Éditeur(s) : HAL CCSD ACSM
Résumé : International audience
PURPOSE AND METHODS: This study was designed to compare the physiological responses and performance of well trained cyclists riding with two different chainring designs, round or eccentric, during a brief and intense cycling exercise: an "all-out" 1-km laboratory test. The eccentrically designed chainring was made of two crank arms sliding into each other, with the inside arm fixed on the center of the arm of a circular chainring and the outside arm sliding along the inside and revolving around an elliptical cam. This design increases crank arm length at the downstroke and decreases it during the upstroke, thus increasing and decreasing the torque. In terms of the chainring's revolution, the crank arm length at 0 degrees and 180 degrees is similar to the arm length of circular chainrings (175 mm). However, during the downstroke (0-180 degrees ), it increases to its maximum length of 200 mm at 90 degrees and then returns to its original length of 175 mm at 180 degrees. During the upstroke, it decreases to a minimum length of 150 mm at 270 degrees and then increases to 175 mm at 360 degrees. Eleven cyclists performed an all-out 1-km laboratory test using each chainring. The study was conducted over two consecutive weeks with the order of chainring use randomized. During all trials, ventilatory data were collected every minute using an automated breath-by-breath system. Heart rate was measured using a telemetry system. RESULTS: None of the cardiorespiratory variables showed significant differences between chainring trials. Performance, however, was significantly improved using the eccentric design (64.25 +/- 1.05 vs 69.08 +/- 1.38 s, P < 0.004, with the eccentric and the round design, respectively). CONCLUSION: We concluded that the eccentric chainring significantly improved the cycling performance during an all-out 1-km test. Further testing with indoor cycling specialists performing on a velodrome would be helpful to define the maximal possibilities of such a chainring.
Medicine & Science in Sports & exercise

hal-00720551
https://hal.univ-antilles.fr/hal-00720551
https://hal.univ-antilles.fr/hal-00720551/document
https://hal.univ-antilles.fr/hal-00720551/file/Article.pdf

Éditeur(s) : HAL CCSD Taylor & Francis: SSH Journals
Résumé : International audience
We analysed stroke phases and arm and leg coordination during front crawl swimming with and without a wet suit. Twelve nationally and internationally ranked French male triathletes performed three swim trials in randomized order using the front crawl stroke with and without a wet suit. All triathletes swam at three different swim velocities, corresponding to the paces appropriate for the 800 m (V800), 100 m (V100) and 50 m (V50) events. The different stroke phases and arm and leg coordination were identified by video analysis. Arm coordination was quantified using a new index of coordination, which expresses the three major modalities of opposition, catch-up and superposition in swimming. At all swim velocities, no significant differences in leg movements with or without the wet suit were noted. However, the wearing of the wet suit was associated with a significantly greater stroke length at the paces appropriate for the 100 and 50 m events (+3.46% and +3.10% at V100 and V50, respectively; P<0.01); a significantly greater stroke index at all three velocities (+5.18%, +5.21% and +5.91% at V800, V100 and V50, respectively; P<0.01); a significantly shorter pulling phase (-10.97%; P<0.05) and lower index of coordination (-21.87%; P<0.01) at the pace appropriate for the 800 m; and a significantly greater entry and catch phase (+9.81%; P<0.05) at the pace appropriate for the 100 m. We conclude that the wet suit amplified the coordination mode of the triathletes (i.e. catch-up coordination) without modifying stroke rate, recovery phase or leg movements.
ISSN: 0264-0414

hal-00720724
https://hal.univ-antilles.fr/hal-00720724

Éditeur(s) : HAL CCSD
Résumé : International audience
The aims of this study were to evaluate the effects of both noncircular (ROT) and conventional (CON) chainring systems on aerobic and anaerobic cycling performances of professional cyclists, while analyzing the influence of varying the crank angle of maximum crank arm length of ROT. Fifteen professional road cyclists performed both incremental and sub-maximal aerobic tests and the Wingate anaerobic test in the laboratory. There were no statistical differences between CON and ROT in the aerobic tests, even when the best ROT position (ROT?) was selected. However, in the anaerobic test, maximal (4.2-9.1%) and mean (0.7-4.7%) power outputs were higher in ROT (P0.05). These differences were greater when the ROT? was selected (11.2 and 7.0%, respectively). Our findings suggest that ROT is able to improve anaerobic but not aerobic cycling performance in professional cyclists. Nevertheless, it must be adapted to each cyclist to ensure these improvements.
EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY

hal-00701238
https://hal.univ-antilles.fr/hal-00701238
https://hal.univ-antilles.fr/hal-00701238/document
https://hal.univ-antilles.fr/hal-00701238/file/Rodriguez-Marroyo-Hue_O.pdf
DOI : 10.1007/s00421-009-0993-x

Éditeur(s) : Gauthier-Villars
Résumé : Echinoderms show phenotypic plasticity in which variation in environmental conditions elicit graded reaction norms of morphological change. With the sea urchin Strongylocentrotus purpuratus under laboratory conditions, decreases in available food caused decreases in dry weights of the gonad and gut coupled with increases in the mass of Aristotle's lantern and length of the demi-pyramids. Spine clipping caused increased spine growth as well as decreases in the gut and gonad masses. Survival rate remained unchanged over a range of feeding and clipping treatments. In the field, at Sunset Bay, Oregon, well-fed sea urchins, with relatively small demi-pyramids, showed survival rates similar to poorly fed sea urchins that had large demi-pyramids. The wide range of morphological change, coupled with the narrow range of-change in survival, suggests that morphological plasticity buffers survival and hence would increase fitness. Phenotypic plasticity shown by other sea urchins includes changes in the relative sizes of Aristotle's lantern in Diadema antillarum and Echinometra mathaei and seasonal variation in the density of pedicellariae in Echinus esculentus. Variation in body size of echinoids and asteroids in different habitats and variation in number of arms in crinoids also may be examples of adaptive plasticity. Seasonal atrophy of internal organs in the sea cucumber Parastichopus californicus has been interpreted as an adaptive response to food limitation but, given the nature of responses in other echinoderms, such an interpretation seems unlikely and the significance of seasonal atrophy of organs in holothurians remains unknown.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1996 , Vol. 19 , N. 3-4 , P. 347-355

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00094/20492/18187.pdf
http://archimer.ifremer.fr/doc/00094/20492/