Measurement of Drag to Assess the Effect of Swim Suits

Veloso, Alves, Fernandes, Conceição, Vilas-Boas (eds.) Portuguese Journal of Sport Sciences Applied Biomechanics in Sports 11 (Suppl. 3), 2011

MEASUREMENT OF DRAG TO ASSESS THE EFFECT OF SWIM SUITS

Huub M. Toussaint1,2,3

Move Institute, Human Movement Sciences, VU University, Amsterdam, The Netherlands1; Academy for Physical Education, Technical University of Applied Sciences Amsterdam 2; InnoSport.NL Fieldlab Swimming, Eindhoven3

The purpose of this study was to demonstrate the effect of different suits on drag for Olympic level swimmers. The effect on drag for some suits were with 5-7% rather large given the small differences observed in competitive time during Olympic finals. It is also found that the same suit may have a drag reducing effect for one swimmer while for the other no or a detrimental effect on drag is observed. Apparently, the simple reasoning to create a level playing field for all swimmers that one suit must be available for all is not as simple as the present FINA rules suggest.

KEY WORDS: active drag, passive drag, performance effect.

INTRODUCTION: Swimming is a highly competitive sport where the difference between success and failure can be very small. For example, the time difference between ‘gold’ and ‘silver’ for the 100 m freestyle finals for men at the last Olympic games is roughly 0.5%, and between the winner and the slowest finalist less than 3%. Small changes to factors determining performance will have significant effects. One of the factors determining the outcome in a 100 m freestyle race is drag. Drag is the force resisting movement through water. The total drag (Fd) swimming at a constant speed consists of frictional (Ff), pressure (Fp), and wave drag (Fw) components, namely (Toussaint & Beek, 1992):

Fd = Ff + Fp + Fw (1)

In different phases of the race the components of drag that dominate total drag may vary as they depend on speed and swimming depth. After the start, the swimmer dives into the water and below a certain depth, wave drag may be negligible [insert animal boil] leaving pressure and friction drag as relevant components. Frictional or viscous drag originates from fluid viscosity, and produces shear stresses in the boundary layer (a layer of water extending out from the body to the point at which it is moving at 99% of free stream speed; (Prandtl & Tietjens, 1957)). The magnitude of frictional drag will depend on the wetted surface area of the body and flow conditions within the boundary layer (Webb, 1975). The basic causes of pressure drag are vortices and this type of drag depends on the difference between the dynamic pressures at the front and rear of a moving body and the exposed area to flow (Aleyev, 1977). When swimming near the surface, the pressure field around the swimmer sets up a wave system. At race speeds exceeding about 1.6 m•s-1 wave drag will be important (Vennel, Pease, & Wilson, 2006). It was estimated that wave drag amounts to 50% of total drag (Toussaint & Truijens, 2005).

Active drag versus passive drag: Drag can be measured in a passive and active condition. Passive drag is the resistance on the body of the passive swimmer, when towed through the water. The relevance of measuring passive drag is to evaluate drag as occurs during the gliding phase of swimming after start and turns. This is relevant since about 15% of the distance covered in a race occurs in a passive state (Bixler, Pease, & Fairhurst, 2007). Active drag is the resistance on the body of the swimmer when propulsion is generated. This form of drag would be more closely related to changes in body position and may thus be influenced by swimming technique (Chatard, Bourgoin, & Lacour, 1990). Another factor that may influence the magnitude of both active and passive drag is the swimming suit as was first demonstrated by Toussaint et al in 1989. In the present study the effect of different suits on both passive and active drag is studied.

ISBS 2011 77 Porto, Portugal

Veloso, Alves, Fernandes, Conceição, Vilas-Boas (eds.) Portuguese Journal of Sport Sciences Applied Biomechanics in Sports 11 (Suppl. 3), 2011

METHODS:METHODS:TheThe measurement measurement of of drag drag while while swimming swimming front front crawl crawl (i.e. (i.e. ‘active’ ‘active’ drag) drag) is a is a challenge.challenge. Unlike Unlike activities activities on on land land (like (like running) running) the theswimmer swimmer is not is usingnot using a fixed a fixedpoint pointto to generategenerate propulsion. propulsion. If Ifthere there would would be bea fixeda fixed point, point, it would it would be thebe idealthe ideal spot spotto put to a put force a force transducertransducer to to measure measure the the forces forces involved involved in swimming.in swimming. The The Measuring Measuring Active Active Drag-system Drag-system (MAD-system).(MAD-system). The The MAD-system MAD-system provides provides the the swimmer swimmer with with a series a series of fixed of fixed push-off push-off points points mountedmounted below below the the water water surface, surface, such such that that a front- a front-crawlcrawl like like‘swimming’ ‘swimming’ movement movement can becan be mademade (Figure (Figure 1). 1). The The push-off push-off forces forces from from the the hands hands are aremeasured measured with witha force a force transducer. transducer. If If thethe swimmer swimmer ‘swims’ ‘swims’ at atconstant constant speed speed the the average average drag drag will willequal equal the averagethe average propulsion. propulsion. ThusThus the the MAD-system MAD-system approach approach relies relies on on a balance a balance of resistive of resistive and and propulsive propulsive forces. forces. PropulsivePropulsive forces forces of of the the leg leg action action can can not not be bemeasured measured using using this thisapproach, approach, so the so legs the arelegs are tiedtied together together with with a a rubber rubber strap strap and and supported supported by by a pull a pull buoy buoy to keep to keep the body the body in a in a horizontalhorizontal position position similar similar to to that that during during actual actual swimming. swimming. The The swimmer swimmer swims swims a series a series of of lapslaps on on the the system system whereby whereby each each lap lap is swumis swum at aat constant a constant speed. speed. Each Each lap results lap results in one in one speed-dragspeed-drag data data point. point. For For a a range range of of lap-speeds, lap-speeds, drag drag is measured is measured and and the relation the relation betweenbetween speed speed and and drag drag is is calculated calculated using using a least a least squares squares fitting fitting approach approach (see (see also: also: Toussaint,Toussaint, et et al., al., 1988; 1988; Toussaint, Toussaint, de de Looze, Looze, van van Rossem, Rossem, Leijdekkers, Leijdekkers, & Dignum, & Dignum, 1990; 1990; Toussaint,Toussaint, Knops, Knops, de de Groot, Groot, & &Hollander, Hollander, 1990). 1990). Measurement Measurement of drag of drag of a of swimmer a swimmer in a in a passive,passive, stretched stretched position position (i.e. (i.e. ‘passive’ ‘passive’ drag) drag) is re islatively relatively easy. easy. An example An example of such of such a a contraptioncontraption to to do do so so is isgiven given in inFigure Figure 1 (right 1 (right panel). panel).

Figure 2: Results of passive drag testing using towing device (see Figure 1 right panel). Each swimmer was towed three times at each speed and the average recorded drag value for each lap is plotted. The relation ship between speed and drag was least square fitted to give Drag = A•velocityn. The testing speed was between 1.8 and 3 m•s-1. The high speeds were set to evaluate the effect of the suit after start and turns were the swimmer is gliding through the water.

FigureFigure 1: 1: Schematic Schematic drawing drawing of ofthe the MAD-system MAD-system (left (left panel) panel) mounted mounted in a 25in am 25 pool. m pool. The MAD- The MAD- systemsystem allows allows the the swimmer swimmer to topush push off off from from fixed fixed pads pads with with each each stroke. stroke. These These push-off push-off pads pads areare attached attached to to a a 22 22 m m long long rod. rod. The The distance distance between between the the push-off push-off pads pads can becan adjusted be adjusted (normally(normally 1.35 1.35 m). m). The The rod rod is ismounted mounted ± 0.8 ± 0.8 m belowm below the thewater water surface. surface. The rodThe is rod connected is connected to to aa force force transducer transducer enabling enabling direct direct measurement measurementof pushof push-off -forcesoff forces for eachfor each stroke stroke (see lower(see lower panel).panel). Swimming Swimming one one lap lap on on the the system system yields yields one one data data-point-point for thefor speedthe speed-drag--dragcurve.-curve. (note: (note: thethe cord cord leading leading to to the the calibration calibration device device is detached is detached during during drag drag-measurement)-measurement). Towing. Towing devicedevice for for passive passive drag drag measurem measurementent (right (right panel). panel). A force A force transducer transducer is mounted is mounted in the in yellow the yellow buoy.buoy.

RESULTSRESULTS: :Tests Tests were were conducted conducted at atthe the end end of Mayof May 2008. 2008. For Foreach each swimmer swimmer 2 suits 2 suitswere were evaluatedevaluated to to decide decide what what to towear wear during during the the finals finals in the in theOlympic Olympic Games. Games. It should It should be noted be noted thatthat for for s ubjectsubject ‘Maarten’ ‘Maarten’ the the ‘LZR ‘LZR racer racer legskin’ legskin’ was was tested tested and andthat thatthis suitthis onlysuit onlycovered covered Figure 3: Results for active drag using the MAD-system (see Figure 1 left panel). Each swimmer thethe legs. legs. All All other other suits suits were were ‘full’ ‘full’ suits suits covering covering both both legs legs and and torso. torso. ‘Old’ ‘Old’ indicates indicates the the was swimming 10-11 laps in a range of speeds, but each lap was swum at a constant speed. FastskinFastskin FS-Pro FS-Pro that that was was launched launched by bySpeedo Speedo in 2007.in 2007. Blue Blue indicates indicates the blue-70the blue-70 swimsuit. swimsuit. The average recorded drag per lap is plotted dependent on the recorded swimming speed. The DuringDuring passive passive drag drag measurements measurements swimmers swimmers kept kept the thehead head between between the outstretchedthe outstretched arms arms relation ship between speed and drag was least square fitted to give Drag = A•velocityn. The (see(see Figure Figure 1 1right right panel). panel). The The towing towing depth depth was was set setat 1 at m 1 below m below the waterthe water surface surface to evade to evade testing speeds were between 1.0 and 2 m•s-1. thethe effect effect of of wave wave drag. drag.

ISBS 2011 78 Porto, Portugal Veloso, Alves, Fernandes, Conceição, Vilas-Boas (eds.) Portuguese Journal of Sport Sciences Applied Biomechanics in Sports 11 (Suppl. 3), 2011

METHODS: The measurement of drag while swimming front crawl (i.e. ‘active’ drag) is a challenge. Unlike activities on land (like running) the swimmer is not using a fixed point to generate propulsion. If there would be a fixed point, it would be the ideal spot to put a force transducer to measure the forces involved in swimming. The Measuring Active Drag-system (MAD-system). The MAD-system provides the swimmer with a series of fixed push-off points mounted below the water surface, such that a front-crawl like ‘swimming’ movement can be made (Figure 1). The push-off forces from the hands are measured with a force transducer. If the swimmer ‘swims’ at constant speed the average drag will equal the average propulsion. Thus the MAD-system approach relies on a balance of resistive and propulsive forces. Propulsive forces of the leg action can not be measured using this approach, so the legs are tied together with a rubber strap and supported by a pull buoy to keep the body in a horizontal position similar to that during actual swimming. The swimmer swims a series of laps on the system whereby each lap is swum at a constant speed. Each lap results in one speed-drag data point. For a range of lap-speeds, drag is measured and the relation between speed and drag is calculated using a least squares fitting approach (see also: Toussaint, et al., 1988; Toussaint, de Looze, van Rossem, Leijdekkers, & Dignum, 1990; Toussaint, Knops, de Groot, & Hollander, 1990). Measurement of drag of a swimmer in a passive, stretched position (i.e. ‘passive’ drag) is relatively easy. An example of such a contraption to do so is given in Figure 1 (right panel).

Figure 1: Schematic drawing of the MAD-system (left panel) mounted in a 25 m pool. The MAD- system allows the swimmer to push off from fixed pads with each stroke. These push-off pads are attached to a 22 m long rod. The distance between the push-off pads can be adjusted (normally 1.35 m). The rod is mounted ± 0.8 m below the water surface. The rod is connected to a force transducer enabling direct measurement of push-off forces for each stroke (see lower panel). Swimming one lap on the system yields one data-point for the speed-drag-curve. (note: the cord leading to the calibration device is detached during drag-measurement). Towing device for passive drag measurement (right panel). A force transducer is mounted in the yellow buoy.

RESULTS: Tests were conducted at the end of May 2008. For each swimmer 2 suits were evaluated to decide what to wear during the finals in the Olympic Games. It should be noted that for subject ‘Maarten’ the ‘LZR racer legskin’ was tested and that this suit only covered Figure 3: Results for active drag using the MAD-system (see Figure 1 left panel). Each swimmer the legs. All other suits were ‘full’ suits covering both legs and torso. ‘Old’ indicates the was swimming 10-11 laps in a range of speeds, but each lap was swum at a constant speed. Fastskin FS-Pro that was launched by Speedo in 2007. Blue indicates the blue-70 swimsuit. The average recorded drag per lap is plotted dependent on the recorded swimming speed. The During passive drag measurements swimmers kept the head between the outstretched arms relation ship between speed and drag was least square fitted to give Drag = A•velocityn. The (see Figure 1 right panel). The towing depth was set at 1 m below the water surface to evade testing speeds were between 1.0 and 2 m•s-1. the effect of wave drag.

ISBS 2011 79 Porto, Portugal Veloso, Alves, Fernandes, Conceição, Vilas-Boas (eds.) Portuguese Journal of Sport Sciences Applied Biomechanics in Sports 11 (Suppl. 3), 2011

For the passive tests (Figure 2), the LZR gives lower drag values for one male swimmer in MEASURING ENERGY EXPENDITURE IN SWIMMING TO ASSESS GROSS comparison to the Nike suit, but the LZR legskin is not as good as a full blue 70 suit for the MECHANICAL EFFICIENCY other male swimmer (upper 2 panels). For the two female swimmers the LZR gives a drag reduction especially at higher speeds. Carlo Baldari, Laura Guidetti and Marco Meucci

DISCUSSION: The difference in results of the two swimmers in the 2 lower panels of Figure 3 suggests that a drag reducing effect of a suit may be subject-specific. Although both Exercise and Sport Sciences Unit, Department of Health Sciences, University of swimmers were testing similar suits (both fitting each swimmer well), for one of them the Rome "Foro Italico", Rome, Italy older Fastskin provided a drag reduction while swimming, while for the other no drag differences were found. When swimming at submaximal speeds the rate of energy expenditure can be estimated from respiratory analysis. Over the past decades many methods for stationary non- aqueous evaluation of respiratory and ventilatory parameters in swimmers has emerged. Testing of the suits in both active and passive condition helped choosing the CONCLUSION: Recently there have been advances in portable telemetric systems (Cosmed K4 b2, Italy) swim suit that appeared most advantageous to swim races in Olympic finals. It also that can measure these variables from rest to maximal activity while swimming without demonstrates that the idea that a good fitting suit of a certain fabric will have an equal effect the need to stop the exercise. Preliminary data show that the last modified snorkel on all swimmers may be not correct. This reasoning seems the underpinning of the present system can be considered as a valid device for collecting expired gas for BxB analysis, FINA regulations that may therefore be in need for revision. comparable to the standard facemask, with the advantage of being suitable for measurements during swimming.

REFERENCES: KEY WORDS: Swimming, oximetry, validation, snorkel system. Aleyev, Y. G. (1977). Nekton (B. M. Meerovich, Trans.). Den Haag: Dr W. Junk BV.

Bixler, B., Pease, D. L., & Fairhurst, F. (2007). The accuracy of computational fluid dynamics Efficiency is defined as the work accomplished divided by the energy analysis of the passive drag of a male swimmer. Sports Biomechanics, 6, 81-98. INTRODUCTION: expended to do that work (Stainsby, Gladden, Barclay & Wilson, 1980). Since it is often more Chatard, J. C., Bourgoin, B., & Lacour, J. R. (1990). Passive drag is still a good evaluator of convenient to express these quantities as time-related, the gross efficiency has also been swimming aptitude. European Journal of Applied Physiology, 59, 399-404. defined as the mechanical power output (Po) with respect to the rate of energy expenditure Prandtl, L., & Tietjens, O. G. (1957). Applied hydro- and Aerodynamics (2nd ed. ed.). New or power input (Pi) (Miller, 1975). This definition of overall or gross efficiency seems to be York: Dover Publishers. simple and straightforward, but in fact the way in which both mechanical power and rate of Toussaint, H. M., & Beek, P. J. (1992). Biomechanics of competitive front crawl swimming. energy expenditure are defined and measured have been considered with different Sports Medicine, 13(1), 8-24. approaches (Montpetit, Leger, Lavoie & Cazorla, 1981; Toussaint, Knops, de Groot & Toussaint, H. M., Bruinink, L., Coster, R., de Looze, M., van Rossem, B., van Veenen, R., et Hollander, 1990; Barbosa, Keskinen, Fernandes, Colaço, Lima & Vilas-Boas, 2005; Reis, al. (1989). Effect of a triathlon wet suit on drag during swimming. Medicine and Science in Marinho, Policarpo, Carneiro, Baldari & Silva, 2010). To measure the true gross efficiency it Sports and Exercise, 21, 325-328. is necessary to quantify the total mechanical power output (Po) and the rate of energy expenditure (power input :Pi). In this presentation we will focus only on the quantification of Toussaint, H. M., de Groot, G., Savelberg, H. H. C. M., Vervoorn, K., Hollander, A. P., & van the Pi. Ingen Schenau, G. J. (1988). Active drag related to velocity in male and female swimmers. At submaximal swimming speeds, the power input of the swimmer is reflected by the power Journal of Biomechanics, 21, 435-438. equivalence of the oxygen uptake (Toussaint et al., 1990). The rate of energy input (Pi) in Toussaint, H. M., de Looze, M., van Rossem, B., Leijdekkers, M., & Dignum, H. (1990). The Watts can be estimated from the oxygen uptake (lmin-1, STPD = standard temperature and effect of growth on drag in young swimmers. International Journal of Sport Biomechanics, 6, pressure in dry air) using the formula (Cavanagh & Kram, 1985): 18-28. Toussaint, H. M., Knops, W., de Groot, G., & Hollander, A. P. (1990). The mechanical Pi = _(4,940 RER + 16,040) VO2 (1) efficiency of front crawl swimming. Medicine and Science in Sports and Exercise, 22(3), 402- 60 408. Toussaint, H. M., & Truijens, M. J. (2005). Biomechanical aspects of peak performance in where RER equals the respiratory exchange ratio. human swimming. Animal Biology, 55(1), 17-40. In this sense, the oxygen consumption (VO2) and the related cardiorespiratory parameters Vennel, R., Pease, D. L., & Wilson, B. D. (2006). Wave drag on human swimmers. Journal of have traditionally been used to study the energy expenditure of swimming in humans. The Biomechanics, 39, 664-671. existing body of knowledge on the relationships between swimming and respiratory Webb, P. W. (1975). Hydrodynamics and energetics of fish propulsion. Bulletin of the parameters is based on experiments using either Douglas bags or mixing chamber gas Fisheries Research Board of Canada, 190, 1-158. analyses (Dal Monte, Sardella, Alippi, Faina & Manetta, 1994; di Prampero, Pendergast, Wilson & Rennie, 1974; Holmer 1972; Lavoie & Montpetit, 1986, Toussaint, Meulemans, de Groot, Hollander, Schreurs & Vervoorn, 1987). More recently, a portable telemetric system (Cosmed K4 b2, Italy) consisting of a facemask, a flow meter, a gas analyzer with a transmitter, and a receiver has been developed for breath by breath gas analysis to evaluate VO2 at steady state condition and VO2 kinetics during free movements.

ISBS 2011 80 Porto, Portugal