Mocking enactments: a case study of multimodal stance-stacking

Although research into multimodal stance-taking has gained momentum over the past years, the multimodal construction of so-called stacked stances has not yet received systematic attention in the literature. Mocking enactments are a prime example of such complex social actions as they are layered both interactionally and stance-related, and they rely significantly on the use of bodily visual resources, depicting rather than describing events and stances. Using Du Bois' Stance Triangle as a framework, this study investigates mocking enactments as a case study to unravel the multimodal aspects of layered stance expressions. Drawing on three data sets-music instruction in Dutch, German, and English, spontaneous face-to-face interactions among friends in Dutch, and narrations on past events in Flemish Sign Language (VGT)-this study provides a qualitative exploration of mocking enactments across different communicative settings, languages, and modalities. The study achieves three main objectives: (1) illuminating how enactments are used for mocking, (2) identifying the layers of stance-taking at play, and (3) examining the multimodal construction of mocking enactments. Our analysis reveals various different uses of enactments for mocking. Aside from enacting the target of the mockery, participants can include other characters and viewpoints, highlighting the breadth of the phenomenon under scrutiny. Second, we uncover the layered construction of stance on all axes of the Stance Triangle (evaluation, positioning, and alignment). Third, we find that mocking enactments are embedded in highly evaluative contexts, indexed by the use of bodily visual resources. Interestingly, not all mocking enactments include a multimodally exaggerated depiction, but instead, some merely allude to an absurd hypothetical scenario. Our findings contribute to the growing body of literature on multimodal stance-taking, by showing how a nuanced interpretation of the Stance Triangle can offer a useful framework for analyzing layered stance acts.

Unsupervised Gait Event Identification with a Single Wearable Accelerometer and/or Gyroscope: A Comparison of Methods across Running Speeds, Surfaces, and Foot Strike Patterns

We evaluated 18 methods capable of identifying initial contact (IC) and terminal contact (TC) gait events during human running using data from a single wearable sensor on the shank or sacrum. We adapted or created code to automatically execute each method, then applied it to identify gait events from 74 runners across different foot strike angles, surfaces, and speeds. To quantify error, estimated gait events were compared to ground truth events from a time-synchronized force plate. Based on our findings, to identify gait events with a wearable on the shank, we recommend the Purcell or Fadillioglu method for IC (biases +17.4 and -24.3 ms; LOAs -96.8 to +131.6 and -137.0 to +88.4 ms) and the Purcell method for TC (bias +3.5 ms; LOAs -143.9 to +150.9 ms). To identify gait events with a wearable on the sacrum, we recommend the Auvinet or Reenalda method for IC (biases -30.4 and +29.0 ms; LOAs -149.2 to +88.5 and -83.3 to +141.3 ms) and the Auvinet method for TC (bias -2.8 ms; LOAs -152.7 to +147.2 ms). Finally, to identify the foot in contact with the ground when using a wearable on the sacrum, we recommend the Lee method (81.9% accuracy).

Altered coordination strategies during upright stance and gait in teachers of the Alexander Technique

Deterioration in movement and posture often occurs with aging. Yet there may be approaches to movement training that can maintain posture and movement coordination patterns as we age. The Alexander Technique is a non-exercise-based approach that aims to improve everyday movement and posture by increasing awareness and modulating whole-body postural muscle activity. This study assessed whether nineteen 55-72-year-old Alexander Technique teachers showed different posture and movement coordination patterns than twenty age-matched controls during a standing and walking protocol using 3D inertial sensors. During upright stance, Alexander Technique teachers showed lower centroidal sway frequency at the ankle (p = .04) and lower normalized jerk at the sternum (p = .05) than controls. During gait, Alexander Technique teachers had more symmetrical gait cycles (p = .04), more symmetrical arm swing velocity (p = .01), greater arm swing velocity (p < .01), greater arm swing range of motion (p = .02), and lower range of acceleration of the torso in the frontal plane (p = .03) than controls. Smoother control of upright posture, more stable torso motion, and less restrained arm mobility suggest that Alexander Technique training may counter movement degradation that is found with aging. Results highlight the important balance between mobility and stability within the torso and limbs.

"We may conclude that:" a corpus-based study of stance-taking in conclusion sections of RAs across cultures and disciplines

Research article conclusions form an important sub-genre in the academic community. This study aims to compare the use of stance markers in English and Chinese research article conclusions and investigate how stance markers may vary in soft and hard sciences. Based on Hyland's stance model, an analysis of stance markers over 20 years was made in two corpora, which were compiled with 180 research article conclusions in each language from four disciplines. It was found that English writers and soft science writers tended to make statements more tentatively by hedges and craft their persona more explicitly through self-mentions. However, Chinese writers and hard science writers made their claims with more certainty by boosters and showed their affective attitude more frequently through attitude markers. The results reveal how writers from different cultural backgrounds construct their stances and also unveil the disciplinary differences involved in stance-taking. It is hoped that this corpus study will inspire future research on stance-taking in the conclusion section and also help cultivate writers' genre awareness.

Balance Adaptation While Standing on a Compliant Base Depends on the Current Sensory Condition in Healthy Young Adults

Background

Several investigations have addressed the process of balance adaptation to external perturbations. The adaptation during unperturbed stance has received little attention. Further, whether the current sensory conditions affect the adaptation rate has not been established. We have addressed the role of vision and haptic feedback on adaptation while standing on foam.

Methods

In 22 young subjects, the analysis of geometric (path length and sway area) and spectral variables (median frequency and mean level of both total spectrum and selected frequency windows) of the oscillation of the centre of feet pressure (CoP) identified the effects of vision, light-touch (LT) or both in the anteroposterior (AP) and mediolateral (ML) direction over 8 consecutive 90 s standing trials.

Results

Adaptation was obvious without vision (eyes closed; EC) and tenuous with vision (eyes open; EO). With trial repetition, path length and median frequency diminished with EC (p < 0.001) while sway area and mean level of the spectrum increased (p < 0.001). The low- and high-frequency range of the spectrum increased and decreased in AP and ML directions, respectively. Touch compared to no-touch enhanced the rate of increase of the low-frequency power (p < 0.05). Spectral differences in distinct sensory conditions persisted after adaptation.

Conclusion

Balance adaptation occurs during standing on foam. Adaptation leads to a progressive increase in the amplitude of the lowest frequencies of the spectrum and a concurrent decrease in the high-frequency range. Within this common behaviour, touch adds to its stabilising action a modest effect on the adaptation rate. Stabilisation is improved by favouring slow oscillations at the expense of sway minimisation. These findings are preliminary to investigations of balance problems in persons with sensory deficits, ageing, and peripheral or central nervous lesion.

Degenerative cervical myelopathy delays responses to lateral balance perturbations regardless of predictability

The aim of this study was to quantify balance impairments in standing in people with degenerative cervical myelopathy (PwDCM) in response to external perturbations. PwDCM have damage to their spinal cord due to degeneration of the cervical vertebral column, but little is known about balance. Balance was quantified by capturing kinetics, kinematic, and electromyographic data during standing in response to lateral waist pulls. Participants received pulls during predictable and unpredictable contexts in three stance widths at two magnitudes. In response to lateral waist pulls, PwDCM had larger center of mass excursion (P < 0.001) and delayed gluteus medius electromyography onset (P < 0.001) and peak (P < 0.001) timing. These main effects of history of myelopathy were consistent across predictability, stance width, and magnitude. A multilinear regression determined that gluteus medius peak timing + tibialis anterior peak timing most strongly predicted center of mass excursion (R² = 0.50, P < 0.001). These data suggest that PwDCM have delays in generating voluntary and reactive motor commands, contributing to balance impairments. Future rehabilitation strategies should focus on generating rapid muscular contractions. Additionally, frontal plane postural control is regulated by the gluteus medius and the tibialis anterior, whereas other muscles (e.g. gluteus minimus, ankle invertors/evertors) not studied here may also contribute.NEW & NOTEWORTHY Frontal plane reactive postural control is impaired in persons with degenerative cervical myelopathy because of delayed muscle responses. Additionally, postural control varies across stance width, predictability, and perturbation magnitude.

Specific Posture-Stabilising Effects of Vision and Touch Are Revealed by Distinct Changes of Body Oscillation Frequencies

We addressed postural instability during stance with eyes closed (EC) on a compliant surface in healthy young people. Spectral analysis of the centre of foot pressure oscillations was used to identify the effects of haptic information (light-touch, EC-LT), or vision (eyes open, EO), or both (EO-LT). Spectral median frequency was strongly reduced by EO and EO-LT, while spectral amplitude was reduced by all "stabilising" sensory conditions. Reduction in spectrum level by EO mainly appeared in the high-frequency range. Reduction by LT was much larger than that induced by the vision in the low-frequency range, less so in the high-frequency range. Touch and vision together produced a fall in spectral amplitude across all windows, more so in anteroposterior (AP) direction. Lowermost frequencies contributed poorly to geometric measures (sway path and area) for all sensory conditions. The same subjects participated in control experiments on a solid base of support. Median frequency and amplitude of the spectrum and geometric measures were largely smaller when standing on solid than on foam base but poorly affected by the sensory conditions. Frequency analysis but not geometric measures allowed to disclose unique tuning of the postural control mode by haptic and visual information. During standing on foam, the vision did not reduce low-frequency oscillations, while touch diminished the entire spectrum, except for the medium-high frequencies, as if sway reduction by touch would rely on rapid balance corrections. The combination of frequency analysis with sensory conditions is a promising approach to explore altered postural mechanisms and prospective interventions in subjects with central or peripheral nervous system disorders.

Recurvatum of the Knee in Cerebral Palsy: A Review

Recurvatum is defined as hyperextension of the knee in the stance phase of gait. Recurvatum knee is a naturally occurring common gait deviation in those with cerebral palsy, along with crouch knee, jump knee, and stiff knee gaits. Early and late recurvatum occur in the first and second halves of stance. Early recurvatum is associated with dynamic calf contraction that raises the heel and pushes the knee into hyperextension as the forefoot contacts the floor. Late recurvatum occurs after the foot is already flat on the floor. As the body weight comes forward over the foot, the tibia stops its forward motion too early as the ankle comes to its range-of-motion limit. The advancing body then moves forward over a hyperextending knee. Surgical hamstring lengthening can have recurvatum as a side effect. There are several strategies to decrease this risk. Medial hamstring lengthening may be safer than combined medial and lateral lengthening. The concept here is that less lengthening or less aggressive lengthening means less recurvatum risk. However, combined medial and lateral lengthening can be reasonably safe from the risk of causing recurvatum if the knee is showing enough preoperative flexion in stance to warrant the increased surgery. More flexion in stance relates to less risk, while less flexion in stance relates to more risk. Knee flexion in stance can be measured. This is done by measuring knee flexion at initial contact and knee flexion in stance in a gait lab or with stop-action video. If there is minimal knee flexion in stance, hamstring lengthening might not be advisable, even if the hamstrings are tight on popliteal angle testing. There are other factors that contribute to recurvatum risk, such as knee hyperextension on static exam, equinus contracture, and jump knee gait. For treatment of recurvatum, the mainstay is the use of ankle foot orthoses set in dorsiflexion. Surgical equinus correction in those with early stance recurvatum can be effective but it is not likely to be effective in those with late stance recurvatum.

Heel Lift for Skiing to Compensate for Corrected Sagittal Vertical Axis After Spinal Surgery: A Case Report

Lateral lumbar interbody fusion (LLIF) and pedicle subtraction osteotomy are common procedures to correct adult spinal deformities. Little is known about returning postoperatively to a high-performance sport such as skiing after spinal surgery. We report a case of an alpine skier who underwent a LLIF procedure combined with a posterior corrective osteotomy and posterior instrumentation, who had difficulties returning to skiing postoperatively because of new spinal biomechanics. The case report describes the possible consequences of spinal sagittal deformity surgery on postoperative skiing. A 63-year-old man with a complex lumbar spinal surgery history showed severe adjacent segment degenerative spondylolistheses at L1-L2 and at L5-S1. A lateral approach at L1-L2 combined with a posterior corrective osteotomy at L3 and instrumentation from T10 to the pelvis were performed. At his 1-year follow up, he made excellent progress and returned to skiing. However, he reported that skiing did not feel the same, and his center of gravity felt as if it shifted backwards. Consequently, he placed a 2-cm wedge in his ski binding, which improved his skiing experience. Sagittal vertical axis changes after spinal surgery affect the biomechanics of the entire body. After surgery, the body's ligaments, muscles, and fascia adapt to the new body posture. Activities such as skiing, where body posture plays an essential role, are particularly affected by spine surgeries. Surgeons should discuss this issue before spinal surgery with patients, especially if patients are involved in high-intensity sports.

A 60:40 split: Differential mass support in dogs

Dogs have been bred for different sizes and functions, which can affect their locomotor biomechanics. As quadrupeds, dogs must distribute their mass between fore and hind legs when standing. The mass distribution in dogs was studied to determine if the proportion of supported mass on each limb couplet is dependent on body size. A total of 552 dogs from 123 breeds ranging in size from Chihuahua to Mastiff were examined. Each dog was weighed on a digital scale while standing, alternating foreleg, and hind leg support. The overall "grand" mean proportion of mass on the forelegs to the total mass was 60.4% (range: 47.6-74.4%). The data set indicated no significant change in the ratio with total mass but there was a significant difference by sex. When separated into American Kennel Club categories, no group was notably different from the grand mean or from each other, but when sex was also considered, there was a significant difference that was not specifically discerned by post hoc analysis. The mean for female Hounds was notably below the grand mean. For clades based on genetics, the mean for European origin mastiffs was notably greater than the grand mean and significantly different from UK origin herders and coursers. The mass of the head, chest, and musculature for propulsion could explain the mass support differential. Mass distribution and terrestrial locomotion in dogs shows substantial variation among breeds.

Distance running stride-to-stride variability for sagittal plane joint angles

Recent research indicates that distance running stride-to-stride variability (SSV) is related to performance and injury. Previous studies have primarily focused on stride characteristics (stride length and time). We assessed SSV for sagittal plane joint angles with the primary purpose of testing for significant differences among the lower body joints. The secondary purpose was to determine if strong correlations exist among joint SSV measures. Thirty recreational adult runners participated in the study (8 females, 22 males, 39 ± 10 years; 53.1 ± 25.7 km/week). A 6-camera motion capture system (200 Hz) collected kinematic data during treadmill running at a preferred pace. A 2 by 3 repeated measures factorial ANOVA (phase-stance, swing; joint-hip, knee, ankle) was run (p = 0.05). There was a significant interaction effect (p < 0.001) and post hoc analysis revealed knee swing to be the most variable condition by far. For all three joints, there were strong correlations between stance and swing SSV (r = 0.80 to r = 0.88) and correlations among the joints were moderate to strong (r = 0.55 to 0.86). This study helps to better understand the joints/phases that contribute most to variability in the overall stride. Also, the strong correlations suggest that runners appear to have an overall SSV pattern that is similar across joints/phases.

Loudness Trumps Pitch in Politeness Judgments: Evidence from Korean Deferential Speech

Social meaning is not conveyed through words alone, but also through how words are produced phonetically. This paper investigates the role of loudness and pitch in determining the perception of politeness-related judgments in Korean. It has been proposed that high pitch is universally associated with polite or deferential social meanings. In contrast to this, Experiment 1 examined the perceptual effect of pitch and found no effect. Experiment 2 tested the effect of loudness, and found that listeners associate quieter speech with deference. Finally, Experiment 3 investigated the simultaneous effects of loudness and pitch, and found again that loudness had a consistent effect, whereas pitch only had a weak effect. Analyses of individual differences suggest that in contrast to loudness, which is interpreted uniformly across Korean listeners, pitch has more variegated social meanings: Some listeners associate high pitch with deferential meaning, others associate low pitch with deferential meaning. Thus, we find loudness to be a more unambiguous indicator of deferential speech than pitch. These findings shed light on how different acoustic properties contribute to the indexing of social stances, and they suggest that the role of pitch in conveying politeness may have been overstated in past research.

Dynamics of Postural Control in Elite Sport Rifle Shooters

Thirteen shooters and eleven non-shooters completed two-legged and single-legged stance on a force platform. The dynamics of the center of pressure trajectory was assessed using sample entropy, correlation dimension and entropic half-life. Additionally, the body sway was quantified as the elliptical area of the trajectory. The shooters had lower sample entropy and tended to have longer entropic half-life during the single-legged stance. Across the two tasks, the correlation dimension in the anterior-posterior direction and the body sway in both directions were lower in the shooters. This suggests that extensive training in quiet stance is associated with altered postural control, especially during challenging single-legged stance and to a lesser extend during two-legged stance.

Everything": Analyzing Caregiver Uncertainty and Control Through Stance Marking

Informal caregivers immersed in the daily care of loved ones at end-of-life stages face such challenges as medical and household issues, worries, doubts, and uncertainties. Using a macro-mezzo-micro approach to discourse, we analyzed parent study interview data involving 46 caregivers facing end-of-life realities. At the mezzo level, we examined caregivers' expressed perceptions of control. We then more finely analyzed discursive expressions of affective stances pertaining to caregivers' emotions and feelings, and epistemic stances pertaining to their knowledge and belief states. Theories of uncertainty and control inextricably interweave areas of cognition, affect, and behavior regarding how caregivers perceive their realities and how they engage in or disengage from coping mechanisms in the process. The findings in this three-tiered approach make salient specific discursive patterns gleaned from systematic and fastidious attention to caregivers' own ways of using language that methodically afford deeper entry into the emotional, physical, and cognitive challenges in their everyday lived experiences.

Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking

Lower limb exoskeletons require the correct support magnitude and timing to achieve user assistance. This study evaluated whether the sign of the angular velocity of lower limb segments can be used to determine the timing of the stance and the swing phase during walking. We assumed that stance phase is characterized by a positive, swing phase by a negative angular velocity. Thus, the transitions can be used to also identify heel-strike and toe-off. Thirteen subjects without gait impairments walked on a treadmill at speeds between 0.5 and 2.1 m/s on level ground and inclinations between −10 and +10°. Kinematic and kinetic data was measured simultaneously from an optical motion capture system, force plates, and five inertial measurement units (IMUs). These recordings were used to compute the angular velocities of four lower limb segments: two biological (thigh, shank) and two virtual that were geometrical projections of the biological segments (virtual leg, virtual extended leg). We analyzed the reliability (two sign changes of the angular velocity per stride) and the accuracy (offset in timing between sign change and ground reaction force based timing) of the virtual and biological segments for detecting the gait phases stance and swing. The motion capture data revealed that virtual limb segments seem superior to the biological limb segments in the reliability of stance and swing detection. However, increased signal noise when using the IMUs required additional rule sets for reliable stance and swing detection. With IMUs, the biological shank segment had the least variability in accuracy. The IMU-based heel-strike events of the shank and both virtual segment were slightly early (3.3–4.8% of the gait cycle) compared to the ground reaction force-based timing. Toe-off event timing showed more variability (9.0% too early to 7.3% too late) between the segments and changed with walking speed. The results show that the detection of the heel-strike, and thus stance phase, based on IMU angular velocity is possible for different segments when additional rule sets are included. Further work is required to improve the timing accuracy for the toe-off detection (swing).

Implementation of a Central Sensorimotor Integration Test for Characterization of Human Balance Control During Stance

Balance during stance is regulated by active control mechanisms that continuously estimate body motion, via a "sensory integration" mechanism, and generate corrective actions, via a "sensory-to-motor transformation" mechanism. The balance control system can be modeled as a closed-loop feedback control system for which appropriate system identification methods are available to separately quantify the sensory integration and sensory-to-motor components of the system. A detailed, functionally meaningful characterization of balance control mechanisms has potential to improve clinical assessment and to provide useful tools for answering clinical research questions. However, many researchers and clinicians do not have the background to develop systems and methods appropriate for performing identification of balance control mechanisms. The purpose of this report is to provide detailed information on how to perform what we refer to as "central sensorimotor integration" (CSMI) tests on a commercially available balance test device (SMART EquiTest CRS, Natus Medical Inc, Seattle WA) and then to appropriately analyze and interpret results obtained from these tests. We describe methods to (1) generate pseudorandom stimuli that apply cyclically-repeated rotations of the stance surface and/or visual surround (2) measure and calibrate center-of-mass (CoM) body sway, (3) calculate frequency response functions (FRFs) that quantify the dynamic characteristics of stimulus-evoked CoM sway, (4) estimate balance control parameters that quantify sensory integration by measuring the relative contribution of different sensory systems to balance control (i.e., sensory weights), and (5) estimate balance control parameters that quantify sensory-to-motor transformation properties (i.e., feedback time delay and neural controller stiffness and damping parameters). Additionally, we present CSMI test results from 40 subjects (age range 21-59 years) with normal sensory function, 2 subjects with results illustrating deviations from normal balance function, and we summarize results from previous studies in subjects with vestibular deficits. A bootstrap analysis was used to characterize confidence limits on parameters from CSMI tests and to determine how test duration affected the confidence with which parameters can be measured. Finally, example results are presented that illustrate how various sensory and central balance deficits are revealed by CSMI testing.

The relation between patient characteristics and their carers' use of a directive versus collaborative support stance

OBJECTIVES

Collaborative support provided by carers (family and friends) of individuals with eating disorders has been shown to be integral to patient motivation and clinical outcome. Little is known about factors that contribute to carers' use of collaborative, as opposed to directive, support stance. This exploratory research investigated associations between patient characteristics and carers' support beliefs and behaviors.

METHOD

Eating disorder patients (n = 72) completed measures of readiness for change, eating disorder, and psychiatric symptom severity, and interpersonal functioning. Their carers (n = 72) completed measures of collaborative and directive support.

RESULTS

Patient demographic variables, readiness for change, and psychiatric symptom severity were not associated with carer beliefs or behaviors. However, some patient interpersonal functioning scores were; higher Domineering/Controlling scores were associated with carers viewing directive support as more helpful, and with their use of more directive support behaviors. Higher Vindictive/Self-Centered and Intrusive/Needy scores in patients were also associated with carers viewing directive support as more helpful.

DISCUSSION

This exploratory study suggests that carers may be more prone to utilizing a directive, rather than a collaborative, support stance with patients experiencing higher levels of threat, anger, and hostility, and lower levels of safety, closeness, and trust.

Social support satisfaction in adults with eating disorders: Does stance matter?

Although the role of social support is clearly established in the recovery of youth with eating disorders, little is known about factors that contribute to support satisfaction and improved treatment outcome in adults. This study examined the contribution of patient factors and perceived support stance used by family and friends in determining social support satisfaction. Individuals meeting DSM-IV criteria for an eating disorder (n = 182) completed measures of eating disorder and psychiatric severity, interpersonal functioning, perceived support stance used by family and friends, and social support satisfaction. Correlations indicated that both patient factors (lower psychiatric distress and fewer interpersonal difficulties) and perceived support stance (higher concerned and lower directive support) were associated with patient support satisfaction. Multiple regression analyses indicated that perceived support stance accounted for greater variance in social support satisfaction than did patient factors. Patient age was associated with differences in preferred support stance: expressions of caring were most critical for younger patients, whereas not being criticized or told what to do was most significant for older patients. This research suggests that the stance used when offering support is vital to the care of individuals with eating disorders.

Support stance in carers of adults with eating disorders: Factors associated with collaborative versus directive approaches

The support provided by family and friends is integral to patient motivation and clinical outcomes across health care populations. However, little is known about factors that promote or interfere with the type of support offered.

OBJECTIVE

This research examined factors associated with collaborative versus directive support among carers of adults with eating disorders.

METHOD

Participants were mothers, fathers, partners, friends, and siblings (N = 141) of eating disorder patients in hospital or residential treatment. Two methodologies were used to assess directive and collaborative support stance: a questionnaire of support behaviors and coded responses to clinical vignettes. Measures of interpersonal functioning, psychiatric distress, caregiving experience, and closeness with their loved one were also completed.

RESULTS

Although carers rated a collaborative stance as more helpful than a directive stance, 60% of responses to the clinical vignettes were directive. Across both methodologies, collaborative support behaviors were associated with beliefs about helpful support and with a less vindictive and cold interpersonal style. Whereas use of a directive support stance was exclusively associated with negative caregiving experiences, collaborative responses were associated with both positive and negative experiences.

DISCUSSION

Although the benefits of collaborative support have been well established, this is the first study to examine factors associated with the use of support stance. Findings suggest a number of ways to help carers create and maintain collaborative relationships, including addressing beliefs and interpersonal style and capitalizing on both positive and negative experiences with their loved one. © 2016 Wiley Periodicals, Inc.(Int J Eat Disord 2017; 50:498-505).

The Biomechanics of Standing Start and Initial Acceleration: Reliability of the Key Determining Kinematics

The reliability of the key determining kinematic variables associated with short sprint performance provide insight into how and why movement may vary between individual trials. Currently, literature surrounding these determinants is scarce when investigating the first three strides of a sprint. The purpose of this study was to investigate the reliability of sprint acceleration and the key kinematic determinants involved during the first three steps of the movement. The aim was to use a practical method of kinematic analysis to help explain why changes may occur in sprint performance via the use of correlative statistics and to provide reference values for intervention research to make conclusions about their change scores. Ten male volunteers from various team sports attended two separate testing sessions, a minimum of 48 hours apart. They performed three maximal sprint trials over a 10m distance from a standing start, where researchers captured 5m and 10m sprint times alongside high speed camera footage, from which the key kinematic variables were measured. Results demonstrated that although 5m and 10m sprint times depicted moderate to large levels of similarity between sessions, neither of these variables met the criteria to be classified as adequately, or highly reliable. Kinematic measures typically produced ICC values > 0.70 and CV% < 10%, demonstrating all relevant statistical traits to be categorised as reliable measures. Step frequency and flight time during the third step showed the largest correlation with performance, exhibiting 'r' values of -0.386 and 0.396, respectively. These findings demonstrate that kinematic variables may not have an influential role with sprint times; therefore suggesting kinetic concepts may in fact be the key determinants of speed. Future research is required investigating the interaction of kinetic and kinematic variables associated with sprinting and how the variability in these concepts effects the reliability of performance.

Higher Balance Task Demands are Associated with an Increase in Individual Alpha Peak Frequency

Balance control is fundamental for most daily motor activities, and its impairment is associated with an increased risk of falling. Growing evidence suggests the human cortex is essentially contributing to the control of standing balance. However, the exact mechanisms remain unclear and need further investigation. In a previous study, we introduced a new protocol to identify electrocortical activity associated with performance of different continuous balance tasks with the eyes opened. The aim of this study was to extend our previous results by investigating the individual alpha peak frequency (iAPF), a neurophysiological marker of thalamo-cortical information transmission, which remained unconsidered so far in balance research. Thirty-seven subjects completed nine balance tasks varying in surface stability and base of support. Electroencephalography (EEG) was recorded from 32 scalp locations throughout balancing with the eyes closed to ensure reliable identification of the iAPF. Balance performance was quantified as the sum of anterior-posterior and medio-lateral movements of the supporting platform. The iAPF, as well as power in the theta, lower alpha and upper alpha frequency bands were determined for each balance task after applying an ICA-based artifact rejection procedure. Higher demands on balance control were associated with a global increase in iAPF and a decrease in lower alpha power. These results may indicate increased thalamo-cortical information transfer and general cortical activation, respectively. In addition, a significant increase in upper alpha activity was observed in the fronto-central region whereas it decreased in the centro-parietal region. Furthermore, midline theta increased with higher task demands probably indicating activation of error detection/processing mechanisms. IAPF as well as theta and alpha power were correlated with platform movements. The results provide new insights into spectral and spatial characteristics of cortical oscillations subserving balance control. This information may be particularly useful in a clinical context as it could be used to reveal cortical contributions to balance dysfunction in specific populations such as Parkinson’s or vestibular loss. However, this should be addressed in future studies.

Functional (psychogenic) dizziness

Functional and psychiatric disorders that cause vestibular symptoms (i.e., vertigo, unsteadiness, and dizziness) are common. In fact, they are more common than many well-known structural vestibular disorders. Neurologists and otologists are more likely to encounter patients with vestibular symptoms due to persistent postural-perceptual dizziness or panic disorder than Ménière's disease or bilateral vestibular loss. Successful approaches to identifying functional and psychiatric causes of vestibular symptoms can be incorporated into existing practices without much difficulty. The greatest challenge is to set aside dichotomous thinking that strongly emphasizes investigations of structural diseases in favor of a three-pronged approach that assesses structural, functional, and psychiatric disorders simultaneously. The pathophysiologic mechanisms underlying functional and psychiatric causes of vestibular symptoms are better understood than many clinicians realize. Research methods such as advanced posturographic analysis and functional brain imaging will push this knowledge further in the next few years. Treatment plans that include patient education, vestibular rehabilitation, cognitive and behavioral therapies, and medications substantially reduce morbidity and offer the potential for sustained remission when applied systematically. Diagnostic and therapeutic approaches are necessarily multidisciplinary in nature, but they are well within the purview of collaborative care teams or networks of clinicians coordinated with the neurologists and otologists whom patients consult first.

Force-controlled biting alters postural control in bipedal and unipedal stance

Human posture is characterised by inherent body sway which forces the sensory and motor systems to counter the destabilising oscillations. Although the potential of biting to increase postural stability has recently been reported, the mechanisms by which the craniomandibular system (CMS) and the motor systems for human postural control are functionally coupled are not yet fully understood. The purpose of our study was, therefore, to investigate the effect of submaximum biting on postural stability and on the kinematics of the trunk and head. Twelve healthy young adults performed force-controlled biting (FB) and non-biting (NB) during bipedal narrow stance and single-leg stance. Postural stability was quantified on the basis of centre of pressure (COP) displacements, detected by use of a force platform. Trunk and head kinematics were investigated by biomechanical motion analysis, and bite forces were measured using a hydrostatic system. The results revealed that FB significantly improved postural control in terms of reduced COP displacements, providing additional evidence for the functional coupling of the CMS and human posture. Our study also showed, for the first time, that reductions in the sway of the COP were accompanied by reduced trunk and head oscillations, which might be attributable to enhanced trunk stiffness during FB. This physiological response to isometric activation of the masticatory muscles raises questions about the potential of oral motor activity as a strategy to reduce the risk of falls among the elderly or among patients with compromised postural control.

Nonlinear variability of body sway in patients with phobic postural vertigo

Background: Subjective postural imbalance is a key symptom in the somatoform phobic postural vertigo (PPV). It has been assumed that more attentional control of body posture and / or co-contraction of leg muscles during standing is used to minimize the physiological body sway in PPV. Here we analyze nonlinear variability of body sway in patients with PPV in order to disclose changes in postural control strategy associated with PPV.

Methods: Twenty patients with PPV and 20 age-matched healthy subjects (HS) were recorded on a stabilometer platform with eyes open (EO), eyes closed (EC), and while standing on a foam rubber with eyes closed (ECF). Spatio-temporal changes of the center of pressure (CoP) displacement were analyzed to assess the structure of postural variability by computing the scaling exponent α and the sample entropy (SEn) of the time series.

Results: With EO on firm ground α and SEn of CoP displacement were significantly lower in patients (p < 0.001). For more difficult conditions (EC, ECF) postural variability in PPV assimilated to that of HS.

Conclusion: Postural control in PPV patients differs from HS under normal stance condition. It is characterized by a reduced scaling behavior and higher regularity. These changes in the structure of postural variability might suggest an inappropriate attentional involvement with stabilizing strategies, which are used by HS only for more demanding balance tasks.

Recovery of vestibular ocular reflex function and balance control after a unilateral peripheral vestibular deficit

This review describes the effect of unilateral peripheral vestibular deficit (UPVD) on balance control for stance and gait tests. Because a UPVD is normally defined based on vestibular ocular reflex (VOR) tests, we compared recovery observed in balance control with patterns of recovery in VOR function. Two general types of UPVD are considered; acute vestibular neuritis (AVN) and vestibular neurectomy. The latter was subdivided into vestibular loss after cerebellar pontine angle tumor surgery during which a vestibular neurectomy was performed, and vestibular loss following neurectomy to eliminate disabling Ménière's disease. To measure balance control, body-worn gyroscopes, mounted near the body's center of mass (CoM), were used. Measurement variables were the pitch (anterior-posterior) and roll (lateral) sway angles and angular velocities of the lower trunk/pelvis. Both patient groups showed balance deficits during stance tasks on foam, especially with eyes closed when stable balance control is normally highly dependent on vestibular inputs. Deficits during gait were also present and were more profound for complex gait tasks such as tandem gait than simple gait tasks. Major differences emerged between the groups concerning the severity of the deficit and its recovery. Generally, the effects of acute neuritis on balance control were more severe but recovered rapidly. Deficits due to vestibular neurectomy were less severe, but longer lasting. These results mostly paralleled recovery of deficits in VOR function. However, questions need to be raised about the effect on balance control of the two modes of neural plasticity occurring in the vestibular system following vestibular loss due to neuritis: one mode being the limited central compensation for the loss, and the second mode being some restoration of peripheral vestibular function. Future work will need to correlate deficits in balance control during stance and gait more exactly with VOR deficits and carefully consider the differences between insufficient central compensation compared to inadequate peripheral restoration of function.

OPTOTRAK Measurement of the Quadriceps Angle Using Standardized Foot Positions

OBJECTIVE: While there is evidence to suggest that the magnitude of the quadriceps (Q) angle changes with alterations in foot position, a detailed quantitative description of this relationship has not been reported. Our purpose was to determine the effect of varying foot placement on the magnitude of the Q angle. DESIGN AND SETTING: A mixed between-within, repeated-measures design was used to compare Q angles derived under static weight-bearing conditions with the feet positioned in self-selected versus standardized stance positions. SUBJECTS: Twenty healthy young-adult men and women with no history of acute injury to or chronic dysfunction of the lower limbs. MEASUREMENTS: We placed light-emitting diodes bilaterally on the left and right anterior superior iliac spines, the tibial tuberosities, and the midpoints of the patellae to bilaterally define the Q angles. An OPTOTRAK motion-measurement system was used to capture x,y coordinate data at a sampling rate of 60 Hz. These data were subsequently filtered and used to calculate the magnitude of the left and right Q angles. RESULTS: A repeated-measures analysis of variance revealed that when measured statically, Q angles differed significantly between stance positions (P <.001) and limbs (P <.05). Depending on the stance adopted, mean Q angles varied from 7.2 degrees to 12.7 degrees and 11.0 degrees to 16.1 degrees in the left and right lower limbs, respectively. Q-angle measurements taken in conjunction with the Romberg foot position most closely resembled those gathered with the feet in a self-selected stance (Pearson r = 0.86 to 0.92). CONCLUSIONS: Q-angle magnitude varies with changes in foot position, increasing or decreasing as the foot rotates internally or externally, respectively. These data demonstrate the need for a standardized foot position for Q-angle measurements.