1,720,965 research outputs found
Prolonged static stretching causes acute, non-metabolic fatigue and impairs exercise tolerance during severe intensity cycling
Full text linkWe tested the hypothesis that static stretching, an acute, non-metabolic fatiguing intervention, reduces exercise tolerance by increasing muscle activation and affecting muscle bioenergetics during cycling in the "severe" intensity domain. Ten active men (24±2 years, 74±11 kg, 176±8 cm) repeated an identical constant load cycling test, two tests were done in control conditions and two after stretching, that caused a 5% reduction of maximal isokinetic sprinting power output. We measured: i) oxygen consumption (VO2); ii) electromyography: iii) deoxyhemoglobin iv) blood lactate ([La-]); v) time to exhaustion (TTE) vi) perception of effort. Finally, VO2 and deoxyhemoglobin kinetics were determined. Force reduction following stretching was accompanied by augmented muscle excitation at a given workload (p=0.025), and a significant reduction in TTE (p=0.002). The time to peak of VO2 was reduced by stretching (p=0.034), suggesting an influence of the increased muscle excitation on the VO2 kinetics. Moreover, stretching was associated with a mismatch between O2 delivery and utilization during the on-kinetic, increased perception of effort and [La-], that are all compatible with an increased contribution of the glycolytic energy system to sustain the same absolute intensity. These results suggest a link between exercise intolerance and the decreased ability to produce force. Novelty bullets: • We provided the first characterization of the effects of prolonged stretching on the metabolic response during severe cycling. • Stretching reduced maximal force, augmented muscle activation in turn increasing the metabolic response to sustain exercise
An Intensity-dependent Slow Component of HR Interferes with Accurate Exercise Implementation in Postmenopausal Women
Full text linkHeart rate (HR) targets are commonly used to administer exercise intensity in sport and clinical practice. Yet, as exercise protracts, a time-dependent dissociation between HR and metabolism can lead to a mis-prescription of the intensity ingredient of the exercise dose. Purpose: we tested the hypothesis that a slow component of HR (i.e. scHR) occurs in all intensity domains, greater than the slow component of oxygen uptake (scV[Combining Dot Above]O2), and we developed an equation to predict it across exercise intensities. Method: 18 healthy, postmenopausal women (54 ± 4 years) performed on a cycle-ergometer: i) a ramp incremental test for thresholds and V[Combining Dot Above]O2max detection; ii) 30-min constant-work exercise at 40, 50, 60, 70, and 80 %V[Combining Dot Above]O2max for the measurement of scHR, scV[Combining Dot Above]O2, stroke volume (SV) and body temperature (T°). scHR and scV[Combining Dot Above]O2 were compared by two-way RM-ANOVA (intensity and variable); Pearson correlation was calculated between the slow component of all variables, relative intensity, and domain; scHR (b·min-2) was predicted with a linear model based on exercise intensity relative to the respiratory compensation point (RCP). Results: A positive scHR was present in all domains, twice the size of scV[Combining Dot Above]O2 (p < 0.001) and significantly correlated with the slow components of V[Combining Dot Above]O2 (r2 = 0.46), T° (r2 = 0.52) and with relative intensity (r2 = 0.66). A linear equation accurately predicts scHR based on %RCP (r2 = 0.66, SEE = 0.15). Discussion: A mismatch exists between the slow components of HR and metabolic intensity. Whenever exercise is prescribed based on HR, target values should be adjusted over time to grant that the desired metabolic stimulus is maintained throughout the exercise session
Performance and anthropometrics of classic powerlifters: which characteristics matter?
No full textThe purpose of this study is: (a) provide normative performance and anthropometric data of Southern European classic powerlifters of both sexes; (b) determine the possible relationships between these variables and performance; and (c) develop population-specific predictive equations for single lifts and overall powerlifting performance. During an unofficial national-level competition, we recruited 74 athletes (51 men and 23 women) and recorded their individual, anthropometric, and performance characteristics and divided them into sex and 2 performance categories based on their Wilks points. Weaker (<370 Wilks points) and stronger (>370 Wilks points) athletes of both sexes were compared by two-way analysis of variance. Simple correlation and multiple linear regression between individual/anthropometric characteristics and performance were modeled. We applied a step-forward multiple linear regression model to predict single lifts and overall performance. All parameters significantly differed between sexes (p < 0.05 for all comparisons). Stronger male athletes had a significantly larger neck (42 ± 2.8 cm; effect size [ES] = 0.59), and flexed (40.6 ± 3.3 cm; ES = 1.18) and relaxed upper-arm (37.5 ± 3.1 cm; ES = 1.34) and thigh girths (63.6 ± 7.0 cm; ES = 0.77) compared to weaker male athletes. Furthermore, stronger women had significantly larger flexed (32.6 ± 3.3 cm; ES = 0.88) and relaxed upper-arm (33 ± 1.5 cm; ES = 2.28) and chest girths (99.3 ± 9.2 cm; ES = 1.10) compared to weaker female athletes. A combination of experience, fat mass, and upper-limb and lower-limb muscle mass indexes can accurately and precisely predict overall and individual lift performance (r ≥ 0.83 for all the predictions). This is the first study to provide normative performance and anthropometric data in Southern European male and female powerlifters
Application and performance of heart-rate-based methods to estimate oxygen consumption at different exercise intensities in postmenopausal women
No full textPurpose: Heart rate (HR) is a widespread method to estimate oxygen consumption ([Formula: see text]O2), exercise intensity, volume, and energy expenditure. Still, accuracy depends on lab tests or using indexes like HRnet and HRindex. This study addresses HR indexes' applicability in postmenopausal women (PMW), who constitute over 50% of the aging population and may have unique characteristics (e.g., heart size) affecting HR use. Methods: Fourteen PMW underwent a cycling ramp incremental test to establish the relationships between [Formula: see text]O2 (in MET) and absolute HR, HRnet, and HRindex. In a second group of ten PMW, population-specific and general equations were tested to predict MET and energy expenditure during six constant work exercises at various intensities. Pulmonary gas exchange and HR were continuously measured using a metabolic cart. Correlations, Bland-Altman analysis, and two-way RM-ANOVA were used to compare estimated and measured values. Results: Strong linear relationships between the three HR indexes and MET were found in Group 1. In Group 2, population-specific equations showed medium-to-high correlations, precision, and no significant biases when estimating MET and energy expenditure. HRnet and HRindex outperformed absolute HR in accuracy. General HR equations had similar correlations but exhibited larger biases and imprecision. Statistical differences between measured and estimated values were observed at all intensities with general equations. Conclusion: This investigation confirms the suitability of HR for estimating aerobic metabolism in one of the most significant aging populations. However, it emphasizes the importance of considering individual variability and developing population-specific models when utilizing HR to infer metabolism
Indexes of Fat Oxidation from Ramp vs. Graded Incremental Protocols in Postmenopausal Women
Full text linkThe maximal rate of fat oxidation (MFO, in g∙min−1) and the relative exercise intensity at which it occurs (FATmax, as %V̇O2max) are indexes of metabolic flexibility. The time-consuming, graded exercise protocol required for MFO/FATmax determination hinders the extensive use of these indexes for individualized exercise prescription and monitoring. Purpose: validate ramp testing for MFO and FATmax measures in postmenopausal women. Methods: Seventeen healthy women (age: 54 ± 4 years, BMI 22 ± 3 kg·m−2, and V̇O2max 36.4 ± 5.3 mL·min−1), who were 4 ± 3 years from menopause, performed on a cycle-ergometer, a ramp, and a graded incremental test. Based on V̇O2 and respiratory exchange ratio from the ramp and graded protocol (i.e., the 5th minute of each step), MFO and FATmax were determined. Data from the two protocols were compared using paired t-tests, linear regression, and Bland–Altman analysis. Results: The MFO measured with a ramp protocol was not different from (0.24 ± 0.09 vs. 0.20 ± 0.08 g·min−1, p = 0.10), and moderately associated with, that of the graded protocol (r2 = 0.46). FATmax occurred at similar exercise intensity for both protocols (47.8 ± 5.1 vs. 47.5 ± 4.3 %V̇O2max, p = 0.91, r2 = 0.52). The comparison of MFO and FATmax across the protocols yields a non-significant bias but a relatively large limit of agreement (respectively, 0.05 g·min−1, LOA = −0.08, and 0.19 g·min−1; 0.3 %V̇O2max, LOA = −7.8, and 10.6 %V̇O2max). Conclusions: In postmenopausal women, ramp testing offers a valid alternative to the graded protocol for identifying MFO and FATmax. The availability of a time- and cost-efficient approach, which can be incorporated into standard ramp incremental testing, can facilitate using these indexes of metabolic flexibility in research and medicine
Easy Prediction of the Maximal Lactate Steady-State in Young and Older Men and Women
No full textMaximal Lactate steady-state (MLSS) demarcates sustainable from unsustainable exercise and is used for evaluation/monitoring of exercise capacity. Still, its determination is physically chal-lenging and time-consuming. This investigation aimed at validat-ing a simple, submaximal approach based on blood lactate accu-mulation ([ increment lactate]) at the third minute of cycling in a large co-hort of men and women of different ages. 68 healthy adults (40 male, 28 female, 43 +/- 17 years (range 19 -78), VO2max45 +/- 11 ml-1 center dot kg-1 center dot 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. During each trial, [ increment lactate] was calculated as the dif-ference between the third minute and baseline. A multiple linear regression was computed to estimate MLSS based on [ increment lactate], subjects` gender, age and the trial PO. The estimated MLSS was compared to the measured value by paired t-test, correlation, and Bland-Altman analysis. The group mean value of estimated MLSS was 180 +/- 51 W, not significantly different from (p = 0.98) and highly correlated with (R2 = 0.89) measured MLSS (180 +/- 54 watts). The bias between values was 0.17 watts, and imprecision 18.2 watts. This simple, submaximal, time-and cost-efficient test accurately and precisely predicts MLSS across different samples of healthy individuals (adjusted R2 = 0.88) and offers a practical and valid alternative to the traditional MLSS determination
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
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
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