The Biomechanics of

An examination oi recent recommendations relating t< ning stroke mech

BY JAN PRINSAQUATIC RESEARCH LABORATORY, UNIVERSITY OF HAWAII

Swimming analysis has been, for the most part a qualitative endeavor. We coach and teach mostly by infer-ence, that is, we experiment, and if the result is a faster swimming time, we assume that our suggestions h avemerit. Although this may be a reasonable assumption, we cannot be certain.

Recently, suggestions for improving stroke mechanics have addressed a number of areas of interest: (1) Armrecovery in the Freestyle: "Straight arm " vs. the traditional "High Elbow \ (2) Body Roll: The question of howmuch we should be advocating conscious rolling of the torso; and (3) Intentional re-positioning of the chest andshoulders, referred to as "Pressing down on the T".

As can be expected, some of these recommendations require drastic alterations in the way stroke mechanics aretaught and, consequently, warrant closer examination.

The basis for effectivemotionBefore we tackle any one of thesequestions, let us be clear as to whatbiomechanics can do for swimmingstroke analysis. Biomechanics is thestudy of motion. It incorporates thedisciplines of Anatomy and Phys-ics to examine the movements ofbiological organisms. Since we havea specific goal in swimming, whichis more efficient propulsion, we hadbest focus on how our musculoskele-tal system carries out the wide rangeof movements required for movingthrough the water.

By way of introduction, it may beuseful to remind ourselves of a well-established axiom which holds truefor both biomechanics and physiol-ogy: "We train movements, notmuscles." We have a limited numberof skeletal muscles, 640 by approxi-mation, but our capacity to producemotion is vast. Consequently, toproduce a specific movement, eitherrudimentary or subtle, requires aseries of coordinated signals fromthe brain to the muscles, so that theselected action, in all its complexities,can take place around the anatomicaljoints in question.

When coordination of muscle activ-ity is essential, it is "timing", orwhat has been termed a "patternedsequence" of muscle activation,that determines when, and whichmuscles come into play. Attemptsto apply muscle tension either byre-positioning portions of the body,as in consciously rolling the hips, orby holding a specific set of joints ina predetermined place, as in extend-ing the chest forwards, will affect the"timing" of muscle activation.

With regards to "joint positioning,"muscles do best when the bonesthat connect the joints in questionare held at optimum positions withrespect to each other. This "spatialorientation" is vital because musclesdo best when they pull in specificdirections, and these directions aredetermined by the relative positionsof the bones to which the muscles areattached.

The "Straight-Arm"Recovery in theFreestyleAlthough freestyle swimmers havealways shown variations in thedegree to which they allow theirelbows to flex during the arm recov-ery, the prevailing recommendationhas been to hold the arms in "asrelaxed a fashion as possible" duringthe above-water phase of the stroke.Consequently, if the arm is held withminimal tension we see the typicalappearance of the "high elbow recov-ery." In addition, the relaxed wrist isa subtle but important indicator thatthe entire arm is moving through themovement with minimal effort.

The primary rationale for the "highelbow" recovery has been the factthat the motion does not directlycontribute to the propulsion of thebody, and therefore should be car-ried out with the least possible effort.However, In spite of the obviousbiomechanical advantage of the"high elbow," there are now a selectnumber of coaches, primarily thoseworking with elite swimmers, whoare experimenting with, and conse-quently recommending, a "straight-arm" freestyle arm recovery, i.e., onethat is made with a conscious exten-sion of the elbows.

With the increased adoption of thistype of arm recovery, it will be use-ful to discuss the trade-off betweenits advantages and the cost in extramuscular work.

Possible advantages of astraight-arm recovery.There is a good reason that themajority of "straight-arm recovery"freestylers are sprinters. The motion,when executed effectively, appearsto assist in a faster stroke rate. Whythis is so is interesting for the follow-ing reasons:• Contrary to the notion that it is

easier and quicker to move thearms through the air when theelbows are held straight, theperceived increase in stroke rate(rate of turnover), is most likely

due to the reduction in time be-tween the time of "hand entry"and the beginning of the "catch."This means that in all likelihood,the apparent quickness of thistype of recovery is due to theelimination of the "arm exten-sion" phase of the underwaterpull.

• This abbreviated phase of armextension also results in a reduc-tion in the amount of "bodyroll."Although we don't know forcertain how much this affects thepotential for force production,we do know that excessive bodyroll is counterproductive.

Biomechanical Implicationsof the "straight-arm"recovery.We can agree that a faster turnoveron its own cannot guarantee tasterswimming times. As to the biome-chanical implications associated withthe "straight-arm" recovery, thereare three areas of concern.

1. The velocity of the hand at thepoint of entry:The biomechanics related to thisaspect deals with "angular motion,"in this case, the motion of the armaround the shoulder joint. Figuresla and lb illustrate the paths of the"tips of the fingers" with the tworecoveries. The video trails, super-imposed when analyzed by motionanalysis software, show clearly thedifference between the trajectoriesand provicie the following informa-tion:• The hand travels further when

the arm is held straighter.This is because when an objectis rotated about an axis, thelonger the object, the further thedistance the extremity travelsthrough the arc of the motion.

• The hand travels at a higherangular velocity that the rest ofthe arm.This point is particularly im-portant during the hand entryphase. The higher velocityincreases the risk of the hand

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entering too quickly and the"catch" being made too rapidly,without adequate purchase onthe water.

This last factor has been identifiedby a number of advocates of thestraight-arm recovery. Coach PaulBergen, one of the key proponentsof the "straight-arm" recovery, hasvery perceptively stressed the needfor emphasizing a "soft entry," It isclear that in order to take advantageof the faster turnover, an effectivecatch is essential before beginningthe rest of the underwater pull phase.

2, Lateral trunk motion.This factor is one that needs littleintroduction. We have been aware,for as long as Freestyle has beenswum, that there is the increasedlikelihood of lateral shifting of thetorso and hips, especially if the arn:isare held relatively straight. It is easyto observe the so-called "wigglingfrom side-to-side," when the armsare recovered low over the water.The closer to the surface the arms areswung around, particularly whenheld straight, the more likely thetrunk will oscillate from side to side.

We are also aware that,in the absence of a stablebase of support, forexample when we standfirmly on the ground,the only way we canneutralize this lateraldrift is by either slow-ing the rate of recovery,or ensuring the kick issufficiently effective toprovide longitudinalstability.

3, Moment of InertiaThe final, and mostimportant point, is notas obvious. Althoughthe term sounds techni-cal, "moment of inertia"refers to an object'sresistance to changeswhen objects of differentlengths travel around acurved path. What thismeans is that it is notjust the mass of the body

that is important, but also the dis-tance that mass is distributed fromthe axis of rotation.

Because of the waythe mass of the arm isdistributed, an out-stretched arm has alarger moment of inertiawhen compared toan arm carried with a"high elbow." Regard-less of the fact that thetotal mass of the armhas stayed the same,more muscular effort isneeded to recover thearm when it is held inan extended position.

To demonstrate thisconcept, we present afrontal view of a freesty-ler, using both the "highelbow" and a "straight-arm" recovery. Aftercapturing the selectedframes, a grid wassuperimposed on thephotographs {Figures2 and 3). What this helps us do isexamine the approximate difference

in the "moment of inertia" of the armwhen viewed from head on.

We see that at the instant the arm isin line with the shoulders, there isapproximately a 20% difference inthe distance the hand is extended outlaterally.

What makes this an issue? Asmentioned above, because of theincreased "moment of inertia," re-covering with a straight arm requiresmore muscular work to begin therotation, to keep it rotating, andfinally, considerably more work toslow it down.

The vertical angle of the armrecoveryThe question arises as to whetherthere is a difference in effort whenwe vary the angle of elevation of a"straight-arm" recovery, i.e., doesit make a difference if we have a"high overhead" trajectory, or a "lowrecovery, a path more horizontallyover the water"?

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Technically, the moment of inertiais the same. We still have the massof the arm distributed further awayfrom the shoulder than if the elbowis bent. However, the higher the arcof the recovery, the less the sus-tained effort needed by the shouldermuscles which are responsible forcarrying the arm up and aroundthe water. We know this is the casebecause it feels easier to lift our arms"more vertically up and around"than when swinging them aroundparallel to the surface. The mostlikely reason for this difference isbecause of the effects of gravity.

In the more vertically orientedrecovery, at the peak of its path, andslightly before and after, the musclesget a "break" in the effort neededto hold the arm up. This is becausewhen it is passing through the verti-cal phase of the trajectory the weightof the arm is primarily supported bythe shoulder rather than by muscularcontraction. This is in contrast towhat happens when the recovery isflatter, lower over the surface of thewater. In this case, during the entiretime of recovery, the weight of thearm must be counteracted by the in-ternal torque developed by the activemuscles, making it more fatiguing.

Reminder.Straight-arm recoveries may feel eas-ier to perform because there is lesskinesthetic skill required to completethe motion. However, this is primar-ily because the timing of when torelax the arm and allow the elbow tonaturally flex, is not a factor. This isalso the reason we teach Freestyle tobeginners by starting with a straightarm recovery.

However, once a degree of swim-ming skill has been acquired, itappears that the high elbow recoveryis a natural progression of strokedevelopment. We can infer that"high elbows" evolved, in spite ofthe increased level of skill neededto perfect the motion, because of thedifference in the amount of muscularwork required between the two typesof recovery.

In conclusion, it should be stressedthat due to the contributing fac-tors that could negatively affectthe "catch" and body orientation,the "straight arm" recovery shouldbe taught to swimmers only afterthey have reached a certain level ofkinesthetic awareness. Simply put,this maneuver should be taught toswimmers who have been swimmingcompetitively for a number of years,and not to relative newcomers.

Postscript:Final preparation of this manuscripttook place during the Beijing Olym-pics. Thanks to the view providedby the cameras moving laterallyon tracks, keeping abreast with theswimmers, it was possible to observethe differences in arm recoveries thattook place in the Freestyle events.

Although a more detailed examina-tion should produce more illustra-tive data, particularly since a "lowstraight-arm recovery" could notbe seen from a lateral view of cam-eras, it is clear that the "straight-armrecovery" was used only by a selectfew swimmers. Furthermore, whenemployed successfully, it was limitedto the shorter events. The dispro-portionate difference between thenumbers of swimmers using thesetwo styles amply demonstrates theintuitive need to reduce the amountof muscular work employed duringthe above-water phase of the stroke.

Conscious, Voluntary"Body Roll"The concept of "body roll" in swim-ming never fails to elicit interest.This is because it is clear that whenswimming Freestyle and Backstroke,the torso rolls around a longitudinalaxis. The recommendations associ-ated with "body roll" range from"lie as flat as you can" to "lead withthe hips." The latter, although wellintentioned, brings up intriguinganatomic contortions if taken liter-ally!

The underlying question is whetherhip action is accomplished by (a.)Conscious, voluntary hip rotation.

performed either immediately beforeor when accompanying the arm ac-tion, or, (b.) Whether the torso andtrunk rotate as a consequence ofwhat the arms accomplish, i.e., thetorso begins and continues to rollduring the hand entry and arm ex-tension and, this is important, ceasesto roll at the end of the extension,as the hand is initiating the "catch"phase ofthe pull.

Biomechanical implications of "con-scious body roll." When we attemptto use our arms for actions such asthrowing and hitting, we start witha firm foot-plant. This is called"ground reaction force" (GRF). Oncea stable base of support has beenestablished, we then try to harnessthe available muscular forces, start-ing from the lower extremities, upthrough the trunk, finally adding themuscles of the shoulders and arms toexecute the movement, This attemptto sequentially add the availablemuscle groups used in the respectivemovements is viewed as utilizing thesegments of the "kinetic chain."

In this scenario, when GRF is avail-able, voluntary hip motion, if timedcorrectly, can improve the outcomeof the movement. The final result,as for example, we see in throwingor hitting, is the ability to generate aforce thaf is much greater than thatwhich could be realized from just themuscles of the shoulders, arms andhands.

The scenario is quite different in thewater where there is no "ground re-action force." In the absence of a firmfooting, the trunk has to provide thestable platform for the muscles thatcontrol both the upper and lowerextremities to generate propulsiveforces.

A commonly used principle inbiomechanics states that "proximalstability is needed for distal mobil-ity." It does not imply that the torsoremains in a state of rigidity. Whatit does mean is that the more stableour trunk, the better we are able togenerate the desired muscular forceat the "far" or distal end when using

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our arms and legs for propulsion.The important point is that in theabsence of GRf, as in swimming, orfor that manner when leap up intothe air as in volleyball, we are relyingon the inertia of the torso to act as thestable base of support to allow us todo things with our arms and legs.

At this point, a reasonable questionto ask is how the flutter kick fits intothis picture? We know the kick pro-vides at least three functions, all ofwhich can provide maximum benefitprovided proper movement mechan-ics are followed.1. Let's dispense with the first fac-

tor, which is the contribution ofthe kick to overall propulsion.Clearly, the additional propul-sion provided by the kick makesa difference over the competitivedistances and therefore the trendto develop and emphasize a "six-beat" kick is well warranted.

2. The second factor deals withthe recognition that the flutterkick is used to maintain bodyposition. The hydrodynamiclift force provided by the flutterkick enables the body to lie closeto the surface, and also providelongitudinal stability.

3. The third factor, itturns out, is the onethat is most affectedby conscious body roll.Conscious hip rota-tion will increase thelateral spread of thefeet during predictablesegments of the strokecycle. The reason forthis "splaying" out ofthe feet is that the feetare responding to theneed to counter the "ro-tational torque" devel-oped by the consciousangular displacementof the trunk. Counter-ing this torque can beperceived as preventingthe body from rollingexcessively by allowingthe feet to spread out(Fig. 3a).

The most damagingaspect of this action is

clearly the increase in frontal resis-tance that accompanies the lateralspreading of the hips.

Figures 3b is the correspondinglateral view at the point of maximumconscious body roll. The orientationof the hips appears to be almost atright angles to the surface, and theposition of the feet demonstratesthe need to stabilize the body withincreased amplitude of the kick.

Current rationaleThe argument can and has beenmade that all it would take to reducethe lateral spread of the legs whenconsciously rolling the hips, is tokick with less amplitude. Certainly,an increased emphasis on the "flut-ter kick" can reduce the sidewaysexcursions of the feet. However, thisargument belies the negative conse-quences of excessive body roll.

For one, not everyone is going togravitate to an increase in kickingcadence, even though, as mentioned,there is a well-founded emphasis forincreasing the cadence of the flut-ter kick over competitive distances.What is questionable is the assump-

tion that kicking rhythmically andconsciously rolling the hips can beaccomplished seamlessly. If the in-tent is to use the kick to increase pro-pulsion, it appears doubly importantto maintain a stable torso to providefor the proximal stability of the lowerextremities.

There are also other factors to consid-er when examining excessive bodyroll. "Conscious" body roll clearlyincreases the overall time spent oneach stroke cycle. When we observeswimmers consciously rolling theirbodies we see the shoulders and hipstranscribing a much larger change inangular motion, which as explainedin the section on arm recovery, willtake longer. Not exactly conduciveto faster swimming!

In conclusion, given the clear biome-chanical implications of this mo-tion, we need to closely examine theconsequences of consciously rollingthe hips and decide whether the rollof the hips should be initiated "con-sciously" or be allowed to naturallyfollow optimum arm extension andlongitudinal body orientation.

For a more detailed examinationof this topic the reader may accessthe manuscript that appeared in theJournal of Swimming Research, andcited at the end of this article.

"Pressing the T"This idea stems from the notion thatin order to improve the position ofthe upper torso when lying prone inthe water, it is necessary to "flatten"the back; and as one description hasit, "lean forwards like someone'spressing on your shoulder blades"!{The exclamation point is the writ-er's).

To illustrate this concept, we areasked to imagine a vertical axis thatcan be drawn along the center of thespine from the region of the neckto the lower trunk, and add to it,the horizontal axis connecting theshoulder joints. This then can bevisualized as being "T shaped." If

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we follow the recommended sugges-tions, this is now the portion of ourshoulders and spine that we are ex-pected to "push forwards," therebyaltering the profile of the chest andupper back with the expectation ofan improved body profile.

Biomechanical Implications.In a discussion titled "Shoulders inMotion" (University of California -Berkeley Wellness Letter - June 2008),the writers describe the shoulderjoint and associated muscles as a"beautiful piece of biological engi-neering ... and as with all beautifulpieces of engineering, much cango wrong." As discussed in at thebeginning of this article, it wouldnot be unreasonable in the context ofswimming, to add that the likelihoodof things "going wrong" can and willbe amplified by altering the naturalspatial arrangement of any joint, inthis case the shoulder.

The anatomic focus of this rec-ommended "pressing" action isthe shoulder girdle (scapula andclavicle), and the shoulder (gle-nohumeral) joints. When dealingwith movements of the arms, themost important point we must keepin mind is that the shoulder girdleand shoulder joint, work in "con-cert," i.e., move together. The term"scapulo-humeral rhythm" has beenused to describe the combined activ-ity of these two sets of bones. Thisis possible because they are linkedby ligaments and other soft tissuestructures.

When we lift our arms out of the wa-ter during the recovery, the scapuladoes two things, it "rotates upwards"and "protracts," i.e., moves awayfrom the spine. During arm exten-sion, performing the underwaterpull, the reverse actions take place,i.e., "downward rotation" and "re-traction."

Therefore, it should be evidentthat isolating scapula motion, suchas suggesting that the swimmer" should feel like someone is pressingon your shoulder blades" is counter-productive insofar that it interferes

with natural motion of the shoulderand shoulder girdle complex.

The ConsequencesA good example of the negativeeffect of altered shoulder girdlepositioning is the ensuing problembaseball pitchers have during the ini-tial backwards or "cocking" phase ofthe arm in preparation for throwing.If we want to perform an effectiveforward throwing action, it is im-perative that the initial movement beaccomplished with minimum tensionfelt in the shoulder. Hunching theshoulders, defined as conscious "pro-traction," will limit the ability to pullthe arm backwards and consequentlyresult in a reduced throwing effort.

The mirror image of this abovescenario can be made in swimming,If one was to consciously push thechest forwards and "retract" theshoulder blades while simultaneous-ly trying to pull the arms tlirough thewater, the motion will be similarlyimpaired. Although the arms willappear to travel through a prescribedpath, the range and timing of the mo-tion will be very much affected andconsequently, result in a reduction inthe application of muscular force.

A more subtle consequence of con-sciously pushing the chest forwardsis the effect it has on the muscles ofthe neck. When the arms are pulleddownwards, as in the underwaterpulling action in swimming, thescapula retracts and rotates down-ward. There are 4 muscles activelyinvolved with this action, one ofwhich, the "levator scapula," is at-tached to the base of the neck.

If the scapulae, or shoulder blades,are consciously pulled close to thespine, i.e., retracted, this muscle willbe required to shorten. Therefore,when the arm is called on to performthe pulling action, which requireslengthening of these muscles, wecan expect the tension of this alreadyshortened muscle to be transferredto the base of the neck, resulting ina need to lift the head up in order torelieve some of the developing ten-sion.

To test this, simply tilt your head for-wards with the shoulders in a neutralposition. A certain degree of ten-sion in the muscles at the back of theneck will be felt. Then consciouslypull the scapulae back, as discussedabove, and tilt the head forwards.The difference in tension can be im-mediately felt.

A similar argument can be madeduring the recovery phase of thearm. The accompanying action atthe shoulder girdle is termed "up-ward rotation." The upper and lowerthirds of the "trapezius" muscleare major upward rotators of thescapulae. The upper trapezius is alsoattached close to the base of the neck,and consequently a similar scenariocan be expected to occur when ac-companied by conscious retractionof the scapula when the arm is liftedover the water.

To illustrate this discussion. Figures6 and 7 show lateral and overheadviews of a swimmer lying on a"swim bench," performing the armrecovery, with and without "scapularetraction" or conscious "pressingdown on theT."

In Figure 6a, we see the scapula con-sciously pulled towards the spine, asin the recommended "flattening ofthe back." A visual inspection of thedorsal surface of the swimmer's backshows considerable contraction ofthe muscles controlling the scapula.The lateral view (Figure 6b), showsthe subconscious but instinctive el-evation of the head to relieve tensionin the neck. In Figures 7a and 7b, theswimmer was asked to perform therecovery without extraneous shoul-der activity. The result is clearlydifferent. '

The argument can be made thatthe elevation of the head in Figure6b does not appear to be excessive,and that many swimmers do indeedhave a slight upward tilt of the chin.Although this may be true, the dif-ference between consciously liftingthe chin up and having to lift it up to

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alleviate the onset of cervical tensionare two entirely different matters.

As a critical side-note, one of thefirst things a good orthopedic sur-geon does when swimmers presentthemselves with shoulder pain, isto examine the manner in which thescapula sits in relation to the rib cage.This is because many of the causesof shoulder injuries diagnosed as"overuse" as per swimming, throw-ing, and hitting activities, are nowthought to be the result of improperpositioning of the shoulder girdle.Alterations in scapula positioningare the result of a number of dif-ferent types of movements. Thesemovements range from imbalancesbetween the anterior and posteriormuscle groups of the shoulder, tothe conscious way we hold our chestduring the course of upper extremityactivities.

It stands to reason therefore, that weshould scrupulously avoid devel-oping postures that interfere withnatural shoulder motion, and moreimportantly, those movements thatcan potentially injure the very jointsthat we extensively rely on for swim-ming propulsion.

ConclusionLike "anatomy" and "physiology,"the field of "biomechanics," aidedby the rapidly improving technol-ogy, will help us test our ideas andprovide a more objective assessmentof what we think will work in thewater.

What we must always rememberis that while we continue to ex-periment, we need to tread carefullywhen proposing untested ideas, re-maining aware of the anatomical andbiomechanical implications of what

we recommend, particularly when itleads to literally thousands of repeti-tive movements at every workout.«

References:Prins, Jan H., Swimming stroke mechanics:A biomechanical viewpoint on the role ofthe hips and trunk in swimming. Journal ofSwimming Research. Vol 17, Spring 2007University of California - Berkeley WellnessLetter (June 2008)Volckening, Bill. Windmill Revolution.Swimming Technique: July-September. 2004.

AcknowledgementsI would like to thank the following col-leagues for their feedback in preparing thismanuscript: Ted Becker, Forbes Carlile, andJoel Stager.

Thanks also to University of Hawaii Var-sity Coach Victor Wales, his staff, and thefollowing swimmers for being enthusiasticsubjects: Mark Higley, Darren Maxwell andEmma Berry.

Jan Prins can be reached at jprins@hawaii.edu.

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