Effects of triceps surae muscle strength and tendon stiffness on the reactive dynamic stability and adaptability of older female adults during perturbed walking

This study aimed to examine whether the triceps surae (TS) muscle-tendon unit (MTU) mechanical properties affect gait stability and its reactive adaptation potential to repeated perturbation exposure in older adults. Thirty-four older adults each experienced eight separate unexpected perturbations during treadmill walking, while a motion capture system was used to determine the margin of stability (MoS) and base of support (BoS). Ankle plantar flexor muscle strength and Achilles tendon (AT) stiffness were analyzed using ultrasonography and dynamometry. A median split and separation boundaries classified the subjects into two groups with GroupStrong (n = 10) showing higher ankle plantar flexor muscle strength (2.26 +/- 0.17 vs. 1.47 +/- 0.20 N center dot m/kg, means +/- SD: P < 0.001) and AT stiffness (544 +/- 75 vs. 429 +/- 86 N/mm; P = 0.004) than GroupWeak in = 12). The first perturbation caused a negative Delta MoS (MoS in relation to unperturbed baseline walking) at touchdown of perturbed step (Pert(R)), indicating an unstable position. GroupStrong required four recovery steps to return to Delta MoS zero level, whereas GroupWeak was unable to return to baseline within the analyzed steps. However, after repeated perturbations, both groups increased Delta MoS at touchdown of Pert(R) with a similar magnitude. Significant correlations between Delta BoS and Delta MoS at touchdown of the first recovery step and TS MTU capacities (0.41 < r < 0.57: 0.006 < P < 0.048) were found. We conclude that older adults with TS muscle weakness have a diminished ability to control gait stability during unexpected perturbations, increasing their fall risk, but that degeneration in muscle strength and tendon stiffness may not inhibit the ability of the locomotor system to adapt the reactive motor response to repeated perturbations. NEW & NOTEWORTHY Triceps surae muscle weakness and a more compliant Achilles tendon partly limit older adults' ability to effectively enlarge the base of support and recover dynamic stability after an unexpected perturbation during walking, increasing their fail risk. However, the degeneration in muscle strength and tendon stiffness may not inhibit the ability of the locomotor system to adapt the reactive motor response to repeated perturbations

Transcranial direct current stimulation (tDCS) over the left prefrontal cortex does not affect time-trial self-paced cycling performance: Evidence from oscillatory brain activity and power output

To test the hypothesis that transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) influences performance in a 20-min time-trial self-paced exercise and electroencephalographic (EEG) oscillatory brain activity in a group of trained male cyclists. There were no differences (F = 0.31, p > 0.05) in power output between the stimulation conditions: anodal (235W[95%CI 222–249 W]; cathodal (235W[95%CI 222–248 W] and sham (234W[95%CI 220–248 W]. Neither heart rate, sRPE nor EEG activity were affected by tDCS (all Ps > 0.05). tDCS over the left DLFC did not affect self-paced exercise performance in trained cyclists. Moreover, tDCS did not elicit any change on oscillatory brain activity either at baseline or during exercise. Our data suggest that the effects of tDCS on endurance performance should be taken with caution.This project was supported by grants from from the Spanish Ministerio de Economía, Industria y Competitividad-PSI2016-75956-P to D. S. and M.Z., a predoctoral grant from the Spanish Ministerio de Economía, Industria y Competitividad (BES-2014-069050) to L.F.C., and a Spanish “Ministerio de Educación, Cultura y Deporte” predoctoral grant (FPU14/06229) to D.H. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Transcranial direct current stimulation (tDCS) over the left prefrontal cortex does not affect time-trial self-paced cycling performance: Evidence from oscillatory brain activity and power output

Objectives: To test the hypothesis that transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) influences performance in a 20-min time-trial self-paced exercise and electroencephalographic (EEG) oscillatory brain activity in a group of trained male cyclists. Design: The study consisted of a pre-registered (https://osf.io/rf95j/), randomised, sham-controlled, single-blind, within-subject design experiment. Methods: 36 trained male cyclists, age 27 (6.8) years, weight 70.1 (9.5) Kg; VO2max: 54 (6.13) ml.min-1.kg-1, Maximal Power output: 4.77 (0.6) W/kg completed a 20-min time-trial self-paced exercise in three separate sessions, corresponding to three stimulation conditions: anodal, cathodal and sham. tDCS was administered before each test during 20-min at a current intensity of 2.0 mA. The anode electrode was placed over the DLPFC and the cathode in the contralateral shoulder. In each session, power output, heart rate, sRPE and EEG (at baseline and during exercise) was measured. Results: There were no differences (F = 0.31, p > 0.05) in power output between the stimulation conditions: anodal (235 W [95%CI 222–249 W]; cathodal (235 W [95%CI 222–248 W] and sham (234 W [95%CI 220–248 W]. Neither heart rate, sRPE nor EEG activity were affected by tDCS (all Ps > 0.05). Conclusion: tDCS over the left DLFC did not affect self-paced exercise performance in trained cyclists. Moreover, tDCS did not elicit any change on oscillatory brain activity either at baseline or during exercise. Our data suggest that the effects of tDCS on endurance performance should be taken with caution

Status Of The FAIR Synchrotron Projects SIS18 And SIS100

A large fraction of the program to upgrade the existingheavy ion synchrotron SIS18 as injector for the FAIR synchrotron SIS100 has been successfully completed. With the achieved technical status, a major increase of theaccelerated number of heavy ions could be reached. Thenow available performance especially demonstrates thefeasibility of high intensity beams of medium charge stateheavy ions with a sufficient control of the dynamicvacuum and connected charge exchange loss. Two furtherupgrade measures, the installation of additional magneticalloy (MA) acceleration cavities and the exchange of themain dipole power converter, are presently beingimplemented. For the FAIR synchrotron SIS100, theprocurement of all major components with longproduction times has been started. With the delivery andtesting of several pre-series components, the phase ofoutstanding technical reserach and developments could becompleted and the readiness for series productionachieved

Improved sensorimotor adaptation after exhaustive exercise is accompanied by altered brain activity

Acute exercise has been shown to exhibit different effects on human sensorimotor behavior; however, the causes and mechanisms of the responses are often not clear. The primary aim of the present study was to determine the effects of incremental running until exhaustion on sensorimotor performance and adaptation in a tracking task. Subjects were randomly assigned to a running group (RG), a tracking group (TG), or a running followed by tracking group (RTG), with 10 subjects assigned to each group. Treadmill running velocity was initially set at 2.0 m s− 1, increasing by 0.5 m s− 1 every 5 min until exhaustion. Tracking consisted of 35 episodes (each 40 s) where the subjects' task was to track a visual target on a computer screen while the visual feedback was veridical (performance) or left-right reversed (adaptation). Resting electroencephalographic (EEG) activity was recorded before and after each experimental condition (running, tracking, rest). Tracking performance and the final amount of adaptation did not differ between groups. However, task adaptation was significantly faster in RTG compared to TG. In addition, increased alpha and beta power were observed following tracking in TG but not RTG although exhaustive running failed to induce significant changes in these frequency bands. Our results suggest that exhaustive running can facilitate adaptation processes in a manual tracking task. Attenuated cortical activation following tracking in the exercise condition was interpreted to indicate cortical efficiency and exercise-induced facilitation of selective central processes during actual task demands

Dynamic Control of Synchronous Activity in Networks of Spiking Neurons.

Oscillatory brain activity is believed to play a central role in neural coding. Accumulating evidence shows that features of these oscillations are highly dynamic: power, frequency and phase fluctuate alongside changes in behavior and task demands. The role and mechanism supporting this variability is however poorly understood. We here analyze a network of recurrently connected spiking neurons with time delay displaying stable synchronous dynamics. Using mean-field and stability analyses, we investigate the influence of dynamic inputs on the frequency of firing rate oscillations. We show that afferent noise, mimicking inputs to the neurons, causes smoothing of the system's response function, displacing equilibria and altering the stability of oscillatory states. Our analysis further shows that these noise-induced changes cause a shift of the peak frequency of synchronous oscillations that scales with input intensity, leading the network towards critical states. We lastly discuss the extension of these principles to periodic stimulation, in which externally applied driving signals can trigger analogous phenomena. Our results reveal one possible mechanism involved in shaping oscillatory activity in the brain and associated control principles

The interrelation between sensorimotor abilities, cognitive performance and individual EEG alpha peak frequency in young children

Objective: The aim of this study was to identify the interrelation between sensorimotor abilities, cognitive performance and individual alpha peak frequency (iAPF), an EEG marker of global architectural and functional properties of the human brain, in healthy preschool children. Methods: 25 participants completed a one minute eyes-closed EEG recording, two cognitive tests assessing processing speed and visual working memory and a sensorimotor test battery. Results: We found positive correlations between selective sensorimotor abilities and iAPF; however, no significant correlations were observed between iAPF and cognitive performance. Specifically, locomotor skills correlated with iAPF across all cortical regions, except for the occipital cortex. Furthermore, a close relationship was found between sensorimotor and cognitive performance indicating that children with improved sensorimotor abilities were faster and/or more accurate in cognitive task performance. The cumulative pattern of our results indicates that a close relationship exists between sensorimotor and cognitive performance in young children. However, this relationship is dissociated from the iAPF. Conclusion: In contrast to adults, in young children the iAPF is related to locomotor skills and not to cognitive processing speed or visual working memory function. Significance: The global architectural and functional properties of the brain are closely related to locomotor skills during development. (C) 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved

Effects of different exercise intensities in the morning on football performance components in the afternoon

The aim of this study was to investigate the effect of two different exercise interventions in the morning on football-specific components of performance in the afternoon under conditions simulating a competition day. In the morning on 3 experimental days, 12 football players (age 24.1 +/- 5.5 years) completed three different preload interventions that were applied in a counter-balanced order: (1) no intervention (NI); (2) moderate-intensive exercise (MI); and (3) high-intensive exercise (HI). The subjects performed the preload exercises, consisting of a small-sided game and repeated maximal sprints, from 10:00-11:00 a.m. At 3:00 p.m., the Bangsbo test (BT) was applied to examine the effects of the different morning interventions on football-specific endurance capacity. The results showed that the HI led to significantly higher blood-lactate concentrations (moderate to very large effect) and heart rates (very large to extremely large effect) compared to the MI. In addition, there was a significant measurementx intervention effect on concentrations of adrenalin and noradrenalin in the urine, which reached higher values immediately after the HI (very large effect) and MI (moderate effect) compared to NI. All effects disappeared by the time of the BT in the afternoon. During all trials, after the preload intervention, reaction time and critical flicker fusion frequency increased significantly compared to the baseline morning values (reaction time: small; critical flicker fusion: trivial to small effect), but no measurementx intervention interaction was found. During the BT, the mean total distance covered (trivial to small effect) and the pacing pattern did not differ significantly among the trials despite numerous small individual effects. We conclude that exercise interventions of various intensities in the morning have no general effect on football-specific components of performance in the afternoon despite significant metabolic, endocrinological and cognitive short-term effects. Coaches should consider individual preferences when prescribing competition-day procedures

Frequency tuning curve.

<p>Frequency of the network synchronous oscillations as a function of noise intensity. Noise causes the peak frequency of the network oscillations to shift from the baseline frequency <i>ω</i>_<i>o</i> towards the critical frequency <i>ω</i>_<i>c</i>. The peak frequency is plotted according to numerical simulations of the network dynamics (red dotted curve), the mean-field approximation (grey; as per <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161488#pone.0161488.e014" target="_blank">Eq 10</a>) and using the frequency tuning curve (black; as per <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161488#pone.0161488.e036" target="_blank">Eq 17</a>). Other parameters are taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161488#pone.0161488.g003" target="_blank">Fig 3</a>.</p

Network stability and equilibrium are shaped by noise.

<p>A. Fixed point of the system as per <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161488#pone.0161488.e019" target="_blank">Eq (11)</a> as a function of increasing noise intensity. Noise generically decreases the equilibrium, due to an increased recruitment of recurrent connections. B. Network susceptibility as a function of noise intensity. A gradual shift towards the critical susceptibility <i>R</i>_<i>c</i> occurs under the action of noise, causing the system to transit from slow non-linear oscillations to fast linear oscillations. C. System’s eigenvalues for moderate (D = 0.01) and strong (D = 0.1) noise levels. The eigenvalues gradually shift towards the left hand side of the imaginary plane. Critical eigenvalues (pairs of roots inside the black boxes) translate towards the imaginary axis (Re(<i>λ</i>) = 0) i.e. closer to the critical state. Other parameters are <i>α</i> = 100Hz, <i>β</i> = 2500/mV, <i>g</i> = −2mV/Hz, <i>s</i> = 4mV/Hz, <i>τ</i> = 25ms.</p