Two-dimensional turbulence above topography: Vortices and potential vorticity homogenization.

The evolution of unforced and weakly damped two-dimensional turbulence over random rough topography presents two extreme states. If the initial kinetic energy [Formula: see text] is sufficiently high, then the topography is a weak perturbation, and evolution is determined by the spontaneous formation and mutual interaction of coherent axisymmetric vortices. High-energy vortices roam throughout the domain and mix the background potential vorticity (PV) to homogeneity, i.e., in the region between vortices, which is most of the domain, the relative vorticity largely cancels the topographic PV. If [Formula: see text] is low, then vortices still form but they soon become locked to topographic features: Anticyclones sit above topographic depressions and cyclones above elevated regions. In the low-energy case, with topographically locked vortices, the background PV retains some spatial variation. We develop a unified framework of topographic turbulence spanning these two extreme states of low and high energy. A main organizing concept is that PV homogenization demands a particular kinetic energy level [Formula: see text]. [Formula: see text] is the separator between high-energy evolution and low-energy evolution.

Polar vortex crystals: Emergence and structure.

Vortex crystals are quasiregular arrays of like-signed vortices in solid-body rotation embedded within a uniform background of weaker vorticity. Vortex crystals are observed at the poles of Jupiter and in laboratory experiments with magnetized electron plasmas in axisymmetric geometries. We show that vortex crystals form from the free evolution of randomly excited two-dimensional turbulence on an idealized polar cap. Once formed, the crystals are long lived and survive until the end of the simulations (300 crystal-rotation periods). We identify a fundamental length scale, Lγ=(U/γ)1/3, characterizing the size of the crystal in terms of the mean-square velocity U of the fluid and the polar parameter γ=fp/a2p, with fp the Coriolis parameter at the pole and ap the polar radius of the planet.

Local intraspecific aggregation in phytoplankton model communities: spatial scales of occurrence and implications for coexistence.

The coexistence of multiple phytoplankton species despite their reliance on similar resources is often explained with mean-field models assuming mixed populations. In reality, observations of phytoplankton indicate spatial aggregation at all scales, including at the scale of a few individuals. Local spatial aggregation can hinder competitive exclusion since individuals then interact mostly with other individuals of their own species, rather than competitors from different species. To evaluate how microscale spatial aggregation might explain phytoplankton diversity maintenance, an individual-based, multispecies representation of cells in a hydrodynamic environment is required. We formulate a three-dimensional and multispecies individual-based model of phytoplankton population dynamics at the Kolmogorov scale. The model is studied through both simulations and the derivation of spatial moment equations, in connection with point process theory. The spatial moment equations show a good match between theory and simulations. We parameterized the model based on phytoplankters' ecological and physical characteristics, for both large and small phytoplankton. Defining a zone of potential interactions as the overlap between nutrient depletion volumes, we show that local species composition-within the range of possible interactions-depends on the size class of phytoplankton. In small phytoplankton, individuals remain in mostly monospecific clusters. Spatial structure therefore favours intra- over inter-specific interactions for small phytoplankton, contributing to coexistence. Large phytoplankton cell neighbourhoods appear more mixed. Although some small-scale self-organizing spatial structure remains and could influence coexistence mechanisms, other factors may need to be explored to explain diversity maintenance in large phytoplankton.

The effect of mobility-related anxiety on walking across the lifespan: a virtual reality simulation study.

Older adults who report a fear of falling are more likely to subsequently fall, yet, some gait anxiety-related alterations may protect balance. We examined the effect of age on walking in anxiety-inducing virtual reality (VR) settings. We predicted a high elevation-related postural threat would impair gait in older age, and differences in cognitive and physical function would relate to the observed effects. Altogether, 24 adults (age (y) = 49.2 (18.7), 13 women) walked on a 2.2-m walkway at self-selected and fast speeds at low (ground) and high (15 m) VR elevation. Self-reported cognitive and somatic anxiety and mental effort were greater at high elevations (all p < 0.001), but age- and speed-related effects were not observed. At high VR elevations, participants walked slower, took shorter steps, and reduced turning speed (all p < 0.001). Significant interactions with age in gait speed and step length showed that relatively older adults walked slower (ß = - 0.05, p = 0.024) and took shorter steps (ß = - 0.05, p = 0.001) at self-selected speeds at high compared to low elevation settings. The effect of Age on gait speed and step length disappeared between self-selected and fast speeds and at high elevation. At self-selected speeds, older adults took shorter and slower steps at high elevation without changing step width, suggesting that in threatening settings relatively older people change gait parameters to promote stability. At fast speeds, older adults walked like relatively younger adults (or young adults walked like older adults) supporting the notion that people opt to walk faster in a way that still protects balance and stability in threatening settings.

The perceived control model of falling: developing a unified framework to understand and assess maladaptive fear of falling.

BACKGROUND: fear of falling is common in older adults and can have a profound influence on a variety of behaviours that increase fall risk. However, fear of falling can also have potentially positive outcomes for certain individuals. Without progressing our understanding of mechanisms underlying these contrasting outcomes, it is difficult to clinically manage fear of falling. METHODS: this paper first summarises recent findings on the topic of fear of falling, balance and fall risk-including work highlighting the protective effects of fear. Specific focus is placed on describing how fear of falling influences perceptual, cognitive and motor process in ways that might either increase or reduce fall risk. Finally, it reports the development and validation of a new clinical tool that can be used to assess the maladaptive components of fear of falling. RESULTS: we present a new conceptual framework-the Perceived Control Model of Falling-that describes specific mechanisms through which fear of falling can influence fall risk. The key conceptual advance is the identification of perceived control over situations that threaten one's balance as the crucial factor mediating the relationship between fear and increased fall risk. The new 4-item scale that we develop-the Updated Perceived Control over Falling Scale (UP-COF)-is a valid and reliable tool to clinically assess perceived control. CONCLUSION: this new conceptualisation and tool (UP-COF) allows clinicians to identify individuals for whom fear of falling is likely to increase fall risk, and target specific underlying maladaptive processes such as low perceived control.

Stokes drift and its discontents.

The Stokes velocity [Formula: see text], defined approximately by Stokes (1847, Trans. Camb. Philos. Soc., 8, 441-455.), and exactly via the Generalized Lagrangian Mean, is divergent even in an incompressible fluid. We show that the Stokes velocity can be naturally decomposed into a solenoidal component, [Formula: see text], and a remainder that is small for waves with slowly varying amplitudes. We further show that [Formula: see text] arises as the sole Stokes velocity when the Lagrangian mean flow is suitably redefined to ensure its exact incompressibility. The construction is an application of Soward & Roberts's glm theory (2010, J. Fluid Mech., 661, 45-72. (doi:10.1017/S0022112010002867)) which we specialize to surface gravity waves and implement effectively using a Lie series expansion. We further show that the corresponding Lagrangian-mean momentum equation is formally identical to the Craik-Leibovich (CL) equation with [Formula: see text] replacing [Formula: see text], and we discuss the form of the Stokes pumping associated with both [Formula: see text] and [Formula: see text]. This article is part of the theme issue 'Mathematical problems in physical fluid dynamics (part 1)'.

Protective or harmful? A qualitative exploration of older people's perceptions of worries about falling.

BACKGROUND: worries about falling are common in older people. It has been suggested that these worries can reduce balance safety by acting as a distracting dual-task. However, it is also possible that worries may serve a protective purpose. The present work adopted a qualitative approach to conduct an in-depth exploration of older people's experiences of worries about falling. METHODS: semi-structured interviews were conducted with 17 community-dwelling older people (mean age = 79 years; males = 5/17) who reported experiencing worries about falling. Reflexive thematic analysis was used to analyse the data. RESULTS: experiencing a fall-or otherwise recognising one's balance limitations-brought the physical realities of participants' ageing bodies to the forefront of their awareness. This led to the recognition of their susceptibility for an injurious fall, which triggered worries about falling in situations that threatened their balance. When preventing the subject of their worries (i.e. an injurious fall) was perceived to be within the individual's locus of control, worries led to protective adaptations to behaviour. In contrast, when the subject of their worries was perceived to be outside their control, worries triggered feelings of panic-leading to unhelpful changes in behaviour. CONCLUSION: these findings provide novel insight into the development and consequences of worries about falling in older people. They highlight the importance of considering an individual's perception of control before deciding to clinically intervene to reduce worries about falling.

Short-latency inhibition mitigates the relationship between conscious movement processing and overly cautious gait.

BACKGROUND: Overly cautious gait is common in older adults. This is characterised by excessively slow gait, shortened steps, broadened base of support and increased double limb support. The current study sought to (1) evaluate if overly cautious gait is associated with attempts to consciously process walking movements, and (2) explore whether an individual's ability to rapidly inhibit a dominant motor response serves to mitigate this relationship. METHODS: A total of 50 older adults walked at a self-selected pace on an instrumented walkway containing two raised wooden obstacles (height = 23 cm). Trait conscious movement processing was measured with the Movement-Specific Reinvestment Scale. Short-latency inhibitory function was assessed using a validated electronic go/no-go ruler catch protocol. We used linear regressions to explore the relationship between these variables and gait parameters indicative of overly cautious gait. RESULTS: When controlling for general cognitive function (MoCA), and functional balance (Berg Balance Scale), the interaction between trait conscious movement processing and short-latency inhibition capacity significantly predicted gait velocity, step length and double limb support. Specifically, older adults with higher trait conscious movement processing and poorer inhibition were more likely to exhibit gait characteristics indicative of cautious gait (i.e. reduced velocity, shorter step lengths and increased double limb support). Neither conscious movement processing nor inhibition independently predicted gait performance. CONCLUSION: The combination of excessive movement processing tendencies and poor short-latency inhibitory capacity was associated with dysfunctional or 'overly cautious' gait. It is therefore plausible that improvement in either factor may lead to improved gait and reduced fall risk.

Conscious Control of Gait Increases with Task Difficulty and Can Be Mitigated by External Focus Instruction.

Objectives: We aimed to address whether increased task difficulty is sufficient to induce heightened conscious control and influence gait performance in older adults through the manipulations of either task difficulty or attentional focus. Method: Fifty older adults, split into high- (HR) and low-reinvestor (LR) groups, performed a walking task on a 7.4 m straight walkway in two conditions: firm level-ground surface (GW) and foam surface (FW). They subsequently performed the same walking task under two attentional focus conditions: Internal focus (IF) and External focus (EF). Electroencephalography (EEG) T3-Fz and T4-Fz coherences were used to indicate real-time conscious motor control and visual-spatial control, respectively. Results: We observed significantly higher T3-Fz and T4-Fz coherences under FW compared to GW. HR reduced their gait speed at a greater extent than LR under FW. Significantly lower T3-Fz coherence and faster gait were demonstrated under EF compared to IF. LR walked slower under IF compared to Baseline while gait speed of HR did not differ. Discussion: Visual-spatial and conscious movement processing increase as a function of task difficulty during gait. Our findings also advocate the use of external focus instructions in clinical settings, with the potential to reduce conscious control and promote movement automaticity, even in relatively complex gait tasks.

The direction of postural threat alters balance control when standing at virtual elevation.

Anxiogenic settings lead to reduced postural sway while standing, but anxiety-related balance may be influenced by the location of postural threat in the environment. We predicted that the direction of threat would elicit a parallel controlled manifold relative to the standing surface, and an orthogonal uncontrolled manifold during standing. Altogether, 14 healthy participants (8 women, mean age = 27.5 years, SD = 8.2) wore a virtual reality (VR) headset and stood on a matched real-world walkway (2 m × 40 cm × 2 cm) for 30 s at ground level and simulated heights (elevated 15 m) in two positions: (1) parallel to walkway, lateral threat; and (2) perpendicular to walkway, anteroposterior threat. Inertial sensors measured postural sway acceleration (e.g., 95% ellipse, root mean square (RMS) of acceleration), and a wrist-worn monitor measured heart rate coefficient of variation (HR CV). Fully factorial linear-mixed effect regressions (LMER) determined the effects of height and position. HR CV moderately increased from low to high height (p = 0.050, g = 0.397). The Height × Position interaction approached significance for sway area (95% ellipse; ß = - 0.018, p = 0.062) and was significant for RMS (ß = - 0.022, p = 0.007). Post-hoc analyses revealed that sagittal plane sway accelerations and RMS increased from low to high elevation in parallel standing, but were limited when facing the threat during perpendicular standing. Postural response to threat varies depending on the direction of threat, suggesting that the control strategies used during standing are sensitive to the direction of threat.

Exploring attentional focus of older adult fallers during heightened postural threat.

OBJECTIVES: Threats to balance, and subsequent increases in fall-related anxiety, can disrupt attentional processing during gait in older adults, leading to behavioral adaptations which may increase fall risk. However, limited research has investigated what changes in attention occur to contribute to these disruptions. The aim of this research was to describe changes in attention that occur during gait when older adults' balance is threatened, while exploring how previous fall history and trait movement reinvestment (conscious monitoring and control of movement) also influence attention. METHODS: Forty older adults reported where they focus their attention when walking during two scenarios: (1) when they are relaxed and there is little risk of falling, and; (2) when their balance is threatened and they are anxious of falling. RESULTS: During the high-threat condition, participants reported greater attention towards movement processes, threats to balance, worries/disturbing thoughts and self-regulatory strategies, with less attention directed towards task-irrelevant thoughts. However, fall history influenced attentional focus, with fallers directing greater attention towards worries/disturbing thoughts. Contrary to predictions, trait movement reinvestment was not associated with attention directed towards movement processes. DISCUSSION: As processing worries/disturbing thoughts will likely reduce attentional resources available for effective postural control, we highlight this as one potential area to target interventions aimed at reducing the likelihood of repeated falling.

The role of attentional focus on walking efficiency among older fallers and non-fallers.

BACKGROUND: This study evaluated the effect of attentional focus instructions on movement efficiency during a level-ground walking task in older adults with and without a history of falls. METHODS: One hundred and thirty-four community-dwelling older adults were categorised into older fallers (OF) (n = 37) and older non-fallers (ONF) (n = 97). Each participant was instructed to walk at a self-selected pace along a 6 m walkway under three attentional focus conditions (i.e. internal, goal-directed and control) for a total of nine trials. Average muscle activity indices of lower limb co-contractions were measured using surface electromyography. RESULTS: Both shank and thigh muscle co-contractions were higher in OF than in ONF in all three conditions. OF also demonstrated higher shank muscle co-contraction under the internal relative to the goal-directed condition, with no such change observed in ONF. CONCLUSION: Despite no significant between-group differences in functional balance and balance confidence, relative walking inefficiencies were observed in OF compared with ONF. This finding demonstrates the debilitating consequences of falling that can occur with relative independence from various physiological or psychological factors that are commonly associated with falling and used to rationalise behavioural change. We also provide evidence that OF are more susceptible to conditions that provoke them to allocate attention internally. Therefore, in clinical contexts (e.g. gait rehabilitation), verbal instructions that refer to body movements (internal focus) might serve to compromise movement efficiency in older adults with a history of falls. Such changes will, theoretically, lessen the ability to react efficiently to changing environments experienced in daily life.

Investigating Changes in Real-time Conscious Postural Processing by Older Adults during Different Stance Positions Using Electroencephalography Coherence.

Background/Study Context: Adjustments of posture in response to balance challenges may lead to subsequent increases in conscious posture processing. If cognitive resources are stretched by conscious processing of postural responses fewer resources will be available to attend to environmental trip or fall hazards. The objective of the study was to explore brain activity related to conscious processing of posture as a function of movement specific reinvestment and fear of falling. Method: Forty-three older adults (M = 71.4, SD = 4.1) stood with a wide or narrow stance on a force-plate while neural coherence between verbal-analytical (T3) and motor planning (Fz) regions of the brain was assessed using electroencephalography. The propensity for movement specific reinvestment was assessed using the Chinese version Movement Specific Reinvestment Scale (MSRS-C) and fear of falling was assessed using the Chinese version Fall Efficacy Scale International (FES-I[CH]). Results: Scores from the MSRS-C were negatively correlated with changes in T3-Fz coherence that occurred when participants shifted from wide to narrow stance. Together, MSRS-C and FES-I(CH) uniquely predicted the percentage change in T3-Fz coherence between the two stance conditions. Conclusion: Presented with two postural tasks of different complexities, participants with a lower propensity for conscious control of their movements (movement specific reinvestment) exhibited larger changes in real-time brain activity (neural coherence) associated with conscious postural processing.

Cognitively and socially induced stress affects postural control.

Postural control is an adaptive process that can be affected by many aspects of human behavior, including emotional contexts. The main emotional contexts that affect postural control are postural threat and passive viewing of aversive or threatening images, both of which produce a reduction in postural sway. The aim of the present study was to assess whether similar stress-related changes in postural sway can be observed using stress induced by social evaluative threat (SET) while performing arithmetic tasks. Twelve young adults performed an arithmetic and a postural control task separately, concurrently, and concurrently with added time pressure in the arithmetic task. In the final condition, participants were given negative feedback about their performance in the arithmetic task and performed it again while being observed (SET condition). Results showed that stress increased linearly with task demand. Postural sway and reaction times were not affected by the first two conditions; however, when time pressure was introduced, reaction times became faster and sway amplitude increased. Finally, introduction of SET caused the predicted reduction in postural sway and an increase in reaction times relative to the time pressure condition. Our results suggest that stress induced using a combination of arithmetic tasks and social evaluative threat leads to systematic changes in postural control. The paradigm developed in the present study would be very useful in assessing interactions between cognition, stress, and postural control in the context of postural instability and falls in older adults.

Recalibrating disparities in perceived and actual balance abilities in older adults: a mixed-methods evaluation of a novel exergaming intervention.

BACKGROUND: Published reports suggest a disparity between perceived and actual balance abilities, a trait associated with increased fall-risk in older adults. We investigate whether it is possible to 'recalibrate' these disparities using a novel gaming intervention. METHODS: We recruited 26 older adults for a 4-week intervention in which they participated in 8-sessions using a novel gaming intervention designed to provide explicit, augmented feedback related to postural control. Measures of perceived balance abilities (Falls Efficacy Scale-International) and actual postural control (limits of stability) were assessed pre- and post-intervention. We used focus groups to elicit the opinions of participants about how the game may have influenced balance abilities and confidence. RESULTS: A stronger alignment was observed between postural control and perceived balance capabilities post-intervention (i.e., significant correlations between Falls Efficacy Scale-International scores and limits of stability which were not present pre-intervention). Also, significant improvements in measures of postural control were observed, with these improvements confined to the aspects of postural control for which the exergame provided explicit, augmented feedback. Qualitative data revealed that the intervention made participants more "aware" of their balance abilities. CONCLUSIONS: Our results demonstrate that it is possible to recalibrate the perceptions of older adults relating to their balance abilities through a targeted, short-term intervention. We propose that the post-intervention improvements in postural control may have been, in part, the result of this recalibration; with altered perceptions leading to changes in balance performance. Findings support the application of novel interventions aimed at addressing the psychological factors associated with elderly falls.

Examining links between anxiety, reinvestment and walking when talking by older adults during adaptive gait.

Falls by older adults often result in reduced quality of life and debilitating fear of further falls. Stopping walking when talking (SWWT) is a significant predictor of future falls by older adults and is thought to reflect age-related increases in attentional demands of walking. We examine whether SWWT is associated with use of explicit movement cues during locomotion, and evaluate if conscious control (i.e. movement specific reinvestment) is causally linked to fall-related anxiety during a complex walking task. We observed whether twenty-four older adults stopped walking when talking when asked a question during an adaptive gait task. After certain trials, participants completed a visuospatial recall task regarding walkway features, or answered questions about their movements during the walk. In a subsequent experimental condition, participants completed the walking task under conditions of raised postural threat. Compared to a control group, participants who SWWT reported higher scores for aspects of reinvestment relating to conscious motor processing but not movement self-consciousness. The higher scores for conscious motor processing were preserved when scores representing cognitive function were included as a covariate. There were no group differences in measures of general cognitive function, visuospatial working memory or balance confidence. However, the SWWT group reported higher scores on a test of external awareness when walking, indicating allocation of attention away from task-relevant environmental features. Under conditions of increased threat, participants self-reported significantly greater state anxiety and reinvestment and displayed more accurate responses about their movements during the task. SWWT is not associated solely with age-related cognitive decline or generic increases in age-related attentional demands of walking. SWWT may be caused by competition for phonological resources of working memory associated with consciously processing motor actions and appears to be causally linked with fall-related anxiety and increased vigilance.

Dynamic walking features and improved walking performance in multiple sclerosis patients treated with fampridine (4-aminopyridine).

BACKGROUND: Impaired walking capacity is a frequent confinement in Multiple Sclerosis (MS). Patients are affected by limitations in coordination, walking speed and the distance they may cover. Also abnormal dynamic walking patterns have been reported, involving continuous deceleration over time. Fampridine (4-aminopyridine), a potassium channel blocker, may improve walking in MS. The objective of the current study was to comprehensively examine dynamic walking characteristics and improved walking capacity in MS patients treated with fampridine. METHODS: A sample of N = 35 MS patients (EDSS median: 4) underwent an electronic walking examination prior to (Time 1), and during treatment with fampridine (Time 2). Patients walked back and forth a distance of 25 ft for a maximum period of 6 min (6-minute 25-foot-walk). Besides the total distance covered, average speed on the 25-foot distance and on turns was determined separately for each test minute, at Time 1 and Time 2. RESULTS: Prior to fampridine administration, 27/35 patients (77 %) were able to complete the entire 6 min of walking, while following the administration, 34/35 patients (97 %) managed to walk for 6 min. In this context, walking distance considerably increased and treatment was associated with faster walking and turning across all six test minutes (range of effect sizes: partial eta squared = .34-.72). Importantly, previously reported deceleration across test minutes was consistently observable at Time 1 and Time 2. DISCUSSION: Fampridine administration is associated with improved walking speed and endurance. Regardless of a treatment effect of fampridine, the previously identified, abnormal dynamic walking feature, i.e. the linear decline in walking speed, may represent a robust feature. CONCLUSIONS: The dynamic walking feature might hence be considered as a candidate for a new outcome measure in clinical studies involving interventions other than symptomatic treatment, such as immune-modulating medication. TRIAL REGISTRATION: DRKS00009228 (German Clinical Trials Register). Date obtained: 25.08.2015.

A Perspective on Using Virtual Reality to Incorporate the Affective Context of Everyday Falls Into Fall Prevention.

Virtual reality (VR) is a promising and cost-effective tool that has the potential to reduce the prevalence of falls and locomotor impairments in older adults. However, we believe that existing VR-based approaches to prevent falls do not mimic the full breadth of perceptual, cognitive, and motor demands that older adults encounter in daily life. Researchers have not yet fully leveraged VR to address affective factors related to fall risk, and how stressors such as anxiety influence older adult balance and real-world falls. In this perspective paper, we propose developing VR-based tools that replicate the affective demands of real-world falls (eg, crossing the street) to enhance fall prevention diagnostics and interventions by capturing the underlying processes that influence everyday mobility. An effort to replicate realistic scenarios that precipitate falls in VR environments will inform evidence-based diagnostics and individualize interventions in a way that could reduce falls in older adults in daily life.

Balance capacity influences the effects of conscious movement processing on postural control in older adults.

Older adults rely increasingly on conscious processes to control balance. While this could be in response to age-related declines in balance capacity, it is unclear whether such strategy is adaptive or not. We investigated whether balance capacity modified the effects of conscious movement processing (CMP) on postural control in older adults. Forty-seven older adults (Mage = 74.8, range = 61-88) completed 60-s, narrow-stance balance trials on a force platform, under conditions designed to increase (high-CMP; through movement-monitoring instructions) or reduce conscious processing (low-CMP; distraction task). Balance capacity was operationalised as a composite score of Berg Balance Scale and Timed-up-and-Go. Balance capacity influenced the effects of the CMP manipulation on mediolateral sway amplitude (p = .023). Specifically, it positively associated with sway amplitude during the high-CMP condition (ß = 0.273), but not low-CMP condition (ß = -0.060). In other words, higher balance capacity was associated with increased sway during high-CMP, confirming our hypothesis that CMP does not uniformly negatively impact balance performance. Rather, CMP was maladaptive for those with better balance. Results also indicated that older adults' balance capacity influenced the degree to which they could engage conscious or automatic postural control processes. Specifically, we found that, overall, participants showed reduced mediolateral sway frequency and complexity for the high-CMP vs. low-CMP condition (p's ≤ 0.018), indicating reduced automaticity of balance (as expected). However, these effects were significantly attenuated as balance capacity reduced (i.e., smaller changes in those with lower balance capacity, p's < 0.010). Hence, the ability to readily shift between conscious and automatic modes of postural control seems more constrained as balance becomes worse. Overall, these findings suggest clinicians need to consider older adults' balance capacity when using providing instructions or feedback likely to influence CMP within rehabilitation settings.

Standing up to threats: Translating the two-system model of fear to balance control in older adults.

The 'two-system' view of fear builds on traditional conceptualisations of emotion; proposing that the mechanisms responsible for behavioural and physiological responses to threat may be distinct from those underpinning the (conscious) emotional experience itself. We empirically tested this notion within a novel, applied context of social and economic importance: fear of falling in older adults. Older adults stood on the edge of a raised platform and were stratified based on whether they reported fear in response to this postural threat. Irrespective of whether participants reported fear, we observed behaviours indicative of postural 'stiffening' during the threat condition. Self-reports indicated that participants cognitively monitored these changes in balance, and fear of falling was experienced in those who interpreted these behaviours to imply that harm was likely to occur. Fearful participants exhibited additional changes in balance (increased movement complexity and altered utilisation of sensory feedback) - behaviours likely influenced by attempts to consciously control balance. Taken together, these findings provide novel insight into the systems that regulate behavioural and emotional responses to postural threats. The novel conceptual framework developed from these findings helps identify specific mechanisms that might be targeted through clinical intervention.