Swimming Strategies Research Articles

Freshwater Wild Swimming, Health and Well-Being: Understanding the Importance of Place and Risk

Spending time in or around bodies of water or ‘blue spaces’ can benefit human health and well-being. A growing body of evidence suggests immersion in blue space, e.g., participating in ‘wild’ swimming, can be particularly beneficial for both physical and mental health. To date, wild swimming and health research has primarily focused on the experience of individuals who swim in the sea. Empirical studies of the health-promoting potential of swimming in freshwater environments, such as lochs and lakes, are lacking, despite the popularity of this practice in many countries and the vastly different physical and hydrological properties of freshwater and coastal environments. The aim of this study was to explore the relationship between loch (lake) swimming and health and well-being for adults living in Scotland and determine the importance of perceptions of place and risk in this relationship. Semi-structured interviews were conducted with twelve wild swimmers who regularly swim in lochs in Scotland. Interview data were analysed thematically using Nvivo. The findings suggest loch swimming has a variety of health and well-being benefits that can be categorised over three domains of health: physical, mental and social. Of these domains, mental health benefits e.g., mindfulness promotion, resilience building and increasing one’s ability to listen to their body, were particularly prominent. Our findings also highlight important physical and hydrological characteristics of loch environments, e.g., calm water conditions (relative to the sea), which contribute to positive wild swimming experiences. Finally, the perceived risks of loch swimming and mitigation strategies for these risks are established. Collectively, our findings further support the notion that wild swimming is a unique health-promoting practice. Our findings also highlight differences (in terms of experience and perceived risk) between swimming in freshwater and coastal environments, which can inform public health and water management policy.

Constraining optimum swimming strategies in plesiosaurs: The effect of amplitude ratio on tandem pitching foils

Identical tandem flippers of plesiosaurs, which are unique among all animals, have been a source of debate regarding the role of hind flippers in their locomotion. Here, inspired by the kinematics of plesiosaur flippers, the effect of the amplitude ratio on the propulsive performance of in-line tandem pitching foils is investigated through a series of particle image velocimetry experiments. Three leader-to-follower amplitude ratios are considered for the foils pitching over a range of 0–2π phase difference. For the first time, it is shown that the amplitude ratio can significantly affect the performance of the hind foil at spacing larger than one chord length. It is found that the thrust generation of the hind foil at the optimum phase difference augments by 130% when it is pitching at the twice angular amplitude of the upstream foil. Although the total performance of the rear-biased and equal amplitude models reaches similar values, thrust production of the hind foil in the equal amplitude model increases only by 23%. By contrast, the performance of the forward-biased model decreases drastically for all phase differences due to the destructive wake–foil interaction of the hind foil. Studying the instantaneous wake–foil interactions, it is found that high thrust generation is associated with the formation of a vortex pair on the suction side of the hind foil, which causes stronger trailing edge vortices to shed with a greater total wake spacing. Finally, through scaling analysis, high-thrust configurations of tandem models are ranked based on the total efficiency of the system.

Force and torque-free helical tail robot to study low Reynolds number micro-organism swimming.

Helical propulsion is used by many micro-organisms to swim in viscous-dominated environments. Their swimming dynamics are relatively well understood, but a detailed study of the flow fields is still needed to understand wall effects and hydrodynamic interactions among swimmers. In this letter, we describe the development of an autonomous swimming robot with a helical tail that operates in the Stokes regime. The device uses a battery-based power system with a miniature motor that imposes a rotational speed on a helical tail. The speed, direction, and activation are controlled electronically using an infrared remote control. Since the robot is about 5 cm long, we use highly viscous fluids to match the Reynolds number, Re, to be less than 0.1. Measurements of swimming speeds are conducted for a range of helical wavelengths, λ, head geometries, and rotation rates, ω. We provide comparisons of the experimental measurements with analytical predictions derived from resistive force theory. This force and torque-free neutrally buoyant swimmer mimics the swimming strategy of bacteria more closely than previously used designs and offers a lot of potential for future applications.

Search strategy analysis of Tg4-42 Alzheimer Mice in the Morris Water Maze reveals early spatial navigation deficits

Spatial disorientation is one of the earliest symptoms in Alzheimer’s disease and allocentric deficits can already be detected in the asymptomatic preclinical stages of the disease. The Morris Water Maze (MWM) is used to study spatial learning in rodent models. Here we investigated the spatial memory of female 3, 7 and 12 month-old Alzheimer Tg4-42 mice in comparison to wild-type control animals. Conventional behavior analysis of escape latencies and quadrant preference revealed spatial memory and reference memory deficits in female 7 and 12 month-old Tg4-42 mice. In contrast, conventional analysis of the MWM indicated an intact spatial memory in 3 month-old Tg4-42 mice. However, a detailed analysis of the swimming strategies demonstrated allocentric-specific memory deficits in 3 month-old Tg4-42 mice before the onset of severe memory deficits. Furthermore, we could show that the spatial reference memory deficits in aged Tg4-42 animals are caused by the lack of allocentric and spatial strategies. Analyzing search strategies in the MWM allows to differentiate between hippocampus-dependent allocentric and hippocampus-independent egocentric search strategies. The spatial navigation impairments in young Tg4-42 mice are well in line with the hypometabolism and synaptic deficits in the hippocampus. Therefore, analyzing search strategies in the Tg4-42 model can be a powerful tool for preclinical drug testing and identifying early therapeutic successes.

Evaluation of Volitional Swimming Behavior of Schizothorax prenanti Using an Open-Channel Flume with Spatially Heterogeneous Turbulent Flow.

Simple SummaryA lack of information on fish volitional swimming behavior in response to various instream flow conditions may inhibit the development of an effective fishway. In this study, Schizothorax prenanti, Tchang, 1930 (S. prenanti), an endemic species in the Jinsha river basin, was tested for volitional swimming behavior in a self-designed open-channel flume. Quantified indices, describing preferred hydraulic characteristics, swimming strategies, and swimming speeds, were collected to analyze fish behavioral responses to turbulent flow. The results showed that S. prenanti preferred to select regions with low flow velocities (0.25–0.50 m/s) and turbulent kinetic energy (<0.05 m2/s2) and employed steady swimming behavior to search for flow velocities lower than the average current to conserve energy in low- and moderate-flow regimes. Additionally, the average and maximum burst speeds of S. prenanti were 2.63 ± 0.37 and 3.49 m/s, respectively. The aim of this study was to apply fish volitional swimming behavior data on the the design and optimization of fishways for specific target species, as well as a novel test method for other migratory fish species.Effective fishway design requires knowledge of fish swimming behavior in streams and channels. Appropriate tests with near-natural flow conditions are required to assess the interaction between fish behavior and turbulent flows. In this study, the volitional swimming behavior of S. prenanti was tested and quantified in an open-channel flume with three (low, moderate, and high) flow regimes. The results showed that, when confronted with alternative flow regimes, S. prenanti preferred to select regions with low flow velocities (0.25–0.50 m/s) and turbulent kinetic energy (<0.05 m2/s2) for swimming, while avoiding high-turbulence areas. Moreover, S. prenanti primarily employed steady swimming behavior to search for flow velocities lower than the average current to conserve energy in low- and moderate-flow regimes. It is hypothesized that in regions with higher flow velocities, fish may change their swimming strategy from energy conservation to time conservation. Additionally, the average and maximum burst speeds of S. prenanti were 2.63 ± 0.37 and 3.49 m/s, respectively, which were 2.21- and 2.28-fold higher than the average (1.19 m/s) and maximum (1.53 m/s) burst speeds estimated from the enclosed swim chamber for fish of similar length. This study contributes a novel research approach that provides more reliable information about fish volitional swimming behavior in natural habitats, as well as recommendations for hydraulic criteria for fishways and the identification of barriers to fish migrations.

A Novel Fish-Inspired Robot with a Double-Cam Mechanism

Fishes have evolved different excellent swimming strategies. To study the influence of tail fin swing on the swimming performance of bionic robot fish, with one joint under the same tail swing frequency and amplitude, we designed a novel robot fish, driven by a double-cam mechanism. By designing the profile of the cam in the mechanism, the robot fish can achieve different undulatory motion trajectory of the caudal fin under the same tail swing frequency and amplitude. The mechanism simulated the undulatory motion of crucian carp. We studied the influence of undulatory motion on the swimming speed of robot fish, which was analyzed by dynamic analysis of the undulatory motion and experiments. According to the experimental results, we can find that the swimming speed of the robotic fish is different under various wave motions. When other conditions are the same, the speed that the robot fish can achieve by imitating the swing motion of the real fish is 1.5 times that of the robot fish doing the cycloid motion. The experimental results correspond to the kinetic analysis results. Furthermore, it is proven that the robot fish with a low caudal peduncle stiffness swims faster under a low swinging frequency, and the speed of a robot fish with a high caudal peduncle stiffness is higher under a high tail swinging frequency.

Hydrodynamic Characteristics of Remora’s Symbiotic Relationships

Symbiotic relationships have developed through natural evolution which can provide advantages to parties in terms of survival. For example, that of the remora fish attached to the body of a shark to compensate for their poor swimming ability. From the remora's perspective, this could be associated to an increased hydrodynamic efficiency in swimming and this needs to be investigated. To understand the remora's swimming strategy in the attachment state, a systematic study has been conducted using the commercial Computational Fluid Dynamics CFD software, STAR-CCM+ to analyse and compare the resistance characteristics of the remora in attached swimming conditions. Two fundamental questions are addressed: what is the effect of the developed boundary layer flow and the effect of the adverse pressure gradient on the remora's hydrodynamic characteristics? By researching the hydrodynamic characteristics of the remora on varying attachment locations, the remora's unique behaviours could be applied to autonomous underwater vehicles (AUVs), which currently cannot perform docking and recovery without asking the mother vehicle to come for a halt.

Reinforcement learning with function approximation for 3-spheres swimmer

We study the swimming strategies that maximize the speed of the 3-spheres swimmer using reinforcement learning methods. First of all, we ensure that for a simple model with few actions, the Q-learning method converges. However, tabular methods like the previous one are not suitable for generalization to more complex environments where states or actions have to be continuous to obtain all directions in the swimmer's reachable set. This is the case, for instance, in the presence of a boundary. To overcome this issue, we investigate another method from reinforcement learning which uses function approximation, and benchmark its results in absence of walls.

Design and Analysis of Mechanical Microswimmers

The fascinating field in present civilization scenario at the edge of science is micro-swimmers, which is a combination of bio physics with self-propulsion mechanisms involving swimming strategies at low Reynolds number. These micro swimming robots offer many advantages in biomedical applications such as drug delivery to some specific locations in our human body and also conducting some surgical operations like opening of blocked arteries etc. In recent times, blocked arteries become a major case in the medical world. This is can be diagnosed by Angioplasty (is a minimally invasive, endovascular procedure to widen narrowed or obstructed arteries or veins, typically to treat arterial atherosclerosis) method. So this is the main reason to choose the aorta as our domain for analysis purpose. This paper presents a micro-swimmer with three different heads they are spherical head, Capsule type head and Tapered cylindrical or elliptical head and modelled using SOLIDWORKS and analysis in ANSYS FLUENT.

Clostridioides difficile Single Cell Swimming Strategy: A Novel Motility Pattern Regulated by Viscoelastic Properties of the Environment.

Flagellar motility is important for the pathogenesis of many intestinal pathogens, allowing bacteria to move to their preferred ecological niche. Clostridioides difficile is currently the major cause for bacterial health care-associated intestinal infections in the western world. Most clinical strains produce peritrichous flagella and are motile in soft-agar. However, little knowledge exists on the C. difficile swimming behaviour and its regulation at the level of individual cells. We report here on the swimming strategy of C. difficile at the single cell level and its dependency on environmental parameters. A comprehensive analysis of motility parameters from several thousand bacteria was achieved with the aid of a recently developed bacterial tracking programme. C. difficile motility was found to be strongly dependent on the matrix elasticity of the medium. Long run phases of all four motile C. difficile clades were only observed in the presence of high molecular weight molecules such as polyvinylpyrrolidone (PVP) and mucin, which suggests an adaptation of the motility apparatus to the mucin-rich intestinal environment. Increasing mucin or PVP concentrations lead to longer and straighter runs with increased travelled distance per run and fewer turnarounds that result in a higher net displacement of the bacteria. The observed C. difficile swimming pattern under these conditions is characterised by bidirectional, alternating back and forth run phases, interrupted by a short stop without an apparent reorientation or tumbling phase. This motility type was not described before for peritrichous bacteria and is more similar to some previously described polar monotrichous bacteria.

Understanding of remora's \u201chitchhiking\u201d behaviour from a hydrodynamic point of view

Symbiotic relationships have developed through natural evolution. For example, that of the remora fish attached to the body of a shark. From the remora’s perspective, this could be associated to an increased hydrodynamic efficiency in swimming and this needs to be investigated. To understand the remora's swimming strategy in the attachment state, a systematic study has been conducted using the commercial Computational Fluid Dynamics (CFD) software, STAR-CCM + to analyse and compare the resistance characteristics of the remora in attached swimming conditions. Two fundamental questions are addressed: what is the effect of the developed boundary layer flow and the effect of the adverse pressure gradient on the remora’s hydrodynamic characteristics? According to the results, the resistance of the remora can generally be halved when attached. Besides, the results have also demonstrated that the drag reduction rate increases with the developed boundary layer thickness and can be estimated using the boundary layer thickness ratio and velocity deficit. The paper demonstrates that the most frequent attachment locations are also the areas that provide the maximum drag reduction rate.

On the swimming strategies to escape a rip current: a mathematical approach

Rip currents represent significant hazards to swimmers all around the world. The danger arises when a misinformed swimmer uses an inadequate strategy to escape the rip, such as fighting the current directly. This can lead to fatigue, panic, and in some cases drowning. There exists a range of strategies put forward by experts (both lifeguards and scientists) to escape rip currents. However, these recommendations are based on a limited number of scientific studies and there is still much discrepancy surrounding the best strategy to escape a rip. Thus, here we present a simple, physics-based theoretical model aimed at assessing different escape strategies in terms of their associated ‘energetic cost’ (in work and power) for any given rip current and swimmer’s proficiency level. Many combinations of swimmers and rips are considered, including both idealised and a realistic rip current. Our quantitative results back the common knowledge that swimming against the rip (which is strongly discouraged by lifeguards) is almost universally the worst possible strategy, especially when compared against strategies favoured by experts, such as floating with the current before attempting to swim back to the shore. For a realistic rip, our results suggest that swimming directly against the rip can require several times more power from the swimmer than other strategies advised by lifeguards, thus lending further scientific support to experts’ recommendations. This study may help promote education around the dangers posed by rip currents and how best to address them.

Behavioral characteristics as potential biomarkers of the development and phenotype of epilepsy in a rat model of temporal lobe epilepsy

The present study performed a detailed analysis of behavior in a rat model of epilepsy using both established and novel methodologies to identify behavioral impairments that may differentiate between animals with a short versus long latency to spontaneous seizures and animals with a low versus high number of seizures. Temporal lobe epilepsy was induced by electrical stimulation of the amygdala. Rats were stimulated for 25 min with 100-ms trains of 1-ms biphasic square-wave pluses that were delivered every 0.5 s. Electroencephalographic recordings were performed to classify rats into groups with a short latency (< 20 days, n = 7) and long latency (> 20 days, n = 8) to the first spontaneous seizure and into groups with a low number of seizures (62 ± 64.5, n = 8) and high number of seizures (456 ± 185, n = 7). To examine behavioral impairments, we applied the following behavioral tests during early and late stages of epilepsy: behavioral hyperexcitability, open field, novel object exploration, elevated plus maze, and Morris water maze. No differences in stress levels (e.g., touch response in the behavioral hyperexcitability test), activity (e.g., number of entries into the open arms of the elevated plus maze), or learning (e.g., latency to find the platform in the Morris water maze test during training days) were observed between animals with a short versus long latency to develop spontaneous seizures or between animals with a low versus high number of seizures. However, we found a higher motor activity measured by higher number of entries into the closed arms of the elevated plus maze at week 26 post-stimulation in animals with a high number of seizures compared with animals with a low number of seizures. The analysis of the Morris water maze data categorized the strategies that the animals used to locate the platform showing that the intensity of epilepsy and duration of epileptogenesis influenced swimming strategies. These findings indicate that behavioral impairments were relatively mild in the present model, but some learning strategies may be useful biomarkers in preclinical studies.

Offshore Dispersal and Predation of Sea Turtle Hatchlings I: A Study of Hawksbill Turtles at Chagar Hutang Turtle Sanctuary, Malaysia

Sea turtle hatchlings emerge from underground nests at night, rapidly crawling seaward to swim off shore. Once in the water, hatchlings might experience high predation rates while in shallow water before reaching deeper water where encounters with predators, and consequently mortality rates, likely decline. Behavioral studies have described different swimming strategies used by hatchlings to counter nearshore predation. Coastal and oceanographic conditions are also likely to influence dispersal away from near shore to the open ocean. This study assessed predation rates of Hawksbill Turtle (Eretmochelys imbricata) hatchlings as they dispersed from shore at Chagar Hutang Bay, Malaysia and the role surface currents play in the transport of hatchlings off shore in the nearshore environment. An acoustic doppler current profiler was used to measure surface currents, and direct observations of hatchlings swimming off shore were made from a kayak using GPS loggers to track hatchling swimming paths. Six of the 31 hatchlings tracked (19.4%) were predated, most within 50 m of shore, indicating that predators are more abundant in shallower areas of the bay where a coralline-rocky bottom predominates. Survival tended to be greater under dark conditions when moonlight was absent or minimal. We quantified the relative importance of the tidal current in a hatchling's offshore swim, and found that in most cases, tidal surface currents assisted the offshore movement of Hawksbill hatchlings as they dispersed from the beach. These findings provide a better understanding of how sea turtle hatchling dispersal is affected by predation, moonlight, and physical oceanographic conditions at Chagar Hutang Turtle Sanctuary.

Reconfigurable Curved Beams for Selectable Swimming Gaits in an Underwater Robot

Rowing is a swimming motion employed by a number of animals via tuned passive biomechanics and active gait strategies. This gait generates positive net thrust (or moment) by having a higher drag profile in the power stroke compared with the recovery stroke, which is obtained via faster actuation speed or higher effective area. In this letter, we show that using the preferential buckling of curved beams in swimming robots can, via a passive reduction of effective area in recovery stroke, be used to generate positive net thrust and moment. Additionally, these curved beams can be actively tuned to alter their behavior on demand for use in swimming applications, and can be used in an underwater robot to switch between rowing and flapping gaits. A dynamic model has been developed to model the swimming behavior of a robot using buckling joints. A design optimization has been carried out, using the Covariance Matrix Adaption Evolution Strategy (CMA-ES), to find the design and gait parameters that maximize the robot's forward swimming speed. A series of experimental gait searches have subsequently been conducted on the resulting optimal design, again using CMA-ES with the goal of finding the optimal gait pattern across a number of swimming strategies such as paddling, flapping, and undulation. By actively altering the curved beam's buckling limits, an untethered robot has been developed that maneuvers in water across each of these swimming strategies. The findings suggest that tuning the preferential buckling limits of curved beams can be an effective and potentially advantageous approach for producing directional thrust and moments.

Optimal gaits for drag-dominated swimmers with passive elastic joints.

In this paper we identify optimal swimming strategies for drag-dominated swimmers with a passive elastic joint. We use resistive force theory to obtain the dynamics of the system. We then use frequency-domain analysis to relate the motion of the passive joint to the motion of the actuated joint. We couple this analysis with elements of the geometric framework introduced in our previous work aimed at identifying useful gaits for systems in drag-dominated environments to identify speed-maximizing and efficiency-maximizing gaits for drag-dominated swimmers with a passive elastic joint.

Computational analysis of hydrodynamic interactions in a high-density fish school

Numerical simulations are employed to study hydrodynamic interactions between two-dimensional fish-like bodies under a traveling wavy lateral motion in high-density diamond-shaped fish schools. This study focuses on two different streamwise spacings, a dense school with 0.4 body length (BL) spacing and a sparse school with 2.0 BL spacing, respectively. An immersed-boundary-method-based incompressible Navier–Strokes flow solver is then employed to quantitatively simulate the resulting flow patterns and associated propulsive performance of the schools. The results suggest that a fish in the dense school achieves higher thrust production and higher propulsive efficiency than that in the sparse school due to a strong wall effect from neighboring fishes. In addition, results from changing the lateral spacing in the dense school have shown that the wall effect is enhanced as the lateral spacing decreases. Flow analyses have shown that the wake pattern of the fish swimming diagonally behind the leading fish in a dense diamond-shaped school transfers from 2S to 2P when the lateral spacing is smaller than 0.6 BL. As a result, an angled jet is produced behind the school and brings more momentum downstream. At the same time, the appearance of the trailing fish results in a stronger pressure region behind the leading fish and leads to a higher hydrodynamic performance of the leading fish in the dense school. The insights revealed from this study will contribute to understanding physical mechanisms in fish schools and providing a new swimming strategy for bio-inspired underwater swarm robots.

Environmental and Biological Factors Influencing Dispersal of Neonate Leatherback Turtles (Dermochelys coriacea) From an Endangered Costa Rican Nesting Population

Quantifying early life movements is essential to understanding migratory pathways and habitat use that can impact individuals’ success later in life. To gauge how neonatal movements set the stage for later habitat use, we tracked neonate leatherback turtles (n=94) with acoustic tags from Pacuare, Costa Rica, in 2016 and 2018. We analyzed movements using a first passage time analysis and random walk models, the results of which indicated neonates followed a fixed compass direction as they traveled away from shore and that strong currents in these areas resulted in advection. We combined the tracking data with concurrent environmental variables in a generalized additive mixed model framework. Our results showed the south-east current flow in this area has spatial and temporal structure that was not driven by the tidal current or local wind speed. Accounting for advection by the currents, in-water neonate swimming speed was significantly related to current speed, first passage time, and the year. Neonates had three main response strategies to currents above 0.5 m s-1, with most increasing their swimming speed and the rest maintaining either a constant or decreased swimming speed. Neonates were significantly larger in 2018 than in 2016 but their average swimming speed was not significantly related to body size, indicating that environmental factors were more important contributors to their dispersal. We conclude that abiotic factors, including the strength and direction of the currents, significantly affect the swimming and dispersal strategy of neonate leatherback turtles and these results can help to inform strategies for releases of neonate turtles from hatcheries, future tracking studies, and conservation efforts.

The role of suction thrust in the metachronal paddles of swimming invertebrates

An abundance of swimming animals have converged upon a common swimming strategy using multiple propulsors coordinated as metachronal waves. The shared kinematics suggest that even morphologically and systematically diverse animals use similar fluid dynamic relationships to generate swimming thrust. We quantified the kinematics and hydrodynamics of a diverse group of small swimming animals who use multiple propulsors, e.g. limbs or ctenes, which move with antiplectic metachronal waves to generate thrust. Here we show that even at these relatively small scales the bending movements of limbs and ctenes conform to the patterns observed for much larger swimming animals. We show that, like other swimming animals, the propulsors of these metachronal swimmers rely on generating negative pressure along their surfaces to generate forward thrust (i.e., suction thrust). Relying on negative pressure, as opposed to high pushing pressure, facilitates metachronal waves and enables these swimmers to exploit readily produced hydrodynamic structures. Understanding the role of negative pressure fields in metachronal swimmers may provide clues about the hydrodynamic traits shared by swimming and flying animals.

Solitary choanoflagellate dynamics and microconfined directed transport

In evolutionary biology, choanoflagellates are broadly investigated as the closest animal ancestors. Under suitable environmental cues, choanoflagellate Salpingoeca rosetta can differentiate into two types of solitary motile cells. Each group is recognized by its own strategy to swim and its morphology. Moreover, under nutrient limited conditions, S. rosetta experience a haploid-to-diploid transition evidenced by the presence of gametes. It is challenging to determine if there is a connection between the two types of swimming strategies and the male and female gametes. Therefore a current interest is to isolate and concentrate the fast swimming cells, for instance, using a microfluidic device. Following this aim we measured their body sizes and characterized their motilities. We determined that fast cells swim remarkably different from slow cells and proposed a phenomenological model to reproduce the observed dynamics. We solved the Langevin dynamical equations of motion using experimental parameters for choanoflagellates swimming in a confined flat microdevice divided by a wall of asymmetric obstacles. A systematic study of the directed transport efficiency was performed in order to optimize the geometry of the obstacles wall. Numerical results showed that fast choanoflagellates can be directed efficiently for a wide range of geometric parameters of the obstacles wall while slow cells are hardly directed independently of its geometry. The clear differences found in the rectification of fast and slow choanoflagellates suggest that an efficient micro-sorter device could be designed for further applications in evolutionary biology.