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21.
Two mechanisms have been suggested to explain stretching-induced maximum force depression: a mechanical alteration in the stretched muscle and an impairment of neural activation. Electrical stimulation allows standardization of the level of muscle activation without being limited by neural control. The aim of this study was to evaluate the stretching-induced changes in the electrical and mechanical properties of muscle during electrically elicited contractions. Twelve participants (age 22 +/- 1 years; body mass 75 +/- 2 kg; stature 1.79 +/- 0.02 m; mean +/- standard error) underwent six electrical stimulations of the medial gastrocnemius muscle before and after stretching. During the contractions, surface electromyogram (EMG) and mechanomyogram (MMG) were recorded simultaneously together with force. After stretching we found: (i) no differences in EMG parameters; (ii) MMG amplitude decreased by 4 +/- 1% (P < 0.05); and (iii) the peak force, the peak rate of force development, and the acceleration peak of force development decreased by 12 +/- 3%, 14 +/- 1%, and 24 +/- 5%, respectively (P < 0.05). In conclusion, acute passive stretching did not change EMG properties but altered the mechanical characteristics of the contracting muscle. Indeed, muscle force-generating capacity and stiffness of the muscle-tendon unit were significantly impaired. 相似文献
22.
Cadore E Lhullier F Brentano M Silva E Ambrosini M Spinelli R Silva R Kruel L 《Journal of sports sciences》2008,26(10):1067-1072
The aim of present study was to examine the relationships between serum and salivary values of free testosterone, dehydroepiandrosterone, and cortisol before and after a session of resistance exercise. Twenty-eight healthy men (mean age 40 years, s = 4) participated in the present study. Serum and salivary samples were collected at rest and after a multiple-sets resistance exercise protocol, of approximately 25 minutes duration. Concentrations of free testosterone, dehydroepiandrosterone, and cortisol were measured using radioimmunoassay kits. No significant correlation was observed between serum free testosterone and salivary testosterone (r = 0.22 to 0.26, P > 0.05). Serum cortisol was significantly correlated with salivary cortisol before (r = 0.52, P = 0.005) and after (r = 0.62, P = 0.001) the exercise protocol. Serum and salivary concentrations of dehydroepiandrosterone were significantly correlated before (r = 0.68, P < 0.001) and after (r = 0.7, P < 0.001) exercise. The results of the present study suggest that even under exercise conditions, the salivary values of cortisol and dehydroepiandrosterone can reflect the behaviour of these hormones in blood. However, further studies are necessary to verify if salivary testosterone reflects the behaviour of serum free testosterone during resistance exercise. 相似文献
23.
Elena Seminati Dario Cazzola Ezio Preatoni Grant Trewartha 《Sports biomechanics / International Society of Biomechanics in Sports》2017,16(1):58-75
Tackling in Rugby Union is an open skill which can involve high-speed collisions and is the match event associated with the greatest proportion of injuries. This study aimed to analyse the biomechanics of rugby tackling under three conditions: from a stationary position, with dominant and non-dominant shoulder, and moving forward, with dominant shoulder. A specially devised contact simulator, a 50-kg punch bag instrumented with pressure sensors, was translated towards the tackler (n = 15) to evaluate the effect of laterality and tackling approach on the external loads absorbed by the tackler, on head and trunk motion, and on trunk muscle activities. Peak impact force was substantially higher in the stationary dominant (2.84 ± 0.74 kN) than in the stationary non-dominant condition (2.44 ± 0.64 kN), but lower than in the moving condition (3.40 ± 0.86 kN). Muscle activation started on average 300 ms before impact, with higher activation for impact-side trapezius and non-impact-side erector spinae and gluteus maximus muscles. Players’ technique for non-dominant-side tackles was less compliant with current coaching recommendations in terms of cervical motion (more neck flexion and lateral bending in the stationary non-dominant condition) and players could benefit from specific coaching focus on non-dominant-side tackles. 相似文献
24.
The present paper provides a qualitative and quantitative approach to natural lighting design for the Hall of Two Hundred in Palazzo Vecchio (the present town hall) in Florence. Starting from transient simulation of natural lighting inside the Hall in its present state, using the commercial software Radiance, a design proposal was suggested, detecting the optimal conditions for tapestry conservation and maintenance and taking into account their periodical exhibition, designing a proper wall show-case solution. The suggested design does not modify the architecture and structure of the building. The distribution of natural lighting and consequently of the illuminance and luminance inside the ambient, suggested a solution for exhibition of the historical tapestries, which can guarantee not only tapestry conservation but also the Hall structure and its present uses. The design proposal provides a comfortable lighting environment, rehabilitation and improvement of the historical perception and sight of these works of art, under variable sun and sky conditions throughout the year. 相似文献
25.
Nicole Rodruigez Michel Lavacry Michel Banckaert 《Educational Media International》2013,50(4):200-207
Abstract This article discusses the application of digital video to multimedia, and looks at the pros and cons of two different approaches. It also considers the standards of equipment for various uses. 相似文献
26.
27.
Michel Pagnier 《Higher Education Quarterly》1973,27(3):323-345
28.
Elena Pelzer 《Communication Research Reports》2019,36(2):136-147
Surveys on choices oftentimes rely on Likert-type scales. However, they prevent researchers from identifying the relative importance of different stimulus features for the choice decision. Here, it is shown that conjoint analysis offers a variety of advantages emerging from its use of questions that force the subject to trade off conflicting attribute levels. This study discusses some problems of Likert-type scale measures and shows when conjoint analysis may solve some of these problems. Differences between measurements are illustrated in a uses and gratifications study, assessing convergent validity on Likert-type scale measures with traditional conjoint analysis and choice-based conjoint analysis. Results show that subjects prefer “cognitive needs” by Likert-type scale measures against “tension release needs” by both conjoint analyses. The different outcome is independent from linguistic variation and from dual-process models of information processing. Implications for communication research are discussed. 相似文献
29.
Elena Longhi Irene Senna Nadia Bolognini Hermann Bulf Paolo Tagliabue Viola Macchi Cassia Chiara Turati 《Child development》2015,86(2):632-641
The development of human body perception has long been investigated, but little is known about its early origins. This study focused on how a body part highly relevant to the human species, namely the hand, is perceived a few days after birth. Using a preferential‐looking paradigm, 24‐ to 48‐hr‐old newborns watched biomechanically possible and impossible dynamic hand gestures (Experiment 1, N = 15) and static hand postures (Experiment 2, N = 15). In Experiment 1, newborns looked longer at the impossible, compared to the possible, hand movement, whereas in Experiment 2 no visual preference emerged. These findings suggest that early in life the representation of the human body may be shaped by sensory‐motor experience. 相似文献
30.