computer simulations model and analyze the behavior of real world systems . simulations are essentially &# 34 ; animation with a sense of purpose .&# 34 ; the present invention &# 39 ; s software applies the principles of physics to model accurately and with fidelity competitive sports by considering factors such as velocity , displacement , acceleration , deceleration and mass of the player and the objects the player interacts with , and controls , in the virtual world simulation . the present invention tracks the player &# 39 ; s motion , or more precisely , three dimensional displacements in real time using optical position sensing technology . the measurements are currently being made in three degrees - of - freedom ( axis of translation ) from x , y , z translations . displacements are the distance traveled by the player in the x , y or z planes from a fixed reference point and is a vector quantity . the present invention measurement constructs employ displacements over time in their calculations . accurate quantification of quantities such as work , force , acceleration and power are dependent on the rate of change of elementary quantities such as body position and velocity . accordingly , the present invention calculates velocity ( v ) as follows : v = d / t , where v has the units of meters per second ( m / s ), d is distance in meters and t is time in seconds . in three - dimensional space , d is computed by taking the change in each of the separate bilateral directions into account . if dx , dy , dz represent the positional changes between successive three dimensional bilateral directions , then the distance d is given by the following formula where &# 34 ; sqrt &# 34 ; represents the square root operation . the velocity can be labeled positive for one direction along a path and negative for the opposite direction . this procedure can also be used to calculate the acceleration a of the player along the movement path by taking the change in velocity ( v ) between two consecutive points and dividing by the time ( t ) interval between these points . this approximation of the acceleration a of the player is expressed as a rate of change with respect to time as follows where dv is the change in velocity and t is the time interval . acceleration is expressed in terms of meters per second per second . knowledge of the player &# 39 ; s acceleration enables calculation of the force ( f ). the force is related to the mass ( m ), given in kilograms , and acceleration by the formula the international standard of force is a newton , which is equivalent to a kilogram mass undergoing an acceleration of one meter per second per second acting on the player by the distance that the player moves while under the action of the force . the expression for work ( w ) is given by the unit of work is a joule , which is equivalent to a newton - meter . power p is the rate of work production and is given by the following formula the standard unit tor power is the watt and it represents one joule of work produced per second . the present invention creates a unique and sophisticated computer sports simulator faithfully replicating the ever - changing interaction between offensive and defensive opponents . this fidelity with actual competition enables a global and valid assessment of an offensive or defensive player &# 39 ; s functional , sport - specific performance capabilities . several novel and interrelated measurement constructs have been derived and rendered operable by specialized position - sensing hardware and interactive software protocols . the position - sensing hardware tracks the player 36 in the defined physical space 12 at a sample rate of 500 hz . the 500 hz sampling rate is attained by modifying commercially available electromagnetic , acoustic and video / optical technologies well known to those of ordinary skill in the art . additionally , other preferred specifications imposed upon the system 10 include : a preferred tracking volume approximately 432 cubic feet ( 9 ft . w × 8 ft . d × 6 ft . h ) beginning at a suitable viewing distance from the monitor , absolute position accuracy of one inch or better in all dimension over the tracking volume ; resolution of 0 . 25 inch or better in all dimensions over the tracking volume for smooth , precise control of the high resolution video feedback ; a video update rate approximately 30 hz ; and measurement latency less than 30 milliseconds to serve as a satisfying , real - time , feedback tool for human movement . compliance -- a novel global measure of the player &# 39 ; s core defensive skills is the ability of the player to maintain a synchronous relationship with the dynamic cues that are often expressed as an offensive virtual opponent . the ability to faithfully maintain a synchronous relationship with the virtual opponent is expressed either as compliance ( variance or deviation from a perfect synchronous relationship with the virtual opponent ) and / or as absolute performance measures of the player &# 39 ; s velocity , acceleration and power . an integral component of such a synchronous relationship is the player &# 39 ; s ability to effectively change position , i . e ., to cut , etc . as discussed below . compliance is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 210 , coordinates in the virtual environment equivalent to the player &# 39 ; s 212 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 214 as a function of dimensions x , y and x , and time ( x , y , z , t ) to a virtual position b 216 . d ) in response , the player moves along path2 ( x , y , z , t ) 218 to a near equivalent physical position c 220 . the player &# 39 ; s objective is to move efficiently along the same path in the physical environment from start to finish , as does the avatar in the virtual environment . however , since the virtual opponent typically moves along random paths and the player is generally not as mobile as the virtual opponent , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) the system calculates at each sampling interval the player &# 39 ; s new position , velocity , acceleration , and power , and determines the player &# 39 ; s level of compliance characterized as measured deviations from the original virtual opponent 210 - player 212 spacing at position a . f ) the system provides real time numerical and graphical feedback of the calculations of part e . opportunity -- at such time as the player assumes an offensive role , the player &# 39 ; s ability to create an asynchronous movement event is quantified . the player &# 39 ; s ability to execute abrupt changes ( to cut ) in his or her movement vector direction , expressed in the aforementioned absolute measures of performance , is one of the parameters indicative of the player &# 39 ; s ability to create this asynchronous movement event . opportunity is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 222 , coordinates in the virtual environment equivalent to the player &# 39 ; s 224 coordinates in the physical environment . c ) the player moves along path2 ( x , y , z , t ) 226 to a physical position c 228 . the player &# 39 ; s objective is to maximize his / her movement skills in order to elude the virtual opponent 222 . d ) in response , the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 230 to an equivalent virtual position b 232 . the virtual opponent &# 39 ; s movement characteristics are programmable and modulated over time in response to the player &# 39 ; s performance . e ) the system calculates at each sampling interval the player &# 39 ; s new position velocity , acceleration , and power , and determines the moment the player has created sufficient opportunity to abruptly redirect his / her movement along path3 ( x , y , z , t ) 234 to intersect the virtual opponent &# 39 ; s x - y plane to elude and avoid collision with the virtual opponent . f ) the system provides real time numerical and graphical feedback of the calculations of part e . a number of performance components are essential to successfully executing the two aforementioned global roles . accordingly the present invention assesses the following : 1 .) dynamic reaction time -- dynamic reaction time is a novel measure of the player &# 39 ; s ability to react correctly and quickly in response to cueing that prompts a sport specific response from the player . it is the elapsed time from the moment the virtual opponent attempts to improve its position ( from the presentation of the first indicating stimuli ) to the player &# 39 ; s initial correct movement to restore a synchronous relationship ( player &# 39 ; s initial movement along the correct vector path ). dynamic reaction time is a measurement of ability to respond to continually changing , unpredictable stimuli , i . e ., the constant faking , staccato movements and strategizing that characterizes game play . the present invention uniquely measures this capability in contrast to systems providing only static cues which do not provide for continual movement tracking . reaction time is comprised of four distinct phases : the perception of and interpretation of the visual and / or audio cue , appropriate neuromuscular activation and musculoskeletal force production resulting in physical movement . it is important to note that dynamic reaction time , which is specifically measured in this protocol , is a separate and distinct factor from rate and efficiency of actual movement which are dependent on muscular power , joint integrity , movement strategy and agility factors . function related to these physiological components is tested in other protocols including phase lag and 1st step quickness . faced with the offensive player &# 39 ; s attempt to create an asynchronous event , the defensive player must typically respond within fractions of a second to relevant dynamic cues if the defensive player is to establish or maintain the desired synchronous relationship . with such minimum response time , and low tolerance for error ; the defensive player &# 39 ; s initial response must typically be the correct one . the player must continually react to and repeatedly alter direction and / or velocity during a period of continuous movement . any significant response lag or variance in relative velocity and / or movement direction between the player and virtual opponent places the player irrecoverably out of position . relevant testing must provide for the many different paths of movement by the defensive player that can satisfy a cue or stimulus . the stimulus may prompt movement side to side ( the x translation ), fore and aft ( the z translation ) or up or down ( the y translation ). in many instances , the appropriate response may simply involve a twist or torque of the player &# 39 ; s body , which is a measure of the orientation , i . e ., a yaw , pitch or roll . dynamic reaction time is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 236 , coordinates in the virtual environment equivalent to the player &# 39 ; s 238 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 240 to a virtual position b 242 . d ) in response , the player moves along path2 ( x , y , z , t ) 244 to a near equivalent physical position c 246 . the player &# 39 ; s objective is to move efficiently along the same path in the physical environment from start to finish as does the virtual opponent in the virtual environment . however , since the virtual opponent typically moves along random paths and the player is generally not as mobile as the virtual opponent , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) once the virtual opponent reaches position b 242 , it immediately changes direction and follows path3 ( x , y , z , t ) 248 to a virtual position d 250 . the dynamic reaction timer is started after the virtual opponent &# 39 ; s x , y , or z velocity component of movement reaches zero at position b 242 and its movement along path3 ( x , y , z , t ) 248 is initiated . f ) the player perceives and responds to the virtual opponent &# 39 ; s new movement path by moving along path4 ( x , y , z , t ) 252 with intentions to comply to virtual opponent &# 39 ; s new movement path . the dynamic reaction timer is stopped at the instant the player &# 39 ; s x , y , or z velocity component of movement reaches zero at position c 246 and his / her movement is redirected along the correct path4 ( x , y , z , t ) 252 . g ) the system calculates at each sampling interval the player &# 39 ; s new position velocity , acceleration , and power . h ) the system provides real time numerical and graphical feedback of the calculations of part g and the dynamic reaction time . 2 .) dynamic phase lag -- another novel measurement is &# 34 ; phase lag &# 34 ;; defined as the elapsed time that the player is &# 34 ; out of phase &# 34 ; with the cueing that evokes a sport specific response from the player . it is the elapsed time from the end of dynamic reaction time to actual restoration of a synchronous relationship by the player with the virtual opponent . in sports vernacular , it is the time required by the player to &# 34 ; recover &# 34 ; after being &# 34 ; out - of - position &# 34 ; while attempting to guard his opponent . phase lag is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 254 , coordinates in the virtual environment equivalent to the player &# 39 ; s 256 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 258 to a virtual position b 260 . d ) in response , the player moves along path2 ( x , y , z , t ) 262 to a near equivalent physical position c 264 . the player &# 39 ; s objective is to move efficiently along the same path in the physical environment from start to finish as does the avatar in the virtual environment . however , since the virtual opponent typically moves along random paths and the player is generally not as mobile as the virtual opponent 254 , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) once the virtual opponent reaches position b 260 , it immediately changes direction and follows path3 ( x , y , z , t ) 266 to a virtual position d 268 . f ) the player perceives and responds to the virtual opponent &# 39 ; s new movement path by moving along path4 ( x , y , z , t ) 270 . the phase lag timer is started at the instant the player &# 39 ; s x , y , or z velocity component of movement reaches zero at position c 264 and his / her movement is directed along the correct path4 ( x , y , z , t ) 270 to position e 272 . g ) when the player &# 39 ; s position e finally coincides or passes within an acceptable percentage of error measured with respect to the virtual opponent &# 39 ; s at position d 268 the phase lag timer is stopped . h ) the system calculates at each sampling interval the player &# 39 ; s new position velocity , acceleration , and power . i ) the system provides real time numerical and graphical feedback of the calculations of part h and the phase lag time . 3 .) first step quickness -- a third novel measurement is the player &# 39 ; s first step quickness . in certain protocols of the present invention , first step quickness is measured as the player attempts to establish or restore a synchronous relationship with the offensive virtual opponent . first step quickness is equally important for creating an asynchronous movement event for an offensive player . acceleration is defined as the rate of increase of velocity over time and is a vector quantity . in sports vernacular , an athlete with first step quickness has the ability to accelerate rapidly from rest ; an athlete with speed has the ability to reach a high velocity over longer distances . one of the most valued attributes of a successful athlete in most sports is first step quickness . this novel measurement construct purports that acceleration is a more sensitive measure of &# 34 ; quickness &# 34 ; over short , sport - specific movement distances than is average velocity or speed . this is especially true since a realistic simulation of sports movement challenges , which are highly variable in distance , would not be dependent upon fixed start and end positions . a second reason that the measurement of acceleration over sport - specific distances appears be a more sensitive and reliable measure in that peak accelerations are reached over shorter distances , as little as one or two steps . first step quickness can be applied to both static and dynamic situations . static applications include quickness related to base stealing . truly sports relevant quickness means that the athlete is able to rapidly change his movement pattern and accelerate in a new direction towards his goal . this type of quickness is embodied by michael jordan &# 39 ; s skill in driving to the basket . after making a series of misleading movement cues , jordan is able to make a rapid , powerful drive to the basket . the success of this drive lies in his first step quickness . valid measures of this sports skill must incorporate the detection and quantifying of changes in movement based upon preceding movement . because the vector distances are so abbreviated and the player is typically already under movement prior to &# 34 ; exploding &# 34 ;, acceleration , power and / or peak velocity arc assumed to be the most valid measures of such performance . measures of speed or velocity over such distances may not be reliable , and at best , are far less sensitive indicators . numerous tools are available to measure the athlete &# 39 ; s average velocity between to two points , the most commonly employed tool is a stopwatch . by knowing the time required to transit the distance between a fixed start and end position , i . e ., a known distance and direction , the athlete &# 39 ; s average velocity can be accurately calculated . but just as an automobile &# 39 ; s zero to sixty - mph time , a measure of acceleration , is more meaningful to many car aficionados than its top speed , an average velocity measure does not satisfy interest in quantifying the athlete &# 39 ; s first step quickness . any sport valid test of 1st step quickness must replicate the challenges the athlete will actually face in competition . in situations where the athlete &# 39 ; s movement is over short , sport - specific distances that are not fixed start and stop positions , the attempt to compare velocities in various vectors of unequal distance is subject to considerable error . for example , comparison of bilateral vector velocities achieved over different distances will be inherently unreliable in that the athlete , given a greater distance , will achieve higher velocities . and conventional testing means , i . e ., without continual tracking of the player , can not determine peak velocities , only average velocities . only by continuous , high - speed tracking of the athlete &# 39 ; s positional changes in three planes of movement can peak velocity , acceleration , and / or power be accurately measured . for accurate assessment of bilateral performance , the measurement of power , proportional to the product of velocity and acceleration , provides a practical means for normalizing performance data to compensate for unequal distances over varying directions since peak accelerations are achieved within a few steps , well within a sport - specific playing area . first step quickness is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) alt position a , software scaling parameters make the virtual opponent 224 , coordinates in the virtual environment equivalent to the player &# 39 ; s 276 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 278 to a virtual position b 280 . d ) in response , the player moves along path2 ( x , y , z , t ) 282 to a near equivalent physical position c 284 . the player &# 39 ; s objective is to move efficiently along the same path in the physical environment from start to finish as does the virtual opponent in the virtual environment , however ; since the virtual opponent typically moves along random paths and the player is generally not as mobile as the virtual opponent , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) once the virtual opponent reaches position b 280 , it immediately changes direction and follows path3 ( x , y , z , t ) 286 to a virtual position d 288 . f ) the player perceives and responds to the virtual opponent &# 39 ; s new movement path by moving along path4 ( x , y , z , t ) 290 with intentions to comply to virtual opponent &# 39 ; s new movement path . g ) the system calculates at each sampling interval the player &# 39 ; s new position , velocity , acceleration , and power . within a volume 292 having radius r , either the measurement of peak acceleration or the measurement of peak power , proportional to the product of peak velocity and acceleration , characterizes first step quickness . h ) the system provides real time numerical and graphical feedback of the calculations of part g . 4 .) dynamic reactive bounding -- a fourth novel measurement is the player &# 39 ; s ability to jump or bound in response to cueing that evokes a sport specific response in the player . in certain protocols of the present invention , measured constructs include the player &# 39 ; s dynamic reaction time in response to the virtual opponent &# 39 ; s jumps as well as the player &# 39 ; s actual jump height and / or bound distance and trajectory . static measures of jumping ( maximal vertical jump ) have poor correlation to athletic performance . dynamic measurements made within the present invention &# 39 ; s simulation provide sports relevant information by incorporating the variable of time with respect to the jump or bound . a jump is a vertical elevation of the body &# 39 ; s center of gravity ; specifically a displacement of the cm ( center of mass ) in the y plane . a jump involves little , if any , horizontal displacement . in contrast , a bound is an elevation of the body &# 39 ; s center of gravity having both horizontal and vertical components . the resulting vector will produce horizontal displacements in some vector direction . both the high jump and the long jump represent a bound in the sport of track and field . satisfactory measures currently exist to accurately characterize an athlete &# 39 ; s performance in these track and field events . but in these individual field events , the athlete is not governed by the unpredictable nature of game play . many competitive team sports require that the athlete elevate his or her center of gravity ( y plane ), whether playing defense or offense , during actual game play . examples include rebounding in basketball , a diving catch in football , a volleyball spike , etc . unlike field events , the athlete must time her or his response to external cues or stimuli , and most frequently , during periods of pre - movement . in most game play , the athlete does not know exactly when or where he or she must jump or bound to successfully complete the task at hand . it is universally recognized that jumping and bounding ability is essential to success in many sports , and that it is also a valid indicator of overall body power . most sports training programs attempt to quantify jumping skills to both appraise and enhance athletic skills . a number of commercially available devices are capable of measuring an athlete &# 39 ; s peak jump height . the distance achieved by a bound can be determined if the start and end points are known . but no device purports to measure or capture the peak height ( amplitude ) of a bounding exercise performed in sport relevant simulation . the peak amplitude can be a sensitive and valuable measure of bounding performance . as is the case with a football punt , where the height of the ball , i . e ., the time in the air , is at least as important as the distance , the height of the bound is often as important as the distance . the timing of a jump or bound is at as critical to a successful spike in volleyball or rebound in basketball as its height . the jump or bound should be made and measured in response to an unpredictable dynamic cue to accurately simulate competitive play . the required movement vector may be known ( volleyball spike ) or unknown ( soccer goalie , basketball rebound ). this novel measurement construct tracks in real time the actual trajectory of a jump or bound performed during simulations of offensive and defensive play . to measure the critical components of a jump or bound requires continuous sampling at high rates to track the athlete &# 39 ; s movement for the purpose of detecting the peak amplitude as well as the distance achieved during a jumping or bounding event . real time measurements of jumping skills include jump height , defined as the absolute vertical displacement of cm during execution of a vertical jump ; and for a bound , the peak amplitude , distance and direction . reactive bounding is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 294 , or virtual opponent &# 39 ; s coordinates in the virtual environment equivalent to the player &# 39 ; s 296 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 298 to a virtual position b 300 . the virtual opponent &# 39 ; s resultant vector path or bound is emphasized to elicit a similar move from the player 296 . d ) in response , the player 296 moves along path2 ( x , y , z , t ) 302 to a near equivalent physical position c 304 . the player &# 39 ; s objective is to move efficiently along the same path in the physical environment from start to finish as does the virtual opponent in the virtual environment . however , since the virtual opponent typically moves along random paths and the player is generally not as mobile as the virtual opponent , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) the system calculates at each sampling interval the player &# 39 ; s new position , velocity , acceleration , and power . in addition , components of the player &# 39 ; s bounding trajectory , i . e ., such as air time , maximum y - displacement , are also calculated . f ) the system provides real time numerical and graphical feedback of the calculations of part e . the player &# 39 ; s bounding trajectory is highlighted and persists until the next bound is initiated . 5 .) dynamic sports posture -- a fifth novel measurement is the player &# 39 ; s sports posture during performance of sport specific activities . coaches , players , and trainers universally acknowledge the criticality of a player &# 39 ; s body posture during sports activities . whether in a defensive or offensive role , the player &# 39 ; s body posture during sports specific movement directly impacts sport specific performance . an effective body posture optimizes such performance capabilities as agility , stability and balance , as well as minimizes energy expenditure . an optimum posture during movement enhances control of the body center of gravity during periods of maximal acceleration , deceleration and directional changes . for example , a body posture during movement in which the center of gravity is &# 34 ; too high &# 34 ; may reduce stability as well as dampen explosive movements ; conversely , a body posture during movement that is &# 34 ; too low &# 34 ; may reduce mobility . without means of quantifying the effectiveness of a body posture on performance related parameters , discovering the optimum stance or body posture is a &# 34 ; hit or miss &# 34 ; process without objective , real time feedback . optimal posture during movement can be determined by continuous , high speed tracking of the player &# 39 ; s cm in relationship to the ground during execution of representative sport - specific activities . for each player , at some vertical ( y plane ) cm position , functional performance capabilities will be optimized . to determine that vertical cm position that generates the greatest sport - specific performance for each player requires means for continual tracking of small positional changes in the player &# 39 ; s cm at high enough sampling rates to capture relevant cm displacements . it also requires a sports simulation that prompts the player to move as she or he would in actual competition , with abrupt changes of direction and maximal accelerations and decelerations over varying distance and directions . training optimum posture during movement requires that the player strive to maintain their cm within a prescribed range during execution of movements identical to those experienced in actual game play . during such training , the player is provided with immediate , objective feedback based on compliance with the targeted vertical cm . recommended ranges for each player can be based either on previously established normative data , or could be determined by actual testing to determine that cm position producing the higher performance values . optimal dynamic posture during sport - specific activities is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 306 , coordinates in the virtual environment equivalent to the player &# 39 ; s 308 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 310 to a virtual position b 312 . d ) in response , the player moves along path2 ( x , y , z , t ) 314 to a near equivalent physical position c 316 . the player &# 39 ; s objective is to move efficiently and in synchronicity to the virtual opponent &# 39 ; s movement along the same path in the physical environment from start to finish as does the virtual opponent in the virtual environment . however , since the virtual opponent 306 typically moves along random paths and the player 308 is generally not as mobile as the virtual opponent , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) the system calculates at each sampling interval the player &# 39 ; s most efficient dynamic posture defined as the cm elevation that produces the optimal sport specific performance . f ) the system provides real time numerical and graphical feedback of the calculations of part c . a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) the player 308 assumes the dynamic posture that he / she wishes to train . c ) the system provides varying interactive movement challenges over sport specific distances and directions , including unplanned movements . d ) y - plane positions , velocity , accelerations and power measurements that are greater or less than or equal to the pre - set threshold or window will generate real - time feedback of such violations for the player 308 . e ) the system provides real - time feedback of compliance with the desired dynamic posture during performance of the protocols . 6 .) functional cardio - respiratory status -- the sixth novel functional measurement is the player &# 39 ; s cardio - respiratory status during the aforementioned sports specific activities . in most sports competitions , there are cycles of high physiologic demand , alternating with periods of lesser demand . cardiac demand is also impacted upon by situational performance stress and attention demands . performance of the cardio - respiratory system under sports relevant conditions is important to efficient movement . currently , for the purposes of evaluating the athlete &# 39 ; s cardio - respiratory fitness for sports competition , stationary exercise bikes , treadmills and climbers are employed for assessing cardiac response to increasing levels of physical stress . though such exercise devices can provide measures of physical work , they are incapable of replicating the actual stresses and conditions experienced by the competitive athlete in most sports . accordingly , these tests are severely limited if attempts are made to correlate the resultant measures to actual sport - specific activities . it is well known that heart rate is influenced by variables such as emotional stress and the type of muscular contractions , which can differ radically in various sports activities . for example , heightened emotional stress , and a corresponding increase in cardiac output , is often associated with defensive play as the defensive player is constantly in a &# 34 ; coiled &# 34 ; position anticipating the offensive player &# 39 ; s next response . for the cardiac rehab specialist , coach , or athlete interested in accurate , objective physiological measures of sport - specific cardiovascular fitness , no valid tests have been identified . a valid test would deliver sport - specific exercise challenges to cycle the athlete &# 39 ; s heart rate to replicate levels observed in actual competition . the athlete &# 39 ; s movement decision - making and execution skills , reaction time , acceleration - deceleration capabilities , agility and other key functional performance variables would be challenged . cardiac response , expressed as heart rate , would be continuously tracked as would key performance variables . feedback of heart rate vs . sport - specific performance at each moment in time will be computed and reported . functional cardio - respiratory fitness is a novel measurement construct capable of quantifying any net changes in sport - specific performance relative to the function of the cardio - respiratory system . functional cardio - respiratory status is determined as follows : a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) a wireless heart rate monitor ( 36a , fig2 ) is worn by the player . the monitor communicates in real - time with the system . c ) the system provides sport - specific exercise challenges to cycle the player &# 39 ; s heart rate to replicate levels observed in actual sport competition . d ) the system provides interactive , functional planned and unplanned movement challenges over varying distances and directions . e ) the system provides real - time feedback of compliance with a selected heart - rate zone during performance of defined protocols . f ) the system provides a real - time numerical and graphical summary of the relationship or correlation between heart rate at each sample of time and free - body physical activity . 7 .) dynamic reactive cutting -- the seventh novel construct is a unique measure of the player &# 39 ; s ability to execute an abrupt change in position , i . e ., a &# 34 ; cut &# 34 ;. cutting can be a directional change of a few degrees to greater than 90 degrees . vector changes can entail complete reversals of direction , similar to the abrupt forward and backward movement transitions that may occur in soccer , hockey , basketball , and football . the athlete running at maximum velocity must reduce her or his momentum before attempting an aggressive directional change ; this preparatory deceleration often occurs over several gait cycles . once the directional change is accomplished , the athlete will maximally accelerate along his or her new vector direction . measuring both the deceleration during braking prior to direction change ; and for valid testing , the cues ( stimuli ) prompting the cutting action must be unpredictable and interactive so that the cut can not be pre - planned by the athlete , except under specific training conditions , i . e . practicing pass routes in football . it must be sport - specific , replicating the types of stimuli the athlete will actually experience in competition . the validity of agility tests employing ground positioned cones and a stopwatch , absent sport - relevant cueing , is suspect . with knowledge of acceleration and the player &# 39 ; s bodyweight , the power produced by the player during directional changes can also be quantified . a ) a beacon , a component of the optical tracking system , is worn at the player &# 39 ; s waist . b ) at position a , software scaling parameters make the virtual opponent 318 , or virtual opponent &# 39 ; s coordinates in virtual environment equivalent to the player &# 39 ; s 320 coordinates in the physical environment . c ) the system &# 39 ; s video displays the virtual opponent &# 39 ; s movement along path1 ( x , y , z , t ) 322 to a virtual position b 324 . d ) in response , the player 320 moves along path2 ( x , y , z , t ) 326 to a near equivalent physical position c 328 . the player &# 39 ; s objective is to move efficiently along the same path in the physical environment from start to finish as does the virtual opponent 318 in the virtual environment . however , since the virtual opponent typically moves along random paths and the player is generally not as mobile as the virtual opponent , the player &# 39 ; s movement path usually has some position error measured at every sample interval . e ) once the virtual opponent 310 reaches position b 324 , it immediately changes direction and follows path3 ( x , y , z , t ) 330 to a virtual position d 332 . f ) the player perceives and responds to the virtual opponent &# 39 ; s new movement path by moving along path4 ( x , y , z , t ) 334 to physical position e 336 . g ) once the virtual opponent 318 reaches virtual position d 332 , it immediately changes direction and follows path5 ( x , y , z , t ) 338 to virtual position f 340 . h ) the player perceives and responds to the virtual opponent &# 39 ; s new movement path by moving along path6 ( x , y , z , t ) 342 to physical position g 344 . i ) subsequent virtual opponent 318 movement segments are generated until sufficient repetition equivalency is established for all vector movement categories represented during the performance of sport - specific protocols , including unplanned movements over various distances and direction . j ) the system calculates at each sampling interval the player &# 39 ; s new position and / or velocity and / or acceleration and / or power and dynamic reactive cutting . k ) the system provides real time numerical and graphical feedback of the calculations of part j . it should be noted that these motor - related components of sports performance and fitness are equally important to safety , success and / or productivity in demanding work environments , leisure sports , and many activities of daily living . the surgeon general &# 39 ; s report on physical activity and health defined physical fitness as &# 34 ; an ability to carry out daily tasks with vigor and alertness , without undue fatigue , and with ample energy to enjoy leisure - time pursuits and to meet unforeseen emergencies .&# 34 ; the report further defined physical fitness by performance and health related attributes . the performance - related components are often characterized as either the sport - specific , functional , skill or motor - related components of physical fitness . these performance - related components are obviously essential for safety and success in both competitive athletics and vigorous leisure sports activities . it should be equally obvious that they are also essential for safety and productive efficiency in demanding physical work activities and unavoidably hazardous work environments such as police , fire and military -- as well as for maintaining independence for an aging population through enhanced mobility and movement skills .