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Advances for Indoor Fitness Tracking, Coaching, and Motivation: A Review of Existing Technological Advances

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There is growing consumer demand for digital technologies that help users track, motivate, and receive coaching for both aerobic and anaerobic activities. In this article, we provide a review of existing technological advances in tracking, coaching, and motivating users during indoor training in contexts such as gymnasiums. This study lists the advantages and limitations of various apparatuses and applications used for this purpose. Our review and discussion are intended to help entrepreneurs and engineers improve their products to better meet users? needs and aid researchers in identifying potential new areas.
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4 IEEE SYS TEMS , MAN, & CYBE RNET ICS MAGAZ INE January 2021
Digital Object Identifier 10.1109/MSMC.2020.3017936
Date of cur rent version: 14 Januar y 2021
There is growing consumer demand for digital
technologies that help users track, motivate,
and receive coaching for both aerobic and
anaerobic activ ities. In this article, we pro-
vide a review of existing technologica l
advances in tracking, coaching, and motivating users
during indoor training in contexts such as gymnasiums.
This study lists the advantages and limitations of various
Advances for
Indoor Fitness
Tracking, Coaching,
and Motivation
by Tianyi Wang, Yanglei Gan,
Scott D. Arena, LubomirT.Chitkushev,
Guanglan Zhang, and
Reza Rawassizadeh
A Review of Existing Technological Advances
©SHUTTERSTOCK.COM/FLAMINGO IMAGES
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January 2021 IEEE SYS TEMS , MAN, & CYBE RNETICS MAGAZ INE 5
apparatuses and applications used for this purpose. Our
review and discussion are intended to help entrepreneurs
and engineers improve their products to better meet
users’ needs and aid researchers in identifying potential
new areas.
Indoor Physical Activities
Due to the rapid growth of urbanization, many populations
participate in sports and training in indoor environments,
chiefly gyms. Physical activ ity fosters well-being and
reduces the risk of various chronic
diseases. As cases of diabetes [1]
and cardiovascular disease [2] are
on the rise worldwide, the demand
for gyms has continually increased.
The U.S. fitness industry is estimat-
ed at a US$30 billion value and has
been growing at an annual rate of
3–4% over the past 10 years [3].
This demand creates a large mar-
ket for digital apparatuses and
applications that assist users in
fitness tracking, coaching, and
motivation [4].
Indoor activities are usually
classified into two types: aerobic and anaerobic exercise.
Aerobic exercise, often known as cardio, is suitable for
users who want to lose weight and improve or maintain
their cardiopulmonary condition. Modern gyms and
homes use equipment such as treadmills, stair mills, row-
ing machines, and spin bikes, which support a variety of
aerobic exercise. Anaerobic exercise is primarily accom-
plished with weight training activities, which contribute
to training specific muscles. The U.S. Department of
Health and Human Services recommends incorporating
strength training exercise for all ma jor muscle groups into
a fitness routine at least twice per week [3], indicating
that it is as impor tant as aerobic exercise.
In par ticular, there are two types of equipment used
in the gym that apply to weight training: free weights
and fixed resistance. Despite the wide variety of technol-
ogies related to indoor physical activities, most existing
technologies are focused on fitness trackers and aerobic
exercise [5], while anaerobic exercise, such as weight
training, is underrepresented [6]. Therefore, we believe it
is crucial to outline the latest advancements related to
indoor fitness and list the potential areas for further
improvement to contribute to the research and engineer-
ing communities’ work in this area. To have a better
understanding of the challenges and opportunities in
this area, the first par t of this article introduces existing
systems. First, we describe data collection tools a nd
methods, including applications and sensors. Next, we
present different approaches to motivate users to per-
form and stay committed to physical exercise. This
includes a brief review of the coaching tools that employ
artificial agents or real humans to coach users, social-
ization approaches that support users in communicating
and competing with each other, and gamification and
exergaming approaches intended to promote healthy
lifestyles and fitness activ ities. Afterward, we explore
the interaction interfaces used in these systems as a sub-
section of motivational advances.
The latter part of this article lists the challenges and
opportunities that we identified, which can help the
research and the engineering community move forward in
this promising direction, with an
eye toward further advancements.
Existing Systems
Data Collection Tools
Most technological advances have
focused on data collection. Here,
we provide a brief overview of the
types and characteristics of sen-
sors used for data collection.
Sensor Classification
The core of data collection devic-
es is their sensors, and existing
activ ity tracking systems can be broadly classified into
two categories: proximity [7] and mobile/wearable [8]
sensors. However, there is no clear border between the
categories, and it is possible for a single sensor to
belong to both [7]. At the time of writing this article,
wearable sensors are being commercialized and widely
available in the consumer market. On the other hand,
proximity sensors are in their infancy and not yet wide-
ly in use; we believe that they will soon be commercial-
ized by fitness service providers. However, unlike
wearables, which are personalized, they should be
shared by a specific group of users. Because wearable
devices are heterogeneous, for example, the recent Wear
operating system improves battery use compared to its
old version [9], and because proximity sensors are not
yet widely in use, werefrain from prov iding a quantita-
tive comparison in this research.
Proximity Sensors
A proximity (environmental) sensor is fixed and does not
move with the user [see Figure 1(a)]. In contrast, a mobile
sensor is wearable and will move with its user [see Fig-
ure 1(b)]. An example of a proximity sensor is a pulse
sensor (used to measure heart rate), which is mounted
on the handle of a device —for example, an elliptical—to
read a user’s pulse rate. This information will be dis-
played on the device’s ambient screen, which may also
show some basic coaching advice, such as a recommend-
ed maximum heart rate based on the age the user inputs,
or a suggestion of when to decrease the intensity of the
exercise. Heart rate sensors and ambient displays have
In particular, there
are two types of
equipment used in
the gym that apply
to weight training:
free weights and
fixed resistance.
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6 IEEE SYS TEMS , MAN, & CYBE RNET ICS MAGAZ INE January 2021
Proximity Sensors Wearable Sensors
Camera
Connection (Count Reps)
Weight (Count Weights)
Gym Mat
Ankle
Smart Textile/Short
Smart Textile/Shirt
Wrist
Ear Forehead
Chest Strap/Necklace
Bicep
Waist
Hand/Gloves
Leg
Accelerometer
Gyroscope
Barometric
Heart Rate
Camera
Pressure Sensor
Depth Camera Electromyography
RFID
Figure 1. The different locations of (a) proximity and (b) wearable sensors. reps: repetitions; RFID: radio-frequency identification.
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January 2021 IEEE SYS TEMS , MAN, & CYBE RNETICS MAGAZ INE 7
been widely adapted in existing aerobic exercise
machines. The use of radio-frequency identification
(RFID) tags, pressure sensors, or accelerometers on
dumbbells has been commercialized as well (https://
www.bowflex.com/selecttech/1090/710000.html).
Many researchers have developed systems that inte-
grate proximity sensors. For example, Chaudhri et al.
[10] and Ding et al. [11] introduced a system that employs
RFID: they attached RFID tags to equipment such as
dumbbells and fixed resistance machines to allow users
to track anaerobic exercise by connecting a tag reader
with the tag located on the device. Sundholm et al. [12]
presented a mat with a resistive pressure sensor matrix
built inside it that can distinguish gym exercises, such as
push-ups, abdominal crunches, squats, and so on.
To provide visual feedback on workout quality, Nagar-
koti et al. [13] proposed a system that can use a 2D ca mera
to detect users’ errors in workout form. Another body of
work employs depth cameras for activity tracking.
Although Microsoft stopped the production of Kinect sen-
sors in 2017, several in-depth camera approaches to indoor
exercise tracking inspired by the Kinect sensor have been
developed. For example, Khurana et al. [14] proposed a
Kinect sensor-based system that can detect, recognize, and
track exercise without user intervention. Lin et al. [15]
offered a method to monitor energy expenditure during
physical activity using Kinect sensors. Specifically, they
employed Kinect to collect skeletal data and then mapped
the data to a regression model. Another approach using
Kinect sensors, this one proposed by Reily et al. [16], can
evaluate users’ performance on the pommel horse bench—
measuring the consistency of the user’s timing and body
angle. Compared to a traditional gym-based exercise, a 3D
camera approach can enhance postural control and opti-
mize user experience [17].
A salient advantage of proximity sensors is their unob-
trusiveness. Users do not need to wear anything or bring
their own tracking devices. However, to archive their
information, they should transfer their data to personal
storage (e.g., a smartphone), which is not easy in proximity
to sensor devices. This is due to the fact that there is a bur-
den for users to connect the proximity device into their
personal storage; they must perform actions such as log-
ging into their account or establishing a Bluetooth connec-
tion with the device.
Wearable Sensors
About a decade ago, the success of activity tracking appli-
cations on smartphones [18]–[20] led to the introduction of
single-purpose wearable devices for activity tracking—fit-
ness trackers. The wide availability of fitness trackers in
the consumer market and the variety of wearable and
mobile sensors make them popular tools for the automatic
data collection of aerobic exercise. Wearable sensors are
typically embedded with accelerometers, gyroscopes, and
electrical and optical heart rate sensors and can actively
track a user’s heart rate along with instances of aerobic
exercise, such as cycling, running, and swimming [see Fig-
ure 1(a)]. Wearable sensors can communicate with ubiqui-
tous personal dev ices such as smartphones and construct a
wireless-body sensor network (BSN). Studies have shown
that many human-centric applications such as m-Health
and fitness/wellness systems benefit from BSNs [21]–[23].
Wrist-worn wearables are the most common type in
this category. For example, smartwatches are commer-
cialized and used widely. However, a recent study found
that ankle-worn wearables offer more reliable and sensi-
tive results than do wrist-worn wearables [24]. Remark-
able initial work from Nam and Park [25] proposed a
waist-worn system embedded with an accelerometer and
a barometric pressure sensor that can detect activ ities
such as climbing up and down and so forth. Iskandar et al.
[3] combined an electrocardiogram with a necklace to
determine a user’s heart rate. Cruz et al. [26] suggested
adopting an earpiece that uses infrared thermometry to
detect heart rate. Akpa et al. [5] offered a glove that can
track fitness activities when the user touches exercise
equipment; 16 force-sensitive resistor sensors on the glove
allow it to track anaerobic exercises such as flexibility
training (e.g., side lunge stretches), dynamic strength
training (e.g., squats), static strength tra ining (e.g.,
planks), and circuit training (e.g., push-ups, bench dips,
and lunges). Another force-sensitive approach proposed
by Zhou et al. [27] introduces a real-time assisted training
feedback system. Their system uses a smart textile on a
shirt as a fabr ic sensor [28] to track muscle activities by
measuring the pressure on the fabric. Using data acquired
from the shirt sensor, the system can classify anaerobic
exercise such as push-ups, bicep curls, handstands, and
so on. Textile wearables track anaerobic exercises by ana-
lyzing muscle responses via electromyography (EMG)
sensors during weight training activities. Another exam-
ple utilizing EMG was offered by Taha et al. [29]. They sug-
gested attaching an EMG sensor to the user’s bicep to
monitor exercise intensity and muscle fatigue.
There are few reports about the feasibility of wearing
gloves or adapting smart shir ts while exercising. In addi-
tion, in contrast to smartwatches and other wrist-worn
wearables, we have not obser ved a proliferation of smart
clothes in the wearable market. This might be due to their
high cost as well a s hygiene concer ns about the frequent
use of smart clothes. There is a need, however, for further
scientific investigation in this area to quantify the chal-
lenges that hinder acceptance of other wearables.
One advantage of using wearables for activity
tracking is their personalized information collection
approach. In other words, no effort from users is needed
to collect or retain their own data, in contrast to proxim-
ity sensors, where data collection devices are shared
among users. Table 1 summarizes some common data col-
lection approaches, based on the type of sensors, i.e.,
wearable and proximity settings.
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8 IEEE SYS TEMS , MAN, & CYBE RNET ICS MAGAZ INE January 2021
Motivational Approaches
There are motivational applications intended to increase
user participation in physical activities, reduce their sed-
entar y behavior, or improve the quality of their physical
activ ities. Based on our analysis of the literature, we cat-
egorize motivational approaches into three groups:
coaching, socialization, and gamification/exergaming. To
our knowledge, there is little research done on motiva-
tional approaches. This limitation does not allow us to
generalize our findings and make a conclusive remark.
We believe that in the near future, more motivational
applications will enter the market because of artificial
intelligence (AI) advances.
Coaching
In addition to activity data collection in fitness tracking
applications, users can interact with applications for anal-
ysis of the collected data. Early work in this area by Hiil-
loskorpi et al. [36] introduced a coaching approach widely
adopted by aerobic exercise devices: calculation of the
user’s maximum heart rate. The field of coaching applica-
tions is slowly advancing. Rawassizadeh et al. [37] suggest-
ed a coaching approach in which textual recommendations
are provided once a day because the small screen of most
wearable devices cannot accommodate graphs and num-
bers. Their approach compares users’ daily activities and
heart rate to their personal averages using a machine
learning algorithm and notifies them if their activity level
has decreased.
Another coaching approach proposed by Pessemier and
Martens [38] compares the data collected from heart rate
sensors mounted on exercise equipment or within wear-
able devices. Their use guides users in adjusting pace dur-
ing an aerobic exercise to avoid overexercise injuries or
more effectively reach their fitness goals.
Adaptation AI could improve fitness coaching applica-
tions considerably. Li et al. [39] proposed an AI fitness sys-
tem that can recognize fitness actions by applying
evaluation methods on image sequences. Furthermore, the
AI of Things (AIoT), which integrates AI, deep learning,
and the Internet of Things (IoT), is also advancing rapidly.
For example, Chu et al. [40] proposed an AIoT system that
consists of both biological IoT sensors on the body and
motion sensors on weight training equipment. Their sys-
tem can detect incorrect movements and provide coaching
advice to the trainee. Coaching approaches are still in
their infancy, and there is plenty of room for improvement,
as we explain later in detail.
Socialization
Some other approaches focus on motivating users by shar-
ing their activity data through social network applications,
that is, through socialization. Studies have pointed out that
sharing physical activities can increase user motivation
[41], [42] by enabling users to compare their performance
with each other.
In this context, Häkkilä et al. [43] introduced a virtual
city jogging concept that simulates the subject’s move-
ment on a treadmill in a 3D virtual city. This application
combines a map-based presentation of the user’s jogging
distance and a 3D representation of the city. Users can
see previous joggers’ results and compete with them.
Cassola et al. [44] built an online gym system that satis-
fies users’ socialization and fitness needs from their
homes. The practice of employing socialization for moti-
vation is mature enough that it has penetrated the
mobile health market [e.g., Runkeeper (https://play
.google.com/store/apps/details?id=com.fitnesskeeper
. runkeeper.pro), Nike Run Club (https://play.google
.com/store/apps/details?id=com.nike.plusgps), and
Sensor
Type Location Sensor Reference
Proximity Gym
equipment
RFID [10]
Environment Depth camera [30]
Environment Depth camera [14]
Environment Depth camera [15]
Environment Depth camera [16]
Environment Depth camera [17]
Environment Camera [13]
Gym mat Pressure sensor [12]
Wearable Gloves Pressure sensor [5]
Waist Accelerometer,
gyroscope sensor
[31]
Waist Accelerometer,
gyroscope sensor,
Barometric pressure
sensor
[25]
Ankle, waist Accelerometer,
gyroscope sensor
[24]
Smart textile Pressure sensor, EMG [28]
Bicep EMG [29]
Necklace Heart rate sensor [32]
Ear Heart rate sensor [26]
Ear Heart rate sensor [33]
Leg, chest,
and hand
Accelerometer,
gyroscope sensor
[34]
Leg, hand,
and arm
Accelerometer,
gyroscope sensor
[35]
Table 1. Some prominent examples of the
proximity and wearable sensors used for
indoor activity tracking.
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January 2021 IEEE SYS TEMS , MAN, & CYBE RNETICS MAGAZ INE 9
MyFitnessPal (https://play.google.com/store/apps/
details?id=com.myfitnesspal.android)].
Gamification and Exergaming
Gamification [45] and exergaming [46] are two motivation-
al approaches with the goal of changing users’ sedentary
lifestyles. Gamification is defined as the use of video gam-
ing elements in nongame contexts [45]. For example, Con-
solvo et al. [47] developed UbiFit Garden, which embeds
body sensors and a mobile display to encourage their users
to participate in physical activ ities. In addition to gamifi-
cation, another game-related area is exergaming, which is
popular in indoor environments. Oh and Yang [46] defined
the most common exergames as video games that require
physical activity in order to play. In a prominent example,
Nurkkala et al. [48] used video projectors to develop an
exergaming simulator for gym training, exercise testing,
and rehabilitation.
Rabbi et al. [49] and Rawassizadeh et al. [50] found that
users are not motivated to ma nually log their exercise,
especially when they are not accompanied by personal
trainers. Therefore, external motivation, like gamifica-
tion, is required to encourage manual data entry. With
that in mind, Rabbi et al. [49] proposed a vir tual exercise
assistant with a virtual reality head mounted display and
an attached, miniature IoT sensing device that can track
users’ activities. Another prominent example of physical
activ ity gamification is Pokémon GO [51], which resulted
in US$100 million sales a month after its release [90],
although this app does not have an indoor context.
Interaction Interface
Multiple ty pes of interaction interfaces and methods are
used to communicate with users and provide analysis of
collected physical activity information. Through a review
of the literature, we found that GUIs, sound, vibrotactile
sensations, and ambient interfaces are being used for this
purpose. Figure 2 presents an example that includes three
interaction interfaces (except ambient interface).
GUIs
Modern smartphones are powerful enough to handle
intensive computational tasks such as image processing
[52]. Data gathered from wearable sensors can be trans-
mitted to a smartphone for further processing or visualiza-
tion [53]. However, unlike wearables, smartphones are not
compact enough to be comfortably carried by the user
while exercising [54]. In addition, the proximity of wear-
able devices to users is higher than that of smartphones
[55], which makes them more accurate in collecting users’
physical activity data. Therefore, a hybrid approach that
uses wearables for data collection and smartphones for
analysis and review is common.
Wrist-worn wearables have miniature screens that
present information and collect user input. The most
accepted approach, used by the vast majority of mobile
and wearable applications, is to present physical activities
using numbers and graphs. However, existing approaches
that present information with graphs and numbers lack
actual coaching advice on the exercise sessions [56]. For
example, GUIs may present the calories burned and the
average heart rate during the exercise session, but not
instruct users to adjust body movements and advise them
about how to avoid injury while exercising. This is because
most wearables are attached to users; without a third-per-
son point of view [53], such devices can collect informa-
tion about only a very limited number of body movements.
The screens of wearables and sma rtphones are person-
alized and offer efficient communication, but they still
require users to look at them, which increases users’
cognitive load and shifts their focus [57]. A big screen
mounted on a wall or a training machine can make the
information easier to digest [30] and mitigate the burden of
cognitive load involved in processing information from a
smartphone or wearable. (These ambient interfaces will
be discussed further in later sections.)
Sound
The ear is like a biological equivalent of a USB port [3].
Many users listen to music while performing physical exer-
cise [58]. Notably, a study by Nakamura et al. [59] ha s
shown that listening to one’s preferred music can improve
exercise endurance. The widespread use of headphones
while exercising leads to the introduction of headphones
with sensors, i.e., earpieces.
GUI
Sound
Vibrotactile Sensation
Figure 2. The different types of interaction interfaces.
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10 IEEE SYSTEMS, M AN, & CYBE RNETI CS MAGAZI NE January 2021
Integrated sensors in earpieces for activity tracking
are growing. Poh et al. [33] introduced a pair of earbuds
that are embedded with ref lective photosensors [often
called photoplethysmography (PPG)] to measure the
user’s heart rate. After connecting the earbuds to the
phone, users can get a ref lection of whether their heart
rate is within the ideal range. A recent proposal from
Matsumoto et al. [60] reported the use of an earpiece
with an eardrum (tympanic) temperature sensor and a
galvanic skin conductance sensor. That earpiece can
monitor vital parameters such as body temperature and
sweat concentration. Advances in computing-capable ear-
pieces have led to their recent adoption by the consumer
market (https://www.wearableinear.com/best-heart-rate
-monitor-earbuds).
Without the distraction from a screen, audio coaching
earbuds use sound to communicate with the user to pro-
vide information and coaching tips such as average heart
rate, pace, time of exercise, and recommendations to
increase or decrease training intensity. The salient advan-
tage of earpieces over GUI is the reduction in cognitive
load so that they can dedicate more of their attention
directly to exercise.
Vibrotactile Sensation
Vibrotactile or tactile sensation is another way to pro-
vide information to and communicate with users. To
our knowledge, existing methods are largely imple-
mented in smart textiles [61]. By providing force feed-
back to certain muscle groups, users can receive
direct guidance for body movements. Hadi et al. [3]
found that haptic feedback improves users’ perfor-
mance in physical activities. In one such application,
Kishishita et al. [62] proposed a force-feedback suit
to provide real-time vibrotactile feedback to the
upper limb with a set of pneumatic gel muscles.
Coaching advice on muscle movement can then be
directly provided to the relevant muscle group. How-
ever, the pressure on different parts of the body could
be confusing [63] for the user and this might lead to
misundersta nding of the given coaching advice. Nev-
ertheless, in comparison to other interfaces, this
force-feedback system places a significantly smaller
cognitive load on the user.
Ambient Interfaces
Gross [64] explained that “ambient interfaces go beyond
the classical GUI and use the whole environment of the
user for the interaction between the user and the system.”
According to Ramos et al. [65], the environment that is
equipped with an ambient interface should recognize the
person who is using the device. The ambient interface
should also provide real-time feedback ba sed on the user’s
needs and behaviors [66].
A prominent example of an ambient interface can be
found in the work of Vales-Alonso et al. [67]. They provid-
ed an ambient interface that personalizes training ses-
sions using a wireless sensor network (WSN) deployed in
the training field. The WSN har vests location-related
data including wind speed, temperature, and so on and
then transmits them to users’ sma rtphones. Users’ train-
ing equipment is equipped with sensors that collect
information such as users’ heart rates. The decision
component located in the training field estimates each
user’s future heart rate and recommends actions based
on environmental conditions (e.g., temperature of the
training field) and the user’s current heart rate. Table 2
provides a comparison to the communication capacity,
obtrusiveness, and personalization among different
interaction interfaces.
Challenges and Opportunities
Despite promising applications for indoor activities, there
are limitations of existing approaches that present oppor-
tunities to further advance the field.
Accuracy and Flexibility
After digital pedometers, smartphones were the first
device used for activ ity recognition. However, due to their
proximity, which did not continuously access the user’s
body movement 24/7 [68], they were replaced by wearable
devices. However, wearables also suffer from inaccuracy
in their data collection [69]).
Khurana et al. [14] found that the detection of ascend-
ing motion, such as climbing stairs, is more accurate when
an iner tial measurement unit is attached to users’ bags
than when it is attached to their shirts. For similar rea-
sons, data collected by smar twatches can not be accurate-
ly used for exercise tracking because it is limited to wrist
movements and thus cannot recognize weight training
moves such as leg presses. Smartwatches are also located
on the wrist, where PPG signals are unreliable due to low
blood flow [70], resulting an inaccurate heart rate values.
The tight connection between a smartwatch and wrist
adds extra pressure to skin that leads to reduced blood
Communication
Capability Obtrusiveness
Personalized
Interaction
GUI High High High
Sound High Medium High
Vibrotactile
sensation
Low Low High
Ambient
interfaces
High Low Low
Table 2. Three different types of
interaction interfaces; the ambient
interface is usually a public display
that is shared among users and not
shown in this figure.
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January 2021 IEEE SYS TEMS , MAN, & CYBE RNETICS MAGAZ INE 11
flow [71]. Therefore, the heart rate data collected by smart-
watches is not reliable.
To our knowledge, there is a very limited number of
tools and systems available on the market that can track
both aerobic and anaerobic exercise. Currently, fitness
tracking applications on wearable dev ices [e.g., Google Fit
Workout on Google WearOS (https://www.wearableinear
.com/best-heart-rate-monitor-earbuds) and Fitplan on
Apple WatchOS (https://apps.apple.com/us/app/fitplan
-gym-home-workouts/id1064119547) require users to man-
ually input data on anaerobic exercise. This is mainly
because existing approaches can only access a limited
number of body parts. As a solution, Rawassizadeh et al.
[53] proposed the concept of a companion robot that uses
cameras and image recognition algorithms as a third-per-
son perspective to unobtrusively record indoor exercises.
However, no such prototype has been implemented and
evaluated in a real-world setting.
Energy Efficiency
Energy efficiency can typically be achieved by either
advancing battery technology or minimizing energy con-
sumption algorithmically [55]. The size, shape, and capaci-
ty of the battery must be compatible with the compact
design of wearables [9]. Carbon nanomaterial-based (car-
bon nanotubes, graphene, and so forth) batteries are
expected to offer higher energy density and capacity [73],
but they remain under development.
Lithium-ion (Li-ion) and Li-ion polymer batteries are the
most common types used in wearable devices. Due to their
low energy density and shor t life cycle, most wearables
suffer from the need for frequent charging and battery
aging problems [55]. Recently, wireless charging, which
provides more flexibility than cable charging, has become
more popular. Some manufacturers are starting to make
their smartphones with wireless charging capabilities.
Although it can extend the use time of wearables, wireless
charging is still limited by its low speed [74].
Another promising direction is energy harvesting
[75]. Wearables can collect energy from the ambient
environment, such as sunlight [76], [77]; heat [78]; a nd
human motion [79]–[81]. Although a promising field,
energy harvesting from the ambient environment is still
in its infancy.
Security and Privacy
The majority of fitness tracking approaches use Bluetooth
Low Energy (BLE) for wireless communication [55]. How-
ever, studies have shown that BLE is vulnerable to cyber-
attacks such as eavesdropping [82]–[84] and traffic
analysis [82]. Rahman et al. [85] developed a prototype that
can attack Fitbit devices using eavesdropping, injection,
and denial of service to prove the vulnerability of the
device. This raises user privacy concerns, as fitness track-
ing approaches include biometric information. This
becomes more challenging when it is taken consideration
that recent advances are using wearable biometric finger-
prints for digital authentication [86].
Video cameras are not yet in widespread use for fitness
tracking, but they are starting to attract the research com-
munity’s attention [14], [16], [17]. The privacy risks of video
cameras remain, and they are higher than those of other
activ ity tracking devices [87]. More privacy issues arise
when considering a semipublic display, such as a wall-
mounted display in a gym, as some might not want to
share their data on a large screen.
Personalized Professional Intervention
Most coaching approaches implemented for wearables are
not designed to connect users with professionals such as
physicians and personal trainers [88]. Each coaching plan
should be unique because users’ fitness needs vary and a
one-size-fits-all approach does not work. Even common
goals, such as achieving 10,000 steps per day, are not sup-
ported by scientific evidence. To satisfy the need for per-
sonalization, Dharia et al. [89] proposed a system that can
customize each user’s fitness session based on their health
profile and daily activities.
However, without inter vention from a professional and
motivation provided by coaching, users might discontinue
their fitness routine or suffer long-term injur ies. We identi-
fied a scientific gap that will require the research commu-
nity to develop new approaches that provide personalized
professional support to meet the needs of each user.
Although there are applications that connect real profes-
sional coaches to users [e.g., Keep Trainer (https://play
.google.com/store/apps/details?id=com.gotokeep.keep
.intl&hl=en_US) and Trainerize (https://play.google.com/
store/apps/details?id=com.trainerize.Trainerize&hl=en_
US)], no machine intelligence is involved. Most coaches
and physicians are still using their human-acquired knowl-
edge to manually evaluate athletes’ performance and phys-
ical condition. This is helpful, but it could be further
augmented by the assistance of AIoT [40] or companion/
coaching robots [72].
Conclusion
There is a growing need for indoor fitness activities. Dur-
ing the COVID-19 pandemic, most people have had to stay
at home to maintain socia l distance. To avoid a sedentary
lifestyle, more people have realized the importance of
seeking coaching advice and finding motivation to keep
their indoor fitness routine on track. In this article, we
first reviewed existing data collection tools and classified
them according to the proximity to the users. Next, we dis-
cussed various motivational approaches to help users stay
committed to nonsedentary behaviors, including coaching,
socialization, gamification, and exergaming. We then
looked at the interaction interface of these approaches.
Finally, we highlighted the challenges and future opportu-
nities for both the research community and the commer-
cial market.
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12 IEEE SYSTEMS, M AN, & CYBE RNETI CS MAGAZI NE January 2021
Acknowledgment
We thank Jian Cao for drawing the illustrations used in
this article.
About the Authors
Tianyi Wang (twang93@bu.edu) earned his B.A. degree
in finance in 2015 from Kent State University, his M.Sc.
degree in financial management in 2018, and his M.Sc.
degree in computer information systems in 2020 from
Boston University. His research interests include artifi-
cial intelligence, natural language processing, machine
learning, ubiquitous computing, and wearables.
Yanglei Gan (ygan1005@bu.edu) earned his B.A.
degree in economics and mathematics in 2018 from the
University of Connecticut and his M.Sc. degree in com-
puter information systems in 2019 from Boston Universi-
ty, where he is currently a graduate student in the Depart-
ment of Computer Science, Metropolitan College, Boston,
Massachusetts, USA. His research interests include artifi-
cial intelligence, natural language processing, machine
learning, ubiquitous computing, and wearables.
Scott D. Arena (sdarena@bu.edu) is a senior lecturer in
the Department of Computer Science at Metropolitan
(MET) College, Boston University, Massachusetts, USA. He
spent 38 years in the R&D labs of Bell, where he worked for
ATT/Bell/Verizon Labs. He has been granted nearly a dozen
patents in the areas of file optics/networking and security.
He joined MET full time and is the networking curriculum
coordinator, where he enjoys high-order networking and
security-related coursework.
Lubomir T. Chitkushev (ltc@bu.edu) earned his Dipl.
Ing. degree in electrical engineering from the University of
Belgrade, his M.Sc. degree in biomedical engineering from
the Medical College of Virginia at Virginia Commonwealth
University, and his Ph.D. degree in biomedical engineering
from Boston University, where he is an associate professor
of computer science and the director of health informatics
and health sciences at Metropolitan College, Boston Uni-
versity, Boston, Massachusetts, USA. He is also an associ-
ate director of the Center for Reliable Information Systems
and Cyber Security at Boston University. His research inter-
ests are focused on the modeling of complex systems, com-
puter networks security and architecture, and biomedical
and health informatics.
Guanglan Zhang (guanglan@bu.edu) earned her
Ph.D. degree from the School of Computer Engineering,
Nanyang Technological University, Singapore, for her
doctoral work in bioinformatics. She is currently an
associate professor in the Department of Computer Sci-
ence, Metropolitan College, Boston University, Boston,
Massachusetts, USA. Her research interests include the
computational modeling of complex biological process-
es, such as the identification of vaccine targets; develop-
ing solutions for biomedical data management; and the
building of analytical tools for pattern recognition from
biomedical data.
Reza Rawassizadeh (rezar@bu.edu) earned his B.Sc.
degree in software engineering and his M.Sc. and Ph.D.
degrees in computer science from the University of Vienna,
Austria. He is currently an assistant professor in the Depart-
ment of Computer Science and is affiliated faculty in the
Health Informatics Research Lab, Metropolitan College,
Boston University, Boston, Massachusetts, USA. His
research interests include on-device machine learning, ubiq-
uitous computing, wearables, and interaction interfaces for
fitness activity tracking.
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