Unsteady flow phenomena in human undulatory swimming: a numerical approach

The undulatory underwater sequence is one of the most important phases in competitive swimming. An understanding of the recurrent vortex dynamics around the human body and their generation could therefore be used to improve swimming techniques. In order to produce a dynamic model, we applied human joint kinematics to three-dimensional (3D) body scans of a female swimmer. The flow around this dynamic model was then calculated using computational fluid dynamics with the aid of moving 3D meshes. Evaluation of the numerical results delivered by the various motion cycles identified characteristic vortex structures for each of the cycles, which exhibited increasing intensity and drag influence. At maximum thrust, drag forces appear to be 12 times higher than those of a passive gliding swimmer. As far as we know, this is the first disclosure of vortex rings merging into vortex tubes in the wake after vortex recapturing. All unsteady structures were visualized using a modified Q-criterion also incorporated into our methods. At the very least, our approach is likely to be suited to further studies examining swimmers engaging in undulatory swimming during training or competition

COMPARISON OF FORCE CURVES BETWEEN ON-WATER SINGLE SCULL ROWING AND THE ROWPERFECT ERGOMETER

The purpose of this study was to compare the RowPerfect ergometer to single scull rowing in order to validate its use in rowing training and crew selection. Eight national-level rowers were tested over three sets of 500 m, at stroke rates of 24, 26 and 28, on both the RowPerfect ergometer and on-water in a single scull. Blade force and oar angle were measured on-water while force and stroke length were measured on the ergometer. Both force and angle/length were normalised for comparison between the two forms of rowing. Co-efficient of multiple determination revealed high consistency levels for the 5 representative normalised stokes of each subject. Cross-correlation demonstrated high correlations between the force curves of the ergometer and on-water sculling. Thus, the results indicate that the RowPerfect ergometer successfully simulates on-water sculling

THE CONSISTENCY OF FORCE AND MOVEMENT VARIABLES AS AN INDICATOR OF ROWING PERFORMANCE

A portable biomechanical collection system was used to test fourteen male, coxless pair rowing crews under simulated race speeds. The data was used to examine if the consistency of 8 biomechanical variables, calculated using a modified Coefficient of Variation (CoV), were related to the overall performance, in terms of velocity, of the crews. It was found that 6 of the variables demonstrated a significant correlation to overall boat speed, with the consistency of Normal Gate Force (r=0.737), Handle Velocity (r=0.758) and Trunk Velocity (r=.757) showing very strong correlation. It was concluded that while not imperative to the outcome, consistency of force application and movement patterns may be important in rowing performance

A COMPARISON OF UNDERWATER GLIDING AND KICKING TECHNIQUES

Net forces created when towing swimmers through water were examined for gliding and undelwater kicking. Sixteen experienced male swimmers of similar body shape were towed through water via a motorised winch and pulley system. A load cell measured net force (propulsive force - drag force) at velocities of 1.6, 1.9, 2.2, 2.5 and 3.1 ms-', respectively. At each velocity swimmers performed a prone streamline glide; lateral streamline glide; prone freestyle kick; prone dolphin kick; and lateral dolphin kick. A 2- way repeated measures ANOVA revealed significant differences between the gliding and kicking conditions at different velocities. Results suggest that there is an optimal velocity at which to begin undelwater kicking in order to prevent energy loss from excessive active drag

MORPHOLOGY AND HYDRODYNAMIC RESISTANCE IN YOUNG SWIMMERS

Morphology and hydrodynamic drag were measured of 6 males and 6 females, from each of the 9, 11 and 13 yr age groups. Net forces were examined when towing swimmers while prone streamlined gliding and flutter kicking at 1.3 to 2.5 ms-1. The passive drag force at 1.9, 2.2 and 2.5 ms-1 increased with age and anthropometry, but no changes were found at 1.3 and 1.6 ms-1. Stepwise regression revealed passive drag best predicted net active drag at velocities of 1.3, 1.9, 2.2 and 2.5 ms-1. Results supported the Froude number theory that increased height will reduce wave-making drag

A Novel Sperm-Delivered Toxin Causes Late-Stage Embryo Lethality and Transmission Ratio Distortion in C. elegans

The evolutionary fate of an allele ordinarily depends on its contribution to host fitness. Occasionally, however, genetic elements arise that are able to gain a transmission advantage while simultaneously imposing a fitness cost on their hosts. We previously discovered one such element in C. elegans that gains a transmission advantage through a combination of paternal-effect killing and zygotic self-rescue. Here we demonstrate that this element is composed of a sperm-delivered toxin, peel-1, and an embryo-expressed antidote, zeel-1. peel-1 and zeel-1 are located adjacent to one another in the genome and co-occur in an insertion/deletion polymorphism. peel-1 encodes a novel four-pass transmembrane protein that is expressed in sperm and delivered to the embryo via specialized, sperm-specific vesicles. In the absence of zeel-1, sperm-delivered PEEL-1 causes lethal defects in muscle and epidermal tissue at the 2-fold stage of embryogenesis. zeel-1 is expressed transiently in the embryo and encodes a novel six-pass transmembrane domain fused to a domain with sequence similarity to zyg-11, a substrate-recognition subunit of an E3 ubiquitin ligase. zeel-1 appears to have arisen recently, during an expansion of the zyg-11 family, and the transmembrane domain of zeel-1 is required and partially sufficient for antidote activity. Although PEEL-1 and ZEEL-1 normally function in embryos, these proteins can act at other stages as well. When expressed ectopically in adults, PEEL-1 kills a variety of cell types, and ectopic expression of ZEEL-1 rescues these effects. Our results demonstrate that the tight physical linkage between two novel transmembrane proteins has facilitated their co-evolution into an element capable of promoting its own transmission to the detriment of organisms carrying it

OPTIMISING KINETICS IN THE FREESTYLE FLIP TURN PUSH-OFF

INTRODUCTION: Turning technique is an important component in swimming performance with turn times positively correlating with final event time. However, little is known about the mechanics of an effective turn. This study sought to provide an exploratory analysis of how various kinetic and hydrodynamic variables during wall push-off are related to the wall exit velocity. METHODS: Thirty experienced male swimmers with body types of within one SD of the mean for selected anthropometric parameters reported for elite male adult swimmers (Mazza et al., 1994) were recruited for the study. During three freestyle flip turns, selected kinetic, hydrodynamic and kinematic variables of the wall pushoff were recorded. The wall push-off phase was measured from the point of maximum knee flexion during wall contact until the feet left the wall. Kinetics were recorded via a 2D vertically mounted forceplate which recorded peak push-off force and total impulse. The acceleration of each swimmer’s centre of gravity (CG) and wall exit velocity of the CG were calculated from underwater videography. Hydrodynamic peak drag force and drag impulse were calculated from the kinetic and kinematic data using a derivative of Newton’s second law. RESULTS: A stepwise regression was performed with wall exit velocity as the criterion variable and push-off time, peak propulsive force, total propulsive impulse, peak drag force, and total drag impulse as the independent variables. The stepwise regression yielded peak drag force, peak propulsive force and push-off time in the equation, with beta values indicating that the peak drag force carried the highest weighting of the three variables. CONCLUSIONS: The results of the stepwise regression indicated that an optimal combination of a low peak drag force, high peak propulsive force and increased wall time produced the fastest wall exit velocity. The inclusion of the peak drag force in the regression equation as the most important predictor of wall exit velocity highlights the importance of drag in turning technique. Factors such as very high push-off forces and exaggerated movements during wall push-off may lead to higher peak drag forces which, in turn, could be detrimental to the overall turning performance

CXCR4 expression heterogeneity in neuroblastoma cells due to ligand-independent regulation

<p>Abstract</p> <p>Background</p> <p>CXCR4, the receptor for the chemokine stromal-derived factor 1 (SDF-1), has been shown to mediate many of the processes essential for cancer progression such as tumor cell proliferation, metastasis, and angiogenesis. To understand the role of CXCR4 in the biology of neuroblastoma, a disease that presents with wide spread metastases in over 50% of patients, we screened ten patient derived-neuroblastoma cell-lines for basal CXCR4 expression and sought to identify characteristics that correlate with tumor cell phenotype.</p> <p>Results</p> <p>All cell lines expressed <it>CXCR4 </it>mRNA at variable levels, that correlated well with three distinct classes of CXCR4 surface expression (low, moderate, or high) as defined by flow cytometry. Analysis of the kinetics of CXCR4 surface expression on moderate and high expressing cell lines showed a time-dependent down-regulation of the receptor that directly correlated with cell confluency, and was independent of SDF1. Cell lysates showed the presence of multiple CXCR4 isoforms with three major species of approximately 87, 67 and 55 kDa associating with high surface expression, and two distinct species of 45 and 38 kDa correlating with low to null surface expression. Western blot analysis of CXCR4 immunoprecipitates showed that the 87 and 67 kDa forms were ubiquitinated, while the others were not. Finally, treatment of cells with a proteasome inhibitor resulted in down regulation of CXCR4 surface expression.</p> <p>Conclusions</p> <p>Taken together, these data show that regulation of CXCR4 surface expression in neuroblastoma cells can occur independently of SDF-1 contribution arguing against an autocrine mechanism. Additionally these data suggest that post-translational modifications of CXCR4, in part through direct ubiquitination, can influence trafficking of CXCR4 to the surface of neuroblastoma cells in a ligand-independent manner.</p

Psychological responses after a major fatal earthquake: The effect of preitraumatic dissociation and posttraumatic stress symptoms on anxiety and depression.

Following trauma, most people with initial symptoms of stress recover, but it is important to identify those at risk for continuing difficulties so resources are allocated appropriately. There has been limited investigation of predictors of posttraumatic stress disorder following natural disasters. This study assessed psychological difficulties experienced in 101 adult treatment seekers following exposure to a significant earthquake. Peritraumatic dissociation, posttraumatic stress symptoms, anxiety, depression, and emotional support were assessed. Path analysis was used to determine whether the experience of some psychological difficulties predicted the experience of other difficulties. As hypothesized, peritraumatic dissociation was found to predict posttraumatic stress symptoms and anxiety. Posttraumatic stress symptoms then predicted anxiety and depression. Depression and anxiety were highly correlated. Contrary to expectations, emotional support was not significantly related to other psychological variables. These findings justify the provision of psychological support following a natural disaster and suggest the benefit of assessing peritraumatic dissociation and posttraumatic stress symptoms soon after the event to identify people in need of monitoring and intervention

Understanding the Effects of Training on Underwater Undulatory Swimming Performance and Kinematics

In swimming, the underwater phase after the start and turn comprises gliding and dolphin kicking, with the latter also known as underwater undulatory swimming (UUS). Swimming performance is highly dependent on the underwater phase; therefore, understanding the training effects in UUS and underwater gliding can be critical for swimmers and coaches. Further, the development of technique in young swimmers can lead to exponential benefits in an athlete’s career. This study aimed to evaluate the effects of a training protocol on UUS and underwater gliding performance and kinematics in young swimmers. Seventeen age group swimmers (boys = 10, girls = 7) performed maximal UUS and underwater gliding efforts before and after a seven-week training protocol. Time to reach 10 m; intra-cyclic mean, peak, and minimum velocities; and gliding performance improved significantly after the training protocol. The UUS performance improvement was mostly produced by an improvement of the upbeat execution, together with a likely reduction of swimmers’ hydrodynamic drag. Despite the changes in UUS and gliding, performance was also likely influenced by growth. The findings from this study highlight kinematic variables that can be used to understand and quantify changes in UUS and gliding performance