1,721,049 research outputs found
Myoelectric Fatigue Profiles of Three Knee Extensor Muscles
No full textAims of the present study were to: 1) investigate the differences between the myoelectric fatigue profiles of the vasti muscles of the quadriceps during electrically evoked contractions; 2) compare the myoelectric fatigue profiles of the vasti muscles between sedentary subjects and rowers; 3) analyze motor unit activation order during stimulation of the vasti muscles. In nine sedentary subjects and nine rowers surface EMG signals were detected during electrically elicited contractions of the following three muscles: vastus medialis obliquus (VMO), vastus lateralis (VL), and vastus medialis longus (VML). M-waves were recorded as the muscles were stimulated with both variable (increasing-decreasing) and constant stimulation intensities. Changes in M-wave conduction velocity (CV) during trains with non-constant current were adopted for the study of the motor unit recruitment order. Rates of change of myoelectric signal variables were adopted to assess myoelectric manifestations of fatigue during stimulation trains with constant current. We found that: 1) VL muscle was more fatigable than vastus medialis muscles; 2) VL and VML muscles of rowers resulted less fatigable than sedentary subjects; and 3) in the three muscles, motor units tended to be recruited in order of increasing CV and derecruited in order of decreasing CV with increasing/decreasing stimulation current
Serum adiponectine levels in hypogonadal males: influence of testosterone replacement therapy.
No full textOBJECTIVE: Adiponectin is an adipocyte-specific secretory protein which exhibits antiatherogenic, anti-inflammatory and antidiabetic properties. We hypothesized that testosterone plays an important role in the regulation of its secretion in humans, as adiponectin concentrations are higher in women than in men and as testosterone administration is accompanied by a reduction in serum adiponectin in animals and by reduced protein secretion in cultured adipocytes. This study aimed to evaluate adiponectin levels in hypogonadal men prior to and during testosterone replacement therapy. SUBJECTS AND METHODS: In a retrospective study, adiponectin, total and free testosterone, oestradiol, SHBG, total cholesterol and triglyceride levels were evaluated in 31 hypogonadal men [HM; age, mean +/- SEM: 36.5 +/- 2.4 years; body mass index (BMI) 24.6 +/- 0.8 kg/m2] and 29 weight-matched eugonadal men (EM; age 30.8 +/- 1.5 years; BMI 23.4 +/- 0.6 kg/m2). In 13 HM (age 33.9 +/- 3.2 years; BMI 24.2 +/- 0.9 kg/m2) the same parameters were also evaluated after 6 months of testosterone replacement therapy. Correlation analysis between adiponectin and hormonal, biochemical and anthropometric parameters was performed in all subjects. RESULTS: Testosterone, free testosterone and oestradiol concentrations were significantly lower in HM than in EM (4.4 +/- 0.4 nmol/l, 78.4 +/- 10.9 pmol/l and 36.1 +/- 3.0 pmol/l, respectively, in HM vs. 21.9 +/- 0.7 nmol/l, 507.9 +/- 13.8 pmol/l and 65.2 +/- 1.8 pmol/l, respectively, in EM, P < 0.0001), while SHBG levels in HM were higher than in EM (54.4 +/- 7.5 vs. 30.9 +/- 2.2 nmol/l, P < 0.005). Serum adiponectin levels in HM were significantly higher than in EM (9.53 +/- 0.73 vs. 6.80 +/- 0.55 microg/ml, P < 0.01). Calculation of the Pearson coefficient showed that adiponectin levels in HM were not correlated with any of the anthropometric and hormonal parameters examined, but showed a significant negative correlation with serum triglycerides (r = -0.38, P < 0.05). Serum adiponectin levels were negatively correlated with body weight (r = -0.41, P < 0.05) in EM but not with other anthropometric, hormonal or biochemical parameters. Six months after initiation of testosterone replacement therapy, which increased testosterone and free testosterone levels to the normal range, adiponectin levels were significantly reduced in HM (6.37 +/- 0.93 vs. 9.26 +/- 1.01 microg/ml, P < 0.01) and similar to those recorded in EM. CONCLUSIONS: Compared to eugonadal subjects, hypogonadal men show higher adiponectin levels which are reduced by testosterone replacement therapy. This study indicates that testosterone exerts a regulatory role on adiponectin secretion in humans
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
Effects of Short-Term Dexamethasone Administration on Corticospinal Excitability
No full textPurpose: The short-term administration of glucocorticoids increases maximal voluntary force in healthy humans, but the underlying mechanisms remain poorly understood. The present study investigated the glucocorticoid effects on spinal and corticospinal pathways and on electromechanical properties of the tibialis anterior muscle in response to nerve stimulation.
METHODS:
Twelve healthy men participated in a single-blind randomized study to receive either dexamethasone (8 mg · d(-1), n = 8 subjects) or placebo (n = 4 subjects) for 7 d. Group Ia afferent and corticospinal pathways were assessed, respectively, by recording the amplitude of the Hoffmann (H) reflex and motor-evoked potential (MEP) by transcranial magnetic stimulation. The ankle dorsiflexor torque and EMG activity during a maximal voluntary contraction (MVC) and muscle twitch evoked by electrical stimulation were also assessed before and after the intervention.
RESULTS:
The MVC torque (+14%) and the associated tibialis anterior EMG (+16%) increased after glucocorticoid treatment (P 0.05). The H-reflex amplitude did not change (P = 0.58), but the MEP threshold was significantly (P = 0.008) reduced after treatment. Moreover, the slope of the MEP input-output relation and the silent period/MEP ratio increased (P = 0.049) and decreased (P = 0.029), respectively, after treatment. The amount of change in MEP amplitude and MVC torque were positively associated (r(2) = 0.59) for the dexamethasone group.
CONCLUSION:
This is the first study indicating that short-term glucocorticoid administration in healthy subjects increased corticospinal excitability that contributed to enhance MVC torque
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
Spinal involvement and muscle cramps in electrically elicited muscle contractions
No full textElectrical stimulation of innervated muscles has been investigated for many decades with alternations of high and low clinical interest in the fields of rehabilitation medicine and sports sciences. Early work demonstrated that afferent fibers have lower thresholds and are usually activated first (therefore eliciting an H-reflex). In the case of nerve trunk stimulation, the order of recruitment is mostly conditioned by the axonal dimension and excitability threshold. In the case of muscle motor point stimulation, the spatial distribution of nerve branches plays a predominant role. Sustained stimulation produces a progressive increase of force that is often maintained in subsequent voluntary activation by stroke patients. This observation suggested a facilitation mechanism at the spinal and/or supraspinal level. Such facilitation has been observed in healthy subjects as well, and may explain the generation of cramps elicited during stimulation and sustained for dozens of seconds after the stimulation has been interrupted. The most recent interpretations of facilitation resulting from peripheral stimulation focused on presynaptic (potentiation of neurotransmitter release from afferent fibers) or postsynaptic (generation of "persistent inward currents" in spinal motor neurons or interneurons) mechanisms. The renewed attention to these phenomena is once more increasing the interest toward electrical stimulation of the neuromuscular system. This is an opportunity for a structured investigation of the field aimed to resolving elements of confusion and controversy that still plague this area of electrophysiolog
Dispelling 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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