1,720,961 research outputs found
Calculation of the metabolic demands of a successful cycling world-hour record by a validated mathematical model
No full textThe cycling world hour record (WHR) is one of the most mythical and prestigious cycling performances. For one hour, cyclists aim to cover the longest distance possible on a cycling velodrome. Many of the most successful and legendary cyclists, such as Fausto Coppi, Jacques Anquetil, Francesco Moser, Eddy Merckx, Miguel Indurain or Bradley Wiggins have focused on improving the WHR during their careers. Despite the increasing scientific information on professional cycling performance (1–4), scientific data on the WHR is rather limited
Calculation of the metabolic demands of a successful cycling world-hour record by a validated mathematical model
No full textThe cycling world hour record (WHR) is one of the most mythical and prestigious cycling performances. For one hour, cyclists aim to cover the longest distance possible on a cycling velodrome. Many of the most successful and legendary cyclists, such as Fausto Coppi, Jacques Anquetil, Francesco Moser, Eddy Merckx, Miguel Indurain or Bradley Wiggins have focused on improving the WHR during their careers. Despite the increasing scientific information on professional cycling performance (1–4), scientific data on the WHR is rather limited
A Single Night in Hypoxia Either with or without Ketone Ester Ingestion Reduces Sleep Quality Without Impacting Next Day Exercise Performance
No full textBackground: Sleeping at altitude is highly common in athletes as an integral part of altitude training camps or sport competitions. However, concerns have been raised due to expected negative effects on sleep quality, thereby potentially hampering exercise recovery and next-day exercise performance. We recently showed that ketone ester (KE) ingestion beneficially impacted sleep following strenuous, late evening exercise in normoxia, and alleviated hypoxemia.
Therefore, we hypothesized that KE ingestion may be an effective strategy to attenuate hypox(em)ia-induced sleep dysregulations.
Methods: Eleven healthy, male participants completed three experimental sessions including normoxic training and subsequent sleep in normoxia or at a simulated altitude of 3,000m while receiving either KE or placebo post-exercise and pre-sleep. Sleep was evaluated using polysomnography, while next-day exercise performance was assessed through a 30-min all-out time trial (TT30’). Physiological measurements included oxygen status, heart rate variability, ventilatory parameters, blood acid-base balance and capillary blood gases.
Results: Hypoxia caused a ~3% drop in sleep efficiency, established through a doubled wakefulness after sleep onset and a ~22% reduction in slow wave sleep. KE ingestion alleviated the gradual drop in SpO2 throughout the first part of the night, but did not alter hypoxia-induced sleep dysregulations. Neither KE, nor nocturnal hypoxia affected TT30’ performance, but nocturnal hypoxia hampered heart rate recovery following TT30’.
Conclusions: We observed that sleeping at 3,000m altitude impairs sleep efficiency. Although this hypoxia-induced sleep disruption was too subtle to limit exercise performance, we for the first time indicate that sleeping at altitude might impair next-day exercise recovery. KE alleviated nocturnal hypoxemia only when SpO2 values dropped below ~85%, but this did not translate into improved sleep or next-day exercise performance.The authors declare that they have no competing interests. This research was supported by the Research Foundation – Flanders (FWO Weave, research grant G073522N) and Slovene Research Agency grant (N5-0247). CP is supported by an FWO senior postdoctoral research grant (12B0E24N)
Exogenous ketosis attenuates acute mountain sickness and mitigates normobaric high-altitude hypoxemia
No full textAcute mountain sickness (AMS) represents a considerable issue for individuals sojourning to high altitudes with systemic hypoxe-mia known to be intimately involved in its development. Based on recent evidence that ketone ester (KE) intake attenuates hy-poxemia, we investigated whether exogenous ketosis might mitigate AMS development and identified underlying physiological mechanisms. Fourteen healthy, male participants were enrolled in two 29-h protocols (simulated altitude of 4,000-4,500 m) receiving either KE or a placebo (CON) at regular timepoints throughout the protocol in a randomized, crossover manner. Physiological responses were characterized after 15 min and 4 h in hypoxia, and the protocol was terminated prematurely upon development of severe AMS (Lake Louise Score ! 10). KE ingestion induced a consistent diurnal ketosis (D-b-hydroxybutyrate, [bHB] of $3 mM), whereas blood [bHB] remained low (<0.6 mM) in CON. Each participant tolerated the protocol equally long or longer (n ¼ 6 or n ¼ 8, respectively) in KE. Protocol duration increased by 32% on average with KE, and doubled upon KE for severe AMS-developing participants (n ¼ 9). Relative to CON, KE induced a mild metabolic acidosis, hyperventilation, and relative sympathetic dominance. KE also inhibited the progressive hypoxemia that was observed between 15 min and 4 h in hypoxia in CON, while concomitantly increasing cerebral oxygenation and capillary PO 2 within this timeframe despite a KE-induced reduction in cerebral oxygen supply. These data indicate that exogenous ketosis attenuates AMS development. The key underlying mechanisms include improved arterial and cerebral oxygenation, in combination with lowered cerebral blood flow and oxygen delivery, and increased sympathetic dominance. NEW & NOTEWORTHY Ketone ester intake attenuated the development of acute mountain sickness at a simulated altitude of 4,000-4,500 m. This likely resulted from a mitigation of arterial and cerebral hypoxemia, reduced cerebral blood flow, and increased sympathetic drive. acute mountain sickness
Post-exercise ketosis improves endurance performance, but not cardiac function during an 8-week training intervention
No full textPost-exercise ketosis improves endurance performance, but not cardiac function during an 8-week training intervention
No full textCirculating Endocannabinoids Are Associated with Mental Alertness During Ultra-Endurance Exercise
No full textIntroduction: Ultra-endurance exercise events result in central fatigue, impacting on mental alertness and decision making. Endocannabinoids are typically elevated during endurance exercise and have been implicated in central processes such as learning and memory, but their role in central fatigue has never been studied. Materials and Methods: Twenty-four recreational male ultrarunners participated in a 100-km trail run, and 18 of them completed at least 60 km and were included in the analyses. A cognitive test battery to assess median reaction time (MRT) and median movement time during a reaction time task and median response latency during a rapid visual information processing task was completed prior to and immediately after the trail. Blood serum samples pre- and postexercise were analyzed for endocannabinoids and related lipids (anadamide: AEA; 2-arachidonoylglycerol: 2-AG; palmitoylethanolamide: PEA; oleoylethanolamide: OEA; stearoylethanolamine: SEA) via liquid chromatography-mass spectrometry. Results: Ultra-endurance exercise worsened all cognitive parameters and increased abundance of AEA, PEA, OEA, and SEA but not 2-AG. Interestingly, the exercise-induced change in MRT showed moderate, positive correlations with the change in different endocannabinoids, that is, AEA (r = 0.5164, p = 0.0338), PEA (r = 0.5466, p = 0.0251), and OEA (r = 0.5442, p = 0.0239). Conclusion: These results indicate a potential role of endocannabinoids on mental alertness following ultra-endurance exercise.Sebastiaan Dalle and Chiel Poffé: shared first-autho
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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