1,721,015 research outputs found
Neuromuscular performance after rapid weight loss in Olympic-style boxers
No full textThe present study investigated the effect of a 3% rapid weight loss (RWL) procedure on neuromuscular performance in elite, Olympic-style boxers. Nine boxers were randomly assigned to two experimental procedures (RWL and control, in a randomized counter-balance order) to perform 5-s maximum isometric voluntary contractions (MVC) of the dominant leg knee extensors prior to (MVC1), and following (MVC2), a sustained, isometric contraction at 70% MVC until exhaustion. The voluntary activation (VA) was determined using percutaneous muscle stimulation and interpolated twitch technique. High (at 80 Hz) and low (at 20 Hz) frequency tetanic impulses were also delivered before and after the sustained 70% MVC to assess peripheral fatigue. Hydration status, hemodynamic parameters, and lactate concentration were assessed throughout the study. Body-mass was reduced by ∼3% (during RWL) compared to control (p =.001). As a result of the RWL protocol, MVC1 force output was 12% lower and VA deficits of 7% were observed after the fatigue protocol compared to control (p =.001). Following RWL, time to exhaustion for the sustained 70% MVC was 69 ± 20 s compared to 86 ± 34 s for control (p =.020). Peak lactate production was 53% lower in RWL compared to control (p =.001). In conclusion, the 3% RWL procedure translated into significant decline in neuromuscular performance for both brief and sustained contractions in competitive boxers
Pathophysiological mechanisms of reduced physical activity: Insights from the human step reduction model and animal analogues
No full textPhysical inactivity represents a heavy burden for modern societies and is spreading worldwide, it is a recognised pandemic and is the fourth cause of global mortality. Not surprisingly, there is an increasing interest in longitudinal studies on the impact of reduced physical activity on different physiological systems. This narrative review focuses on the pathophysiological mechanisms of step reduction (SR), an experimental paradigm that involves a sudden decrease in participants' habitual daily steps to a lower level, mimicking the effects of a sedentary lifestyle. Analogous animal models of reduced physical activity, namely, the "wheel-lock" and the "cage reduction" models, which can provide the foundation for human studies, are also discussed. The empirical evidence obtained thus far shows that even brief periods of reduced physical activity can lead to substantial alterations in skeletal muscle health and metabolic function. In particular, decrements in lean/muscle mass, muscle function, muscle protein synthesis, cardiorespiratory fitness, endothelial function and insulin sensitivity, together with an increased fat mass and inflammation, have been observed. Exercise interventions seem particularly effective for counteracting these pathophysiological alterations induced by periods of reduced physical activity. A direct comparison of SR with other human models of unloading, such as bed rest and lower limb suspension/immobilisation, is presented. In addition, we propose a conceptual framework aiming to unravel the mechanisms of muscle atrophy and insulin resistance in the specific context of reduced ambulatory activity. Finally, methodological considerations, knowledge gaps and future directions for both animal and human models are also discussed in the review
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
Assessing Cardiac Electro-Mechanical Deconditioning during Bed Rest Using Smartphone's Inertial Sensors
No full textThis study evaluated the potential of using smartphone-acquired seismocardiographic (SCG) signals for monitoring cardiac deconditioning after prolonged bed rest (BR). Ten healthy volunteers were enrolled in a 10-day BR. By positioning a smartphone on subject's chest, 1-minute SCG was acquired before the BR (PRE), on the 10th day of BR (BR10), and one day after reambulation (R+1). Signals were pre-processed and automatic beat identification was performed. Heart rate and variability indices (SDAO-AO, RMSSD, SDAO-AO/RMSSD) were calculated. Isovolumetric contraction (IVC), aortic valve opening (AO) and closure (AC) points were identified on the SCG, from which amplitude difference (AMPAO-IVC) and slope were derived. Finally, linear (iKlin) and rotational (iKrot) kinetic energies were calculated. At BR10 sympathetic modulation at awakening increased. Also, SCG morphology was affected, with increased AMPAO-IVC and IVC-AO slope. Further, at BR10 changes in morphology recovered, while iKlin/iKrot ratio increased. These findings support smartphones' potential as portable and non-invasive cardiac health monitoring devices for cardiac deconditioning
Sex-based comparison of trunk flexors and extensors functional and contractile characteristics in young gymnasts
Full text linkPurpose. Gymnastics is a sport characterized by acrobatic and postural strength exercises that require great trunk muscles activation and control. Males and females can be characterized by different morphological and neuromuscular characteristics of such muscles, and this might be of importance for training and injury prevention. The aim of this study was to measure different aspects of trunk flexors and extensors characteristics in a sample of young female and male gymnasts. Methods. Twenty-eight sub-elite adolescent female (n = 14, 16 y, 14-17) and male (n = 14, 17 y, 14-18) gymnasts participated in this cross-sectional study. Tensiomyography was used to assess muscle contractile properties of the rectus abdominis (m.RA) and erector spinae (m.ES), while muscle thickness was assessed for abdominal muscles and lumbar multifidus (m.LM) with ultrasound. Flexors, extensors, and lateral endurance tests were performed. Results. Females presented smaller m.ES radial displacement (p < 0.001, p & eta;(2) = 0.535), smaller internal oblique thickness (p < 0.001, p & eta;(2) = 0.543), and shorter lateral endurance (p = 0.002, p & eta;(2) = 0.302). A significant side x sex interaction was found for the external oblique thickness (p = 0.004, p & eta;(2) = 0.276). Conclusion. Present findings report sex-based differences in abdominal and lumbar muscles characteristics and support the development of different sex-based training and rehabilitation protocols in adolescent gymnasts
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
Effects of marked skeletal muscle hypertrophy in humans on oxidative function in vivo and in vitro
No full textDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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