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Critical power and fatigue

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https://www.readbyqxmd.com/read/27806677/power-duration-relationship-physiology-fatigue-and-the-limits-of-human-performance
#1
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
https://www.readbyqxmd.com/read/27802700/response-measurement-by-laser-doppler-vibrometry-in-vibration-qualification-tests-with-non-gaussian-random-excitation
#2
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
https://www.readbyqxmd.com/read/27788474/compression-fatigue-behavior-and-failure-mechanism-of-porous-titanium-for-biomedical-applications
#3
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...
September 28, 2016: Journal of the Mechanical Behavior of Biomedical Materials
https://www.readbyqxmd.com/read/27571960/development-of-superlattice-crn-nbn-coatings-for-joint-replacements-deposited-by-high-power-impulse-magnetron-sputtering
#4
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
https://www.readbyqxmd.com/read/27478563/comparison-of-proximally-versus-distally-placed-spatially-distributed-sequential-stimulation-electrodes-in-a-dynamic-knee-extension-task
#5
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
https://www.readbyqxmd.com/read/27396243/mechanically-robust-39-ghz-cut-off-frequency-graphene-field-effect-transistors-on-flexible-substrates
#6
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
https://www.readbyqxmd.com/read/27128663/disease-induced-skeletal-muscle-atrophy-and-fatigue
#7
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
https://www.readbyqxmd.com/read/27121994/an-eeg-based-fatigue-detection-and-mitigation-system
#8
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
https://www.readbyqxmd.com/read/27031742/critical-power-an-important-fatigue-threshold-in-exercise-physiology
#9
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
https://www.readbyqxmd.com/read/26868642/critical-load-a-novel-approach-to-determining-a-sustainable-intensity-during-resistance-exercise
#10
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...
February 11, 2016: Journal of Sports Medicine and Physical Fitness
https://www.readbyqxmd.com/read/26801204/physiological-and-pathophysiological-reactive-oxygen-species-as-probed-by-epr-spectroscopy-the-underutilized-research-window-on-muscle-ageing
#11
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
https://www.readbyqxmd.com/read/26792027/rate-of-utilization-of-a-given-fraction-of-w-the-curvature-constant-of-the-power-duration-relationship-does-not-affect-fatigue-during-severe-intensity-exercise
#12
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
https://www.readbyqxmd.com/read/26558616/network-events-on-multiple-space-and-time-scales-in-cultured-neural-networks-and-in-a-stochastic-rate-model
#13
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
https://www.readbyqxmd.com/read/26422317/cyclic-deformation-in-metallic-glasses
#14
Z D Sha, S X Qu, Z S Liu, T J Wang, H Gao
Despite the utmost importance and decades of experimental studies on fatigue in metallic glasses (MGs), there has been so far little or no atomic-level understanding of the mechanisms involved. Here we perform molecular dynamics simulations of tension-compression fatigue in Cu50Zr50 MGs under strain-controlled cyclic loading. It is shown that the shear band (SB) initiation under cyclic loading is distinctly different from that under monotonic loading. Under cyclic loading, SB initiation takes place when aggregates of shear transformation zones (STZs) accumulating at the MG surface reach a critical size comparable to the SB width, and the accumulation of STZs follows a power law with rate depending on the applied strain...
October 14, 2015: Nano Letters
https://www.readbyqxmd.com/read/26308828/decreasing-power-output-increases-aerobic-contribution-during-low-volume-severe-intensity-intermittent-exercise
#15
COMPARATIVE STUDY
Felipe D Lisbôa, Amadeo F Salvador, João A G Raimundo, Kayo L Pereira, Rafael A de Aguiar, Fabrizio Caputo
High-intensity interval training applied at submaximal, maximal, and supramaximal intensities for exercising at V[Combining Dot Above]O2max (t95V[Combining Dot Above]O2max) has shown similar adaptation to low-volume sprint interval training among active subjects. Thus, the aim of the present study was to investigate t95V[Combining Dot Above]O2max during 2 different intermittent exercises in the severe-intensity domain (e.g., range of power outputs over which V[Combining Dot Above]O2max can be elicited during constant-load exercise) and to identify an exercise protocol that reduces the time required to promote higher aerobic demand...
September 2015: Journal of Strength and Conditioning Research
https://www.readbyqxmd.com/read/26272315/locomotor-muscle-fatigue-is-not-critically-regulated-after-prior-upper-body-exercise
#16
M A Johnson, G R Sharpe, N C Williams, R Hannah
This study examined the effects of prior upper body exercise on subsequent high-intensity cycling exercise tolerance and associated changes in neuromuscular function and perceptual responses. Eight men performed three fixed work-rate (85% peak power) cycling tests: 1) to the limit of tolerance (CYC); 2) to the limit of tolerance after prior high-intensity arm-cranking exercise (ARM-CYC); and 3) without prior exercise and for an equal duration as ARM-CYC (ISOTIME). Peripheral fatigue was assessed via changes in potentiated quadriceps twitch force during supramaximal electrical femoral nerve stimulation...
October 1, 2015: Journal of Applied Physiology
https://www.readbyqxmd.com/read/26136542/performance-enhancement-what-are-the-physiological-limits
#17
REVIEW
C Lundby, P Robach
Our objective is to highlight some key physiological determinants of endurance exercise performance and to discuss how these can be further improved. V̇o2max remains remarkably stable throughout an athletic career. By contrast, exercise economy, lactate threshold, and critical power may be improved in world-class athletes by specific exercise training regimes and/or with more years of training.
July 2015: Physiology
https://www.readbyqxmd.com/read/26104881/influence-of-blood-flow-occlusion-on-the-development-of-peripheral-and-central-fatigue-during-small-muscle-mass-handgrip-exercise
#18
R M Broxterman, J C Craig, J R Smith, S L Wilcox, C Jia, S Warren, T J Barstow
Critical power represents an important threshold for neuromuscular fatigue development and may, therefore, dictate intensities for which exercise tolerance is determined by the magnitude of fatigue accrued. Peripheral fatigue appears to be constant across O2 delivery conditions for large muscle mass exercise, but this consistency is equivocal for smaller muscle mass exercise. We sought to determine the influence of blood flow occlusion during handgrip exercise on neuromuscular fatigue development and to examine the relationship between neuromuscular fatigue development and W '...
September 1, 2015: Journal of Physiology
https://www.readbyqxmd.com/read/25994386/complex-network-models-reveal-correlations-among-network-metrics-exercise-intensity-and-role-of-body-changes-in-the-fatigue-process
#19
Vanessa Helena Pereira, Maria Carolina Traina Gama, Filipe Antônio Barros Sousa, Theodore Gyle Lewis, Claudio Alexandre Gobatto, Fúlvia Barros Manchado-Gobatto
The aims of the present study were analyze the fatigue process at distinct intensity efforts and to investigate its occurrence as interactions at distinct body changes during exercise, using complex network models. For this, participants were submitted to four different running intensities until exhaustion, accomplished in a non-motorized treadmill using a tethered system. The intensities were selected according to critical power model. Mechanical (force, peak power, mean power, velocity and work) and physiological related parameters (heart rate, blood lactate, time until peak blood lactate concentration (lactate time), lean mass, anaerobic and aerobic capacities) and IPAQ score were obtained during exercises and it was used to construction of four complex network models...
2015: Scientific Reports
https://www.readbyqxmd.com/read/25913608/strong-similarities-in-the-creep-and-damage-behaviour-of-a-synthetic-bone-model-compared-to-human-trabecular-bone-under-compressive-cyclic-loading
#20
Philip Purcell, Stephen Tiernan, Fiona McEvoy, Seamus Morris
Understanding the failure modes which instigate vertebral collapse requires the determination of trabecular bone fatigue properties, since many of these fractures are observed clinically without any preceding overload event. Alternatives to biological bone tissue for in-vitro fatigue studies are available in the form of commercially available open cell polyurethane foams. These test surrogates offer particular advantages compared to biological tissue such as a controllable architecture and greater uniformity...
August 2015: Journal of the Mechanical Behavior of Biomedical Materials
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