"Critical power"

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We experimentally investigate fluctuations in the spectrum of ultrashort laser pulses propagating in air, close to the critical power for filamentation. Increasing the laser peak power broadens the spectrum while the beam approaches the filamentation regime. We identify two regimes for this transition: In the center of the spectrum, the output spectral intensity increases continuously. In contrast, on the edges of the spectrum the transition implies a bimodal probability distribution function for intermediate incident pulse energies, where a high-intensity mode appears and grows at the expense of the original low-intensity mode...

We tested the hypothesis that a %SmO2 (muscle O2 saturation) slope can distinguish the heavy-severe exercise domain boundary and the highest steady-state metabolic rate. Thirteen participants (5 women) performed a graded exercise test (GXT) to determine peak oxygen consumption (V̇o2peak ) and lactate turn point (LTP). On a separate study day, a %SmO2 zero-slope prediction trial included completing 5-min cycling bouts in an estimated heavy domain, at an estimated critical power, and in an estimated severe domain...

BACKGROUND: Forced displacement is a crucial determinant of poor health. With 31 people displaced every minute worldwide, this is an important global issue. Addressing this, the Participation Revolution workstream from the World Humanitarian Summit's Localisation commitments has gained traction in attempting to improve the effectiveness of humanitarian aid. Simultaneously, digital health initiatives have become increasingly ubiquitous tools in crises to deliver humanitarian assistance and address health burdens...

The observation that prior heavy or severe-intensity exercise speeds overall oxygen uptake ([Formula: see text]O2 ) kinetics, termed the "priming effect", has garnered significant research attention and its underpinning mechanisms have been hotly debated. In the first part of this review, the evidence for and against (1) lactic acidosis, (2) increased muscle temperature, (3) O2 delivery, (4) altered motor unit recruitment patterns and (5) enhanced intracellular O2 utilisation in underpinning the priming effect is discussed...

PURPOSE: To compare methods of relative intensity prescription for their ability to normalise performance (i.e., time to exhaustion), physiological, and perceptual responses to high-intensity interval training (HIIT) between individuals. METHODS: Sixteen male and two female cyclists (age: 38 ± 11 years, height: 177 ± 7 cm, body mass: 71.6 ± 7.9 kg, maximal oxygen uptake ([Formula: see text]O2max ): 54...

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PURPOSE: The purpose of this study was to examine the suitability of a single ramp incremental test to predict critical power (CP) and W'. We hypothesized that CP would correspond to the corrected power output (PO) at the respiratory compensation point (RCP) and W' would be calculable from the work done above RCP. METHODS: 153 healthy young people (26 ± 4 yr, 51.4 ± 7.6 mL·min-1·kg-1) performed a maximal ramp test (20, 25 or 30 W·min-1), followed by three to five constant load trials to determine CP and W'...

Recent studies have concluded that high-intensity interval training should be seen as a "viable alternative" to, and may be more enjoyable than, moderate-intensity continuous exercise. If true, these claims have the potential to revolutionize the science and practice of exercise, establishing high-intensity interval training as not only a physiologically effective exercise modality but also a potentially sustainable one. However, these claims stand in contrast to voluminous evidence according to which high levels of exercise intensity are typically experienced as less pleasant than moderate levels...

Maximal Lactate steady-state (MLSS) demarcates sustainable from unsustainable exercise and is used for evaluation/monitoring of exercise capacity. Still, its determination is physically challenging and time-consuming. This investigation aimed at validating a simple, submaximal approach based on blood lactate accumulation ([Δlactate]) at the third minute of cycling in a large cohort of men and women of different ages. 68 healthy adults (40♂, 28♀, 43 ± 17 years (range 19-78), VO2max 45 ± 11 ml-1· kg-1· min-1 (25-68)) performed 3-5 constant power output (PO) trials with a target duration of 30 minutes to determine the PO corresponding to MLSS...

When a low-power, monochromatic Gaussian beam is focused by a thin lens in air and the waist of the beam is in the plane of the lens, there is a shift of the focus position if the waist of the beam is much smaller than the size of the lens. The point of maximum intensity relative to the geometrical focal point shifts closer to the lens. We show that for ultra-intense light beams, when the Kerr effect is unavoidable, there is a nonlinear focal shift. The nonlinear focus position shifts closer to the lens for laser powers below the critical power...

The filamentation of the femtosecond vortex beam has attracted much attention because of the unique filamentation characteristics, such as annular distribution and helical propagation, and related applications. The critical power for self-focusing of the femtosecond vortex beams is a key parameter in the filamentation process and applications. But until now, there is no quantitative determination of the critical power. In this work, we experimentally determine the self-focusing critical power of femtosecond vortex beams in air by measuring fluorescence using a photomultiplier tube...

No abstract text is available yet for this article.

No abstract text is available yet for this article.

NEW FINDINGS: What is the central question of this study? Does prescribing exercise intensity using physiological thresholds create a more homogeneous exercise stimulus than using traditional intensity anchors? What is the main finding and its importance? Prescribing exercise using physiological thresholds, notably critical power, reduced the variability in exercise tolerance and acute metabolic responses. At higher intensities, approaching or exceeding the transition from heavy to severe intensity exercise, the imprecision of using fixed % <mml:math xmlns:mml="https://www...

Small-scale, primary electrochemical energy storage devices ("microbatteries") are critical power sources for microelectromechanical system (MEMS)-based sensors and actuators. However, the achievable volumetric and gravimetric energy densities of microbatteries are typically insufficient for intermediate-term applications of MEMS-enabled distributed internet-connected devices. Further, in the increasing subset of Internet of Things (IoT) nodes, where actuation is desired, the peak power density of the microbattery must be simultaneously considered...

BACKGROUND: The effects of pre-sleep protein supplementation on endurance athletes remain unclear, particularly whether its potential benefits are due to the timing of protein intake or solely to an increased total protein intake. We assessed the effects of pre-sleep protein supplementation in professional cyclists during a training camp accounting for the influence of protein timing. METHODS: Twenty-four professional U23 cyclists (19 ± 1 years, peak oxygen uptake: 79...

KEY POINTS: Oxygen delivery is viewed as tightly coupled to demand in exercise below critical power because increasing oxygen delivery does not increase the rate of oxygen uptake. Whether the "normal" adjustment of oxygen delivery in small muscle mass exercise below critical power is optimal for excitation-contraction coupling is not known. Here we show in humans that increasing oxygen delivery above "normal" improves excitation-contraction coupling. These results suggest that, in the heavy exercise intensity domain, the "normal" matching of oxygen delivery to metabolic demand is not optimal for muscle excitation-contraction coupling...

INTRODUCTION: Several studies report that pulmonary oxygen uptake (V̇O2) at the respiratory compensation point (RCP) is equivalent to the V̇O2 at critical power (CP), suggesting that the variables can be used interchangeably to demarcate the threshold between heavy and severe intensity domains. But if RCP is a valid surrogate for CP, their values should correspond even when assessed in patients with chronic obstructive pulmonary disease (COPD) in whom the 'normal' mechanisms linking CP and RCP are impeded...

The physiological determinants of high-intensity exercise tolerance are important for both elite human performance and morbidity, mortality and disease in clinical settings. The asymptote of the hyperbolic relation between external power and time to task failure, critical power, represents the threshold intensity above which systemic and intramuscular metabolic homeostasis can no longer be maintained. After ~ 60 years of research into the phenomenon of critical power, a clear understanding of its physiological determinants has emerged...