Stance Width Influences Postural Stability and Motion Sickness

Sitting vs. standing: an urgent need to rebalance our world

During their activities of daily living, humans run, walk, stand, sit and lie down. Recent changes in our environment have favored sedentary behavior over more physically active behavior to such a degree that our health is in danger. Here, we sought to address the problem of excessive time spent seated from various theoretical viewpoints, including postural control, human factors engineering, human history and health psychology. If nothing is done now, the high prevalence of sitting will continue to increase. We make a case for the standing position by demonstrating that spending more time upright can mitigate the physiological and psychological problems associated with excessive sitting without lowering task performance and productivity. The psychological literature even highlights potential benefits of performing certain tasks in the standing position. We propose a number of recommendations on spending more time (but not too much) in the standing position and on more active, nonambulatory behaviors. There is a need to inform people about (i) harmful consequences of excessive sitting and (ii) benefits of spending more time performing active, nonambulatory behaviors. One clear benefit is to reduce detrimental health consequences of excessive sitting and to provide potential additional benefits in terms of productivity and performance.

Introduction to a Twin Dual-Axis Robotic Platform for Studies of Lower Limb Biomechanics

This paper presents a twin dual-axis robotic platform system which is designed for the characterization of postural balance under various environmental conditions and quantification of bilateral ankle mechanics in 2 degrees-of-freedom (DOF) during standing and walking. Methods: Validation experiments were conducted to evaluate performance of the system: 1) to apply accurate position perturbations under different loading conditions; 2) to simulate a range of stiffness-defined mechanical environments; and 3) to reliably quantify the joint impedance of mechanical systems. In addition, several human experiments were performed to demonstrate the system's applicability for various lower limb biomechanics studies. The first two experiments quantified postural balance on a compliance-controlled surface (passive perturbations) and under oscillatory perturbations with various frequencies and amplitudes (active perturbations). The second two experiments quantified bilateral ankle mechanics, specifically, ankle impedance in 2-DOF during standing and walking. The validation experiments showed high accuracy of the platform system to apply position perturbations, simulate a range of mechanical environments, and quantify the joint impedance. Results of the human experiments further demonstrated that the platform system is sensitive enough to detect differences in postural balance control under challenging environmental conditions as well as bilateral differences in 2-DOF ankle mechanics. This robotic platform system will allow us to better understand lower limb biomechanics during functional tasks, while also providing invaluable knowledge for the design and control of many robotic systems including robotic exoskeletons, prostheses and robot-assisted balance training programs. Clinical and Translational Impact Statement- Our robotic platform system serves as a tool to better understand the biomechanics of both healthy and neurologically impaired individuals and to develop assistive robotics and rehabilitation training programs using this information.

Sex differences in the association of postural control with indirect measures of body representations

Besides anthropometric variables, high-order body representations have been hypothesised to influence postural control. However, this has not been directly tested before. Moreover, some studies indicate that sex moderates the relationship of anthropometry and postural control. Therefore, as a proof of concept we investigated the association of body representations with postural control as well as the influence of participants’ sex/gender. Body image measures were assessed with a figural drawing task. Body schema was tested by a covert and an overt task. Body sway was measured during normal bipedal quiet standing with eyes closed (with/without neck extended). Statistical analysis consisted of hierarchical multiple linear regressions with the following regression steps: (1) sensory condition, (2) sex/gender, (3) age, (4) anthropometry, (5) body schema, (6) body image, (7) sex/gender-interactions. Across 36 subjects (19 females), body schema was significantly associated with body sway variability and open-loop control, in addition to commonly known influencing factors, such as sensory condition, gender, age and anthropometry. While in females, also body image dissatisfaction substantially was associated with postural control, this was not the case in males. Sex differences and possible causes why high-order body representations may influence concurrent sensorimotor control of body sway are discussed.

Feasibility of full immersive virtual reality video game on balance and cybersickness of healthy adolescents

Various virtual reality (VR) games with head-mounted displays (HMDs) can provide immersive experiences, but are often accompanied by negative experiences. We investigated the feasibility of immersive virtual reality game on balance and cybersickness in healthy adolescents. This is cross-over design. This study included 11 healthy adolescents. Balance and cybersickness were measured in the following three conditions. First, as a baseline, only balance was measured while no immersive virtual reality game was being played. Second, balance and cybersickness were measured while the participants played an immersive virtual reality game with a fixed background. Third, balance and cybersickness were measured while the participants played an immersive virtual reality game with a moving background. A force plate was used to measure balance, while the Questionnaire (VRSQ) and Simulator Sickness Questionnaire (SSQ) were used to measure cybersickness. Sway velocity and length significantly increased during the game with a moving background compared to baseline and a fixed background game (p < 0.05). VRSQ and SSQ scores significantly increased during the game with a fixed and moving background compared to baseline (p < 0.05) and were significantly higher with use of the moving versus fixed background (p < 0.05). This study demonstrated that playing an immersive virtual reality game with a moving background could negatively affect balance and cybersickness. These results will help to select game contents that can reduce side effects when applying VR HMD to various fields in the future.

The relationship between postural stability and cybersickness: It's complicated - An experimental trial assessing practical implications of cybersickness etiology

Virtual reality (VR) is known to cause cybersickness, and studies report that deteriorations of postural stability coincides with the onset cybersickness. It is unclear whether these deteriorations are the cause or a consequence of cybersickness. Thus, it is also unclear whether measures of postural stability may either predict susceptibility (cause) or objectively measure (consequence) the malaise. To examine whether deteriorations of postural stability can either predict or objectively measure cybersickness, healthy active adults (n = 50) were exposed to one of two different 10 min 360˚ VR videos. Postural stability was assessed, using a force platform, before exposure with eyes open (baseline) and eyes closed, during the first and last minute of exposure, and approximately 10 min after exposure. The deterioration of postural stability from baseline to the first minute of exposure was larger in participants who reported cybersickness, compared to those who did not, for both total trace length (p = 0.017) and standard deviation velocity (p = 0.008). However, there was substantial individual variation and overlap between sick and well participants. Deteriorations of postural stability from baseline to the eyes closed condition did not differ between sick and well participants (trace length, p = 0.270; standard deviation velocity, p = 0.112). There was a significant correlation between the severity of cybersickness and the change of postural stability from the first to the last minute of VR exposure for trace length (r_s=0.32, p = 0.027), but not standard deviation velocity (r_s=0.20, p = 0.187). The deteriorations had returned to baseline levels 10 min after exposure. These findings suggest that deteriorations of postural stability was both a predictor and objective measure at a group level. However, the large individual variation, substantial overlap between sick and well participants, and the limited strength of correlations suggest that deterioration of postural stability has limited practical value as both a predictor and objective measure. These findings emphasize the complicated nature of the relationship between cybersickness and postural stability.

Postural precursors of motion sickness in head-mounted displays: drivers and passengers, women and men

Motion sickness is preceded by distinctive patterns of postural activity that differ between the sexes. We asked whether such postural precursors of motion sickness might exist before participants were exposed to a virtual driving game presented via a head-mounted display. Men and women either controlled a virtual vehicle (drivers), or viewed a recording of virtual vehicle motion (passengers). Before exposure to the game, we recorded standing body sway while participants performed simple visual tasks (staring at a blank page vs. counting target letters in a block of text). Following game exposure, participants were classified into Well and Sick groups. In a statistically significant interaction, the multifractality of body sway varied as a function of sex, vehicle control, and motion sickness status. The results confirm that postural precursors of motion sickness differ between the sexes, and extend these to the control of virtual vehicles in head-mounted displays. Practitioner Summary: We asked whether postural sway might predict motion sickness during exposure to a driving game via a head-mounted display. Participants drove a virtual car (drivers), or watched recorded car motion (passengers). Beforehand, we measured standing body sway. Postural precursors of motion sickness differed between the sexes and drivers and passengers. Abbreviations: M: meters; SD: standard deviation; kg: kilograms; COP: centre of pressure; AP: anterior-posterior; ML: mediolateral; cm: centimeters; s: seconds; min: minutes; MF: DFA: multifractal detrended fluctuation analysis; DFA: detrended fluctuation analysis; ANOVA: analysis of variance; CI: confidence interval; Hz: hertz; SE: standard error of the mean.

Effects of physical driving experience on body movement and motion sickness among passengers in a virtual vehicle

Virtual vehicles (e.g., driving video games) can give rise to visually induced motion sickness. Typically, people drive virtual vehicles. In the present study, we investigated motion sickness among participants who were exposed to virtual vehicles as passengers; that is, they observed vehicle motion, but did not control it. We also asked how motion sickness and the postural precursors of motion sickness might be influenced by participants' previous experience of driving physical vehicles. Participants viewed a recording of a virtual automobile in a driving video game. Drivers were young adults with several years of experience driving physical automobiles, while non-drivers were individuals in the same age group who did not have a driver's license and had never driven an automobile. During exposure to the virtual vehicle, we monitored movement of the head and torso. The independent measures included the incidence and severity of motion sickness. After exposure to the virtual vehicle, the incidence and severity of motion sickness did not differ between Drivers and Non-Drivers. By contrast, postural movement differed between participants who later became motion sick and those who did not. In addition, during exposure to the virtual vehicle, physical driving experience was related to patterns of postural activity that preceded motion sickness. The results are consistent with the postural instability theory of motion sickness, and illuminate relations between the control of physical and virtual vehicles.

Are Modern Head-Mounted Displays Sexist? A Systematic Review on Gender Differences in HMD-Mediated Virtual Reality

Modern head-mounted displays (HMDs) are a promising technology. Thanks to their affordable cost and versatility, HMDs are gaining attention from different sectors. However, the experience reported by the users of these technologies is sometimes negative. A number of people, when using an HMD, complain of various types of physical discomfort as well as symptoms like headache, disorientation, and nausea. These symptoms, developed during or after exposure to virtual environments, are commonly referred to with the term simulator sickness. Some scientific studies have shown that women are commonly more sensitive to simulator sickness. However, a gender imbalance in the susceptibility to simulator sickness has not been widely studied in the context of modern HMDs, and the studies that have been done have reported heterogeneous findings. The present systematic review aims to gather the pieces of evidence that support and oppose a gender difference in the susceptibility of simulator sickness in the framework of modern HMDs. We also aim to individuate other gender differences in the experience of the use of these technologies to establish whether there is sufficient evidence to support a gender discrepancy in the user experience.

Perceptual Validation of Nonlinear Postural Predictors of Visually Induced Motion Sickness

Virtual reality (VR) technology has become increasingly prevalent in our society and has been used for a myriad of applications ranging from psychotherapy to training members of the military. However, one issue that arises from the use of VR is motion sickness, thus making predictors and indicators of motion sickness desirable. To date, a number of indicators of motion sickness have been derived based on nonlinear characteristics of human motion recorded using motion capture systems. While it is known that nonlinear measures can be used to predict motion sickness, it is not known whether people are perceptually sensitive to these particular nonlinear parameters. The aims of this study included establishing whether individuals consistently sort phase plots of sick and well individuals' postural motion without being explicitly told to do so; determining what nonlinear movement parameters could be used to represent these judgments; and assessing the stability of nonlinear measures found to be successful at predicting motion sickness by Smart et al. (2014). Through two methods of analysis (perceptual and quantitative), this research demonstrated that participants can indeed sort the graphic depictions of sick and well participants' postural motion and seem to be perceptually sensitive to nonlinear parameters (normalized path length, path length, elliptical area) that are known to be predictive of motion sickness.

Effects of head motion on postural stability in healthy young adults with chronic motion sensitivity

Background

Motion sensitivity, or motion sickness, is common in modern vehicular and visually stimulating environments. Several studies have shown a relationship between motion sensitivity and decreased postural stability. We aimed to evaluate the effects of head motion (horizontal and vertical) on postural stability in healthy adults with and without chronic motion sensitivity (CMS).

Methods

Sixty healthy adult men and women (age, 20–40 years) with CMS (CMS group, n = 30) and without CMS (non-CMS group, n = 30) participated in the study. Postural stability was assessed during three conditions (static, horizontal head motion, and vertical head motion) using computerized dynamic posturography. Group and condition-related differences in equilibrium scores were evaluated.

Results

There was no significant group x condition interaction (F_2,114 = 0.9, partial ƞ² = 0.04, p = 0.35). However, significant condition-related differences in equilibrium scores were observed (F_2,114 = 26.4, partial ƞ² = 0.31, p < 0.001). Equilibrium scores were significantly worse in the horizontal and vertical head motion conditions compared to those in the static condition (p < 0.001), but were comparable in vertical and horizontal head motion conditions (p = 0.27).

Conclusions

Postural stability was lower in the horizontal and vertical conditions compared to the static condition. However, horizontal and vertical head motions had comparable effects on postural stability in both CMS and non-CMS groups, contrary to our expectations.

Emotional and Cognitive Modulation of Cybersickness: The Role of Pain Catastrophizing and Body Awareness

OBJECTIVE

The goal was to investigate the influence of the tendency to catastrophize somatic symptoms and body awareness on motion-related sickness.

BACKGROUND

Influences of emotional and cognitive-evaluative processes on the genesis of motion sickness or cybersickness have rarely been investigated. Brain imaging studies showed activation during cybersickness, resembling the pattern found for pain processing. Two aspects often investigated in this context are pain catastrophizing and body awareness. The present two studies investigated the relationship of motion-related sickness to two tendencies involved in pain processing: pain catastrophizing and body awareness.

METHOD

In the first study, 115 participants reported their motion sickness history, pain catastrophizing, and body awareness. In the second study, 40 participants were exposed to a virtual reality and reported their experience of cybersickness as well as their pain catastrophizing and body awareness.

RESULTS

Pain catastrophizing was positively correlated to motion sickness history and cybersickness. Body awareness did not show a linear effect on motion sickness history or cybersickness. However, the interaction effect of pain catastrophizing and body awareness was significant in both studies.

CONCLUSION

Pain catastrophizing seems to have a detrimental effect on cybersickness symptoms. Body awareness moderated the relationship in the sense that the combination of high pain catastrophizing and low body awareness lead to the highest sickness levels.

APPLICATION

Affective and cognitive modulation of cybersickness symptoms should be considered when exposing risk groups to motion-related adverse stimuli.

Real-time visual feedback about postural activity increases postural instability and visually induced motion sickness

BACKGROUND

Several studies have shown that the kinematics of standing body sway can be influenced by the provision of real time feedback about postural activity through visual displays.

RESEARCH QUESTION

We asked whether real time visual feedback about the position of the body's center of pressure (COP) might affect body sway and the occurrence of visually induced motion sickness.

METHODS

Standing participants (women) were exposed to complex visual oscillation in a moving room, a device that nearly filled the field of view. During exposure to complex visual oscillations, we provided real time feedback about displacements of the body's center of pressure through a visual display presented on a tablet computer.

RESULTS

The incidence of motion sickness was greater than in a closely related study that did not provide real time feedback. We monitored the kinematics of the body's center of pressure before and during exposure to visual motion stimuli. Body sway differed between participants who reported motion sickness and those who did not. These differences existed before any participants experienced subjective symptoms of motion sickness.

SIGNIFICANCE

Real time visual feedback about COP displacement did not reduce visually induced motion sickness, and may have increased it. We identified postural precursors of motion sickness that may have been exacerbated by the COP display. The results indicate that visual feedback about postural activity can destabilize postural control, leading to negative side effects. We suggest possible alternative types of visual displays that might help to stabilize posture, and reduce motion sickness.

Effects of decades of physical driving on body movement and motion sickness during virtual driving

We investigated relations between experience driving physical automobiles and motion sickness during the driving of virtual automobiles. Middle-aged individuals drove a virtual automobile in a driving video game. Drivers were individuals who had possessed a driver’s license for approximately 30 years, and who drove regularly, while non-drivers were individuals who had never held a driver’s license, or who had not driven for more than 15 years. During virtual driving, we monitored movement of the head and torso. During virtual driving, drivers became motion sick more rapidly than non-drivers, but the incidence and severity of motion sickness did not differ as a function of driving experience. Patterns of movement during virtual driving differed as a function of driving experience. Separately, movement differed between participants who later became motion sick and those who did not. Most importantly, physical driving experience influenced patterns of postural activity that preceded motion sickness during virtual driving. The results are consistent with the postural instability theory of motion sickness, and help to illuminate relations between the control of physical and virtual vehicles.

The virtual reality head-mounted display Oculus Rift induces motion sickness and is sexist in its effects

Anecdotal reports suggest that motion sickness may occur among users of contemporary, consumer-oriented head-mounted display systems and that women may be at greater risk. We evaluated the nauseogenic properties of one such system, the Oculus Rift. The head-mounted unit included motion sensors that were sensitive to users' head movements, such that head movements could be used as control inputs to the device. In two experiments, seated participants played one of two virtual reality games for up to 15 min. In Experiment 1, 22% of participants reported motion sickness, and the difference in incidence between men and women was not significant. In Experiment 2, motion sickness was reported by 56% of participants, and incidence among women (77.78%) was significantly greater than among men (33.33%). Before participants were exposed to the head-mounted display system, we recorded their standing body sway during the performance of simple visual tasks. In both experiments, patterns of pre-exposure body sway differed between participants who (later) reported motion sickness and those who did not. In Experiment 2, sex differences in susceptibility to motion sickness were preceded by sex differences in body sway. These postural effects confirm a prediction of the postural instability theory of motion sickness. The results indicate that users of contemporary head-mounted display systems are at significant risk of motion sickness and that in relation to motion sickness these systems may be sexist in their effects.

Visual Information and Support Surface for Postural Control in Visual Search Task

When standing on a reduced support surface, people increase their reliance on visual information to control posture. This assertion was tested in the current study. The effects of imposed motion and support surface on postural control during visual search were investigated. Twelve participants (aged 21 ± 1.8 years; six men and six women) stood on a reduced support surface (45% base of support). In a room that moved back and forth along the anteroposterior axis, participants performed visual search for a given letter in an article. Postural sway variability and head-room coupling were measured. The results of head-room coupling, but not postural sway, supported the assertion that people increase reliance on visual information when standing on a reduced support surface. Whether standing on a whole or reduced surface, people stabilized their posture to perform the visual search tasks. Compared to a fixed target, searching on a hand-held target showed greater head-room coupling when standing on a reduced surface.

Postural sway in men and women during nauseogenic motion of the illuminated environment

We exposed standing men and women to motion relative to the illuminated environment in a moving room. During room motion, we measured the kinematics of standing body sway. Participants were instructed to discontinue immediately if they experienced any symptoms of motion sickness, however mild. For this reason, our analysis of body sway included only movement before the onset of motion sickness. We analyzed the spatial magnitude of postural sway in terms of the positional variability and mean velocity of the center of pressure. We analyzed the multifractality of postural sway in terms of the width of the multifractal spectrum and the degree of multiplicativity of center of pressure positions. Results revealed that postural sway differed between participants who later reported motion sickness and those who did not, replicating previous effects. In a novel effect, postural responses to motion of the illuminated environment differed between women and men. In addition, we identified statistically significant interactions that involved both Sex and motion sickness status. Effects were observed separately in the spatial magnitude and multifractality of sway. The results were consistent with the postural instability theory of motion sickness (Riccio and Stoffregen in Ecol Psychol 3:195-240, 1991) and suggest that Sex differences in motion sickness may be related to Sex differences in the control and stabilization of bodily activity.

Relationship between Spectral Characteristics of Spontaneous Postural Sway and Motion Sickness Susceptibility

Motion sickness (MS) usually occurs for a narrow band of frequencies of the imposed oscillation. It happens that this frequency band is close to that which are spontaneously produced by postural sway during natural stance. This study examined the relationship between reported susceptibility to motion sickness and postural control. The hypothesis is that the level of MS can be inferred from the shape of the Power Spectral Density (PSD) profile of spontaneous sway, as measured by the displacement of the center of mass during stationary, upright stance. In Experiment 1, postural fluctuations while standing quietly were related to MS history for inertial motion. In Experiment 2, postural stability measures registered before the onset of a visual roll movement were related to MS symptoms following the visual stimulation. Study of spectral characteristics in postural control showed differences in the distribution of energy along the power spectrum of the antero-posterior sway signal. Participants with MS history provoked by exposure to inertial motion showed a stronger contribution of the high frequency components of the sway signal. When MS was visually triggered, sick participants showed more postural sway in the low frequency range. The results suggest that subject-specific PSD details may be a predictor of the MS level. Furthermore, the analysis of the sway frequency spectrum provided insight into the intersubject differences in the use of postural control subsystems. The relationship observed between MS susceptibility and spontaneous posture is discussed in terms of postural sensory weighting and in relation to the nature of the provocative stimulus.

Sex differences in visual performance and postural sway precede sex differences in visually induced motion sickness

Motion sickness is more common among women than among men. Previous research has shown that standing body sway differs between women and men. In addition, research has shown that postural sway differs between individuals who experience visually induced motion sickness and those who do not and that those differences exist before exposure to visual motion stimuli. We asked whether sex differences in postural sway would be related to sex differences in the incidence of visually induced motion sickness. We measured unperturbed standing body sway before participants were exposed to visual motion stimuli that induced motion sickness in some participants. During postural testing, participants performed different visual tasks. Results revealed that postural sway was affected by visual tasks, consistent with the literature. In addition, we found a statistically significant three-way interaction between visual tasks, sex, and (subsequent) motion sickness status. These results suggest that sex differences in motion sickness may be related to sex differences in the control of postural balance.

Use of controlled diaphragmatic breathing for the management of motion sickness in a virtual reality environment

Evidence indicates that activation of the parasympathetic nervous system (PNS) suppresses physiological responses associated with motion sickness. Research also shows paced breathing increases PNS activation; the current study examines the use of paced diaphragmatic breathing (DB) training to quell motion sickness symptoms. Healthy participants (N = 60) were pre-screened for motion sickness susceptibility. Participants were then randomly assigned to either a control condition, focusing on environmental awareness, or to an experimental condition implementing paced DB. Following this, participants were exposed to a virtual reality (VR) motion sickness experience, while heart rate variability, breathing rate (RPM), and motion sickness ratings were collected. Results demonstrated participants in the DB condition had higher PNS activation and reported fewer motion sickness symptoms during the VR experience than the participants in the control condition. Results suggest that the DB protocol can be used to significantly increase PNS tone and decrease the development of motion sickness symptoms.

The impact of vehicle motion during transport on animal welfare

Motion sickness is a common response in humans and some species of farm livestock during transport, but research on the impact of motion has been primarily focused on the use of animal models for humans. During livestock transportation, animals seek to minimise uncontrolled movements to reduce energy consumption and maintain posture. Road and sea transport of livestock can produce motion sickness and stress responses. Clinical signs are the result of autonomous nervous system activation. Studies conducted on road transportation effects in domestic animals showed several motion sickness behaviours including vomiting and, in ruminants, a reduction in rumination. However, there is a lack of knowledge on the impact of sea transport motion. Despite the paucity of data on livestock, there is sufficient evidence to believe that motion might affect animal welfare when animals are transported by road or sea.

Coupling of postural activity with motion of a ship at sea

On land, body sway during stance becomes coupled with imposed oscillations of the illuminated environment or of the support surface. This coupling appears to have the function of stabilizing the body relative to the illuminated or inertial environment. In previous research, the stimulus has been limited to motion in a single axis. Little is known about our ability to couple postural activity with complex, multi-axis oscillations. On a ship at sea, we evaluated postural activity using measures of body movement, as such, and we separately evaluated a direct measure of coupling between body movement and ship motion. Participants were tested while facing fore-aft and athwartship. We compared postural activity between participants who had been seasick at the beginning of the voyage and those who had not. Coupling of postural activity with ship motion differed between body axes as a function of body orientation relative to the ship. In addition, coupling differed between participants who had been seasick at the beginning of the voyage and those who had not. We discuss the results in terms of implications for general theories of postural control, and for prediction of susceptibility to seasickness in individuals.

Motion sickness: more than nausea and vomiting

Motion sickness is a complex syndrome that includes many features besides nausea and vomiting. This review describes some of these factors and points out that under normal circumstances, many cases of motion sickness go unrecognized. Motion sickness can occur during exposure to physical motion, visual motion, and virtual motion, and only those without a functioning vestibular system are fully immune. The range of vulnerability in the normal population varies about 10,000 to 1. Sleep deprivation can also enhance susceptibility. Systematic studies conducted in parabolic flight have identified velocity storage of semicircular canal signals-velocity integration-as being a key factor in both space motion sickness and terrestrial motion sickness. Adaptation procedures that have been developed to increase resistance to motion sickness reduce this time constant. A fully adequate theory of motion sickness is not presently available. Limitations of two popular theories, the evolutionary and the ecological, are described. A sensory conflict theory can explain many but not all aspects of motion sickness elicitation. However, extending the theory to include conflicts related to visceral afferent feedback elicited by voluntary and passive body motion greatly expands its explanatory range. Future goals should include determining why some conflicts are provocative and others are not but instead lead to perceptual reinterpretations of ongoing body motion. The contribution of visceral afferents in relation to vestibular and cerebellar signals in evoking sickness also deserves further exploration. Substantial progress is being made in identifying the physiological mechanisms underlying the evocation of nausea, vomiting, and anxiety, and a comprehensive understanding of motion sickness may soon be attainable. Adequate anti-motion sickness drugs without adverse side effects are not yet available.

Precursors of post-bout motion sickness in adolescent female boxers

Athletic head trauma (both concussive and sub-concussive) is common among adolescents. Head trauma often is followed by motion sickness-like symptoms, by changes in cognitive performance, and by changes in standing body sway. We evaluated adolescent female boxers who did and did not report motion sickness after a bout (i.e., a boxing match), together with a control group of non-boxers. We asked whether pre-bout body sway would differ between boxers who experienced post-bout motion sickness and those who did not. In addition, we asked whether pre-bout cognitive performance would differ between non-boxers and boxers with and without post-bout motion sickness. Seven of twenty boxers reported motion sickness after a bout. Pre-bout measures of cognitive performance and body sway were different in boxers who reported post-bout motion sickness than in boxers without post-bout sickness or controls. The results suggest that susceptibility to motion sickness-like symptoms in adolescent female boxers may be manifested in characteristic patterns of body sway and cognitive performance. It may be possible to use pre-bout data to predict susceptibility to post-bout symptoms.

Spontaneous postural sway predicts the strength of smooth vection

This study asked whether individual differences in the influence of vision on postural stability could be used to predict the strength of subsequently induced visual illusions of self-motion (vection). In the experiment, we first measured spontaneous postural sway while subjects stood erect for 60 s with their eyes both open and both closed. We then showed our subjects two types of self-motion display: radially expanding optic flow (simulating constant velocity forwards self-motion) and vertically oscillating radially expanding optic flow (simulating constant velocity forwards self-motion combined with vertical head oscillation). As expected, subjects swayed more with their eyes closed (compared to open) and experienced more compelling illusions of self-motion with vertically oscillating (as opposed to smooth) radial flow. The extent to which participants relied on vision for postural stability-measured as the ratio of sway with eyes closed compared to that with eyes open-was found to predict vection strength. However, this was only the case for displays representing smooth self-motion. It seems that for oscillating displays, other factors, such as visual-vestibular interactions, may be more important.

Body load and the postural precursors of motion sickness

Physical properties of the body affect the control of standing body sway. One example occurs when loads are added to the body, such as occurs when wearing a backpack. Other research has shown that subjective symptoms of motion sickness are preceded by differences in body sway between individuals who later report motion sickness and those who do not. In the present study we asked whether loads worn on the body would affect relations between body sway and motion sickness. We measured standing body sway without load and then with loads worn at the shoulders or thighs. Then participants were exposed to potentially nauseogenic visual motion stimulation while wearing shoulder or thigh loads. We measured body sway continuously during exposure to visual motion. Thirteen of 36 participants (36%) reported motion sickness. Body sway was affected by loads and by load position, consistent with previous research. Also consistent with previous research, sway differed between well and sick participants both before and during exposure to visual motion stimuli. In addition, during room motion the well and sick participants responded differently to loads. The results are consistent with the hypothesis that physical properties of the body can affect relations between body sway and motion sickness.

Cognitive and postural precursors of motion sickness in adolescent boxers

Athletic head trauma (both concussive and sub-concussive) is common among adolescents. Concussion typically is followed by motion sickness-like symptoms, by changes in cognitive performance, and by changes in standing body sway. We asked whether pre-bout body sway would differ between adolescent boxers who experienced post-bout motion sickness and those who did not. In addition, we asked whether pre-bout cognitive performance would differ as a function of adolescent boxers' post-bout motion sickness. Nine of nineteen adolescent boxers reported motion sickness after a bout. Pre-bout measures of cognitive performance and body sway differed between boxers who reported post-bout motion sickness and those who did not. The results suggest that susceptibility to motion sickness-like symptoms in adolescent boxers may be manifested in characteristic patterns of body sway and cognitive performance. It may be possible to use pre-bout data to predict susceptibility to post-bout symptoms.

Getting Your Sea Legs

Sea travel mandates changes in the control of the body. The process by which we adapt bodily control to life at sea is known as getting one's sea legs. We conducted the first experimental study of bodily control as maritime novices adapted to motion of a ship at sea. We evaluated postural activity (stance width, stance angle, and the kinematics of body sway) before and during a sea voyage. In addition, we evaluated the role of the visible horizon in the control of body sway. Finally, we related data on postural activity to two subjective experiences that are associated with sea travel; seasickness, and mal de debarquement. Our results revealed rapid changes in postural activity among novices at sea. Before the beginning of the voyage, the temporal dynamics of body sway differed among participants as a function of their (subsequent) severity of seasickness. Body sway measured at sea differed among participants as a function of their (subsequent) experience of mal de debarquement. We discuss implications of these results for general theories of the perception and control of bodily orientation, for the etiology of motion sickness, and for general phenomena of perceptual-motor adaptation and learning.

Standing body sway in women with and without morning sickness in pregnancy

Morning sickness typically is attributed to hormonal changes in pregnancy. We asked whether morning sickness is associated with changes in standing postural equilibrium, as occurs in research on visually induced motion sickness. Twenty-one pregnant women (mean age=30 years, mean height=163cm; mean weight=63kg) were tested during the first trimester. Laboratory-based balance measures were collected, along with perceived postural stability, the presence of morning sickness, and the severity of subjective symptoms. We varied the distance between the feet and the visual task performed during stance. Participants were classified as either experiencing (Sick, n=12) or not experiencing (Well, n=9) morning sickness. Perceived balance stability was lower for Sick than for Well women. The positional variability of sway was reduced for the Sick group, relative to the Well group. Positional variability decreased with wider stance width, and was reduced during performance of a more demanding visual task. Stance width and visual task also influenced the temporal dynamics of sway. Effects of stance width and visual task on postural sway were similar to effects in non-pregnant adults, suggesting that sensitive tuning of posture is maintained during the first trimester. The findings suggest that women with morning sickness may attempt to stabilize their bodies by reducing overall body sway. It may be useful to recommend that women adopt wider stance early in pregnancy.