2,291 research outputs found
Block height influences the head depth of competitive racing starts
The purpose of this study was to determine whether or not starting block height has an effect on the head depth and head speed of competitive racing starts. Eleven experienced, collegiate swimmers executed competitive racing starts from three different starting heights: 0.21 m (pool deck), 0.46 m (intermediate block), and 0.76 m (standard block). One-way repeated measures ANOVA indicated that starting height had a significant effect on the maximum depth of the center of the head, head speed at maximum head depth, and distance from starting wall at maximum head depth. Racing starts from the standard block and pool deck were significantly deeper, faster, and farther at maximum head depth than starts from the intermediate block. There were no differences between depth, speed, or distance between the standard block and pool deck. We conclude that there is not a positive linear
relationship between starting depth and starting height, which means that starts do not necessarily get deeper as the starting height increases
Competitive swimmers modify racing start depth upon request
To expand upon recent findings showing that competitive swimmers complete significantly shallower racing starts in shallower pools, 12 more experienced and 13 less experienced swimmers were filmed underwater during completion of competitive starts. Two starts (1 routine and 1 ârequested shallowâ) were executed from a 0.76 m block height into water 3.66 m deep. Dependent measures were
maximum head depth, head speed at maximum head depth, and distance from the starting wall at maximum head depth. Statistical analyses yielded significant main effects (p < 0.05) for both start type and swimmer experience. Starts executed by the more experienced swimmers were deeper and faster than those executed by the less experienced swimmers. When asked to dive shallowly, maximum head depth
decreased (0.19 m) and head speed increased (0.33 ms-1) regardless of experience. The ability of all swimmers to modify start depth implies that spinal cord injuries
during competitive swimming starts are not necessarily due to an inherent inability to control the depth of the start
Racing start safety: head depth and head speed during competitive starts into a water depth of 1.22 m
From the perspective of swimmer safety, there have been no quantitative 3-dimensional
studies of the underwater phase of racing starts during competition. To do
so, 471 starts were filmed during a meet with a starting depth of 1.22 m and block
height of 0.76 m. Starts were stratified according to age (8 & U, 9â10, 11â12,
13â14, and 15 & O) and stroke during the first lap (freestyle, breaststroke, and
butterfly). Dependent measures were maximum head depth, head speed at maximum
head depth, and distance from the wall at maximum head depth. For all
three variables, there were significant main effects for age, F(4, 456) = 12.53, p
< .001, F(4, 456) = 27.46, p < .001, and F(4, 456) = 54.71, p < .001, respectively,
and stroke, F(2, 456) = 16.91, p < .001, F(2, 456) = 8.45, p < .001, and F(2, 456)
= 18.15, p < .001, respectively. The older swimmers performed starts that were
deeper and faster than the younger swimmers and as a result, the older swimmers
may be at a greater risk for injury when performing starts in this pool depth
Start depth modification by adolescent competitive swimmers
To expand upon previous studies showing inexperienced high school swimmers can complete significantly shallower racing starts when asked to start âshallow,â 42 age group swimmers (6-14 years old) were filmed underwater during completion of competitive starts. Two starts (one normal and one ârequested shallowâ) were executed from a 0.76 m block into 1.83 m of water. Dependent measures were maximum depth of the center of the head, head speed at maximum head depth, and distance from the starting wall at maximum head depth. Statistical analyses yielded significant main effects (p < 0.05) for start type and age. The oldest swimmersâ starts were deeper and faster than the youngest swimmersâ starts. When asked to start shallowly, maximum head depth decreased (0.10 m) and head speed increased (0.32 ms-1) regardless of age group. The ability of all age groups to modify start depth implies that spinal cord injuries during competitive swimming starts are not necessarily due to age-related deficits in basic motor skills
Water depth influences the head depth of competitive racing starts
Recent research suggests that swimmers perform deeper starts in deeper water (Blitvich, McElroy, Blanksby, Clothier, & Pearson, 2000; Cornett, White, Wright, Willmott, & Stager, 2011). To provide additional information relevant to the depth adjustments swimmers make as a function of water depth and the validity of values reported in prior literature, 11 collegiate swimmers were asked to execute racing starts in three water depths (1.53 m, 2.14 m, and 3.66 m). One-way repeated measures ANOVA revealed that the maximum depth of the center of the head was significantly deeper in 3.66 m as compared to the shallower water depths. No differences due to water depth were detected in head speed at maximum head depth or in the distance from the wall at which maximum head depth occurred. We concluded that swimmers can and do make head depth adjustments as a function of water depth. Earlier research performed in deep water may provide overestimates of maximum head depth following the execution of a racing start in water depth typical of competitive venues
Racing start safety: head depth and head speed during competitive backstroke starts
Research on competitive swim start safety has focused on starts involving a dive from above the water surface. The purpose of this study was to determine the depths, speeds, and distances attained when executing backstroke starts, which begin in the water, and to investigate whether or not these variables are a function of age. Backstroke starts (n = 122) performed in 1.22 m of water during competition were stratified according to age group (8&U, 9-10, 11-12, 13-14, and 15&O). Dependent measures were maximum depth of the center of the head (MHD), head speed at maximum head depth (SPD), and distance from the wall at maximum head depth (DIST). Main effects were shown for age group for MHD (F = 8.86, p < 0.05), SPD (F = 4.64, p < 0.05), and DIST (F = 17.21, p < 0.05). Because they performed starts that were deeper and faster than the younger swimmers, the older swimmers seem to be at a greater risk for injury when performing backstroke starts in shallow water
Racing start safety: head depth and head speed during competitive swim starts into a water depth of 2.29m
The head depths and head speeds of swimmers attained following the execution of racing starts during competition have not been well described. To address this, 211 competitive starts were filmed into a starting depth of 2.29 m with a block height of 0.76 m. Starts were stratified according to age, sex, stroke, and swim meet. Dependent measures were maximum depth of the center of the head, head speed at maximum head depth, and distance from the wall at maximum head depth. Significant main effects existed for age for all three measures: F(1, 106) = 13.33, p
< .001, F(1, 106) = 18.60, p < .001 and F(1, 106) = 70.59, p < .001, respectively. There was a significant age by sex interaction, F(1, 106) = 5.36, p = 0.023, for head speed. In conclusion, older swimmers performed starts that were deeper and faster than younger swimmers and nearly all starts exceeded the threshold speeds for injury. As compared to starts previously reported into 1.22 m, starts
were deeper, slower, and farther from the starting wall at maximum head depth
Cluster Cores, Gravitational Lensing, and Cosmology
Many multiply--imaged quasars have been found over the years, but none so far
with image separation in excess of 8\arcsec. The absence of such large
splittings has been used as a test of cosmological models: the standard Cold
Dark Matter model has been excluded on the basis that it predicts far too many
large--separation double images. These studies assume that the lensing
structure has the mass profile of a singular isothermal sphere. However, such
large splittings would be produced by very massive systems such as clusters of
galaxies, for which other gravitational lensing data suggest less singular mass
profiles. Here we analyze two cases of mass profiles for lenses: an isothermal
sphere with a finite core radius (density , and a Hernquist profile (). We find that small core radii
kpc, as suggested by the cluster data, or large a \gsim 300 h^{-1} kpc, as
needed for compatibility with gravitational distortion data, would reduce the
number of large--angle splittings by an order of magnitude or more. Thus, it
appears that these tests are sensitive both to the cosmological model (number
density of lenses) and to the inner lens structure, which is unlikely to depend
sensitively on the cosmology, making it difficult to test the cosmological
models by large--separation quasar lensing until we reliably know the structure
of the lenses themselves.Comment: 17 pages, uuencoded compressed tarred postscript file including text
and 1 figure. To appear in January 20, 1996 issue of ApJ Letter
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