Changes in swimming technique during time to exhaustion at freely chosen and controlled stroke rates

Abstract

The aim of this study was to assess technical changes during constrained swimming in time-to-exhaustion tests. Ten swimmers of national standard performed a maximal 400-m front crawl and two sets of exhaustion tests at 95%, 100%, and 110% of mean 400-m speed. In the first set (free), swimmers had to maintain their speeds until exhaustion and mean stroke rate was recorded for each test. In the second set (controlled), the same speed and individual corresponding stroke rate were imposed. The durations of the exhaustion tests, relative durations of the stroke phases, and arm coordination were analysed. For each speed in the “controlled” set, the exhaustion tests were shorter. Moreover, variables were consistent, suggesting a stabilization of stroke technique. Under the free condition, stroke rate increased to compensate for the decrease in stroke length. At the same time, swimmers reduced the relative duration of their non-propulsive phases in favour of the propulsive phases. Thus, swimmers changed their arm coordination, which came close to an opposition mode. These two constraints enable swimmers both to maintain their stroking characteristics and develop compensatory mechanisms to maintain speed. Moreover, stroke rate can be seen as a useful tool for controlling arm technique during paced exercise.     

Kinesthetic Perception of the Vertical as a Function of Sport Experience

Abstract

Near-infrared spectroscopy is currently used to assess changes in the oxygen saturation of the muscle during exercise. The primary purpose of this study was to assess the reliability of near-infrared spectroscopy in determining muscle oxygen saturation (StO₂) in the vastus lateralis during cycling and the gastrocnemius during running for exercise intensities at lactate threshold and maximal effort. Test-retest reliability was determined from an intraclass correlation coefficient obtained from a one-way analysis of variance. Reliability of muscle StO₂ for the gastrocnemius at lactate threshold was R = .87, and R= .88 at maximal effort. Reliability of muscle StO₂ for the vastus lateralis at lactate threshold was R= .94 and R = .99 at maximal effort.     

Effects of volleyball match-induced fatigue on knee joint position sense

Abstract

It has been suggested that a greater number of injuries during the last third of practice sessions or matches could be related to alteration of lower limb neuromuscular control due to neuromuscular fatigue. This fatigue-related effect can be mediated by changes in joint proprioception. In athletes, the use of functional fatigue protocols could have the advantage of mimicking the demands of sporting activity, thus reflecting more specifically the changes in neuromuscular control and proprioception observed in sport settings. The purpose of the present study was to assess the effect of fatigue induced by a volleyball match on knee joint position sense in elite volleyball players. Seventeen female volleyball players aged 18.9±4.2 years from the Portuguese national team volunteered for the study. Knee joint position sense was evaluated by an open kinetic chain technique and active knee positioning, and was reported using absolute, relative, and variable angular errors. Joint position sense measures were obtained before and immediately after a simulated volleyball match of five sets. To ensure that the match was sufficiently intense to induce fatigue, the perceived exertion or exercise intensity was assessed at the end of the match using Borg’ s rating of perceived exertion (RPE) scale. All participants completed the volleyball match (90min duration), reaching or exceeding 15 on the RPE scale (15.59±0.71; range 15–17), equivalent to “hard/heavy work”. After the volleyball match, a significant increase in absolute (2.11°) and relative (1.71°) angular errors was detected. Match-induced fatigue significantly exacerbated the overestimation of the test position. Moreover, the reliability and accuracy in estimating knee angles decreased from rest to the fatigued state, as shown by the increase (264%) in variable error. Our results show that fatigue induced by a volleyball match has a marked effect on knee joint position sense in elite female volleyball players. Knee joint position sense was less accurate and less consistent after the volleyball match. Fatigue induced by a simulated competitive volleyball match resulted in proprioceptive deficits, decreasing sensorimotor system acuity in female volleyball players.     

Classifying documents with link-based bibliometric measures

Automatic document classification can be used to organize documents in a digital library, construct on-line directories, improve the precision of web searching, or help the interactions between user and search engines. In this paper we explore how linkage information inherent to different document collections can be used to enhance the effectiveness of classification algorithms. We have experimented with three link-based bibliometric measures, co-citation, bibliographic coupling and Amsler, on three different document collections: a digital library of computer science papers, a web directory and an on-line encyclopedia. Results show that both hyperlink and citation information can be used to learn reliable and effective classifiers based on a kNN classifier. In one of the test collections used, we obtained improvements of up to 69.8% of macro-averaged F ₁ over the traditional text-based kNN classifier, considered as the baseline measure in our experiments. We also present alternative ways of combining bibliometric based classifiers with text based classifiers. Finally, we conducted studies to analyze the situation in which the bibliometric-based classifiers failed and show that in such cases it is hard to reach consensus regarding the correct classes, even for human judges.     

Book reviews

Bazzana, André; Cressier, Patrice; and Guichard, Pierre. Les châteaux ruraux d'al‐Andalus. Histoire et archéologie des husūn du sud‐est de l'Espagne. Preface by Pierre Toubert (Série Archéologie, XI). Madrid: Publications de la Casa de Velázquez, 1988. 326pp; illustrations (plates, maps, tables); bibliography, index.

Tāha, CAbdulwāhid Dhanūn. The Muslim Conquest and Settlement of North Africa and Spain (Exeter Arabic and Islamic Series, 3). London: Routledge, 1989. xiv + 280pp; £49.50.

Leaman, Oliver. Averroes and his Philosophy Oxford: Clarendon Press, 1988. 204pp.; £25.

Mas^cūdî. The Meadows of Cold: the Abbasids. Ed. & tr. P. Lunde & C. Stone. London: Kegan Paul International, 1989. 469 pp., 2 maps; £30.

Sirat, Colette. La philosophie juive médiévale en terre d'Islam. Paris: Presses du CNRS, 1988. 278 pp.

Epalza, Míkel de and others. Baños Arabes en el país Valenciano. [Valencia], Generalitat Valenciana: Consellería de Cultura, Educado i Ciència, 1989.157 pp., plates, figures., maps (unnumbered).

Waines, David In a Caliph's Kitchen.Medieval Arabic Cooking for the Modern Gourmet. London: Riad el‐Rayyes Books, 1989. 112pp., many illustrations; £14.

Abed, Shukri B. Aristotelian Logic and the Arabic Language in Alfārābi. Albany: State University of New York Press, 1991. xxv+201pp., two appendices, bibliography, index.

Meyerson, Mark D. The Muslims of Valencia in the Age of Fernando and Isabel: Between Coexistence and Crusade. Berkeley: University of California Press, 1991. xi + 372 pp.

Zacour, Norman. Jews and Saracens in the Consilia of Oldradus de Ponte. Toronto: Pontifical Institute of Medieval Studies, 1990. x+144pp., index; paperback.