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The inherent hydrodynamic resistance force, or passive drag, of a swimmer directly influences how they move through the water. For swimmers with physical impairments the strength of association between passive drag and swimming performance is unknown. Knowledge on this factor could improve the World Para Swimming classification process. This study established the relationship between passive drag and 100 m freestyle race performance in Para swimmers with physical impairments. Using a cross-sectional study design, an electrical-mechanical towing device was used to measure passive drag force in 132 international-level Para swimmers. There was a strong, negative correlation between normalised passive drag force and 100 m freestyle race speed in the combined participant cohort (ρ = -0.77, P < 0.001). Type of physical impairment was found to affect the relationship between passive drag and 100 m freestyle race speed when included in linear regression (R2 = 0.65, χ2 = 11.5, P = 0.025). These findings contribute to the body of evidence that passive drag can provide an objective assessment of activity limitation in Para swimmers with physical impairments. The effect of physical impairment type on the relationship between passive drag and swimming performance should be accounted for in Para swimming classification.

Curvatures of the body can disrupt fluid flow and affect hydrodynamic resistance. The purpose of this study was to evaluate the effect of a feedback intervention on glide performance and torso morphology. Eleven male and female national swimmers performed glides before and after augmented feedback. Feedback consisted of self-modelling visual feedback and verbal cuing, to manipulate body curvatures that affect hydrodynamic resistance. Two-dimensional landmark position data (knee, hip and shoulder) were used to enable computation of glide factor and glide coefficient as indicators of glide efficiency; posture (trunk incline and hip angle); and performance (horizontal velocity). Underwater images of the swimmers were manually traced to derive transverse and sagittal diameters, cross-sectional areas, and continuous form outlines (anterior and posterior) of the torso. Maximum rate of change in cross-sectional area and form gradient progressing caudally, were calculated for torso segments: shoulder-chest, chest-waist, waist-hip. Mean velocity, glide factor and glide coefficient values significantly (p

Engineered surfaces and coatings can passively manipulate flow over a bluff-body without significant retrofitting and are of great technological interest for a broad range of applications in the engineering field. A microfiber coating with a hair-like structure is developed and studied as a passive drag reduction method for flow over a cylinder that features both attached and separated flow. The impact of the microfiber coating on drag is experimentally investigated at a Reynolds number of 6.1 × 104 based on the cylinder diameter. Microfiber coatings of various lengths between 1.1% and 8.0% of the cylinder diameter are fabricated using flocking technology and applied to various positions on the cylinder surface between the leading and trailing edges. It is shown that the microfiber length and location are both influential parameters in drag reduction. Two types of drag reduction can be seen depending on the location of the microfiber coating: (1) Drag is reduced significantly if the microfiber coating is applied before flow separates over the cylinder (2) Drag is reduced moderately if the microfiber coating is applied after the point of flow separation on the cylinder. The former case’s best performance is achieved with a microfiber length of less than 1.8% of the cylinder diameter. The latter case shows better performance with relatively long fibers, where the microfiber’s length is greater than 3.3% of the cylinder diameter.

Riblet is one of the most promising passive drag reduction techniques in turbulent flows. In this paper, hot-wire measurements on a turbulent boundary layer perturbed by a drag-reducing riblet surface are carried out to further understand the riblet effects on the turbulent flows and the drag reduction mechanism. Compared with the smooth case, different energy variations in the near-wall region and the logarithmic region are observed over riblets. Then, by using a spectral filter of a given wavelength, the time series of the hot-wire data are decomposed into large- and small-scale components. It is indicated that large-scale structures in the logarithmic region impose a footprint (amplitude modulating effect) on the near-wall small-scale structures. By quantifying this footprint, it is found that the interactions between large- and small-scale structures over riblets are weakened in the near-wall region. Furthermore, the bursting process of large and small scales is studied. For both large- and small-scale structures, a shorter bursting duration and a higher bursting frequency are observed over the riblet surface, which indicates that riblets impede the formation of large- and small-scale bursting events. The flow physics behind these phenomena are also discussed in detail.

The resistance of ships is often dominated by friction between the hull and the water. This study explores possibilities of reducing skin-friction drag in a way inspired by dolphins. These possess a soft skin believed to diminish drag by delaying the transition from laminar to turbulent flow. The underlying mechanism builds on a stabilization of the laminar boundary layer by the compliant surface. To transfer this mechanism to ship hulls, coatings similar to dolphin skin have been designed numerically, made from polymeric materials, and tested in a water tunnel. For the best coating, a drag reduction by almost 3% has been predicted in the boundary layer along the hull model of a small search-and-rescue vessel. The trends of the numerical predictions have been confirmed in the experiments. 1. Overview Dolphins are able to sustain a swimming speed of about 9 m/sec across long distances (Carpenter et al. 2000). This fascinating endurance has stimulated the hypothesis that the pliable dolphin skin interacts with the surrounding flow so as to maintain low-drag laminar flow via a delay of transition to turbulence (Gad-el-Hak 1996). Although this hypothesis is under debate (Fish & Lauder 2006), laboratory experiments have indeed demonstrated that soft coatings delay laminar-turbulent transition (Gaster 1987). According to boundary-layer linear stability theory (LST), compliant surfaces are able to mitigate the amplification of Tollmien-Schlichting (TS) waves, the forerunners of transition in low-disturbance environments (Carpenter & Garrad 1985). However, wall compliance may also promote transition in that the flow may excite instability waves borne by the soft coating material. These waves are known as fluid-induced surface instabilities (FISI) (Carpenter & Garrad 1985) or travelling-wave flutter (Gad-el-Hak 1996). FISI waves may in turn via nonlinear effects develop into quasi-steady surface corrugations ("divergence") (Carpenter & Garrad 1986). This process is associated with an absolute instability mechanism (Tsigklifis & Lucey 2015) that rapidly triggers transition via the bypass route. The boundary-layer instability over a compliant coating is hence more complex than that over a rigid surface owing to the presence of two wave-bearing media. Compliant-wall boundary layers also support non-modal transient growth inducing bypass transition (Tsigklifis & Lucey 2015).

This study investigates differences in propulsive force between the water surface and underwater conditions in the flutter kick swimming technique. The subjects were well-trained university male swimmers. A towing device was set up in a 25 m swimming pool to measure the towing force and velocity of the swimmer under two conditions: the swimmer was near the water surface and at a depth of 0.60 m. The swimmers performed the gliding trials and the kicking trials with maximum effort with five towing velocities from 1.2 to 2.4 m/s. The passive drag and the resultant force of the propulsive and drag forces in kick swimming were formulated, respectively. The propulsive force was calculated from the difference between the two formulas. A difference of the propulsive force under conditions in high swimming velocity was observed. This suggests that the water surface condition has advantages of raising the foot above water.

The passive drag (Dp) during swimming is affected by the swimmer&rsquo, s morphology, body density and body position. We evaluated the relative contribution of morphology, body composition, and body position adjustments in the prediction of a swimmer&rsquo, s Dp. This observational study examined a sample of 60 competitive swimmers (31 male and 29 female) with a mean (&plusmn, SD) age of 15.4 &plusmn, 3.1 years. The swimmer&rsquo, s Dp was measured using an electro-mechanical towing device and the body composition was assessed using a bioelectrical impedance analyser. Body lengths and circumferences were measured in both the standing position and the simulated streamlined position. Partial correlation analysis with age as a control variable showed that Dp was largely correlated (p &lt, 0.05) with body mass, biacromial- and bi-iliac-breadth, streamline chest circumference and breadth. Body mass, Body Mass Index, chest circumference and streamline chest circumference showed a significant and moderate to strong effect (&eta, 2 &gt, 0.55) on Dp. Body mass was the best predictor of Dp explaining 69% of the variability. These results indicate that swimmers with lower Dp values were: (i) slimmer, with lower fat and fat-free mass, (ii) thinner, with lower shoulder breadth, chest circumference, and streamline trunk diameters (iii), shorter, with lower streamline height. These findings can be used for talent identification in swimming, with particular reference to the gliding performance.

The purpose of this study was to compare active drag during front-crawl swimming performed by competitive swimmers with passive drag acting on the same group of swimmers with a streamlined position at various velocities. Seven male competitive swimmers participated in this study, and the testing was conducted in a swimming flume. Active drag was evaluated for front-crawl swimming with upper and lower limb motion using a methodology that estimates the drag in swimming using measured residual thrust values (MRT method). Passive drag was measured by a load cell connected to the swimmers with a streamlined position using a stainless-steel wire. In each case, drag was estimated at six staged velocities ranging from 1.0 to 1.5 m/s. To compare the drags at various velocities, we calculated coefficients a and b by applying the measured force value at each velocity to the equation D = a vb (D: drag, v: velocity). The active drag estimated from the MRT method (a = 35.7 ± 5.3, b = 2.80 ± 0.22) was larger than passive drag (a = 23.6 ± 3.1, b = 2.08 ± 0.23). Furthermore, the difference between active and passive drag was large at high velocities. Therefore, it is possible that the effects of factors other than posture and/or body shape have a large influence on active drag, especially at high velocity.

To quantify swimwear-induced differences under triathlon-specific conditions, we compare the swimming performance, the metabolic cost, and the standardised passive drag of well-trained triathletes when wearing (1) five speedsuit models by different manufacturers from 2017, (2) usual swimming trunks/swimsuits (men/women), and (3) individually preferred competition trisuits. Because of the complexity of the underlying hydrodynamic and biomechanical effects, three separate experimental stages were realized, each with 6–12 well-trained short- and middle-distance triathletes (male and female, mean age 22 ± 5 years) from the German national elite or junior elite level. All measurements were conducted on the basis of real athletes’ motion in the water to correctly account for all relevant effects, including skin and muscle vibrations. First, the athletes took part in a series of 100 m short-distance tests at maximal effort in a long-course pool to quantify swim-time differences in absolute terms. Second, the subjects completed multiple submaximal 400 m tests at 95% of their individual maximal speed in a swimming flume, with their swimwear-related differences in metabolic load being explored in terms of blood lactate and heart rate. Third, the passive drag of the triathletes was measured in the flume during a towing test under standardised conditions in velocity steps of 0.2 m/s within the triathlon-relevant range of 1.1–1.7 m/s. In all three test stages, the speedsuits exhibited performance advantages over trunks/swimsuits: in the 100 m maximal test, the mean swim time with speedsuits decreased by 0.99 ± 0.30 s (≙ − 1.5%). During the 400 m submaximal flume test, the mean heart rate showed a reduction of 7 ± 2 bpm (≙ − 4.0%), while the post-exercise blood lactate accumulation decreased by 1.0 ± 0.2 mmol/L (≙ − 26.2%). Similarly, the passive drag in the towing test was lowered by 3.2 ± 1.0 W (≙ − 6.9% as for normalised power and − 5.2% as for normalised force) for the speedsuits. Wearing speedsuits instead of usual trunks/swimsuits is shown to improve the swimming performance and to reduce the metabolic cost for well-trained triathletes under triathlon-specific test conditions. The reduction in passive drag of the passively towed athlete’s body due specific speedsuit surface textures seems to be only one reason for performance advantages: the effective reduction in muscular, soft tissue, and skin vibrations at the trunk and thighs during active propulsive motion of the swimmer seems to further contribute substantially.

Using theoretical principles, the components of drag (friction D F, pressure D PR and wave D W) of a single-seat kayak were analysed. The purpose was to examine the effect of changes in wetted surf...

Drag is the resistant force that opposes a swimmer displacing through water and significantly affects swimming performance. Drag experienced during active swimming is called active drag (D a ), and its direct determination is still controversial. By contrast, drag experienced while gliding in a stable streamlined body position is defined as passive drag (D p ), and its assessment is widely agreed upon. D p reduction preserves the high velocity gained with the push-off from the starting block or wall after starting and turning or improves the gliding phase of the breaststroke cycle. Hence, this paper reviewed studies on swimming that measured D p under different conditions of gliding. In the present research, accurate descriptions of the main methods used to directly or indirectly determine D p are provided and the main advantages, limitations and critical features of each method are discussed. Since D p differs in methods but not in reported values and is consistent regardless of the measuring method, the information provided in this paper might allow coaches and practitioners to identify the most suitable method for assessing and determining the drag of their swimmers.

The reliability of active drag values was examined using a method that compared free swim speed with measurements taken by towing swimmers slightly faster than their maximum swim speed, while allowing their intra-stroke speed fluctuations. Twelve national age and open level swimmers were tested on two alternate days (Day 1 and Day 2). All participants completed four maximum swim speed, three passive drag and five active drag trials on each of the days. The reliability was determined using within-participant intra-class correlation coefficients (ICC) within each day and between the days. The ICCs for Day 1 and Day 2 were 0.82 and 0.85, respectively, while the comparison of the mean active drag values between days was 0.93. The data showed that the assisted towing method (ATM) with fluctuating speed was only moderately reliable within a single test. However, this method was more reliable when using the average value of active drag from both days (ICC = 0.93). This study identified that the ATM method with fluctuating speed had moderate reliability within-participant trials on values in a single day but high reliability for the average active drag values across different days.

The aim of this study was to investigate the effect of the head position on passive drag with a towing-line experiment in a swimming pool. The tests were performed on ten male swimmers with regional level swimming skills and at least 10 years of competitive swimming experience. They were towed underwater (at a depth of 60 cm) at three speeds (1.5, 1.7 and 1.9 m/s) and in two body positions (arms above the swimmer’s head and arms alongside the body). These two body positions were repeated while the swimmer’s head was positioned in three different ways: head-up, head-middle and head-down in relation to the body’s horizontal alignment. The results showed a reduction of 4-5.2% in the average passive drag at all speeds when the head was down or aligned to the swimmer’s arms alongside the body, in comparison to the head-up position. A major significant decrease of 10.4-10.9% (p < 0.05) was shown when the head was down or aligned at the swimmer’s arms above the swimmer’s head. The passive drag tended to decrease significantly by a mean of 17.6% (p < 0.001) for all speeds examined with the arms alongside the body position rather than with the arms above the head position. The swimmer’s head location may play an important role in reducing hydrodynamic resistance during passive underwater gliding.

Drag is one of the major factors that influences kayaking performance. To focus on the drag of the kayak's hull shape and the paddlers' weight per se, the passive drag (Dp) was measured on a flat-water sprint course for one paddler with added weights. Dp was measured by an electromechanical towing device using a load cell, at incremental and constant velocities from 2.78 to 5.56 m/s. Three kayaks of different sizes and shapes (Nelo® K1 Quattro-M, ML, and L) were used and the paddlers' body weight was adjusted with weights so the total paddler weight in the kayak was 65, 75, and 85 kg. The mean Dp increased by the power function of D = kv(n) (mean R(2) = .990; SD .006). The Dp went from 21.37 ± 1.29 N at 2.78 m/s to 89.32 ± 6.43 N at 5.56 m/s. For the two lighter weighted kayaks (65 and 75 kg), the lowest Dp was observed with different kayak sizes (M, ML, or L) depending on the target velocity. The manufacturers suggest that paddlers should select a kayak size according to their body weight to minimise drag; however, the results of this study suggest that target velocities, and thus competition distance should also be factored into kayak selection.

The purpose of this study was to test the hypothesis that the passive drag acting on a gliding swimmer is reduced if the swimmer adopts an abdominal breathing manoeuvre (expanding the abdominal wall) rather than chest breathing manoeuvre (expanding the rib cage). Eleven male participants participated in this study. A specialised towing machine was used to tow each participant with tension set at various magnitudes and to record time series data of towing velocity. Participants were asked to inhale air by expanding the abdominal wall or the rib cage and to maintain the same body configuration throughout gliding. The steady-state velocity was measured and the coefficient of drag was calculated for each towing trial to compare between the breathing manoeuvres. The results showed that the towing velocity was increased by 0.02 m/s with a towing force of 34.3 N and by 0.06 m/s with a towing force of 98.1 N. The coefficient of drag was reduced by 5% with the abdominal breathing manoeuvre, which was found to be statistically significant (p

A new model triathlon suit (NMS) was developed to help the swimming performance of athletes. The NMS is made of highly compressed and highly water-repellent fabric, which is used in competitive swimwear. The aim of this study was to evaluate the NMS by measuring the passive drag and body position during underwater streamline position. The NMS and the old model suit (OMS) were worn by 11 highly competitive varsity swimmers (eight males and three females). The passive drag and body position were measured when both suits were worn in the circulating water channel. The coefficient of passive drag was calculated by the equation. On average, for the whole measurements, there was a reduction in passive drag when wearing the NMS suit of 1.1±5.3% compared with the OMS, whereas there was no statistically significant. The coefficient of the passive drag was not significant difference between both suits. Wearing the NMS showed higher body position compared to the OMS at any velocity, although not significantly. These results suggest that wearing the NMS might help improve swimming performance.

This study explored and quantified gender differences in passive drag and instantaneous net drag force profile for elite backstroke swimmers (FINA points 938 ± 71). Nine female and ten male backstroke swimmers completed eight maximum speed trials. During the passive drag condition participants were towed at the speed achieved within the maximum effort backstroke swimming trials, while holding a supine stationary streamline position. The remaining trials, swimmers performed their natural swimming stroke, while attached to an assisted towing device. Male participant’s passive (P < .001) and mean net drag force (P < .001) were significantly higher compared with female participants. In addition, there were no significant differences by gender between either the minimum or maximum net drag forces produced during the left and right arm strokes. Instantaneous net drag force profiles demonstrated differences within and between individuals and genders. The swimmers who recorded the fastest speed also recorded the smallest difference in net drag force fluctuations. The instantaneous net drag force profile within elite backstroke swimming provides further insight into stroke technique of this sport.

We aimed to develop a new method for evaluating the drag in front-crawl swimming at various velocities and at full stroke. In this study, we introduce the basic principle and apparatus for the new method, which estimates the drag in swimming using measured values of residual thrust (MRT). Furthermore, we applied the MRT to evaluate the active drag (Da) and compared it with the passive drag (Dp) measured for the same swimmers. Da was estimated in five-stages for velocities ranging from 1.0 to 1.4 m s−1; Dp was measured at flow velocities ranging from 0.9 to 1.5 m s−1 at intervals of 0.1 m s−1. The variability in the values of Da at MRT was also investigated for two swimmers. According to the results, Da (Da = 32.3 v3.3, N = 30, R2 = 0.90) was larger than Dp (Dp = 23.5 v2.0, N = 42, R2 = 0.89) and the variability in Da for the two swimmers was 6.5% and 3.0%. MRT can be used to evaluate Da at various velocities and is special in that it can be applied to various swimming styles. Therefore, the evaluation of drag in swimming using MRT is expected to play a role in establishing the fundamental data for swimming.

At constant average speed (v), a balance between thrust force (Ft) and drag force (Fd) should occur: Ft−Fd = 0; hence the power generated by thrust forces (Pt = Ft·v) should be equal to the power needed to overcome drag forces at that speed (Pd = Fd·v); the aim of this study was to measure Pt (tethered swims), to estimate Pd in active conditions (at sprint speed) and to compare these values. 10 front crawl male elite swimmers (expertise: 93.1 ± 2.4% of 50 m world record) participated to the study; their sprint speed was measured during a 30 m maximal trial. Ft was assessed during a 15 s tethered effort; passive towing measurement were performed to determine speed specific drag in passive conditions (kP = passive drag force/v2); drag force in active conditions (Fd = kA·v2) was calculated assuming that kA = 1.5·kP. Average sprint speed was 2.20 ± 0.07 m·s-1; kA, at this speed, was 37.2 ± 2.7 N·s2·m-2. No significant differences (paired t-test: p > 0.8) were observed between Pt (399 ± 56 W) and Pd (400 ± 57 W) and a strong correlation (R = 0.95, p < 0.001) was observed between these two parameters. The Bland-Altman plot indicated a good agreement and a small, acceptable, error (bias: -0.89 W, limits of agreement: -25.5 and 23.7 W). Power thrust experiments can thus be suggested as a valid tool for estimating a swimmer’s power propulsion.

In order to understand the physical origin of passive resistance in swimming the resistance breakdown for a swimmer is investigated. A combination of empirical methods and theoretical analysis is used to predict passive resistance in the speed range 0 – 2ms-1 and is shown to provide similar results to those from experimental testing. Typical magnitudes of wave, viscous pressure and skin friction resistance contribute 59%, 33% and 8% of total passive resistance respectively at free swim speed. A comparison is made between the widely used Velocity Perturbation Method and a Naval Architecture based approach in predicting active drag. For the swimmer investigated the two approaches predict active drag of 131.4N and 133.9N for a swimming speed of 1.53ms-1. However, the results predicted from the Velocity Perturbation Method have a much higher uncertainty and the Naval Architecture based approach is suggested as a more robust method of predicting active drag.

JANSSEN, M., B. D. WILSON, and H. M. TOUSSAINT. Effects of Drafting on Hydrodynamic and Metabolic Responses in Front Crawl Swimming. Med. Sci. Sports Exerc., Vol. 41, No. 4, pp. 837–843, 2009. Purpose: Effects of drafting on the hydrodynamic and metabolic responses of the drafter behind and at the side of a passive and an active lead swimmer were related to the influence of a lead swimmer on the flow field of the draftee. Methods: Passive drag of the draft swimmer was compared for the nondrafting condition, in the drafting conditions behind a passive and an active lead swimmer, and at the side of a passive and an active lead swimmer. The effect was also evaluated with oxygen uptake measurements. Fluid pressure measurements were made behind and at the side of a passive and an active lead swimmer to examine the flow field. Results: Behind a passive lead swimmer, passive drag was significantly reduced by 20%, and behind an active lead swimmer, it was reduced by 9%. At the side of a passive lead swimmer, passive drag was significantly increased by 9%, and at the side of an active lead swimmer, it increased by 8%. Oxygen uptake was significantly reduced by 25% behind a passive lead swimmer, by 11% behind an active lead swimmer, and only marginally changed at the side of a lead swimmer. The pressure measurements indicated a 33% decrease in mean flow velocity behind an active lead swimmer but an increase in peak flow velocities due to the kick of the lead swimmer. These increases could explain the lesser decrease in passive drag behind an active versus a passive lead swimmer. Conclusion: The best position for a draft swimmer was found to be directly behind an active lead swimmer at a distance of 0.50 m between the toes of lead swimmer and the hands of drafter, with significant reductions in both passive drag and oxygen uptake when drafting. Key Words: TRIATHLON, DRAG, PRESSURE MEASUREMENT, OPTIMAL POSITION

The purpose of this study was to use the planimetric method to determine frontal area (Ap) throughout the stroke cycle in the four swimming strokes as well as during “streamlined leg kicking”. The minimum Ap values in all strokes are similar to those assessed during “streamlined leg kicking” (about 0.13 m2). Active drag (Da = 1/2 ρ Cd Ap v2) was then calculated/estimated based on the average Ap values, as calculated for a full cycle in each condition. Da is the lowest in the “streamlined leg kicking” condition (Da = 19.5v2, e.g., similar to the values of passive drag reported in the literature), is similar in front crawl (Da = 30.0v2), backstroke (Da = 26.9v2) and butterfly (Da = 28.5v2) and is the largest in the breaststroke (Da = 37.5v2). Based on the C vs. v relationships reported in the literature for the four strokes it is then possible to estimate drag efficiency: for a speed of 1.5 m s−1, it ranges from 0.035–0.038 (breaststroke and backstroke, respectively) to 0.052–0.058 (butterfly and front crawl, respectively). This study is the first to establish Ap values throughout the swimming cycle for all swimming strokes and these findings have implications for active drag estimates, for the energetics of swimming and for swimming speed.

In the last decade, great attention has been given to the improvements in swimming performance that can be obtained by wearing �technical swimsuits�; the technological evolution of these materials only marginally involved swim caps production, even if several studies have pointed out the important role of the head (as main impact point with the fluid) on hydrodynamics. The aim of this study was to compare the effects on passive drag (Dp) of 3 swim cap models: a smooth silicon helmet cap (usually used during swimming competitions), a silicon helmet cap with �dimples,� and a silicon helmet cap with �wrinkles.� Experiments were performed on 10 swimmers who were towed underwater (at a depth of 60 cm) at 3 speeds (1.5, 1.7, and 1.9 m·s-1) and in 2 body positions: LA (arms above the swimmer's head) and SA (arms alongside the body). The Dp values obtained in each trial were divided by the square of the corresponding speed to obtain the speed-specific drag (the k coefficient = Dp/v2). No differences in k were observed among swim caps in the LA position. No differences in k were observed between the smooth and dimpled helmets also in the SA position; however, the wrinkled swim cap helmet showed a significant larger k (4.4%) in comparison with the model with dimples, when the swimmers kept their arms alongside the body (in the SA position). These data suggest that wearing a wrinkled swim cap helmet can be detrimental to performance at least in this specific position.

This study investigates the effect of the distance separating the lead and draft swimmers on the metabolic and hydrodynamic responses of the draft swimmer.A nondrafting swim of 4 min at 95% of the best 1500-m pace for 11 swimmers was compared with swimming in a drafting position at four different distances directly behind another swimmer (0, 50, 100, and 150 cm). Swimming performance was assessed by stroke rate and stroke length; the metabolic response by oxygen uptake, heart rate, and blood lactate; and the rating of perceived exertion by the Borg scale. Passive drag was assessed at these drafting distances by passive towing. Then, passive drag was measured in six swimmers towed in six lateral drafting positions, with swimmers separated by approximately 40 cm, and then measured in two positions at the rear of the lead swimmer with a reduced lateral distance between swimmers of 50 and 0 cm.Oxygen uptake, heart rate, blood lactate, rating of perceived exertion, and stroke rate were significantly reduced and stroke length was significantly increased in all drafting positions compared with the nondrafting position. For drag, the most advantageous drafting distances were 0 and 50 cm back from the toes of the lead swimmer. Drag was reduced by 21% and 20%, respectively. In lateral drafting, drag was significantly reduced by 6% and 7%, respectively, at 50 and 100 cm back from the hands of the lead swimmer.Swimming behind another swimmer at a distance between 0 and 50 cm back from the toes was the most advantageous, whereas in lateral drafting the optimal distance was 50-100 cm back from the hands of the lead swimmer.

ROBERTS, B. S., K. S. KAMEL, C. E. HEDRICK, S. P. MCLEAN, and R. L. SHARP. Effect of a FastSkin TM Suit on Submaximal Freestyle Swimming. Med. Sci. Sports Exerc., Vol. 35, No. 3, pp. 519 –524, 2003. Purpose: Nine male collegiate swimmers swam three 183-m freestyle trials at “moderate, moderately hard, and hard” paces while wearing a traditional brief-style suit and on another occasion while wearing a newly designed suit covering the torso and legs with a material designed to reduce drag (FS). Methods: Postswim blood lactate concentration, V u O2, and rating of perceived exertion were measured. Average stroke length and rate, and breakout distance were determined for each swimming trial. Passive drag and buoyant force were also determined on swimmers while wearing both suits. Results: Swimmers swam at a higher mean velocity while wearing the FS (pooled mean % difference 2%), but this was accompanied by a significant increase in V u O2 (4% difference, P 0.05) and blood lactate concentration (10% difference, P 0.05). Comparison of physiological responses at standardized freestyle swimming speeds of 1.4 and 1.6 m·s 1 revealed no significant difference between the two suit conditions. Passive drag of the swimmers while being towed was not significantly different between the suits. Swimmers were significantly more buoyant while wearing the brief-style suit than the FS suit ( P 0.05). Conclusion: These findings provide no evidence of either physical or physiological benefits of wearing these suits during submaximal freestyle swimming. ompetitive swimming suits made from a proprietary fabric purported to reduce water resistance (active drag) and increase buoyancy were recently designed and are being worn by these athletes in hopes of improving performance. Although it is widely accepted that reducing active drag and increasing buoyancy will decrease the physiological cost of any given swimming speed (2–5,8 –18), currently only one study has investigated the drag characteristics of these swimsuits. Toussaint et al. (17) found no difference in active drag with the use of one of these body suits (FastSkin TM by Speedo ® ). However, this study provided no insight into the buoyant characteristics of these suits and, more importantly, examined no physiological variables as they related to the use of these suits. Trappe et al. (18) showed that wearing a neoprene wet suit significantly reduced both V u O2 and V u E during swimming at velocities ranging from 0.9 to 1.3 m·s 1 . Furthermore, the magnitude of this effect was positively related to the amount of body surface covered by the suits. Because neoprene is highly buoyant, part of the explanation for the reduced physiological demands of swimming is likely the added buoyancy provided by the wet suit. However, it is also possible that simply covering the skin might also reduce physiological cost by decreasing active drag independent from changes in buoyancy. Starling et al. (14) showed that wearing torso suits made from the same fabric as standard brief-style swimsuits reduced both V u O2 (by 4%) and blood lactate concentration (by 16%) while increasing distance per stroke (by 4%) during freestyle swimming at a standardized speed. These findings are consistent with the results of Sharp and Costill (12), who showed that shaving exposed body hair reduced the physiological cost of breaststroke swimming at a standardized speed. In this study V u O2 was reduced 9%, postswim blood lactate concentration was reduced 20%, and distance per stroke during the swim was increased 12%. Combined with the reduced velocity decay during a push-off and glide test, these results were attributed to a reduction in active drag after shaving exposed body hair. Collectively, the results of these studies suggest that successful attempts to either reduce active drag or increase the buoyancy of the swimmer will reduce physiological cost of swimming and increase distance per stroke. It was the purpose of the present study to examine the effects of wearing a FastSkin TM suit made from a putative dragreducing fabric on physiological and biomechanical responses to freestyle swimming.

A cross-sectional comparison between the buoyancy, passive and net active drag force characteristics of full-length, Fastskin™ swimsuits with that of standard swimsuits was completed with nine Open National level swimmers (5 males and 4 females). Subjects were weighed in a hydrostatic tank and then towed via a mechanical winch on the surface and 0.4 m deep at 1.6, 2.2 and 2.8 m/s. The subjects performed a prone streamlined glide and maximum effort flutter kick at each towing velocity and depth. Hydrostatic weight differences between swimsuit types were not significant (p> 0.05. Fastskin™ passive drag values were significantly less than normal swimsuits during surface towing at 1.6 and 2.8 m/s; and at 0.4 m deep towing at 1.6, 2.2 and 2.8 m/s. Net active drag force values also were lower for the Fastskin™ suits when compared with those of normal swimsuits and a significant difference existed for surface towing at all three velocities of 1.6, 2.2 and 2.8 m/s. The full-length, Fastskin™ swimsuits created less total hydrodynamic resistance than normal swimsuits while providing no additional buoyancy benefits.

[This corrects the article DOI: 10.1371/journal.pone.0130868.].

This paper presents a review of the techniques used to reduce aerodynamic drag over bluff bodies such as cylinders, spheres, 2D bodies with blunt backs and their application to commercial road vehicles. The recent research carried out on the drag reduction is presented and categorised. A new classification of the techniques is introduced and major contributions under them are shown. It can be concluded that there is not much work done with realistic 3D bluff bodies, especially using passive methods.ABSTRAK: Kertas kerja ini membentangkan kaji selidik semula teknik yang digunakan untuk mengurangkan seret aerodinamik ke atas jasad tubir seperti silinder, sfera, jasad 2D dengan belakang tumpul dan aplikasinya terhadap kenderaan jalan raya komersial. Pengurangan seretan dibentangkan dan dikategorikan dengan kajian terkini. Klasifikasi teknik terkini diperkenalkan dan sumbangan utamanya diperbentangkan. Secara kesimpulannya terdapat banyak tugasan yang tidak yang dapat dijalankan dengan menggunakan jasad tubir 3D sebenar, terutamanya dengan penggunaan kaedah pasif.

The aim of this study was to analyze the effect of depth on the hydrodynamic drag coefficient during the passive underwater gliding after the starts and turns. The swimmer hydrodynamics performance was studied by the application of computational fluid dynamics (CFD) method. The steady-state CFD simulations were performed by the application of k - omega turbulent model and volume of fluid method to obtain two-phase flow around a three-dimensional swimmer model when gliding near water surface and at different depths from the water surface. The simulations were conducted for four different swimming pool size, each with different depth, i.e., 1.0, 1.5, 2.0 and 3.0 m for three different velocities, i.e., 1.5, 2.0 and 2.5 m/s, with swimmer gliding at different depths with intervals of 0.25 m, each starting from the water surface, respectively. The numerical results of pressure drag and total coefficients at individual average race velocities were obtained. The results showed that the drag coefficient decreased as depth increased, with a trend toward reduced fluctuation after 0.5m depth from the water surface. The selection of the appropriate depth during the gliding phase should be a main concern of swimmers and coaches.

To reduce the aerodynamic drag of a truck, two different passive drag reduction methods are investigated to a real truck. First, a simulation model of the truck is built. The external flow field of the truck is studied in details using CFD method. Then a fairwater is added on the top of truck’s head. The effects of different shrink angles of the fairwater on the flow flied and the aerodynamic drag are studied. It is found that the fairwaters can effective decrease the total drag. Then different sizes of cylinders are attached to the top and bottom edges of the tail. A detailed analysis of the flow field and the effect on drag are carried out. At last, these two methods are both applied to the truck and the value of the effective parameters is optimized. A maximum percentage of the drag reduction upped to 24.8% can be obtained.

The metabolic and drag responses, together with the distance between the draftee and the leader, were studied in six female triathletes swimming behind a lead swimmer who used either a two- or a six-beat kick, at an average velocity of 1.24 m x s(-1) (range 1.20-1.31). Drag was measured by passive towing. Oxygen consumption [49.1 (3.8) versus 50.4 (5.0) ml x min(-1) x kg(-1)], blood lactate [6.7 (2.3) versus 6.8 (1.9) mM], heart rate [172 (13.6) versus 173.5 (12.5) beats x min(-1)), rating of perceived exertion [13.7 (1.2) versus 13.5 (1.0)], stroke rate [38.3 (1.5) versus 39.5 (1.4) cycle x min(-1)], stroke length [1.95 (0.09) versus 1.89 (0.15) m x cycle(-1)] were not statistically different between the two-beat and the six-beat kick situations. The energy cost of swimming per unit of distance [0.65 (0.06) versus 0.67 (0.08) ml O2 x m(-1)] and the passive drag were similar for both kicks. The distance separating the draftee from the lead swimmer was between 14 cm and 85 cm and was inversely correlated with passive drag: r=-0.82, P0.05, for the two-beat kick and r=-0.82, P0.05, for the six-beat kick. The higher the passive drag, the closer the hand of the draftee to the feet of the lead swimmer. It was of no more benefit to triathletes to draft behind a two-beat kick swimmer than behind a six-beat kick swimmer.