Active drag related to velocity in male and female swimmers

Propulsive arm forces of 32 male and 9 female swimmers were measured during front crawl swimming using arms only, in a velocity range between 1.0 m s-1 and 1.8 m s-1. At constant velocity, the measured mean propulsive force Fp equals the mean active drag force (Fd). It was found that Fd is related to the swimming velocity v raised to the power 2.12 +/- 0.20 (males) or 2.28 +/- 0.35 (females). Although many subjects showed rather constant values of Fd/v2, 12 subjects gave significantly (p less than 0.01) stronger or weaker quadratic relationships. Differences in drag force and coefficient of drag between males and females (drag: 28.9 +/- 5.1 N, 20.4 +/- 1.9 N, drag coefficient: 0.64 +/- 0.09, 0.54 +/- 0.07 respectively) are especially apparent at the lowest swimming velocity (1 m s-1), which become less at higher swimming velocities. Possible explanations for the deviation of the power of the velocity from the ideal quadratic dependency are discussed.     

Active drag, useful mechanical power output and hydrodynamic force coefficient in different swimming strokes at maximal velocity.

By comparing the time of the same distance swum with and without an added resistance, under the assumption of an equal power output in both cases, the drag of 73 top swimmers was estimated. The active drag Fr(a.d.) at maximal swimming velocities varied considerably across strokes and individuals. In the females Fr(a.d.) ranged from 69.78 to 31.16 N in the front-crawl, from 83.04 to 37.78 N in dolphin, from 93.56 to 45.19 N in breaststroke, and from 65.51 to 37.79 N in back-stroke. In the males Fr(a.d.) ranged from 167.11 to 42.23 N in front-crawl, from 156.09 to 46.95 N in dolphin, from 176.87 to 55.61 N in breaststroke, and from 146.28 to 46.36 N in back-stroke. Also, the ratio of Fr(a.d.) to the passive drag Fr(a.d.) as determined for the analogical velocity in a tugging condition (in standard body position-front gliding) shows considerable individual variations. In the female swimmers variations in Fr(a.d.)/Fr(p.d.) ranged from 145.17 to 59.94% in front-crawl, from 192.39 to 85.57% in dolphin, from 298.03 to 124.50% in breaststroke, and from 162.87 to 85.61% in back-stroke. In the male swimmers variations in Fr(a.d.)/Fr(p.d.) ranged from 162.24 to 62.39% in front-crawl, from 191.70 to 70.38% in dolphin, from 295.57 to 102.83% in breaststroke, and from 198.82 to 74.48% in back-stroke. The main reason for such variations is found in the individual features of swimming technique and can be quantitatively estimated with the hydrodynamic force coefficient, which thus provides an adequate index of technique.     

Upstroke Thrust, Drag Effects, and Stroke-glide Cycles in Wing-propelled Swimming by Birds

A number of bird species swim underwater by wing propulsion.Both among and within species, thrust generated during the recoveryphase (upstroke) varies from almost none to more than duringthe power phase (downstroke). More uneven thrust and unsteadyspeed may increase swimming costs because of greater inertialwork to accelerate the body fuselage (head and trunk), especiallywhen buoyant resistance is high during descent. I investigatedthese effects by varying relative fuselage speed during upstrokevs. downstroke in a model for wing-propelled murres which descendat relatively constant mean speed. As buoyant resistance declinedwith depth, the model varied stroke frequency and glide durationto maintain constant mean descent speed, stroke duration, andwork per stroke. When mean fuselage speed during the upstrokewas only 18% of that during the downstroke, stroke frequencywas constant with no gliding, so that power output was unchangedthroughout descent. When mean upstroke speed of the fuselagewas raised to 40% and 73% of mean downstroke speed, stroke frequencydeclined and gliding increased, so that power output decreasedrapidly with increasing depth. Greater inertial work with moreunequal fuselage speeds was a minor contributor to differencesin swimming costs. Instead, lower speeds during upstrokes requiredhigher speeds during downstrokes to maintain the same mean speed,resulting in nonlinear increases in drag at greater fuselagespeeds during the power phase. When fuselage speed was relativelyhigher during upstrokes, lower net drag at the same mean speedincreased the ability to glide between strokes, thereby decreasingthe cost of swimming.     

Propelling efficiency of front-crawl swimming

In this study the propelling efficiency (ep) of front-crawl swimming, by use of the arms only, was calculated in four subjects. This is the ratio of the power used to overcome drag (Pd) to the total mechanical power (Po) produced including power wasted in changing the kinetic energy of masses of water (Pk). By the use of an extended version of the system to measure active drag (MAD system), Pd was measured directly. Simultaneous measurement of O2 uptake (VO2) enabled the establishment of the relationship between the rate of the energy expenditure (PVO2) and Po (since when swimming on the MAD system Po = Pd). These individual relationships describing the mechanical efficiency (8-12%) were then used to estimate Po in free swimming from measurements of VO2. Because Pd was directly measured at each velocity studied by use of the MAD system, ep could be calculated according to the equation ep = Pd/(Pd + Pk) = Pd/Po. For the four top class swimmers studied, ep was found to range from 46 to 77%. Total efficiency, defined as the product of mechanical and propelling efficiency, ranged from 5 to 8%.     

Mechanical and propelling efficiency in swimming derived from exercise using a laboratory-based whole-body swimming ergometer

Determining the efficiency of a swimming stroke is difficult because different "efficiencies" can be computed based on the partitioning of mechanical power output (W) into its useful and nonuseful components, as well as because of the difficulties in measuring the forces that a swimmer can exert in water. In this paper, overall efficiency (η(O) = W(TOT)/?, where W(TOT) is total mechanical power output, and ? is overall metabolic power input) was calculated in 10 swimmers by means of a laboratory-based whole-body swimming ergometer, whereas propelling efficiency (η(P) = W(D)/W(TOT), where W(D) is the power to overcome drag) was estimated based on these values and on values of drag efficiency (η(D) = W(D)/?): η(P) = η(D)/η(O). The values of η(D) reported in the literature range from 0.03 to 0.09 (based on data for passive and active drag, respectively). η(O) was 0.28 ± 0.01, and η(P) was estimated to range from ～0.10 (η(D) = 0.03) to 0.35 (η(D) = 0.09). Even if there are obvious limitations to exact simulation of the whole swimming stroke within the laboratory, these calculations suggest that the data reported in the literature for η(O) are probably underestimated, because not all components of W(TOT) can be measured accurately in this environment. Similarly, our estimations of η(P) suggest that the data reported in the literature are probably overestimated.     

Estimating propulsive forces--sink or swim?

The purpose of this study was to investigate the validity of hydrodynamic force estimation in swimming as calculated by the quasi-static approach. To achieve this a full-scale mechanical arm was developed, built and tested. The mechanical arm, covered with a prosthetic shell and driven at the shoulder was used to simulate a single plane underwater rotation at four elbow configurations. A computer program controlled the shoulder movement to achieve a replicable angular velocity profile for each arm movement. A strain gauge system was used to directly measure the generated arm torque. Repeated trials were conducted at fixed elbow angles of 110 degrees, 135 degrees, 160 degrees and 180 degrees. All trials were filmed using a three-dimensional underwater set-up. Each trial was digitised at 25 Hz and the hydrodynamic drag force profile of the hand calculated using the quasi-static procedure. From these data, the estimated shoulder torque was calculated and compared to the direct measurement of shoulder torque from the mechanical arm. The results showed that the arm produced a repeatable movement through the water. The shoulder torque profiles using the direct measure (the arm) and the indirect measures (quasi-static approach) differed considerably. The quasi-static approach appears not to accurately reflect the hydrodynamic force profile generated by the arm movement in swimming. Furthermore, it seems that the swimmer's hand contribution is overstated in up to date studies. It is essential that the propulsive mechanisms in swimming be further investigated if factors underpinning an optimal technique are to be established.     

Unilateral ablation of trunk superficial neuromasts increases directional instability during steady swimming in the yellowtail kingfish Seriola lalandi

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail‐beat frequency, stride length, caudal fin‐beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A₀) was significantly increased in SN‐disrupted fish compared with sham‐operated controls. In addition, the orientation of caudal fin‐tip relative to the overall swimming direction of SN‐disrupted fish was significantly deflected (two‐fold) in comparison with sham‐operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body‐wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN‐disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (L_F) s^?1. In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion.     

Effect of leg kick on active drag in front-crawl swimming: Comparison of whole stroke and arms-only stroke during front-crawl and the streamlined position

The purpose of this study was to examine the effect of leg kick on the resistance force in front-crawl swimming. The active drag in front-crawl swimming with and without leg motion was evaluated using measured values of residual thrust (MRT method) and compared with the passive drag of the streamlined position (SP) for the same swimmers. Seven male competitive swimmers participated in this study, and the testing was conducted in a swimming flume. Each swimmer performed front-crawl under two conditions: using arms and legs (whole stroke: WS) and using arms only (arms-only stroke: AS). Active drag and passive drag were measured at swimming velocities of 1.1 and 1.3 m s⁻¹ using load cells connected to the swimmer via wires. We calculated a drag coefficient to compare the resistances of the WS, AS and SP at each velocity. For both the WS and AS at both swimming velocities, active drag coefficient was found to be about 1.6–1.9 times larger than that in passive conditions. In contrast, although leg movement did not cause a difference in drag coefficient for front-crawl swimming, there was a large effect size (d = 1.43) at 1.3 m s⁻¹. Therefore, although upper and lower limb movements increase resistance compared to the passive condition, the effect of leg kick on drag may depend on swimming velocity.     

The effect of spine postures on the hydrodynamic drag in Epinephelus ongus larvae

Laboratory behavioural observation and computational fluid dynamics (CFD) analysis were conducted to examine whether the movement of the elongated dorsal and pelvic spines changed the hydrodynamic drag in white‐streaked grouper Epinephelus ongus larvae. The behavioural observation in the tank revealed that the larvae extended the dorsal and pelvic spines during passive transport and retracted during swimming; the angles of the dorsal and pelvic spines in relation to the anteroposterior axis were larger during the passive transport (mean ± s.d . = 28·84 ± 14·27 and 20·35 ± 15·05°) than those during the swimming (mean ± s.d . = 2·59 ± 5·55 and 0·32 ± 6·49°). The CFD analysis indicated that the relative hydrodynamic drag acting on the larvae was approximately 1·25 times higher when the spines were extended (passive transport) than when the spines were retracted (swimming), suggesting that the E. ongus larvae have an ability to adjust their hydrodynamic drag depending on the behavioural context.     

Hydrodynamic analysis of human swimming based on VOF method

A 3-D numerical model, based on the Navier-Strokes equations and the RNG k-ε turbulence closure, for studying hydrodynamic drag on a swimmer with wave-making resistance taken into account is established. The volume of fluid method is employed to capture the undulation of the free surface. The simulation strategy is evaluated by comparison of the computed results with experimental data. The computed results are in good agreement with data from mannequin towing experiments. The effects of the swimmer’s head position and gliding depth on the drag force at different velocities are then investigated. It is found that keeping the head aligned with the body is the optimal posture in streamlined gliding. Also wave-making resistance is significant within 0.3 m depth from the free surface.     

Drag characteristics of competitive swimming children and adults

The aims of this study were to compare drag in swimming children and adults, quantify technique using the technique drag index (TDI), and use the Froude number (Fr) to study whether children or adults reach hull speed at maximal velocity (vmax). Active and passive drag was measured by the perturbation method and a velocity decay method, respectively, including 9 children aged 11.7+/-0.8 and 13 adults aged 21.4+/-3.7. The children had significantly lower active (kAD) and passive drag factor (kPD) compared with the adults. TDI (kAD/kPD) could not detect any differences in swimming technique between the two groups, owing to the adults swimming maximally at a higher Fr, increasing the wave drag component, and masking the effect of better technique. The children were found not to reach hull speed at vmax, and their Fr were 0.37+/-0.01 vs. the adults 0.42+/-0.01, indicating adults' larger wave-making component of resistance at vmax compared with children. Fr is proposed as an evaluation tool for competitive swimmers.     

Simulated and experimental estimates of hydrodynamic drag from bio-logging tags

Drag force acting on swimming marine mammals is difficult to measure directly. Researchers often use simple modeling and kinematic measurements from animals, or computational fluid dynamics (CFD) simulations to estimate drag. However, studies that compare these methods are lacking. Here, computational simulation and physical experiments were used to estimate drag forces on gliding bottlenose dolphins (Tursiops truncatus). To facilitate comparison, variable drag loading (no-tag, tag, tag + 4, tag + 8) was used to increase force in both simulations and experiments. During the experiments, two dolphins were trained to perform controlled glides with variable loading. CFD simulations of dolphin/tag geometry in steady flow (1–6 m/s) were used to model drag forces. We expect both techniques will capture relative changes created by experimental conditions, but absolute forces predicted by the methods will differ. CFD estimates were within a calculated 90% confidence interval of the experimental results for all but the tag condition. Relative drag increase predicted by the simulation vs. experiment, respectively, differed by between 21% and 31%: tag, 4% vs. 33%; tag + 4, 47% vs. 68%; and tag + 8, 108% vs. 77%. The results from this work provide a direct comparison of computational and experimental estimates of drag, and provide a framework to quantify uncertainty.     

Physiological Performance and Stream Microhabitat use by the Centrarchids Lepomis megalotis and Lepomis macrochirus

Two centrarchids, Lepomis megalotis and L. macrochirus, were compared in laboratory studies of prey capture success, swimming endurance, morphology, hydrodynamic drag, and thermal tolerance, as well as field observations of focal point velocity and depth. For both species, capture of planktonic prey declined as current velocity increased, but L. megalotis was more efficient than L. macrochirus at higher current velocities. Capture of floating prey was not influenced by current velocity, but L. megalotis was more efficient overall at all velocities. Of the two species, L. megalotis was significantly more streamlined, had relatively lower hydrodynamic drag, and had higher swimming endurance in current. Both species had significantly higher critical thermal maxima (CTMax) in summer than in winter, but variance in CTMax was greater for L. megalotis than for L. macrochirus in both summer and winter. Differences between L. megalotis and L. macrochirus in performance and morphology may have direct influence on their relative abundances in small streams. Field observations showed L. megalotis was more common than L. macrochirus in faster, shallower microhabitats.     

Estimation of hand forces and propelling efficiency during front crawl swimming with hand paddles

The aim of the study was to investigate possible modifications caused by hand paddles in the relative contribution of the lift and drag forces of the hand and in the propelling efficiency, during front crawl swimming. Eight female swimmers swam 25 m with maximal intensity without paddles, with small (116 cm(2)) and with large paddles (268 cm(2)). Four cameras operating at 60 Hz were used to record the images and the Ariel Performance Analysis System was used for the digitisation. The results showed that, although during swimming with hand paddles the hand's velocity decreased, the greater propulsive area of the hand paddle caused an increase in the drag, lift, resultant and effective forces of the hand. However, the relative contribution of lift and drag forces on swimming propulsion was not modified, nor was the direction of the resultant force. Hand paddles also increased the propelling efficiency, the stroke length and the swimming velocity, mainly because of the larger propulsive areas of the hand in comparison with free swimming. However, the significant decrease of the stroke rate, might argue the effectiveness of hand paddle training, particularly when large paddles are used in front crawl swimming.     

Concentration of free oxaloacetate in the mitochondrial compartment of isolated liver cells.

The concentration of metabolically active (i.e. 'free') oxaloacetate in the mitochondrial compartment of isolated liver cells was investigated by two independent approaches. On the basis of mitochondrial aspartate aminotransferase maintaining equilibrium and the direct measurements of mitochondrial aspartate, 2-oxoglutarate and glutamate, the concentration of free oxaloacetate was calculated to be 5 microM after incubation of hepatocytes in the presence of 1.5 mM-lactate and 0.05 mM-oleate. Gradually increasing oleate up to 0.5 mM decreased the free oxaloacetate to 2 microM. Very similar results were obtained when free oxaloacetate concentration was derived from the CO2 production of hepatocytes as a measure of citrate flux through the tricarboxylic acid cycle, and the kinetic data on citrate synthase in situ. The decrease in free oxaloacetate on increasing oleate concentration was associated with lowered rates of cycle-dependent CO2 output and O2 uptake, indicating a decrease in the disposal of acetyl-CoA into the tricarboxylic acid cycle. This decrease could explain 25-30% of the increase in ketone-body production occurring at elevated fatty acid supply. This work documents on a quantitative basis the role of free oxaloacetate in the regulation of ketogenesis.     

Relative vs. absolute physiological measures as predictors of mountain bike cross-country race performance

The aims of this study were to document the effect terrain has on the physiological responses and work demands (power output) of riding a typical mountain bike cross-country course under race conditions. We were particularly interested in determining whether physiological measures relative to mass were better predictors of race performance than absolute measures. Eleven A-grade male cross-country mountain bike riders (VO2max 67.1 +/- 3.6 ml x kg(-1) x min(-1)) performed 2 tests: a laboratory-based maximum progressive exercise test, and a 15.5-km (six 2.58-km laps) mountain bike cross-country time trial. There were significant differences among the speed, cadence, and power output measured in each of 8 different terrain types found in the cross-country time trial course. The highest average speed was measured during the 10-15% downhill section (22.7 +/- 2.6 km x h(-1)), whereas the cadence was highest in the posttechnical flat sections (74.3 +/- 5.6 rpm) and lowest on the 15-20% downhill sections (6.4 +/- 12.1 rpm). The highest mean heart rate (HR) was obtained during the steepest (15-20% incline) section of the course (179 +/- 8 b x min(-1)), when the power output was greatest (419.8 +/- 39.7 W). However, HR remained elevated relative to power output in the downhill sections of the course. Physiological measures relative to total rider mass correlated more strongly to average course speed than did absolute measures (peak power relative to mass r = 0.93, p < 0.01, vs. peak power r = 0.64, p < 0.05; relative VO2max r = 0.80, p < 0.05, vs. VO2max r = 0.66, p < 0.05; power at anaerobic threshold relative to mass r = 0.78, p < 0.05, vs. power at anaerobic threshold r = 0.5, p < 0.05). This suggests that mountain bike cross-country training programs should focus upon improving relative physiological values rather than focusing upon maximizing absolute values to improve performance.     

Movement characteristics and power output of guinea-pig and hamster spermatozoa in relation to activation

Spermatozoa were collected from the cauda epididymidis of golden hamsters and guinea-pigs, and the acrosome reaction was induced in vitro. Movement characteristics of the spermatozoa were assessed with high-speed cinemicrography. Before the initiation of the acrosome reaction (preactivated spermatozoa), sperm movement in both species was characterized by progressive swimming by regular flagellar waves of moderate amplitude and relative high frequency. After the acrosome reaction (activated spermatozoa), sperm movement in both species was not progressive, and was characterized by whiplash-like flagellar undulations of significantly (P less than 0.05) higher amplitude and lower frequency. Calculation of the hydrodynamic power output by a new theory indicated that no significant change occurred after activation.     

Energetic consequences of an inducible morphological defence in crucian carp

Crucian carp (Carassius carassius) increases in body depth in response to chemical cues from piscivores and the deeper body constitutes a morphological defence against gape-limited piscivores. In the field, deep-bodied individuals suffer a density-dependent cost when competing with shallow-bodied conspecifics. Here, we use hydrodynamic theory and swimming respirometry to investigate the proposed mechanism underlying this effect, high drag caused by the deep-bodied morphology. Our study confirms that drag is higher for deep-bodied crucian carp, both in terms of estimated theoretical drag and power curve steepness. However, deep-bodied fish swimming at the velocity associated with minimum cost of transport, U _mc, did not experience higher costs of transport than shallow-bodied fish. Deep-bodied crucian carp had significantly lower standard metabolic rates, i.e. metabolic rates at rest, and also lower U _mc, and the resulting costs of transport were similar for the two morphs. Nevertheless, when deep-bodied individuals deviate from U _mc, e.g. when increasing foraging effort under competition, their steeper power curves will cause substantial energy costs relative to shallow-bodied conspecifics. Furthermore, there is evidence that reductions in standard metabolic rate incur costs in terms of lower stress tolerance, reduced growth rate, and life history changes. Thus, this work provides links between hydrodynamics, a cost-reducing mechanism, and a density-dependent fitness cost associated with an inducible defence. Received: 22 March 1999 / Accepted: 14 June 1999     

Numerical model for the locomotion of spirilla

The swimming of trailing, leading, and bipolar spirilla (with realistic flagellar centerline geometries) is considered. A boundary element method is used to predict the instantaneous swimming velocity, counter-rotation angular velocity, and power dissipation of a given organism as functions of time and the geometry of the organism. Based on such velocities, swimming trajectories have been deduced enabling a realistic definition of mean swimming speeds. The power dissipation normalized in terms of the square of the mean swimming speed is considered to be a measure of hydrodynamic efficiency. In addition, kinematic efficiency is defined as the extent of deviation of the swimming motion from that of a previously proposed ideal corkscrew mechanism. The dependence of these efficiencies on the organism's geometry is examined giving estimates of its optimum dimensions. It is concluded that appreciable correlation exists between the two alternative definitions for many of the geometrical parameters considered. Furthermore, the organism having the deduced optimum dimensions closely resembles the real organism as experimentally observed.