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Bodysuit yourself: but first think about it

Ross Sanders1, Brent Rushall2, Huub Toussaint3, Joel Stager4, and Hideki Takagi5
1 Department of Physical Education, Sport and Leisure Studies, The University of Edinburgh, UK
2 Department of Exercise and Nutritional Sciences, San Diego State University, USA
3 Institute for Fundamental and Clinical Human Movement Sciences (IFKB), Vrije Universiteit, Amsterdam, The Netherlands
4 Department of Kinesiology, Indiana University, USA
5 Faculty of Education, Mie University, Tsu, Japan
The swimming attire worn at the recent 2000 Olympics is of interest from a fluid dynamics perspective. In previous Olympics,
the application of ideas from fluid dynamics has played an important role in performance improvements in various sports. In the
2000 Olympics the issue of 'hydrodynamic' bodysuits 'made a splash'.
While there is little doubt that advancements from a clever application of fluid dynamics has improved performance in sports
such as cycling and flat-water kayak racing, the 'jury is still out' with respect to 'hydrodynamically' designed swimsuits. At the
2000 Olympics, gold medals were won with and without the new swimsuits, with varying degrees of use, and in their various
forms (Figure 1).
One is left unsure of whether these suits actually improve performance. Seeking a scientific basis for why they should or should
not have an effect could provide answers. This article reviews theoretical aspects, the scientific rationale underlying design,
scientific evidence relating to the actual effects, and some alternative explanations for benefits or decrements in performance that
may be attributable to the suits. It is not written because the answers to many questions are known. Rather, it is an exploration of
what should be considered.
Progression through water depends on the interaction of propulsive and resistive forces. A swimmer can improve by increasing
propulsive forces and/or reducing resistive forces that act on the body at a given speed. The physiological cost of any strategy
must also be considered.
When swimmers are not creating propulsive forces of sufficient magnitude, they slow down. It is frequently observed that some
individuals seem to 'slip' through the water requiring less effort than others. Some swimmers look to be swimming well at slow
speeds but when they attempt to increase speed they do not improve as much as others. One of the main reasons for these
differences is the amount of resistance, more commonly referred to as 'resistive drag', created by the swimmer.
Figure 1. Swimming attire worn by a selection of gold medallists at the 2000 Olympic Games.
An understanding of factors contributing to resistance is important in modern swimming and coaching. It is a topic of renewed
interest and is now considered more important than previously thought. It appears that adjustments in technique to reduce
resistive drag may be as beneficial as subtle adjustments to improve propulsive force.
While resistance to forward movement of limbs and body should be minimised, resistance to backward movements should be
maximised as these movements generate propulsive forces. Thus, when the forearms and hands are moving backwards their
orientation, position, and direction of movement should maximise drag resistance.
Form drag. The orderly flow over the swimmers' body may 'separate' at a certain point, depending on the shape, size, and
velocity of the swimmer. Behind the separation-point, the flow reverses and may 'roll up' into distinct eddies. Consequently, a
pressure differential arises between the front and the rear of the swimmer, resulting in forces termed 'form' or 'pressure drag'.
These forces are proportional to the pressure differential times the cross sectional area of the swimmer. Form drag of a body is
proportional to the square of flow velocity and so becomes increasingly important and influential as swimming speed increases.
To minimize form drag, a swimmer seeks a 'streamlined' position. Thus, swimming with a 'head-up' position in backstroke
increases form drag because the hips 'drop', thereby increasing the cross-sectional area presented by the body as it moves through
the water. If a swimmer's action or swimming 'posture' creates an increased cross-sectional area, then progress through the water
will be resisted more than if in a streamlined position.
Form drag is one of the easiest factors to control and can be minimised by adopting streamlined postures at every opportunity
(i.e., the swimmer has to create the thinnest and straightest form while going through the water). A general concept for most
strokes is to have the shoulder/chest area create a gap in the water and the hips and legs follow through that space. That usually
translates into swimming with the body as level as possible. Many new advances in technique have aimed at maximising
streamlining, that is, reducing form drag. Kolmogorov and Duplishcheva (1992) showed that swimmers of similar body size
(height and weight) could have drastically different drag values during swimming. The streamlined position of Kieren Perkins
probably contributed considerably to his outstanding performances in the 1500m (Rushall & Cappaert, 1994; Figure 2).
A factor that could affect streamlining, and thus form drag, is the buoyant force of the swimmer (Chatard et al., 1990, McLean &
Hinrichs, 1998; 2000). The buoyant force (buoyancy) and body weight form a force couple that creates a torque that tends to
disrupt streamline. If the bodysuit increases the magnitude of the buoyancy force, or shifts the point of application toward the
feet, it could have a form drag reducing effect. This feature will be discussed in more detail below.
Wave drag. Speed at the water surface is constrained by the formation of surface waves. As a swimmer swims at the surface,
water is pushed out of the way. Waves result from pressure variation due to differential water velocities around the swimmer. As
velocity increases, the bow wave, with increased size and inertia, cannot flow out of the way quickly enough and hinders velocity
increases of the swimmer. Eventually, there is an effective speed limit, which for conventional ships with a fixed displacement
hull is called 'hull speed' (see, for example, Aigeldinger and Fish, 1995). Wave drag results from the increased work required to
climb the bow wave and from the transfer of kinetic energy from the swimmer to the water. Wave drag increases steeply and
becomes the dominant drag component as hull speed approaches. Accentuated vertical movements increase Wave drag, for
example, 'flying' out of the water in butterfly and lifting the head when breathing in front crawl. Any action that produces a force
that is not directed along the longitudinal axis of the body in the direction of travel will cause lateral (rotational) movements of
the body, hips, or legs, unless the motion is counter-balanced by another action. Unfortunately, the human anatomy does not
permit all forces to be directed along the longitudinal axis. However, some swimmers have techniques that minimise lateral
movements more than others. Any bouncing or jerkiness in a swimmer's style also creates wave drag. When lateral and vertical
movements are larger than necessary, performance is limited by excessive wave drag.
Lane lines are used to minimise the effect that the mostly lateral waves have on adjacent swimmers in races. Waves have
sufficient energy to assist a swimmer when they are in concert with the direction of progression (one form of 'drafting'), and to
slow a swimmer (when they collide with an oncoming swimmer). A stiff, streamlined body just touching the interface between
air and water experiences five times as much drag as the same body at a depth of more than three times its width (Hertel, 1966).
Thus, wave drag is reduced when a swimmer is completely immersed at a depth of about 0.7 m. The international governing body
of swimming (FINA) at various times has instituted rules to limit the amount of underwater swimming that can be performed.
Primarily for safety and to a lesser degree the spectacle of the sport, rules have been instituted to limit the underwater swimming
distances, and in the case of breaststroke, the amount of immersion per stroke.
Wave drag is potentially the greatest limitation to a swimmer's performance because it increases in proportion to the cube of
swimming velocity. Fortunately, a swimmer has some control over wave drag. Wave drag can be minimised by reducing
unnecessary vertical and lateral movements. Attempts to over-extend forward and backward that produce even the slightest
bending of the body up or down are not worthwhile because of increased wave drag. Similarly, attempts to swim 'over' the water
in crawl stroke and butterfly increase wave drag.
There are some beneficial vertical movements that can contribute to forward propulsion. A wave action that travels down the
body in modern butterfly and possibly breaststroke could be helpful (Sanders et al, 1995; 1998; Sanders, 1995). However, if that
action is exaggerated to the point where the undulation is too large and the wave is not as fast as the swimmer's velocity, then it
will actually slow the swimmer more than if no wave action was attempted at all.
It is unlikely that a bodysuit would have much effect on wave drag. Large movements, rather than the surface of the mover, cause
Surface drag. Often called 'skin friction', surface drag is commonly attributed to the forces tending to slow the water flowing
along the surface of a swimmer's body. The magnitude of the surface drag depends on the velocity of the flow relative to that of
the body, the surface area of the body, and the characteristics of the surface. Skin roughness, body contouring, hair, and swimsuit
fabric are examples of the surface characteristics that create friction as a swimmer moves through water. At the high Reynolds
numbers (>105) that occur during swimming (Toussaint et al., 1988a) increases in velocity cause a relatively much smaller
increase in surface drag than in form drag and wave drag.
There is some evidence that shaving hair off the body and legs can reduce surface drag. The reduced resistance causes a reduction
in the energy per stroke when compared to an unshaven condition (Sharp & Costill, 1990). Because the forearms are used to
produce propulsive drag, there is no advantage in shaving the forearms. Wearing a latex cap provides a smoother surface than
does a head of hair and thus, reduces drag. Tight swimsuits of sheer fabrics with a structure that minimizes seams and edges may
reduce surface drag. Recently developed bodysuit surfaces are supposed to generate less resistance than natural shaved skin.
In summary, total resistance encountered during competitive swimming is the result of the summed effect of form drag, wave
drag, and surface drag. For each component it is possible to estimate the magnitude using general formulae. However, care
should be exercised since:
1. Formulae are normally based on objects with constant shape and orientation to the water flow. A swimmer's shape and
orientation to the fluid flow, changes even when only in a glide position.
2. When a body of constant shape and orientation is pulled through water at constant speed, or put in constant water flow
such as a flume, the patterns of water flow around the object are not consistent and change dynamically. Therefore,
fluctuation in resistive forces is an inevitable natural occurrence. Even when forces are measured over a period of
towing and averaged, calculated coefficients will vary (see for example the variability in calculated coefficients of a
swimmer's hand reported by Sanders, 1999).
3. Coefficients and constants in formulae are not completely independent of velocity (see Toussaint et al., 1988a).
Although the coefficients remain reasonably constant for particular ranges of velocities, those ranges vary according to
the shape of the object. Swimmers are almost constantly changing shape. Given that the swimmer is in the interface of
air and water, a change of velocity might invoke additional changes through variations in technique and position in the
water. For example, an increase in speed might allow the swimmer to 'hydroplane' and reduce the surface area of the
body in the water thereby reducing the surface drag and possibly form drag.
4. If velocity changes during the measuring period, there is an additional force due to acceleration of a mass of water (see
for example Pai and Hay, 1988; Sanders, 1999).
However, given the above barriers, some practical estimates of resistive forces are possible. Tests of swimmers in a constant
glide position yield measures of 'passive drag'. Tests of swimmers actually performing a swimming stroke yield much more
realistic estimates of resistive forces (Toussaint et al., 2000; Vaart et al., 1987). This latter measure is termed 'active drag'. Active
drag is difficult to determine directly because the forces that act on the swimmer must be measured without disrupting the natural
swimming movement. An exact way of doing this has not been found. However, the method used by Toussaint et al is considered
to yield very good estimates of active drag. To measure the effect of the suit on active drag, swimmers must be consistent in
technique and effort when swimming with and without the bodysuit.
Research involving bodysuits is, at best, very difficult. The number of factors that need to be controlled (e.g., the fit of the suits,
the conditions of testing, placebo effect, maintenance of constant wetness, etc.) is intimidating. Few objective scientific studies
have been conducted. Manufacturers claim scientific bases and studies for their products but have failed to make such work
available for independent evaluation.
A basic problem with researching the effects of bodysuits on swimming performances is the theoretical bases used. Most
hydrodynamic models are based on static objects (e.g., boat hulls, hydrofoils), but swimmers are constantly dynamic. With arms
and legs moving in all planes through four different swimming forms, generalizing from static to the dynamic models, and then
across swimming strokes would be spurious. Many theoretical models would be inappropriate for swimming as would be testing
of materials in an environment other than swimming.
Bergen (2001), a swimming coach, conducted a practical test of the effects of Speedo's Fastskin suit on swimming performance.
Without any statistical analysis, simply comparing the means of groups of 25-m sprint performances between Fastskins and
conventional suits, he concluded:
The bodysuit had a significant advantage for underwater kicking and above-water swimming for both crawl stroke and
There was no advantage in wearing the suits for backstroke for either underwater kicking or above water swimming.
The bodysuit had negative effects on breaststroke underwater kicking and swimming.
The differences were only apparent when compared with a normal racing suit (not a 'jammer' or other variation) and
with 'unshaved' swimmers.
Physical and mechanical advantages are gained from shaving before important competitions (Sharp & Costill, 1989). Bergen's
conclusions are only valid for unshaved swimmers. It is possible that once shaved, a previously unshaved swimmer would equal
or surpass the performance benefits from the suits. The benefits of bodysuits might only apply to unshaved conditions. It is also
possible, that a statistical analysis might not support Bergen's 'eyeball' conclusions. A further possibility for Bergen's opinions lie
in the 'conventional' suits used. Swimmers in competitions wear suits that are particularly tight, usually several sizes smaller than
a 'normal' fit. However, in training, 'comfortable' suits are worn possibly contributing to greater drag because of looseness of fit.
Thus, Bergen's results could be partly attributed to the slowing of the swimmer due to the conventional 'training' suits rather than
bodysuit enhancements. Despite those misgivings, Bergen did conclude the bodysuits to be of no value for backstroke or
breaststroke, and that the bodysuits' restriction on movements might even hinder races involving turns.
Some further understanding of the 'bodysuit-versus-conventional-suit' question was provided through a scientific investigation by
Toussaint et al (in press). It was found that when compared to conventional suits on unshaved swimmers performing crawl
the amount of drag reduction with Speedo's Fastskin bodysuits was nonsignificant,
there was a suggestion of a subjects by speed interaction, and
there was no consistent effect across subjects or swimming velocities.
This study suggests that Bergen's non-statistical conclusion of the suits benefiting crawl swimming was presumptuous. Toussaint
et al did report an improvement in drag reduction for bodysuits, but it was insignificant and contradicted the claims of the
manufacturers. It is realized that Bergen's estimates were based on swimming speeds, while Toussaint et al considered drag
reductions. However, a more controlled, statistically analyzed study did not verify the practical interpretations of Coach Bergen,
at least for crawl stroke. As an aside, Toussaint and colleagues opined that loose conventional suits could have increased drag,
and provided an example of it contributing to a large drag reduction by the bodysuit worn by one swimmer.
A further confounding factor that has not been controlled, is the wetness of the bodysuits. In a dry state, bodysuits float very well
and take a long time to sink unless forced into and moved in water. Floatation, or buoyancy force, is provided by trapped air and
surface bubbles (see Figure 6).
It is possible that early swims in any study could enhance bodysuit benefits through floatation. Swimmers (see for example,
Gould, 2000) reported a floating sensation when swimming with a bodysuit for the first time. As a study progresses, and each
trial begins with an increasingly wet bodysuit, the floatation effect would dissipate. It is possible that floatation could affect
performance for one or only a very few trials when bodysuits are dry (as in a race). Toussaint et al used the bodysuits repeatedly
and did not control for wetness in the suits. They concluded that floatation was not a factor in these suits, which would be true
once the suits were thoroughly wet.
Adding buoyancy does not simply reduce frontal area, and hence, form resistance. It is important to look at the couple that is
formed by the weight and buoyancy forces in the swimmer. The couple equals the torque that tends to sink the feet to a lower
position creating a less streamlined position by increasing form drag. A major purpose of most kicking actions in all swimming
strokes is to counter-balance that torque. This is also a reason why not covering the lower legs with resistance-reducing materials
is important. If that was done, a swimmer would have to kick harder, and therefore exacerbate fatigue, to remain streamlined. A
counter argument would be that the floatation provided by bodysuits at the shank extremity would require less kicking.
Buoyancy could also explain the interaction of bodysuits with body types. By covering body parts on the legs side of the center
of buoyancy, torque would be reduced. The further the added buoyancy is from the natural buoyancy center, the greater would be
the effect. Swimmers whose feet sink easily, would gain most from covering the hips and legs with a buoyant material. Male
swimmers generally experience leg-sinking more than females. A popular form of bodysuit worn by males, the 'Jammer', is not a
bodysuit at all. It covers only the lower hips and thighs and therefore, provides floatation on the legs side of the center of mass.
That would assist males to streamline easier as it would support the hips and legs.
Females are required to wear a torso covering for modesty. The upper body cover would cancel out the lower-body torque-
reducing floatation effect. However, while the suits remain dry, the overall floatation factor would serve to reduce the frontal area
of the swimmer by the swimmer floating higher out of the water.
Using buoyant materials in devices is against the rules of swimming. The international governing body for swimming, FINA, has
'approved' bodysuits for competitions and ignored the rule governing devices and buoyancy.
The changing velocities of swimmers during a stroke cycle present another research difficulty. Cappaert & Rushall (1994)
illustrated the velocity curves of Kieren Perkins swimming his gold medal race at the Barcelona Olympic Games (see Figure 2).
One curve represents the right hip, the other the center of mass/gravity. Since the relative velocity of the water influences all
forms of drag resistance, it is invalid to imply consistent effects of the surface of a swimmer on drag because the nature of the
fluid flow will vary considerably within a stroke cycle. With form drag, the point of separation would be influenced by fluid
velocity and that would differ on the various parts of the body, arms, and legs in the stroke cycle.
The information disseminated by manufacturers about their devices is at best confusing. The mechanism to reduce drag used in
the Speedo Fastskin, is purported to be embedded microscopic vortex generators. Vortex generators are supposed to create
microturbulence in the boundary layer, which postpones flow separation. If effective, these devices would reduce form drag, not
surface resistance. However, discussions and advertisements covering bodysuits allude to reductions in surface resistance through
slipping through the water or 'channeling' flow. Vortex generators are useful only at those places where flow separation is
imminent, usually just upstream from the point of flow separation. But, as has been stated above, if flow separation changes
frequently within a stroking cycle, the position of the vortex generators would have to change. One can only assume, that to
overcome this relocation need, the Speedo Fastskin bodysuits have in-built vortex generators all over them. Thus, in the majority
of places before flow separation, the generators would increase resistance, and after separation would be useless. Added to this, is
the effect of the generators on resistance when they move in a direction that is opposite that for which they are designed. For
example, when the legs are drawn-up in the preparatory phase of kicking in breaststroke, they would increase both surface and
form resistance. Perhaps, that is one explanatory factor for Bergen's conclusion that bodysuits actually hinder the performance of
breaststroke swimmers. This design factor is rather 'strange.'
Figure 2. Positions and velocity curves for Kieren Perkins at 70m from the finish of his gold medal 1500m race at the 1992
Olympic Games in Barcelona. The two curves illustrate within-stroke velocity variations, which will affect the amount of drag
that exists at any one moment (from Cappaert and Rushall, 1994).
Besides the position of vortex generators on each moving part of a swimmer, their size is important as well. The protrusion of the
'generator' must not be too small or large. Waring (1999) concluded that for a swimmer, the optimal height of a vortex generator
would be about 2.5 mm (.1 inch). That is much larger than the embedded vortex generators in the Speedo Fastskin.
The influence of surface drag on total resistive drag is relatively small. However, the designers of the bodysuits have reasoned
that in the serious competitive situation where 1/100th second may determine the difference between rankings or breaking a
record, reducing drag is important. Indeed this idea is not new. We see it in the attempts to reduce frictional air resistance in
competitive attire in skiing, cycling, speed skating, and track events.
A popular suit worn at the 2000 Olympic Games was a Fastskin™ released for sale in 2000 by Speedo to reduce the drag. The
key feature is its fabric, which was designed to mimic the properties of a shark's skin (Figure 3) by superimposing vertical resin
stripes. The designers' intent was for the stripe to produce vertical vortices or spirals of water, which keep the passing water
closer to the swimmer's body and reduce the formation of separation bubbles and hence, form drag - a phenomenon known as the
'riblets effect'. However, for riblets to be effective they have to be aligned with fluid flow. When they are displaced, resistance
can increase. Thus, when swimmers roll from side to side, as in crawl and backstroke, or move vertically in butterfly and
breaststrokes, the Fastskin could actually hinder performance. Based on passive drag tests a reduction in total drag of up to 7.5%
was claimed when wearing the Fastskin (Speedo press release: Fastskin fact sheet). As was indicated above, that claim was
refuted by Toussaint et al (in press).
Figure 3. A scanning electron microscope image of a shark's skin. Credit: John Mansfield/Microbeam Analysis Society
However, the assumption underlying the proposal that riblets are performance enhancing is itself controversial. Vogel (1996)
questioned that tenet.
'Drag reduction has been claimed for just about every feature of the surface of every large and rapidly swimming
animal. The present chief candidate is the ridging characteristic of the dermal scales of sharks. These are claimed to be
lined up with the local flow direction. Experiments with analogous physical systems have been successful enough to
result in the production of a coating material ('riblets') that has been used on racing yachts. The ridges have
apparently evolved separately in several lineages of fast-swimming sharks. It should be emphasized that in both sharks
and artificial coating these are tiny ridges, closely spaced-less than 100 micro-meters apart and still less in height -
and that what is involved is a reduction of skin friction and not postponement of flow separation. Two matters, though,
get omitted from popular accounts. First, no one seems to have any direct evidence that the ridges actually reduce the
drag of sharks or that they work on sharks by the proposed mechanism. And second, the drag reduction achieved with
the artificial coatings are less than 10%, enough to create excitement in the hypercompetitive world of boat racing,
enough perhaps to make a difference to fitness in the competitive world of pelagic predation, but nothing approaching
the difference in skin friction between laminar and turbulent flows.
Writers of popular material in science are biased toward believing what scientists claim or even suggest. Perhaps they
don't appreciate sufficiently the difference between the enthusiasm associated with a novel and exciting hypothesis and
the more restrained satisfaction that accompanies decent confirmation and achievement. But we cannot escape by
shifting blame; I think what is needed at this point is a bio-fluid version of Koch's famous postulates in bacterial
epidemiology. A claim of drag reduction should be viewed with skepticism until it: (1) has been tied to a plausible
physical mechanism, (2) has been shown to work on physical models under biologically relevant conditions, and (3)
has been shown to work by some direct test on real organisms under controlled and reproducible conditions. Much less
desirable alternatives to the third are interspecific comparisons of morphology and correlation's of morphological
differences with differences in habit and habitat.' (Vogel, 1996, p. 153)
Another feature of the Speedo bodysuits is the placement of ridges of stitching that are supposed to 'channel' water flow more
effectively. There is a problem with this hypothesis. Ridges act as resistance-enhancers when they are positioned at an angle to
the fluid flow. In those cases, they baffle the fluid flow. Since swimmers often change the alignment of their body segment
surfaces during strokes, it would seem ridges of stitching would increase resistance rather than reduce it. It is not difficult to
imagine the detrimental effect of these ridges in breaststroke when the legs are drawn up, in opposition to the fluid flow,
preparatory to kicking. Generally, even with static bodies such as boat hulls, ridges are minimised except for functions such as
stability. Some other manufacturers have copied the Speedo ridge concept. However, it should be noted that the Speedo brand is
the only one that uses the 'shark skin' analogy. Other manufacturers use different strategies for drag reduction. Unfortunately,
these strategies are not well documented. This prevents objective analysis and understanding of the claims.
In addition to the reduction in form drag by reduced separation bubble formation, it is claimed that the new whole-body swimsuit
assists in reducing form drag by making the swimmer's body more 'streamlined' in shape. Furthermore, wearing a tightly fitting
swimsuit has the advantage that it tends to flatten out the contours of the body and reduce the amount of water that flows between
the suit and the skin surface thereby reducing form drag.
This discussion has centered mainly around the Speedo Fastskin bodysuit because of its availability. Other manufacturers, such
as Adidas, Tyr, and Mizuno, have produced bodysuits often with design differences. For example, Adidas reported the following.
From the Swimming Times (September, 1999) -- Adidas claimed the following in its advertisement 'Adidas revolutionizes
'This is how it (the Equipment Bodysuit) works:
Increased speed and endurance through the compression effect of Lycra Power which reduces muscle and skin
vibration, cutting turbulence and fatigue, increases stroke accuracy, allowing more efficient performance.
Reduced drag through the 'second skin' fit as the Equipment bodysuit remains static through extreme movement,
preventing water from penetrating at the neck, wrists and ankles; the Teflon-coated silhouette gives a hydrodynamic
profile and prevents water retention. [This is an admission the bodysuit is a floatation device.]
Maximum flexibility and comfort from a perfect fit which avoids any rubbing.'
Finally, Adidas stated:
'In tests, the Adidas Equipment Bodysuit has been scientifically proven to enhance athletic performance, allowing
swimmers to be faster and more efficient through the water.'
The concepts and 'science' behind Adidas' product are very different from those of Speedo.
While manufacturers cite their own research to support claims that bodysuits improve swimming performance, independent
assessment of that research will not be possible until it is made available for public scrutiny. Thus, one cannot be sure the
manufacturers' research was conducted scientifically, validly, and objectively.
Assuming bodysuits reduce resistive drag without affecting propulsion or increasing physiological cost, the best way to establish
the effects of the suits is to measure active drag with and without a suit. Such a study was conducted recently by one of the
authors (Toussaint et al, in press) using an established method for the measurement of active drag (M.A.D system, Toussaint et
al, 1988b). With this system, swimmers push off pads that are instrumented with force transducers. At constant swimming
velocity, the mean propelling force is equal to the mean drag force (Vaart et al., 1987). By measuring the forces applied at each
pad and the velocity of the swimmer, the researchers can determine the mean drag force. Using this system, active drag was
calculated for six males and seven females swimming at different velocities (1.10 up to 2 m•s-1) with the Fastskin neck-to-ankle
bodysuit and with conventional swimwear.
For the Fastskin suit, a nonsignificant reduction in drag of ~2% (p = 0.31; Figure 4) was found, a figure considerably less than the
7.5% claimed by Speedo. Drag differences varied with velocity and swimmers. In most instances, there was no clear reduction in
resistance with the Fastskin.
Figure 4. Drag data for all subjects showing active drag dependent on swimming velocity wearing the Fastskin and conventional
suits. Fitted curves are presented as well. The overlap of all data demonstrates the lack of difference between each form of
For some subjects an active drag advantage seemed present. The most extreme case is shown in Figure 5. At 1.65 m•s-1 an 11%
reduction in active drag was observed, a value that was nevertheless still not statistically significant. The non-significance means
that observed differences may be due to uncontrolled factors (e.g., measurement errors, variability in swimmers' postures,
placebo effects, the fit of the suits) rather than to the effect of the bodysuits. It was with this swimmer that the authors opined that
the 11% 'reduction" came not so much from a benefit of the bodysuit, but an increase in resistance from an ill-fitting conventional
Figure 5. Drag data for the subject who appeared to gain the greatest advantage from the Fastskin compared to a conventional
suit. Fitted curves are presented as well. Although the curves differ, it is invalid to assert the differences are due solely to the type
of suit used.
Stager (2000) used an alternative method to evaluate the impact of bodysuits. At the 2000 US Olympic Trials, all swimmers were
issued with bodysuits, from several manufacturers but mostly Speedo. If these suits improved performance as manufacturers
advertised, it would be reasonable to expect a 'step-like' improvement in all performances at the trials. Such sudden and
noticeable improvements commonly occur when there is a rule change that advantages the swimmer.
Using data from US Olympic Trials from 1968 to 1996, several regression equations were developed, and the power curve best-
line-of-fit was used to predict 'normal progression' times for the 2000 Trials. If the suits were as effective as proposed, most
recorded times would exceed predicted times. Thus, Stager's work assessed whether bodysuits contributed to a better than
expected level of performance. If there were no obvious improvements, the suits would be declared as not performance
enhancing, and swimmers' performances would be in accord with reasonably expected progress.
Only two results differed significantly from predicted times. The women's 200m backstroke was significantly slower and the
women's 100m breaststroke faster than predicted. No improvement impact associated with bodysuits was evident.
Stager's analysis considered shaved swimmers and adds one more bit of information. For what is known with shaved swimmers,
the bodysuits do not provide an advantage.
Toussaint et al. (2000) indicated that swimming exercise intensity relates to the drag coefficient times swimming speed cubed.
This can be used to evaluate manufacturer's claims. If the 7.5% reduction in total drag from Fastskins claimed by Speedo was
correct, a 2.5% increase in swimming velocity could be expected. A 2.5% reduction in 100-m race time (2.5% of 49s = 1.2s)
would be a sensational result. Stager determined the mean difference between predicted and actual times to be approximately
1/10th of this, a non-significant difference. It is interesting to note that the winner of the men's 100m freestyle race at the 2000
Olympic Games broke the existing world record by .34 seconds while wearing only a waist-to-ankle suit.
At this stage it has not been shown that performance is improved by a bodysuit. Clearly, some believe that the suits do improve
performance. Among those, the improvement is popularly attributed to the reduction of resistive drag. However, if the suits do
aid performance then there may be alternative explanations.
One explanation is increased buoyancy. In particular, when buoyancy is increased in the hips and legs, streamline is improved
and frontal area is reduced. This could be a reason why the waist-to-ankle suits are popular with males, who tend to sink more in
the legs than females (see, for example, MacLean & Hinrichs, 1998; 2000). Toussaint et al. (1989) found that wetsuits worn by
triathletes reduced drag by approximately 15%. This was attributed to their effect of shifting the centre of buoyancy away from
the head and towards the feet. Thus, if bodysuits provide buoyancy and the buoyancy is distributed rearward, they may provide
an advantage in a similar way. At the 2000 Olympic Games all male crawl-stroke gold medallists, other than Ian Thorpe (400m
free) wore waist-to-ankle suits. Full bodysuits were shunned by Anthony Ervin, Gary Hall Jr., Pieter van den Hoogenband, and
Grant Hackett. However, in the other three competitive strokes, bodysuits and suits-to-ankles were not nearly as popular as in
crawl stroke events. It would seem, at least among males, that Bergen's findings of assistance for crawl and butterfly strokes is
verified by the preferences of the best swimmers.
Figure 6. Underwater photographs of the Fastskin suit on the leg of a swimmer. The light refraction is due to air bubbles trapped
in the fabric. The 'spots' are surface bubbles adhering to the fabric. Both are sources of floatation.
According to FINA-rules, devices that improve flotation are not allowed in competitive pool swimming. In that context
swimwear manufacturers try to optimise their products by focussing on the reduction of surface drag. However, Rushall (2000a)
cited pilot study results from Australia using the latest bodysuits (Speedo's 'Fastskin' and 'Adidas Equipment Bodysuit'). There is
an initial buoyancy effect from the suits because it takes considerable time for the fabric to become saturated. In the meantime air
trapped within and around the suit contributes to buoyancy. Until the fabric is saturated the suits aid buoyancy. The light
refracted from the surface of the suits shown in Figure 6 is due to trapped air in the micro-channels.
Aleyev (1977) identified the possibility that tight suits might reduce drag by preventing large oscillating deformations of
subcutaneous adipose tissue when swimming at higher speeds. It has also been proposed that the tightness of the suit may assist
venous blood return.
Rushall (2000b) hypothesised that some swimmers might benefit from an indirect mechanical effect. Some swimmers have a
technique flaw that causes excessive hip sway back and forth in crawl and backstroke, or rise and fall in butterfly. Excessive hip
movements usually result from faulty stroke entries. These movements cause an increase in active drag, mainly from two sources:
i) increased form drag, and ii) increased wave drag. Rushall proposed that because neck-to-knee bodysuits fit very tightly, hip
sway is reduced. The reduction in movement range reduces these two forms of resistive drag, resulting in faster swimming for the
same amount of energy expenditure. If there is, in fact, an improvement in performance due to the suits in the case of some
swimmers, then it may be for this reason rather than due to a reduction on surface or form drag.
Rushall has also hypothesised that the suits might help some swimmers by having an added 'ergogenic' effect. The suits might
maintain good posture and alignment to reduce form drag. If this were the case, then a swimmer would expend less muscular
energy to maintain a streamlined posture. The energy freed from such a task could then be used to generate propulsion.
From observation of the various preferences of swimmers, it is clear that some swimmers favour the suits, but the body area
covered by the suits varies among swimmers. Some swimmers believe that they are better off without the bodysuits. Thus,
swimmers themselves are not convinced that the suits yield an advantage. It seems that swimmers need to be sure about what
'suits them'. Rushall (2000c) provides several interesting facts that have emerged from observation of various swimmers in
different swim meets. For example, Michael Klim discarded a Speedo neck-to-ankle suit in favour of a Speedo waist-to-ankle suit
to break his world 100m Butterfly record twice in three days.
Some swimmers complain that the suits remove 'feel' for the water. The loss of direct proprioception of the water could cause
imprecise movements and a departure from their optimal technique. For this reason most swimmers have now rejected full
versions of the suits, particularly the sleeves. Another reason for opting for versions without arms was the feeling that the suits
restricted arm actions, making a high recovery more difficult. Tightness has been found to restrict movements around the
shoulders and arms in all strokes, and around the knees in backstroke and breaststroke.
Although there has been insufficient research, there is a view that the muscle compression caused by suits may improve
performance through increased muscle fibre recruitment. However, Rushall has identified that because some muscles would be
affected and others not affected, the total movement pattern may be disrupted and efficiency reduced.
Professor Horacio Vielmo of the Federal University of Rio Grande do Sul, Brazil (personal communication, July 20, 2000), a
prominent hydrodynamics scientist, evaluated the assistance promoted by Speedo's 'Aquablade' suit (1996 vintage). While
Speedo promoted distinct advantages and figures for that suit, most of which were theoretically derived, in practical
circumstances the 'old' Aquablade provided negligible assistance.
Rushall cited several reasons why the texture that is supposedly effective in reducing drag in sharks may not be effective for
humans. The most profound of these is that a shark's body is streamlined with few protuberances to disrupt the flow of water
during movement. In contrast, a human has a very irregular body surface. Thus, as it moves through the water it produces
turbulent flow. Waring (1999) found that strategic placement of vortex generators can reduce form drag by minimizing the size of
the separation bubbles behind the buttocks and in the small of the back of a submerged swimmer (Figure 7). However, the tests
conducted in Waring's study applied only to a submerged swimmer in a constant glide posture such as that maintained for very
short periods following starts and turns. The tests do not apply to swimmers actively using arms and legs, their movements
creating irregular flow. The tests were also unsuitable for surface swimming where the effect of the air-water interface must be
taken into account.
Figure 7. Model showing the locations of separation bubbles found by Waring (1999).
The above review indicates that there remains much to be learnt about whether bodysuits provide an advantage. It is clear that the
transfer of manufacturers' 'results' to competitive performances has not occurred. The claims have not been vindicated by the
performances of moderate to highly skilled performers. The advent of bodysuits has not resulted in a performance 'revolution' or
any noticeable performance increase in any class of event.
While there is a rationale underlying these suits, whether the suits are effective in a real swimming situation is not yet
established. The science underlying the design and production of bodysuits is particularly spurious. Similarly, the science
refuting their value is sparse. Neither the case for or against has a solid footing. In general, scientists are sceptical of
manufacturers' claims, and emerging studies seem to be siding with the scientists.
However, coaches and scientists do seem to agree on several aspects of bodysuit use. Those agreements lead to the following
conclusions and recommendations.
1. When swimmers are unshaved and wear normal training swimsuits, freestyle and butterfly performances might
improve in some individuals if they wear bodysuits.
2. It is unlikely that bodysuits will enhance racing performances in championship meets when swimmers are shaved and
wear tight conventional racing suits.
3. Backstroke and breaststroke swimming is not enhanced by bodysuits, whether a swimmer is unshaved or shaved.
4. Some individuals will be assisted by bodysuits. The determination of assistance should only be made after careful
5. Once bodysuits become wet, they contain more water than do tight conventional suits, and are likely to cause a
swimmer to go slower, rather than faster, particularly in races longer than 200 m.
6. Some bodysuits, because of coatings on their fabrics, will take longer to "get wet" than others, but even they will
eventually suffer the same problems as those that wet quickly.
7. Particularly tight bodysuits could hamper the range of movement at important joints, such as the shoulders, hips, and
knees, and consequently, will hinder the correct execution of turns and dives.
If you are a swimmer contemplating purchasing one of these devices, suit yourself, but think about it first and be sure that the
bodysuit suits you.
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Return to Table of Contents for The Bodysuit Problem.
... Swimming velocity is determined by a function of energy supply rate, drag and swimming efficiency (promotion efficiency and mechanical efficiency) (Seifert et al., 2015). Although the energy demand-to-supply ratio and swimming efficiency were dependent on the swimming skill of the individual, the drag varies not only with their posture (Capelli et al., 1995;Zamparo et al., 2009) and technique (Gatta et al., 2015; Sanders et al., 2001;Seifert et al., 2015) but also with the swimsuit type (Benjanuvatra et al., 2002;Marinho et al., 2012;Mollendorf et al., 2004;Morales et al., 2019;Starling et al., 1995). Therefore, it would be changed in drag-velocity relationships, propulsive power, and IAP if newly developed swimsuit affects swimming posture as manufacturers have claimed and some studies have suggested (Morales et al., 2019;Sanders et al., 2001). ...
... Although the energy demand-to-supply ratio and swimming efficiency were dependent on the swimming skill of the individual, the drag varies not only with their posture (Capelli et al., 1995;Zamparo et al., 2009) and technique (Gatta et al., 2015; Sanders et al., 2001;Seifert et al., 2015) but also with the swimsuit type (Benjanuvatra et al., 2002;Marinho et al., 2012;Mollendorf et al., 2004;Morales et al., 2019;Starling et al., 1995). Therefore, it would be changed in drag-velocity relationships, propulsive power, and IAP if newly developed swimsuit affects swimming posture as manufacturers have claimed and some studies have suggested (Morales et al., 2019;Sanders et al., 2001). Although effect sizes in all maximal swimming velocities were low or moderate, RS used in this study significantly increased swimming velocity in both pull and swim compared with CS. ...
... During front-crawl swimming, IAP is influenced by the co-activation of trunk muscles associated with the movement of upper and lower limbs (Moriyama et al., 2014a(Moriyama et al., , 2014b. If RS helps maintain 'horizontal posture' associated with trunk muscle activity, as claimed by manufacturers and some studies (Morales et al., 2019;Sanders et al., 2001), it is predicted that decreases in IAP would be observed during swimming because the load on trunk muscles would be reduced. However, in contrast, IAP showed no significant differences during maximal swimming between RS and CS with small effect sizes. ...
We investigated the effects of jammer-type racing swimsuits (RS) on swimming performance during arm-stroke-only (pull) and whole-body stroke (swim) in 25-m front-crawl with maximal effort. Twelve well-trained male collegiate swimmers wore RS and a conventional swimsuit (CS) and performed three tests: pull, swim, and pull using the system to measure active drag (MAD pull). Swimming velocity and intra-abdominal pressure (IAP) were determined in all tests. Stroke indices during pull and swim and drag–swimming velocity relationship and maximum propulsive power during MAD pull were also determined. Swimming velocities during pull and swim while wearing an RS (1.59 ± 0.13 and 1.77 ± 0.09 m·s⁻¹, respectively) were significantly higher than those wearing a CS (1.57 ± 0.14 and 1.74 ± 0.08 m·s⁻¹, respectively). Stroke length during pull and swim was significantly greater while wearing an RS (1.68 ± 0.12 and 1.83 ± 0.13 m, respectively) than wearing a CS (1.63 ± 0.10 and 1.81 ± 0.13 m, respectively). However, no significant differences were confirmed between the other variables in all tests. In conclusion, swimming performance is improved when wearing an RS compared with a CS.
... For the purposes of this study, we will refer to the knee-length competition swimsuits as compression race suits. Studies describing performance benefit of racing suits have shown inconclusive results (Marinho et al., 2012;Montagna et al., 2009;Pendergast et al., 2006;Roberts et al., 2003;Sanders et al., 2001;Toussaint et al., 2002). Certain studies have suggested that racing suits reduce drag (Aleyev, 1977;Benjanuvatra et al., 2002;Mollendorf et al., 2004;Sanders et al., 2001;Toussaint et al., 2002) and improve swimming performance (Starling et al., 1995). ...
... Studies describing performance benefit of racing suits have shown inconclusive results (Marinho et al., 2012;Montagna et al., 2009;Pendergast et al., 2006;Roberts et al., 2003;Sanders et al., 2001;Toussaint et al., 2002). Certain studies have suggested that racing suits reduce drag (Aleyev, 1977;Benjanuvatra et al., 2002;Mollendorf et al., 2004;Sanders et al., 2001;Toussaint et al., 2002) and improve swimming performance (Starling et al., 1995). The science behind drag reduction and increased performance appears multifactorial. ...
... Other researchers have concluded that these types of suits neither reduce drag nor improve performance (Roberts et al., 2003;Sanders et al., 2001;Toussaint et al., 2002). According to Sanders et al. (2001), the science underlying the design and production of compression suits is particularly spurious. ...
Purpose The purpose of this investigation was to quantify the extent to which forced vital capacity (FVC) in competitive swimmers may differ from nonswimmers and determine if compression race suits reduced FVC when compared to practice swimsuits. Identification of the differences in FVC between swimmers and nonswimmers as well as pulmonary function differences secondary to swimsuit construction may inform assessment of the competitive swimmer with paradoxical vocal fold motion (PVFM). Method Using a prospective, mixed within- and between-groups, repeated measures design with 10 female competitive swimmers and 13 female nonswimmers, FVC was measured and compared between the two groups. Further FVC assessment was completed with the swimmers to identify FVC differences between a practice suit and a compression racing suit. Results FVC in swimmers was significantly larger than FVC in nonswimmers by over 1 L. The predicted FVC volumes were significantly smaller than the actual FVC volumes for swimmers. No significant differences were identified between the practice swimsuit and the compression race suit or between the predicted and actual FVCs for the nonswimmer group. Conclusions Swimmers have unique pulmonary function and physiology that require consideration during the assessment for PVFM to ascertain the extent to which the pulmonary system may be compromised from PVFM, reduced exercise intensity, or both. Knowledge of differential diagnoses and adequate characterization of pulmonary volumes in swimmers will improve assessment processes.
... However, they were not authorized by Fédération Internationale de Natation: International Swimming Federation (FINA) until 8 October 1999 (Craik, 2011;Foster et al., 2012) and in the runup to the 2000 Olympic Games they revolutionized competitive swimming (Craik, 2011). Furthermore, in that year medals were won with and without these new swimsuits (Sanders et al., 2001). ...
... To all of this, one could add that excessive compression in the area of the thighs could alter the surface (Yermahanova et al., 2016), the area and the profile of the body (Sanders et al., 2001), reducing the size of the air pockets (Mountjoy et al., 2009), along with the muscular oscillations and skin vibration (Marinho et al., 2012), improving stroke coordination and frequency (Roberts et al., 2003;Chatard and Wilson, 2008). On the other hand, this compression could suppress blood circulation and the mitochondrial aerobic respiratory system (Kainuma et al., 2009), stimulating anaerobic glycolisis which would favor short distance events, due to the instantaneous strength of the white muscle fibers. ...
... From Barcelona ′ 92 to Rome 2009, there was a generational improvement (Parnell, 2008;Mountjoy et al., 2009;Berthelot et al., 2010;Craik, 2011;Foster et al., 2012;Drašinac et al., 2015) that revolutionized competitive swimming over almost two decades, causing some swimmers to consider whether to use them or not, regardless of the results and the medals obtained (Sanders et al., 2001), even when faced with a generalized contrary effect . Even so, the improvement in terms of times and records that still stand (O'Connor and Vozenilek, 2011;SwimNews, 2011) has been demonstrated in a significant and longitudinal manner, despite the controversies received (Moloney, 2008a(Moloney, ,b, 2009Jeffery, 2009). ...
Full-text available
The goal of this research was to review the experimental studies that have analyzed the influence of "high-speed swimsuits" on sports performance up to the appearance of the model "Jammer" in competitive swimmers. The design was a review following PRISMA Methodology, in which 43 studies were reviewed of a total of 512. Several searches were conducted in electronic databases of the existing research in this field (Google Scholar, Dialnet, Web of Sciences, and Scopus). The only studies excluded were those that reviewed the effects with neoprene and tests with triathletes. The studies that were included were published and peer-reviewed from 1999 to 2018 in which the effect of high-speed swimsuits was analyzed. The results showed the possible effects that high-speed swimwear can have in relation or not to competitive performance, biomechanical, physiological and psychological factors, flotation, drag, the material and the design until the introduction of the model "Jammer." As conclusions, the lack of consensus due to the variety of fields of study means that improvements in competitions are still not clarified. In addition, the change in the rules may have effects on swimmers even though they have beaten records with other swimwear. Finally, the debate concerning whether medals were won unfairly or not is proposed.
... It is thus recommended to focus on reducing drag in the hrst instance, and then develop a stronger propulsion force as long as positions for minimal resistance are maintained. Sanders et al. (2001) also suggested that swimming performance may be best enhanced by slightly adjusting a stroke technique to reduce drag, rather than by chasing improvement in the propulsive force. ...
... On one occasion a signihcant drag reduction of 11% was observed and was reported to be more due to a misplacement of the body position or an ill-ht of the conventional suit, rather than as a result of wearing the Fastskin suit. Sanders et al. (2001) recalled that in order to measure drag digerences between diEerent suits, the swimmers must be able to repeat active swims with both the same technique and eEort. In addition to drag measurements d#culties, the drag assessment of body suits for swimmers is a very complex problem due to the large number of factors involved (suit htting, placebo egect, suit wetness, etc.). ...
Swimming as an Olympic sport is getting ever more competitive. Since the ban of the full-body length suits in 2009, research in swimming has had the aim of re-establishing new world records. This research investigates the likely dominance of the flow regime around the swimmer’s head on their overall drag resistance. Both pool testing of swimmers and numerical simulations were initially undertaken to provide an insight into the measurement challenges at stake when evaluating a swimmer's resistance. Due to the inherent variability of a swimmer's performance, limited access to elite swimmers and excessive computational requirements the work concentrates on the use of rigid models for testing in a towing tank. A methodology aimed at breaking down the complexity of the flow physics around a swimmer's body is developed through the study of three models arrangements: a sphere, a head and a mannequin. A surface-piercing sphere is drag-tested over the critical Re-Fr range (1x10<sup>5</sup> ≤ Re ≤ 7x10<sup>5</sup>, and 0.4 ≤ Fr ≤ 1.5). Using a combination of above-water still photographs/videos and drag/vertical force measurements, a flow taxonomy is established. The existence of a drag crisis over the laminar to turbulent boundary layer transition is highlighted as a key feature that influences a swimmer’s resistance. It is coupled with a sharp change of free surface deformation, from a large breaking wave to a thin sheet of fluid that passes cleanly over the sphere. A similar flow taxonomy is observed in the case of a head and visual observations of a flow regime change over the head are noticed when part of the mannequin. Various caps/goggles and head positions/shapes are tested on either the head only or with the mannequin’s body. These studies indicate that equipment can have a large influence on a swimmer’s resistance. Although a pre-selection process in a towing tank environment proved to be useful for manufacturers, an elite athlete still needs to be drag-tested to determine the best equipment for their head shape and body morphology. An initial protocol to select the best equipment (goggles, cap and suit) for each individual athlete is therefore suggested.
... 9,26-28 At present, the styles of noncompetitive female swimsuits can be divided into one-piece swimsuits, two-piece swimsuits and bikini swimsuits. 28 Different types of swimsuits cover different areas of the body and exert different pressure on the body, 29,30 confirming that different styles of swimsuits result in differences in sports performance and physical comfort. 22,23 In addition, Berthelot et al. (2010) 25 pointed out that women tend to suffer more pressure on body parts because their curves are more concave and convex than those of men. ...
... Similarly, due to the lack of data, more research is needed to confirm whether the swimmer's body characteristics and the suitability of a swimsuit are decisive for comfort. 29,31 In terms of the fit between body type and swimsuit, the effect of different body shapes on swimsuit design has been extensively studied in the literature. Several surveys have found that female body types can usually be divided into five categories: 'hourglass', 'pear', 'apple', 'strawberry' and 'flat'. ...
Full-text available
Among the fitness and body shaping exercises of Chinese women, swimming has become an increasingly popular sporting activity. Swimsuits are fundamental to participation in this sport and paramount to achieving the wearers' aim of participation. A survey of 3348 Chinese women showed that body fit is central to the purchase of a swimsuit, whether one piece or two piece, with the two-piece swimsuit proving the most popular in terms of comfort. This survey revealed that the comfort of a swimsuit is relative to the design variables of the swimsuit style, the material/body cover factor and, informed by the female form, body size and body shape. This is particularly pertinent in both the right and left anterior mammary regions and also the left lateral mammary region for the female wearer to stay comfortable during swimming when she moves in the water. This study investigated the factors that affect the comfort of women wearing swimsuits when they swim. The two-piece swimsuit was considered the most comfortable. It was also found that swimsuits negatively affect women's chest area. These results present important considerations for swimsuit manufacturers.
... These experimental data suggest that the water flow was tripped by frictional drag, remained attached to the swimmer body, thus decreasing form drag (Polidori et al., 2006;Marinho et al., 2009b). Pendergast et al. (2006) stated that studies of the effects of a drag reducing textile suit on active drag at low to moderate velocities failed to show a clear benefit, although at the fastest velocity the textile suit reduced the drag of some swimmers (Sanders et al., 2001;Toussaint et al., 2002). Other authors used physiological approaches, and the results were controversial as well (Starling et al., 1995;Roberts et al., 2003). ...
Computational FLuiddynamics
... 3,4 SPEEDO's swimsuit, which extracts structural features from the shark's surface by bionics, reduces resistance to surrounding fluids by about 7.5 percent. 5 Gruber et al. 6,7 studied the noise reduction mechanism of bionic tail edge sawtooth with different parameters through experiments, and found that bionic non-smooth tailing edge surface can effectively suppress the noise in low frequency range. Jones and Sandberg 8 further studied the experimental results of Gruber using DNS numerical simulation method. ...
Full-text available
The hydraulic and acoustic performance of centrifugal pump is closely related to hydraulic structure parameters, and they are contradictory. In order to solve this contradiction, this paper introduces the pit bionic structure, and proposes an optimization method based on multi-objective test design and response surface to improve the hydraulic and acoustic performance. Taking the bionic vane pit diameter, axial spacing and radial spacing as design variables. Taking the maximum hydraulic efficiency and total sound pressure level reduction of centrifugal pump as the corresponding objectives. The multiple regression response surface model was constructed to determine the optimal parameter combination of hydraulic performance and noise collaborative optimization. The optimization results were verified by numerical simulation and experimental test. The results show that the response surface multi-objective optimization method has high prediction accuracy, has obvious synergistic effect on the hydraulic and acoustic performance. The highest point of the efficiency curve after optimization is shifted to the direction of large flow, which widens the high efficiency working area of centrifugal pump. Under the rated condition, the hydraulic efficiency is increased by 3.03%, the efficiency increase rate is 4.21%, the total sound pressure level is reduced by 4.96 dB, and the noise reduction rate is 3.01%.
... Speedo® also made a bionic swimsuit from the fabric with Riblet effect (Fig. 6e) [3]. On the underwater photography of swimsuits, there are air bubbles "trapped" in the fabric, which allows the swimsuit to stay dry for a longer time (Fig. 6f) [39]. Thanks to the innovative design, the water drag is reduced by 3 % compared to similar products [32]. ...
Conference Paper
Full-text available
Biomimetics, biomimicry and bionics are synonyms for the scientific discipline of creating new structures inspired by nature. Biomimetics systematically analyses the evolutionary processes of living organisms, their structural relationships, the characteristics of natural materials and it studies how this knowledge can be used to create the optimal products and new sustainable materials. In the past decade, the biomimetics has received an incentive for the development by the technology modernization, and above all, by making it possible to study the micro- and nanolevels of biological structures. On the other hand, the miniaturization of technological devices has increased the need to understand the tribological phenomena on micro- and nanolevel, where is a huge potential for technological innovation. The integration of advanced research methods made it possible to discover new aspects in the structure and properties of biological materials and transfer that knowledge into new concepts or products. State-of-the-art of biomimetics progress is discussed, as well as, its goals and the potential to simultaneously achieve the financial and ecological contribution by realization of bio-inspired concepts. An overview of biomimetic researches is also provided, with special emphasis on the possibility of their tribological applications. The characteristic examples have been presented and those examples show how the structural and mechanical properties of the material were used as the basis for developing new creative solutions to solve the problem of friction in engineering applications.
The Chapter opens up with a brief chronological background of growth of composite applications. In fact, the ‘applications of thermoplastic composites’ still deserve to be called as a niche area. They have taken over some of the applications which traditionally metals and thermoset composites have been dominating. Fiber reinforced polymer (FRPs) composites have already made several in‐roads into modern Automotives, aerospace, marine and military applications. Once the processing and properties of a chosen composite are optimised injection molding of the same can provide much faster production volumes in a short time. This can meet the demands of a larger population. In fact, the modern sports equipment and several tools are made up of composites or nanocomposites. Construction activities of civil engineering derive several benefits out of composites and nanocomposites. In fact, repairs and re‐facilitation of bridges, buildings and high‐ways can be attended swiftly and safely. Emergency seismic repairs can be attended with the FRPs. Some electrical applications such as super capacitors, electro‐magnetic interference shielders are possible because of the knowledge of the composites. Graphene and CNTs are bringing out several surprizing applications. Another domain of growing applications is in bio‐medical area where composites of graphene, CNTs and natural fibers are bringing out several surprizes and break‐throughs. Bio‐composites specially with PEEK, PLA and other polymers are finding advanced applications in bio‐medical devices and implants. Bio‐mimetics is an area which is growing as man never stopped learning from nature. The Chapter closes with a gist of Lotus effect, Gecko effect etc.
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This study investigated the relationship of gender and buoyancy to sprint swimming performance. The center of buoyancy (CB) and center of mass (CM) were measured using reaction board principles. Performance was evaluated as the time needed to complete the middle 13.7 m of a 22.9-m sprint for kicking and swimming trials. Nineteen female swimmers (mean ± SD, 21.9 ± 3.2 years) had significantly more body fat (24.1 ± 4.5%) than 13 male swimmers (21.7 ± 4.2 years, 14.8 ± 5.0%). Males swam and kicked significantly faster (p <.01) than females. Percent body fat, upper body strength, the distance between the CB and CM (d), and the buoyant force measured in 3 body positions all met the criteria for entrance into a regression equation. When gender was not controlled in the analysis, these variables accounted for 70% of the variance in swim time (p <.008). When gender was controlled in the analysis, these variables accounted for 45% of the variance in swim time (p = .06). Percent body fat accounted for the largest amount variance in both regression analyses (39%, p <.001; 18%, p = 0.02, respectively). Upper body strength accounted for 14% of the variance in swim time (p = .006) when gender was not controlled but only 4% when gender was controlled (p = .27). The distance d as measured in a body position with both arms raised above the head was the buoyancy factor that accounted for the greatest amount of variance in swim time (6% when gender was not controlled, p = .06, 10%; when gender was controlled, p = .07). Percent body fat, d, and the buoyant force accounted for no significant amount of variance in kick time. These data suggested that a swimmer's buoyancy characteristics did have a small but important influence on sprint swimming performance.
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The main purpose of this study was to develop a model for calculating forces produced by a swimmer's hand, with the thumb adducted, accelerating in the direction of flow. The model included coefficients to account for the velocity and acceleration of the hand. These coefficients were designed to calculate forces in the direction opposite the motion (drag) and two components of lift orthogonal to the direction of motion. To determine the coefficients, three-dimensional forces acting on a resin cast of a swimmer's hand were recorded while accelerating the hand from rest to 0.45 m · s-1 and 0.6 m · s-1 in a towing tank. The hand orientation was varied throughout the entire range at 5°increments. Three-dimensional surfaces describing the magnitude of the coefficients as functions of pitch and sweepback angle were produced. It was found that acceleration coefficients as well as velocity coefficients are required for accurate modeling of the forces produced by the hand in swimming. The forces generated by the hand are greatest when pitch angles approach 90°due to the large contribution by the drag component. However, at pitch angles near 45°and sweepback angles near 45°and 135°, lift forces contribute substantially.
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The purpose of this study was to investigate the wave characteristics of breaststroke swimming. Particular emphasis was accorded the question of whether modern breaststroke is 'flylike' (referring to the butterfly stroke) and whether 'waves' travel along the body during the breaststroke cycle. Selected body landmarks and the center of mass (CM) of 8 Olympic breaststroke swimmers were quantified. Fourier analysis was conducted to determine the amplitude, frequency composition, and phase characteristics of the vertical undulations of the vertex of the head, shoulders, hips, knees, and ankles. The differences in phase between these landmarks for the first (H1) and second (H2) Fourier frequencies were investigated to establish whether body waves traveled in a caudal direction. While the motion of the upper body was somewhat flylike, the velocity of the H1 wave from the hips to ankles was variable among subjects and, for all subjects, was ton slow to be propulsive. Contrary to what one would expect, the range of vertical motion of the CM was inversely related to the range of hip vertical motion. The two highest placing subjects, based on preliminary heat times (S1 and S4), were distinguished by a large range of hip vertical motion and a small range of CM vertical motion.
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The purpose of the present investigation was to evaluate the contribution of passive drag (Dp) to the prediction of a 400-m swim. A second aim was to evaluate the relation between Dp and some anthropometric factors. In a first experiment, 84 swimmers (both sexes) had their Dp (at 1.4 m.s-1) and VO2max measured in water and put into relation with the performance time of a 400-m swim. Performance times were mainly related to VO2max (r = 0.70 and 0.72, p less than 0.01, for male and female swimmers, respectively). Inclusion of Dp as a second variable improved significantly (p less than 0.01) the accuracy of the regression up to 0.75 and 0.78. Passive drag was also significantly (p less than 0.01) related to height (r = 0.80 and 0.60, p less than 0.01, for male and female swimmers, respectively), weight (r = 0.78 and 0.54, p less than 0.01, for males and females, respectively), and body surface area (r = 0.80 and 0.58, p less than 0.01, for males and females, respectively). In a second group of 7 male swimmers, it was found that Dp values were increased on average by 34% (p less than 0.01) when measured after a maximal expiration as compared to measurements after a maximal inspiration. In a third group of swimmers (n = 41) for which generalized joint laxity was measured, it was found that this variable contributes significantly to the Dp variability. The present results show that Dp can be considered as contributing significantly to prediction of performance in swimming.(ABSTRACT TRUNCATED AT 250 WORDS)
The purpose of this study was to determine the validity of the quasi-static assumption—that fluid forces exerted under unsteady flow conditions are equal to those exerted under similar steady flow conditions—in the case of a cylindrical model oscillating in a vertical plane about a transverse axis normal to the flow. The findings indicated that the quasi-static approach is applicable only to cyclic motions with low frequencies and small accelerations. For swimming motions that involve high frequencies and high accelerations, like those that occur in competitive swimming, the vortex shedding effect and the added mass effect must be taken into account if accurate values are to be obtained for hydrodynamic forces.
Both a landmark text and reference book, Steven Vogel's "Life in Moving Fluids" has also played a catalytic role in research involving the applications of fluid mechanics to biology. In this revised edition, Vogel continues to combine humor and clear explanations as he addresses biologists and general readers interested in biological fluid mechanics, offering updates on the field over the last dozen years and expanding the coverage of the biological literature. His discussion of the relationship between fluid flow and biological design now includes sections on jet propulsion, biological pumps, swimming, blood flow, and surface waves, and on acceleration reaction and Murray's law. This edition contains an extensive bibliography for readers interested in designing their own experiments.
There has been a paucity of research that has investigated whether skilled performers of a complex sports skill can readily change their technique. This study was designed to investigate whether swimmers skilled in the conventional breaststroke technique could adjust readily to the wave action technique. Nine masters swimmers with well established and stable movement patterns for the conventional technique were coached in the wave action breaststroke technique. The swimmers were videotaped from the side during maximum speed trials of the conventional breaststroke technique before coaching and the wave action technique after ten 45-minute coaching sessions. The amplitude and phase of the waveforms comprising the vertical displacements of the body parts were determined by Fourier analysis. In response to the coaching, the amplitude of the fundamental frequency of the vertex of the head, shoulders, hips, and knees increased significantly (p < 0.01). The percentage of power contained in the fundamental frequency of the shoulder and hip vertical displacements also increased significantly (p < 0.01). All subjects changed the relative phase of the fundamental frequencies of the vertex, shoulder, and hip vertical displacements. It was concluded that in this complex skill, major changes to the low frequency waveforms comprising the motion were achieved readily.
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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.