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Critical power and fatigue

Evangelia Akoumianaki, Nicolas Dousse, Aissam Lyazidi, Jean-Claude Lefebvre, Severine Graf, Ricardo Luiz Cordioli, Nathalie Rey, Jean-Christophe Marie Richard, Laurent Brochard
BACKGROUND: Early exercise of critically ill patients may have beneficial effects on muscle strength, mass and systemic inflammation. During pressure support ventilation (PSV), a mismatch between demand and assist could increase work of breathing and limit exercise. A better exercise tolerance is possible with a proportional mode of ventilation (Proportional Assist Ventilation, PAV+ and Neurally Adjusted Ventilatory Assist, NAVA). We examined whether, in critically ill patients, PSV and proportional ventilation have different effects on respiratory muscles unloading and work efficiency during exercise...
December 2017: Annals of Intensive Care
Peter Hofmann, Gerhard Tschakert
The regulation of endurance training is usually based on the prescription of exercise intensity. Exercise duration, another important variable of training load, is rarely prescribed by individual measures and mostly set from experience. As the specific exercise duration for any intensity plays a substantial role regarding the different kind of cellular stressors, degree, and kind of fatigue as well as training effects, concepts integrating the prescription of both intensity and duration within one model are needed...
2017: Frontiers in Physiology
Andrew M Jones, Anni Vanhatalo
The curvilinear relationship between power output and the time for which it can be sustained is a fundamental and well-known feature of high-intensity exercise performance. This relationship 'levels off' at a 'critical power' (CP) that separates power outputs that can be sustained with stable values of, for example, muscle phosphocreatine, blood lactate, and pulmonary oxygen uptake ([Formula: see text]), from power outputs where these variables change continuously with time until their respective minimum and maximum values are reached and exercise intolerance occurs...
March 2017: Sports Medicine
C Vanderwel, M Placidi, B Ganapathisubramani
High-resolution particle image velocimetry data obtained in rough-wall boundary layer experiments are re-analysed to examine the influence of surface roughness heterogeneities on wind resource. Two different types of heterogeneities are examined: (i) surfaces with repeating roughness units of the order of the boundary layer thickness (Placidi & Ganapathisubramani. 2015 J. Fluid Mech.782, 541-566. (doi:10.1017/jfm.2015.552)) and (ii) surfaces with streamwise-aligned elevated strips that mimic adjacent hills and valleys (Vanderwel & Ganapathisubramani...
April 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Georgia S Karanasiou, Michail I Papafaklis, Claire Conway, Lampros K Michalis, Rami Tzafriri, Elazer R Edelman, Dimitrios I Fotiadis
Coronary stents have revolutionized the treatment of coronary artery disease. Improvement in clinical outcomes requires detailed evaluation of the performance of stent biomechanics and the effectiveness as well as safety of biomaterials aiming at optimization of endovascular devices. Stents need to harmonize the hemodynamic environment and promote beneficial vessel healing processes with decreased thrombogenicity. Stent design variables and expansion properties are critical for vessel scaffolding. Drug-elution from stents, can help inhibit in-stent restenosis, but adds further complexity as drug release kinetics and coating formulations can dominate tissue responses...
February 3, 2017: Annals of Biomedical Engineering
Matthew I Black, Andrew M Jones, Jamie R Blackwell, Stephen J Bailey, Lee J Wylie, Sinead T J McDonagh, Christopher Thompson, James Kelly, Paul Sumners, Katya N Mileva, Joanna L Bowtell, Anni Vanhatalo
Lactate or gas exchange threshold (GET) and critical power (CP) are closely associated with human exercise performance. We tested the hypothesis that the limit of tolerance (Tlim) during cycle exercise performed within the exercise intensity domains demarcated by GET and CP is linked to discrete muscle metabolic and neuromuscular responses. Eleven men performed a ramp incremental exercise test, 4-5 severe-intensity (SEV; >CP) constant-work-rate (CWR) tests until Tlim, a heavy-intensity (HVY; <CP but >GET) CWR test until Tlim, and a moderate-intensity (MOD; <GET) CWR test until Tlim Muscle biopsies revealed that a similar (P > 0...
March 1, 2017: Journal of Applied Physiology
John Murray, Michael McCrudden, Juan M Murias, Volker Nolte, Glen R Belfry
BACKGROUND: This study compared an all-out start (AO) to a constant power start strategy (CON) during a 6 min cycle performance on utilization of W ́ (energy above critical power (CP)), muscle deoxygenation (HHb), oxygen uptake (VO2) and performance in recreationally active individuals. The AO strategy was similar to that employed by rowers. METHODS: Eight healthy males (age = 24 ± 3 y) completed a ramp test to fatigue (VO2peak = 4.42 ± 0.54 L∙min-1; peak power = 385 ± 35 W) and a 3-min all-out test to determine CP and the CON work rate...
December 16, 2016: Journal of Sports Medicine and Physical Fitness
Mark Burnley, Andrew M Jones
The duration that exercise can be maintained decreases as the power requirements increase. In this review, we describe the power-duration (PD) relationship across the full range of attainable power outputs in humans. We show that a remarkably small range of power outputs is sustainable (power outputs below the critical power, CP). We also show that the origin of neuromuscular fatigue differs considerably depending on the exercise intensity domain in which exercise is performed. In the moderate domain (below the lactate threshold, LT), fatigue develops slowly and is predominantly of central origin (residing in the central nervous system)...
November 3, 2016: European Journal of Sport Science
M Troncossi, R Di Sante, A Rivola
In the field of vibration qualification testing, random excitations are typically imposed on the tested system in terms of a power spectral density (PSD) profile. This is the one of the most popular ways to control the shaker or slip table for durability tests. However, these excitations (and the corresponding system responses) exhibit a Gaussian probability distribution, whereas not all real-life excitations are Gaussian, causing the response to be also non-Gaussian. In order to introduce non-Gaussian peaks, a further parameter, i...
October 2016: Review of Scientific Instruments
Fuping Li, Jinshan Li, Tingting Huang, Hongchao Kou, Lian Zhou
Porous titanium and its alloys are believed to be one of the most attractive biomaterials for orthopedic implant applications. In the present work, porous pure titanium with 50-70% porosity and different pore size was fabricated by diffusion bonding. Compression fatigue behavior was systematically studied along the out-of-plane direction. It resulted that porous pure titanium has anisotropic pore structure and the microstructure is fine-grained equiaxed α phase with a few twins in some α grains. Porosity and pore size have some effect on the S-N curve but this effect is negligible when the fatigue strength is normalized by the yield stress...
January 2017: Journal of the Mechanical Behavior of Biomedical Materials
Papken Ehiasarian Hovsepian, Arutiun Papken Ehiasarian, Yashodhan Purandare, Arunprabhu Arunachalam Sugumaran, Tim Marriott, Imran Khan
The demand for reliable coating on medical implants is ever growing. In this research, enhanced performance of medical implants was achieved by a CrN/NbN coating, utilising nanoscale multilayer/superlattice structure. The advantages of the novel high power impulse magnetron sputtering technology, namely, its unique highly ionised plasma, were exploited to deposit dense and strongly adherent coatings on CoCr implants. Transmission electron microscopy analysis revealed coating superlattice structure with bi-layer thickness of 3...
September 2016: Journal of Materials Science. Materials in Medicine
Marco Laubacher, Efe A Aksöz, Stuart Binder-Macleod, Kenneth J Hunt
Spatially distributed sequential stimulation (SDSS) has demonstrated substantial power output and fatigue benefits compared to single electrode stimulation (SES) in the application of functional electrical stimulation (FES). This asymmetric electrode setup brings new possibilities but also new questions since precise placement of the electrodes is one critical factor for good muscle activation. The aim of this study was to compare the power output, fatigue and activation properties of proximally versus distally placed SDSS electrodes in an isokinetic knee extension task simulating knee movement during recumbent cycling...
June 13, 2016: European Journal of Translational Myology
Wei Wei, Emiliano Pallecchi, Samiul Haque, Stefano Borini, Vanessa Avramovic, Alba Centeno, Zurutuza Amaia, Henri Happy
Graphene has been regarded as a promising candidate channel material for flexible devices operating at radio-frequency (RF). In this work we fabricated and fully characterized double bottom-gate graphene field effect transistors on flexible polymer substrates for high frequency applications. We report a record high as-measured current gain cut-off frequency (ft) of 39 GHz. The corresponding maximum oscillation frequency (fmax) is 13.5 GHz. These state of the art high frequency performances are stable against bending, with a typical variation of around 10%, for a bending radius of up to 12 mm...
August 7, 2016: Nanoscale
Scott K Powers, Gordon S Lynch, Kate T Murphy, Michael B Reid, Inge Zijdewind
Numerous health problems, including acute critical illness, cancer, diseases associated with chronic inflammation, and neurological disorders, often result in skeletal muscle weakness and fatigue. Disease-related muscle atrophy and fatigue is an important clinical problem because acquired skeletal muscle weakness can increase the duration of hospitalization, result in exercise limitation, and contribute to a poor quality of life. Importantly, skeletal muscle atrophy is also associated with increased morbidity and mortality of patients...
November 2016: Medicine and Science in Sports and Exercise
Kuan-Chih Huang, Teng-Yi Huang, Chun-Hsiang Chuang, Jung-Tai King, Yu-Kai Wang, Chin-Teng Lin, Tzyy-Ping Jung
Research has indicated that fatigue is a critical factor in cognitive lapses because it negatively affects an individual's internal state, which is then manifested physiologically. This study explores neurophysiological changes, measured by electroencephalogram (EEG), due to fatigue. This study further demonstrates the feasibility of an online closed-loop EEG-based fatigue detection and mitigation system that detects physiological change and can thereby prevent fatigue-related cognitive lapses. More importantly, this work compares the efficacy of fatigue detection and mitigation between the EEG-based and a nonEEG-based random method...
June 2016: International Journal of Neural Systems
David C Poole, Mark Burnley, Anni Vanhatalo, Harry B Rossiter, Andrew M Jones
: The hyperbolic form of the power-duration relationship is rigorous and highly conserved across species, forms of exercise, and individual muscles/muscle groups. For modalities such as cycling, the relationship resolves to two parameters, the asymptote for power (critical power [CP]) and the so-called W' (work doable above CP), which together predict the tolerable duration of exercise above CP. Crucially, the CP concept integrates sentinel physiological profiles-respiratory, metabolic, and contractile-within a coherent framework that has great scientific and practical utility...
November 2016: Medicine and Science in Sports and Exercise
Vivian M Arakelian, Renata G Mendes, Renata Trimer, Flavia C Rossi Caruso, Nuno M de Sousa, Vanessa C Borges, Camila do Valle Gomes Gatto, Vilmar Baldissera, Ross Arena, Audrey Borghi-Silva
BACKGROUND: A hyperbolic function as well as a linear relationship between power output and time to exhaustion (Tlim) has been consistently observed during dynamic non-resistive exercises. However, little is known about its concept to resistance exercises (RE), which could be defined as critical load (CL). This study aimed to verify the existence of CL during dynamic RE and to verify the number of workbouts necessary to determine the optimal modeling to achieve it. METHODS: Fifteen healthy men (23±2...
May 2017: Journal of Sports Medicine and Physical Fitness
Engy A Abdel-Rahman, Ali M Mahmoud, Abdulrahman M Khalifa, Sameh S Ali
Reactive oxygen and nitrogen species (ROS and RNS) play crucial roles in triggering, mediating and regulating physiological and pathophysiological signal transduction pathways within the cell. Within the cell, ROS efflux is firmly controlled both spatially and temporally, making the study of ROS dynamics a challenging task. Different approaches have been developed for ROS assessment; however, many of these assays are not capable of direct identification or determination of subcellular localization of different ROS...
August 15, 2016: Journal of Physiology
Kristopher Mendes de Souza, Jeanne Dekerle, Paulo Cesar do Nascimento Salvador, Ricardo Dantas de Lucas, Luiz Guilherme Antonacci Guglielmo, Camila Coelho Greco, Benedito Sérgio Denadai
What is the central question of this study? Does the rate of utilization of W' (the curvature constant of the power-duration relationship) affect fatigue during severe-intensity exercise? What is the main finding and its importance? The magnitude of fatigue after two severe-intensity exercises designed to deplete the same fraction of W' (70%) at two different rates of utilization (fast versus slow) was similar after both exercises. Moreover, the magnitude of fatigue was related to critical power (CP), supporting the contention that CP is a key determinant in fatigue development during high-intensity exercise...
April 2016: Experimental Physiology
Guido Gigante, Gustavo Deco, Shimon Marom, Paolo Del Giudice
Cortical networks, in-vitro as well as in-vivo, can spontaneously generate a variety of collective dynamical events such as network spikes, UP and DOWN states, global oscillations, and avalanches. Though each of them has been variously recognized in previous works as expression of the excitability of the cortical tissue and the associated nonlinear dynamics, a unified picture of the determinant factors (dynamical and architectural) is desirable and not yet available. Progress has also been partially hindered by the use of a variety of statistical measures to define the network events of interest...
November 2015: PLoS Computational Biology
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