized that a 60 Hz MF exposure focused on this cortical region could acutely modulate human physiological tremor. Ten healthy volunteers (age: 23.8 ± 4 SD) were fitted with a MRI-compatible EEG cap while exposed to 11 MF conditions (60 Hz, 0 to 50 mTrms, 5 mTrms increments). Simultaneously, physiological tremor (recorded from the contralateral index finger) and EEG (from associated motor and somatosensory brain regions) were measured. Results showed no significant main effect of MF exposure conditions on any of the analyzed physiological tremor characteristics. In terms of EEG, no significant effects of the MF were observed for C1, C3, C5 and CP1 electrodes. However, a significant main effect was found for CP3 and CP5 electrodes, both suggesting a decreased mu-rhythm spectral power with increasing MF flux density. This is however not confirmed by Bonferroni corrected pairwise comparisons. Considering both EEG and tremor findings, no effect of the MF exposure on human motor control was observed. However, MF exposure had a subtle effect on the mu-rhythm amplitude in the brain region involved in tactile perception. Current findings are to be considered with caution due to the small size of this pilot work, but they provide preliminary insights to international agencies establishing guidelines regarding electromagnetic field exposure with new experimental data acquired in humans exposed to high mT-range MFs.

Postural activity and visual vigilance performance during rough seas.

BACKGROUND: Motion of a ship at sea often challenges crew performance. In previous studies, the influence of rough weather on stance at sea has been evaluated in terms of the likelihood of staggers or falls. Few studies have evaluated the influence of sea state on visual performance. Effects of rough seas on visual vigilance performance, subjective mental workload, and the kinematics of postural control have not been demonstrated. METHOD: Crewmembers of the R/V Thomas G. Thompson stood on a force plate, from which we obtained data on the center of pressure (COP). We varied stance width (the distance between the feet in side-by-side stance; 5 cm, 17 cm, and 30 cm) and the difficulty of visual vigilance tasks (Easy vs. Hard). Separately, we evaluated subjects' self-selected foot positioning. RESULTS: Visual performance was better on the Easy task (mean d' = 4.20) than on the Hard task (mean d' = 3.57). Overall vigilance performance (mean d' = 3.88) was worse than when the same subjects were tested under mild sea states (mean d' = 4.11). Subjective mental workload (mean = 28.0) was greater than under mild sea states (mean = 19.9). Relative to mild sea states the variability of postural activity was greater and its predictability was reduced. In addition, postural dynamics were influenced by controlled variations in stance width. CONCLUSIONS: Rough seas affect visual vigilance performance and postural activity, but do not eliminate the effects of vigilance task difficulty or stance width that have been found in mild seas.

Visual vigilance performance and standing posture at sea.

BACKGROUND: Research on land has demonstrated interactions between visual tasks and the control of stance. Variations in visual tasks can influence postural activity; conversely, changes in stance can influence quantitative measures of visual performance. At sea, crewmembers may alter their bodily movements to compensate for ship motion while simultaneously adjusting movements to optimize visual performance. Mutual influence of visual tasks on postural movements and of postural movements on visual tasks has not been demonstrated at sea. METHODS: Crewmembers stood on a force plate, from which we obtained data on the positional variability of the center of pressure (COP). We varied stance width (5 cm, 17 cm, and 30 cm) and the difficulty of visual vigilance tasks (Easy vs. Hard). We collected data on visual performance and we assessed subjective mental workload. RESULTS: Visual performance was better on the Easy task (mean d' = 4.28) than on the Hard task (mean d' = 3.55). Consistent with this result, subjective mental workload was greater for the Hard task than for the Easy task. The variability of postural activity was greater during the Easy task (mean = 2.0 cm x s(-1)) than during the Hard task (mean = 1.9 cm x s(-1)). Stance width influenced postural activity, but also (in 2-way and 3-way interactions) influenced visual performance. Both the magnitude and dynamics of postural activity changed over days at sea. CONCLUSIONS: In mild seas, variations in stance width modulate standing posture and influence the performance of computer-based visual tasks.

Interpersonal postural coordination on rigid and non-rigid surfaces.

When two standing people converse with each other there is an increase in their shared postural activity, relative to conversation with different partners. We asked pairs of participants to converse with each other or with experimental confederates while standing on rigid and nonrigid surfaces. On the rigid surface, shared postural activity was greater when participants conversed with each other than when they conversed with confederates. In addition, the strength of interpersonal coupling increased across trials, but only when members of a dyad conversed with each other. On the nonrigid surface, postural sway variability increased, but we found no evidence that shared postural activity was different when participants conversed with each other, as opposed to conversing with confederates. We consider several possible interpretations of these results.

Body sway at sea for two visual tasks and three stance widths.

BACKGROUND: On land, body sway is influenced by stance width (the distance between the feet) and by visual tasks engaged in during stance. While wider stance can be used to stabilize the body against ship motion and crewmembers are obliged to carry out many visual tasks while standing, the influence of these factors on the kinematics of body sway has not been studied at sea. METHODS: Crewmembers of the RN Atlantis stood on a force plate from which we obtained data on the positional variability of the center of pressure (COP). The sea state was 2 on the Beaufort scale. We varied stance width (5 cm, 17 cm, and 30 cm) and the nature of the visual tasks. In the Inspection task, participants viewed a plain piece of white paper, while in the Search task they counted the number of target letters that appeared in a block of text. RESULTS: Search task performance was similar to reports from terrestrial studies. Variability of the COP position was reduced during the Search task relative to the Inspection task. Variability was also reduced during wide stance relative to narrow stance. The influence of stance width was greater than has been observed in terrestrial studies. CONCLUSIONS: These results suggest that two factors that influence postural sway on land (variations in stance width and in the nature of visual tasks) also influence sway at sea. We conclude that--in mild sea states--the influence of these factors is not suppressed by ship motion.

Walking changes the dynamics of cognitive estimates of time intervals.

Cognitive performance exhibits patterns of trial-to-trial variation that can be described as 1/f or pink noise, as do repeated measures of locomotor performance. Although cognitive and locomotor performances are known to interact when performed concurrently, it is not known whether concurrent performance affects the tasks' pink noise dynamical structure. In this study, participants performed a cognitive task (repeatedly producing a temporal interval) and a motor task (walking on a treadmill) in single- and dual-task conditions. In single-task conditions both tasks exhibited pink noise structure. For concurrent performance the dynamical structure of the cognitive task changed reliably in the direction of white (random) noise. The dynamical structure of locomotion remained pink noise. The change in cognitive dynamics occurred despite no reliable changes in mean or standard deviation measures for either task. The results suggest a functional reorganization of cognitive dynamics supporting successful task performance in dual-task conditions.

Stance width and angle at sea: effects of sea state and body orientation.

BACKGROUND: On land, the distance and angle between the feet in side-by-side stance tend to have characteristic values. Ship motion mandates changes in the control of stance, but there have been no direct assessments of how stance width and angle are controlled at sea. We predicted that participants would adopt a wider stance at sea. METHOD: On two ships, we measured experienced crewmembers' stance width and stance angle during quiet stance when facing forward and when facing athwartship. Each ship was 84 m long and displaced 3500 tons. Measurements were repeated over consecutive days at sea. For one ship, we tested crew-members on land prior to the cruise. RESULTS: On land, stance width (mean = 19.0 cm) and stance angle (mean = 16.19 degrees) were similar to previous reports. At sea, stance width tended to be greater than on land. When facing athwartship on Ship B, changes in stance width across days were correlated with changes in motion of the ship in its surge axis (r = 0.968). Stance angle at sea did not differ from stance angle on land. CONCLUSIONS: The results suggest that preferred stance width is influenced by the fact of being at sea and by the sea state. These variations may be related to the efficiency of postural control on land and at sea. Future research should examine changes in stance width as novices acclimate to life at sea.

Coupling of head and body movement with motion of the audible environment.

The authors asked whether standing posture could be controlled relative to audible oscillation of the environment. Blindfolded sighted adults were exposed to acoustic flow in a moving room, and were asked to move so as to maintain a constant distance between their head and the room. Acoustic flow had direct (source) and indirect (reflected) components. Participants exhibited strong coupling of postural motion with room motion, even when direct information about room motion was masked and was available only in reflected sound. Patterns of hip-ankle coordination closely resembled patterns observed in previous research involving coupling of sway with a visible moving room. The results demonstrate that blindfolded adults can control the dynamics of stance relative to motion of the audible environment.

Postural instability and motion sickness in a virtual moving room.

OBJECTIVE: We examined motion sickness in an oscillating virtual environment presented via a video projector system. BACKGROUND: Visible oscillation of the physical environment is known to induce both postural instability and motion sickness, but it cannot be assumed that the same phenomena will occur in a virtual simulation of such motion. METHOD: Standing participants (3 men and 9 women, 20-22 years of age) were exposed to oscillation of a virtual room. The stimulus was a computer-generated simulation of a laboratory device that is known to induce postural instability and motion sickness. Participants viewed the simulation for up to 40 min and were instructed to discontinue if they experienced symptoms of motion sickness. RESULTS: Motion sickness incidence (42%) did not differ from that in studies using the corresponding physical moving room. Prior to motion sickness onset, the sick group exhibited changes in movement, relative to the well group, as predicted by the postural instability theory of motion sickness. Differences in movement between the sick and well groups developed over time, in contrast with previous studies using physical moving rooms, in which such movement differences have not evolved. CONCLUSION: The results indicate that changes in postural activity precede motion sickness that is induced by an oscillating virtual environment, but they also reveal differences in postural responses to virtual and physical motion environments. APPLICATION: Potential applications of this research include recommendations for the use of virtual environments as models for perception and action in physical environments.

Dynamic stability of locomotor respiratory coupling during cycling in humans.

We explored the locomotor respiratory coupling (LRC) during a 50-min constant-load submaximal cycling exercise. A 4-week recombinant human erythropoietin (r-HuEPO) treatment improved participants' aerobic capabilities, but did not elicit significant changes in LRC. The distributions of the respiratory frequency over pedalling frequency ratios were systematically bimodal, with a preferred use of 1/3 and 1/2, and a progressive shift of the higher mode from 1/3 towards 1/2 with exercise duration. These results are interpreted in the framework of the sine circle map as the result of coordination dynamics between the physiological subsystems involved in the breathing pedalling cooperation.

Strengths and weaknesses of established indirect models to detect recombinant human erythropoietin abuse on blood samples collected 48-hr post administration.

We studied indirect detection models of erythropoietin abuse (EPO) on blood samples collected 48-hr after administration of the drug during 6 weeks of recombinant human erythropoietin (rHuEPO) treatment. Although the efficiency of OFF-models was preserved, we found a loss of sensitivity of ON-models. This study also revealed an increased percentage of stomatocytes in athletes receiving rHuEPO