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 Public Library of Science
Résumé : 51 pages; 15figures; 3 tables, accepted for publication in PloS ONE
International audience
We present a study about AFM imaging of living, moving or self-immobilized, bacteria in their genuine physiological liquid medium. No external immobilization protocol, neither chemical nor mechanical, was needed. For the first time, the native gliding movements of Gram-negative Nostoc cyanobacteria upon the surface, at speeds up to 900microns/h, were studied by AFM. This was possible thanks to an improved combination of a gentle sample preparation process and an AFM procedure based on fast and complete force-distance curves made at every pixel, drastically reducing lateral forces. No limitation in spatial resolution or imaging rate was detected. Gram-positive and non-motile R. wratislaviensis bacteria were studied as well. From the approach curves, Young modulus and turgor pressure were measured for both strains at different gliding speeds and are ranging from 20±3 to 105±5MPa and 40±5 to 310±30kPa depending on the bacterium and the gliding speed. For Nostoc, spatially limited zones with higher values of stiffness were observed. The related spatial period is much higher than the mean length of Nostoc nodules. This was explained by an inhomogeneous mechanical activation of nodules in the Nostoc. We also observed the presence of a soft extra cellular matrix (ECM) around the Nostoc. Both strains left a track of polymeric slime with variable thicknesses. For R. wratislaviensis, it is equal to few hundreds of nanometers, likely to promote its adhesion to the sample. While gliding, the Nostoc secretes a slime layer the thickness of which is in the nanometer range and increases with the gliding speed.
ISSN: 1932-6203

hal-00769765
https://hal.archives-ouvertes.fr/hal-00769765
https://hal.archives-ouvertes.fr/hal-00769765v3/document
https://hal.archives-ouvertes.fr/hal-00769765/file/REsubmission_In-situ_determination_Dhahri_Plos_One_R2_Hal.pdf