Retention and generalizability of balance recovery response adaptations from trip-perturbations across the adult lifespan

For human locomotion, varying environments require adjustments of the motor system. We asked whether age affects gait balance recovery adaptation, its retention over months and the transfer of adaptation to an untrained reactive balance task. Healthy adults (26 young, 27 middle-aged and 25 older; average ages 24, 52 and 72 years respectively) completed two tasks. The primary task involved treadmill walking: either unperturbed (control; n=39) or subject to unexpected trip perturbations (training; n=39). A single trip perturbation was repeated after a 14-week retention period. The secondary transfer task, before and after treadmill walking, involved sudden loss of balance in a lean-and-release protocol. For both tasks the anteroposterior margin of stability (MoS) was calculated at foot touchdown. For the first (i.e. novel) trip, older adults required one more recovery step ( P=0.03) to regain positive MoS compared to younger, but not middle-aged, adults. However, over several trip perturbations, all age groups increased their MoS for the first recovery step to a similar extent (up to 70%), and retained improvements over 14 weeks, though a decay over time was found for older adults ( P=0.002; middle-aged showing a tendency for decay: P=0.076). Thus, although adaptability in reactive gait stability control remains effective across the adult lifespan, retention of adaptations over time appears diminished with aging. Despite these robust adaptations, the perturbation training group did not show superior improvements in the transfer task compared to aged-matched controls (no differences in MoS changes), suggesting that generalizability of acquired fall-resisting skills from gait-perturbation training may be limited

Honey bee foraging distance depends on month and forage type

To investigate the distances at which honey bee foragers collect nectar and pollen, we analysed 5,484 decoded waggle dances made to natural forage sites to determine monthly foraging distance for each forage type. Firstly, we found significantly fewer overall dances made for pollen (16.8 %) than for non-pollen, presumably nectar (83.2 %; P < 2.2 × 10−23). When we analysed distance against month and forage type, there was a significant interaction between the two factors, which demonstrates that in some months, one forage type is collected at farther distances, but this would reverse in other months. Overall, these data suggest that distance, as a proxy for forage availability, is not significantly and consistently driven by need for one type of forage over the other

Chronic Ankle Instability Subjects Demonstrate Lower Rate of Torque Development in Ankle Eversion, Hip Abduction Muscles Compared to Healthy, Coper Groups

Chronic ankle instability (CAI) is a pathological condition characterized by repeated lateral ankle sprains. Many ankle sprains are not a singular occurrence and can lead to perpetual disability, with some patients reporting repeated episodes of the ankle “giving way” during activity. CAI is multifactorial in nature, with contributors such as ligamentous laxity, strength deficit, and proprioceptive impairment (1). Each of these contributors negatively affects the muscles of the ankle complex. Rate of torque development (RTD) is a metric demonstrating explosive muscle capability, and is related to measurement of maximal voluntary isometric contraction (MVIC). RTD is a more accurate reflection of functional strength than MVIC because peak torque generally occurs 300ms or more after the onset of torque generation (2) while the time available for torque production in a functional daily movement context is generally between 50-250ms (3). RTD is generally measured within the first 200ms of the trial and therefore better captures the muscle’s ability to generate strength for daily activities. Understanding the relationship between RTD of the ankle evertor/invertor muscles and hip abductor muscles in individuals with CAI against healthy controls will better inform rehabilitation strategies and provide a benchmark of improvement for individuals recovering from CAI. PURPOSE: The purpose of this study was to better understand how CAI affects the force production capabilities of the ankle evertors/invertors, as well as the hip abductors. We hypothesized that individuals with CAI would demonstrate lower RTD in all three muscle groups in comparison to healthy and coper controls. METHODS: A total of 58 males and females participated in this study, and participants were divided into three cohorts. The first was a CAI patient group, a “coper” group, defined as individuals who can return to pre-injury levels of performance after LAS, and a healthy control group. CAI individuals and LAS copers were identified using the guidelines provided by the International Ankle Consortium (4). Subject exclusion criteria included previous history of lower extremity surgery, fracture, neurological disease affecting the lower extremity, or any injury to the lower extremity in the 3 months leading up to the study. Before data was obtained participants were familiarized with experimental procedures and protocols. Signed consent was obtained from each subject prior to data collection. The study was approved by the university institutional review board (Approval number: F2019-338). The study design required two visits from the subjects. The first visit was to familiarize subjects with the ankle eversion, inversion, and hip abduction movements they would be required to perform. On this day patients were also made familiar with the Biodex dynamometer (System Pro 4, Biodex Medical Systems, Inc., Shirley, NY; sampling rate: 100 Hz). On the second day subjects were seated on the dynamometer and performed 3 maximal voluntary isometric contractions (MVIC) of each movement. Patients were instructed to perform the movements as quickly as possible and to hold each trial for 5 seconds. Three trials were collected for each movement, with a minute separating each trial. Subjects were encouraged to give maximal effort through verbal cues. RTD and MVIC were calculated from each torque-time curve using custom code written in MatLab (MathWorks 2021a, Natick, MA). RTD was defined as the rate of change of the first 200ms of each trial; MVIC was defined as the peak value of each trial. RTD and MVIC values were averaged for each subject. RESULTS: No statistically significant differences in sex, age, height, or mass were detected among subjects (Table 1). Table 2 shows mean RTD for each group for the ankle eversion, inversion, and hip abduction movements. Notable results from Table 2 include the finding that CAI patients demonstrated significantly lower RTD than healthy controls (p = .02) and lower RTD than LAS copers (p = .03). Furthermore, CAI patients showed lower hip abductor RTD than healthy controls (p = .04). Table 3 shows MVIC data for each group for each movement and demonstrates that CAI patients showed significantly lower MVIC of the ankle eversion muscles than healthy controls (p = .02). No statistically significant differences in any strength metrics were detected between LAS copers and healthy controls, nor were there differences detected between groups in the ankle inversion movement. DISCUSSION: The primary finding from this study was that CAI ankle eversion RTD was significantly lower than RTD in healthy controls. This is significant because it provides insight on the adverse effects of repeated LAS on the muscles of the ankle complex. One of the factors determining RTD is the force transmission capabilities of the tendinous structures (10), and it is possible that the stretching of the ankle ligaments during LAS negatively affects its ability to efficiently transmit force generated from the muscle. Given the correlation between CAI patients and decreased RTD of ankle eversion muscles, it is possible that focusing on improvement in RTD of this muscle group could improve CAI symptoms. Numerous studies have focused on modalities targeted at improving RTD of the leg extensors muscle groups with generally positive results (5, 9), the majority of which include protocols that would be easily modifiable to the ankle eversion muscle group. Another notable finding from this study was that RTD of the hip abductors in the CAI group was significantly less than that of the healthy group. Although studies exist that have measured maximal hip abduction isometric strength in CAI groups, to our knowledge this is the first study analyzing the RTD of hip abduction. Our findings of deficits in hip abduction strength coincide with those of previous studies (6-8). Whether deficits in hip abduction strength increase potential for LAS or arise as a result of CAI is unclear, but it is becoming evident that the two factors are related. This is a promising area of CAI research and further study is required to fully elucidate the relationship between CAI and hip abductor strength. CONCLUSION: RTD of the ankle evertors in individuals with CAI is significantly lower than in LAS copers and healthy controls. Additionally, CAI patients demonstrated significantly lower RTD in hip abduction than healthy controls. While the need for exploring muscle force production capabilities in individuals with CAI persists, we suggest exploring modalities targeted at improving ankle eversion and hip abduction strength in patients with CAI. It is possible that improving strength in these areas will help return CAI patients to pre-injury levels of function and further our understanding of CAI

Heat trace asymptotics with singular weight functions

We study the weighted heat trace asymptotics of an operator of Laplace type with Dirichlet boundary conditions where the weight function exhibits radial blowup. We give formulas for the first few terms in the expansion in terms of geometrical data

CP violation in the effective action of the Standard Model

Following a suggestion by Smit, the CP odd terms of the effective action of the Standard Model, obtained by integration of quarks and leptons, are computed to sixth order within a strict covariant derivative expansion approach. No other approximations are made. The final result so derived includes all Standard Model gauge fields and Higgs. Remarkably, at the order considered in this work, all parity violating contributions turn out to be zero. Non vanishing CP violating terms are obtained in the C-odd P-even sector. These are several orders of magnitude larger than perturbative estimates. Various unexpected regularities in the final result are noted.Comment: 32 pages, no figures. Section added. To appear in JHE

Strong ellipticity and spectral properties of chiral bag boundary conditions

We prove strong ellipticity of chiral bag boundary conditions on even dimensional manifolds. From a knowledge of the heat kernel in an infinite cylinder, some basic properties of the zeta function are analyzed on cylindrical product manifolds of arbitrary even dimension.Comment: 16 pages, LaTeX, References adde

Risk of major depressive disorder among older persons living in HIV-endemic central and southwestern Uganda.

: Major depressive disorder (MDD) is projected to become the second most common cause of disability by 2020 calling for a better understanding its antecedents across the lifespan and in diverse socio-cultural settings. In this paper we describe the risk factors of MDD among older people (50 years +) living in HIV-endemic central and southwestern Uganda. A cross-sectional study was undertaken among 471 respondents (50 years +) participating in the Wellbeing of Older People's Study cohort of the MRC/UVRI Uganda research Unit on AIDS in Uganda. Participants were from five strata: HIV negative, HIV positive on ART, HIV positive not on ART, having an adult child on ART, and having an adult child who died of HIV. Overall MDD prevalence was 9.2% (95% CI 6.7-12.2%) with a prevalence among males of 7.4% (95% CI 4.0-12.3%) and females of 10.3% (95% CI 7.0-14.3%). Factors significantly associated with MDD included: declining socio-economic status, increasing disability scores, decreasing mean grip strength, reported back pain, and not having hypertension. Marginally associated with MDD was being HIV infected and not on ART.<br/

Differences in motor response to stability perturbations limit fall-resisting skill transfer

This study investigated transfer of improvements in stability recovery performance to novel perturbations. Thirty adults (20-53 yr) were assigned equally to three treadmill walking groups: groups exposed to eight trip perturbations of either low or high magnitude and a third control group that walked unperturbed. Following treadmill walking, participants were exposed to stability loss from a forward-inclined position (lean-and-release) and an overground trip. Lower limb joint kinematics for the swing phase of recovery steps was compared for the three tasks using statistical parametric mapping and recovery performance was analysed by margin of stability and base of support. The perturbation groups improved stability (greater margin of stability) over the eight gait perturbations. There was no group effect for stability recovery in lean-and-release. For the overground trip, both perturbation groups showed similar enhanced stability recovery (margin of stability and base of support) compared to controls. Differences in joint angle kinematics between treadmill-perturbation and lean-and-release were more prolonged and greater than between the two gait perturbation tasks. This study indicates that: (i) practising stability control enhances human resilience to novel perturbations; (ii) enhancement is not necessarily dependent on perturbation magnitude; (iii) differences in motor response patterns between tasks may limit transfer

Pole structure of the Hamiltonian ζ\zeta-function for a singular potential

We study the pole structure of the $\zeta$-function associated to the Hamiltonian $H$ of a quantum mechanical particle living in the half-line $\mathbf{R}^+$, subject to the singular potential $g x^{-2}+x^2$. We show that $H$ admits nontrivial self-adjoint extensions (SAE) in a given range of values of the parameter $g$. The $\zeta$-functions of these operators present poles which depend on $g$ and, in general, do not coincide with half an integer (they can even be irrational). The corresponding residues depend on the SAE considered.Comment: 12 pages, 1 figure, RevTeX. References added. Version to appear in Jour. Phys. A: Math. Ge

Heat-kernel expansion on non compact domains and a generalised zeta-function regularisation procedure

Heat-kernel expansion and zeta function regularisation are discussed for Laplace type operators with discrete spectrum in non compact domains. Since a general theory is lacking, the heat-kernel expansion is investigated by means of several examples. It is pointed out that for a class of exponential (analytic) interactions, generically the non-compactness of the domain gives rise to logarithmic terms in the heat-kernel expansion. Then, a meromorphic continuation of the associated zeta function is investigated. A simple model is considered, for which the analytic continuation of the zeta function is not regular at the origin, displaying a pole of higher order. For a physically meaningful evaluation of the related functional determinant, a generalised zeta function regularisation procedure is proposed.Comment: Latex, 14 pages, no figures. The version to be published in JM