THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

AQUATIC SPORTS INJURIES AND REHABILITATION

0278-5919/99 $8.00

+ .OO

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING John P. Troup, PhD

With the availability of swimming treadmills, computerized equipment, video technologies, and automated diagnostics, better information from swimming science has become possible; today, sports science can provide critical information that can lead to improved performances. Much of the current interest in applied swimming research can be attributed to the declining rates of change in performance times observed in swimmers over the last 20 years. To a greater extent than at any time in the past, scientists are searching for means to identify those young athletes who might be the gold medalists of future Olympic games. The purpose of this article is to provide an overview of the applied swimming sciences as a reference guide to practitioners involved in the sport. Although current information (post-1985) in physiology and biomechanics are discussed in this article, more extensive reviews are available in other p~blications.2~, 32 PART I: THE PHYSIOLOGY OF SWIMMING

Introduction

Physiology is the science of how muscles and other organs function. Sports physiology is the science of how muscles and other organs function to produce high-level performance in athletic activities. Physiology integrates fields, such as cellular metabolism, muscle fiber function, nutrition, and energy metabolism.

From the International Center for Aquatic Research, United States Swimming; and Research and Development, Nutrition-Worldwide, Novartis Consumer Health SA, Nyon Switzerland

CLINICS IN SPORTS MEDICINE VOLUME 18 * NLTMBER 2 * APRIL 1999

267

268

TROUP

Body Composition and Anthropometric Considerations

Unlike most land-based sports, swimming sports emphasize and reward upper extremity strength. Successful aquatic athletes are, generally, lean and tall, with long limbs and wide shoulders, and have relatively large muscle mass, especially in their middle and upper bodies. Araujo2and Ackland et all reported that male swimmers are primarily ectomesomorph somatotypes, and females are endomesomorphic. Elite swimmers also tend to have longer arms and larger hand surface areas. Based on this biomechanical description, certain anthropometric variables can influence performance capacity. When swimmers are examined by stroke, freestyle sprinters and backstrokers are found to be the tallest and heaviest (greater muscle mass), with the breaststrokers being the ”shorte~t.”~ ClarysT4studied the differences in body dimensions between elite and subelite swimmers and evaluated how these differences related to performance. He concluded that changes in drag forces because of changes in body configuration are not the reasons for better swimming performance. Rather, it is the better application of these effective forces during swimming that will improve performance. Talent Identification Based on Anatomic Factors

Recent studies examining growth and developmenF7,43 have provided information for identifying individuals that show potential as swimmers. Although most of this information is based on the rate of it can provide sport practitioners with the tools to determine reasonable growth potential. When considered with performance data, physical rate of change can indicate what the athlete’s potential in sport may be. KavouraP described the rate of improvement in performance based on 320 swimmers of various ages. Rates of improvement are associated with the developmental progress of 43 those factors affecting performance. As an example, VOvnaxhas been to reach a peak rate of development at 15.5 years. After that point, only slight improvements in VOvnaxare observed. Similarly, anaerobic profiles reach peak development at 16.5 years. From a practical point of view, it seems reasonable to begin specific training of a certain variable after peak development of that factor is achieved. Nutritional Concerns

Costill et all6reported changes in glycogen values following interval training in swimming. Glycogen levels had fallen to significantly low levels following short, high-intensity intervals. It has been suggested that 6 hours of rest between the morning and evening workouts of the first day may not be adequate to restore glycogen levels. Fuel Use During Training

During prolonged swim training, there is an increased carbohydrate requirement to maintain glycogen levels and exercise capacity. If glycogen stores are not maintained and no carbohydrates are provided, a shift in fuel use toward fats will result: Therefore, carbohydrate supplements appear to be useful during the training phase. Other studies5 support the thesis that high carbohydrate

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

269

food intake within 30 minutes of training helps accelerate the resynthesis of muscle glycogen; nutritional practices before training and competition should be designed to ensure ample muscle and liver glycogen stores. Few investigations are available that describe the protein requirements of athletes?' Consequently, it is difficult to determine whether swimmers have an increased protein requirement that could not be met simply by increasing caloric intake." Generally, it appears that swimmers can meet their protein requirements by consuming adequate calories. Body f a t Considerations

Percent of body fat of both elite male and female swimmers is lower than that seen for the average population (approximately 15% to 20% body fat for males, 20% to 25% body fat for females). As seen by the rather large range in percent body fat in the most successful swimmers, low percent body fat appears to have little effect on swimming performance. Although there may be an ideal range of percent body fat, there is no support for use of a single "ideal" value. Perhaps the best use of percent body fat is only to be sure that rapid weight loss is avoided. When determining influencing factors of performance, muscle strength and power play a more important role. Flexibility

It has been suggested that increased joint flexibility enables the swimmer to achieve a greater range of motion during the arm stroke,2O and K a v 0 ~ 1 -has a~~~ shown that elite swimmers are more flexible around the shoulders and ankles than their nonelite counterparts. This relationship is true for age group as well as Olympic competitors. Flexibility is influenced by the functional anatomy (tendons, ligaments, etc.) about a single or composite joint and the size of the supporting musculature. This is a major concern for athletes and coaches as they try to achieve increases in strength with increases in muscle mass, without inhibiting flexibility (range of motion) and related biomechanical factors.29 Flexibility varies with gender and between swimmers of different stroke specialties. Females tend to be more flexible than males of the same age and ability. Breaststrokers have more flexible ankles (inversion and eversion) and a greater lateral hip rotation compared with swimmers of other strokes. Butterfly swimmers have greater back (trunk extension) and shoulder (horizontal extension and flexion) fle~ibility.3~ Muscle: Strength and Power

The availability and use of "dry-land" testing devices, such as swimbenches, has provided a method for the measurement of muscle power in a pulling motion that nearly duplicates the swimming stroke. Costill and MillerI8 and Sharp et a161 demonstrated that swimming is a power-limited sport. For highly skilled swimmers already achieving a certain power value, however, further improvement of this value appears to be less important. Rather, the ability to maintain a high percent of peak power throughout the swimming event may be a more valuable attribute. This capacity is related to swimming technique and the mechanical efficiency of the athlete12;indeed, once a certain level of peak power can be generated to achieve elite status, the swimmer who

270

TROW

has a higher propelling efficiency, in spite of a lower maximal power output, will be a faster swim me^.'^ Power generation during sprint swimming is dependent on the maximal force production and velocity potential of the muscle’s contractile elements (rate of force development).62 The maximal force and velocity potential of a muscle is in part a function of the energy-producing potential of the contractile elements. Muscles with a large cross-sectional area can generate large maximal force. Longer muscles will have greater potential for achieving rapid shortening velocity.” Muscle Fiber Typing and Performance

Studies examining muscle fiber analysis of swimmers have reported varying results. Fiber typing studies involving swimmers have documented fiber type percentages ranging from 30% to 70% type I fibers. Gollnick et a1,26 Lavoie et a1,4O Costill et al,’5 Prin~,5~ and Nygaard and N e i l ~ e nhave ~ ~ shown that swimmers exhibit a full range of fiber type ratios, so it is clear that muscle fiber type alone does not provide a good method of predicting performance level. Training design should incorporate different concepts for endurance or sprint swimming. Motor units or muscle fibers are recruited in a ramp-like fashion,’O which is of practical importance when considering the specific muscle function requirements of swimming races. During distance competitions ( e g , 800 and 1500 m), muscle force at each pulling stroke is relatively low. It is suggested that type I fibers are activated preferentially during these races, as they are most resistant to fatigue. For the generation of submaximal forces during the 400- and 200-m race, type I and IIa fibers are recruited. The type IIa fibers produce considerably more force than type I fibers, but they fatigue rather easily.1° Type I, IIa, and the ”fastest” (type IIb) may be recruited in short swimming events (50 and 100 m), where maximal and explosive forces are required. Type IIb fibers produce high forces in short times, but they are fatigue sensitive,’O which will limit performance during sprint swimming. Anaerobic Power and Capacity

The fact that most swimming races (> 80%) are 200 m or less (about 130 seconds or less) emphasizes the importance of anaerobic energy demand and capacity. The anaerobic profiles of swimmers are difficult to determine, but tests using highly technical equipment and invasive techniques have been 58 Tests of oxygen deficit, oxygen debt, postexercise peak blood de~eloped?~, lactate concentration, tethered swimming tests, adapted Wingate tests, swim bench tests, and others all have been developed to estimate anaerobic energy demand and the anaerobic contribution to swimming. Recently, a test to measure anaerobic capaciq 49 has been adapted to swimming conditions31based on the use of a swimming economy test. Measuring the anaerobic characteristic is dependent upon calculating the estimated total energy demand required for very high intensity swimming. Because swimming economy involves a series (four or more) of submaximal steady-state swims, it is descriptive of the aerobic demands of swimming at a range of speeds. The resulting relationship of energy cost versus swimming speed (i.e., the swimming economy profile) can be used to determine the energy demand or cost of swimming at speeds requiring well-developed anaerobic energy.

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

271

Swimming economy can be influenced by technique. Thus, the more efficient a swimmer is (influenced in part by good biomechanical technique), the lower the energy demand will be for a given swimming speed. This influencing factor will result in a flatter slope of the economy profile as seen in better trained and faster swimmers. The swimming economy profile, therefore, can be used to determine the total energy demand for a given intensity of work. The energy demand at any given swimming speed can be measured, and the selected work intensity can be determined by an interpolation of the economy profile and assuming linearity at a maximal range of speeds. The total energy demand then can be calculated as the product of energy cost at a given speed and the time of the test swim. Specifically, the description of the anaerobic characteristic (i.e., 0, deficit) is determined by selecting a test speed corresponding to an intensity of 100% of VOhax with test administration lasting for a duration of at least 4 minutes. Once the total energy demand is known for the test swim, accumulated O2 uptake is measured at 10 second increments and the O2 deficit value taken as the difference between the calculated energy demand and the accumulated 0, uptake value at each 10 second increment for the duration of the test swim. The 0, deficit test protocol can be used to describe the anaerobic characteristic of the individual. Results based on this 0, deficit test have shown that elite competitors have larger anaerobic capacities and smaller rates of adjustment (larger use of the anaerobic system) during high-intensity exercise as compared to their subelite counterparts.4s, 66 For example, the world-class swimmer has a larger anaerobic ability and will derive more energy from anaerobic sources to meet the energy demands of the exercise; thus, the rate of change of his or her oxygen kinetic curve will be relatively flat. On the other hand, the national caliber swimmer will not be able to rely on his or her anaerobic energy stores for very long (because they are relatively small), and the slope of his or her oxygen kinetic curve will be relatively steep. This testing protocol provides a good opportunity to describe the total energy system capabilities of the individual athlete, and it becomes possible to examine how an athlete's energy system responds to workloads of the various intensities and durations seen in swimming. Aerobic and Cardiopulmonary Capacities

Because of the nature of the training regimens used in competitive training, swimmers have large cardiopulmonary and aerobic ca~acities.~, It is interesting that similar VOhax values have been recorded by European and American swimmers (males and females) from the two recent Olympic games, even though swimming performance has improved. Montpetit et a15"found changes in VOlmax during a 2-month period before an international competition and concluded that VO,,,, is only a small factor in swimming performance and is not a good predictor for it. Studies by Van Handel et aP8 also confirm this finding. Apparently, improved swimming performance is not related closely to aerobic capacity. Limitations to Optimal Swimming Performance

The aquatic environment presents a unique set of problems and questions to the coach and the sport scientist because the physiologic responses to exercise in water differ from corresponding responses on land. For example, cardiovascu-

272

TROUP

lar response, body fluid balance, and thermoregulation are affected uniquely when humans exercise in water. Limitations Imposed by Energy Metabolism

Intramuscular adenosine triphosphate (ATE'), phosphocreatine (PCr), and glycogen stores are the main fuel sources during high-intensity exercise? The energy for all competitive swimming events (the longest event being the 1500 meter freestyle, lasting about 15 minutes) comes from fuel stored in the muscle at the beginning of the race. Owing to the high-intensity of competitive events and nonsteady state conditions, it is difficult to study and quantify the metabolic demands of competitive swimming races. It is quite obvious, however, that the amount of glycogen available is not the limiting factor when racing, and only a small fraction of a muscle's stored glycogen (normal level) is Problems or limitations in performance may arise, however, when pre-exercise glycogen levels are severely depleted following high volume training. Three other possibilities could explain limitations during performance imposed by energy metabolism: (1) the reduction of intramuscular ATP and PCr stores; (2) limitations in the rate of energy production and use48;and (3) the disturbance of muscle function related to changes in intramuscular PH.,~,56 The rate of energy delivery is related to the flux through the metabolic pathway as regulated by enzymatic activity;3 so, potentially, the greater this activity, the greater the anaerobic profile may be. Limitations Imposed by Cardiopulmonary Response

Water immersion is accompanied by an increase in the pressure acting on the surface of the body. In addition, the supine body posture and the restrictions placed on breathing by the stroking pattern lead to cardiovascular and respiratory adjustments that are unique to swimming. As seen out of the water, the supine position allows for an increase in venous filling of the heart (greater end diastolic volume) which allows for a lower heart rate at a given cardiac o u t p ~ t .For ~ , a~ given ~ submaximal V02r42,44 heart rate is lower in swimming than in running or cycling on land. Holmer and Be1-gh,3~ however, found similar heart rates at a given VO, during swimming and running. Respiratory volume and frequency in swimming is in part determined by the limitations imposed by the swimming stroke. In an effort to help swimmers better cope with these demands, many coaches employ "hypoxic" training. "Hypoxic" swimming is completed by taking fewer breaths than n0rrna1.l~ Instead of breathing every stroke cycle, breathing is completed every second or third stroke cycle. In theory, the decrease in frequency of ventilation causes a higher extraction of 0, by working muscles, and increases the level of CO, (i.e., PCO,).u Increases in PCO, have been related to complaints of headache and loss of conscience.21Gullstrand and H0lme13~found lower heart rate and blood lactate levels during 100- and 200-m interval training, when hypoxic training was compared with normal breathing, whereas C ~ u n s i l m a nfound ~ ~ an increase in heart rate during hypoxic training. More studies are needed to better understand the physiologic demands of hypoxic training and to discover if it is beneficial as a training aid.

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

273

Limitations Imposed by Body Fluid and Thermoregulatory Response

Water immersion causes a shift in body fluids. The extent of this shift is affected by body position before entering the water and after immersion. The depth of immersion also influences fluid shifts, but depth is basically constant in competitive swimming. The temperature of the water also affects both body fluid balance and heat exchange. Fluid is shifted during water immersion mainly because of a "relief" of the gravitational effects placed on the body. For example, a 70-kg swimmer may weigh (depending on body composition) about 10 kg in water. Moving from standing on land to supine immersion in the water triggers a renal diuresis and subsequent hemoconcentration.8,38, 46, 69 This is the reason that many swimmers may feel an urge to urinate not long after entering the water. Temperature regulation during water immersion and swimming has received much greater attention.*Very little of the research, however, has involved swimming intensities commonly elicited in training and competition. Nevertheless, the results of these studies do have practical implications for the marathon and channel swimmer, and provide a fundamental basis for understanding temperature control in water. In swimming, even though metabolic rates are increased to similar levels, evaporation is prevented by the surrounding water and convection is the major means for heat loss. Activity level influences thermoregulation in water, and subsequently thermal comfort. Virtually all swimming competitions are governed by Federation International Natation Amateur (FINA) regulations that specify the water temperature within a "competitive" range, 25" to 27°C. Swimming training presents more of a thermoregulatory problem than does swimming competition, mainly because working at high intensities for long, mostly continuous, periods produces high body heat. On entering the water, the skin temperature is in equilibrium with the water tern~erature.~~ If the water is below 33" to 34°C (thermoneutrality), and the swimmers are not performing work or are at a low level of energy expenditure, they become hypothermic after prolonged immersion.33,52 Bardzukas et a15 reported that core temperature is significantly elevated during high-volume swimming training. They found an increase in core temperature (1" to 2°C) in swimmers completing workouts of 8,000 to 10,000 m in length.

PART II: THE BIOMECHANICS OF SWIMMING Hydrodynamics The science of the movement of bodies within a fluid medium is called hydrodynamics. The heart of swimming science is learning about those factors that influence the rapid movement of the human body through a liquid medium-water. The science of human movement and propulsion is biomechanics. Therefore, the study of human propulsion through water is a combination of the fields of biomechanics and hydrodynamics. Any discussion of hydrodynamics requires an understanding of the basic *References 23, 25, 30, 45, 47, 51, 52, and 54.

technical issues that determine good biomechanics. The basic terminology includes the following: Form Drag

Form drag is water resistance that is dependent on body position. The more horizontal the body position is in the water, the less form drag. A slanted body position will enlarge the frontal surface area in the vertical direction and increase the form drag. Extreme lateral swaying in the water is another example of increasing the form drag, owing to increased frontal surface area. Given equal streamlining in body position, form drag is greatest at the surface (the interface between air and water). Most strokes must, of necessity, be swum at or near the surface. There are certain situations, however, where underwater swimming is definitely faster than swimming at the surface. For example, present rules in competitive swimming allow for underwater swimming on the starts and turns in breaststroke (one stroke and kick off the wall), backstroke (15 m underwater), and butterfly (unlimited underwater swimming) before breaking the surface. The "trade-off" comes when comparing the energy requirements of holding one's breath for a prolonged period of time versus gaining a big lead because of the decreased drag while swimming under water. Wave Drag

Wave drag is caused by turbulence at the water surface created by the moving swimmer. Wave drag will rebound off the sides and bottom of a pool, which is why deeper pools are generally "faster" pools. The dissipation of the wave drag from the bottom of deep pools is much greater than for shallow pools. Two and three lanelines per lane are used at high level competitions to disperse the wave drag between lanes. Pools designed for competition will have many features that will decrease this form of drag. Frictional Drag

Frictional drag originates from the contact of the skin and hair with the water. Swimmers shave body hair before important meets to minimize the effects of frictional drag, although actual benefits of shaving are questionable. Some researchers have suggested that shaving reduces the frictional drag, whereas others have developed bathing suit materials that decrease the frictional drag of the body in the water. Form and wave drag resistance, however, are much more significant than frictional drag. Using Drag and Lift Forces for Propulsion

The drag force also is used for propulsion during the pulling pattern and the kick. The Bernoulli principle first described the lift component of fluid forces. Bernoulli's principle expresses the relationship between flow velocity and the pressure differential created on two sides of an airfoil. In swimming, water flows around the hand during the pulling pattern and meets on the back edge of the hand. The water flowing around the back of the hand has a longer distance to travel because of the roundedness of the thumb and the pitch of the hand. The resulting force created by this pressure differential is directed toward the low

THE PHYSIOLOGY AND BIOMECHANICS OF C0MPE"IVE SWIMMING

275

pressure zone and is called lift force. The lift force is perpendicular to the drag force. Streamlining and Sculling

There are two hydrodynamic principles that seem to apply equally to swimming the four strokes for fun and competition. These principles are streamlining and sculling. If these two principles can be mastered, they generally will lead to successful swimming. Streamlining

In all four competitive swimming strokes, a "streamlined" position is of importance to efficient forward propulsion. A "torpedo" position, used during starts and turns, is an example of streamlining. Important in many sports, such as running and speed skating, streamlining takes on added importance in swimming because the body is being made to move through a much denser medium. Sculling

Forward propulsion in swimming is created by a sculling motion of the hand in the water. Sculling is achieved by movement of the hand in the water at an oblique angle to the direction of travel. Like the motion of a propeller, sculling creates forward "lift," thereby moving the body forward in the water. The amount of force produced by the hand at any time during the stroke cycle is dependent upon the orientation of the hand and its speed or velocity. Hydrodynamic and Mechanical Efficiencies

Swimming at fast speeds requires power. Because swimming occurs in water, however, not all of a swimmer's power output is used for propulsion. The total power output from a swimmer is used in two ways: (1)to propel the swimmer forward by overcoming the drag of water; and (2) to give water energy by moving masses of water. As a swimmer's hand moves through the water, energy is given to the water and the water moves. "Pushing off of still water" allows swimmers to generate more force. One reason swimmers use the S-shaped pulling pattern is to continually find still water that is not moving to propel themselves forward. Total power output is, then, a combination of the power used to overcome drag and the power used to move water and give it energy. To create this power output during swimming the body needs energy. This energy is generated by the working muscles from anaerobic and aerobic sources. The ratio between power output and power input is called mechanical efficiency, measurements of which provide information about how efficiently a swimmer's body uses its energy to move through water. Typical values for mechanical efficiency in swimming range between 2% to 10%. This means that the body wastes most of its energy, energy which leaves the body in the form of heat. StudiesI2support the idea that technique is better maintained during slower speeds. At highly anaerobic, race sprint speeds, technique begins to deteriorate.

276

TROW

Proper technique (high propelling efficiency) helps elite swimmers maintain higher propelling efficiencies at fast speeds than average level swimmers. Drafting

Drafting, used mostly in land sports, is a racing technique in which a following athlete positions himself in the turbulence of a leading athlete. Turbulent air, which is moving forward behind the lead competitor, allows the drafting athlete to slip through the air with less resistance. The use of this strategy frequently gives a weaker athlete the opportunity to keep pace with someone who is much faster. Drafting is similar in swimming; the trailing swimmer (who is in an adjacent lane) will move through the turbulent, forward flowing wake of the lead swimmer with less energy cost. Although there may be psychologic cost, research shows that there is no difference in physiologic cost between swimming alone and "pulling" a drafting swimmer.ffi Muscle Mechanics and Fatigue

Research that muscle activity increases with the onset of fatigue in an attempt to maintain prefatigue levels of force and power. There is a decrease in the efficiency of the muscles as the firing increases and the force decreases. Increased electromyography (EMG) activity is interpreted as an increase in motor unit recruitment in an attempt to maintain the same propulsive forces. To delay the effects of fatigue at the muscle level, coaches and athletes can stress high intensity anaerobic training to build up higher levels of tolerance to fatigue. Additionally, both dry-land (for older swimmers) and swim aerobic training is needed to add to the aerobic base of the muscles. Stroke Length and Stroke Rate

Acute fatigue during competition shows a consistent pattern in terms of stroke rate and stroke length. As fatigue sets in, stroke length decreases. This trend is seen in all levels of swimming up to the Olympics. Analysis of the swimming competitions during the 1988 and 1992 Olympic games showed that performance times were highly correlated with stroke rate during the last half of the race. Swimmers who achieved medals in their respective events were able to increase stroke rate to maintain swimming speed. Pulling Pattern Forces

To evaluate the pull pattern of each stroke, forces acting at and on the hand as it pulls through the water can be measured. On these hand force graphs, the top curve on the graph represents the resultant, or total, force the hand produces during each phase of the pulling pattern. Schleihaufmhas shown that the total, or resultant, force is a three-dimensional vector that can be pointing in any combination of directions (up, down, sideways, forward, backward). The lower curve on the graph represents the propulsive force. The propulsive component of the force is the amount of the total force that points directly forward. In general, fast hand velocity will help to maximize the magnitude of

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

277

this force. Hand position directs the total force and therefore has an important impact on maximizing the forward propulsive force generated by the hand as it pulls through the water. The demands of competition most certainly result in changes in mechanics that may contribute to a loss of performance capacity. The following analyses, taken from swimmers at a national competition, allow calculation of several parameters for the hands, including (1) total force, (2) velocity, (3) angle of pitch, and (4) effective force index (EFI, propulsive force divided by total force). During the progression of a typical middle distance swimming race, the magnitude of the hand forces decreases significantly. This is due primarily to a decrease in the angle of pitch, and a loss in hand velocity between the first and last lengths of the race. These changes also reflected slower swimming split times, suggesting that biomechanical technique does affect performance. Biomechanics of Specific Strokes

A discussion of the biomechanics of each of the four competitive swimming strokes is as follows: Freestyle

The freestyle pulling pattern can be divided into a number of different phases. For simplicity, the arm stroke will be discussed using the following five phases: hand entry, catch, insweep, finish, and recovery. The entry into the water begins with the fingertips. Fingertips enter out in front of the head between the body midline and the shoulder. The hand enters the water with the thumb pointed slightly downward to minimize the water drag. For the most streamlined entry, the wrist and elbow follow the hand in the same “hole” that was opened by the fingertips. As the wrist and elbow enter the water, the hand stretches forward until the arm is extended out in front of the swimmer. The catch phase begins at the end of the forward hand stretch, as the wrist flexes approximately 40” and the palm rotates outward. The hand then presses downward and outward, wider than the shoulder. This catch phase continues until the widest part of the downsweep motion. This widest point in the pulling pattern can be up to 2 feet below the surface of the water for men, and 1.5 feet for women. For some swimmers, the end of the catch phase is also the deepest point in the pulling pattern. For others, the deepest point occws during the insweep phase. The insweep phase is between the end of the catch and the narrowest point of the pulling pattern. At the beginning of the insweep, the palm rotates inward, and the hand sweeps inward toward the swimmer’s chest. The narrowest point of the pulling pattern is generally near the midline of the body. The finish phase begins as an outward and backward sweep of the hand as it comes out from underneath the body. As this phase continues, there is a sweep upward and still backward toward the surface of the water. The finish phase ends as the hand exits the water. The recovery phase occurs between hand exit and hand entry into the water. The elbows should be high in the air and bent. The key to this phase is to relax the arm as much as possible to allow it to be a true recovery. Anatomically, the swimming motion at the shoulder joint (glenohumeral joint) may be reduced to two general movements: abduction and adduction, and internal and external rotation. During the recovery phase of the stroke, the

glenohumeral joint is abducted and externally rotated, whereas the catch and pull-through phases represent adduction and internal rotation of the glenohumeral joint. During recovery, the deltoid and rotator cuff muscles (supraspinatus, infraspinatus, subscapularis, and teres minor) bring the shoulder to an overhead and externally rotated position. During the pull-through, the latissimus dorsi and pectoralis major muscles forcefully adduct and internally rotate the glenohumeral joint. It is clear that during the swimming motion, a great deal of emphasis is placed on the nearly "global" motion of the glenohumeral joint. The greater the flexibility of this joint, the better the swimmer is able to generate power through the entire pull-through phase. Unfortunately, the spectrum of flexibility runs from joint stability to joint instability, in which case the humeral head may become unstable in relation to the glenoid (socket). Stabilization of the scapula (of which the glenoid is a part) by the levator scapulae, rhomboids, and trapezius muscles, and stabilization of the humeral head by the rotator cuff muscles is critical to maintaining the normal relationship of the humeral head to the glenoid socket. Simultaneous with this shoulder motion, the elbow flexes and extends during each cycle of the stroke. Active, forceful flexion by the coracobrachialis and biceps brachii muscles, allows the hand to follow the first half of the well known " S pattern underwater, whereas extension of the elbow by the triceps brachii allows the "push" and finish of the " S pattern underwater. The elbow also flexes and extends during the recovery phase. The muscles of the dorsal and volar forearm (wrist flexors and extensors), as well as the intrinsic muscles of the hand, are critical to the positioning of the hand during hand entry and pull-through. As seen previously, this positioning of the hand is crucial to determining the forward propulsive (lift) forces on the hand during swimming. It is difficult to underestimate the influence of body roll during the crawl stroke. During each stroke cycle, the upper body will roll through nearly 160", so that during recovery the shoulder is out of the water, whereas the shoulder is deep in the water during pull-through. This roll of the torso produces the large forces that pull the hand and arm through the water, and is a manifestation of the large paraspinous muscles of the back and the abdominal muscles anteriorly. The power of the thigh and calf muscles, through the kicking action of the legs, are purposely timed to enhance and provide power to body roll, and, therefore, pull-through power. Perhaps the greatest difference between elite and novice swimmers is the lack of body roll, and therefore power, in the latter. The most common kicking patterns used during the freestyle, the six-beat and two-beat flutter kicks, differ in their timing. The two-beat flutter kick has one downbeat and one upbeat of each leg during one stroke cycle. The six-beat flutter kick has three downbeats and three upbeats during one stroke cycle. The downbeat phase is the propulsive phase of the kick and the upbeat serves as a recovery phase for the legs. These down- and upbeats also have a lateral component to help stabilize the body roll. The upbeat or recovery portion of the kick is mostly a motion of hip extension. The knee stays fully extended and the ankle is slightly plantar flexed. The main muscles contributing to hip extension are gluteal muscles of the buttocks and the hamstrings (including biceps femoris, semitendinosus, semimembranosus, and gracilis). The ankle is plantar flexed by the soleus and gastrocnemius muscles, along with tibialis posterior, peroneus longus and peroneus brevis muscles.

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

279

The downbeat of the kick is generated by flexion at the hip. The foot lags behind the thigh during the beginning of the downbeat due to flexion of the knee. The knee continues the downbeat motion by extending, and the ankle remains plantar flexed. The iliopsoas muscles and the rectus femoris of the quadriceps muscle group are strong hip flexors. Extension of the knee is caused by the quadriceps, and plantar flexion at the ankle is caused by the soleus, gastrocnemius, tibialis posterior, peroneus longus and peroneus brevis muscles. Resistance from the water during the downbeat also helps to plantar flex the ankle. Butterfly

With the exception of the obvious lack of body roll, the gross motions, and the forward propulsive actions of the shoulder, elbow, and wrist, the conditions for the butterfly are nearly the same as for the freestyle. Shoulder motion is, again, abduction and adduction and internal and external rotation. This again is coordinated with flexion and extension of the elbow and maintenance of wrist and hand position is needed to create forward propulsion and to produce the insweep and outsweep "S" pattern of pulling through the water. In this case, of course, both upper extremities are working simultaneously, rather than sequentially, as in freestyle. The lack of body roll is compensated by lift of the body out of the water, followed by plunging both shoulders underwater immediately following the hand entry phase of the butterfly stroke. Once again, the large muscles of the torso (paraspinous muscles, abdominal muscles) are critical in producing this coordinated body undulation that places the upper extremities in a stable position for pull-through. The two legs kick in unison with a two-beat rhythm. The downbeats of both kicks can be propulsive with proper ankle plantar flexion. The upbeat of the kick is mainly hip extension. The knees stay extended and the ankles are slightly plantar flexed. The muscles contributing to hip extension are gluteus maximus, medius, and minimus and the hamstrings. The ankles are plantar flexed by the gastrocnemius and soleus muscles, along with tibialis posterior, peroneus longus, and peroneus brevis. The downbeat motion of the kick is flexion at the hips. The knees flex at the beginning of the downbeat and then extend to complete the kick. Plantar flexion of the ankle is critical during the downbeat to maximize the propulsion. The iliopsoas muscles and the rectus femoris of the quadriceps ,are strong hip flexors. Extension of the knee is caused by the quadriceps and plantar flexion is caused by the gastrocnemius, soleus, tibialis posterior, peroneus longus, and peroneus brevis. Resistance from the water during the downbeat also helps to plantar flex the ankle. Timing

The first downbeat occurs during the entry and catch phase of the pulling pattern. The second downbeat occurs during the finish phase of the pulling pattern. Research on world class butterfliers shows that both kicks should be emphasized equally in terms of length and depth of kick. Equal propulsion can be generated from both kicks. Swimmers who stayed lower (lower trunk angle) in the water were able to extend their elbows to a straighter position during the finish phase of the pulling pattern. Additionally, a larger elbow angle was positively correlated with the

280

TROW

efficiency of the finish phase indicating that more propulsive forces were generated by swimmers who were able to extend their elbows to a straighter position (150" vs. 100"). Combining these findings suggests that staying lower in the water may be advantageous to the butterfly pulling pattern. In order to stay lower in the water the vertical undulation must be minimized to a certain extent. In another study,'* the wavelike characteristics of the butterfly stroke were investigated. The findings of this study strongly suggest that elite butterfly swimming is wavelike in nature. The wavelike characteristics have two components: (1)a one-beat sine wave (harmonic) seen in the head and shoulders, and (2) a two-beat sine wave that is twice the frequency of the first harmonic, seen in the hips, knees, and ankles. Up to 99% of the wave patterns in elite swimmers were contained in the first two harmonics (one- and two-beat sine waves). Swimmers were considered less harmonic if more than 7% of the wave pattern was contained in a three-beat sine wave. Theoretically, a three-beat sine wave could only occur if the timing of the butterfly stroke were not correct. An example of this may be unequal emphasis of the two kicks. Correlations of the harmonic wave patterns with performance times revealed that swimmers who had the fastest performance times were also the most harmonic (more than 95% of the wave patterns were contained in the one- and two-beat waves). Additionally, the progression of the one and two beat oscillations (or undulations) suggests that these waves travel down the body from head to foot at a greater velocity than the swimmer's forward motion. This greater wave velocity may signify that dissipation of the wave to the water at the feet may have a reaction to drive the swimmer forward and contribute to the swimmer's forward propulsion. The data from the preceding studies emphasize the importance of the undulation motion, but this undulation motion should not be excessive. A common problem for novice swimmers is too little undulation. This can be caused by not leading the wave motion with the head motion downward during the arm entry. Excessive undulation may be caused by lifting the head too high during the breathing. Swimmers should concentrate on driving the head forward when taking a breath. Backstroke

Remarkably, when one studies the motions and muscle recruitment patterns of the upper extremity for the backstroke, there is a close similarity to the front crawl and butterfly. Once again, the stroke may be broken down into handentry, pull-through, hand finish, and recovery phases. Shoulder motion, as in freestyle, is represented as abduction and external rotation during the out-of-water recovery phase of the stroke, whereas propulsive power again is generated by forceful adduction and internal rotation of the glenohumeral joint. During the pull-through phase, the elbow is forcefully flexed; the hand again demonstrates a sculling motion, creating a resultant lift force on the dorsum of the hand. Once again, body roll is important. Coaches regularly instruct novice backstrokers to "lead with the shoulder" during the recovery phase; by leading with the recovering arm, the opposite shoulder will be deep in the water, allowing the hand to trace an " S shaped curve, producing the same forward lift force. Use of the legs and body are very similar to freestyle swimming, with either the four- or six-beat kick. Forward propulsion is developed with flexion and extension of the knee and ankle, in concert with the rolling action of the body. Again, the major muscle groups in use are the gluteal muscles of the buttocks,

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

281

the quadriceps and hamstring muscles of the thigh, and the anterior and posterior muscles of the calf (tibialis anterior and posterior, peroneus longus and brevis, and the gastrocnemius and soleus muscles). Breaststroke

The breaststroke pulling pattern can be divided into the following phases: (1)outsweep, (2) insweep, and (3) recovery. The outsweep begins with the hands stretched forward in front of the body and the arms fully extended. The palms of the hands turn outward, the wrist flex slightly, and the arms begin to sweep outward and slightly upward. The hands are pitched approximately 40" with respect to the line of motion of the hands. This outsweep continues until the hands are 12 to 15 inches wider than the shoulders. The insweep phase begins as the palms rotate down and inward. The insweep motion is a lateral inward scull toward the shoulders. The hands are pitched as in sculling at approximately 40" to 50" relative to the hand's line of motion. The insweep phase ends as the hands meet underneath the body. Streamlining of the hands is critical during the recovery phase of the pulling pattern. As the hands meet at the end of the insweep phase, they begin to move forward together with the fingertips leading. This phase continues until the arms are fully extended out in front of the swimmer and are ready to begin the next outsweep. The outsweep motion of the pulling pattern is a lateral outward sweep with the hands (beginning with the arms overhead). Inward rotation of the shoulder keeps the palms facing outward. Posterior deltoid, infraspinatus, and teres minor muscles assist in the lateral motion, whereas anterior deltoid and pectoralis major assist in the inward rotation at the shoulder. Triceps brachii are active to keep the elbow relatively extended and the wrist flexors (flexor carpi ulnaris and radialis, flexor digitorum profundus) hold the wrist in a slightly flexed position against water resistance. At the beginning of the insweep, supination of the elbow by the biceps brachii and supinator muscles as well as outward rotation of the shoulder (posterior deltoid, infraspinatus and teres minor) turns the palms inward. The adduction motion at the shoulder is caused by pectoralis major, latissimus dorsi, and anterior deltoid muscles. Biceps brachii and coracobrachialis flex the elbow until the completion of this phase when the hands come together. Supination at the elbow continues into the beginning of the recovery phase to turn the hands toward each other (biceps brachii and supinator). Forward recovery of the arms requires anterior deltoid, pectoralis major, and long head of biceps brachii for flexion at the shoulder. Triceps brachii extend the elbows throughout this phase. The kick can be divided into the recovery, outward sweep, and inward sweep. The recovery of the legs begins during the insweep phase of the arms. The feet should recover as closely to a straight line as possible toward the body. The knees and hips flex as the feet are drawn toward the body. Once the feet are near the body, the feet turn outward so that the inside of the foot is facing away from the swimmer. The outward rotation of the feet is critical at this point to maximize the propulsion from the kick by maximizing the surface area. The feet begin to push slightly outward, downward, and backward. The width of the knees during the outward sweep should be slightly wider than the hips. The inward sweep of the kick begins at the widest point in the kicking pattern. The foot path continues backward, downward, and now inward. This phase ends when the feet come together and the knees are straight.

During the recovery of the legs, the feet are brought toward the body by a combination of knee flexors (hamstrings, gastrocnemius, sartorius, and gracillis) and hip flexors (iliopsoas and rectus femoris). These two motions combined allow the feet to stay near the water surface without breaking it. The action of peroneus longus and brevis turn the feet outward, and slight hip inward rotation (iliopsoas, tensor fascia latae, and the anterior fibers of gluteus medius and minimus) helps to maximize this foot position. Tibialis anterior and extensor digitorum longus dorsiflex the ankle in preparation for the outward sweep, which is a combination of hip and knee extension accomplished by the hamstrings and quadriceps muscle groups respectively. Hip and knee extension (hamstrings and quadriceps) continue throughout the inward sweep. The legs are adducted from the hip through contractions of adductor magnus, adductor longus, adductor brevis, pectineus, and gracilis muscles. This phase also includes slight hip outward rotation as the feet come together (gluteus maximus, sartorius, and the posterior fibers of gluteus medius and minimus). To finish the kick in a streamlined position, the feet plantar flex, which is executed by gastrocnemius, soleus, tibialis posterior, peroneus longus, and peroneus brevis muscles. Also, the legs are lifted slightly (hamstrings) so that they fall in line with the path of the body. Over the past 20 years, undulation of the body has taken on considerable importance during breaststroke swimming. Like the butterfly, there is negligible body roll possible with the breaststroke. Keeping the body at the surface of the water during each stroke cycle increases the form drag of the swimmer because surface resistance is greater than that either above or below the surface. Elite breaststrokers now lift the upper body during each stroke cycle (also for breathing), followed by plunging the shoulders beneath the surface during the kicking phase; therefore, the actual time of maximal surface form drag is minimized. This results not only in decreased total surface form drag, but also simulates the undulations of the butterfly stroke, improving forward propulsion. SUMMARY

Fast swimming, either in the pool, in open water swimming, or in water polo and synchronized swimming, requires maximizing the efficiencies with which the human body can move through a liquid medium. A multitude of factors can affect the ability to swim fast as well as the final outcome. Physiology and biomechanics are the present tools used by sports scientists to determine which factors are important to fast swimming and, subsequently, to determine how the swimmer may maximize these factors to improve performance. References 1. Ackland TR, Mazza JC, Carter L, et al: A survey of physique of world champion aquatic athletes. Sports Coach 14:10-11,1991 2. Araujo CGS Somatotyping of top swimmers by the health-carter method. In Swimming Medicine IV.Baltimore, University Park Press, 1978, pp 188-199 3. Arborelius M Jr, Balldin UI, Lilja B, et a1 Hemodynamic changes in man during immersion with the head above water. Aerospace Med 43:592-598, 1972 4. Astrand PO, Rodahl K: Textbook of Work Physiology. New York, McGraw-Hill, 1986 5. Bardzukas AP, Trappe TA, Jozsi AC, et al: The effects of hydrating on thermal load

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

283

and plasma volume during high intensity swimming training. Med Sci Sports Exerc 25:S20, 1993 6. Bergstrom J, Hultman E: Nutrition for maximal sports performance. JAMA 221:9991006, 1972 7. Berning J R The effect of carbohydrate feedings on four-hour swimmers. In Troup JP (ed): International Center for Aquatic Research Annual. Colorado Springs, U.S. Swimming Press, 1992, pp 145-149 8. Boening D, Ulmer HV, Meier U, et al: Effects of a multi-hour immersion on trained and untrained subjects: I. Renal function and plasma volume. Aerospace Med 43:300305, 1972 9. Boulgakova N Selection et preparation des jeunes nageus. Paris, Vigot, 1990 10. Burke RE: Motor units: Anatomy, physiology, and functional organization. In Brooks VB (ed): Handbook of Physiology. Section I, The Nervous System 11, Washington, American Physiological Society, 1981, pp 345422 11. Butterfield G: Amino acids and high protein diets. In Lamb DR, Williams MH (eds): Ergogenics-Enhancement of Exercise and Sports Performance. Perspectives in Exercise Science and Sports Medicine, vol4. Carmel, IN, Benchmark Press, 1991, pp 87-122 12. Cappaert JM: The importance of propelling and mechanical efficiencies. In Troup JP (ed): International Center for Aquatic Research Annual. Colorado Springs, US. Swimming Press, 1991, pp 75-80 13. Cappaert JM, Bone M, Troup JP: Intensity and performance related differences in propelling and mechanical efficiencies. In Mac Laren D, Reilly T, Lees A (eds): Swimming Science VI. London, E. & EN. Spon, 1992, pp 53-56 14. Clarys JP: Human body dimensions and applied hydrodynamics: Selection criteria for top swimmers. SNIPES Journal, 23:3241, 1986 15. Costill DL, Fink WJ, Hargreaves M, et a1 Metabolic characteristics of skeletal muscle during detraining from competitive swimming. Med Sci Sports Exerc 17339-343,1985 16. Costill DL, Flynn MG, Kirwan JP, et al: The effects of repeated days of intensified training on muscle glycogen and swimming performance. Med Sci Sports Exerc 20:249254, 1988 17. Costill DL, Maglischo EW, Richardson AB: Swimming. London, Blackwell Scientific, 1992 18. Costill DL, Miller J: Nutrition for endurance sport: Carbohydrate and fluid balance. Int J Sports Med 1:2-14, 1980 19. Counsilman JE: Hypoxic and other methods of training evaluated. Swimming Techniques 1219-26, 1975 20. Counsilman JE: The Science of Swimming. Upper Saddle River, NJ, Prentice Hall, Inc, 1968 21. Craig AB: Summary of 58 cases of consciousness underwater during swimming. Med Sci Sports 8:171-175, 1976 22. Craig AB: The fallacies of hypoxic training in swimmers. In Terauds J, Bedingfield W (eds): Swimming 111. Baltimore, University Park Press, 1979, pp 235-239 23. Craig AB, Dvorak M Thermal regulation of man exercising during v5ater immersion. J Appl Physiol25:28-35, 1968 24. Faulkner J A Physiology swimming and diving. In Falls HB (ed): Exercise Physiology. New York, Academic Press, 1968, pp 415-416 25. Galbo H, Houston ME, Christensen NJ, et a1 Hormonal response of swimming man. Acta Physiol Scand 105:326-337, 1979 26. Gollnick PD, Armstrong RB, Sawbert CW, et al: Enzyme activity and fibre composition in skeletal muscle of trained and untrained men. J Appl Physiol3312-319, 1972 27. Gullstrand L, Holmer I Physiological responses to swimming with controlled frequency of breathing. Scandinavian Journal of Sports Science 21-6, 1980 28. Gullstrand L, Lawrence S Heart rate and blood lactate response to short intermittent work at race pace in highly trained swimmers. Aust J Sci Med Sport 19:lO-14, 1987 29. Hay JG: The Biomechanics of Sports Techniques. Upper Saddle River, NJ, Prentice Hall, 1985, pp 343-394 30. Hayward JS, Eckerson JD, Collis ML: Thermoregulatory heat production in man:

284

TROW

Prediction equation based on skin and core temperatures. J Appl Physiol 42377-384, 1977 31. Hollander AP, Troup JP, Bone M, et al: Estimation of the anaerobic contribution to energy consumption in swimming different distances. J Sports Sci 9:87-88, 1991 32. Holmer I Physiology of swimming man. Exerc Sports Sci Rev 787-124, 1979 33. Holmer I, Bergh U: Metabolic and thermal responses to swimming in water at varying temperatures. J Appl Physiol 37702-705, 1974 34. Huijing PA: Mechanical muscle models. In Komi PV (ed): Strength and Power in Sports. London, Blackwell Scientific, 1992, pp 151-168 35. Ivy JL, Katz AL, Cutler CL, et a1 Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J Appl Physiol 65:1703-1709, 1986 36. Kavouras SA: Growth, Maturation and Performance Evaluation of Elite Age Group Swimmers: 1992 United States Swimming Camp Report. Colorado Springs, U.S. Swimming Press, 1993 37. Kavouras S A Developmental Stages of Competitive Swimmers: 1991 United States Swimming Camp Report. Colorado Springs, US.Swimming Press, 1992 38. Khosla SS, Dubois AB: Osmoregulation and interstitial fluid pressure changes in humans during water immersion. J Appl Physiol51:68&692, 1981 39. Lange L, Lange S, Echt M, et al: Heart volume in relation to body posture and immersion in a thermo-neutral bath. Pfluegers Arch 352:219-226, 1974 40. Lavoie JM, Taylor AW, Montpetit RR: Histochemical and biochemical profile of elite swimmers before and after six month training period. In Poortmans J, Nisert G (eds): Biochemistry of Exercise. Baltimore, University Park Press, 1981, pp 259-266 41. Lemon PWR, Proctor DN: Protein intake and athletic performance. Sports Med 12:313325, 1991 42. Magel JR Comparison of the physiologic response to varying intensities of submaximal work in tethered swimming and treadmill running. J Sports Med Phys Fitness 11:203312, 1971 43. Malina RM, Bouchard C: Growth, Maturation, and Physical Activity. Champaign, IL, Human Kinetics, 1988 44. McArdle WD, Glaser RM, Magel JR Metabolic and cardiorespiratory response during free swimming and treadmill walking. J Appl Physiol30:733-738, 1971 45. McArdle WD, Magel JR, Lesmes GR, et a1 Metabolic and cardiovascular adjustment to work in air and water at 18, 25 and 33 degrees C. J Appl Physiol40:85-90, 1976 46. McCally M Body fluid volumes and renal response of human subjects to water immersion. AMRL-TR-65-115, Aerospace Medical Research Laboratories, Wright-Patterson Air Force Base, 1965 47. McMurray RG, Horvath SM Thermoregulation in swimmers and runners. J Appl Physiol46:1086-1092, 1979 48. Medbo JI, Burgers S: Effect of training on the anaerobic capacity. Med Sci Sports Exerc 22501-507, 1990 49. Medbo JI, Mohn A-C, Tabata I, et al: Anaerobic capacity determined by maximal accumulated O2deficit. J Appl Physiol M50-60, 1988 50. Montpetit R, Duvallet A, Cazorla G, et al: The relative stability of maximal aerobic power in elite swimmers and its relation to training performance. Journal of Swimming Research 3:15-18, 1987 51. Nadel ER Thermal and energetic exchanges during swimming. In Nadel ER (ed): Problems with Temperature Regulation During Exercise. New York, Academic Press, 1977, pp 91-119 52. Nadel ER, Holmer I, Bergh U, et al: Energy exchanges of swimming man. J Appl Physiol 36:465-471, 1974 53. Newsholme E A Basic aspects of metabolic regulation and their application to provision of energy in exercise. In Hebbelinck M, Shephard RJ (eds): Principles of Exercise Biochemistry. Basel, Karger, 1988, pp 40-77 54. Nielsen B: Temperature regulation during exercise in water and air. Acta Physiol Scand 98:500-508, 1976 55. Nygaard E: Nielsen E: Skeletal muscle fibre capillarisation with extreme endurance training in man. In Eriksson B, Furberg B (eds): Swimming Medicine Iv:Proceedings

THE PHYSIOLOGY AND BIOMECHANICS OF COMPETITIVE SWIMMING

56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69.

285

of the Fourth International Congress on Swimming Medicine. Baltimore, University Park Press, 1978, pp 282-293 Olbrecht J, Mader A, Heck H, et al: Importance of a calculation scheme to support the interpretation of lactate tests. In Mac Laren D, Reilly T, Lees A (eds): Swimming Science VI. London, E & FN SPON, 1992, pp 243-249 Prins J: Muscles and their function. In Flavell ER (ed): Biokinetics Strength Training. Albany, CA, Isokinetics, 1981, pp 72-77 Rohrs DM, Mayhew JL, Arabas C, et al: The relationship between seven anaerobic tests and swim performance. Journal of Swimming Research 6:15-19, 1990 Saltin B Metabolic fundamentals in exercise. Med Sci Sports Exerc 5:137-146, 1973 Schleihauf RE: A hydrodynamic analysis of swimming propulsion. In Hollander AP, Huijing PA, De Groot G (eds): Swimming III. Champaign, IL, Human Kinetics Publishers, Inc, 1979, pp 173-183 Sharp RL, Armstrong LE, King DS, et al: Buffer capacity of blood in trained and untrained males. In Knuttgen HG, Vogel JA, Poortmans J (eds): Biochemistry of Exercise. Champaign, IL, Human Kinetics, 1983, pp 595-599 Strass D Effects of maximal strength training on sprint performance of competitive swimmers. In Ungerechts BE, Wilke K, Reischle K (eds): Swimming Science V. Champaign, IL, Human Kinetics, 1988, pp 149-156 Toussaint HM: Mechanics and energetics of swimming. Dissertation, Vrije Universiteit Amsterdam, 1988 Trappe SW, Trappe TA, Troup JP: The relationship between maximal accumulated oxygen deficit and selected skeletal muscle characteristics. J Appl Physiol, in review Troup JP: International Center for Aquatic Research Annual, 1989-1990. Colorado Springs, CO, US Swimming Press, 1990 Troup JP, Hollander AP, Bone M, et al: Performance-related differences in the anaerobic contribution of competitive freestyle swimmers. J Sports Sci 9:106-107, 1991 Troup JP, Trappe S, Crickard G, et al: Aerobic-anaerobic contributions during various interval training distances at common work Rest ratios. J Sports Sci 9:108, 1991 Van Handel PJ, Katz A, Troup JP, et al: Aerobic economy and competitive swim performance of U.S. elite swimmers. In Ungerechts BE, Wilke K, Reischle K (eds): Swimming Science V. Champaign, IL, Human Kinetics Publishers, 1988, pp 219-227 Vogt FB, Johnson PC: Study of the effect of water immersion on healthy adult male subjects: Plasma volume and fluid-electrolyte changes. Aerospace Med 36M7-451, 1965

Address reprint requests to: John P. Troup, PhD Novartis Consumer Health SA Case Postale 269 CH-1260 Nyon 1 Switzerland

-

e-mail: jptroupQaol.com