© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE
Conference on Virtual Reality and 3D User Interfaces.

Solitary Jogging with A Virtual Runner using Smartglasses
Takeo Hamada*Ari Hautasaari†

Michiteru Kitazaki‡

Noboru Koshizuka§

The University of Tokyo

The University of Tokyo

Toyohashi University of Technology

The University of Tokyo

Figure 1: (a) Joggers can see a virtual runner which has each of three body visibilities: (b) full-body, (c) point-light, and (d) limb-only.

A BSTRACTGroup exercise is more effective for gaining motivation than exercising alone, but it can be difficult to always find such partners.
In this paper, we explore the experiences that joggers have witha virtual partner instead of a human partner and report on the results of two controlled experiments evaluating our approach. In
Study 1, we investigated how participants felt and how their behavior changed when they jogged indoors with a human partner or witha virtual partner compared to solitary jogging. The virtual partner
was represented either as a full-body, limb-only, or a point-lightavatar displayed on smartglasses. In Study 2, we investigated thedifferences between the three representations as virtual partners forcasual joggers in an outdoor setting. Based on our results, we propose implications for the design of virtual runners as casual jogging
partners and speculate on their relationship with human users.

jog to achieve set exercise goals as well as use the data to monitor
their progress and gain motivation.
Group exercise has been shown a more effective way of getting
motivated than exercising alone. The mere presence of others tends
to affect physical activity, and individuals perform better on simple
or well-rehearsed tasks with other people (social facilitation). For
example, cyclists who competed with another cyclist increased their
speed compared to when competing with a clock [74], and in thecase of synchronized rowing, when training with another person therower’s pain threshold was increased compared to individual training[13]. Furthermore, even the presence of an attentive spectator canincrease a jogger’s pace [69, 78].
In conjunctive tasks [68] where the superior coworker cannot
continue working on the task after a less capable member stops,
such as in the case of team mountaineers, the weaker member tends
to get more motivated to try harder [27]. Especially, the greatest
motivational gain occurs with a slightly superior partner [42]. Thesephenomena are referred to as the Köhler effect and are caused by upward social comparison and group indispensability when performing
the task [34], not the mere presence of others. That is, less capable
members try significantly harder under conjunctive tasks than under
additive tasks [27] where the group score is just the sum of theindividual member contributions, such as in the case of tug-of-war.
While conjunctive exercise with a slightly superior partner seems toprovide the most benefit, for casual joggers it is difficult to always
find such a rare partner and prior works have examined transforming
solitary jogging into a social activity to overcome this limitation(i.e., jogging over a distance [47]). Furthermore, in times of global
crises requiring efforts such as social distancing, opportunities forgroup exercise, sports and the use of training facilities may be scarceleaving solitary exercise the only viable option.
In this paper, we aim to explore how casual joggers feel and how
their behavior changes when jogging with a virtual partner displayedon smartglasses. Since smartglasses are lighter than ordinary augmented reality (AR) glasses (e.g., Microsft HoloLens 2) and canalways present virtual person’s movement in the user’s field of view(FOV), unlike the visual display of smartwatches, we adopted smartglasses as a device to display a virtual partner while jogging. While
many joggers wear earphones and use audio-based smartphone apps,
the Köhler effect requires a presentation of the partner’s movement
but the effect has only been verified with visual information so far(e.g., [18, 49]).

Index Terms: Human-centered computing—Human computerinteraction (HCI)—Interaction paradigms—Mixed / augmented reality; Applied computing—Life and medical sciences—Consumer
health1 I NTRODUCTION
Considering the global trend of insufficient physical activity [20],technologies for getting sedentary people motivated to exercise havetaken an increasingly important role. Especially intrinsic motivation
facilitates long-term adherence to physical activity [59, 62]. Intrinsic
motivation, defined as behavior driven by an activity’s inherent
satisfactions [58], is relevant for motivation during solitary exercises.
Jogging is running at a gentle pace - a daily exercise that canbe done anytime and anywhere requiring no scheduling with otherindividuals. Joggers may often use wearable devices to gather information and to get immediate feedback about the jogging distance,
steps, pace, burned calories, and heart rate. By comparing the difference between these data and their feeling, joggers can adjust their* e-mail: htakeo@iii.u-tokyo.ac.jp† e-mail: a.hautasaari@iii.u-tokyo.ac.jp‡ e-mail: mich@cs.tut.ac.jp§ e-mail: noboru@koshizuka-lab.org

1© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
Ensuring the jogger’s safety while presenting appropriate visual
information about a partner is challenging. Thus, in this work we
adjust the virtual partner’s body visibility based on our previous
research [21, 22] in order not to obscure the jogger’s FOV (Fig. 1).
In summary, we investigate the following research questions:

not always guaranteed that they will be paired with someone who isa good match in terms of interests and abilities.
2.2

Technologies to help runners evaluate their performance are widely
accepted, with many runners wearing smartphones, smartwatches
and activity meters to provide feedback on their runs by presenting
running pace and distance as voice notifications from apps such as
Nike Run Club [51]. In this way, these feedback usually lead to assist
running movement through user interpretation. However, it can bedifficult especially for novice runners to determine how they could
adjust their running movement based on such information representations. Adversely, the coercive way to improve running movement
using electrical muscle stimulation (EMS) has been explored inprevious work [25, 39]. The EMS enables quick manipulation ofundesirable movement, but also runs a risk that the user may get
injured if inappropriate stimulation is accidentally applied.
There are also information representations that involuntarilychange the running movement. Dyck et al. found that music tempo
can spontaneously impact running cadence [75]. Nylander et al. proposed Runright, a system that provides audio feedback on runningmovements [53]. Oliver and Flores-Mangas developed MPTrain, an
automatic music selection system that determines which music toplay according to predetermined running goals and physiologicalresponses [54]. Fortmann et al. developed PaceGuard, a system that
presents a rhythmic pulse beat to encourage appropriate cadence forthe user [19]. Nowadays, playlists to guide people to the desired
cadence are also available on popular smartphone apps of music
services such as Spotify [67]. Besides, a few exergames support
outdoor jogging. A smartphone app “Zombies, Run!” [71] enables
usual jogging to convert into narrative-focused game experienceof running away from zombies [77]. Tan et al. developed an outdoor jogging system using AR game approach in consideration of
attention on the real-world actions [70]. All these systems provide
audio feedback suitable for outdoor jogging, but it can be difficult tounderstand others’ running behavior from audio stimuli alone.

RQ1: How do virtual runners affect joggers in terms of their motivation compared to a human runner and solitary jogging?
RQ2: Can virtual runners guide joggers’ cadence to a desirable one?
RQ3: Which factors of virtual runners influence the jogger’s experience?
In Study 1, participants were randomly assigned to one of three representations: a full-body avatar, a point-light avatar, or a limb-only
avatar, and they jogged indoors under three conditions: alone, witha virtual partner, and with a human partner. In Study 2, participants
jogged outdoors with each of the three virtual partner representations.
Our results showed that jogging with virtual jogging partners evenwith low body visibility was rated higher in enjoyment comparedto solitary jogging, and jogging with the full-body partner outdoors
was more enjoyable than with the point-light or limb-only designs.
This exploratory study provides implications for the design of virtual
jogging partners.
2
2.1

Information Representation for Assisting Running
Movement

R ELATED W ORKSocial Aspect of Running

Running has a social aspect that influences runners’ performanceand psychological state through interactions with others. Morgan
et al. identified that athlete runners use two strategies to increase
their performance: association and dissociation [45]. An associative
strategy focuses on their bodily sensations and adjusting the runningpace, whereas a dissociative strategy focuses on the landscape andspectators to reduce boredom and pain while running. In this way,runners in dissociation are especially affected by the presence ofothers (i.e., social facilitation [69, 78]). Knaving et al. studied
amateur runners and found that not only competition plays a rolein the running experience, but that support from other runners is
critical to motivation [35]. They also reported that even for runners
who prefer to run alone, connection with other runners is desirable.
Shipway et al. researched the running community and reported thatthe running group often plays an important role in providing a senseof belonging and form a place to share their running experiences[65]. Spectators’ support, even if it is remote, can positively affectrunners [14, 56, 79], but it can also have a negative effect dependingon the runner’s physical or mental state [9, 79]. Hence, in our work
we focus on exploring the effects of a jogging partner that is neither
a competitor nor a spectator.
Jogging is a form of exercise that can be done anywhere, anytime,
but requires coordination of location and time to get together forothers to participate. To address this problem, JoggingBuddy [1] isa website matching people who want to jog, offering the opportunity
to run with strangers in their neighborhood. Explore the World[61] and Zwift Run [83] bring treadmill runners from around theworld in virtual worlds to run together. Mueller et al. have also
developed an audio-based support system that allows people who are
geographically separated from each other to feel like they are running
together [47]. Although significant ability difference between two
people exercising together is known to decrease motivation [42],their system excludes this effect by localizing the sound source
representing the partner’s presence back and forth based on her/his
heart rate rather than jogging distance. This method allows people
to share information about how hard they are pushing against theirability to communicate with each other. While these solutions cangreatly increase the number of individuals people can run with, it is

2.3

Exercise with Software-based Partners

Exergames are a global trend aiming to gamify physical activity.
To improve athletic performance and motivation, many exergames
focusing on various exercises with virtual partners have been developed (stationary cycling [5–7,32,37,40,43,63,64,66], plank [16–18],
rowing [29, 49], in place running [31], and treadmill running [52]).
They are intended for use in an indoor laboratory environment using screens and a virtual reality (VR) headset. However, jogging,
cycling, and swimming require attention to the real environment,
which makes it difficult to apply exergame’s method directly to these
activities.
There have been attempts to involve a robotic partner in outdoor
jogging. Tominaga et al. used a display attached to an escort robot
moving in front of a jogger to provide self-images [72]. On theother hand, Mueller and Muirhead proposed a method of presenting
a drone as a partner for jogging which does not interfere with theperception of the surrounding environment except for the part occupied by the drone [48]. However, ensuring joggers’ safety on theroad should be the priority when jogging outdoors, and controlling arobot safely in a crowded environment with people and buildings isstill challenging.
To solve these problems, systems that can display a softwarebased runner in front of a jogger using see-through AR glasses orlarge displays have been proposed [2, 3, 76]. However, these approaches have not yet been made commercially available for thegeneral public to experience. On the other hand, we have been
exploring the experience of jogging with a virtual runner using an
optical see-through display (smartglasses) without AR functionality2© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
in terms of motivation and performance changes [21–23]. As opposed to [22] we explore the effects of three different virtual avatar
designs as partners for indoor jogging, and also expand the analysis
to more realistic outdoor settings [21].
2.4that enable the virtual partner to be seamlessly superimposed on thereal world without paying attention to the display panes.
To determine if joggers’ feeling and behavior depend on the virtual runner’s appearance, we used three types of the body visibility:
a full-body, a point-light, and a limb-only avatar (Fig. 1). A man who
is one of the standard models of a game engine Unity was used as
the full-body avatar. The point-light and the limb-only avatars were
designed as a minimized visual representation of human motion tominimize obstructions in the jogger’s FOV. The point-light avatar
consisted of 16 point lights representing the main joints of a human.
The limb-only design with only hands and feet was inspired by the
research of Kondo and colleagues [36].
The virtual partner is shown to be running 10-meters ahead fromthe jogger’s viewpoint. This is the closest distance where the virtual
partner’s whole body is visible considering the view angle of thesmartglasses. We used the Jog Forward motion in the 3D animation
sequences provided by Mixamo’s online services [4] to generate
the virtual partner’s jogging motion. The virtual partner jogs at
180 steps per minute, which has been reported as an ideal runningcadence to avoid injuries caused by over-striding [15]. The virtual
partner stands still and starts running only when the user’s motion isdetected and stops running when the user slows down or stops. The
user’s motion and steps are detected by the smartglasses’ built-in
accelerometer with VR-STEP’s algorithm [73], and a decision ismade every second whether to show the virtual partner running or
stationary.
Joggers can always see the virtual partner at the FOV regardless of
their head motion. This design choice was based on our own impressions from preliminary experiments when jogging with an avatar thatis localized on ground level using the built-in inertial measurement
unit (IMU) sensors. This representation does not use AR technologies, and the smartglasses are used simply as a wearable display. It is
possible to implement AR applications on the smartglasses using thebuilt-in camera and IMU sensors. However, if the user moves fast,
such as while jogging, the environmental recognition is delayed dueto their rapid head motion. Consequently, the virtual partner would
seem to run in the sky and sink into the ground leading the users tofeel frustrated with the virtual partner’s restless movement caused by
the vigorous shaking at their eye level, insufficient sensor accuracy,
and insufficient processing power. Moreover, they would easilylose sight of the virtual partner due to the overwhelmingly narrower
FOV in the smartglasses compared to the human eye. Therefore, we
stabilized the motion of the virtual partner without mapping it into
the real world.

Other’s Avatar Representation

The effects of other’s avatar representation on an individual’s perception have been studied in immersive VR and AR telepresence
systems. Latoschik et al. [38] explored the effect of an avatar’s
realism on the uncanny valley [28, 46] by comparing abstract (basedon a wooden mannequin) with realistic avatars (generated from photogrammetry 3D scan methods) through gestural social interaction
between self and another avatar in VR. They found that the difference between rated eeriness and attractiveness was not significant
even though the real avatar’s humanness was rated significantly
higher. Heidicker et al. [26] studied the effect of an avatar’s completeness on social presence [10] by comparing three different typesof avatars: complete body with regular predefined movement, one-toone mapping of the user’s movement, and only head and hands witha one-to-one mapping of the user’s movement in VR. Interestingly,
they reported that the incomplete avatar body was not worse, butrather even better than the complete body with predefined movementin terms of co-presence and behavioral interdependence consistingof social presence. Yoon et al. researched the effect of avatar appearance with different levels of body part visibility (head and hands,
upper body, and whole body) and two different character styles (realistic and cartoon-like) on social presence while performing remotecollaboration tasks in AR [80]. They found that a realistic avatarwith a whole body was the best for remote collaboration, but upper
body avatar or cartoon style could be considered as a substitutedepending on the collaboration context. Besides, they pointed outthat the head and hands avatar should be avoided in AR remotecollaboration because it could not give appropriate communicativecues such as continuous movement, gaze point, and gestures. In summary, these studies show that although a realistic full-body avatar isdesirable in an AR telepresence system, an abstract avatar with lowlevel of body part visibility could also be an alternative to a full-bodyavatar if the avatar can provide the necessary communicative cues.
In cases where only the general movement of a person is presented, the richness of the avatar visualization can be reduced. Johansson reported that even the movement of point lights representing
the positions of major joints can be recognized as human walking,running, and dancing [33]. Kondo et al. also reported that whenobserving an avatar from behind with only hands and feet (white
gloves and socks) moving in synchronization with the observer in
VR space, the invisible body was interpolated into the transparent
space between the avatar’s hands and feet causing illusory bodyownership [36]. This illusion was also comparable to avatars withfull body visualization [36]. That is, these avatar designs which
include less visual information may also be suitable for presenting
simple, periodic movements in real space, such as the movements ofa virtual jogging partner.
This study compares an avatar with low level of body part visibility to a full-body avatar that can reduce the area occupied by thejogger’s FOV while prioritizing unobstructed attention to the surrounding environment while jogging outdoors. Since our system is
not designed to be used face-to-face communication with the avatars,
avatars with low level of body part visibility are also presented withthe lower body.
3

4

4.1

S TUDY 1: C OMPARING THE EFFECTS OF JOGGING PARTNER AND BODY VISIBILITY OF VIRTUAL PARTNER ON CA SUAL JOGGERS ’ MENTAL CONDITION AND BEHAVIOR
MethodWe conducted a controlled experiment to investigate how joggers
feel and how their behavior changes with jogging partner (jogging
alone, jogging with a human partner, jogging with a virtual runner)as the within-subjects factor, and three types of avatar visibility
as the between-subjects variables. The participants were asked tojog three times, excluding a warm-up phase, inside a gymnasiumwith a lap length of about 160 meters. The order of jogging partner
condition was counterbalanced. The participants were asked to keep
wearing the smartglasses for the duration of the experiment.
Under jogging alone condition, participants were asked to simply
jog for five minutes. Under jogging with a human partner condition,
participants were asked to jog behind an experimenter for 5 minutes.
In this condition, a 32-year-old male experimenter wearing training
clothes jogged at 180 steps per minute in front of the participant toplay the role of the human partner while listening to 180 beats per
minute sound using headphones. The experimenter was an untrained
pacesetter, however, he tried to adapt the pace to the participants

V IRTUAL J OGGING PARTNER

To present the virtual jogging partner to experiment participants, weused smartglasses (EPSON MOVERIO BT-300, 1280 (width) x 720(height) pixel for each eye, 69 grams) to display each avatar. The
smartglasses contain a pair of organic light-emitting diode displays3© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
Five items (Cronbach’s α =.91) in the IMI Interest/Enjoyment (“Ienjoyed doing this activity very much”, “This activity was fun to do”,
“I would describe this activity as very interesting”, “I thought thisactivity was quite enjoyable”, and “While I was doing this activity, I
was thinking about how much I enjoyed it”) formed a reliable scale,and five items (Cronbach’s α =.81) in the IMI Pressure/Tension(“I did not feel nervous at all while doing this”, “I felt very tense
while doing this activity”, “I was very relaxed in doing these”, “I
was anxious while working on this task”, and “I felt pressured
while doing these”) formed reliable scales. The participants’ ratings(1=Not at all true, 7=Very true) were averaged to create the measuresof IMI Interest/Enjoyment and IMI Pressure/Tension.
To assess the participants’ perceptions of the working relationshipwith the partner (team perceptions), we used a 5-item questionnaire(“I felt I was part of a team”, “I thought of my partner as a teammate”, “I felt I was working collaboratively”, “I felt I was working
together”, and “I felt I wasn’t working separately”) [17, 50, 55, 60].
Each item was rated on a 9-point scale (1=Not at all true, 9=Verytrue), and these ratings were averaged to create the measure of teamperceptions (Cronbach’s α =.87).
To measure the participants’ perceived ability discrepancy withthe partner we used a single item questionnaire: “How do you
feel you compared to your partner?” rated on 7-point Likert scale(1=Much less capable than my partner, 7=Much more capable thanmy partner) [40].
To measure the participants’ level of cadence coordination, we
counted their steps from a video recording of their jog and calculated
the average steps per minute (i.e., cadence). As both the human andvirtual partner were jogging at a cadence of 180, we then calculated
the difference between the participants’ cadence from 180 in eachcondition, and this difference was used as a measure of a level ofcadence coordination.

while implicitly confirming a distance between them when turning acorner. Under jogging with a virtual runner condition, participants
were asked to jog for 5 minutes while seeing the virtual partner on
their smartglasses. While the jogging time was short, it matched thetime that our target users, sedentary people, could jog comfortably
rather than straining themselves and risk injury. Their jogging wasrecorded with a video camera.
To determine if the participants’ mental condition or behavior
depend on the virtual runner’s body visibility, we used the bodytypes of the virtual partner (full-body, limb-only, point-light avatar)as the between-subjects variables as illustrated in Fig. 1. Participants were randomly assigned to one of three groups using each
virtual partner body type, respectively. Each of the three groups thenfollowed the within-subjects design of jogging partner conditions
described above. After each jogging condition, the participants answered a questionnaire about their jogging experience, which took
less than 10 minutes for all participants. After all three sessions,
we interviewed participants while they were still exhausted. Theinterviews were semi-structured and recorded; we focused on theparticipants’ experience, asking questions such as: “what were thedifferences between the 3 conditions?” and “did the partner influence your jogging experience and if so, how?” Most interviews
lasted approximately 10 minutes and the overall experiment took
about one hour to complete. All interview data were transcribed,
and initially analyzed by deductive content analysis to find themes
related to intrinsic motivation, team perceptions, and cadence coordination. The remaining comments from the participants were open
coded and analyzed using an inductive method to reveal a salient
theme related to the jogging experience besides intrinsic motivation, team perceptions, and cadence coordination. The experiment
was approved by the local ethics committee and conformed to thecommittee’s guidelines and regulations.
4.2

Participants5

We recruited 39 people (19 male, 20 female) aged between 21 to
58 years old (average 39.3 years) and monetary compensated themthrough a temp agency. To make it easy for even sedentary people
to register for the experiment, the recruiting condition was specified
as the ability to jog for about 30 minutes (no pace specified). All
participants stated that they had normal vision and no health problems preventing them from participating in this experiment basedon the results of their most recent medical examination, and agreed
to take safety precautions and participate in the experiment at theirown risk before completing an informed consent form. Twenty-two
participants jog more than once per week. None of the participants
wore corrective glasses. They were randomly assigned to one ofthree groups, with 13 participants per group.
4.3

5.1

S TUDY 1: R ESULT
Jogging Experience with a Virtual Runner

A summary of the results is shown in Table 1. To explore ourresearch questions, we conducted a quantitative analysis of bothsubjective and objective data collected during the experiment, as wellas qualitative analysis of interview data. For quantitative measures
we used 3 (virtual runner body visibility: full body vs. point-lightvs. limb only) × 3 (jogging partner: alone, vs. human vs. virtual)
Mixed ANOVAs, and non-parametric tests when the data was notnormally distributed.
P erceived Exertion - RPE: The data for RPE were not normally
distributed (Shapiro-Wilk, p<.05), and hence, we employed nonparametric tests for the statistical analysis. Results from a Friedman
test indicated no significant effect of jogging partner on the participants’ RPE (χ 2 [1]=0.18, p=.92), and results from a Kruskal-Wallis
test showed no significant effect of virtual runner body visibility
on participants’ RPE in the virtual partner condition (H[2]=0.17,
p=.29), or the human partner condition (H[2]=0.004, p=.50).
W orkload - NASA-TLX: There was no significant main effectof jogging partner on the participants’ NASA-TLX scores (F[2,72]=0.51, p=.60). The main effect of virtual runner body visibility
was also not significant (F[2, 36]=0.62, p=.80), and there wasno significant interaction between the jogging partner and virtual
runner body visibility (F[4, 72]=0.37, p=.83) on the participants
NASA-TLX scores.
I ntrinsic Motivation - IMI Interest/Enjoyment: Mauchly’s
Test of Sphericity indicated that the assumption of sphericity had
been violated (χ 2 [2]=6.28, p<.05) for the IMI Interest/Enjoyment
data with an estimated Huynh-Feldt epsilon of .859, and therefore,

Measures

To verify whether the participants’ physical exercise intensity wascontrolled in each condition, we measured perceived exertion using
the Rating of Perceived Exertion (RPE) scale (6=no exertion to
20=maximal exertion) [11], which is designed to estimate heart
rate by multiplying response value by 10. The participants also
rated their perceived workload during the jog on the six subscales in
the NASA Task Load Index (NASA-TLX) on a 1 to 10 scale [24],which were averaged to create the measure of workload (Cronbach’s
α =.67).
To measure the participants’ intrinsic motivation, we used theIntrinsic Motivation Inventory (IMI) scale [57], which has beenused in several previous works on sports and exergames [12, 41, 82].
Similarly to previous research examining the maintenance of high intrinsic motivation with a virtual co-actor [6], we used only two of theseven subscales in this experiment: Interest/Enjoyment considered
the self-report measure of intrinsic motivation, and Pressure/Tension
a negative predictor of intrinsic motivation.

1 One participant could not be recorded due to the malfunction of a video
camera, and we replaced the null values with the condition average for thestatistical analyses.

4© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
Table 1: Summary of demographics and results for each group (mean ± std. dev.) of Study 1.
Body Visibility ofVirtual Runner

Full-bodyn13

Demographics

Male=6
Female=7
Age=38±12

Point-light13

Male=7
Female=6
Age=38±13

Limb-only

13

Male=6
Female=7
Age=42±10

Variable

Alone

RPE
NASA-TLXIMI Enjoyment
IMI Tension
Team Perceptions
Ability Discrepancy
Cadence [spm]1
RPE
NASA-TLXIMI Enjoyment
IMI Tension
Team Perceptions
Ability Discrepancy
Cadence [spm]1
RPE
NASA-TLXIMI Enjoyment
IMI Tension
Team Perceptions
Ability Discrepancy
Cadence [spm]12.31±2.29
5.09±2.20
3.91±1.60
2.77±1.53——
171.13±10.71
13.27±2.65
5.36±2.50
3.75±1.53
3.46±1.83——
165.55±8.66
12.27±2.70
4.95±2.36
4.17±1.68
3.40±1.88——
170.25±8.35

Jogging Partner
Human
12.38±2.02
5.56±1.92
4.69±1.16
3.31±1.67
6.65±2.25
3.54±1.13
173.21±8.1312.58±2.16
5.04±2.39
4.85±1.38
2.82±1.68
6.28±2.22
3.00±1.22
171.94±6.74
12.23±2.34
5.09±2.64
4.92±1.52
3.18±1.85
6.82±2.44
2.46±1.33
171.90±8.07

Virtual12.15±2.23
5.06±2.18
5.32±1.11
2.82±1.72
5.45±2.06
4.15±0.90
169.64±8.94
12.04±2.33
4.78±2.60
4.68±1.25
2.69±1.45
4.95±2.01
3.54±1.13
167.01±4.84
12.23±2.55
4.95±2.53
4.88±1.60
2.91±1.93
5.42±2.73
3.54±1.20
169.71±9.02

T eam Perceptions: The data for Team Perceptions were not normally distributed (Shapiro-Wilk, p<.05), and hence, we employed
non-parametric tests for the statistical analysis. Results from a Friedman test indicated a significant effect of jogging partner on the participants’ team perceptions (χ 2 [1]=6.74, p=.009), where the humanpartner (Mdn=7.00, IQR=2.00) was rated higher than the avatar
partner (Mdn=5.00, IQR=4.00). Results from a Kruskal-Wallis
test showed no significant effect of virtual runner body visibility
on participants’ team perceptions in the virtual partner condition(H[2]=0.54, p=.77), or the human partner condition (H[2]=1.61,
p=.45).
A bility Discrepancy: The data for Ability Discrepancy were
not normally distributed (Shapiro-Wilk, p<.05), and hence, we employed non-parametric tests for the statistical analysis. Results froma Friedman test indicated a significant effect of jogging partner on
the participants’ ability discrepancy (χ 2 [1]=11.64, p=.001), where
the average ability discrepancy scores were lower for human partner (Mdn=3.00, IQR=2.00) than the avatar partner (Mdn=4.00,
IQR=0.50). Results from a Kruskal-Wallis test showed no significant effect of virtual runner body visibility on participants’ teamperceptions in the virtual partner condition (H[2]=3.37, p=.19), or
the human partner condition (H[2]=4.42, p=.11).
C adence Coordination: The data for participants’ cadence coordination were not normally distributed (Shapiro-Wilk, p<.05), andhence, we employed non-parametric tests for the statistical analysis.
Results from a Friedman test indicated a significant effect of jogging partner on the participants’ cadence adjustment (χ 2 [1]=18.69,
p<.001), where the participants’ average cadence was closer to thepartner’s cadence (180 steps per minute) in the human partner condition (Mdn=15.34, IQR=11.42) compared to the virtual partner
condition (Mdn=18.14, IQR=10.30). Results from a Kruskal-Wallis
test showed no significant effect of virtual runner body visibility
on participants’ cadence adjustment in the virtual partner condition(H[2]=0.20, p=.91), or the human partner condition (H[2]=0.34,
p=.85).

Figure 2: IMI Interest/Enjoyment and Pressure/Tension scores for
jogging alone, jogging with a human partner, and jogging with a virtual
runner conditions. Error bars represent the standard error of themean.

a Huynh-Feldt correction was used. There was a significant main
effect of jogging partner on the participants’ IMI interest/enjoyment
scores(F[1.90, 68.25]=9.87, p<.001) (Fig. 2, left). Post-hoc pairwise comparisons with Bonferroni correction indicated that the participants rated their enjoyment significantly higher with either ahuman (M=4.82, SD=1.11, p=.012) or an avatar partner (M=4.89,
SD=1.08, p=.001) compared to jogging alone (M=3.94, SD=1.45).
The enjoyment ratings between human and avatar partner were notstatistically significant. The main effect of virtual runner body visibility was not statistically significant (F[2, 36]=0.29, p=.75), andthere was no significant interaction between the jogging partner andvirtual runner body visibility (F[3.79, 68.25]=0.81, p=.63) on theparticipants IMI Interest/Enjoyment scores.
I ntrinsic Motivation - IMI Pressure/Tension: There was no
significant main effect of jogging partner on the participants’ IMI
Pressure/Tension scores (F[2, 72]=1.12, p=.33) (Fig. 2, right). The
main effect of virtual runner body visibility was also not significant(F[2, 36]=0.46, p=.86), and there was no significant interaction
between the jogging partner and virtual runner body visibility (F[4,72]=0.80, p=.53) on the participants IMI Pressure/Tension scores.

5.2

Exploring Factors Affecting Jogging Experience witha Virtual Runner

The following sections detail the results from the deductive andinductive analysis of the post-experiment interviews. In addition5© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
6

to themes further explaining the results of statistical analyses on
jogging experience described above, one theme emerged from theinductive analysis of remaining interview data: desire for being
encouraged.
5.2.1

BODY VISIBILITY WHEN JOGGING OUTDOORS

6.1

Feeling of Jogging Together

While the results of the statistical analysis showed that the humanrunner was rated higher in terms of team perceptions, the virtual
runner also induced some level of team perceptions with the participants. In total, twelve participants reported that they regard thevirtual runner as a companion, and felt like they were running together: “I felt like someone [full-body] was running with me, but I
was running by myself.” [P34]
These results further answered our RQ1, where the statistical analyses and post-experiment interviews revealed that the virtual partner
can be seen as jogging partner similarly to a human partner.
5.2.3

6.2

Participants

We recruited 12 people (6 male, 6 female) aged between 21 to 57
years old (average 41.7 years) who were compensated through atemp agency2 . The recruiting condition was set as the ability tojog for about 30 minutes (no pace specified) similarly to Study 1.
The participants were casual joggers who jog on average 9 times
per month and their average jogging distance is 4 kilometres for aduration of 36 minutes3 . They reported that they have normal vision
without health problems for participating in the experiment before
completing an informed consent form. None of the participants wore
corrective eyeglasses or participated in Study 1.

Running Comfort

Twenty-three participants perceived the human partner as the best
condition based on their criteria such as running comfort, whereas
14 participants chose the virtual partner, and five preferred the alone
condition (including multiple answers): “I can hear his [human partner’s] footsteps and he is actually there, and I can just follow them.”[P16]“With a real person, if the distance between me and the person in frontof me gets a little bit bigger, I get really worried, but with that person[limb-only runner], I felt like the distance was the same.” [P10]Combined with the statistical analysis regarding cadence coordination, this result in part answered our RQ2. Overall, the participants
matched the human partner’s cadence more closely than the virtual
partner’s cadence, and coincidentally, more participants found thehuman partner more comfortable as a jogging partner. However, as
indicated by the interview results, some participants would prefer
the virtual partner as a motivator for them to run longer.
5.2.4

MethodIn Study 1, our results showed a significant difference between thevirtual partner, the human partner, and no partner on the participants’ mental condition or behavior, but did not show a significant
difference between the body types of the virtual partner. In order
to explore RQ3 in more detail (which factors of virtual runners
influence the jogger’s experience?), we conducted a second experiment with a within-subjects design, where the virtual avatar body
type was set as the within-subjects independent variable. Moreover,participants’ feedback when jogging outdoors is necessary for thepractical use of our proposed system, and hence, the second experiment was conducted in an outdoor setting on a 300-meter straightsidewalk where many people usually enjoy jogging. The experiment
procedure and virtual runner designs were similar to Study 1 and as
depicted in Fig. 1 (full-body, point-light, limb-only). Participants
were asked to jog for 5 minutes with each of the virtual partners, thatis, three times excluding a warm-up phase. The order of experiencing each virtual runner body type was counterbalanced. After eachcondition, they answered a questionnaire about their jogging experience. After all three sessions, we interviewed the participants while
they were still exhausted, similarly to Study 1. Most interviews
lasted approximately 10 minutes and the overall experiment took
about one hour. All interview data were transcribed, open coded
and analyzed using an inductive method to reveal salient themes
related to the jogging experience besides intrinsic motivation. The
participants were asked to wear the smartglasses throughout theexperiment.

Engagement in Jogging

Twenty participants complained about boredom while jogging alone.
The participants distracted themselves by paying attention to thepassage of time (P1, 12, 15, 17, 21, 24, 25, 26, 31, 37), to thesurrounding scenery (P12, 25, 28), or the post-workout meal (P7,30). On the other hand, few similar comments were observed in bothpartner conditions (2 participants in the virtual partner condition
only). Furthermore, when asked which of the conditions they felt
the passage of time was the shortest, 19 participants answered when
jogging with the human partner, 13 mentioned the virtual partner,and only 4 chose the alone condition: “The time [with experimenter]
went by so fast that it felt like two-thirds of the time.” [P33]“I was in sync with his [limb-only] running tempo, so running did not
become a burden or stress for me.” [P25]
These results corroborated the results from our statistical analyses
regarding enjoyment, and further answered our RQ1 indicating ahigher motivation towards jogging itself whether jogging with ahuman or a virtual partner.
5.2.2

S TUDY 2: C OMPARING THE EFFECTS OF VIRTUAL RUNNER

6.3

Measures

Similarly to Study 1, we also counted their cadence as cadence
coordination and used the other questionnaires: intrinsic motivation(IMI Interest/Enjoyment): Cronbach’s α =.92; intrinsic motivation(IMI Pressure/Tension): Cronbach’s α =.76; workload (NASATLX): Cronbach’s α =.74; team perceptions: Cronbach’s α =.87;
and ability discrepancy. Contrary to Study 1, all seven items in the
IMI Interest/Enjoyment (“I enjoyed doing this activity very much”,“This activity was fun to do”, “I thought this was a boring activity”,“This activity did not hold my attention at all”, “I would describe
this activity as very interesting”, “I thought this activity was quite
enjoyable”, and “While I was doing this activity, I was thinking
about how much I enjoyed it”) formed a reliable scale.

Desire for being encouraged

Fifteen participants wished their virtual partners would offer support,
gestures of concern, and coaching: “I think it [full-body] would havebeen nice if I could hear his breathing, and if there had been an
occasional look back or movement of concern, I think I would haveenjoyed it a little more.” [P1]
“It would be better if he [point-light runner] could show me thegap between ideal and current running form if I want to run more
seriously.” [P17]In regards to our RQ3, the participants wished the virtual runners to
be more interactive and offer encouragement during the jog.

77.1

S TUDY 2: R ESULT
Jogging Experience with a Virtual Runner

A summary of the results is shown in Table 2. For statistical analyses,
we employed one-way repeated measures ANOVAs to compare the2 We initially hired 13 participants but excluded the data from one maleparticipant (31 years old) due to hardware malfunction.
3 One male participant (37 years old) did not answer about his jogging
habits.

6© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
Table 2: Summary of results for the virtual body visibility (mean ± std.
dev.).

Variable

Virtual Runner’s Body Visibility
Full-body
Point-lightLimb-only

NASA-TLXIMI Enjoyment
IMI Tension
Team Perceptions
Ability Discrepancy
Cadence [spm]4.51±1.52
4.77±1.17
2.80±0.78
4.57±1.94
3.67±1.07
171.92±7.14

4.96±1.74
3.73±1.42
2.63±1.04
3.42±2.21
3.58±1.73
172.33±7.86

7.2

Exploring Factors Affecting Jogging Experience witha Virtual Runner

The following sections detail the results from the inductive analysis of the post-experiment interviews. The analysis revealed threethemes related to the jogging experience with a virtual partner thatwere not part of the deductive analysis described above: attractiveness and synchronization.

4.68±1.40
4.14±1.37
2.43±1.11
4.43±1.88
3.83±1.59
172.33±8.95

7.2.1

AttractivenessThe interview analysis revealed that the participants’ experienceswere affected by how attractive the virtual partner design was. Thatis, the level of visual richness may have affected how much attention
the participants paid to the avatar, but at the same time they werealso concerned about their safety when jogging with a rich virtual
partner design.
Six participants sometimes unconsciously ignored the virtual runners. Especially limb-only and point-light runners were deprecated:“When it was just dots or limbs, I honestly did not feel much different
than usual, like just popping up in my vision and disappearing.” [P4]Four participants reported that the full-body runner attracted theirattention and sometimes prevented them from checking their surroundings, making them feel unsafe. On the other hand, limb-only
and point-light runners made them feel that they had better visibility:“[The virtual runner of] hands and feet was the easiest to run because
I could run while checking my surroundings.” [P9]Figure 3: IMI Interest/Enjoyment and Pressure/Tension scores for
jogging with a virtual full-body, point-light, and limb-only runner conditions. Error bars represent the standard error of the mean.

7.2.2

Synchronization

There were five participants who matched their movements to theavatars: “When I ran, the hands and feet in the video would run, so
I’d get into a rhythm with the guy.” [P1]
On the other hand, four participants also wanted the avatar to workwith their motions to improve their jogging form: “If there were asystem that could detect the misalignment, it might make people
think about running with more correct form.” [P5]The limb-only and the point-light avatars’ motions often gave theillusion of being linked to three participants themselves: “I felt as if
it [point-light] was running along with my rhythm.” [P11]“The limbs did not feel much like a person, but when I slowed downbecause I was tired, [the limbs] slowed down too.” [P2]effects of virtual runner’s body visibility on the dependent variablesin the three conditions.
W orkload: We observed no significant effect for NASA-TLX(F[2, 10] = 0.79, p = .48) from one-way repeated measures ANOVA.
However, when asked about their subjective perspective on the easeof running with each virtual partner, five participants chose the fullbody, four participants chose the limb-only, two participants chosethe point-light partner, and one participant was undecided.
I ntrinsic Motivation: Results from a repeated-measures
ANOVA indicated a significant effect of virtual runner’s body visibility on IMI Interest/Enjoyment, F[2, 10] = 8.97, p = .006, where
the participants’ rating was higher with the full-body partner compared to both the point-light partner (p<.05) and limb-only partner(p<.05) (Fig. 3, left). The difference between point-light and limbonly virtual runner body visibility was not statistically significant(p>.05). In contrast, we observed no significant effects for IMI
Pressure/Tension (F[2, 10] = 0.98, p = .41) (Fig. 3, right).

8

D ISCUSSION

Overall, the results from our two studies suggested that virtualavatars can elicit team perceptions in casual joggers, and increase
their enjoyment over solitary jogging. In outdoor settings, joggers’
enjoyment was the highest with a rich full-body avatar compared
to reduced point-light or limb-only avatar designs. However, ourresults also showed that a human is still superior to a virtual avatar
as a jogging partner, and future studies should investigate ways toimprove on the virtual avatar designs.

T eam Perceptions: The data for Team Perceptions were not normally distributed (Shapiro-Wilk, p<.05), and hence, we employed anon-parametric test for the statistical analysis. Results from a Friedman test indicated no significant effect of the virtual runner’s body
visibility on participants’ team perceptions (χ 2 [2] = 3.73, p = .16).

8.1

Jogging Experiences with a Virtual Runner

The results from the quantitative evaluation in Study 1 suggested
that jogging with a virtual runner can be more enjoyable and moreengaging than solitary jogging. The higher enjoyment measured
on the IMI scale also suggests a higher level of intrinsic motivation
when jogging with a virtual partner compared to solitary jogging (Fig.
2). Our results regarding improved enjoyment compared to solitary
exercise also run parallel with previous exergaming literature [8, 44]
regardless that the virtual partner in our study could hardly interact
with the participants in a real environment or in an attractive virtualworld. However, comments from the participants also hinted thata short run in an unfamiliar place and in an unrealistic setting of a
gymnasium may have led them to be distracted by their surroundings
when running alone, whereas they only had to focus on the partnerpresence when running with a human or a virtual partner.

A bility Discrepancy: We observed no significant effects for Ability Discrepancy (F[2, 10] = 0.12, p = .89) from one-way repeatedmeasures ANOVA. None of the participants mentioned the discrepancy between the virtual partner and themselves in the interviews.
C adence Coordination: The participants’ average cadence wasslower than the virtual partner’s cadence (180 steps per minute) inall conditions. The difference between the participants’ cadence
and virtual partner’s cadence was the largest in the full-body condition (M = 8.08, SD = 7.45) compared to both point-light (M =7.67, SD = 8.21) and limb-only conditions (M = 7.67, SD = 9.35),
but these comparisons were not statistically significant (p>.05).

7

© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
The participants perceived a greater ability discrepancy when
jogging with the human partner compared to a virtual partner. Thismay be due to the additional cues (e.g., sound of footsteps) forrecognizing the partner’s performance which were not available forthe virtual partner. Besides the competitive pressure, the humanpartner also affected the jogger’s cadence, where similarly to aprevious study [75] entrainment may have occurred due to the soundof footsteps. However, the participants also perceived the virtual
partner as slightly superior to them, that is, even with the distancebeing constant and the absence of footsteps. This upward social
comparison may be partially explained by one of the mechanisms of
the Köhler effect, but further investigation is required.
Our results also suggested that the participants perceived their
human partner more strongly as their teammate compared to thevirtual partner. This result was not consistent with the results of aprevious study [16] which compared exercising with low-fidelity
humanoid avatars or a real human partner. As opposed to our results,
this previous study did not find a significant difference between
the avatar and human partner in terms of team perceptions, and thediscrepancy may be explained by the experiment setting. In the
study by Feltz et al. [16], the participants shared individual basic
information (e.g., name, hometown, what you like to do for fun)with their partner, but in our experiment, only the human partner(experimenter) gave a self-introduction.
A virtual runner may be a suitable partner for both sedentary
people who do not have exercise habits as well as casual joggers.
The results from the quantitative evaluation in Study 1 suggested thatthe virtual runner provided enjoyment to the jogger, but did not put
pressure on them or increase their perceived exertion or mental andphysical workload. Results from Study 2 further suggested that thefull body avatar design, as opposed to reduced limb-only or pointlight avatars, lead to the highest level of enjoyment for the joggers.
Moreover, jogging with the virtual runner may lead their jogging
cadence to match that of the ideal cadence of the avatar, and thus,
reduce the risk of injuries [15]. Comments from the post-experimentinterviews in our two studies suggested that the participants often
matched the movements of the avatar. Therefore, the virtual runnercan be expected to encourage jogging habit while having fun.

to design a safer jogging experience by lowering the visibility. Also,in situations such as running on a well-developed running course in
the middle of a sunny day, a full-body avatar can be used to makethe virtual partner more visible, which can be expected to increase
motivation.
8.2.2

8.3

Future Work and Limitations

In both studies, we recruited participants who “were able to jog
safely for 30 minutes”, that is, people who could be consideredat least casual joggers. The reason for this was that our target
users are casual joggers as well as sedentary people, and we aimed
to recruit participants who were at least casual joggers to limit
potential injuries caused by the jogging exercise. However, we
could not ascertain their actual level of jogging experience, eventhough the participants were inquired how often they jog. Moreover,experienced joggers may provide different feedback from casualjoggers and sedentary people, and while out of the scope of ourresearch, their experiences should be examined in future works.
Different users may focus on different body parts, such as legs
only or the arm swing, exclusively. In our two studies, we based thethree avatar designs on previous research, but it is unclear whether
these designs represent the minimal standard for inducing motivation
during jogging. That is, future works should investigate, for example,
whether a lower/upper body only avatar designs or showing only thefootprints of an avatar would also be practical for balancing jogger
motivation and safety. Furthermore, as displaying a completely
opaque avatars on optical see-through displays is not possible withcurrent technology, future works should investigate the effects ofavatar opacity on joggers’ experience with video see-through headmounted displays while considering the trade-offs with user comfort
and limited FOV compared to smartglasses as in our two studies.
Lastly, we employed smartglasses without AR functionality todisplay the virtual avatar in our two studies. Hence, presenting
the jogging speed of the avatar and distance from the user weredifficult to implement. In order to measure the Köhler effect beyond
joggers’ cadence, future works should implement these factors using
smartglasses hardware with AR functionality.

8.2 Designing Virtual Runners as Partners for Solitary
Casual Joggers
Based on our analyses from both Study 1 and Study 2, we identified
two dimensions for designing virtual runners: Level of Visual Attractiveness and Synchronization in Movement. While these design
dimensions should be understood as a proposal based on the initialstudies, future investigations, such as longitudinal studies, may provide further insights that lead to a revision of the dimensions. In
the following section, summarize the design guidelines under these
dimensions.
8.2.1

Synchronization in Movement

Guideline 2: Design for synchronization in movement with virtual
partner to improve jogging form
Some participants responded that they wanted the avatar to match
their movements in order to check their performance. Interestingly,
few participants in both studies also thought that the avatar moved
according to their movements, and they may have unintentionallymatched their cadence with that of the avatar considering that jogging is a simple rhythmic motion. Displaying the avatar movements
as matching the jogger’s movement is reasonable because creating
an external visual image that observes oneself from another person’s
point of view can lead to performance improvement. For safety
reasons during outdoor jogging, a motion capture system using awearable camera (e.g., [30, 81]) or IMU sensors should be adopted.

Level of Visual Attractiveness

Guideline 1: Design for virtual jogging partner to balance jogger
enjoyment and safety by matching body visibility to environmental
conditions.
Our results suggested that joggers can adaptively choose how
they view their virtual partner’s body visualization in response toenvironmental information, thus expanding the possibilities of avatar
design. Indoors, where the virtual partner was clearly visible, theparticipants’ motivation increased even when body visibility was
lowered. On the other hand, when the participants were outdoors
during the day, their motivation increased when the body visibility
was higher. As observed from the participants’ comments, this may
be due to the fact that it was not always possible to see the virtual
partner outdoors during the day. When the contrast between the
background environment and the virtual partner is sufficient, or
when there are pedestrians or obstacles to watch, it may be possible

9

C ONCLUSION

We evaluated a jogging experience with a virtual runner with threebody types: full-body, point-light, and limb-only avatar. The resultsfrom our two experiments showed the potential of a virtual jogging
partner as a motivator for solitary casual joggers as well as sedentary
people, and highlighted the trade-offs between jogger’s enjoyment
and safety considering the virtual partner body visibility. Based on
the results of our quantitative analyses and participant interviews, we
present three design guidelines for future virtual jogging partners.
ACKNOWLEDGMENTS
This work was supported by JSPS KAKENHI Grant Number
JP18K18137 and JST ERATO (JPMJER1701).

8© 2022 IEEE. This is the author’s version of the article that has been published in the proceedings of IEEE Conference on
Virtual Reality and 3D User Interfaces.
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