Intra-Individual Head Depth Variability During the Competitive Swim Start

The research on the competitive swim start primarily consists of group mean and maximum depths with little attention given to individual variability. The purpose of this study was to quantify intra-individual racing start depth variability and use it to assess minimum water depth standards. Twenty-two competitive swimmers executed five racing starts into a water depth of 3.66 m. Intra-individual variability was quantified by taking the standard deviation of the maximum depth of the center of the head for the five racing starts executed by each swimmer. The mean value was 0.09 m with a standard deviation of 0.06 m. Analysis of means and standard deviations showed that about one-third of swimmers would be expected to have a head depth deeper than the current minimum water depth requirement (i.e., 1.22 m) for at least 10% of starts. Based on this research conducted in deep water, it seems that swimmers should demonstrate both consistency and control of racing start depth before being permitted to execute starts in shallow water

Vertical Head Velocity During Worst-Case Scenario Swim Starts

The potential for injury exists during the execution of a competitive swim start if an athlete contacts the pool bottom. The aim of the study was to provide vertical head velocities (VHV) at predetermined water depths when competitive swimmers perform worst-case scenario swim starts. A total of 22 swimmers performed starts from a standard starting block into a diving well with a water depth of 3.66 m. The starts were considered worst-case because the swimmers were asked to modify their typical start trajectory by traveling directly towards the pool bottom. VHV was 3.67 ± 0.66 m⋅s-1 at a water depth of 1.0 m and decreased to 1.67 ± 0.62 m⋅s-1 at a depth of 2.5 m. VHV was correlated (p \u3c .05) with height and mass at the seven different depths evaluated. The potential for injury during worst-case starts existed at all depths measured. In terms of risk management for injury potential, there seems to be modest additional benefit to increasing water depth from 1.75 to 2.50 m as more than one third of swimmers would still have a 15% risk of catastrophic neck injury should an impact occur at 1.75 m water depth

The serotonergic psychedelic N,N-dipropyltryptamine alters information-processing dynamics in cortical neural circuits

Most of the recent work in psychedelic neuroscience has been done using non-invasive neuroimaging, with data recorded from the brains of adult volunteers under the influence of a variety of drugs. While this data provides holistic insights into the effects of psychedelics on whole-brain dynamics, the effects of psychedelics on the meso-scale dynamics of cortical circuits remains much less explored. Here, we report the effects of the serotonergic psychedelic N,N-diproptyltryptamine (DPT) on information-processing dynamics in a sample of in vitro organotypic cultures made from rat cortical tissue. Three hours of spontaneous activity were recorded: an hour of pre-drug control, and hour of exposure to 10$\mu$M DPT solution, and a final hour of washout, once again under control conditions. We found that DPT reversibly alters information dynamics in multiple ways: first, the DPT condition was associated with higher entropy of spontaneous firing activity and reduced the amount of time information was stored in individual neurons. Second, DPT also reduced the reversibility of neural activity, increasing the entropy produced and suggesting a drive away from equilibrium. Third, DPT altered the structure of neuronal circuits, decreasing the overall information flow coming into each neuron, but increasing the number of weak connections, creating a dynamic that combines elements of integration and disintegration. Finally, DPT decreased the higher-order statistical synergy present in sets of three neurons. Collectively, these results paint a complex picture of how psychedelics regulate information processing in meso-scale cortical tissue. Implications for existing hypotheses of psychedelic action, such as the Entropic Brain Hypothesis, are discussed.Comment: 19 pages, 2 figure