Collaborative Digital Sports Systems
that Encourage Exercise
Ayaka Sato1, Anna Yokokubo2, Itiro Siio2 , Jun Rekimoto1,3
1

The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan,
2
Ochanomizu University, 3 Sony Computer Science Laboratories.

ayakasato@acm.org, anna.yokokubo@is.ocha.ac.jp, siio@acm.org,
rekimoto@acm.org

Abstract. Although the importance of health and exercising as a way tomaintain fitness and physical wellbeing is widely recognized, it is often difficultfor people to persist with a regular workout schedule. In this paper, we propose
a solution to this problem through “Collaborative Digital Sports.” This is adigital sports environment where participants are given a shared goal. Throughthe use of body motion sensors and video projection feedback, this environment
works as a fitness playground that requires physical movements by participants.
This environment is adaptable to the fitness levels of the participants, as its
sensor-feedback loop is digital and unencumbered by real sports equipment.
Based on this concept, we designed and implemented two collaborative digital
sporting activities. The “Group Jump Rope Orchestra” is a simulated jump rope
environment where people are required to synchronize jumping over a projectedrope as it periodically swings by. The “How Many Legged Race!?” is avariation of the three-legged race that can accommodate any number ofparticipants as they synchronize their steps. We tested these sports
environments with numerous participants and discovered that the cooperative
nature of these digital sports helps motivate the players and fosters a sharedsense of caring among them.

1

Introduction

Fitness is an effective exercise to maintain and enhance health. However, exercisingalone can be tedious and demotivating, and hence difficult to continue with on aregular basis. In contrast, competitive team sports, such as soccer and basketball,demand that each player exhibit responsibility and make a serious effort. However,players need a certain degree of training and skill in order to enjoy sports.
We thus propose “Collaborative Digital Sports,” an environment that aims to keep
users motivated to exercise. This environment effectively combines digital technology
with the social aspect of team sports to enable users to stay motivated to work out,
and also nurtures camaraderie among them. In this paper, we describe two instancesof collaborative digital sports systems and report on feedback from the participants.

2

Collaborative Digital Sports

We define Collaborative Digital Sports as composed of the following three elements:
1. Encourages collaboration among participants
A collaborative sport is a competitive physical activity that requires that all
participants work together. The collaborative element encourages participants to makean effort, stay committed to the activity and not give up because they are part of ateam.
2. Easy to play
Complicated rules make it difficult for people to participate in any activity. We have
kept the rules of the sports and the required movements simple, so that anyone canplay.
3. Adaptable
In order to keep participants motivated, we make use of digital technology so that theparameters of the sports – the skill level of the sport, the number of participants, etc. –can easily be adapted to the situation. We believe that this flexibility in the design ofour digital sports prevents participants from abandoning the activity on account ofboredom or lack of skill, and also enhances their enjoyment.
We have implemented two examples of collaborative digital sports systems inaccordance with the aforementioned elements. The first sport is “The Group Jump
Rope Orchestra”, which is modeled on the game jump rope and orchestral music. The
second sport is “How many legged races!?”, which is a variation of the well-known
three-legged race. Both sports involve teamwork.

3

Example 1: Group Jump Rope Orchestra

Group Jump Rope Orchestra is a collaborative digital sport system that is a mixture of
the game jump rope and the dynamics of an orchestra. In this sport, the participants
jump over a virtual rope that is projected onto two screens, one on the floor under theparticipants’ feet and the other on the wall, as shown in Fig.1. Their collective activity
causes orchestral music to play.

Fig. 1. The Group Jump Rope system. A virtual rope is projected on two screens at the front
and the floor. Participants jump when the rope passes under their feet.

Elements of Group Jump Rope. Group Jump Rope is a sport that involves twoplayers holding a long rope and swinging it together, and any number of players in
between them trying to jump over the rope so that it passes under their feet and overtheir heads. The game becomes more challenging as the number of players increases.
In order to succeed at it, all participants have to adapt to a shared pace and rhythm.
This instills a sense of unity and collective satisfaction in them.

Orchestral Elements. An orchestra consists of a large group of musicians playing
different instruments. The music becomes grander as the number of musicians andinstruments increases. In order to sound harmonious, all musicians need to play theirrespective parts in accordance with the directions of the conductor.
The first of our two digital sports combines the elements of Group Jump Rope andan orchestra.
3.1

System Configuration

The system consists of two screens, two projectors, pressure sensors embedded infoot-shaped sponges, two speakers, phidgets (USB I/O module), and a PC (Fig.2).
Two animations are projected on two screens, one each on the floor under the players’
feet and on the wall facing them. The front screen shows a girl swinging a rope, while
the image of a rope swinging in correspondence with the movement of the girl’s arm
is projected on the screen on the floor. The pressure sensors embedded in the foot-shaped sponges on the screen on the floor detect whether the participants are jumping
at the right time. The sensors are connected to the phidgets1 and the PC, which
produce relevant animations and sounds. The PC – a MacBook Pro – runs the Adobe
Flash Builder software.

Fig. 2. System configuration for Group Jump Rope Orchestra.

3.2

Usage and Feedback

The virtual rope makes a sound as it “brushes” the floor, at which time the players aresupposed to jump over it. When one player jumps at the correct time and avoids therope, the sound of one orchestral instrument – a violin, say – is played. When anotherplayer does the same, the sound of another instrument is played. When all players
jump at the correct time, all instruments in an orchestra are played. A new participant
can join the game at any time. Pictures of the musical instruments being played areprojected onto the front screen according to the number of players and the instrument“played” by each player (Fig.3-1). If a player fails to clear the virtual rope, the music
stops, a discordant sound is played and the animation changes as shown in Fig.3-2. If
the participants manage to play an entire piece of music, the sound of applause isplayed and the animation changes, as in Fig.3-3.
Participants of the Group Jump Rope Orchestra system have a variety of musicalcompositions and animations to choose from. The speed of the rope can also be
adjusted.
1

Phidgets: http://www.phidgets.com/

Fig. 3. The front screen animations: (1) Pictures of musical instruments appear according to thenumber and the role of the participants. (2) When someone fails to clear the rope, the music
stops, a discordant sound is played and the animation changes. (3) When the musical piece issuccessfully played to completion, applause is heard and the animation changes.

4

Example 2: How Many Legged Race!?

“How many legged race!?” is a Collaborative Digital Sport that combines the threelegged race and digital technology. A three-legged race is one in which a team of two
people runs together, with one person’s right leg tied to the other person’s left leg.
This sport requires that the participants cooperate and synchronize their steps to move
forward quickly. As the number of players per team increases, to a maximum of fourin our system, the race becomes more challenging.

Fig. 4. Overview of How Many Legged Race!?

4.1

System Configuration

This system consists of a screen, a projector, two pressure sensors per participant, aGainer (USB I/O module) 2 and a PC (Fig.5). A screen is set in front of theparticipants and a simulation is projected. When all participants step in concordance,
the simulation moves, enabling the participants to take a video tour of the simulated
environment while racing. The software runs on Flash and the values of the pressure
sensors are obtained through Gainer.

Fig. 4. System configuration of the “How Many Legged Race!?” system.

Use of sensor values. The values from eight pressure sensors, in case four players are
involved, are used to detect two factors: the number of participants and the harmonyof each team’s step. As shown in Fig.6, if sensors 1 and 2 are pressed, the system
detects one player; if sensors 3 and 4 are pressed, the system detects two players, andso on. A new player can join in at any time. In contrast with the Group Jump Rope
Orchestra system, the speed of the players’ movement is not determined by thesystem in this sport. Participants can move at the pace of their choice so long as all
players in a team move at the same speed and step in concert. Unlike the actual threelegged race, teammates in this digital incarnation do not actually have adjacent feettied together, and so can easily join into or drop out of the game. However, eachplayer still needs to move as if one of her feet were tied to that of her partner’s. For
instance, when there are two players on a team, they should take steps 1 and 4, and 2
and 3 in concert. When a team consists of four players, they should take steps 1, 4, 5
and 8, and 2, 3, 6 and 7 in concert.

2

Gainer: http://gainer.cc/

Fig. 5. (1) The number of players and (2) whether they are stepping correctly are both detectedfrom the values of pressure sensors.

4.2

System Usage

The system launches when participants step on the foot-shaped contours and start
walking or running. The participants can see if their steps have been detected on thescreen before them. The screen also indicates participants’ speed. When a team’s
stepping is concordant, the virtual video on the screen progresses; and when a team’s
steps are discordant, its indicated speed decreases, all the way to a complete stop if
the team does not correct its step. The players can control the speed of progression of
the movie by stepping quickly. The greater the number of players per team, the fasterits speed.

5User Experience

We tested these two sports systems with numerous participants at exhibitions andthrough demonstrations at conferences. In this section, we report the feedback from awide range of participants.
The Group Jump Rope Orchestra system was exhibited for three days at the finalsof the International Virtual Reality Contest3 (IVRC), held at National Museum of
Emerging Science and Innovation (Tokyo, Japan) from August 23-25, 2010. It wasalso demonstrated at Entertainment Computing conference in Japan in 2010, and at
the ACE in the same year [5]. We will report the results of our IVRC exhibition,
where visitors of all ages took an interest in the system.
A number of children visited our exhibit and began playing Group Jump Rope
Orchestra even before being instructed, and seemed to enjoy it a lot. They returned toour exhibit several times to play the sport over and over again. It seemed that people
were more motivated to play with others than alone. A few children were initiallyscared to play the game but enjoyed it a lot once they tried it. People who were
initially poor at the sport improved markedly with time, and even asked us to raise theskill level.
3

IVRC 2010: http://ivrc.net/2010/

The How Many Legged Race!? was shown for six days at an exhibition at the
University of Tokyo from June 10-15, 2010. It was also demonstrated at the Virtual
Reality Conference in Japan in 2011. Most reactions to the system were similar to
those to the Group Jump Rope Orchestra. Most participants were calling out “one,two, one, two...” as they took steps in order to keep step with each other. It appearedthat this practice made them feel more motivated and friendly.
We also noticed that safety was a major attraction of these digital sports. The
danger of serious injury often inhibits people from playing physical sports. Our digital
sports have no such associated risk, which is a major advantage.

6

Related work

Many studies have been conducted on supplementing sports with digital technologies.
PingPongPlus adds visual effects to a ping-pong table by sensing ball-impact timing
and position using acoustic sensors [1]. Although the visual appearance of the gameis altered, the game remains unchanged. In contrast, Eureka Computers introduced“E-Sports Ground,” where a projection on a floor becomes a major part of the sport[2]. Since a player’s motion is recognized by 3D sensors (such as Kinect), it ispossible to design digital sports without using physical instruments. For example,
players can “kick” a projected virtual ball. Our collaborative sports also use digitalprojection and sensors and introduce the idea of collaboration to foster camaraderie
and keep players motivated.
Rope Revolution combines physical rope motion with digital projection [3].
Similar to our Group Jump Rope Orchestra, Rope Revolution supports multiple
players on the same field. Combining physical equipment with digital sports would
provide greater engagement between player and sport, but it might also limit sport
design flexibility. For instance, with the use of a real rope, it becomes more difficult
to change its speed according to the player’s skill. We choose a fully digital solution
for our sports systems because of its flexibility and cost-effectiveness. We also
think that our collaborative sports scenarios are sufficiently real to prompt players toactually use their body movement.
“Jogging Over a Distance” supports communication between and among joggers [4].
Combining GPS and 3D audio, it supports pace-awareness between runners, so thatcollaborative or competitive running is possible even when runners are geographicallyseparated. At present, our systems only support co-located collaboration, but wealso think that our design can be extended to accommodate distributed collaboration.

7

Discussions

7.1

Tradeoff between Reality and Flexibility

In our design, we have chosen purely digital environments where the feedback toparticipants is in the form of image projection and sound effects and no sporting
equipment is used. At the same time, we could also design a similar environment witha hybrid of real and virtual objects, as in the case of Rope Revolution [3].
We think that there is a tradeoff between the two approaches. On the one hand,participants using physical instruments, such as an actual rope or a real racket, mightexperience the sport more realistically and would be able to engage it more seriously.
They might also be able to better use their bodies with the real instrument, such as
spinning the rope or swinging the racket. On the other hand, such physicalinstruments might limit the flexibility of the sporting design. For instance, when the
motion of the simulated rope is directly correspondent to a real rope, it might become
difficult to control its speed according to the skill-level of the participants. In addition,
fully digital sporting environments might be less expensive than real ones. We also
expect that giving players a common goal would help them take the sport more
seriously, even when the environment does not have a physical instrument.
7.2

Possibility of Distributed Collaborative Digital Sports

In our current systems, the participants are expected to gather at the same place andwork out. We are now considering extending this to a distributed version, where
people can remotely participate in the same sports field even when they are
geographically separated. For example, a distributed version of Group Jump Rope
Orchestra would connect players to their remote teammates by showing their body
motions as projected silhouettes. Other communication channels, such as audio,
would also be used. In addition to normal voice communication among participants,
this audio channel would also convey nonverbal information, such as the sound of
their footsteps. We expect that the existence of a common goal would help keep
players motivated to play, even in a distributed environment.

8

Conclusion

In this paper, we proposed “Collaborative Digital Sports”, a digital sports
environment where participants are given a shared goal. We designed andimplemented two example systems based on the concept of Collaborative Digital
Sports, and tested with numerous participants at exhibitions and conferences. The
feedbacks from these places confirmed that these systems motivated participants. We
believe that there still is a potential for this Collaborative Digital Sports such as
adjusting levels on each participant, and using in distant places.

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