Challenges in Virtual Reality Exergame Design

Lindsay Alexander Shaw1 Burkhard Claus Wunsche1 Christof Lutteroth1

Stefan Marks2 Rodolphe Callies3

1 Department of Computer ScienceUniversity of Auckland, Auckland, New Zealand

Email: lsha074@aucklanduni.ac.nz, burkhard@cs.auckland.ac.nz, lutteroth@auckland.ac.nz

2 Colab, Faculty of Design and Creative TechnologiesAUT University, Auckland, New Zealand,

Email: stefan.marks@aut.ac.nz

3 Ensicaen, Caen, FranceEmail: rodolphe.callies@hotmail.fr

Abstract

Exercise video games have become increasingly pop-ular due to their potential as tools to increase usermotivation to exercise. In recent years we have seenan emergence of consumer level interface devices suit-able for use in gaming. While past research has indi-cated that immersion is a factor in exergame effective-ness, there has been little research investigating theuse of immersive interface technologies such as headmounted displays for use in exergames.

In this paper we identify and discuss five major de-sign challenges associated with the use of immersivetechnologies in exergaming: motion sickness causedby sensory disconnect when using a head mounteddisplay, reliable bodily motion tracking controls, thehealth and safety concerns of exercising when usingimmersive technologies, the selection of an appropri-ate player perspective, and physical feedback latency.We demonstrate a prototype exergame utilising sev-eral affordable immersive gaming devices as a casestudy in overcoming these challenges. The results ofa user study we conducted found that our prototypegame was largely successful in overcoming these chal-lenges, although further work would lead to improve-ment and we were able to identify further issues asso-ciated with the use of a head mounted display duringexercise.

Keywords: exergame, motion tracking, head-mounteddisplay

1 Introduction

In recent years a number of virtual and augmentedreality technologies have become commercially avail-able. Head-mounted displays such as the OculusRift and motion tracking tools such as the MicrosoftKinect or Playstation Camera are widely available ata reasonable price. Many games have been developedto take advantages of these newly available technolo-gies, and some work has been done around combin-ing motion tracking and head-mounted displays, butno work has been done combining these technologies

Copyright c©2015, Australian Computer Society, Inc. This pa-per appeared at the Sixteenth Australasian User Interface Con-ference (AUIC 2015), Sydney, Australia. Conferences in Re-search and Practice in Information Technology (CRPIT), Vol.162. Stefan Marks and Rachel Blagojevic, Eds. Reproductionfor academic, not-for-profit purposes permitted provided thistext is included.

to create an immersive exergame based entirely on abodily interface.

Whilst these new technologies show a lot of po-tential for the creation of immersive exergames, theyalso bring with them a number of challenges. Wehave identified the following five major challenges as-sociated with the use of immersive technologies in ex-ergaming. Firstly, careless game design when using ahead-mounted display is likely to cause motion sick-ness (Merhi et al. 2007). This may be due to sen-sory disconnect, or cue conflict (Reason 1978, Duhet al. 2004). Secondly, when using motion controls ina game, these motion controls need to be accurate,otherwise they will lead to frustration for the player(Kiili & Merilampi 2010, Hernandez et al. 2012). Thethird challenge lies in selecting an appropriate viewfor the player based on the display technology beingused. The fourth challenge is the collection of healthand safety risks associated with the use of bodily mo-tion controls and head-mounted displays during highintensity exercise. The fifth challenge we identifiedduring user testing of our exergame prototype, and isthe issue of feedback latency. When an exergame isgiving sensory feedback to the user, it is importantthat this feedback occurs with minimal delay.

In this paper, we discuss these challenges and theirpotential solutions, and show a prototype exergamewe developed as a case study in overcoming thesechallenges. The results with respect to the efficacyof this prototype as an exercise motivational tool fol-lowing our user study are discussed in another paper(Shaw et al. 2015). Section 2 reviews relevant researchon virtual reality interaction and immersive exergamedesigns. Section 3 presents a brief summary of the de-sign and implementation of our case study exergame.Section 4 discusses the major challenges we identifiedin virtual reality exergame design, talks about thesteps we took to overcome these challenges, and eval-uates the effectiveness of these steps in light of howour prototype performed during our user study. Weconclude our research in Section 5 and identify someareas suitable for further research.

2 Related Work

Reviewing related literature led to the identificationof several potential challenges in VR exergaming.One challenge associated with VR is simulator sick-ness, discussed in several papers. Kolasinski (1995)offers a thorough evaluation of the potential causesand factors associated with motion sickness in vir-

tual reality environments. The paper identifies fac-tors that may be associated with motion sickness anddivides them into three categories. The first cate-gory is subject factors, which are characteristics ofthe individual using the simulator such as age andsimulation experience which may predispose them tomotion sickness. The second category is simulatorfactors, characteristics of the simulation mechanismsuch as poor calibration or framerate which make itmore likely to cause motion sickness. The third cate-gory is task factors, characteristics of the specific vir-tual environment and task such as duration and theuser’s degree of control which may make it more likelyto cause motion sickness. The design of an immersivevirtual reality exergame should take into considera-tion these factors, in particular the simulation andtask factors.

Moss & Muth (2011) also examine simulator sick-ness. Their work is particularly relevant due to itsfocus on head-mounted displays. In our work weare using a head mounted display to provide an im-mersive experience to the user. The paper examineshow various conditions including update delay, im-age scale factor, and peripheral vision affect the in-cidence of motion sickness among individuals usinghead-mounted displays. While many of the findingsare mainly applicable for the design of head-mounteddisplay hardware, it shows consistent results with pre-vious research both in theories of cue conflicts leadingto motion sickness (Reason 1978, Duh et al. 2004),and in postural instability leading to motion sick-ness (Riccio & Stoffregen 1991, Stoffregen & Smart Jr1998).

The paper “Design of an Exergaming Station forChildren with Cerebral Palsy”, by Hernandez et al.(2012) is one of the few past works that exam-ines human-computer-interaction considerations inexergaming. This paper is similar to our paper, inthat it discusses challenges in the design of an ex-ergaming system. However, the particular challengesthis paper examines are those associated with the lim-itations caused by cerebral palsy, for example the ne-cessity of providing proper support for a user who maynot be able to support themselves. In this paper, theauthors design and evaluate an exercycle gaming de-vice to be used by children who suffer from cerebralpalsy, as well as some simple exergames using thisdevice. Whilst the findings of this paper are mostlyapplicable to designing for users suffering from cere-bral palsy, its examination of pedalling input methodsis interesting. It found that any disconnect or latencybetween changes to the player’s pedalling speed andthe reflection of that speed in game was quickly no-ticed and disliked by the players, even when the dis-connect appeared to make the game easier.

Sinclair et al. (2007) also discuss interaction con-siderations for exergame design. Unlike our work, thispaper evaluates several existing commercial exergam-ing products and motion control systems, and dis-cusses the psychological, exercise, and interface fac-tors that affect an exergame. Of interest is the exam-ination of interface factors. The authors state thatthe player should be able to focus on a narrow fieldof attention, either the game being played or the in-put device being used. As an example, they iden-tify the frequency of exercise bikes being used as theprimary input device, where the user is stable andthus able to focus on the game instead of the device.They also point out a two similar devices with differ-ent success levels, Dance Dance Revolution and theNintendo Power Pad. In Dance Dance Revolution,the game provides simple visual information, allow-ing the players to focus on their input. The Nintendo

Power Pad is a similar device, but with more elabo-rate games requiring a split in the player’s attention,which the authors suggest may have led to it beingless successful.

Some attempts have been made to investigate theeffects of immersion in exergames. Mokka et al.(2003) developed an exergame using immersive tech-niques to attempt to provide a more motivating ex-perience. For this paper, the authors produced anexergame similar in many design aspects to our pro-totype. The game involved using an exercise bike tonavigate a 3D virtual environment containing a cy-cle track, with the goal of completing the track ina suitable time. The game provided realistic soundssuitable to the scene, and the resistance of the exer-cise bike changed with the gradient of the terrain; ifthe terrain was an uphill slope, the resistance wouldincrease, and vice versa. A pilot study was conductedand found that whilst use of the immersive game wasa pleasant experience, it still felt like exercise, ratherthan gaming. It should be noted that this study wassomewhat limited, containing only nine participants,none of whom played video games regularly.

The work of Mestre et al. (2011) also looks at therelationship between immersion in exergames and thegeneral experience of exercise. Using gaze tracking,the authors found that sensory stimulation such asthat provided by an exergame distracted participantsfrom the exercise, and thus improved their perfor-mance and enjoyment. This study was somewhatlacking in that the participants had no meaningfulcontrol over the virtual environment; they were onlyable to control the speed at which a video of a cyclingperspective played, by changing the speed at whichthey pedalled.

Kiili & Merilampi (2010) investigate the use ofsimple, accelerometer driven exergames as tools tomotivate exercise in children. Similarly to our work,their goal is to determine optimal design factors forexergames. However, some of the games in this studyinvolve activity that may have reduced the immer-sion experienced by the participants. These gamesuse exercise that did not have a relation to the ac-tivity occurring in the game; for example, users per-form squats as exercise in order to pull a rope in atug of war game. The participants in the study re-portedly showed less interest these games than in theones with a better mapping between bodily motionand game activity. The participants in this study alsohad a negative reaction to delays between their phys-ical activity and the result in the game and showeda desire for motion control to be accurate. This sug-gests that a close mapping between user’s motion andgame actions in a virtual reality environment is highlyimportant.

Previous research has touched on HCI design chal-lenges in exergames and the challenges of using im-mersive virtual reality technologies. However therehas been no detailed evaluation of these design chal-lenges or guidelines on how to overcome them.

3 Case Study of an Exercycle Game

3.1 Design

We constructed an exergame as a case study for de-signing around the challenges associated with virtualreality exergaming. The primary requirement for thedesign of our exergame was that it be suitable formoderate to high intensity exercise for extended pe-riods of time.

In our game, the user cycles on an exercise bike

in order to move their virtual representation along atrack. The track contains obstacles such as pits whichthe user attempts to avoid by moving their body inorder to control their position in game. The speed atwhich the user moves in game depends on the speedat which they are cycling.

The objective of the game is to achieve the max-imum score within a predetermined time (dependingon player preferences or intended health objectives).The rate at which the player’s score increases dependson the speed at which they are pedalling, and upontheir ability to secure often difficult to obtain bonuses.The player starts the game with a certain number oflives, which may be depleted by failing to avoid pits inthe track, or by being knocked off the track by shotsfrom cannons positioned to the sides of the track. Thenumber of lives may be increased by collecting bonuslives available in the game environment. When theplayer loses a life, the game places them back at apoint just before the location where the life was lost.

The game environment is a semi-linear track sus-pended above water. The entire game environmentis procedurally generated, allowing it to be poten-tially infinite in length, and guaranteeing that no twoplay sessions will be identical. The game environmentcontains obstacles that may be avoided using simplemotion controls: pits and barriers on the track itself,and cannons beside the track that fire at the player.It also contains various bonuses, such as additionallives, extra points, and boosts that temporarily setthe resistance of the exercise bike to the minimumlevel.

3.2 Implementation

The exergame was written using the Unity game en-gine, version 3.5.7. The Unity game engine was cho-sen based on its ability to interface with a broadrange of devices, the quality of its documentation,and its ability to handle procedural content genera-tion. Game objects were developed using the Blendermodelling tools and Unity’s built in primitives. Someof Unity’s standard asset packages (e.g. water, parti-cle effects) were also used.

Our exergame interfaces with a LifeFitness 95CIUpright Exercise Bike, shown in Figure 1. We hadtwo requirements for interfacing with the bike, firstlythat we were able to retrieve from the bike informa-tion about the speed at which the user was pedalling.The second requirement was that we were able to con-trol the resistance of the bike in order to create im-mersion by having the difficulty of pedalling reflectcircumstances within the game (e.g. pedalling diffi-culty increasing as the user attempts to travel up aslope).

For the first requirement, we were able to readexercise data using the bike’s Communications Spec-ification for Fitness Equipment (CSAFE) port. Thisprovides serial communication between the bike anda computer, and specifies a set of commands to whichthe bike will respond. Through this we were able toretrieve a number of useful pieces of information, in-cluding the user’s speed and heart rate.

Whilst CSAFE offers commands for adjusting theresistance and/or incline of exercise equipment, the95CI exercise bike does not support those commands.In order to get around this problem, we used an Ar-duino micro-controller to electronically trigger pressesof the bike’s manual resistance buttons. The ex-ergame maintains a serial connection with the Ar-duino, and whenever it determines that the resistanceshould change, it sends the updated resistance level

to the Arduino. The Arduino then determines the re-quired number of button presses to reach that desiredresistance and begins pressing the buttons. Whilstthis does fulfil our requirement, it suffers from a lackof speed. The minimum interval at which the bikecan recognise subsequent button presses is approxi-mately 160 milliseconds. This means that it can takeseveral seconds for the bike to go from one extremeof resistance to the other.

Due to the required delay when adjusting the resis-tance level of the exercise bike, it is possible for thecomputer to send adjustments to the desired resis-tance level at a higher rate than can be processed. Inorder to keep the actual resistance level synchronisedwith the desired resistance level as much as possible,the Arduino discards all input except for the most re-cent in each cycle. This means that it will always beadjusting the resistance to the current desired level,rather than to a previously queued one.

Figure 1: Exercycle game hardware setup.

We placed the Kinect 2 metres to the right of theuser, and 1.6 metres above the ground (the approx-imate height of the user’s head when seated on thebike). Figure 2 shows the approximate arrangementof devices. We found it advantageous to place theKinect to the side of the user rather than in front ofthe user, as it was able to track them equally wellfrom the side whilst our equipment setup would in-terfere with its ability to detect the user when placedin front of them.

The Kinect did initially have some issues with theOculus Rift in that the Kinect operates at exactlythirty frames per second, but that low framerate cancause motion sickness related discomfort when usinga head-mounted display (Kolasinski 1995). However,this problem was solved by moving the Kinect oper-ations into a separate thread that did not affect theoverall framerate of the game.

4 HCI Challenges

4.1 Motion Sickness due to Sensory Discon-nect

Past work has indicated that video games presentedon a head-mounted display can induce motion sick-ness (Merhi et al. 2007, Moss & Muth 2011). Oneof the theories which may explain this is cue conflict,where different senses give conflicting reports about

Figure 2: Arrangement of Devices

the body’s motion, inducing sickness (Reason 1978,Duh et al. 2004). Motion sickness is highly unde-sirable in an exercise game, thus we endeavoured todesign the game to minimise the likelihood of it oc-curring.

In our early testing, we detected the user leaningleft and right on the exercise bike, and mapped thisleaning to turning left and right in the game. Whilstthis was reasonably straightforward when the gamewas presented on a screen, we found that when thegame was presented on a head-mounted display thiswas counter-intuitive and caused motion sickness re-lated discomfort. We found better results with theuser’s bodily motion mapped to sideways travel. Be-cause of this, we designed the game environment insuch as way as to not require turning, but only linearmotion on any axis. The track proceeds in a specificdirection, and the user’s bodily motion causes theirrepresentation to move to either side of the track.

In order to minimise cue conflicts, we closely mapthe position of the user’s head as detected by theKinect to the position of the game camera. As theuser moves their head to the left, the camera alsomoves to the left, and vice versa.

Our exergame prototype was reasonably effectivein preventing motion sickness through sensory discon-nect. The incidence of motion sickness in our studywas relatively low, likely in part to our use of theKinect to track the user’s head position and updatethe camera position accordingly, thus reducing po-tential sensory mismatch. However, there were somecircumstances where motion sickness related discom-fort did arise. When cycling down ramps or fallingdown pits while wearing the Oculus Rift, several par-ticipants commented on an uncomfortable feeling ofthe bike pitching forwards. We believe that this wasa case of sensory mismatch similar to that identifiedin past works (Reason 1978, Duh et al. 2004), whereconflicting information was being received: the visualsystem indicates that the body is travelling downhill,whilst the vestibular system indicates that the bodyis on a level surface. Of interest is the fact that thiswas only mentioned when moving down, not up. Thismay be because the user feels in control when movingupwards; when moving upwards their motion deceler-ates, in contrast to the acceleration experienced whenmoving downwards as the game included no capacityfor braking one’s motion. Our results on motion sick-ness related discomfort suggest that future designs offully immersive exergames should work to minimise

cue conflicts that may arise, either by avoiding suchtriggering scenarios in the game itself (for example:using artificial boosts rather than slopes), or by util-ising technology that allows for vestibular feedback.

We conducted a minor secondary study using ourexergame to look specifically at motion sickness whilewearing a head-mounted display. In this secondarystudy, participants were instructed to use the gamefor 20 minutes or until they felt sick. During thisstudy, several participants felt some initial discom-fort, but as their session progressed they were able toovercome it and only one participant was unable tocomplete the full 20 minutes, stopping after 2 min-utes due to severe nausea. Our findings of partici-pants who suffered only minor discomfort becomingfamiliar with the virtual environment and no longersuffering discomfort are consistent with past research(Kolasinski 1995).

4.2 Motion Tracking

When using bodily motion controls, past research hasindicated that it is important that these motion con-trols are accurate (Kiili & Merilampi 2010, Hernan-dez et al. 2012). Because of this, we found it neces-sary to evaluate several methods of motion trackingfor their accuracy and suitability for use in our ex-ergame. We required that the tracking method beable to identify to which side and approximately howfar the user was leaning. Ideally, the tracking methodshould also be able to identify motion in a second di-mension. We allowed for small amounts of interfer-ence on the grounds that our game should be able tofilter it out. We evaluated four different methods oftracking the user’s head position: Optical Flow, HaarCascades, FaceAPI, and the Microsoft Kinect. Thesefour methods were evaluated on five criteria items:

1. What portion of the time is the tracking methodable to track the user’s movements?

2. In how many dimensions can the user’s move-ments be tracked?

3. How prone is the tracking method to interfer-ence?

4. How easily can the tracking method be inte-grated with the game in Unity?

5. Will use of a head-mounted display, in particu-lar the Oculus Rift, interfere with the method’sability to track the user?

4.2.1 Optical Flow

The first method, Optical Flow, was tested usingthe OpenCV implementation of the Block Matchingand Lucas-Kanaade algorithms. The video stream onwhich these algorithms was applied was sourced froma standard web camera placed in front of the useron the exercise bike. The vector map generated bythe optical flow process was examined to determinethe centre of the movement. Based on where in theimage the centre of movement fell, the user’s currentposition (and therefore movement) was determined.

Evaluating optical flow against the criteria givenabove, optical flow picked up all movement. However,because it produced regions of movement, it was dif-ficult to reliably identify movement other than fromside to side, meaning that the tracking was essentiallyone dimensional. Optical flow was extremely prone tointerference. Every time the camera settings changed(for example, adjusting to handle a changed light level

in the room as someone out of view passes in front of awindow), the entire image would show movement fora few frames, any motion in the background wouldcause interference, and certain materials showed mo-tion at all times (a user wearing a red woollen jerseyshowed constant movement in the torso area). Opti-cal flow is not natively supported by Unity, but thecreation of a plugin or data streaming tool to allowit to work with Unity is not a complicated process.Because optical flow works just by detecting areas ofmovement, rather than attempting to identify spe-cific features, a user wearing an Oculus Rift (or otherheadgear) is not a problem.

4.2.2 FaceAPI

The second method, FaceAPI provided by SeeingMa-chines proved to be quite effective. Again, the imagesource for this method was a standard web cameraplaced in front of the user. With the web cameraplaced at the necessary range for use with the exercisebike, it did have some difficulty initially detecting theface, though once a face had been identified, it couldtrack it reliably and with high accuracy. However,if a user’s head was turned too far (roughly 60 de-grees) to either side, it would often stop recognisingthe face. FaceAPI was effective at tracking the face inthree dimensions, and was able to provide both posi-tion and orientation data. Generally speaking, it wasnot prone to interference; whilst it might sometimesswitch to tracking another face that entered the cam-era’s field of view at an appropriate range, other facesentering the field of view is something that is easyto control in test conditions. FaceAPI had no unityintegration, and while tools exist for that purpose,they do not work with the currently available version.Again, the creation of a plugin or data streaming toolwould be necessary to make it work with Unity orother game engines. Unfortunately, because FaceAPIis based on detecting facial features, wearing some-thing that obscures a significant portion of the face,such as the Oculus Rift, causes it to stop tracking theuser.

4.2.3 Haar Cascades

The third method, face detection with Haar Cascades,used the OpenCV implementation of the Viola-Jonesobject detection framework (Viola & Jones 2001).Again, the image source for this method was a stan-dard web camera placed in front of the user. Atclose range, this method provided fairly good facialdetection, picking up the user’s face in the majorityof frames (90%). At the range the camera was set upwith the bike, however, it proved less effective, be-ing only able to detect the user’s face approximately50% of the time. Additionally, as the face’s orienta-tion skewed, face detection became less reliable. Be-cause tracking was based on the position of the user’sface in the camera image, this method was able toeffectively track in two dimensions. Some three di-mensional information was also available. Based onthe size of the face detected a rough approximationof depth was possible, but it was insufficiently accu-rate to be useful. This method was prone to someinterference, as a number of faces would be incor-rectly detected in the background. However, filteringout these false positives is generally straightforwardbased on the assumptions that initially a prominentface will be detected near to the centre of the image.From that point forward, there will be a prominentface not far from the location of the primary face ofthe previous frame. Like the previous two methods,

this method is not natively supported by Unity, butthe creation of a plugin or data streamer to providethe information is not difficult.

Like FaceAPI, because this method is based onrecognising a face, wearing the Oculus Rift interfereswith detection. However, this method is able to usealternative data sets as a basis for the feature detec-tion. Using a mouth detection data set (the mouthnot being covered by the Oculus Rift) this methodwas still able to track the user’s face with about 75%accuracy even when wearing the Oculus Rift.

4.2.4 Kinect

The fourth method, skeleton detection using the Mi-crosoft Kinect, used a standard Xbox model Kinectplaced to the side of the user on the bike. Thismethod suffers from the limitation that the Kinectmust be placed at a distance of approximately twometres from the user, as nearer than that the Kinect’sability to identify a person becomes unreliable. TheKinect proved extremely reliable in tracking the user’sposition, although it did require initial calibration tomap its skeletal model to the user. However, afterthis initial calibration, it was able to track the user’shead almost 100% of the time. The Kinect was able toprovide accurate tracking information in three dimen-sions, regardless of the orientation of the user’s head.The Kinect was largely not prone to interference, al-though if someone stood in the middle of its field ofview in such a way that their image in the depthmap was more clearly a person, it would occasionallyswitch to tracking them. Integration with Unity forthe Kinect is straightforward, as Kinect plugins anddocumentation for Unity already exist. As the Kinectdoes not require facial recognition, but rather detectshuman shapes, some types of headgear, including theOculus Rift, do not interfere with its ability to trackusers (although some things such as long thick hairor a headscarf, that make the neck less distinct fromthe head, do make it slightly less reliable at the initialdetection of the head).

Based on the relative accuracy and reliability ofthe four methods we evaluated, we chose to use theKinect. While performing the initial testing and eval-uation of tracking methods, the Kinect proved highlyaccurate with its tracking. However, when conduct-ing a user study on the full game, where the gamewas exposed to a greater range of body types, theKinect’s position did need to be adjusted in order totrack the tallest of participants. However, if therehad been space to position the Kinect further fromthe bike, the greater field of view may have meantthat this would not have been a problem.

Overall, our prototype was good for providing re-sponsive motion controls. The controls were accu-rate and consistent, with the Kinect effectively pick-ing up all of the user’s motion. Nonetheless, the re-sponsiveness of the motion controls was still the sub-ject of some feedback similar to that found by Kiili &Merilampi (2010), particularly when using the Ocu-lus Rift. When a user leans to the side, their motionfirst removes any momentum in the opposite direc-tion, before adding momentum to their desired direc-tion. Thus if users are travelling in one direction, achange of direction may take a second to occur. Thiswas not a major problem when testing the game us-ing a traditional monitor as display, since the thirdperson view of the avatar indicated how the body mo-tion effected the characters pose and cycle direction.However, some participants who played the exergameusing the Oculus Rift prior to playing it on a mon-itor gave negative feedback about the controls. The

exergame might be improved by using instantaneousmovement responses, rather than a momentum basedapproach. Unlike side to side motion, ducking wasimmediately responsive, but the margin of error onducking under overhead beams was very narrow, andsome participants took some time to learn to ducklow enough. We believe that this indicates that fullbody motion controls should be both responsive andforgiving.

4.3 Exercise Health and Safety Considera-tions

When designing an exergame it is important to in-clude the capacity for a warm-up. Past research hasshown conflicting results on the benefits of warmingup, with some studies failing to find a definite ben-efit (De Bruyn-Prevost 1980, Genovely & Stamford1982), and others showing potential physiological andpsychological benefits (Shellock & Prentice 1985). AsGenovely & Stamford (1982) mention that for psy-chological reasons such as fear of injury, participantsmay not exercise at their full capability if not able towarm up, it seems sensible to include a warm-up aspart of the exercise, whether or not it offers concretebenefits.

There are two reasons to include a warm-up aspart of the exergame, rather than encouraging usersto do one beforehand. The first is to ensure that theusers do actually complete a warm-up. The secondis to ensure that the warm-up uses the same musclesas the actual exercise. Shellock and Prentice foundthat a warm-up that uses the same muscles in thesame manner as the exercise to follow offers betterperformance improvements than a passive warm-up(Shellock & Prentice 1985). Our exergame includesa warm-up in the form of a tutorial area. In thistutorial area, the gameplay is the same as the mainportion of the game, but the exercise requirements areundemanding in order to provide a suitable warm-up,and the game elements are introduced slowly one byone in order to allow the user to familiarise themselveswith them at low risk.

A secondary health and safety concern with an ex-ergame utilising immersive virtual reality technologiesis the presence of the cables attached to the variousdevices, in particular the cable attached to the head-mounted display. Should the user catch themselvesin a cable while exercising it would be possible forthem to be injured. In order to minimise the risk ofsuch injuries we maintain a metre clearance aroundthe sides of the exercise bike, and run all cables outover the front of it. This keeps the cables away fromthe moving areas of the user’s body. Ideally, we wouldalso be using a wireless head-mounted display.

Another concern associated with the use of a head-mounted display is the increased risk of the userfalling off the exercycle while wearing the display. Inaddition to the fact that the user is blind to theirsurroundings, some research has indicated that vi-sual conflicts (such as the cue conflicts that may arisewhen using a head-mounted display) may lead to bal-ance related issues such as postural instability anddisequilibrium (Redfern et al. 2001). This means thatwhile exergaming with a head-mounted display, theuser should be positioned such that there is little riskof them losing their balance. Past work has also in-dicated that having something to hold may assist inreducing the incidence of motion sickness (Moss &Muth 2011). From a practical perspective, when us-ing an upright bike the user should always have bothhands on the handlebars, and care should be takenbefore utilising a hand held controller. We chose to

use bodily motion and exercise intensity for all con-trols in our game, allowing the user to keep hold ofthe exercise bike’s handlebars at all times.

Based on events during our user study, the designof our exergame proved to be moderately effectivefrom a health and safety perspective. Our design waseffective at handling the concerns we identified earlierin the paper; none of the participants lost their bal-ance and fell off the bike, and nobody caught them-selves on a wire. However, our design created one riskwhich we believe requires mitigation. The game envi-ronment contains overhead obstacles which the usermust duck to pass underneath. This was not an issuewhen the game was displayed on a screen in front ofthe user, but when wearing the Oculus Rift the userswere no longer able to see the exercise bike, and sev-eral came close to banging their faces on the bike’sdisplay when lowering their heads. This issue shouldbe mitigated simply by making obstacles of that na-ture forgiving, allowing the player to pass with onlya mild ducking motion.

4.4 Appropriate Player View

Figure 3: View of the game on a standard monitor.

The manner in which the player sees the game de-pends on how the game is displayed. When playingthe game on a monitor, the game is displayed using athird-person perspective, with the player representedas two spheres as shown in figure 3. The lower sphereis the body position, showing where the user sits inthe game environment for the purposes of interactionwith parts of the environment. The upper sphere re-flects the user’s head position, as they lean from sideto side the upper sphere moves relative to the lowersphere to reflect this. Figure 3 shows that the player isleaning slightly to the right. When playing the gameusing the Oculus Rift, the game is displayed using afirst-person perspective, as shown in figure 4.

Figure 4: View of the game as shown in the OculusRift.

The first person perspective is ideal from an im-mersion standpoint, and is appropriate for use withthe Oculus Rift as the camera orientation is mappedto the orientation of the user’s head as sensed by theOculus Rift. When not using the Oculus Rift how-ever, the game better suits a third person perspective,as the user lacks the ability to control the camera.Early testing found it difficult to avoid obstacles inthe first person perspective due to the limited field ofview.

During our user study, participants were easilyable to understand the representation of the game infirst and third person perspectives on the screen andOculus Rift respectively, even after playing one ver-sion and then switching to the other. We believe thatchoosing an easily understood view system is veryhelpful in reducing the number of things a player mustfocus on, which has been identified as an importantconsideration for exergaming design (Sinclair et al.2007).

4.5 Feedback Latency

Similar to how it is important that motion controlsbe responsive, we found that it is important that sen-sory feedback from the game is immediate. When anevent occurs in the exergame, the associated feedbackresponse should occur right away. We discovered thisin user testing due to the implementation of our re-sistance feedback.

Due to the fact that we were unable to directlycontrol the resistance of the bike via the bike’sCSAFE port, we adjust the resistance on the bikeby electronically triggering presses of its resistancebuttons with the Arduino. The minimum interval atwhich the bike can recognise and process subsequentbutton presses is approximately 160 milliseconds. Be-cause the exercise bike offers 25 resistance levels, thismeans that it can take several of seconds for the biketo go from one extreme of resistance to the other.During user testing quite a few of our participantsnoticed this fact, with several exhibiting confusion orfrustration at the delay. When the resistance beganto change, they might not notice the first few levelsof change, and thus by the time they did notice thealtered resistance, there was a disassociation betweenthe game event and the response. While we were ableto mitigate some of the delays in resistance changesby making sure we were always adjusting to the mostrecent desired resistance level, given the limitationsof our hardware it might be advisable to adjust thegame design such that it does not require sudden sig-nificant resistance changes.

4.6 Exercise Related Issues

During our user study, we found some additional is-sues with the use of a head-mounted display for an ex-ergame. The level of exercise encouraged by the gamewas of moderate to high intensity, and the increasedbody temperature and sweating of the participantscaused some issues. The lenses on the Oculus Riftfogged up on several occasions, causing the game tobecome difficult to see, particularly when combinedwith the relatively low resolution of the Oculus Riftmodel we were using. This issue will likely be par-tially mitigated by future models having a higher res-olution, but the fogging issue is harder to solve, poten-tially requiring customization of the hardware for thepurposes of exercise. Furthermore, due to the OculusRift having padding pressed against the user’s face,there is the potential hygiene concern of this paddingabsorbing sweat from the user.

5 Conclusion

We have identified five important challenges to beconsidered when using immersive virtual reality tech-nologies in exergaming, and presented methods forovercoming these challenges. We have evaluated fourcommon approaches to tracking the motion of an in-dividual’s head and found that for exergaming pur-poses, this is best accomplished with the use of gam-ing hardware such as the Kinect, as this techniqueproved to be both the most accurate and the mostpowerful.

As a case study, we have presented a novel ex-ergame utilising several interesting technologies. Themethods of interaction with the game: exercise in-put and bodily motion control, proved intuitive andimmersive as well as motivating and enjoyable. Ourwork has demonstrated the potential of easily avail-able hardware for use in virtual reality exergames andwe believe our lessons learned provide useful guide-lines for other developers of exergames using similartechnologies.

5.1 Future Work

There are a number of areas of potential interestfor further investigation into the ideal design of im-mersive virtual reality exergames. In particular, theprevention of motion sickness while using a head-mounted display in exercise is worth further research.Our work has identified a number of ways by whichthe incidence of motion sickness may be reduced, inparticular by eliminating cue conflicts, but we havenot addressed other theories as to the cause of mo-tion sickness, such as postural instability (Riccio &Stoffregen 1991, Stoffregen & Smart Jr 1998), otherthan by designing our case study exergame to allowthe users to hold on to the bike.

The motion tracking used by our game was rela-tively simple, merely the detection of the user’s headposition. However, the tracking method we chose of-fers significantly more potential: the Kinect’s skeletaltracking system can track the user’s entire body. Wefound that the presence of the exercise bike or otherexercise equipment interfered with the Kinect’s abil-ity to track the user’s body by introducing non-bodilyrelated data at similar depth values to the user’s body,but we believe that this issue can be overcome to allowfor the creation of exergames utilising motion controlsbased on the user’s entire body.

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