BACK TO SCHOOL Let s Revise the Basics Part 3 Note from the Editor: In forthcoming issues of our magazine we will use this section as a reminder of the basic knowledge required in our day-to-day involvement with our athletes. These are a selection from the best articles written in this field. BIOMECHANICS OF COMPETITIVE SWIMMING Dr Ralph Richards, Australian Swimming Inc. BACKSTROKE Backstroke rules allow any type of arm and leg movement; the only requirement is that the body remains on the back (i.e. when the shoulders rotate past vertical, or 90 degrees to the surface of the water, the swimmer is no longer on the back). The most efficient Backstroke is a back-crawl technique, which uses a flutter kick (except during the start and turns when a dolphin kick is often used) and an alternating armstroke. Streamlining The body should remain as close to horizontal as possible, to maintain a smooth flow of water over/around the body. Less experienced swimmers may disrupt streamlining if their knees lift out of the water, or the head is held too high. These actions often result in a poor body position, causing the hips to lower and thus increasing frontal resistance. The head should be kept comfortably aligned with the body. A smooth rolling action of the trunk (about the long axis of the body) of approximately 45 degrees to either side will assist in lifting the shoulder for both arm recovery and application of propulsive force by the opposite arm. The head should remain relatively still, not turning from side to side. Kicking Leg action provides the same type of contribution as in the Freestyle. However, because each arm recovery is made using a high, out of the water, motion; there are considerable downward forces acting against the horizontal positioning of the body. Therefore, a strong six beat kick must be used to keep the hips near the surface. The leg action is identical to the flutter kick used in Freestyle swimming, except that because the swimmer is in a supine position the upbeat becomes the propulsive phase. The leg begins to move downward (recovery phase) from an extension at the hip; as the leg reaches the its lowest point the knee is beginning to bend. The upward movement (propulsive phase) begins with the knee flexed somewhat and ends with the knee extended in a whip like action. As the leg drives upward it also angles inward slightly, finishing with the toes breaking the surface. Ankles are extended to increase the propulsive surface area of the leg and reduce eddy resistance. Correct timing of the kick will assist the roll of the hips and trunk; as the right hand completes its underwater push the right leg is completing its upward beat (and similarly on the left side). Armstroke Pattern The stroking (or pulling) pattern is best described as being shaped like an 5 on its side. The arm is straight and extended behind the shoulder as the hand enters the water. Hand entry is made with the little finger edge (palm facing outward) leading; this reduces surface resistance and maintains the momentum developed during the arm recovery. The shoulder will roll substantially toward the entry arm. The hand moves downward and somewhat outward until it reaches the deepest part of the stroke; this is the catch position. From the catch an upsweep of the hand is combined with a slight insweep due to increasing elbow bend until an angle of approximately 90 degrees between the forearm and upperarm is reached. As with freestyle, the elbow must be held so that the full length of the handforearm acts as a propulsive surface. If the elbow points toward the feet, water will slip off the arm surface. The term slip is used when the pulling surface is positioned at a poor angle of attack so that both drag and lift forces are less than optimal. From the 90-degree elbow position the hand speed accelerates during a downsweep action. The propulsive aspects of the downsweep finish as the hand reaches a point level with or deeper than the hip position. At this point the wrist relaxes so that the palm turns inward and the hand begins to move toward the surface in a side-on position (thumb side leading) to minimise surface resistance. The forceful downward push at the end of the downsweep (which also has a slight insweep component) helps the shoulder lift in preparation for the arm recovery. The recovery starts with a lift of the shoulder, which brings the hand out of the water. The arm remains straight but relaxed (elbow fixed at full extension) as it swings upward in an arc directly above the shoulder. As the arm reaches the vertical and begins its downward arc, the hand should rotate (palm facing outward) to prepare for the entry. The mechanics of the arm recovery assist trunk rotation and help to maintain the timing and momentum of the stroke. Breathing Because the swimmer is on the back, with the mouth out of water, it s easy to overlook breathing as a consideration when evaluating technique. However, it s important for backstroke swimmers to maintain body position. The head should remain stable, level, and comfortable.
Timing The timing of stroking and recovery arms should place the hands at almost 180 degrees apart in the full stroke rotation. That is, when viewed from the side, a line along axis of the recovery arm will extend through the upperarm on the pulling side. Breaks in the timing of the arms occurs most frequently when hand entry meets with resistance (i.e. the knuckle side of the hand strikes the water upon entry) or crosses the midline of the body; or the shoulders do not roll evenly to each side; or the head is thrown from side-to-side. Turns As mentioned, the Backstroke turn is a modified Freestyle tumble-turn. As the swimmer approaches the wall a turn begins with the recovery arm crossing over the midline of the body with the elbow bent slightly so that the hand reaches past the opposite shoulder. This begins to rotate the body off the back and into a prone position. As the hand enters the water the head drops, a slight bend at the knee initiates a shallow dolphin kick as the body flexes sharply at the waist to rotate the body into a tuck position. The arm that initiated the turn continues to pull through until the hand is at the thigh as the tumbling action commences. This final stroke is a continuation motion, which is part of the tumble; it is not a freestyle stroke because the opposite arm remains at the side once the shoulders have crossed the vertical plane. The legs rotate straight over the trunk, knees and hip flexed in a tuck position. As the feet strike the wall (with hip and knees still flexed, toes pointed straight up) the arms extend overhead. A forceful extension of the hips and legs drives the swimmer off the wall. The head is held between the arms and the hands are locked together in a streamlined position as the body glides away from the wall. When the swimmer begins to slow (this will only be a short time) a series of dolphin kicks performed while submerged on the back will help to maintain speed (remember, swimming rules require the head to surface within 15m off the wall). Dolphin kicking is only effective if the trunk and extended arms remain streamlined. The hands can be angled slightly (like the rudder on an airplane wing) to direct the swimmer toward the surface. If a swimmer has a poor dolphin kick or poor streamlining technique, then the conventional flutter kick should be used to drive the body to the surface. The first armpull begins a split second before the face breaks the surface; if a dolphin kick has been used a transition is made to flutter kicking. Starting Backstroke events start from water level, this takes away the advantage of an elevated starting position. However, the principles of a good start are the same as in the grab start. The swimmer takes up a position with the feet fixed firmly on the wall, at about hip width. Some swimmers feel more comfortable with one foot slightly higher than the other does; this increases the size of the base of support. Hands may grip the starting block in several different positions, depending upon block design. The most common hand positions are directly in front of the body (grip with palm facing downward) or to the side of the block (palms facing inward). At the command take your mark the swimmer pulls the body forward and slightly upward to raise the COG; toes must remain below the water surface and hips should be at or above the surface. The pre-stretch of muscles in the legs and hip will facilitate the stretch reflex and the release of elastic energy when the start commences. When the starting signal is given the swimmer must try to drive the hips upward and backward while pushing away from the block with the arms. Several simultaneous actions must be completed in a split second. Extension of the hips must initiate the movement, but a forceful swing of the arms (either to the side or straight over the body) will help to project the body s COG over the water in a parabolic pathway. The head tilts back and the back is arched slightly as these movements are made; this increases the body s radius of rotation as the feet leave the wall. The hands meet when the arms reach full extension and the final drive from the knees and ankles completes the movement. The hips should be clear of the surface, legs together and the toes pointed. During the flight phase of the start the Backstroker attempts to shorten the body s radius of rotation by executing a slight pike at the hips or flexing at the knee (i.e. the characteristic flipping of the feet into the air). These actions help the body to angle downward rapidly as the hands enter the water. The body should slide into the water smoothly. If the swimmer s angle of entry is too steep it s possible to level the body by using the hands as a rudder. The upper body must be held in a streamlined position (arms extended, head firmly between the upper arms) during the dolphin kicking phase of the start. As the swimmer approaches the surface (within the 15m limit for underwater swimming allowed by the rules) the kicking changes from dolphin to flutter and the first armpull commences a split second before the face breaks the surface. If the timing is correct the swimmer will have maintained momentum and should continue into rhythmic stroking at race pace. BREASTSTROKE Breaststroke and Butterfly share many aspects of technique. In fact, the evolution of Butterfly can trace its origin to Breaststroke. In recent years Breaststroke technique, through the application of the
wave breaststroke, has been influenced greatly by the Butterfly. Both strokes rely on symmetric movements of the arms and legs in the application of propulsive power. They also rely on alternating surges of propulsive power from the arms and legs. Large bursts of propulsive force (unlike Freestyle and Backstroke where the force is more continuous) must be timed exactly so that forward momentum is conserved. Although technique is critical in every swimming style, perhaps Breaststroke and Butterfly swimming best illustrate how performance can be improved through greater stroke efficiency. Because Breaststroke is the only competition stroke where the arm recovery is performed underwater, it creates the greatest amount of frontal resistance (i.e. water must be displaced to return the arms to the start of a stroke). Resistance is also created by the width of the kick and the inability of the trunk to rotate (competition rules require the body to remain in a prone position). However, the development of the wave technique associated with undulating movement and streamlining of the trunk has allowed the Breaststroke swimmer to achieve more efficient propulsive force by reducing resistance. Greater balance exists in the contribution of arm and leg propulsion than in any other stroke. Some swimmers may still rely on an exceptional kick or exceptional armstroke for peak propulsive force, as evidenced in the stroke variations usually seen among men (power from the arms) and women (power from the legs), but it s the application of precise timing and coordination that produces the best overall result. Streamlining There are three key phases of the stroke where streamlining of all, or part, of the body is critical. First, at the beginning of each stroke cycle the body will be completely streamlined with the head submerged. Arms are extended, hands together, and face pointing down; hips are at (or just below) the surface with the legs fully extended and toes pointed. The second phase of streamlining occurs as the insweep of the arms is completed. At this time the knees have bent slightly and the heels of the feet move toward the buttocks (just under the surface of the water). The shape of the body at this point in the stroke allows water to travel more smoothly backward without being deflected sharply at the thighs. Streamlining the legs in this way helps to maximise the forward propulsion of the armstroke (i.e. by reducing the negative influence of both frontal resistance and surface drag). The third phase of streamlining occurs as the legs drive backward and rotate inward (i.e. the propulsive part of the kick). Streamlining is achieved because the head is being lowered between the extending arms and the trunk is angling forward and slightly downward. Because the trunk is moving along this angle the hips will tend to lift as the feet come together at the finish of the kick. This third phase of streamlining is critical to establishing the wave pattern in the body s movement because it allows the body s COB to change relative to the body s COG (i.e. they move closer together). The leg movement is correctly referred to as a whip kick, which involves simultaneous extension of the hip and knee and inward rotation of the ankles. From a streamlined body position at the start of a stroke cycle the recovery of the kick begins with a subtle bend of knees as the arms reach the widest point of the armstroke (i.e. the transition from out/downsweep to insweep). As the arms sweep inward the body position begins to change; the hips are now at their lowest point as the trunk rises out of the water. This body position presents an acceptable trade-off (i.e. frontal resistance increases, but so does propulsive force); it also allows a rapid increase in the flexion of hip and knee joints as the heels draw closer to the buttocks and the ankles rotate so that the feet point outward. The ankles are dorsi-flexed (i.e. ankle at a right angle position) as well as outwardly rotated to start the propulsive movement. For a split second at the completion of the leg recovery the body position is poorly streamlined; however, this position changes rapidly to allow extension at the hip which creates a powerful thrust during the propulsive phase of the kick. As extension of hip and knee joints begins the arms are extend forward and the head begins to lower (some breaststrokers appear to dive forward). This positions the trunk, arms, and head (the third streamlined position previously noted) to allow the power of the kick to drive the body forward and the hips move toward the surface. The hip movement results from the combination of actions: (1) lowering the head position to streamline the upper body, (2) reducing the flexion in the lower lumbar region of the spine (i.e. a change from a slight concave curve of the lower back to a slightly convex) as the upper body dives forward and, (3) the inward rotation of the feet during the forceful extension of the legs. The leg extension is an accelerating movement combined with inward rotation of the ankles so that the soles of the feet angle inward at the finish of the kick. Armstroke Pattern Propulsion is created from both an outsweep/downsweep and insweep/upsweep of the hands/arms. From a streamlined position the hands move outward, palms angled out and downward. If the starting position of the arms places the hands in a relatively deep catch position (this may be characteristic of swimmers who dive forward/down during the arm recovery), the first movement of the hands may be a slight upward/ outward sweep. As the hands continue to move outward the elbows begin to flex so that the forearm/hand sweeps downward. At the widest point of the outsweep, the arm position in
Breaststroke resembles the early position achieved during the butterfly armstroke. During each sweeping movement hand velocity will accelerate. Due to the positioning of the forearm both lift and drag propulsion are created; a high elbow position is essential. If the elbows slip back past a position even with the sternum, efficiency will be reduced. Because the hands must reverse their direction to continue the application of propulsive force, a slight dead spot exists as a transition is made from outsweep to insweep. The hands pitch inward and are angled appropriately to maximise lift force during the insweep/upsweep. Forceful flexion at the elbow and adduction of the shoulders directs the hands on their inward/upward sweeping movement. As the hands come together the elbows are under the outer edges of the trunk. The hands have travelled on a curved pathway from their deepest point (at the completion of the outsweep) to a point close to, or at the surface, directly below the chin or neck (at the completion of the insweep). Some swimmers try to move the hands forward slightly during the insweep/upsweep in an attempt to round off the armstroke and begin the recovery. While this may have some advantage in producing a faster recovery movement of the arms, it reduces the potential propulsive force application of the insweep. During all propulsive sweeping actions the hands are angled so that pressure is felt on the palm surface. Breaststrokers producing a powerful upward component during the insweep/up sweep will finish the stroke with the hands breaking the surface. This technique is more frequently seen among male breaststrokers (i.e. due to the strength in muscles of the chest and shoulders) and does not present any problem because the hands may recover at/above the surface (note: current rules require that the elbow remains underwater during the arm recovery). The recovery phase of the armstroke (forward extension) is combined with the lowering of the head position. The hands should remain together as the arms are pushed forward with the palms facing downward (they may be angled slightly). The arms extend straight forward just below the surface. Breaststrokers using more of a wave technique may angle the forward extension of the arms slightly downward. Breathing Positioning the head so that a breath can be taken during each stroke cycle is an integral part of the timing of each stroke. The strong upward forces created during the insweep/upsweep of the arms allows the trunk to lift. A slight forward extension of the neck begins as the outsweep of the arms is nearly complete. The face actually breaks the surface of the water during the insweep and a breath is taken before the head is lowered again. Because Breaststrokers keep their shoulders parallel to the surface throughout the stroke, a large wave forms in front of the head/shoulders. When the face comes forward for a breath the chin must clear this wave. Some Breaststrokers prefer to keep the face angled slightly forward/down, while others position the face directly forward when breathing. The key aspect of body position as the breath is taken is that the hips should remain just below the surface; if the hips drop too low streamlining will be lost (i.e. increased frontal resistance). A high shoulder position during the breath is not a problem if an ideal hip/leg position is maintained. Timing Timing in the Breaststroke is critical to optimal propulsion because any unnecessary overlap in the application of power impulses will decrease the potential net result. In addition, errors in timing may result in greater resistance forces. For example, recovery of the legs too early in the stroke cycle will disrupt body position (thus decreasing the net propulsion from the armstroke) and cause the propulsive phase of the kick to overlap too much with the arms (thus decreasing the net affect of the kick). The coach will be able to observe when obvious timing errors are made because the stroke will look jerky. Competitive Breaststroke has changed in recent years because the timing of stroke components has become more precise. Races of 50m or 100m will require a faster stroke rate than the 200m distance. This means that almost no pause is taken at the end of individual stroke components; such as, at the end of the insweep or recovery movements of the arms. Although there appears to be a slight pause of the legs at the end of the propulsive phase of the kick; when a sprint tempo is used the leg recovery will begin almost immediately. Breaststrokers using a fast-rate wave action may appear (from a surface view) as though the legs are dolphin-kicking at the end of the leg action. However, this is not the case as a dolphin kick involves a downward movement of the feet with the knees bent, and this is not permitted within the Breaststroke rules. What actually happens is that the leg recovery begins immediately following the completion of the propulsive phase of the kick. This recovery starts with a bending of the knees, but the feet do not move downward. It must be remembered that at the finish of the kick the feet are actually lifting because: (i) the head and trunk are moving forward and slightly down, and (ii) the feet are rotating inward, which brings the soles of the feet toward the surface. Turns The competition rules for Breaststroke allow the swimmer to stay submerged for one complete stroke. [Note: current FINA rule, one arm stroke completely back to the legs and one leg kick while
wholly submerged. The head must break the surface of the water before the hands turn inward at the widest part of the next arm stroke]. The swimmer should take advantage of the fact that surface turbulence is eliminated at a time when the forward velocity is increased due to the push-off from the wall. The turn actually begins as the swimmer approaches the wall, it s important to adjust the timing of the last few strokes so that a touch is made with the arms extended. The rules require a two-hand touch simultaneously with the shoulders in the horizontal plane; hands may be at, above, or below the water level. It s not required that both hands are level when they touch the wall, only that the shoulders are level with the surface. One hand is immediately pulled away from the wall (this will be called the leading arm ) by bringing the elbow past the trunk; this starts to rotate the trunk into a side facing position. At the same time the knees and hips flex (shortening the radius of rotation) as the feet swing through a 180-degree arc and contact with the wall. The leading arm continues to assist in the rotation of the body; as the hand passes the trunk the palm is turned up. Upward pressure of the leading hand begins to rotate the head and shoulders downward. The trailing arm (i.e. the hand remaining longest in contact with the wall) first acts as a pivot point and then acts as a means of completing the rotation of the body. The trailing hand releases as the feet strike the wall and proceeds to move over the water with the elbow bent (much like a freestyle arm recovery). The push-off is made under the surface by a powerful extension of the hips and knees as the arms and trunk extend. The head is positioned between the extended arms and the body is completely streamlined. During the underwater glide the breaststroker is moving parallel to the surface in a streamlined position. As the swimmer begins to slow (this usually takes about 2 seconds) a long armstroke is taken. The hands finish past the hips, next to the sides of the legs, with palms facing up. This long-pull is similar to a shallow butterfly stroke. With the hands at the hips the body is not in a very streamlined position (i.e. the rounded surface of the head and shoulders create frontal resistance); therefore, only a short glide is held. The hands begin to move forward close to the body, elbows are kept close to the trunk to minimise resistance (i.e. the arms stay close to the cylinder of the body). As the hands move past the chin the legs move into a recovery position quickly; streamlining is reduced, but only for a split second. The arms extend as the legs drive back in a propulsive kick. The body should be angling toward the surface. The underwater stroke is completed as the hands begin their outsweep and the head lifts so as to break the surface of the water. Breaststrokers will use a grab start and may choose to alter the angle of entry slightly so that the underwater glide position is a little deeper than in freestyle. The entry angle is influenced by the amount of forward rotation of the body during the flight phase of the start. By bending slightly more at the hip or knee (i.e. shortening the radius of rotation) the breaststroker will enter at a slightly steeper angle. The underwater sequence of movements is identical to the turn (from the point where the feet leave the wall). The swimmer may be able to hold a glide in the streamlined position slightly longer (perhaps 3-4 seconds) before the long-pull. The hands should be used as rudders to assist the upward angle of the body during the kick. The head must break the surface before the hands turn inward during the first normal stroke. Because the swimmer has been underwater for perhaps 5-6 seconds at the start, inexperienced swimmers may try to take the first breath slightly out of sequence with the normal timing of the stroke. Although the top of the head breaks the surface during the outsweep, the face should not break the surface until the insweep is well under way. BIOMECHANICAL ANALYSIS OF SWIMMING STARTS By Bruce R Mason Ph.D. Inefficiencies in the start may be readily detected through competition analyses. From the present competition analyses output, the only factor that can be identified is the quality of the overall start of a particular swimmer. This is identified by the time it takes (time in seconds) to cover the first 15 metres of the race compared to the starting time of their competitors who are at about the same level of swimming ability. If a problem is detected in the start, the next stage in biomechanical assistance for the coach is technique analysis in the training environment. The critical measurement overall for the start is still the time for the swimmer s head to pass the 15 metre mark. This enables the overall start performance (from the comprehensive biomechanical analysis) to be compared with the swimmer s performance in competition (competition analysis output) where the swimmer produces a 100% effort. However, as the start is broken up into a number of phases by the biomechanical analysis system it is possible to identify poor and good performance aspects of the overall start. This enables the coach to zero in on those aspects of the start causing the poor starting performance. This document provides the phases into which the total start is broken for the different swimming strokes. Each phase will be listed together with the determinants that mark the commencement and termination of the phase. A measure of distance from the starting wall (distance of head from wall) and the time to reach each determination point is provided. Average velocity for each phase as well as
average velocity from the commencement through to the termination of the phase are also provided. Other relevant factors are also computed and are indicated by the breakup under each stroke heading. The method by which this analysis is performed is based primarily on video footage of the swimmer s start performance. A single above water stationary camera is used to capture footage of the initial two starting phases. Video footage used to obtain information on the later phases of the start is taken by two moving cameras (one above and other below water level) which travel along side the swimmer. The images from the two cameras are mixed to produce a single combined above and below water level image of the swimmer s performance. The distance and timing information is obtained through computer analysis of this video footage. Time from the gun is displayed on the image as well as distance markers, which can be seen under the swimmer. Together with the sheet, which provides output from the biomechanical analysis, the coach has the video footage, which may be used to confirm and further diagnose the problems disclosed by the biomechanical analysis. Transducers built into the starting block also provide detailed information about the first phase of the start. Time on the block is assessed by way of an instrumented starting block which produces a detailed graphical output and a printed sheet detailing vertical velocity at takeoff, horizontal velocity at takeoff, time on the blocks (gun until feet leave the blocks), dive angle at takeoff (angle of movement of the centre of gravity of the swimmer), and average acceleration on the block (takes into account both the time on the block and the horizontal velocity upon leaving the block). Analysis of the airborne phase provides stick figures of the swimmer in the starting position, at maximum knee flexion, upon leaving the blocks and contact with the water. Another printout provides stick figures of the swimmer after entry. Trunk angles are provided on these printouts. The distance from the wall at hand entry as well as time of entry are also provided. FREESTYLE Head at 7.5 metres out Inward Swim Rotation Leg Push Off Glide Kicking Break Surface Outward Swim Initiate Turn (last stroke, head tucks under) Feet Contact Wall Feet Leave Wall Initiate First Down kick Start Hand Pull Prior to Break Start Same Hand Pull After Break Number, SL & SF of strokes taken Maximum Knee Flexion Trunk Angle, Time and Distance of Break Number, SL & SF of stokes taken BUTTERFLY Head at 7.5 metres out Inward Swim Number, SL & SF of strokes taken (indicate breath) Hands Contact Wall Rotation Feet Contact Wall Leg Push Off Maximum Knee Flexion Feet Leave Wall Glide Initiate First Down kick Kicking Break Surface Start Hand Pull Prior to Break Trunk Angle, Time and Distance of Break
Outward Swim Start Hand Pull After Break Number, SL & SF of stokes taken (indicate breath) Position of the body is determined by the position of the head s centre. Breaking the surface is determined when the head breaks the surface. Length of entry is the distance on the water surface from hand entry to foot entry. SL = Stroke Length (distance the head moves in one complete stroke). SF = Stroke Frequency (number of such strokes in a period of time). Stroke from Right/Left hand entry to the entry of that same hand. BREASTSTROKE Head at 7.5 metres out Inward Swim Rotation Leg Push Off First Glide Long Pull Second Glide Arm Recovery First Kick Break Surface Outward Swim Hands Contact Wall Feet Contact Wall Feet Leave Wall Start Keyhole Pull with hands End Keyhole Pull with hands Start Arm Recovery Start Kick Start Arm Pull prior to Break Start Next Arm Pull after Break Number, SL & SF of strokes taken Maximum Knee Flexion Trunk angle, Time and Distance of Break Number, SL & SF of Strokes taken BACKSTROKE Head at 7.5 metres out Inward Swim Rotation Leg Push Off Glide Kicking Break Surface Initiate Turn (last stroke, mid recovery, crossover) Feet Contact Wall Feet Leave Wall Initiate First Down kick Start Hand Pull Prior to Break Start Same Hand Pull After Break Number, SL & SF of strokes taken Maximum Knee Flexion Trunk Angle, Time and Distance of Break Outward Swim Number, SL & SF of stokes taken Position of the body is determined by the position of the head s centre. Breaking the surface is determined when the head breaks the surface. Length of entry is the distance on the water surface from hand entry to foot entry. SL = Stroke Length (distance the head moves in one complete stroke). SF = Stroke Frequency (number of such strokes in a period of time).
Stroke from Right/Left hand entry to the entry of that same hand. Biomechanical Analysis of Swimming Turns Inefficiencies in turns may be readily detected through competition analyses. From the present competition analyses output, the only factor that is able to be identified is the quality of the overall turning performance of a particular swimmer through particular turns or over all turns in general. This is identified by the time it takes to cover the distance from 7.5 metres out from the wall through the turn until 7.5 metres out from the wall again compared to the turning time of their competitors who are at about the same level of swimming ability. If a problem is detected in the turn, the next stage in biomechanical assistance for the coach is technique analysis in the training environment. The critical measurement overall for the turn is still the time for the swimmer s head to pass the mark at 7.5 metres out from the wall until it again passes this mark after completing the turn. This enables the overall turn performance (from the comprehensive biomechanical analysis) to be compared with the swimmer s performance in competition (competition analysis output) where the swimmer produces a 100% effort. However, as the turn is broken up into a number of phases by the biomechanical analysis system it is possible to identify poor and good performance aspects of the overall turn. This enables the coach to zero in on those aspects of the turn causing the poor turning performances. This document provides the phases into which the total turn is broken for the different swimming strokes. Each phase will be listed together with the determinants that mark the commencement and termination of the phases. A measure of distance from the turning wall (distance of head from wall) and of the time to reach each determination point is provided (negative times indicate prior to touching wall). Average velocity for each phase as well as average velocity from the commencement of the turn through to the termination of the phase being examined are also provided. Other relevant factors are also computed and are indicated in the breakup under each stroke heading. The method by which this analysis is performed is based primarily on video footage of the swimmer s turning performance. Video footage is used to obtain information on the various phases of the turn and the footage is taken by two moving cameras (one above & other below water level) which travel along side the swimmer. The images from the two cameras are mixed to produce a single combined above and below water level image of the swimmer s performance. The distance and timing information is obtained through computer analysis of this video footage. Time is displayed on the image and the distance markers can be seen under the swimmer. Together with the output from the biomechanical analysis, the coach has the video footage, which may be used to confirm, and further diagnose the problems disclosed by the biomechanical analysis. Transducers built into the turning wall also provide detailed information about the wall contact phase of the turn. Time on the wall is assessed by way of an instrumented turning wait which produces a detailed graphical output and a printed sheet detailing change in horizontal velocity of the swimmer as a consequence of wall contact, contact time on the wall (touch until toe off), push off angle at toe off in the vertical plane (angle of movement of the centre of gravity of the swimmer), and average acceleration on the wall (takes into account both the time on the wall and the change in horizontal velocity upon leaving the wall). Analysis of the turn also provides stick figures of the swimmer in various determination points throughout the turn, which vary according to the swimming stroke. Trunk angles are provided on this printout. The tightness of the tuck can be identified by the stick figure. BREASTSTROKE Gun Time on Blocks Feet leave Blocks Flight Hand contact with water Entry Length of Entry Foot entry in water First Glide Start Keyhole Pull with Hands Second Glide Start Arm Recovery Arm Recovery Start Kick First Kick Start Arm Pull Break Surface Time and Distance of Break Complete Arm Stroke Cycle (start next) Swim Number, SL & SF of strokes taken
Head to 15 metres BACKSTROKE Gun Initiation Hand Release Push-off Feet Leave Wall Flight Hand Entry Entry Distance foot/hand Entry Foot Entry Glide Initiate First Down Kick Kicking Start Hand Pull prior to Breaking Surface Swim Number, SL & SF of stokes taken Position of the body is determined by the position of the head s centre. Breaking the surface is determined when the head breaks the surface. SL = Stroke Length (distance the head moves in one complete stroke). SF = Stroke Frequency (number of such strokes in a period of time). Stroke from Right/Left hand entry to the entry of that same hand. Kick Strokes from Right/Left foot downward action until repeat of the action with the same foot. FREESTYLE Gun Time on Blocks Feet Leave Blocks Flight Hand contact with water Entry Length of Entry Foot entry in water Glide Start first Kick Kicking Start Hand Pull Prior to Breaking Surface Break Surface Time and Distance of Break Start Same Hand Pull After Breaking Surface Swim Number, SL & SF of stokes taken BUTTERFLY Gun Time on Blocks Feet Leave Blocks Flight Hand contact with water Entry Length of Entry Foot entry in water Glide Start first Kick Kicking Start Hand Pull Prior to Breaking Surface Break Surface Time and Distance of Break Start Hand Pull After Breaking Surface Swim Number, SL & SF of stokes taken
Position of the body is determined by the position of the head s centre. Breaking the surface is determined when the head breaks the surface. SL = Stroke Length (distance the head moves in one complete stroke). SF = Stroke Frequency (number of such strokes in a period of time). Stroke from Right/Left hand entry to the entry of that same hand. Kick Strokes from Right/Left foot downward action until repeat of the action with the same foot. BIOMECHANICAL ANALYSIS OF ACTIVE DRAG By Bruce R. Mason Ph.D. A swimmer s maximum speed in free swimming is determined primarily by two major factors. The first of these is the propulsive force exerted by the swimmer on the surrounding water. This is determined by the fitness of the swimmer and the stroke technique (or mechanics) the swimmer utilises. The other major factor is the active drag force exerted by the surrounding water on the swimmer. The maximal swim velocity of the swimmer is attained when the maximum propulsive force of the swimmer reaches an equilibrium with the drag force. Although drag is a factor, which affects all sports involving speed, it probably plays a more predominant role in swimming than in other competitive speech sports. The reason for this is that drag is a function of velocity squared and density of the fluid and as water is much denser than air, then drag is a more significant factor to performance than say in running competition. To enable a swimmer to swim at a higher velocity he or she must either increase propulsive force or reduce the drag force or do both. Swim coaches quite often concentrate upon getting the swimmer to produce greater propulsive force when it would be more cost effective to decrease the drag force. Essentially there are three major sources of active drag in swimming. These are Form Drag, Wave Drag and Surface drag. Form drag occurs primarily because of the shape of the swimmer (primarily frontal surface area) pushing through a wall of water in front of them. Wave drag occurs essentially because the swimmer performs at the interface between two fluids, air and water. As a consequence when the swimmer moves on the surface he or she produce waves. The production of the waves is caused by exerting force against the water which otherwise may have been available for propulsion. Surface drag is a consequence of the surface area of the swimmer in contact with the surrounding water and the smoothness of that surface. In order of magnitude, probably form drag has the greatest influence on performance followed by wave drag and then surface drag. Form drag may be reduced by employing good stroke mechanics and having good streamlining. Wave drag may be reduced by performing sections of the stroke completely under the water surface rather than on the surface. However, this is has to be looked at carefully as obvious features of the stroke, such as arm recovery, should be performed completely out of the water. Reducing surface drag involves such things as shaving down, wearing swim caps as well as using friction reduced swim wear. As drag reduction is just as important to competitive swimming as force production, scientists have tried to develop methods by which active drag can be readily measured. The earliest methods involved measuring passive drag as an indicator of active drag. This is achieved by measuring the force required to tow a swimmer through the water at a competitive speed while the swimmer maintained a static streamline position. Measurement of passive drag has been found to not readily reflect measurement of active drag. Practical measurements of passive drag have arrived at higher values than those of active drag. The reason proposed to explain this involves the intrastroke velocity fluctuations that occur during swimming. Measurement of passive drag is reflected more in the individual s anthropometry and hence the streamline position that the swimmer can attain while being towed. Active drag while still dependent on anthropometry is also dependent on swimming technique. The first successful method of measuring active drag was introduced by biomechanists from the Netherlands. The system used was called the MAD system. Here the swimmers pulled themselves along a bar using a freestyle swim like action with their arms and hands. The submerged bar which extended the length of the pool had handles upon which the swimmer pushed. The bar had force transducers at either end at the pool wall to measure the force exerted by the swimmer on the bar. The force measured here was equivalent to the force, which was required to overcome water resistance. The force was therefore a measure of active drag. The question, which arose with regard to the active drag measurement from the MAD system, was its discriminating ability to assess the different drag forces associated with slightly different swimming techniques. The MAD system would need to be effective here to be used to assist the coach of elite swimmers. Another problem with the MAD system was its inability to be used with other strokes beside front crawl. Kolmogorov and Duplishcheva from the USSR used another method of measuring active drag in 1990. Here swimmers swam at maximal speed with and without towing a passive resistance. The difference in speed was used to compute active drag. The system used at the AIS is an extension of this system. It is assumed that the swimmer who performs a maximum effort using his or her normal stroke in three conditions (unaided, with a resisting force, and with an assisting force) would provide an equal power output in each condition. A different velocity would however be attained in each condition. A
piece of equipment developed at the AIS (flux vector drive dynamometer) is capable of increasing or decreasing the swimmer s velocity by a set amount by resisting and then assisting the swimmer. While doing this, the system monitors both the resistive and assistive force applied to the swimmer together with the actual resultant velocity achieved by the swimmer. The system is also capable of measuring the swimmer s velocity in the unaided condition. The velocity achieved in each of the resisted and assisted conditions should not exceed + or - 10% of the unaided condition. P1 = Maximum Power output of swimmer in unaided condition. P2 = Maximum Power output of swimmer in resisted condition. P3 = Maximum Power output of swimmer in assisted condition. NB P1 = P2 = P3 As the swimmer was performing to a maximum in the unaided condition, the force applied by the swimmer would equal the drag force. Given this Fri = the force applied by the swimmer in unaided condition drag force and v = attained velocity of swimmer then P1= Fri * v I where Frx is the active drag force at velocity vx P2r-Fi-2*v2 and P1=Fi-2*v2 P3a = Fr3 * v3 and P1= Fi-3 * v3 The different velocities vx are due to resistance force v2 and assisted force v3. Another derivation of the active drag force Frx is defined below. Where C is a constant, r is the density of water, S is surface area in metres**2 of the swimmer and Fb is the increased or reduced resistance. Fi-l = 1/2 * C * 1-* S * vl**2 Fi-2 = 1/2 * C * r * S * v2**2 + Fb2 Resisted condition Fr3 = 1/2 * C * i- * S * v3**2 - Fb3 Assisted condition Assuming equal power output in all conditions P1-P2 Pi-l*vl=Fr2*v2 then substitution from Fri and Fr2 above 1/2 * C * i- * S * v I **3 = 1/2 * C * i-* S * v2**3 + Fb2 * v2 therefore C = (Fb2 * v2) /(1/2 * r * S * (vl**3 - v2**3)) Similarly P1-P3 Fi-l*vl~Fi~3 *v3 then substitution of Fri and Fr3 above 1/2 * C * i- * S * v I **3 = 1/2 * C * i- * S * v3**3 - Fb3 * v3 therefore C=(Fb3 * v3)/(1/2 * r* S * (v3**3 -vl**3)) Substituting for C in Fl = 1/2 * C * r * S * vl**2 Fri i- = (Fb2 -v2 * vl**2) / (vl**3 - v2**3) obtained through resistance and Fri a = (Fb3 * v3 * v I **2) / (v3**3 - v I **3) obtained through assistance Active Drag in newtons at velocity vl for the swimmer = (Frir + Fria) / 2 where v I represents the maximum velocity for the swimmer for the stroke concerned. Measurements in all three conditions should be over the same number of complete strokes in each. We use Six Strokes at the AIS.