1,720,971 research outputs found
A regression method for the power–duration relationship when both variables are subject to error
No full textPurpose: The power–duration relationship has been variously modelled, although duration must be acknowledged as the dependent variable and is supposed to represent the only source of experimental error. However, there are certain situations, namely extremely high power outputs or outdoor field conditions, in which the error in power output measurement may not remain negligible. The geometric mean (GM) regression method deals with the assumption that also the independent variable is subject to a certain amount of experimental error, but has never been utilized in this context.
Methods: We applied the GM regression method for the two- and three-parameter critical power models and tested it against the usual weighted least square (WLS) procedure with our previous published data.
Results: There were no significant differences between parameter estimates of WLS and GM. Bias and limit of agreements between the two methods were low, while correlation coefficients were high (0.85–1.00).
Conclusions: GM provided equivalent results with respect to WLS in fitting the critical power model to experimental data and for its conceptual characteristics must be preferred wherever concerns on the precision of P measurement are present, such as for in-field power meters
Energy balance analysis suggests that lactate is not a direct cause of the slow component of oxygen uptake kinetics
Full text linkPurpose: The mechanisms of oxygen uptake (V ̇O2) slow component in the severe exercise intensity domain are still a matter of debate. We tested the hypothesis that the rate of blood lactate ([La]) accumulation above maximal lactate steady state (MLSS) is a major cause of V ̇O2 slow component. Methods: On 13 males exercising on a cycle-ergometer, we measured gas exchanges, heart rate, and [La] during maximal incremental exercise test to determine maximal aerobic power (w.max) and at constant power exercise tests at 60%, 65%, 70%, and 80% of w.max. Results: Maximal V ̇O2 was 3.19 ± 0.37 l·min−1, w.max was 283 ± 28 W. At 60% w.max all variables attained steady state in all subjects. Power at MLSS was 177 ± 21 W. At 80% w.max a clear V ̇O2 slow component was observed in all subjects, exercise lasted 11.3 ± 3.1 min and [La] was 7.4 ± 2.2 mmol at 5 min and 11.5 ± 3.6 mmol at 10 min. The energy balance computed at 80% w.max resulted compatible with the principles of the energetics of muscular exercise, if we assume linear [La] increase, and thus constant metabolic power provided by [La] accumulation. Conversely, the metabolic power provided by V ̇O2 slow component increases with time. This contrast is incompatible with the tested hypothesis that consequently must be rejected. Conclusion: This study excluded [La] accumulation as a main cause of V ̇O2 slow component
Baroreflex dynamics during the rest to exercise transient in acute normobaric hypoxia in humans
Full text linkPurpose We hypothesised that during a rest-to-exercise transient in hypoxia (H), compared to normoxia (N), (i) the initial baroreflex sensitivity (BRS) decrease would be slower and (ii) the fast heart rate (HR) and cardiac output (CO) response would have smaller amplitude (A(1)) due to lower vagal activity in H than N. Methods Ten participants performed three rest-to-50 W exercise transients on a cycle-ergometer in N (ambient air) and three in H (inspired fraction of O-2 = 0.11). R-to-R interval (RRi, by electrocardiography) and blood pressure profile (by photo-plethysmography) were recorded non-invasively. Analysis of the latter provided mean arterial pressure (MAP) and stroke volume (SV). CO = HRSV. BRS was calculated by modified sequence method. Results Upon exercise onset in N, MAP fell to a minimum (MAPmin) then recovered. BRS decreased immediately from 14.7 +/- 3.6 at rest to 7.0 +/- 3.0 ms mmHg(-1) at 50 W (p < 0.01). The first BRS sequence detected at 50 W was 8.9 +/- 4.8 ms mmHg(-1) (p < 0.05 vs. rest). In H, MAP showed several oscillations until reaching a new steady state. BRS decreased rapidly from 10.6 +/- 2.8 at rest to 2.9 +/- 1.5 ms mmHg(-1) at 50 W (p < 0.01), as the first BRS sequence at 50 W was 5.8 +/- 2.6 ms mmHg(-1) (p < 0.01 vs. rest). CO-A(1) was 2.96 +/- 1.51 and 2.31 +/- 0.94 l min(-1) in N and H, respectively (p = 0.06). HR-A(1) was 7.7 +/- 4.6 and 7.1 +/- 5.9 min(-1) in N and H, respectively (p = 0.81). Conclusion The immediate BRS decrease in H, coupled with similar rapid HR and CO responses, is compatible with a withdrawal of residual vagal activity in H associated with increased sympathetic drive
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
The current use of wearable sensors to enhance safety and performance in breath-hold diving: A systematic review
No full textINTRODUCTION: Measuring physiological parameters at depth is an emergent challenge for athletic training, diver's safety and biomedical research. Recent advances in wearable sensor technology made this challenge affordable; however, its impact on breath-hold diving has never been comprehensively discussed. METHODS: We performed a systematic review of the literature in order to assess what types of sensors are available or suitable for human breath-hold diving, within the two-fold perspective of safety and athletic performance. RESULTS: In the 52 studies identified, sensed physiological variables were: electrocardiogram, body temperature, blood pressure, peripheral oxygen saturation, interstitial glucose concentration, impedance cardiography, heart rate, body segment inertia and orientation. CONCLUSIONS: Limits and potential of each technology are separately reviewed. Inertial sensor technology and transmission pulse oximetry could produce the greatest impact on breath-hold diving performances in the future
Breath holding as an example of extreme hypoventilation: experimental testing of a new model describing alveolar gas pathways
No full textNew Findings: What is the central question of this study? We modelled the alveolar pathway during breath holding on the hypothesis that it follows a hypoventilation loop on the O2–CO2 diagram. What is the main finding and its importance? Validation of the model was possible within the range of alveolar gas compositions compatible with consciousness. Within this range, the experimental data were compatible with the proposed model. The model and its characteristics might allow predictions of alveolar gas composition whenever the alveolar ventilation goes to zero; for example, static and dynamic breath holding at the surface or during ventilation/intubation failure in anaesthesia. Abstract: According to the hypothesis that alveolar partial pressures of O2 and CO2 during breath holding (BH) should vary following a hypoventilation loop, we modelled the alveolar gas pathways during BH on the O2–CO2 diagram and tested it experimentally during ambient air and pure oxygen breathing. In air, the model was constructed using the inspired and alveolar partial pressures of O2 ((Formula presented.) and (Formula presented.), respectively) and CO2 ((Formula presented.) and (Formula presented.), respectively) and the steady-state values of the pre-BH respiratory exchange ratio (RER). In pure oxygen, the model respected the constraint of (Formula presented.). To test this, 12 subjects performed several BHs of increasing duration and one maximal BH at rest and during exercise (30 W cycling supine), while breathing air or pure oxygen. We measured gas flows, (Formula presented.) and (Formula presented.) before and at the end of all BHs. Measured data were fitted through the model. In air, (Formula presented.) = 150 ± 1 mmHg and (Formula presented.) = 0.3 ± 0.0 mmHg, both at rest and at 30 W. Before BH, steady-state RER was 0.83 ± 0.16 at rest and 0.77 ± 0.14 at 30 W; (Formula presented.) = 107 ± 7 mmHg at rest and 102 ± 8 mmHg at 30 W; and (Formula presented.) = 36 ± 4 mmHg at rest and 38 ± 3 mmHg at 30 W. By model fitting, we computed the RER during the early phase of BH: 0.10 [95% confidence interval (95% CI) = 0.08–0.12] at rest and 0.13 (95% CI = 0.11–0.15) at 30 W. In oxygen, model fitting provided (Formula presented.) : 692 (95% CI = 688–696) mmHg at rest and 693 (95% CI = 689–698) mmHg at 30 W. The experimental data are compatible with the proposed model, within its physiological range
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