Chapter 10: Development and design of performance swimwear – Functional Textiles for Improved Performance, Protection and Health

10

Development and design of performance swimwear

J. Wu,     Georgia State University, USA

Abstract:

Innovative performance swimwear has been widely used during competitive swimming competitions to reduce drag force and enhance swimmers’ performance. This chapter briefly reviews the history of performance swimwear development and focuses on the question of whether performance swimwear can significantly improve swimming performance in collegiate and professional swimmers. Specifically, this chapter provides information on the material and design of performance swimwear, the basic biomechanics of swimming, the measurement of passive and active drag force, and the effect of performance swimwear on drag forces and physiological and biomechanical responses during swimming. A brief discussion deals with the design and impact of performance swimwear in the future.

Key words

performance swimwear

swimming

drag force

biomechanics

physiology

10.1 Introduction

Swimwear is an article of clothing that is used for swimming and other aquatic activities. Swimwear is usually designed for men, women and children to accommodate their different body configurations. Swimwear design varies drastically in materials, colors, body coverage, level of fit and other factors. Performance swimwear is a type of swimwear that is specially designed to help professional athletes to further improve their swimming performance. Since the Olympic Games in Sydney in 2000, performance swimwear has attracted enormous public attention. Innovative materials and technology have been researched and applied by manufacturers such as Speedo and TYR to revolutionize the design of performance swimwear. The outcome is that a number of new swimming world records have been set over the first decade of the twenty-first century. Although the International Swimming Federation (FINA) banned the usage of full-body performance swimwear starting on 1 January 2010, it is important to review the development of performance swimwear during the last decade and forecast the future direction it might take.

This chapter focuses on the development of performance swimwear and addresses the question of whether performance swimwear can significantly improve swimming performance in collegiate and professional swimmers. Specifically, this chapter provides information on the material and design of performance swimwear, the basic biomechanics of swimming, the measurement of passive and active drag force, and the effect of performance swimwear on drag forces and physiological and biomechanical responses during swimming. Finally, the chapter forecasts the design and impact of performance swimwear in the future.

10.2 Development of performance swimwear

10.2.1 Brief history of the development of swimwear

During the classical period swimming was mainly done in the nude. The earliest swimwear can be traced back to Grecian times and early Pompeii. Wearing a special covering during swimming has occurred for centuries since then. However, no drastic changes in the design of swimwear occurred until the last century or two. The last two decades are the pivotal point in the development of functional and performance swimwear. New materials, designs and technologies have been used collectively to significantly improve the quality of functional and performance swimwear.

When public bathing and swimming became popular in France and England during the eighteenth century, appropriate swimwear was needed to bring men and women together on the beach. However, swimwear at that time was more like bathing gowns rather than functional swimwear. This type of swimwear was far from comfortable due to the materials and designs. To avoid indecent exposure, ladies at that time often sewed additional weights such as lead into the hem of the bathing gown, which in turn reduced the comfort and function of swimwear (Horwood, 2000). With increasing demands for better fit and functional swimwear, the last two centuries have witnessed a revolution in the development of functional and performance swimwear. Specially designed swimwear aimed to protect one’s modesty and more importantly to allow one to participate in swimming and water sports freely. Women’s typical swimwear at the end of nineteenth century had a two-piece design which included a one-piece blouse and trousers and another piece of skirt extending below the knees to conceal the figure. At the beginning of the twentieth century revolutionary designs of swimwear emerged to make swimwear more transparent and briefer (Davies, 1997). Young women of the 1920s adopted a figure-hugging wool jersey sleeveless tank suit. The next 30 years saw increased popularity for feminine cotton-printed swimwear with small overskirts to hide the thighs (Horwood, 2000). This swimwear design was broadly similar to the swimwear of today. During the 1950s a bikini or two-piece women’s swimsuit became a revolutionary milestone in the development of swimwear. With one piece covering the breasts and the other covering the groin or the entire buttocks region, a bikini exposes the rest of the torso. However, a traditional one-piece (also known as tank suit) swimsuit has been the typical performance (or racing) swimwear for women.

Like the evolutionary process in the development of women’s swimwear, men’s swimwear also changed over time. Men’s swimwear from the beginning showed marked differences to women’s swimwear. In contrast to the exaggerated curves used in female swimwear design, boxiness and solidity were the two main characteristics of men’s swimwear (Davies, 1997). One controversial issue that was vigorously debated was whether men should be allowed to bare their chests in public swimming and bathing. As a compromise, men’s typical swimwear during the 1920s had a skirt or a flannel knee pants which were worn outside of the trunks. By 1933, a convertible-style belted suit emerged which allowed the top to be removed by unzipping the newly invented zipper. However, many arrests were still made for indecent exposure. In the same year the BVD company hired Olympic swimmer Johnny Weismuller to advertise a new swimwear line, the first ever pair of bathing trunks (Cunningham, 2009). It was not until 1937 that men finally had the right to wear only the trunks during swimming. With women’s suits becoming more and more daring and flamboyant during the 1950s and beyond, men’s swimwear saw an explosion of color patterns and fancy artwork. In contrast to the almost constant transformation of women’s swimwear, men’s swimwear has been, to a great extent, confined to the basic boxer and brief. This was also the traditional men’s performance swimwear used in the second half of the twentieth century.

10.2.2 Materials used in performance swimwear

When swimwear took the form of bathing gown, mainly functioned as covering suit, it was made of natural fibers such as wool. These bathing gowns were extremely heavy in water when fully soaked, making the action of swimming more difficult. For example, the first Jantzen male swimwear weighed about 4 kg (9 lb) when fully soaked and therefore had a tendency to slip down. Although swimwear was often made of wool knit, other materials were also used including silk and cotton. But all of these natural materials still became extremely heavy when fully soaked. Therefore, the revolution in swimwear demanded snug-fitting fabrics that were lightweight, had recoverable elasticity and possessed dye retention and tensile qualities in the most adverse environments. Furthermore, though tight-fitting, the swimwear could not restrict movement during vigorous exercise.

Initially rayon fiber was used, first manufactured in 1889 from an extract of the mulberry leaf and introduced into the United States as artificial silk in 1910. The Jantzen Company produced the first rib knit stitch swimwear in the 1910s, which gave them a technological advantage over their competitors who still used wool jersey and flat stitch (Allender, 1996). During the following decade, American Rubber’s Lastex, an extruded rubber surrounded by fiber, became a popular staple, despite its failure to retain color and design when stretched, or retain its flex life when exposed to body oils. For example, in 1930s the Jantzen’s Sunsheen fabric was made with Lastex (Allender, 1996), and the BVD’s Sea Satin fabric was made of a rayon acetate fabric backed with Lastex for stretch and used a new knitting stitch called the Gulf stream stitch (Cunningham, 2009).

Searching for less expensive manmade fibers during the Great Depression, Wallace Carothers at Du Pont researched a series of polyamides and finally produced nylon 6,6, one of most commonly used polymers. Although nylon hosiery was introduced as early as 1940, it was not until after World War Two that nylon was fully utilized to improve the elasticity of swimwear. Nylon was found to be molded and heat set to a permanent shape and to display differing textures depending on whether it has been woven or knitted. Also, in the 1940s polyester, another commonly used polymer, was invented and used in the manufacture of swimwear. By the end of the 1950s, research scientists had produced a variety of manmade textile filaments such as Du Pont’s Dacron, Vyrene, Lycra and Spandex. These new materials, whether used alone or blended with other materials, continued to revolutionize the swimwear industry by improving the comfort, function and fashion of swimwear. The revolution of swimwear manufacture in the first decade of the twenty-first century has seen the inclusion of textured, thin fabric and water-repellent coatings used to reduce the drag force acting on the swimwear.

10.2.3 Design of performance swimwear

In the late nineteenth century swimwear was barely modified summer day-time wear for men and women due to social restrictions. This type of swim-wear had the vaguely functional design of sitting on a beach but was not optimal for swimming (Allender, 1996). Johnny Weissmuller, who won five Olympic gold medals in swimming, assisted the BVD Company in developing men’s swimwear in the early 1930s. The Weissmuller model that was introduced in 1931 had low cut armholes to free the arms and a high waist for more room from crotch to waist (Cunningham, 2009). This one-piece swimwear was almost identical to the traditional women’s performance (or racing) swimwear. Other swimwear from the same company had a two-piece design with shirts and trunks separately made with wool and rayon. The women’s swimwear design was more fashionable with a feature of evening gown backs. Almost all the women’s swimwear had the design of a skirted front and back for modesty with minuscule trunks attached underneath (Cunningham, 2009). Performance swimwear, used in general competitive water sports such as swimming, followed the traditional design for the most of the second half of the twentieth century, i.e. boxer trunk or brief for men and one-piece swimwear for women.

The design of traditional men’s and women’s swimwear changed little until the late 1990s. In 1996, Speedo announced the development of the best and fastest swimwear possible on the basis of their award-winning Aquablade swimwear. A special fabric called Fastskin made of polyester and Lycra was introduced in 2000 and its second version Fastskin FSII made of nylon and Lycra was introduced in 2004. With the goal of reducing the total amount of drag over the surface of the swimwear, Speedo moved away from the traditional manufacture of swimwear and looked to nature to mimic the skin of fast-moving creatures. Sharks, creatures that are fast in water but not naturally hydrodynamic, were chosen as a model for the Fastskin and Fastskin FSII swimwear. Scientific research has indicated that sharks’ quickness is to a great extent attributed to the V-shaped ridges on its skin which are called denticles. These denticles decrease surface friction and turbulence on the shark’s skin and allow the water to pass the skin more effectively. Similar denticles added to the Fastskin and FSII swimwear parallel to the path of swimming resemble a series of peaks and valleys. When water flows over the body, only the peaks contact with water and therefore reduce the drag force. In contrast to Speedo’s denticle design, the TYR Company included ridges or tripwires perpendicular to the path of swimming in their performance swimwear. It was claimed that these additional tripwires would reduce both pressure and wave drag force during competitive swimming.

The design of performance swimwear also broke away from the traditional men’s and women’s performance (racing) swimwear. Various design models were available on the market which included waist-to-knee, waist-to-ankle, neck-to-knee, neck-to-ankle and full body including arms. Innovative performance swimwear developed during this period also used the super stretch fabric to increase swimwear fit, improve streamlined shape of the body, and enhance muscle efficiency. It was believed that by compressing the skin and muscles, vibrations in the skin and muscles would significantly reduce to increase muscle power. With the revolutionary body scanning technique and 3-D swimwear pattern design, Speedo researchers and engineers were able to make swimwear for individual swimmers while providing them with a full range of motion during swimming. From anatomic and dynamic points of view, Speedo created a swimwear pattern in which seams act like tendons and provide tension in the swimwear while the fabric panels act like muscles and provide power to complete the swimming activity.

To further reduce the drag force of performance swimwear, Speedo manufactured the next generation Fastskin products, LZR racer swimwear in 2008, which became the predominant swimwear in the Beijing Olympic Games that year. A lightweight LZR Pulse fabric, which was exclusive to Speedo, was claimed to provide better water-repellent capability and more skin compression than Fastskin FSII swimwear. This lightweight fabric is woven rather than knitted from chlorine resistant elastane and ultra fine nylon yarns. Water-repellent coating added on the LZR Pulse fabric via a plasma process provided lower water absorption and a fast water drying rate. Polyurethane panels were placed strategically around the parts of the torso, abdomen and lower back that experience high amounts of drag. Ultrasonic welding was also applied to eliminate the traditional seams and smooth the surface of the swimwear. The design of the sleeveless neck-to-ankle pattern became highly popular in the Beijing Olympic Games that year.

10.2.4 Does performance swimwear enhance the performance of swimming?

World records of competitive swimming have been set at an unprecedented rate since the introduction of innovative performance swimwear in 2000. The Aquatic World Championships in Rome, Italy in 2009, observed 28 new world records set by swimmers wearing the bodysuit-type (neck-to-ankle) swimwear. This year was also the last year before the swimming governing body FINA banned the usage of bodysuit-type performance swimwear. The critics have long argued that the new performance swimwear might have benefited some swimmers more than others. Such advantages may be found in the morphology (i.e. more streamlined shape) of the swimmer and a better angle of buoyancy in the water. Although almost all performance swimwear manufacturers claimed that their products significantly reduce the drag force and increase swimming performance, the question that needs to be addressed is whether scientific research findings have supported these claims. This will be the focus of the next few sections in this chapter. The basic biomechanics of swimming will be briefly reviewed in the next section followed by the summary of peer-reviewed scientific papers on the effect of performance swimwear on competitive swimming.

10.3 Biomechanics of swimming

10.3.1 Fluid mechanics: drag force associated with swimming

While traveling through the water a swimmer displaces some water from his or her path. Resistance from the water can usually be defined as either passive or active drag. Passive drag is the resistance that a swimmer experiences when being towed passively in the water or gliding without other movements underneath the water. In contrast, active drag is the resistance that a swimmer experiences during active swimming. Active drag consists of both passive drag and additional form and wave drags.

When a swimmer displaces water while moving forward, the water reacts to the swimmer by producing three types of resistance: skin friction drag, pressure drag and wave-making drag. This can be written as the formula:

[10.1]

Skin friction drag is the frictional force acting between the water and the surface of the body. Its magnitude can be calculated by the formula (Vorontsov and Rumyantsev, 2000):

[10.2]

where μ is coefficient of viscosity, dV is difference in the velocity of water layers (dV is equivalent to flow velocity V), dZ is difference in the thickness of water layers and Sfriction is wetted body surface area. This formula shows that skin friction drag is linearly proportional to the velocity. Friction drag is considered a primary part of passive drag and therefore significantly affects the gliding velocity of a swimmer underneath the water.

Pressure drag is also called form drag. It is the resistance generated in the pressure difference between the front and rear portions of the swimmer. When the swimmer swims or is towed at a slow speed, water flows surrounding the swimmer can be viewed as thin laminae or layers of water, which are all parallel to each other and move smoothly without any disturbances. The water layer in contact with the body surface travels with the same speed as the swimmer and the adjoining external layers move at slower speeds due to water viscosity. Because the boundary layers of water move relative to the body and each other, they perform mechanical work and separate from the body surface before they reach the rear portion. When the swimming velocity increases, separating water layers form eddies (i.e. rotating water masses with high velocity and low pressure) behind the rear portion of the swimmer, which is called the wake. Therefore, boundary layers are thinner in the leading portion of the body and thicker towards the trailing portion. This pattern causes general laminar flow in the leading portion of the body and more turbulence in the trailing portion. A swimmer thus experiences high pressure on the front surfaces but low pressure in the wake. This pressure gradient causes pressure (form) drag and can be calculated as (Vorontsov and Rumyantsev, 2000):

[10.3]

where CD is coefficient of drag, ρ is density of water, A is the projected frontal area and V is velocity of the swimmer relative to water. It can clearly be seen that pressure drag has a square relationship with the velocity.

Reynolds number (Re) is a criterion used in fluid mechanics to describe whether the flow is laminar or turbulent. It is the ratio of inertial forces to viscous forces. The Reynolds number can be calculated as (Vorontsov and Rumyantsev, 2000):

[10.4]

where ρ is density of water, V is flow velocity, L is length of the body and μ is coefficient of dynamic viscosity. A lower Reynolds number denotes a more laminar fluid flow, and a higher Reynolds number denotes a more turbulent fluid flow. The Reynolds number for competitive swimming ranges between 2 × 105 and 2.5 × 106 (Clarys, 1979). Such a higher value of Reynolds number leads the inertial forces to dominate viscous forces. The boundary layer along the swimmer is thus expected to be predominant with turbulent flow.

Wave-making resistance or wave drag is the third type of drag that a swimmer experiences when swimming on the water surface or at a small depth under water. Some water displaced by the swimmer along the body’s trajectory moves from a high-pressure zone to a low-pressure zone which still has a pressure level above the undisturbed water. This process forms waves and is accompanied by the swimmer’s efforts to work against gravity and lift the water above the surface. Wave formation around a swimmer is clear evidence that certain energy is lost along the swimming path. Wave drag is usually calculated as (Vorontsov and Rumyantsev, 2000):

[10.5]

where ρ is density of water, A is amplitude of the wave, λ is length of the wave, V is swimming velocity, α is the angle between the swimming direction and the front of the wave and ∆t is time unit. This formula indicates that wave drag has a cube relationship with swimming velocity. Parts of the body such as the head, shoulders, upper trunk and buttocks generate waves during swimming and thus slow down the movement of the body. However, when a swimmer moves at a certain depth such as 0.7 m under water, wave drag is too small to slow down the movement of the body.

Formulas of three types of drag force demonstrate that skin friction drag increases linearly with swimming velocity, while pressure and wave drags have the square and cube relationship, respectively, with swimming velocity. With the increase of swimming velocity, both pressure and wave drags become more dominant contributors to the total hydrodynamic resistance. About 90% of the total hydrodynamic resistance was reported to come from pressure drag at a flow velocity of 2 m/s (Rumyantsev, 1982). At nearly maximal swimming velocity, wave drag becomes another major component of the total hydrodynamic resistance. In the meantime, as wave drag becomes negligible during a deep glide, it is beneficial to maintain high gliding velocity using a leg kick only under water. Swimming practice has shown that gliding under water is no slower or even faster than swimming on the surface using the full stroke.

10.3.2 Measurement of drag force

Though we can easily define three types of drag force in swimming, it is extremely difficult to accurately measure the friction, pressure and wave drag due to the fact that the propulsion along the water surface can be considered as a collection of numerous traveling pressure points. It is therefore more common to measure the total drag in relation to velocity. The most reliable and practical method is to measure passive drag since passive hydrodynamic drag is fundamental to understanding active drag in the next step. In fact, a swimmer experiences passive drag when being towed on the surface of or under water, or during glide after the start and turns under water, or during transitional postures in breaststroke and butterfly strokes.

In experiment, passive drag can be measured with an electromechanical towing device to tow a swimmer in a water tank or a swimming flume (Vorontsov and Rumyantsev, 2000). The towing device can either be fixed on a stationary platform or attached to a mobile carriage. The towing device provides the towing force parallel to water surface and its electric motor generates varying power to precisely control the towing velocity during towing. A swimmer usually adopts a steady and immobile body posture during the towing experiment. Studies have found that a swimmer’s body position and orientation significantly affect the total hydrodynamic resistance during towing. A common posture during towing is a prone, streamlined glide position with both arms extended overhead and feet together. Other postures can significantly increase the total hydrodynamic resistance. For instance, arms placed along the body increases the total hydrodynamic resistance by approximately 30% compared to the streamlined glide position, whereas arms extended forward with hands at shoulder width increases the total hydrodynamic resistance by about 10% (Onoprienko, 1968). It was also found that passive drag is affected, to a great extent, by the maximal frontal area of the swimmer and the circumferences of the head and shoulders (Clarys, 1978). This finding together with equation [10.3] emphasizes the importance of pressure drag in the total hydrodynamic resistance. While examining other anthropometric variables such as proportions of the human body, few correlations were observed between passive drag and anthropo-metric variables. Part of the explanation is that the human body is not well streamlined; rather, it has many local pressure points such as the shoulders, knee joints and buttocks.

While passive drag certainly depends upon body shape and orientation in an immobile posture, active drag is associated with swimming techniques and constantly moving body positions. It is thus expected that active drag is much higher than passive drag. Studies with different measuring techniques show that the relationship between active drag and swimming velocity is quadratic (Clarys, 1979; Toussaint et al., 1988). Active drag (FDA) can be established as (Vorontsov and Rumyantsev, 2000):

[10.6]

where CDA is the coefficient of active drag, ρ is density of water, A is anthropometric variable and V is swimming velocity. Comparing this equation with equation [10.3], it clearly implies that pressure drag is a major component of the total hydrodynamic resistance in active swimming. Anthropometric characteristics and passive drag contribute predominantly to active resistance at slow swimming velocities, but reduce substantially at high swimming velocities (Toussaint et al., 1988). However, no correlation has been found between the magnitudes of active and passive drag (Clarys, 1978).

Measurement of active drag has been a challenge to biomechanists and sports scientists. Early techniques used the indirect calculation based on oxygen consumption (VO2) during active swimming (Clarys, 1979; Di Prampero et al., 1974). One of the drawbacks of the indirect method is that it measures aerobic function in swimming and thus is not appropriate for swimming at maximal efforts which include anaerobic function. More recent methods measuring active drag (MAD) include the MAD system (Toussaint et al., 1988) and the velocity perturbation method (Kolmogorov and Duplishcheva, 1992). The MAD method measures the average propulsive force during frontal crawl swimming only. The rationale is that the propulsive force should be equal to active drag acting on the swimmer at constant swimming velocity. The velocity perturbation method, however, can assess active drag in all four swimming strokes. This method manipulates the maximal swimming velocity by using an additional hydrodynamic body with known resistance. The hydrodynamic body is placed behind a swimmer with the distance about four times of the swimmer’s body length. The swimmer performs two swims with maximal efforts with and without the hydrodynamic body. Active drag can be estimated with the measured two maximal velocities and the known resistance from the hydrodynamic body. Both methods reached the same conclusion as shown in Clarys’s (1979) study such that swimming technique is a more important component in determining active drag compared to body composition.

10.3.3 Swimwear design and drag force

It has long been debated whether skin shaving can reduce drag force in swimming. Swimmers who shaved their skin before a race were reported to consume less energy, produce longer stroke distance and swim faster than those without shaving (Sharp and Costill, 1989). This implies that skin friction drag is influenced markedly by the smoothness of the skin. Another approach to reducing skin friction drag is to develop better designs and fabrics for swimwear. This can be achieved by using a water-repellent and ultra thin elastic fabric to increase body smoothness. Woolen swimwear was found to increase drag force by 3% compared to silk swimwear when a female swimmer was towed at 2 m/s (Onoprienko, 1968).

As pressure drag is usually significantly higher than skin friction drag, design of innovative performance swimwear should take pressure drag into consideration. When a well-streamlined swimmer moves at slow velocity, the boundary layers act like smooth laminar flow and little eddy formation occurs behind the body. Skin friction drag is thus the predominant component of the total hydrodynamic resistance. When swimming velocity increases, the boundary layers around the swimmer decreases in thickness and their separation point shifts to the front of the body causing a growing pressure gradient. Many eddies form behind the swimmer and take away kinetic energy from the swimmer. A streamlined swimwear design is therefore warranted to reduce pressure drag during swimming. Compared to fast-swimming fish and sea mammals such as dolphins, the human body with a similar longitudinal contour experiences much greater drag force at the same speed (Vorontsov and Rumyantsev, 2000). This is to a great extent due to many local pressure resistance centers in the human body including the head, shoulders, buttocks, knees and heels. Compression from a tight and fit swimwear is expected to reduce drag force at these local pressure centers and improve the streamline shape of the swimmer. Although swimwear manufacturers have claimed the significant advantages of their innovative performance swimwear, it is still up to carefully designed scientific experiments to verify these claims.

10.4 Effect of innovative swimwear on swimming performance

10.4.1 Water repellency in innovative swimwear

Smoothness and water repellency can significantly affect the physical characteristic of the swimwear fabric surface and therefore reduce drag force. Water repellency is usually measured with contact angle. By definition, contact angle is the angle formed by the water droplet and the fabric surface. A greater contact angle demonstrates a better water-repellent property of the fabric. Figure 10.1 illustrates contact angles for four different types of fabrics. If a fabric is isotropic (i.e. uniformity in all directions) and hydrophilic (i.e. water loving), the contact angle is usually much less than 90° as depicted in Fig. 10.1(a). For an isotropic and hydrophobic (i.e. water-repelling) fabric, the water droplet maintains to some extent a spherical shape and its contact angle is usually greater than 90° as shown in Fig. 10.1(b). However, often a swimwear fabric is made with different materials such as nylon and Lycra. This fabric may not be considered as isotropic; rather, the fabric shows the anisotropic property (i.e. directionally dependent). Figure 10.1(c) shows the contact angle of an anisotropic and hydrophilic fabric. Since the water droplet does not spread evenly in all directions, an elliptical shape of water spreading can often be observed. Contact angles can be measured along the minor axis (θa) and the major axis (θb) of this ellipse and both angles are less than 90°. The ratio between these two contact angles is usually calculated to quantify the spreading asymmetry of the fabric. An innovative performance swimwear requires water-repellent and fast drying properties to avoid water accumulation and penetration. Figure 10.1(d) illustrates contact angles of an anisotropic and hydrophobic fabric. Again contact angles θa and θb can be measured along the minor and major axes, respectively. However, because of the water-repellent property of the fabric, both contact angles should be greater than 90°.

10.1 Illustration of contact angle of water droplets on different fabric surfaces. (a) Isotropic and hydrophilic fabric, (b) isotropic and hydrophobic fabric, (c) anisotropic and hydrophilic fabric and (d) anisotropic and hydrophobic fabric. Note that the fabric of innovative performance swimwear is water repellent and thus more comparable to fabric (d). Contact angle, θ, can be measured along the minor axis, θa, or the major axis, θb.

Rogowski et al. (2006) investigated the effect of fabric characteristics on the performance of butterfly stroke swimming. Three fabrics were tested including a training fabric made of polyamide, a competition fabric made of polyamide and elastane, and the same competition fabric with additional mechanochemical coating treatment to increase water repellency and anisotropy. The contact angle was measured for each fabric to estimate its water repellency. Results showed that the competition fabrics with and without coating have greater contact angles (130–140°) than the training fabric (about 85°), and the competition fabric with coating had a lower spreading asymmetry than the other two fabrics. In the swimming testing session, nine national French male swimmers performed 50 m butterfly stroke at 85% of effort while wearing a conventional swimwear made of the training fabric and the sleeveless neck-to-ankle long swimwear made with the competition fabrics with and without the coating treatment. It was found that overall hip velocity during the propulsive phase of butterfly stroke swimming was not different among the three swimwear; however, both long swimwear significantly increased hip velocity during the recovery phase (i.e. gliding). Furthermore, the long swimwear made with the competition fabric with the coating treatment provided further improvement. Thus, modification of water repellency (i.e. contact angle) has indirectly shown to significantly reduce drag force during swimming.

10.4.2 Effect of innovative swimwear on drag force and physiological and biomechanical responses

Measurement of passive and active drag forces has been described in the earlier sections. Because the goal of developing innovative swimwear is to enhance a swimmer’s performance during competition, it is important to investigate the biomechanical and physiological responses during swimming while wearing innovative swimwear. Physiological responses are usually measured by VO2 and blood lactate accumulation during or after a swimming event. Biomechanical variables usually include stroke distance, stroke rate and swimming velocity. Stroke distance is the distance that a swimmer covers per stroke or per complete swimming cycle. Stroke rate is the number of strokes or complete swimming cycles that a swimmer performs per unit time (usually per second). Swimming velocity is equal to the product of stroke rate and stroke distance and can be defined for an entire race or each part of the race such as the start and turns of the race. A particular ratio of stroke rate and stroke distance is required for a swimmer to achieve the maximal velocity. If a stroke rate is too high, it disturbs muscle coordination because the muscles do not have enough time to recover between two bursts and get fatigued rapidly. On the other hand, if a stroke rate is too low, excessive efforts are needed to produce a high stroke distance, which increases anaerobic activity and decreases a swimmer’s working capability.

Table 10.1 summarizes the studies on performance swimwear and wetsuits over the past 20 years. Findings on the amount of passive drag during towing and active drag during swimming are not conclusive. Three to ten percent of reduction on drag force has been reported by several studies (Benjanuvatra et al., 2002; Chatard and Wilson, 2008; Mollendorf et al., 2004; Pendergast et al., 2006). A shoulder-to-ankle design was found to further reduce drag force compared to other designs such as shoulder-to-knee, waist-to-ankle and waist-to-knee (Mollendorf et al., 2004). In the meantime, both Speedo Fastskin and TYR swimwear, though with different design philosophies as described in the earlier section, showed evidence of reducing drag force during passive towing (e.g. Mollendorf et al., 2004; Pendergast et al., 2006). However, non-significant difference has also been found between innovative and conventional swimwear (Roberts et al., 2003; Smith et al., 2007; Toussaint et al., 2002). As different methods were used to assess drag force and the experimental setup was not identical across the studies, one should be cautious in evaluating the validity of each study and compare the differences between studies. Nonetheless, none of the studies demonstrates that an innovative performance swimwear would increase passive and active drag force. It may be concluded that an innovative performance swimwear can reduce drag force to some degree which may not be as high as that claimed by some swimwear manufacturers.

Table 10.1

Summary of studies on innovative performance swimwear and wetsuits

Note that gains in drag force, physiological responses, and biomechanical measures are compared to conventional swimsuit.

Physiological responses to innovative and conventional swimwear have been reported in favor of innovative performance swimwear (see Table 10.1). Most studies (Chatard and Wilson, 2008; Roberts et al., 2003; Starling et al., 1995;Tiozzo et al., 2009) have shown that an innovative performance swimwear can significantly reduce VO2 by approximately 5% and blood lactate concentration by 10–20%. Three percent of reduction on VO2 was reported while wearing innovative performance swimwear, even though this reduction was not significant (Smith et al., 2007). Lower VO2 during swimming indicates that less effort is needed to complete a race, which may suggest that a lower drag force is associated with innovative performance swimwear. In the meantime, lower blood lactate concentration means that wearing innovative performance swimwear allows muscles to work less hard than when wearing conventional swimwear. In other words, muscles do not get fatigued as rapidly while wearing innovative performance swimwear. In addition, a significant 7% reduction on heart rate was reported after completing a 400 m freestyle swim while wearing innovative performance swimwear (Tiozzo et al., 2009). All of these physiological responses provide positive evidence that innovative performance swimwear can significantly reduce physiological demand and improve swimming performance.

When examining the biomechanical variables, most studies showed significant improvement while wearing innovative performance swimwear (see Table 10.1). While maintaining stroke rate unchanged, stroke distance was found to increase by 2–5% while wearing innovative performance swim-wear (Chatard and Wilson, 2008; Roberts et al., 2003; Starling et al., 1995). This finding implies that drag force may be reduced by innovative swimwear so that a swimmer can cover a long distance per stroke at the same stroke rate. It also suggests that stroke distance rather than stroke rate is the variable that a swimmer manipulates first to increase the velocity when less drag force occurs. Swimming velocity was also found to increase markedly while wearing innovative performance swimwear. For example, the velocity of gliding under water significantly increased by 20% due to the contribution from shoulder-to-ankle performance swimwear (Rogowski et al., 2006).This finding is important because innovative swimwear can significantly benefit a swimmer at the start and turns of a race and therefore markedly enhance the swimmer’s performance. Also, studies on freestyle swimming at submaximal and maximal efforts demonstrate that innovative swimwear can significant increase swim velocity and decrease swimming time (Chatard and Wilson, 2008; Roberts et al., 2003; Tiozzo et al., 2009). Taken together, research confirms that innovative performance swimwear can significantly improve biomechanical characteristics of swimming.

Performance swimwear reviewed above is usually used during competitions in an indoor swimming pool. With increasing popularity of triathlon around the world, a wetsuit specially designed for this sport has attracted increased attention from athletes, coaches, manufacturers and the general public. A wetsuit is a garment usually made of foamed neoprene and covers the full body including the arms and shoulder-to-ankle. Besides reducing drag force, a wetsuit is designed to provide thermal insulation and increase buoyancy during open water swimming. Table 10.1 also summarizes the studies on the effect of wetsuits on drag force and physiological and bio-mechanical measures. While wetsuits were reported to reduce drag force by 12–14% (Toussaint et al., 1989), recent studies found non-significant reduction of active drag while wearing a wetsuit (De Lucas et al., 2000; Tomikawa and Nomura, 2009). Similar inconclusive findings were also reported on physiological responses. Trappe et al. (1996) reported that wearing a wetsuit significantly decreased VO2 by 16-33%, whereas Tomikawa and Nomura (2009) found no reduction on VO2 and blood lactate while wearing a wetsuit. However, when swimming velocity was examined while wearing a wetsuit, all the studies demonstrated 3–7% increase of velocity in 400 m and 1500 m swimming (Crodain and Kopriva, 1991; De Lucas et al., 2000; Tomikawa and Nomura, 2009). All the evidence indicates that wearing a wetsuit can significantly benefit a triathlon athlete by reducing drag force and VO2 to some degree and improving swimming velocity.

The evidence from the research studies reviewed above, even though not totally consistent with each other, suggests that innovative performance swimwear developed in the past 20 years can to a great extent reduce drag force and improve the physiological and biomechanical responses during competitive swimming. It is therefore appropriate to continue the development of new innovative performance swimwear to provide further benefits to professional swimmers and possibly collegiate and amateur swimmers.

10.5 Future trends in innovative performance swimwear

Existing research has demonstrated that the full body or sleeveless shoulder-to-ankle swimwear design can significantly reduce drag force compared to both conventional and waist-to-knee swimwear. However, FINA banned the use of full body and sleeveless shoulder-to-ankle design from January 2010. The current performance swimwear allowed by FINA is the waist-to-knee design for men and shoulder-to-knee design for women. Furthermore, FINA required that only textile fabrics made of natural and synthetic yarns can be used for performance swimwear and these fabrics should be manufactured by weaving, knitting or braiding. In addition, FINA produced detailed guidelines for the fabric surface coating and treatment. With these new guidelines for performance swimwear, creative design and technology are needed to bring the development of performance swimwear to the next stage.

Synthetic materials such as nylon, polyester and Lycra have been widely used in manufacturing performance swimwear. This is to a great extent due to their water-repellent capability. Future research will focus on the development of new synthetic materials which should be comparable to or better than the existing synthetic materials. In the meantime, research needs to address how to manufacture thinner synthetic filaments and produce lighter and thinner swimwear fabrics. Obviously, elasticity and compression are the two important characteristics of swimwear fabrics and can significantly affect the streamline shape of a swimmer. As the buttocks are one of the local pressure centers, a better ergonomic swimwear design is warranted to streamline this area. Three-dimensional body scans as used by Speedo will continue to help individualize the performance swimwear for each swimmer. In addition, theoretical and applied fluid mechanics have been successfully used in developing performance swimwear over the past 20 years. With more advanced computing technology, computational fluid mechanics will be an appropriate tool to help further understand water flow around a swimmer’s body and thus accurately estimate passive and active drag force during competition. This knowledge will in turn revolutionize the development of performance swimwear.

10.6 Sources of further information and advice

Readers are recommended to check the website of FINA (www.fina.org) for the guidelines on performance swimwear. The details can be found under bylaws-swimwear in the rules and restrictions of FINA. As guidelines on performance swimwear change from time to time, it is important for researchers and manufacturers to understand these guidelines and incorporate them into the development of next performance swimwear.

To gain more knowledge on the biomechanics of swimming, a helpful book is Vladimir Zatsiorsky (ed.), Biomechanics in Sport: Performance Enhancement and Injury Prevention (2000). As manufacturers usually claim remarkable advantages for their new performance swimwear over conventional swimwear, it is important to look at the research studies that employ theoretical modeling and scientific experimental design to study drag force and physiological and biomechanical responses associated with new performance swimwear. The following are some excellent journals (not an exclusive list) for readers who are interested in exploring the effect of performance swimwear on competitive swimming: Medicine and Science in Sports and Exercise, Journal of Biomechanics, Journal of Applied Biomechanics and Sports Biomechanics.

In addition, it would be helpful to frequently study the websites and newsletters of the major swimwear manufacturers such as Speedo, TYR and Adidas to follow the new trend of swimwear development. The development of performance swimwear often follows the cycle of the Olympic Games. This means that new performance swimwear is usually released and promoted a year before or in the year of the Olympic Games. As the usage of performance swimwear has expanded from professional swimmers to collegiate and amateur swimmers, the development of new innovative performance swimwear will continue to proceed in the future.

10.7 Acknowledgements

Special thanks are due to Dr Hong Chen and Mr Matthew Bogenberger for their contributions to the literature research and review and for their suggestions and comments on this chapter.

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