advances in the application of information technology to ...advances in the application of...

Advances in the application of information technologyto sport performance

DARIO G LIEBERMANN1 LARRY KATZ2 MIKE D HUGHES3

ROGER M BARTLETT4 JIM McCLEMENTS5 and IAN M FRANKS61Department of Physical Therapy Sackler Faculty of Medicine University of Tel Aviv Israel 2Sport Technology Research

Centre Faculty of Kinesiology University of Calgary Canada 3Centre for Performance Analysis University of Wales

Institute Cardithorn UK 4The Centre for Sport and Exercise Science Sheyacute eld Hallam University UK 5College ofKinesiology University of Saskatchewan Canada and 6School of Human Kinetics University of British Columbia

Vancouver Canada

Accepted 26 January 2002

This paper overviews the diverse information technologies that are used to provide athletes with relevant feed-back Examples taken from various sports are used to illustrate selected applications of technology-basedfeedback Several feedback systems are discussed including vision audition and proprioception Each tech-nology described here is based on the assumption that feedback would eventually enhance skill acquisition andsport performance and as such its usefulness to athletes and coaches in training is critically evaluated

Keywords feedback information technology skill acquisition sport training

Introduction

It is well documented that when feedback is providedin an appropriate manner motor skill acquisitionimproves signireg cantly (see Schmidt and Lee 1999 fora review) Consequently feedback is a major factor inthe improvement of sport skill performance Recentlyadvances in information technology have made itpossible to augment and improve the feedback athletesreceive during training and competition Moreovermodern technology has had such a profound impact onsport that many athletes and coaches now considerinformation derived from technological advances to beinvaluable This might be related to the concept offeedback that originated in mechanical control theoryIn accordance with such engineering models close-loop systems were designed to keep homeostasis orequilibrium around a reference value which in turnwould allow the work of a main actuator (Shannonand Weaver 1949) Deviations from the steady-state

Address all correspondence to Ian M Franks School of HumanKinetics University of British Columbia 210 War Memorial Gym6081 University Boulevard British Columbia V6T 1Z1 Canadae-mail ifranksinterchangeubcca

reference were coded as error which would then drivethe system to compensate or correct That is in move-ment science feedback information about movementwas generally expected to allow systematic correctionsin the performance However feedback will be relevantto the human learner if and only if the individualknows the performance goal and perceives the need tocarry out corrections relative to some expected out-come Under such assumptions a coach should strive toprovide an environment that is conducive to optimumlearning by augmenting the feedback that athletesreceive Feedback should thus enable athletes to modifytheir movements and produce optimum performance

In this paper we provide several sport examples ofhow performance feedback can be augmented by theuse of modern technology The examples are discussedand further used to bridge the theory of motor skillacquisition and the practice of coaching Our main goalis to describe and evaluate technological advancesapplied to sports that could be potentially useful pro-vided they are based on an appropriate exploitation ofthe sensory and cognitive feedback resources availableto the performer However it should be realized that thispaper is not intended to be a comprehensive review ofall the factors that athorn ect the learning of motor skills

Journal of Sports Sciences 2002 20 755plusmn 769

Journal of Sports Sciences ISSN 0264-0414 printISSN 1466-447X online Oacute 2002 Taylor amp Francis Ltdhttpwwwtandfcoukjournals

Video information in training

In normal conditions during training athletes are activein correcting errors However on some occasionscoaches use alternative aids to provide extrinsic(external) visual feedback for example videotapedreplays of the performance In this context video tech-nology has signireg cantly inmacr uenced training methodsAlthough video technology originated in the 1950s itsuse in coaching is an innovation less than two decadesold Its attractions for use in training are its relativelylow cost accessibility and portability It is athorn ordablefor most reg eld workers and perhaps already the mostpopular technology used in sport However using thismedium requires performers to adopt a passive attitudeIndividuals watching their performances cannot alwayscontrol the feedback information received during avideo presentation This feedback is delayed until thetask is complete and therefore cannot always be associ-ated with the internal sensory information at the time ofmotor execution Moreover the information availablemay often exceed the athletersquo s processing ability thusadditional guidance may be required particularlywith inexperienced or young athletes In such cases thecoachrsquos role is to guide and help in associating the visualfeedback generated by the presentation of the videomovie with the expected results

Video-based motion analysis systems although sig-nireg cantly more expensive are also used to facilitatefeedback about performance kinematics Lately thesesystems (eg APAS Ariel Inc httpwwwarielnetcom Silicon Coach SiliconCOACH Ltd httpwwwsiliconcoachcom) have become more accessible oftenbeing available over the Internet They are adaptable toany common technology plusmn most PC platforms videocamera systems and frame grabbing technologies aresupported plusmn and athorn ordable for the coach A combin-ation of common digital technologies allows videorecording in reg eld conditions for example during a golfmatch Images can be downloaded from any digitalvideo camera via FirewireOcirc to hand-held computers(eg HP Jornada Series) They can then be transmittedin a compressed image format to a remote serverthrough GPS (Global Position System satellite service)or directly by a cellular phone to the same server (seehand-held APAS Ariel Inc) The video data can beredistributed and analysed by researchers in any of theavailable server locations providing the service aroundthe world Very basic kinematic proreg les and tabulatedresults plusmn such as shot release speed angle height andphase durations through the put plusmn can be returned to theperformer or coach in the reg eld in minutes These can beaccompanied by similar data from world ranked expertsfor comparison retrieved from a library of proreg les in thespecireg c sport

Video is also recognized as an appropriate mediumfor obtaining qualitative information about the per-formance Video in combination with TV technology(httpwwworadcoil) is suitable for enhancement offeedback using replays real-time three-dimensionalsimulations or superposition of vector graphics It canbe further used for individual notational analysis andgame statistics in remote locations Less abstract andimportant information can be obtained from videoplayback technology for example for on-site immediatecomparison between onersquos performance and that ofother athletes One interesting technology used for thisprocess is based on a superposition of video sequencesappropriately transformed and graphically enhanced(scaled translated and rotated for comparison) Such asuperposition of two footages (one from an expert andanother from a less-experienced individual) is presentedsimultaneously This allows the recognition of essentialdithorn erences between the two performances (httpwwwdartreg shcomtechnologiestechnologies_simulcamhtml)and in this way visual qualitative and meaningfulfeedback is provided to the performer The underlyingassumption of such a motor learning strategy isbased on imitation Humans and other primates imitatemovements from birth (eg facial or hand Meltzothorn andMoore 1977) and continue throughout life bypassingthe need to extract abstract kinetic or kinematicinformation to learn a motor skill Based on the humanand animal models the potential of learning bydemonstration is recognized and implemented in robotmotor learning (see Schaal 1999)

Other video analysis systems such as the `coach-friendlyrsquo Silicon Coach and Quintic (httpwwwquinticcom) emphasize this type of comparative feedback andimitation However a note of caution about this typeof learning activity has been raised by Bartlett (1999)one personrsquos optimal performance is unlikely to be thesame as that of another

One further drawback with all video analysis systemsis the time taken to record manually and accurately thecoordinates of the joints of the body and other pointsimportant in the analysis (see for example Ay andKubo 1999) This precludes immediate feedback ofanything other than the video images themselves andrestricts fast feedback to simple kinematic and temporaldata as noted above More detailed kinematic analysistakes time

Automatic tracking systems (eg Expert VisionAnalysis [EVA] Motion Analysis Corp httpwwwmotionanalysiscom Vicon Oxford Metrics httpwwwviconcom CODA Charnwood Dynamicshttpcharndyncom) use several dithorn erent technologiesto track and record movements some in real time Thesystems that use passive markers and pulsed light arrayswith simultaneous sampling from multiple cameras (eg

756 Liebermann et al

EVA Vicon) are particularly attractive for rapid feed-back in non-competitive sport settings Hubbard andAlaways (1989) reported the early use of the EVAsystem to measure release conditions in the javelinthrow quickly enough for the thrower to improve per-formancersquo in the next throw This system incorporatedan optimization of javelin macr ight for that thrower with thesame release speed and then fed back information onoptimal release angle angle of attack and pitch ratecompared with values for the actual throw As withmuch technologically driven information on the pro-vision of immediate feedback no attention was paid towhether the immediate feedback of such informationcould improve performance In this case we expectfrom over a decadersquos experience that athletes needinformation on how to change their techniques to ethorn ectchanges in release angles and that this information isbest provided with non-immediacy

Automatic tracking systems have not yet been widelyused in athlete feedback probably because of their highcost their use frequently being limited to indoorsand not providing a video image although this can bedone with separate and synchronized video camerasHowever because of the increasing frame rates ofthese systems (the latest Motion Analysis Eagle digitalcameras capture at 500 Hz) real-time display not onlyof stick reg gures but also of joint kinematics and evenof solid body models through packages such as SIMM(Software for Interactive Musculoskeletal Modeling)suggest wider applications in indoor training

Training in three-dimensional virtualenvironments

Visual feedback inherently carries information aboutthe perceived relationship between the individualand the environment Self-motion relative to the sur-roundings initiates perception of the moving environ-ment as a precursor to action (Gibson 1979 Michaelsand Carello 1981) To exploit the link between per-ception and action computer applications create virtualenvironments by using dithorn erent visual ethorn ects Thisrelationship is implicit in simulation trainers that areaccompanied by three-dimensional displays Stereo-vision is a common technique used to create such athree-dimensional ethorn ect based on the principle thateach eye receives a slightly dithorn erent view of the samevisual object Fusion of the two views and further inter-pretation of the three-dimensional image occurs athigher brain centres Red-green or red-blue (passive)reg lters or polarized (active) glasses synchronized witha monitor (see httpwww3d-videode) are among theearliest techniques to show dithorn erent images to the twoeyes They have been used in semi-real environments

or in completely immersed virtual-reality settings (seehttpwwwsgicomvirtual_reality Immerse Reality) Amore recent technology uses glasses that provide a com-plete TV display that is slightly dithorn erent for each eye (seehttpwwwi-glassescom) A simpler and more popularway to provide a three-dimensional experience is byshowing superimposed objects appropriately scaled andput in perspective by creating movement and shadingethorn ects in the planar display This is the case in TV-videogames such as NintendoOcirc and Sony Play StationOcirc

In a simulated three-dimensional virtual environ-ment the coach may regulate important factors thatinmacr uence perception such as speed orientation anddirectional changes simply by operating a joystick ora keyboard Thus skill may result as a by-product oftraining in controlled simulated three-dimensionalvirtual environments Some technologies today havebeen developed for training in conditions that simulatethe real surroundings These technologies are setting astandard for indoor coaching in for example bicycleriding (CompuTrainerOcirc RaceMate Inc) golf (Part-T-GolfOcirc Part-T-Golf Marketing Company) windsurreg ng(Force4 WindSurf Simulator Force4 Enterprises Inc)and other sports

Kelly and Hubbard (2000) reported the design andconstruction of a bobsled simulator for driver trainingThe system comprised a bobsled cockpit motioncontrol system and graphics workstation The shape ofthe track being simulated was derived from construc-tion specireg cations The driverrsquos view of the simulatedtrack was presented to him on a monitor mounted in thecockpit synchronized to roll angle and steering forcefeedback through the motion control system Interest-ingly this development was intended not only to helptrain the US bobsled team but also to provide a `touristattractionrsquo to increase interest in the sport Whether itsucceeded in either intention was not reported

A recent concept is that of remote coaching via theInternet People carry out a computerized exercise pro-gram while a third party supervises the routines andcontrols the mechanism For example a `servo valversquomay be controlled in a remote mode to adjust speedresistance and other parameters during a bench pressor a knee extension on an isokinetic machine (seeAriel Dynamics Ltd httpwwwarielnetcom) Thefeedback is provided by the computer as a graphic dis-play of selected movement parameters plus statisticssuch as peak and mean results of the performancesduring the workout Similarly on-line coaching can bedone for running on a treadmill cycling or training ona stepper (see NetAthlonOcirc or UltraCOACH VROgrave

software IFT Ltd httpwwwreg tcentriccom) The per-former can train in a virtual environment showingscenery of preference that is displayed on a screen whilejogging on a treadmill Wearing appropriate glasses

Information technology and sport performance 757

allows also stereovision and thus the environment maybe seen in three dimensions The same technologyallows athletes to train and compete on-line even atremote distances Web racing is a promising innovationthat has been introduced for example in diverse sportslike bicycle riding wheelchair racing and rowing (seehttpwwwultracchcom)

The potential for such technologies is great certainlyfor recreational purposes and for initial learning of askill However this depends on the feedback informa-tion that can only be used ethorn ectively if it is associatedwith the actual movements Current research suggeststhat visual feedback presented during training in avirtual environment may accelerate the learning pro-cess compared with standard coaching techniques(see Todorov et al 1997 for a table tennis example)In other cases when individuals are asked to estimatewhere a ball would land judgements based on theinformation presented in a three-dimensional virtualenvironment may lead to a dithorn erent visual searchstrategy than the one used in real settings (Zaal andMichaels 1999) This in turn might slow the skilllearning process Thus as far as motor performance isconcerned further research is required to support thegeneral use of such virtual settings for training

The potential advantage is that when three-dimensional virtual environments are used extero-ceptive feedback in combination with internal feed-back may be manipulated to acquire a new skill or toimprove an old one Sometimes the advantage of virtualreality settings is that such environments may be used toenhance indirectly the acquisition of a skill by allowing

pre-practice in simulated unknown conditions Forexample in non-sporting motor activities virtual realityis widely used in combination with actual simulationsPilot training involves practising in simulators thatcombine visual and kinaesthetic feedback to emulatemacr ight conditions thus making the training process morerealistic and ethorn ective without taking risks (Boeing 727and Airbus commercial liners Quadrant Systems Ltd)

The training of car-driving responses using simu-lators is another example (DTS Driver TrainingSimulator Digitran Inc) In such settings a driver isconfronted with unexpected events (eg a dog suddenlycrossing the roadway) that require appropriate actionsDriving simulators allow for adjustments of the dithorn erentparameters during learning of the braking responseThese parameters include driving speed tailgatingdistance the rate of increase of the optic expansion afterthe brake action and the moment the brake lights willturn on The advantages are various considering thatsimulators are relatively inexpensive and safe comparedwith the risks of training such skills in real conditionsFigure 1 shows the set-up used to train cyclists in anenvironment that allows for control of feedback througha virtual reality simulation

The use of intrinsic feedback under vibrationconditions for enhancing muscular capacitytraining

It has been acknowledged that vibrations generatedby low-voltage alternate current may act directly on

Fig 1 Cycling simulation in a virtual reality environment


motor units spindles and pain receptors (Lundeberget al 1984) reducing pain and causing muscularrelaxation Nazarov and Spivak (1987) suggested thatvibratory stimulation of proprioceptors might also havepositive ethorn ects in training muscle elasticity in sportsMore recently mechanical segmental vibrations duringsimple arm lifting movements were used by Liebermannand Issurin (1997) to investigate empirically the ethorn ectof vibration on muscle ethorn ort perception and muscularforce generation They hypothesized that a momentarysensory conmacr ict might help to increase muscle forceoutput That is people would have the feeling of liftingfewer loads during vibration conditions and thuswould lift heavier loads The reg ndings of Liebermannand Issurin showed that participants consistently per-ceived that movements against a load appear èasierrsquowhen vibrations (44 Hz and 3 mm amplitude) wereapplied This conreg rmed that a perceptual factor wasinvolved in the process Stretch remacr exes could certainlyhave been activated by the stimulation of the musclespindles and the following remacr exive contractionscould have summed to change perception and allowedstronger voluntary muscle contraction in the directionof the movement The results of this experiment alsoshowed that participants lifted somewhat heavier loadsand consequently that the ratio of training time tooutput could in principle increase This could make atraining unit more eyacute cient Does the increase in loadingcapacity by using vibratory stimuli justify its use Asfar as acquisition of a skill or improvement of an old oneis concerned (particularly when the skill demandsaccuracy) vibration might have a negative inmacr uenceAfter a muscle or tendon is vibrated there are after-

ethorn ects such as signireg cant changes in position andvelocity sensing (Goodwin et al 1972 Sittig et al1985 1987) These movement illusionsrsquo or distortionsmay cause undershooting or overshooting during limbdisplacements without the participant being aware ofthem It is always preferable to train and tune pro-prioception to the correct movement patterns But con-sidering that success in competitive sport implies anincrease in muscle capability as well as mastering askill a manipulation of intrinsic feedback by applyingvibrations might lead to positive results in the reg nal per-formance We suggest that coaches should criticallyweigh the benereg ts of vibration training against potentialrisks on muscles or against the altered kinematicpatterns that might result as a consequence of theperceptualplusmn sensory conmacr ict created

Some technologies suggest the use of whole-body asopposed to segmental vibrations Vibration devicesadapted to sports might be incorporated to learnand adapt to conditions in which the skill requiresdamped vibrations such as windsurreg ng alpine skiingand mountain biking (Mester 1999) Mester reportedthat positive ethorn ects of whole-body vibrations might beattributed merely to practice in a simulated environ-ment where these vibrations are controlled Intrinsicfeedback is used in such cases to learn to cope with suchvibrations This is illustrated in Fig 2

It has been shown that long exposure to whole-bodyvibrations can pose health hazards in some occupationsplusmn truck drivers suthorn er from back pain and industrialworkers suthorn er from loss of sensitivity in the reg ngersOnce again the coach should evaluate the use of vibra-tion training in light of the risks inherent in the method

Fig 2 Floor irregularities and high speeds in downhill skiing cause vibrations that challenge the musculoskeletal structures andcontrol of movement


plusmn as with any other such as plyometric training If theexposure to vibration is controlled and constrained to alimited time the injury risk factor might be negligibleIf the skill requires prolonged exposure to vibrationconditions however alternative solutions should besearched In fact materials science and its applicationsto sport have developed enough to override some of thehazards posed by directly training sensory and muscularsystems in vibratory conditions `Smart materialsrsquo mayhave become a smarter option For example in downhillskiing which requires quick control of the limbs orin long distance running usually carried out over stithornsurfaces the negative vibration ethorn ects are counteractedby piezo-ceramic materials introduced in the construc-tion of better skis Such skis are equipped to detect andcompensate for vibrations (httpwwwtechreviewcomarticlesapr96TrendSkihtml) through the physicalproperties of the material As pressure is applied to anypart of the ceramic surface piezoelectricity is generated(a static charge produced by elastic deformation) andconverted into a force that attenuates the vibrations plusmnthe ski becomes stithorn er as a function of the charge

It is worth mentioning here that vibratory stimulationis an accepted treatment used in physical therapyAstronaut physical training might also change as a con-sequence of such stimulation since vibrations appliedto skeletal bone present an increasingly positive ethorn ectin the reversal of osteoporosis (Rubin et al 2001) aproblem encountered on prolonged space missions

In summary any training technologies that mightdevelop as a consequence of vibratory stimulationresearch in sports should be critically evaluated Tech-nology has developed to overcome vibrations withoutrequiring adaptation training Materials science anddamping mechanisms might be useful in specireg c sports

Temporal feedback in skill training

One important element in skill performance is timingTemporal variables are easily learned and retained withlittle attention (Liebermann et al 1988) The infor-mation conveyed in temporal structures or rhythmsmay sometimes override the use of spatial informationThat is while people are trained to perform a skillthe duration of the movement is perceived and learnedbetter than some spatial aspects even if the personpays attention to the latter only (Liebermann et al1988) Temporal variables appear to be so robust andeyacute cient for motor learning that coaches often use themintuitively For example they clap their hands at apre-determined tempo encapsulating the rhythm ofthe action that best suits the spatial conreg guration ofthe skill The performer listens and translates this intomotor actions

Temporal templates can be used to train individualsin aerobic workouts The major technological inno-vation here is that performance can be monitored byinteractive Personal Aerobic Training software (virtualPAT Davis and Bobick 1998) that has been developedat the Massachusetts Institute of Technology (MIT)The basis of the approach is a computer algorithmwhich recognizes the silhouette (edges) of the performersituated in front of a wide back-projected infrared lightsource The body eclipses the infrared source and thecameras reg lter out the images plusmn a binary extraction ofblack from white background plusmn to send them digitallyto the computer The pattern recognition algorithmcaptures changes in the silhouette plusmn body motions plusmnfrom frame to frame and temporally codes thesechanges This is translated into auditory feedbackwhich in turn is activated either when performance ofthe exercise declines (negative feedback) or when per-formance is correct (positive feedback) The algorithmsets rhythmical musical patterns for the personalizedaerobic workout The tempo is adjusted interactivelywhile performing and thus the computer-controlledtemporal structure is synchronized with that of theperformer

The apparent complexity in the process of extractingthe information during the motor performance doesnot imply that the feedback itself is complex Quite theopposite technology may help to reduce feedback to themost essential information units For example temporalinformation is simple and natural in any movingbody but may not be as accessible as other forms ofmovement information However once extracted thisinformation may be ethorn ectively delivered and used toenhance motor skill

Providing feedback about team performance

Over the past few years researchers in notationalanalysis have developed many sport analysis systemsThese systems describe in detail not only the actionsof athletes in competition but also the behaviour ofthe coach during practice Indeed considerable ethorn ortis now being made to quantify accurately competitionand practice performance (for a review of severalanalysis systems see Hughes and Franks 1997) Sportanalysis systems many of which are computer-aidedare designed to describe in detail the movements andtechnical actions of the athlete

Information derived from this type of computer-aidedsystem can be used for several purposes (i) immediatefeedback (ii) development of a database (iii) indica-tion of areas requiring performance improvement(iv) evaluation and (v) as a mechanism for selectivesearching through a video recording of the game All


of these functions are of paramount importance to thecoaching process which was the initial raison drsquo reg tre ofnotational analysis

One of the most exciting and potentially signireg cantoutgrowths of computer-aided sport analysis was theadvent of computer interactive video technology Theability of computers to control the video image made itpossible to enhance existing sport-specireg c analyticalprocedures An inexpensive IBM-based system was reg rstdescribed by Franks et al (1989) and then applied tothe analysis of team sport by Franks and Nagelkerke(1988) This computer-controlled system allowed thecoach or the sports analyst to provide the athleteswith digital and graphical data of team performance inaddition to edited videotape instances of action thatcorresponded to these data

The interactive video computer program accessedfrom the stored database the times of all specireg c eventssuch as goals shots and set plays Then from a menu ofthese events the analyst could choose to view any or allof these events within one specireg c category The com-puter was programmed to control the video such that itfound the time of the event on the video and then playedback that excerpt of game action It was also possible toreview the same excerpt with an extended lead inrsquo or`trailrsquo time around that chosen event

This type of interactive system has been the creativespark for more recent and commercially availableanalysis packages that othorn er a generic data-gatheringsystem which can be customized to any sport and inter-act with the on-line video (usually digital) A simpleanalysis of the data is available and the operator canhave immediate access to edited highlights of the per-formance The simplicity of the analyses and the lack ofsophisticated editing facilities restrict these commercialapplications at the moment but the technology isadvancing at a rapid pace

Using computer-assisted video feedback and aspecireg c algorithm for the statistics Dufour (1993)evaluated playersrsquo and team performance in three reg eldsphysical technical and tactical He demonstrated theability of his computer-aided systems to provideaccurate analysis and feedback for coaches on theirplayers and teams

One innovative method of using video was describedby Winkler (1996) He presented a comprehensiveobjective and precise diagnosis of a playerrsquo s perform-ance in training and match-play using a computer-controlled dual video system His system usedcomputer-controlled assessment systems to assessphysical reg tness factors in training In addition he usedtwo video cameras interlinked by computer to enable atotal view of the playing surface area This in turnenabled analysis of all the players in a team throughoutthe whole match both on and othorn the ball plusmn something

that not many systems were able to produce at thattime More recently this problem appears to have beenovercome using the AMISCO system (Billi et al 1996see httpwwwvideosportsfr) The researchers whohave developed this particular system claim it is one ofthe more powerful tools for tactical match analysis Itis made up of various integrated technologies A seriesof video cameras and sensors (approximately 4plusmn 6) isinstalled around the playing surface (usually in astadium setting) to track the movements of all playersthe ball and the oyacute cials This is accomplished throughsophisticated software development that compares pre-dicted trajectories of players and ball with the acquireddata The AMISCO system provides a detailed analysisof each playerrsquo s work rate an interactive representationof all actions recorded during a match and a graphicalreconstruction of all individual actions More impor-tantly it can provide a digital replay of all the playersand ball and synchronize this with a video replay fromany one of the video positions Therefore it enables theresearcher to describe not only the actions àroundthe ballrsquo but also the complete context in which theindividual action was produced Such complete analyseswill enable sport scientists to investigate valid descrip-tions of game performance such as that described inMcGarry et al (2002 this issue) However furtherresearch is still needed to test the reliability and utility ofsuch comprehensive systems

Providing feedback in aiming sports

For aiming sports that require accuracy and provisionsuch as Olympic shooting or archery vision is a primaryfeedback channel Consequently diverse technologieshave been developed to improve skill learning and per-formance in these sports There are many examples inwhich augmented visual feedback is combined withsophisticated technology Perhaps the most representa-tive and clear example is in the use of laser-guidedguns to train aiming skills in Olympic shooting Lasertechnology generally used in industry to detect dis-placements allows performers to correct for deviationsfrom the centre of a target during aiming within verynarrow error margins and at long distances Visual feed-back in combination with computer-generated auditoryfeedback makes the training process very eyacute cient inthis case It allows athletes to immediately correctposture before triggering while aiming (Noptel S-2000Sport Shooter Trainer System Noptel Oy CompanyFinland httpwwwnoptelreg nop_engshooterhtml)The technical principle underlying such a system is thata laser beam attached to the rimacr e hits a laser-sensitivegrid that generates an onplusmn othorn pulse captured by a com-puter through an interface The software transforms the


pulses generated by those sensors that were hit intorelevant coordinates A graphic display of the deviationsfrom the centre of the grid is provided on-line togetherwith an auditory feedback of proportionally higher pitchas the distance from the centre increases A similarapproach is used in training recreational hunting or inthe military where simulated changing environmentsare also integrated as part of the aiming task (Shot-Pro 2000 Shooting Simulator Digitran Systems Inchttpwwwdigitranhqcomshoothtml) This is illus-trated in Fig 3

The use of force platforms and forcetransducers in training

In sports that do not require spatial precision butrequire immediate knowledge of timing radar tech-nology has been adapted to obtain the relevant infor-mation For example sprinting athletes need to knowtheir reaction times relative to the moment of triggeringthe start gun they need to know their instantaneousand mean running speeds and the horizontal forces atthe start of a sprint In track sprinting a device calledthe `Saskatchewan Sprint Start Apparatusrsquo has beendeveloped at the University of Saskatchewan basedon a radar-guided receiver and on force transducersSanderson et al (1991) used this device to provideinformation to athletes immediately after they returnedto the starting blocks This information includedreaction time the resultant reaction force on the starting

block and the linear speed of the athlete in the directionof the sprint It was used to provide feedback andidentify errors information that the coach and athletewould not have available to them in normal trainingAthletes could change their stance or try dithorn erent tech-niques and immediately receive feedback on the changeThis method of training had very positive ethorn ects inimproving performance to a point where feedbackevidence could be used by coaches or by the athletes ontheir own (McClements et al 1996) This is becausethe athletes receive immediate and simple knowledge ofresults that is visually displayed allowing the athlete tocompare the outcome of the performance with internalfeedback at any instant

Imagine a feedback system that relies on on-lineauditory tones to calibrate the position of the centre ofpressure with the desired target position When thecentre of pressure also known as the point of forceapplication is far from some initial target location anidentireg able low-pitch tone follows When it is close it isaccompanied by a high-pitch tone Monitoring con-tinuously the displacement of the centre of pressurebelow the feet in this way allows the association ofmuscle responses with the lack of stability during thestanding posture This can be done by using force orpressure plates

These devices became very popular in biomechanicalresearch They are composed of upper and lowerrectangular metal plates of known dimensions and aremade of stithorn but relatively light materials (aluminiumalloys graphite or titanium) The sensors are usually of

Fig 3 Schematic illustration of laser-based guidance and feedback in Olympic shooting


one of two types (strain gauges or piezoelectric crystals)and are installed in precisely engineered internal sub-structures Generally four sensors are used to measureforces on the vertical direction only or eight formeasuring forces along all three orthogonal axes Theirpurpose is to translate deformations caused by loadingthe upper plate into electrical signals that are amplireg edand calibrated to known external forces If the dis-tribution of force is equal across all points of the plateor for all sensors the centre of pressure will be in themiddle of the geometrical system More importantlyif the centre of pressure is not moving regardless ofthe position on the plate the system rests in a stablebalanced state Olympic shooters need to train stabilitybefore pulling the trigger as do gymnasts during macr oorexercises or when on the beam The incorporation ofcomputer-generated low-frequency tones (auditoryfeedback) may be used to associate stability (proprio-ceptive feedback) and centre of pressure displacements(visual feedback) Low-frequency sound or silencemeans that a relatively stable position is being achievedIncreasing higher-frequency sound means deviationfrom the stable position (auditory feedback) Thus forexample the goal of a gymnast training to improve askill requiring balance will be to maintain the system`silentrsquo for as long as required while keeping the correctbody posture Figure 4 shows two examples of one-legged standing before and after training with feedback

Note that displacement of the centre of pressure belowthe feet is less dispersed in Fig 4b (right) than in Fig 4a(left) This is indicated by the circular area surroundingthe recorded planar displacement of the centre ofpressure in static posture (20 s sampled at 20 Hz)

The areas of the ellipses formed by surrounding thedisplacements may be easily calculated and comparedHowever mere observation shows that in feedbacktraining conditions standing static balance increases(Fig 4b) The above illustration is an example that helpsin understanding how technology provides informationthat is not normally available to the performer but iscritical in the motor learning process

Other force transducers have been used to providefeedback to athletes from force pedals in cycling (egSanderson and Cavanagh 1990 Broker et al 1993)to force transducers in the oar or oarlock for rowers(eg Dal Monte and Komar 1988 Smith et al 1994)An interesting observation from the cycling researchwas that summary and immediate feedback were nodithorn erent in the learning of modireg cations to pedallingtechnique by inexperienced cyclists (Broker et al1993)

Information from oar forces has been considered tobe important not only for evaluation of rowing tech-nique but also for crew selection (eg Gerber et al1985) The focus until recently was on the forcesapplied to the oar by the rower using the bending strain

Fig 4 Two-dimensional graphic representation of the centre of pressure excursions viewed from the top before feedback isavailable (a) and after feedback is allowed (b)


in the oar which depends only on the normal oar forceAs Smith and Loschner report in this issue (Smith andLoschner 2002) a signireg cant force with a propulsivecomponent is transmitted along the long axis of theoar to the pinrsquo the stretcher force is also importantRecent technological developments now allow all forcesthat signireg cantly athorn ect boat speed to be measured (seeSmith and Loschner 2002 for details)

The use of eye movement technology intraining

A popular line of recent research is based on eye-movement recording technology that determines wherethe athletersquo s gaze is focused The underlying assumptionof such research is that the fovea of the eye plusmn a high-resolution area that is densely innervated plusmn is specializedfor the recognition of image contours edges junctionscolours and other features (Marr 1982) Thus the eyeorbit moves to align the fovea in the retina with theprojected image (Carpenter 1988) This information isfurther processed in the brain and consequently theperson sees interprets and perceives However humanscannot see all images and more importantly cannot anddo not need to look simultaneously at all images Thus acognitive process allows scanning with the eyes of thoseaspects and features of objects in the environment thatare more relevant to achieve a task goal The assump-tions underlying practical research applied to sportare reg rst that expert athletes search for the relevantinformation during a performance (Abernethy 1990)The second is that their eye movements (eg saccades)lock momentarily on what is perceived as the relevantinformation in a dithorn erent way from non-experts(Tenenbaum et al 1996) However that the eyes of theathlete focus on specireg c points objects or events duringskill performance does not imply a causal relationshipbetween gaze perception and conscious attention

The expectation that eye movements of experts andtheir correlation to subsequent motor reactions mightpinpoint the important foci of attention that lead tobetter performance (eg in the reception of a volleyballserve) is challenged by the reg nding that athletes mightnot even use all information available Sometimes onlyvisual information obtained at the beginning and end ofthe performance of fast events is enough to performcorrectly for example in cricket (Land and McLeod2000) In practice the cricket player is able to predictand organize motor actions within the time constraintsof the game and those of the visual information-processing system (see httpnewsbbccoukhienglishscitechnewsid_10320001032849stm)

In fast-moving fast-reacting events it cannot beexpected that changes and dithorn erences in the way eyes

move would help in designing better strategies toenhance motor skill acquisition simply because thein-betweenrsquo information is irrelevant in slow events

things might be dithorn erent The premise could thenbe that a visual search strategy might be extractedfrom studying the way experts use eye movementsto look for the important visual information Suchèxpertrsquo strategies might be developed further andused to train less experienced athletes about their eyemovements

This approach is remacr ected in the research of Vickersand co-workers (Vickers and Adolphe 1997 Adolpheet al 1997) on eye movement in volleyball which pro-vides an example of information technology feedback intraining selective gazing Tracking of objects such as aball with the eyes occurs without players being aware ofit Yet expert volleyball players dithorn er from near-expertsin that the latter do not reg xate their eyes on importantevents and locations for as long as experts (Vickers andAdolphe 1997) This is labelled `quiet eyersquo by Vickers(1996) and is dereg ned as an objective spatial and tem-poral measure of gaze (eye reg xation coordinates ortracking movements onset othorn set and duration) Forexample in the reception of a volleyball macr oating serve plusmna relatively slow-motion event plusmn near-experts startstepping towards the ball as the serve starts but beforethe onset of the eye movements for tracking the ballExperts on the other hand are presumably able toreg xate their eyes and track specireg c locations such as anarea of the ball or the movement of the opponent evenbefore they initiate their own movements Howeverin the context of this paper it is most important todescribe the technology used to record gaze while theparticipant is performing the motor skill Vickers andco-workers used a mobile eye tracker device (AppliedSciences Laboratories-ASL 501) for this purpose Thisdevice collected monocular horizontal and verticalgaze coordinates relative to a head-reg xed reference framedereg ned by a helmet attached to the head of the per-former In addition the information obtained was inte-grated with video-recorded scenes that were collectedby micro-optics attached to the visor of the ASL eyetracker This allows `seeingrsquo the scene from the point ofview of performers when the ball moves towards theireyes Thus the location of gaze can be mapped relativeto the sport environment The motor performance isvideotaped using an external video camera placed infront of the participant All systems collect data at a rateof 30 Hz synchronized by a common time code andfurther edited othorn -line The edited video combines gazedirection information (a small dot centred at the pupiland cornea) a view from the perspective of the athletersquo seye and a front view of the performance

Another example that uses the eye movementrecorder in sport training can be found in the sport of


Association Football Franks and Hanvey (1997) andFranks (2000) completed the reg rst stage in the develop-ment and testing of a training programme for goal-keepers intended to help them improve their ability tosave a penalty kick Eight nationally ranked (Canadianyouth under 20 and under 23) goalkeepers were used inthis study which was designed to test the ethorn ectivenessof the training programme

Pre- and post-tests involved each goalkeeper facing40 penalty shots from four dithorn erent penalty takerseach taking 10 shots The information collected fromthese tests included goalkeeper movement (movementtime incorrect or correct prediction of ball placementand save percentage) penalty takerrsquo s non-kicking footplacement ball time and reg nal ball position After thepre-test the goalkeepers were asked what strategies theyused to predict the shot direction

The intervention involved three components Firstthe goalkeepers were shown how the response cue`placement of the non-kicking footrsquo was reliable fordetecting shot direction This took the form of a videopresentation in which a compilation of penalty kicksfrom previous World Cups was shown to the goal-keepers It was made clear to the goalkeepers afterthis presentation and subsequent discussion that theproblem with using this cue was that stimulus (responsecue) identireg cation and response (goalkeeper move-ment) initiation should be kept to an absolute mini-mum Secondly the goalkeepers were brought into thelaboratory and given simulated training that involvedthem viewing a large screen videotape of a penalty takerapproaching them The screen would `blankrsquo at ballcontact and the goalkeeper would move either his left orright arms as quickly as possible to indicate the directionin which he would dive Each goalkeeper wore an eyemovement recorder during this training interventionThe recorder provided the goalkeepers with feedbackabout their gaze control after every simulated penaltykick This feedback was a video of their gaze patternsuperimposed on the scene they were viewing during thepenalty takerrsquo s run-up Fixation on the non-kicking footbefore that foot landed was stressed after each trialas well as encouraging the goalkeepers to adopt a con-sistent strategy in where to look in the events leading upto the run-up

Before the training intervention visual scan pathswithin and between goalkeepers were variable un-reliable and inaccurate in optimum response cue (iethe penalty takerrsquo s non-kicking foot) It was importantfor the goalkeepers to reg xate on the non-kicking footbefore the shot to maximize the benereg ts of using theadvanced response cue With the aid of the feedbackprovided by the eye movement recorder the goal-keepers were able to reduce the variability of their scanpath and concentrate their gaze on the direction of

the penalty takerrsquo s non-kicking foot See Fig 5 for anexample of one goalkeeperrsquos scan path before and aftertraining

In the third stage of the intervention a more realisticset-up was used Goalkeepers still wore the eye move-ment recorder and faced a real penalty Unfortunatelybecause of the fragility and expense of the equipmentand the possibility of injury it was not possible to allowthe goalkeeper to dive for the shot Again from a goal-keeperrsquo s `ready stancersquo they were instructed to movetheir hands to the right or to the left as soon as theydetected shot direction Movement time and shotdirection were measures used in this stage of the studyAlso visual reg xations were recorded as a function oflearning In total the goalkeeper faced 60 simulated and120 real penalty shots in the entire study

Before the feedback intervention goalkeepersrsquo abilityto predict correct direction of the penalty kick wasapproximately 46 similar to an earlier notation studyof World Cup penalty shots by Franks and Hanvey(1997) After training this reg gure improved signireg cantlyto 75 It is clear that goalkeeper training in the use ofadvanced cues should exceed the 120 trials that weregiven in this study However the use of the eye move-ment recorder in helping them concentrate their gazeand adopt eyacute cient and consistent perceptual strategiesunder considerable stress was successful

Combining feedback technologies

During aiming tasks such as archery and shootingthree steps must be performed correctly First astable standing posture should be achieved where theathlete learns how to stabilize the body during aiming plusmnbreathing and heart beat are potential sources ofvariability This stability may be remacr ected in the changesof the centre of pressure as shown in Fig 4 A secondstage follows during which the shooting device is to bemaintained on the target for as long as needed Duringthis second stage the training protocol should con-centrate on visually stabilizing the rimacr e gun or bowLaser beams may serve this purpose Also as previouslyexplained these devices allow the athlete to pointtowards the centre of a visual target situated over a laser-sensitive grid connected to a computer Any deviationfrom the centre of the grid plusmn the maximal score plusmn isaccompanied by auditory tones of dithorn erent frequenciesThe performer can compare internal feedback withexternal feedback When the centre of pressure is in theright position and the individual is aiming at the centreof the target (all auditory tones are silent) he or shecan concentrate on the reg nal stage It is at this thirdand last stage that training gaze may be important inaiming before actual triggering (shooting or releasing


Fig 5 A typical scan path of a goalkeeperrsquos gaze compared with the position of the non-kicking foot during the penalty takerrsquo srun-up to kick the ball (a) before the training intervention and (b) after the training intervention

the bow) All these factors can only be measured usingsophisticated technologies

Is feedback always a prerequisite foracquisition of a skill

Coaches often assume that using immediate feedbackis always a valid way to improve skill Thus it is alsoassumed that technologies that provide immediatefeedback are benereg cial for learning However thismay not always be the case Sometimes it may be just

as ethorn ective to give feedback information after somelonger delay in a more specireg c and limited mannerThis is because an over-exposure to feedback (toomuch information) might interfere with performanceif it is provided but not needed (see Salmoni et al1984 for a review) It should also be mentionedthat training in the presence of immediate feedbackmight create a certain dependency on externalinformation However as performers progress theyshould become more independent and learn to relyon internal sources of information which shouldthen be used as the major error-correction facilitators


We suggest therefore that the frequent use of dithorn erentfeedback sources is important and relevant at thebeginning of the skill acquisition process but lessimportant later (Winstein and Schmidt 1989 seealso Hodges and Franks 2002 this issue for a dis-cussion of pre-practice information provided early inlearning)

Any technology and device that is constructed aroundthe idea of immediate feedback from diverse sourcesmay be relevant for recreational professional or amateurperformers at the initial stages of the skill acquisitionprocess Initially well-dereg ned and understandablefeedback will enhance learning However when experi-ence is acquired individuals are expected to rely onspecireg c feedback from external sources and on intrinsicfeedback That is they should become sensitive to theirown mistakes in skill performance by focusing on rele-vant information and internal sensation At this stageexcessive external feedback even if provided imme-diately after performance may interfere with the acqui-sition of skill Feedback allowance should be reducedprogressively as training proceeds and skill improves Atadvanced standards of performance the athlete shoulduse specialized feedback from external sources that arespecireg c to particular needs of the performer It shouldalso be mentioned that the ability to use internalfeedback to improve performance is shadowed by amore common use of external feedback which is moremanageable Intrinsic feedback is always with us Wecannot manipulate it easily from outside thus it tendsto be ignored Technologies developed to enhance per-formance based on such intrinsic sensory informationare rather specireg c and may depend on the type of skilland the learning phase For example in a balance main-tenance task internal feedback is not as ethorn ective asexternal-focus feedback and instructions (Shea andWulf 1999) However during early phases of the acqui-sition of a skill it has been suggested that externalsources of feedback may be more ethorn ective This willchange from knowledge of results and verbal knowledgeof performance during the initial cognitive stage tovisual feedback during the associative stage Onlyduring the reg nal autonomous stage might intrinsic pro-prioceptive and kinaesthetic feedback be more relevantto guide performance (see Magill 1997) In fact atadvanced stages elaborated `summary feedbackrsquo mightincorporate combined information from all feedbackchannels and have positive ethorn ects on performance(Schmidt et al 1990 Winstein and Schmidt 1990) Inlight of the rather general character of technologiesoften built to train individuals it is unlikely that they canadjust to meet a specireg c need for a feedback sourceHence coaches should be aware of the dithorn erential needsof their athletes at the dithorn erent stages of the trainingprocess

Conclusions

Coaches strive constantly to improve the performanceof athletes The most important aspect of their role isto provide the athlete with a practice environment thatis conducive to ethorn ective and eyacute cient learning Theintroduction of information technology into the sportperformance environment appears to be a positivealthough not always essential step towards achievingthis goal When the athlete can compare internally theexpected optimum performance with the actual move-ment outcome the probability of learning increasesThis review has focused on how information technologyhas been used to provide the athlete and coach withsophisticated objective information about sport per-formance For general purposes of motor learningthe impact of basic external feedback and collateraltechnologies plusmn from simple video movies to complexsimulators plusmn are of major importance and should beseriously considered in the normal practice scheme

Acknowledgements

Preparation of this article was supported by a grant from theSocial Sciences and Humanities Research Council of Canadaawarded to IMF and by a research fellowship from theSport Technology Research Centre Faculty of KinesiologyUniversity of Calgary granted to DGL

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Adolphe RM Vickers JN and Laplante G (1997) Theethorn ects of training visual attention on gaze behaviour andaccuracy a pilot study International Journal of Sports Vision4 28plusmn 33

Ay M and Kubo Y (1999) A biomechanical approach tothe improvement and optimisation of sports techniquesIn Proceedings of the rsquo99 Seoul International Sport Science

Congress pp 865plusmn 887 Seoul Korean Alliance for HealthPhysical Education Recreation and Dance

Bartlett RM (1999) Sports Biomechanics Reducing Injury and

Improving Performance London E amp FN SponBilli E Esposito M Garbarino JM and Giorgi JM

(1996) Proceacutedeacute drsquoanalyse de modeacutelisation et de visualisa-tion de seacutequences de sports collectifs Bulletin oyacute ciel de la

proprieacuteteacute industrielle No 41Broker JP Gregor RJ and Schmidt RA (1993) Extrinsic

feedback and the learning of kinetic patterns in cyclingJournal of Applied Biomechanics 9 111plusmn 123

Carpenter RHS (1988) Movement of the Eyes London PionDal Monte A and Komar A (1988) Rowing and sculling

mechanics In Biomechanics of Sport (edited by CLVaughan) pp 53plusmn 119 Boca Raton FL CRC Press


Davis JW and Bobick AF (1998) Virtual PAT a vir-tual personal aerobics trainer In Workshop on Perceptual

User Interfaces httpvismodwwwmediamitedu~ jdavisPublicationspublicationshtmlinteractive

Dufour W (1993) Observation techniques of humanbehaviour In Science and Football II (edited by TP ReillyA Stibbe and J Clarys) pp 160plusmn 166 London E amp FNSpon

Franks IM (2000) The structure of sport and the collectionof relevant data In Computer Science in Sport (edited byA Baca) pp 226plusmn 240 Vienna obv and hpt publishers

Franks IM and Hanvey T (1997) Cues for goalkeepersSoccer Journal Mayplusmn June pp 30plusmn 38

Franks IM and Nagelkerke P (1988) The use of computerinteractive video technology in sport analysis Ergonomics31 1593plusmn 1603

Franks IM Nagelkerke P and Goodman D (1989) Com-puter controlled video an inexpensive IBM based systemComputers and Education 13 33plusmn 44

Gerber H Jenny J Sudan J and Stussi E (1985) Bio-mechanical performance analysis in rowing with a newmeasuring system Communication to the 10th Congress

of the International Society of Biomechanics Umearing SwedenJune

Gibson JJ (1979) The Ecological Approach to Visual

Perception Boston MA Houghton Miuuml inGoodwin GM McCloskey DI and Matthews PBC

(1972) The contribution of muscle ethorn erents to kinaesthesiashown by vibration induced illusions of movement and itsethorn ects of paralyzing joint athorn erents Brain 95 705plusmn 748

Hodges NJ and Franks IM (2002) Modelling coachingpractice the role of instruction and demonstration Journal

of Sports Sciences 20 793plusmn 811Hubbard M and Alaways LW (1989) Rapid and accurate

estimation of release conditions in the javelin throw Journalof Biomechanics 22 583plusmn 595

Hughes M and Franks IM (1997) Notational Analysis of

Sport London E amp FN SponKelly A and Hubbard M (2000) Design and construction

of a bobsled driver training simulator Sports Engineering 313plusmn 24

Land MF and McLeod P (2000) From eye movementsto actions how batsmen hit the ball Neuroscience 3 1340plusmn1345

Liebermann DG and Issurin V (1997) Ethorn ects of vibratorystimulation on the perception of ethorn ort during isotonic con-tractions Journal of Human Movement Studies 32 171plusmn 186

Liebermann DG Raz T and Dickinson J (1988) Onintentional and incidental learning and estimation of tem-poral and spatial information Journal of Human Movement

Studies 15 191plusmn 204Lundeberg T Nordemar R and Ottoson D (1984) Pain

alleviation by vibratory stimulation Pain 20 25plusmn 44Magill R (1997) Motor Learning Concepts and Applications

New York McGraw-HillMarr D (1982) Vision A Computational Investigation into the

Human Representation and Processing of Visual InformationSan Francisco CA Freeman

McClements JD Sanderson LK and Gander BE(1996) Using immediate kinetic and kinematic feedback

measured by the Saskatchewan Sprint Start System toimprove sprinting performance New Studies in Athletics11 137plusmn 139

McGarry T Anderson DI Wallace SA Hughes MDand Franks IM (2002) Sport competition as a dynamicalself-organizing system Journal of Sports Sciences 20771plusmn 781

Meltzothorn AN and Moore MK (1977) Imitation of facial andmanual gestures by human neonates Science 198 74plusmn 78

Mester J (1999) Biological response to vibration load InAbstracts of the XVIIth Congress of the International Society ofBiomechanics p 32 Calgary Alberta ISB

Michaels CF and Carello C (1981) Direct PerceptionEnglewood Clithorn s NJ Prentice-Hall

Nazarov V and Spivak G (1987) Development of athletesrsquostrength abilities by means of a biomechanical stimulationmethod Theory and Practice of Physical Culture (Moscow) 1237plusmn 39

Newell KM (1981) Skill learning In Human Skills (editedby DH Holding) pp 203plusmn 225 New York Wiley

Rubin CT Turner SA Bain SD Mallinckrodt C andMcLeod K (2001) Extremely low level mechanical signalsare anabolic to trabecular bone Nature 412 603plusmn 604

Salmoni A Schmidt RA and Walter CB (1984)Knowledge of results and motor learning a review andcritical reappraisal Psychological Bulletin 95 355plusmn 386

Sanderson DJ and Cavanagh PR (1990) Use of augmentedfeedback for the modireg cation of pedaling mechanics ofcyclists Canadian Journal of Sport Science 77 245plusmn 251

Sanderson LK McClements JD and Gander BE (1991)Development of apparatus to provide immediate accuratefeedback to sprinters in normal training environment New

Studies in Athletics 6 33plusmn 41Schaal S (1999) Is imitation learning the route to humanoid

robots Trends in Cognitive Sciences 3 233plusmn 239Schmidt RA and Lee T (1999) Motor Control and Learning

Champaign IL Human KineticsSchmidt RA Lange C and Young DE (1990) Optimizing

summary knowledge of results for skill learning Human

Movement Science 9 325plusmn 348Shannon CE and Weaver W (1949) The Mathematical

Theory of Communication Chicago IL University of IllinoisPress

Shea CH and Wulf G (1999) Enhancing motor learningthrough external-focus instructions and feedback Human

Movement Science 18 553plusmn 571Sittig AC Denier van der Gon JJ and Gielen CCAM

(1985) Separated control of arm position and velocitydemonstrated by vibration of muscle tendon in manExperimental Brain Research 60 445plusmn 453

Sittig AC Denier van der Gon JJ and Gielen CCAM(1987) The contribution of athorn erent information onposition and velocity to the control of slow and fast humanforearm movements Experimental Brain Research 6733plusmn 40

Smith RM and Loschner C (2002) Biomechanics feed-back for rowing Journal of Sports Sciences 20 783plusmn 791

Smith RM Galloway M Patton R and Spinks W (1994)Analyzing on-water rowing performance Sports Coach 1737plusmn 40


Tenenbaum G Kohler N Shraga S Liebermann DGand Lidor R (1996) Anticipation and conreg dence ofdecisions related to skilled performance Journal of Sport

Psychology 27 293plusmn 307Todorov E Shadmehr R and Bizzi E (1997) Augmented

feedback presented in a virtual environment accelerateslearning of a diyacute cult motor task Journal of Motor Behavior29 147plusmn 158

Vickers JN (1996) Visual control when aiming at a fartarget Journal of Experimental Psychology Human Perception

and Performance 2 342plusmn 354Vickers JN and Adolphe RM (1997) Gaze behaviour

during a ball tracking and aiming skill International Journal

of Sports Vision 4 18plusmn 27Winkler W (1996) Computer-controlled assessment-

and video-technology for the diagnosis of a playerrsquo s per-formance in soccer training In Notational Analysis of

Sport I and II (edited by MD Hughes) pp 27plusmn 43 Cardithorn UWIC

Winstein CJ and Schmidt RA (1989) Sensorimotorfeedback In Human Skills (edited by DH Holding)pp 17plusmn 47 New York Wiley

Winstein CJ and Schmidt RA (1990) Reduced frequencyof knowledge of results enhances motor skill learningJournal of Experimental Psychology Learning Memory and

Cognition 16 677plusmn 691Zaal FTJM and Michaels CF (1999) Catching and

judging macr y balls in CAVETM In Studies in Perception and

Action V (edited by MA Grealy and JA Thompson)pp 148plusmn 152 Mahwah NJ Lawrence Erlbaum


Video information in training

In normal conditions during training athletes are activein correcting errors However on some occasionscoaches use alternative aids to provide extrinsic(external) visual feedback for example videotapedreplays of the performance In this context video tech-nology has signireg cantly inmacr uenced training methodsAlthough video technology originated in the 1950s itsuse in coaching is an innovation less than two decadesold Its attractions for use in training are its relativelylow cost accessibility and portability It is athorn ordablefor most reg eld workers and perhaps already the mostpopular technology used in sport However using thismedium requires performers to adopt a passive attitudeIndividuals watching their performances cannot alwayscontrol the feedback information received during avideo presentation This feedback is delayed until thetask is complete and therefore cannot always be associ-ated with the internal sensory information at the time ofmotor execution Moreover the information availablemay often exceed the athletersquo s processing ability thusadditional guidance may be required particularlywith inexperienced or young athletes In such cases thecoachrsquos role is to guide and help in associating the visualfeedback generated by the presentation of the videomovie with the expected results

Video-based motion analysis systems although sig-nireg cantly more expensive are also used to facilitatefeedback about performance kinematics Lately thesesystems (eg APAS Ariel Inc httpwwwarielnetcom Silicon Coach SiliconCOACH Ltd httpwwwsiliconcoachcom) have become more accessible oftenbeing available over the Internet They are adaptable toany common technology plusmn most PC platforms videocamera systems and frame grabbing technologies aresupported plusmn and athorn ordable for the coach A combin-ation of common digital technologies allows videorecording in reg eld conditions for example during a golfmatch Images can be downloaded from any digitalvideo camera via FirewireOcirc to hand-held computers(eg HP Jornada Series) They can then be transmittedin a compressed image format to a remote serverthrough GPS (Global Position System satellite service)or directly by a cellular phone to the same server (seehand-held APAS Ariel Inc) The video data can beredistributed and analysed by researchers in any of theavailable server locations providing the service aroundthe world Very basic kinematic proreg les and tabulatedresults plusmn such as shot release speed angle height andphase durations through the put plusmn can be returned to theperformer or coach in the reg eld in minutes These can beaccompanied by similar data from world ranked expertsfor comparison retrieved from a library of proreg les in thespecireg c sport

Video is also recognized as an appropriate mediumfor obtaining qualitative information about the per-formance Video in combination with TV technology(httpwwworadcoil) is suitable for enhancement offeedback using replays real-time three-dimensionalsimulations or superposition of vector graphics It canbe further used for individual notational analysis andgame statistics in remote locations Less abstract andimportant information can be obtained from videoplayback technology for example for on-site immediatecomparison between onersquos performance and that ofother athletes One interesting technology used for thisprocess is based on a superposition of video sequencesappropriately transformed and graphically enhanced(scaled translated and rotated for comparison) Such asuperposition of two footages (one from an expert andanother from a less-experienced individual) is presentedsimultaneously This allows the recognition of essentialdithorn erences between the two performances (httpwwwdartreg shcomtechnologiestechnologies_simulcamhtml)and in this way visual qualitative and meaningfulfeedback is provided to the performer The underlyingassumption of such a motor learning strategy isbased on imitation Humans and other primates imitatemovements from birth (eg facial or hand Meltzothorn andMoore 1977) and continue throughout life bypassingthe need to extract abstract kinetic or kinematicinformation to learn a motor skill Based on the humanand animal models the potential of learning bydemonstration is recognized and implemented in robotmotor learning (see Schaal 1999)

Other video analysis systems such as the `coach-friendlyrsquo Silicon Coach and Quintic (httpwwwquinticcom) emphasize this type of comparative feedback andimitation However a note of caution about this typeof learning activity has been raised by Bartlett (1999)one personrsquos optimal performance is unlikely to be thesame as that of another

One further drawback with all video analysis systemsis the time taken to record manually and accurately thecoordinates of the joints of the body and other pointsimportant in the analysis (see for example Ay andKubo 1999) This precludes immediate feedback ofanything other than the video images themselves andrestricts fast feedback to simple kinematic and temporaldata as noted above More detailed kinematic analysistakes time

Automatic tracking systems (eg Expert VisionAnalysis [EVA] Motion Analysis Corp httpwwwmotionanalysiscom Vicon Oxford Metrics httpwwwviconcom CODA Charnwood Dynamicshttpcharndyncom) use several dithorn erent technologiesto track and record movements some in real time Thesystems that use passive markers and pulsed light arrayswith simultaneous sampling from multiple cameras (eg



























































































Conclusions


Acknowledgements


References







































































































































































Conclusions


Acknowledgements


References














































































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