1,721,016 research outputs found
Effects of acute sympathetic activation on the central artery stiffness after strenuous endurance exercise
No full textPurpose Augmented central arterial stiffness (CAS) increases cardiovascular risk. CAS can be augmented by physical exercise and sympathetic activation (SYMP) induced by stressful stimuli. Interestingly, sympathetic vasoconstriction triggered by a sympathetic stimulant is augmented immediately after a strenuous half-marathon compared to at rest. This study assessed whether CAS also augments more post- than pre-half-marathon in response to SYMP. Such assessment takes on relevance considering the growing popularity of strenuous, long-distance endurance exercises.Methods 13 healthy recreational runners (age 46.1 +/- 6.5 years; V'O-2 max 54.23 +/- 9.31 mlO(2)/min/kg) provided the following measurements prior to and within 10 min following a strenuous half-marathon: beat-by-beat aortic pulse wave velocity (aPWV; index of CAS), mean blood pressure, and heart rate assessment. Measures were performed at rest and during a 2 min handgrip-mediated SYMP. The effects of the half-marathon and SYMP were assessed by two-way repeated-measures ANOVA.Results Measurements of the aPWV pre- and post-race were not significantly different (7.5 +/- 0.8 vs 7.8 +/- 0.8 m/s, p = 0.34; pre- vs post-race). 2 min of SYMP increased the baseline aPWV post-race (7.8 +/- 0.8 vs 8.4 +/- 0.8, p= 0.003; rest vs SYMP) but not pre-race (7.5 +/- 0.8 vs 7.9 +/- 0.9, p = 0.21).Conclusion The baseline aPWV assessed 7 to 8 min after a strenuous half-marathon is similar to that pre-race in healthy runners. This agrees with previous studies suggesting CAS being at or below resting values > 5 min following completion of aerobic exercises. The same sympathetic stressor augments CAS to a greater extent 8-10 min post-race than pre-race, suggesting a greater post-exercise stiffening of central artery segments triggered by the same task
Ergogenic effects of citrulline supplementation on exercise performance and physiological indexes of exercise performance during cycling tests: A review
No full textObjective. - The supplementation of the nitric oxide precursor citrulline has been shown to boost athletic performance and recovery. Citrulline supplementation is appealing since it can be achieved legally through watermelon integration into the diet. However, the conditions where such supplementation improves exercise performance or physiological indexes related to exercise performance during cycling tests are confused and controversial since results differ according to the dosage, intake modality (chronic vs acute), the sport of interest, training status, and exercise intensity taken into account. Thus, an overview is needed to clarify the effects of citrulline during cycling tests. Moreover, the amount of watermelon required to achieve a minimum effective dosage of citrulline is unclear. Methods. - This review analyses studies that investigated the effects of citrulline intake, taken acutely vs chronically, individually vs combined with other amino acids, and assessed through cycling tests in trained and recreationally active individuals. Results. - Previous research allows differentiating the citrulline effects during long-lasting sub-maximal intensity exercises, single sprints, multiple supramaximal sprints, as well as on the subjective feelings of discomfort associated with cycling exercise. Conclusion. - Collectively, 6 g/day of citrulline supplementation for 7 days seems to improve sustained high-intensity laboratory time trials in both trained and recreationally active individuals. Causes may include physiological and psychological mechanisms associated with an improved energetic cost of cycling and a lower perception of fatigue. Performance improvements are also noticeable during single sprints in recreationally active individuals only as well as on the subjective perception of muscle fatigue and soreness during recovery. No improvements are noticeable on repeated sprints in trained individuals. This dosage of citrulline could be achievable through dietary watermelon supplementation symbolscript to 1.68 kg of "Tom Watson" and "Jubilee" fresh watermelon) without adding additional chemical synthesis-derived products. (c) 2022 Elsevier Masson SAS. All rights reserved
The effect of mental fatigue on half-marathon performance: a pragmatic trial
Full text linkPurpose: It is well established that mental fatigue impairs performance during lab-based endurance tests lasting less than 45 min. However, the effects of mental fatigue on longer duration endurance events and in field settings are unknown. The aim of this study was to investigate the effect of mental fatigue on performance during a half-marathon race. Methods: Forty-six male amateur runners (means ± SD: age 43.8 ± 8.6 years, V ̇ O2peak 46.0 ± 4.1 ml/kg/min) completed a half-marathon after being randomly allocated to performing a 50-min mentally fatiguing task (mental fatigue group) or reading magazines for 50 min (control group). Running speed, heart rate, and perceived effort were measured during the race. Results: Runners in the mental fatigue group completed the half-marathon approximately 4 min slower (106.2 ± 12.4 min) than those in the control group (102.4 ± 10.2 min), but this difference was not statistically significant (Cohen’s d = 0.333; p = 0.265). However, equivalence was not established [t(40.88) = 0.239, p = 0.594] and equivalence testing analysis excluded a beneficial effect of mental fatigue on half-marathon performance. Conclusion: Due to its posttest-only design and the achievable sample size, the study did not have enough power to provide evidence that the observed 4-min increase in half-marathon time is statistically significant. However, equivalence testing suggests that mental fatigue has no beneficial effect on half-marathon performance in male amateur runners, and a harmful effect cannot be excluded. Overall, it seems prudent for endurance athletes to avoid mentally fatiguing tasks before competitions
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
Uphill versus downhill high-intensity training effectiveness in preserving vascular function and exercise performance in runners who reduce their regular endurance training
No full textPurposeThe COVID-19 restrictions have limited outdoor physical activities. High-intensity training (HIT) may be a valid indoor alternative. We tested whether an indoor HIT is effective in maintaining vascular function and exercise performance in runners who reduce their usual endurance training, and whether a downhill HIT is as effective as an uphill one for such purposes. MethodsSixteen runners performed the same 6-week HIT either uphill (UP, eight runners) or downhill (DOWN, eight runners). Eight runners continuing their usual endurance training acted as a control group (CON). The following data were collected before vs after our HIT: vascular conductance during rapid leg vasodilation to assess vasodilation capacity; V?O-2max through running incremental test to exhaustion; 2000 m running time; neuromuscular indexes related to lower-limb muscle strength. ResultsBoth uphill and downhill HIT failed in maintaining the pre-HIT leg vasodilation capacity compared to CON, which was, however, blunted more after uphill than downhill HIT. V?O-2max and 2000 m time were similar after downhill HIT compared to CON, and augmented after uphill HIT compared to CON and DOWN. Indexes of lower-limb muscle strength were similar before vs after HIT and among groups. ConclusionOur HIT was ineffective in maintaining the pre-HIT leg vasodilation capacity compared to runners continuing their usual low-intensity endurance training, but did not lead to reductions in V?O-2max, 2000 m time performance, and indexes related to lower-limb muscle strength. Our data show an appealing potential for preserving exercise performance with low cardiorespiratory effort via downhill running
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effects of prefrontal repetitive transcranial magnetic stimulation on the autonomic regulation of cardiovascular function.
No full textSeveral protocols based on repetitive transcranial magnetic stimulation (rTMS) have been proposed for treatment of a variety of neurological disorders. Despite the widespread use, little is known about the effects of rTMS on the autonomic nervous control of the cardiovascular system. Twelve volunteers underwent rTMS sessions consisted in 8-min baseline recording, 8-min 0.7-Hz rTMS stimulation at 100 % of the motor cortex excitability threshold on the prefrontal cortex of one randomly assigned hemisphere. After 8-min recovery, the same procedure was performed on the contra-lateral hemisphere. Non-invasive (Portapres device) beat-by-beat blood pressure and heart period time series were recorded and analyzed by spectral and cross-spectral analysis in the low-frequency (LF ≈ 0.1 Hz) and in the high-frequency (HF = respiratory frequency) range. Repetitive TMS, particularly after stimulation of the right hemisphere, induced a slight increase in the parasympathetic drive and no effects on the sympathetic activity. There was a significant bradycardia after stimulation on the right hemisphere, not significant bradycardia after left stimulation. LF/HF ratio was 3.8 ± 2.1 during baseline and changed to 1.9 ± 0.6 during rTMS on the left and to 1.6 ± 0.6 during rTMS on the right. No significant changes were observed in blood pressure. Low-frequency rTMS of the prefrontal cortex induces a slight parasympathetic activation and no changes in the sympathetic function
Half marathon induces changes in central control and peripheral properties of individual motor units in master athletes
No full textAcute changes in central control and peripheral properties of motor units following a half-marathon has never been examined in master athletes. Therefore, the main purpose of this study was to estimate the firing properties and twitch characteristics of motor units after a 21-km race in a group of ten trained older adults. High-density surface EMG decomposition was used to identify motor unit activity during a submaximal contraction of the tibialis anterior muscle before and after the half marathon. The area of the estimated motor unit twitch profile was found smaller after the race (P = 0.039). This reduction in contractile efficiency was compensated by a significant increase in the initial and average discharge rate of the identified motor units (P < 0.001). By estimating the amount of shared and independent synaptic input to tibialis anterior motor neurons, we demonstrated that adaptations in the discharge properties of master athletes’ motor units are the likely consequence of an increased net excitatory synaptic drive to the motor neuron pool. These findings suggest a potential role of long-distance running in ameliorating declines in muscle function of older adults by enhancing the neural drive to muscle
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