Swimming Kinematics Research Articles

Physics-informed reinforcement learning framework for kinematics optimization of self-propelled articulated swimmers

Our study presents a novel optimization framework dedicated to refining the swimming gaits of self-propelled articulated swimmers. The approach integrates a fluid–structure interaction solver for multibody systems with a single-step deep reinforcement learning optimization algorithm. To overcome the computational costs incurred by evaluations during parameter search, we introduced controlled transfer learning to improve performance and efficiency. By leveraging pre-trained policies on low-fidelity models and adapting them to high-fidelity environments, the learning procedure can be accelerated with significantly less high-fidelity evaluations. Moreover, the optimization algorithm is complemented by an intricate mapping procedure designed to enforce stringent constraints derived from prior knowledge within the expansive high-dimensional design space. Then, this framework is applied to investigate the influence of segment length and number on the optimal swimming kinematics of an articulated fish model. Findings reveal that the variable-length approach may yield more parsimonious yet comparable models with fewer segments compared to the equal-length approach. This study contributes valuable insight into the design and behavior of both natural and robotic swimmers, paving the way for future advancements in optimization algorithms and fish body models.

Crude Oil-Induced Reproductive Disorders in Male Goldfish: Testicular Histopathology, Sex Steroid Hormones, and Sperm Swimming Kinematics.

Crude oil contamination has been shown to impair reproduction in aquatic animals through carcinogenic and genotoxic properties. Here, we assessed the endocrine-disrupting function of crude oil on male reproductive system based on testicular histology, sex steroid hormones, and fertility endpoints in adult male goldfish (Carassius auratus), which were exposed to 0.02- to 2-mg/L crude oil for 21 days (Experiment #1) or to 5- to 250-mg/L crude oil for 9 days (Experiment #2). The crude oil contained 0.22-mg/L nickel (Ni), 1.10-mg/L vanadium (V), and 12.87-mg/L polycyclic aromatic hydrocarbons (PAHs). Twenty-four hours after adding crude oil, the sum of PAHs ranged from 0.30 to 2.28 μg/L in the aquaria containing 0.02- and 250-mg/L crude oil, respectively. Water analyses for heavy metals in Experiment #2 showed high concentrations (mg/L) of Ni (0.07-0-09) and V (0.10-0.21). For both experiments, exposure to crude oil did not impact gonadosomatic index; however, testes showed histopathological defects including hyperplasia or hypertrophy of Sertoli cells, depletion of the Leydig cells, necrosis of germ cells, and fibrosis of lobular wall. In Experiment #1, sperm production and motility, testosterone (T), and 17β-estradiol (E2) were not significantly different among treatments. In Experiment #2, the number of spermiating males decreased by ~50% following exposure to 250-mg/L crude oil. Sperm production, motility kinematics, T, and the T/E2 ratio significantly decreased in males exposed to ≥ 50-mg/L crude oil; however, E2 remained unchanged. Results show crude oil-induced imbalance of sex steroid hormones disrupts spermatogenesis resulting in diminished sperm production and motility.

Swimming kinematics of rainbow trout behind a 3×5 cylinder array: a computationally driven experimental approach to understanding fish locomotion.

Fish in the wild often contend with complex flows that are produced by natural and artificial structures. Research into fish interactions with turbulence often investigates metrics such as turbulent kinetic energy (TKE) or fish positional location, with less focus on the specific interactions between vortex organization and body swimming kinematics. Here, we compared the swimming kinematics of rainbow trout (Oncorhynchus mykiss) holding station in flows produced by two different 3×5 cylinder arrays. We systematically utilized computational fluid dynamics to identify one array that produced a Kármán vortex street with high vortex periodicity (KVS array) and another that produced low periodicity, similar to a parallel vortex street (PVS array), both validated with particle image velocimetry. The only difference in swimming kinematics between cylinder arrays was an increased tail beat amplitude in the KVS array. In both cylinder arrays, the tail beat frequency decreased and snout amplitude increased compared with the freestream. The center of mass amplitude was greater in the PVS array than in only the freestream, however, suggesting some buffeting of the body by the fluid. Notably, we did not observe Kármán gaiting in the KVS array as in previous studies. We hypothesize that this is because (1) vorticity was dissipated in the region where fish held station or (2) vortices were in-line rather than staggered. These results are the first to quantify the kinematics and behavior of fishes swimming in the wake of multiple cylinder arrays, which has important implications for biomechanics, fluid dynamics and fisheries management.

ECR Spotlight – David Sparks and Edwin Rajeev

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. David Sparks and Edwin Rajeev are authors on ‘ Swimming kinematics of rainbow trout behind a 3×5 cylinder array: a computationally driven experimental approach to understanding fish locomotion’, published in JEB. David conducted the research described in this article while a master's student in James Liao's lab at the University of Florida, USA. Edwin conducted the research described in this article while a PhD student in Alberto Canestrelli's lab at the University of Florida, USA. David is a Lab Tech in the lab of Freddyson Martinez-Rivera at the University of Florida, USA, investigating cognitive and sensory capabilities of motile, aquatic animals, especially from a comparative or ecological perspective. Edwin is a Project Engineer/Coastal Consultant in the lab of James Liao at the University of Florida, USA, leveraging high-fidelity modelling, computational analysis and biomimicry to design resilient coastal infrastructure, enhance environmental sustainability and drive climate adaptability through nature-based engineering solutions.

The effects of warm thermal variability on metabolism and swimming performance in wild Atlantic salmon (Salmo salar).

Warmer and more variable temperatures have been implicated in the recent decline of Atlantic salmon (Salmo salar) in Eastern Canada. To date, we know little on how ecologically relevant thermal fluctuations affect swimming performance in fishes. The goal of this study is to determine the effects of warm versus cool diel thermal variability on swimming efficiency and the speed limit for sustainable aerobically fueled swimming. We acclimated wild S. salar juveniles to a cool and a warm ecologically realistic diel thermal profile (16-21 and 19-24°C), and then tested individuals over a common acute change in temperature (16-24°C). We measured metabolic rate and swimming kinematics at a range of swimming speeds, at five temperatures (16, 18, 20, 22, and 24°C) and calculated swimming efficiency. Our temperature acclimation did not appear to significantly affect energetic and kinematic swimming efficiency, but acute exposure to high temperature did increase overall metabolic rate. It appears that wild S. salar can swim efficiently and sustainably during both acute cool and warm exposures, and after acclimation to diel thermal variation of 16-21 or 19-24°C.

Swimming kinematics of deep-sea fishes.

Although the deep oceans represent Earth's largest habitat, the challenges of studying deep-sea organisms in situ have limited our understanding of adaptation, ecology, and behaviour in these important ecosystems. One fundamental trait of fishes that remains largely unexplored in the deep ocean is swimming, a vital process for movement, migration, and dispersal in marine habitats. Deep-sea conditions such as temperature, pressure, and food availability could each impact the speed and efficiency of swimming in fishes. To investigate swimming kinematics of fishes with increasing depth, we analysed in situ video of bony fishes across a 6000-m depth gradient. We compared open-source videos of fishes from National Oceanic and Atmospheric Administration (NOAA)Ocean Exploration with tank-based recordings of shallow-water relatives from Puget Sound, Washington, USA to understand how both habitat depth and phylogeny influence swimming in fishes. We analysed kinematics in four dominant demersal fish groups, the orders Anguilliformes, Gadiformes, Ophidiiformes, and Perciformes. Deep-sea fishes swam consistently slowly. Swimming kinematics varied across temperature, oxygen, body elongation, and depth. These results suggest that swimming kinematics do not change linearly with increasing habitat depth in fishes and that the impacts of deep-sea conditions such as low temperatures, high pressures, and low nutrient availability on swimming behaviour need to be considered independently of one another. These findings provide insight into the evolution of fish form and function in the deep ocean.

Axial muscle‐fibre orientations in larval zebrafish

AbstractMost teleost fish propel themselves with lateral body waves powered by their axial muscles. These muscles also power suction feeding through rapid expansion of the mouth cavity. They consist of muscle segments (myomeres), separated by connective tissue sheets (myosepts). In adult teleosts, the fast axial muscle fibres follow pseudo‐helical trajectories, which are thought to distribute strain (relative fibre length change) approximately evenly across transverse sections during swimming, thereby optimizing power generation. To achieve strain equalization, a significant angle to the longitudinal axis on the frontal plane (azimuth) is necessary near the medial plane, increasing strain. Additionally, a deviation from longitudinal orientation on the sagittal plane (elevation) is required laterally to decrease strain. Despite several detailed morphological studies, our understanding of muscle‐fibre orientations in the entire axial musculature of fish remains incomplete. Furthermore, most research has been done in post‐larval stages, leaving a knowledge gap regarding the changing axial muscle architecture during larval development. Larval fish exhibit different body size, body shape and swimming kinematics compared to adults. They experience relatively high viscous forces, requiring higher tail‐beat amplitudes to overcome increased drag. Additionally, larval fish swim with higher tail‐beat frequencies. Histological studies have shown that in larval fish, muscle fibres in the anal region transition from an almost longitudinal orientation to a pseudo‐helical pattern by 3 dpf (days post‐fertilization). However, these studies were limited to a few sections of the body and were prone to shrinkage and tissue damage. Here, we introduce a novel methodology for quantifying muscle‐fibre orientations along the entire axial muscles. We selected 4 dpf larval zebrafish for our analyses, a stage where larvae are actively swimming but not yet free‐feeding. High‐resolution confocal 3D scans were obtained from four genetically modified zebrafish expressing green fluorescent protein in fast muscle fibres. Fluorescence variation allowed segmentation of individual muscle fibres, which were then converted to fish‐bound coordinates by correcting for the fish's position and orientation in the scan, and normalized to pool results across individuals. We show that at 4 dpf, muscle‐fibre trajectories exhibit a helical pattern tapering towards the tail. Average fibre angles decrease from anterior to posterior, with azimuth varying over the dorsoventral axis and elevation varying over the mediolateral axis. Notably, only the anteriormost 20% of the body displayed higher azimuth angles near the medial plane. Angles between neighbouring fibres were substantial, particularly at the rim of the epaxial and hypaxial muscles. The revealed muscle‐fibre architecture at this age presumably contributes to the swimming performance of these larvae, but that swimming performance is probably not the only driving factor for the fibre pattern. Our methodology offers a promising avenue for exploring muscle‐fibre orientations across ontogenetic series and provides a foundation for in‐depth functional studies on the role of muscle architecture in facilitating swimming performance of larval fish.

Sea Bass (Dicentrarchus labrax) Tail-Beat Frequency Measurement Using Implanted Bioimpedance Sensing

Estimating tailbeat frequency (TBF) is a crucial component of fish swimming kinematics and performance, particularly because it provides information about energetics and behavioral responses to environmental cues. The most commonly used technique for TBF estimation is based on accelerometers. This paper proposes a novel approach using bioimpedance technology. This is the first time bioimpedance has been measured in a freely moving animal. This was made possible by implanting a flexible electrode in the back muscle of seabasses and having them in a swimming tunnel. The experiment first demonstrates that it is possible to measure bioimpedance in an immersed fish despite the high conductivity of seawater. An agreement analysis was then performed to compare a video-based reference measurement of TBF with the newly proposed approach. Several bioimpedance settings, such as the configuration and the extracted electrical parameters, were considered. Data analysis highlights that a 4-point setup for modulus impedance measurement at frequencies over 10 kHz provides the best agreement (r > 0.98 and CCC > 0.97) with the video-based approach. These results attest to the significant benefits of integrating bioimpedance sensors in biologgers, especially considering the complementary parameters that can be extracted from bioimpedance measurements, such as length, weight, condition index, and fat content.

A continuum soft robotic trout with embedded HASEL actuators: design, fabrication, and swimming kinematics

A continuum soft robotic trout with embedded HASEL actuators: design, fabrication, and swimming kinematics

Field kinematics of intermittent swimming in bluegill sunfish (Lepomis macrochirus)—pelagic locomotion and littoral maneuverability

Abstract Objectives Locomotion is essential for the survival of animals. Fishes have evolved mechanisms to minimize the cost of transport. For example, Bluegill Sunfish (Lepomis macrochirus) employ intermittent swimming, which involves swimming at relatively slow speeds with short propulsive bursts alternating with gliding episodes. This typically involves axial undulation powered by slow-twitch muscle, either with or without pectoral fin usage. The propulsive bursts are at higher tailbeat frequencies than observed for a given average speed with constant propulsion, and muscle physiology experiments show that the propulsive bursts produce relatively high power, while the glide reduces fatigue relative to continuous activity. However, Bluegill encounter complex 3D in-shore habitats, in which an intermittent swimming gait may enable successful capture of habitat-specific prey. Methods Field observations of Bluegill Sunfish were made via underwater videography in Lake Waban, Massachusetts. Key Findings In both pelagic and littoral habitats, Bluegill employed intermittent swimming. This provided the maneuverability and muscle activity needed to capture prey items suspended in the water column and enabled effective prey detection and maneuverability for feeding on sessile invertebrates in dense vegetation. Radio telemetry studies demonstrated that bluegill moved regularly between the pelagic and the littoral. Conclusion In both zones, intermittent swimming may provide both energetic and foraging advantages.

Effects of Ammonia Concentration on Sperm Vitality, Motility Rates, and Morphology in Three Marine Bivalve Species: A Comparative Study of the Noble Scallop Mimachlamys nobilis, Chinese Pearl Oyster Pinctada fucata martensii, and Small Rock Oyster Saccostrea mordax.

Ammonium (NH4+) plays a crucial role in the reproductive processes of key biotic groups in aquatic ecosystems-bivalves. This study aims to elucidate the effects of three different ammonium ion concentrations on sperm vitality, swimming kinematics, and morphology of Mimachlamys nobilis, Pinctada fucata martensii, and Saccostrea mordax. The results indicate that the sperm vitality and motility rates of M.nobilis and S. mordax are inversely proportional to the ammonium concentration, especially in the treatment group with an ammonium concentration of 3 mmol/L, where the decrease in sperm vitality and motility is most significant. In contrast, the sperm of P. fucata martensii reacted differently to increasing ammonium concentrations. After the addition of 2 mmol/L of ammonium, the sperm vitality and motility of P. fucata martensii reached a peak, showing a significant stimulatory effect. Additionally, as the ammonium concentration increased, the curling of the sperm flagella in M.nobilis and S. mordax increased. However, sperm flagella curling in P. fucata martensii showed no change compared to the control group. This study provides insights into the effects of ammonium concentrations on the sperm vitality and motility of three marine bivalve species and highlights the importance of sperm flagella curling as a factor affecting sperm.

Body length determines flow refuging for rainbow trout (Oncorhynchus mykiss) behind wing dams.

Complex hydrodynamics abound in natural streams, yet the selective pressures these impose upon different size classes of fish are not well understood. Attached vortices are produced by relatively large objects that block freestream flow, which fish routinely utilize for flow refuging. To test how flow refuging and the potential harvesting of energy (as seen in Kármán gaiting) vary across size classes in rainbow trout (Oncorhynchus mykiss; fingerling, 8 cm; parr, 14 cm; adult, 22 cm; n=4 per size class), we used a water flume (4100 l; freestream flow at 65 cm s-1) and created vortices using 45deg wing dams of varying size (small, 15 cm; medium, 31 cm; large, 48 cm). We monitored microhabitat selection and swimming kinematics of individual trout and measured the flow field in the wake of wing dams using time-resolved particle image velocimetry (PIV). Trout of each size class preferentially swam in vortices rather than the freestream, but the capacity to flow refuge varied according to the ratio of vortex width to fish length (WV:LF). Consistent refuging behavior was exhibited when WV:LF≥1.5. All size classes exhibited increased wavelength and Strouhal number and decreased tailbeat frequency within vortices compared with freestream, suggesting that swimming in vortices requires less power output. In 17% of the trials, fish preferentially swam in a manner that suggests energy harvesting from the shear layer. Our results can inform efforts toward riparian restoration and fishway design to improve salmonid conservation.

Energetics and Basic Stroke Kinematics of Swimming With Different Styles of Wetsuits.

Lim, B, Villalobos, A, Mercer, JA, and Crocker, GH. Energetics and basic stroke kinematics of swimming with different styles of wetsuits. J Strength Cond Res XX(X): 000-000, 2024-This study investigated the physiological responses and basic stroke kinematics while wearing different styles of wetsuits during submaximal intensity front-crawl swimming. Fourteen subjects (6 men and 8 women) completed a swimming-graded exercise test to determine maximal aerobic capacity (V̇O2max) and four 4-minute submaximal front-crawl swims at a pace that elicited 80% of V̇O2max with different wetsuits: regular swimsuit (no wetsuit [NWS]), buoyancy shorts (BS), sleeveless wetsuit (SLW), and full-sleeve wetsuit (FSW). The rate of oxygen consumption (V̇O2), rate of carbon dioxide production (V̇CO2), minute ventilation (V̇E), heart rate (HR), respiratory exchange ratio, and cost of swimming (CS) were determined as the average for the last minute of each trial. The rating of perceived exertion was assessed after each swimming bout. In addition, stroke length and index were determined from swimming pace and stroke rate. V̇O2, V̇CO2, V̇E, HR, and CS differed significantly among wetsuit conditions (p < 0.01). Respiratory exchange ratio and rating of perceived exertion also varied by wetsuit conditions (p < 0.05). However, stroke rate, length, and index were not significantly different across wetsuit conditions (p > 0.05). No differences existed between SLW and FSW for any dependent variable (p > 0.05). Results from this study suggest that swimming at the same pace without a wetsuit is the least economical, and both SLW and FSW are most and equally economical without significant kinematic changes. In addition, BS could be beneficial during training and racing in terms of less physiological demands than a regular swimsuit but not as economical as the SLW or FSW.

Which Strength Manifestation Is More Related to Regional Swimmers' Performance and In-Water Forces? Maximal Neuromuscular Capacities Versus Maximal Mechanical Maintenance Capacity.

To explore the association of the load-velocity (L-V) relationship variables and ability to maintain maximal mechanical performance during the prone bench-pull exercise with sprint swimming performance and in-water forces. Eleven competitive adult male swimmers (50-m front crawl World Aquatics points: 488 [66], performance level 4) performed 1 experimental session. The L-V relationship variables (L0[ie, maximal theoretical load at 0 velocity]; v0 [ie, maximal theoretical velocity at 0 load], and Aline [ie, area under the L-V relationship]) and maximal mechanical maintenance capacity were assessed at the beginning of the session. Afterward, sprint swimming performance and in-water force production were tested through a 50-m front-crawl all-out trial and 15-s fully-tethered swimming, respectively. Only v0 presented high positive associations with 50-m time and swimming kinematics (r > .532; P < .046). The L0, v0,and Aline showed very high positive associations with the in-water forces during tethered swimming (r > .523; P < .049). However, the ability to maintain maximal mechanical performance, assessed by the mean velocity decline during the prone bench pull, was only significantly correlated with stroke rate (r = -.647; P = .016) and stroke index (r = .614; P = .022). These findings indicate that maximal neuromuscular capacities, especially v0, have a stronger correlation with swimming performance and in-water force production than the ability to maintain maximal mechanical performance in level 4 swimmers.

The Effects of Eccentric Training on Undulatory Underwater Swimming Performance and Kinematics in Competitive Swimmers.

This study aimed to evaluate the effects of a five-week training program on undulatory underwater swimming (UUS) in swimmers and to compare the specific effects prompted by two different training protocols on UUS performance and kinematics. Swimmers (n = 14) were divided into in-water only (WO) (18.61 ± 2.62 years, FINA points: 507 ± 60) and water + dry-land training groups (with conical pulleys) (WD) (18.38 ± 2.67 years, FINA points: 508 ± 83). Three countermovement jumps (CMJ) and three maximal UUS trials were performed before and after a five-week training period. The training program comprised 14 × 30-min sessions. The WO group repeated the same 15-min block twice, while the WD group performed one block of 15 min in the water and the other block on land performing lower limb exercises with conical pulleys. Seven body landmarks were auto-digitalized during UUS by a pre-trained neural network and 21 kinematic variables were calculated. The level of statistical significance was set at p < 0.05. Significant time × group interaction in favour of the WD group was observed for mean vertical toe velocity (p = 0.035, = 0.32). The WD group experienced enhancements in mean and maximum underwater velocity, kick frequency, maximum shoulder angular velocity, as well as mean and maximum vertical toe velocity (p < 0.05). The WO group exhibited an enhancement in CMJ height (p < 0.05). In conclusion, UUS performance was improved in adolescent swimmers after five weeks of specific training, only when combining water and conical pulley exercises. Coaches should include dry-land specific lower limb exercises in addition to in-water training to improve UUS performance.

Fish passage solution: European eel kinematics and behaviour in shear layer turbulent flows

High velocity barriers pose a risk to upstream migrating European eels (Anguilla anguilla, Linnaeus) as the flow can be too fast for them to swim against. These barriers delay or even prevent migration, potentially exacerbating population declines of this critically endangered species. Eel tiles are an emerging solution for this application, already successfully deployed to increase passage at gravity barriers. Here, eel tiles mounted to the bed of an open channel recirculating flume were assessed in terms of eel passage, behaviour and kinematics relative to movement in the absence of the tiles. The tiles effectively increased passage and allowed the eels to rest without the need to swim back downstream. The tiles also reduced the amount of energy needed to travel upstream. For the first time eel swimming was examined in a flow with multiple shear layers and turbulent structures of varying lengthscale. Swimming kinematics were analysed for complex turbulent flows and revealed a new swimming gait in the shear layer beside the tile. By allowing the eels to continuously move upstream, the tiles potentially decrease predation and infection risk at resting hotspots. Overall, the tiles were effective in helping eels pass upstream in an experimental flume.

Design and kinematic analysis of a rope-driven linkage frog-like swimming robot with multidirectional controllable motion

In this paper, a rope-driven linkage frog swimming robot is constructed in accordance with the delicate structure of the frog swimming mode. First, a rope-driven linkage limb propulsion mechanism is proposed. This mechanism not only enables the robot to achieve the superior motion characteristics and mechanical performance of the four limbs of a frog swimming in water but also makes the limb structures more flexible and lightweight. Using the D-H parametric method with geometric relations, the swimming kinematic model of this robotic limb propulsion mechanism is established, and the stability margin and recovery moment equations are derived. Second, based on the above mathematical model, the motion space and stability analysis of the robot limb ends are simulated by MATLAB software. Finally, an experimental prototype with a size of 18 cm in length × 7 cm in width × 7 cm in height, combined with a control system, is developed. The experimental result verifies the rationality and correctness of the robot's structural design, theoretical derivation and control system and proves that it has superior motion capability with a straight-line swimming speed of 0.54 m/s, a horizontal surface turning speed of 100°/s (turning radius of approximately 0.18 m), and an upwards and downwards submerged swimming speed of 9 cm/s during a single swim in the water.

Estimating the pressure force around swimming plankton using micro particle image velocimetry

Obtaining pressure force for freely swimming microorganisms is a challenging yet important problem. Here, we report the swimming kinematics and dynamics of the zooplankton Acartia tonsa nauplius investigated using Micro Particle Image Velocimetry (µPIV). Using rigid object tracking, we obtain sub-pixel accurate localization of freely swimming A. tonsa, revealing its highly periodic locomotion. We exploit this periodicity to obtain phase-locked averaged kinematics for position, speed, and acceleration. The swimming speed profile of A. tonsa has a distinct double peak, due to its two power strokes. Next, we investigate the flow field around swimming A. tonsa using µPIV. We dynamically mask A. tonsa in µPIV images using an object-fixed coordinate transformation, leveraging the sub-pixel accurate localization. Our analysis shows of a pair of attached vortices during the two power strokes, which are pushed away during the recovery stroke. Finally, using a semi-implicit pressure velocity algorithm, we calculate the pressure force from the time-dependent flow fields. These calculations indicate a low-pressure region ahead of the A. tonsa during the peak of the power strokes. The vertical pressure force correlates well with the vertical swimming speed.

Oxygen uptake kinetics and biological age in relation to pulling force and 400-m front crawl performance in young swimmers.

Background: The study aimed to assess differences in the biological age (BA) of 13-year-old swimmers and show their ability, as biologically younger-late mature or older-early mature, to develop fast 60-s oxygen uptake () kinetics and tethered swimming strength. Furthermore, the interplay between swimming strength, , and 400-m front crawl race performance was examined. Methods: The study involved 36 competitive young male swimmers (metrical age: 12.9 ± 0.56years). Depending on BA examination, the group was divided into early-mature (BA: 15.8 ± 1.18years, n = 13) and late-mature (BA: 12.9 ± 0.60 years, n = 23) participants, especially for the purpose of comparing tethered swimming indices, i.e., average values of force (F ave) and (breath-by-breath analysis) kinetic indices, measured simultaneously in 1-min tethered front crawl swimming. From the 400-m racing stroke rate, stroke length kinematics was retrieved. Results: In the 1-min tethered front crawl test, early-mature swimmers obtained higher results of absolute values of and F ave. Conversely, when was present relatively to body mass and pulling force (in ml∙min-1∙kg-1∙N-1), late-mature swimmers showed higher relative usage. Late-mature swimmers generally exhibited a slower increase in during the first 30s of 60s. , F ave, BA, and basic swimming kinematic stroke length were significantly interrelated and influenced 400-m swimming performance. Conclusion: The 1-min tethered swimming test revealed significant differences in the homogeneous calendar age/heterogeneous BA group of swimmers. These were distinguished by the higher level of kinetics and pulling force in early-mature individuals and lower efficiency per unit of body mass per unit of force aerobic system in late-mature peers. The higher kinetics and tethered swimming force were further translated into 400-m front crawl speed and stroke length kinematics.

A systematic investigation into the effect of roughness on self-propelled swimming plates

This study examines the effects of surface topography on the flow and performance of a self-propelled swimming (SPS) body. We consider a thin flat plate with an egg-carton roughness texture undergoing prescribed undulatory swimming kinematics at Strouhal number $0.3$ and tail amplitude to length ratio $0.1$ ; we use plate Reynolds numbers $Re=6$ , 12 and $24\times 10^3$ , and focus on $12\,000$ . As the roughness wavelength is decreased, we find that the undulation wave speed must be increased to overcome the additional drag from the roughness and maintain SPS. Correspondingly, the extra wave speed raises the power required to maintain SPS, making the swimmer less efficient. To decouple the roughness and the kinematics, we compare the rough plates to equivalent smooth cases by matching the kinematic conditions. We find that all but the longest roughness wavelengths reduce the required swimming power and the unsteady amplitude of the forces when compared to a smooth plate undergoing identical kinematics. Additionally, roughness can enhance flow enstrophy by up to 116 % compared to the smooth cases without a corresponding spike in forces; this suggests that the increased mixing is not due to increased vorticity production at the wall. Instead, the enstrophy is found to peak strongly when the roughness wavelength is approximately twice the boundary layer thickness over the $Re$ range, indicating the roughness induces large-scale secondary flow structures that extend to the edge of the boundary layer. This study reveals the nonlinear interaction between roughness and kinematics beyond a simple increase or decrease in drag, illustrating that roughness studies on static shapes do not transfer directly to unsteady swimmers.