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A Comparative Study of Immersive 360-degree Virtual Cycling System and Head-mounted Virtual Cycling System for Young adults
Phys Ther Rehabil Sci 2024;13:187-95
Published online June 30, 2024
© 2024 Korean Academy of Physical Therapy Rehabilitation Science.

Wonjae Choia Gyugeong Hwangb Seungwon Leec *

aDepartment of Physical Therapy, Joongbu University, Republic of Korea
bDepartment of Physical Therapy, Graduate School of Sahmyook University, Republic of Korea
cDepartment of Physical Therapy, Sahmyook University, Republic of Korea
Correspondence to: Seungwon Lee (ORCID https://orcid.org/0000-0002-0413-0510)
Department of Physical Therapy, Sahmyook University, Hwarangro 815, Nowon-gu, Seoul, 01795, Republic of Korea [01795]
Tel: +82-10-6249-2135 Fax: +82-2-3399-1639 E-mail: swlee@syu.ac.kr
Received June 11, 2024; Revised June 25, 2024; Accepted June 27, 2024.
cc This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Objective: Physical activity can promote physical and mental well-being. University students are more sedentary recently due to the increased use of computers and other technology. The aim of this study was to investigate differences between immersive 360-degree virtual cycling (IVC) and virtual cycling with head-mounted display (VCHMD) on aerobic capacity and usability in young adults.
Design: A crossover study.
Methods: Twenty-five university students (13 male, 12 female) participated in this study and completed 2 separate 30 min cycling sessions, such as IVC and VCHMD. In the IVC, participants rode on a stationary cycle while watching curved TV where recorded video was played. To enhance the sense of realism, auditory stimulation was given to the headset, and the gyroscope sensor was used to track the screen as the head moved. In the VCHMD, participants rode on the stationary cycle with head-mounted display, and other conditions were the same as IVC. Participants were assessed the aerobic capacity which included gas analyzer and portable near-infrared spectroscopy, and usability which included simulator sickness questionnaire and system usability scale.
Results: Aerobic capacity was significantly difference in the IVC compared with the VCHMD except for the total hemoglobin of right and left rectus femoris and muslce oxygen saturation of left rectus femoris (p 0.05). Cybersickness was < less in the IVC than VCHMD and usability was high in the IVC than VCHMD (p<0.05).
Conclusions: The findings suggested that IVC might be beneficial exericse to improve aerobic capacity and has lower cybersickness and higher usability than VCHMD.
Keywords : Cycling, Virtual reality, Aerobic exercise, Usability
Introduction

Although it is well known that regular physical activity is an important part of leading a healthy life, many young people still lead a predominantly sedentary lifestyle with low physical activity due to the use of computers or smartphones [1, 2]. In particular, college students are less likely to be physically active because of academic responsibilities [3]. The National College Health Assessment guideline recommends more than 30 minutes of moderate physical activity, five to seven times a week. Only 22.7% of men and 18.6% of women were found to follow the recommended guidelines [4]. Previous studies have shown that health-related behaviors are formed and developed between late adolescence and early adulthood [5, 6]. Therefore, it is necessary to develop an innovative system that enables university students to participate in regular physical activities to support physical and mental well-being.

Bicycles are one of the most useful means of transportation in many Asian countries [7], and many prior studies have demonstrated the positive effects of cycling. The characteristic effects of cycling include improvements in aerobic skills, muscle strength, physical functions such as walking or balance, and cognitive functions [8-11]. Low-intensity physical activity that promotes thermogenesis plays an important role in weight control [12], and low-power cycling was found through linear regression analysis to cause changes in the metabolic phenotype of physically inactive people [13]. Stationary cycling is an indoor exercise that can be applied safely to minimize stress to the joints and improve cardiovascular function [14, 15]. However, the promotion of regular exercise in people requires additional factors to generate more interest in the activity.

Virtual reality is used as a strategy to provide an environment that generates interest in regular exercise. Therefore, virtual reality has been used in treatments for young adults with a sedentary lifestyle, or in patients with mental health problems or neurological disorders [16, 17]. The virtual environment can conveniently be created using a head-mounted display. When used in rehabilitation or treatment, the display simulates spatial and depth perception that increases immersion of the user; however, it has the disadvantage of causing cybersickness [18]. Previous studies comparing traditional 360-degree virtual reality with artificial intelligence software intended to enhance 360-degree virtual reality have also evaluated simulator sickness questionnaires, fast motion sickness ratings, and heart rate to assess cybersickness, with significant differences between the two interventions for the simulator sickness questionnaire, but not for the fast motion sickness ratings and heart rate [19]. Therefore, it is necessary to develop a new virtual cycling system that maintains user immersion while reducing cybersickness. In this study, we developed an immersive 360-degree virtual cycling system that reduced cybersickness and user fatigue. Furthermore, we evaluated the system’s immediate effect on aerobic capacity and usability in young adults.

Methods

Participants

This study was conducted between December 4, and December 29, 2017, using a crossover design. A total of 25 college students (13 males and 12 females) were recruited. A notice was posted on the campus bulletin board to recruit subjects. All subjects voluntarily showed their intention to participate and signed the consent form. This study was registered at International Clinical Trials Registry Platform (KCT0006868) after approval by the Ethics Committee of Samyook University (2-1040781-AB-N-01-2017108HR) and in accordance with the Helsinki Declaration of 1975. The inclusion criteria were: young adults between the ages of 19 and 30, nonsmokers, able to perform physical activity, and no prior participation in virtual reality training. Women participated in the exercises during the follicular phase of their menstrual cycle. Subjects with musculoskeletal damage to the lower limbs, cardiovascular disease complications, or those that used supplements that affect body metabolism were excluded from the study.

Experimental procedure

To minimize bias caused by the selection process, immersive 360-degree virtual cycling (IVC) and virtual cycling with a head-mounted display (VCHMD) were randomly assigned to the 25 subjects. Each training program lasted 30 minutes and was carried out at the same location on different day. The aerobic capacity of participants was continuously measured using a portable breath gas analyzer (K4b2, COSMED, Rome, Italy) and near-infrared spectroscopy (Moxy, Fortiori Design, Minneapolis, Minnesota, USA) while the participants were cycling. At the completion of the training, participants were asked to answer a simulator sickness questionnaire (SSQ) and a system usability scale (SUS). The examiners were blinded to whether subjects received the IVC or VCHMD at the time of assessment.

Outcomes measure

Aerobic capacity

Aerobic capacity was evaluated using K4b2 and Moxy. K4b2 was used to measure the oxygen intake and carbon dioxide emission through the breathby-breath method. The equipment was calibrated for reliable data collection before measurement. Each participant wore a disinfected mask secured by a head cap and a harness fixed to the K4b2 device. This equipment has high reliability (interclass correlation coefficient 0.82-0.97; coefficient = of variation, 1.1%-2.8%) [20]. To reduce the thermal effect from energy intake during measurement, the participants were required to fast two hours prior to the measurements [21].

Oxygen saturation of muscles

Muscle oxygen phase (SmO2) and total hemoglobin level (THL) of the right and left rectus femoris muscles were measured using portable near-infrared spectroscopy. The pad was placed midway between the femoral condyle and superior edge of the patella [22]. SmO2 has high reliability, which increases with the severity of the exercise (interclass correlation coefficient=0.77-0.99; coefficient of variation, 4%-31%) [23].

Usability

Usability was evaluated using SSQ and SUS. The SSQ is a questionnaire designed by Kennedy et al. that consists of 16 items. The questionnaire contains three subscales: oculomotor, disorientation, and nausea. Each item is graded on a four-point scale (0-3). The total SSQ score is calculated by multiplying the total score of 16 items by 3.74 [24]. When exposed to a virtual environment, the SSQ cutoff scores are at 75th percentile points, with 15.2, 0.0, and 9.5 for oculomotor, disorientation, and nausea, respectively [24].

SUS scores 10 items on a five-point scale (1-5) and consists of five positive questions (1, 3, 5, 7, and 9) and five negative questions (2, 4, 6, 8, and 10). One point is subtracted from the scores given to each positive item and five points from each negative item score. The sum of these differences is multiplied by 2.5 to give a final score between 0 and 100 for each questionnaire. If the newly developed system scored 68 or higher, it was assumed to have good usability [25]. The SUS has strong test-retest reliability (ICC=0.96) and internal constancy (α=0.79) [26].

Intervention

For IVC, participants rode a stationary cycling bike (7.0r Recumbent, New Balance, Taipei, Taiwan) while watching a video displayed on a 55-inch ultra-high definition (UN55NU7300, Samsung, Seoul, Korea) curved display in front of them. The video was a 360-degree angle recording (KeyMission 360, Nikon, Tokyo, Japan) of the surroundings while riding a bicycle from the perspective of the rider. The video was prerecorded and projected onto a 360-degree environment using the Unity 5 engine platform. The participants were able to control the movement of the images in the video through a gyroscope sensor that detected head movements. Each stationary bike was installed with Hall effect sensors that detected the movement of the magnets attached to the pedals to calculate the revolutions per minute. The revolutions per minute values were used to control the video playback speed, providing visual feedback to the participant. All sensors were processed using the Arduino microcontroller and connected to the computer (VivoBook X510U, ASUS, Taipei, Taiwan) via USB. Using a Bluetooth headset (Beatles M-15, Unicorn, Sungnam, Korea), the sound of the actual natural environment was provided as auditory feedback [27]. In addition, the surrounding environment was darkened with low lighting to allow better immersion into the video (Fig. 1).

VCHMD was conducted under the same conditions as the IVC except that the video was displayed using the head-mounted display (HMD). All participants cycled according to each intervention technique for 30 minutes, which was comprised of 5 minutes of low-speed warm-up (50 to 60 rpm), 20 minutes of cycling at preferred speed, and 5 minutes back to low speed (50 to 60 rpm) for cool down. The participants completed two sessions, and the supervisor was always on standby from behind in both two sessions for preventing the risk of falls due to cybersickness.

Statistical analysis

The sample size was analyzed using G-power software 3.1, based on the results of a previous study [28]. The previous study had a large effect size (f) of 0.5. In our study, we determined that at least 24 people would need to be recruited when calculated for 80% power and medium effect size (f) of 0.3, to increase the reliability of the research results. Thus, 25 subjects were recruited to allow for a drop-out. All analyses were performed using SPSS Statistics for Windows, version 19.0 (IBM, Chicago, IL, USA). The results were recorded using the mean and standard deviation. The normality test was evaluated using the Shapiro-Wilk test and analyzed using repeated measures analysis of variance (ANOVA) to compare the differences between IVC and VCHMD. All statistical significance levels were set at 0.05.

Results

Baseline characteristics

A total of 25 subjects were recruited (13 males and 12 females) and completed two cycling sessions. The average age of recruited subjects was 21.64 years, the average weight was 63.40 kg, the average height was 167.16 cm, and the average body mass index was 22.58 kg/m2 (Table 1). Table 2 shows the aerobic capacity.

Comparisons of aerobic ability and usability during the two cycling systems

Repeated measures ANOVA revealed significant differences between the two cycles for all variables of gas analysis: respiratory frequency (F[1, 24]=6.025, p=0.022); tidal volume (F[1, 24]=6.861, p=0.015); ventilation (F[1, 24] =7.141, p=0.013); oxygen consumption (F[1, 24]=8.545, p=0.007); carbon dioxide production (F[1, 24]=11.396, p=0.003); and heart rate (F[1, 24]=6.571, p=0.017).

SmO2 and THL were measured in both the left and right rectus femoris, but showed significant differences only for the right SmO2 (F[1, 24]=4.891, p=0.037). Table 3 summarizes the usability results. Repeated measures ANOVA revealed significant differences between the two cycling sessions for all variables: nausea (F[1, 24]=8.408, p=0.008); oculomotor (F[1, 24]=35.954, p<0.001); disorientation (F[1, 24]=28.134, p<0.001); and total (F[1, 24]=27.412, p<0.001) of SSQ and SUS (F[1, 24]=14.371, p=0.001).

Discussion

This study investigated the differences between IVC and VCHMD in aerobic capacity and usability. Based on previous research, this study utilized virtual cycling for the known positive effect on aerobic function and assumed IVC as an effective solution for cybersickness caused by a head-mounted display (HMD). The results showed higher aerobic capacity during IVC than VCHMD, inferring that IVC is a better source of motivation for increasing indoor physical activity. IVC also received lower SSQ scores and higher SUS scores from participants, demonstrating less incidences of cybersickness and better convenience of IVC.

IVC has the advantage of simulating diverse environments in simple and multiple ways by using prerecorded videos of real surroundings. While traditional virtual cycling mainly provides 2D animation visual simulations [13, 29, 30], IVC can use real-world images that simultaneously engender familiarity and more immersive virtual recreations to the cycler. Moreover, IVC provides audiovisual stimuli with 360-degree angle video that positively enhances the exercise experience [31].

Cycling is one of the basic aerobic exercises used to strengthen cardio-pulmonary functions. Therefore, it follows that both IVC and VCHMD performed in this study are already known to be great modes of aerobic exercise. However, IVC was significantly higher than VCHMD in all variables measured by the gas analyzer (p 0.05). When calculating < for the energy consumed by oxygen intake (VO2 1L=5kcal) [32], 6.97 kcal and 6.00 kcal were consumed for IVC and VCHMD, respectively. The HR was also 108% higher during IVC than during VCHMD. Both tidal volume and ventilation were significantly higher in the IVC group compared to the VCHMD group, suggesting that IVC may increase respiratory muscle recruitment and improve neuromuscular control [33]. Therefore, IVC may be a more efficient means of aerobic exercise. In addition, portable near-infrared spectroscopy was used to examine the right and left rectus femoris of the participants and indicated a significant difference only in the right SmO2 (p<0.05). This finding was most likely caused by favoring the use of the dominant leg muscles instead of placing equal tension on both during cycling. A study by Pimentel et al. (2019) also demonstrated that cyclists were more asymmetrical in bone mineral density and lean mass of the lower extremities than non-cyclists [34]. In this study, 96% of the test subjects were right dominant and, therefore, expected to use the right rectus femoris more often.

Recently, virtual reality has become rapidly popular, but 20-80% of users are known to experience unpleasant symptoms such as nausea, headaches, blurred vision, and disorientation [35]. In HMD, the close distance between the screen and the eyes causes strain on the eyes [36], and the weight of the headset places pressure and stress on the neck during prolonged wear. In a study by Denison and D’Zmura (2018), participants experienced higher incidences of postural instability and cybersickness while wearing HMD compared to viewing a monitor [37]. Moreover, Rosa et al. (2016) found that 60% of virtual reality users experienced cybersickness, and that cybersickness appeared to be higher in console gamers than in personal computer gamers [38]. VCHMD also showed a higher incidence of cybersickness compared to that of IVC in our study (p<0.05). Motion sickness is generally believed to occur when the sensory information input to the human body does not match the brain’s prediction in traditional virtual reality [37]. For VCHMD, all items of the SSQ received high scores. However, there were complaints of eye strain, difficulty focusing and concentrating, blurred vision, and dizziness when the eyes were open. Cybersickness is likely induced by these symptoms that are caused by the mismatch of information between the visual and vestibular inputs. HMD-associated cybersickness has been found to cause changes in the cutaneous vascular tone with a delayed response time of 20 to 50 ms. In particular, the delay in reaction time was related to the degree of frequency of nausea [39]. IVC appears to have significantly less cybersickness than VCHMD because they do not wear a head-mounted display, which may minimize any mismatch or potential conflict between visual and vestibular signals.

IVC also scored 1.18 times higher than VCHMD in SUS used to evaluate the usability of each system. Participants expressed discomfort in having to set up the HMD equipment and having to remove the HMD helmet to access the video play and stop functions. In addition, the screen was difficult to calibrate into focus, and the helmet was heavy causing strain on the neck after 30 minutes of wear.

Due to the limitations of the cross-sectional study, this research was not able to identify the effects of long-term exercise, objectively assess the discomfort from using an HMD helmet, or evaluate the degree of immersion using an immersive tendency questionnaire. Future research on changes in neck muscle strain caused by wearing HMD is necessary to address these issues. Moreover, participants also expressed discomfort from sweating inside the headset during 30 minutes of exercise. Future research should place greater consideration into providing a pleasant exercising environment through equipment improvements such as bone conduction headphones.

Conclusion

In this study, IVC promoted the effects of aerobic exercise by encouraging higher motivation and interest in the activity compared to the conventionally used VRHMD. IVC is a universally-used virtual reality cycling training. Our results suggest that this system may reduce cybersickness, enhance immersion, and maximize exercise effects by recreating a familiar environment.

Acknowledgments

This work was supported by Sahmyook University and this research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A1B03035018).

Conflict of Interest

The authors declare no conflict of interest

Figures
Fig. 1. Immersive 360-degree virtual cycling system.
Tables

Table 1

Demographics of participants

Variables Mean (SD)
Sex (male / female) 13 / 12
Dominant side (right / left) 24 / 1
Age (years) 21.64 (3.10)
Weight (kg) 63.40 (12.30)
Height (cm) 167.16 (7.93)
BMI (kg/m2) 22.58 (3.53)

BMI, body mass index.


Table 2

Comparison of aerobic capacity between IVC and VCHMD

Variables IVC VCHMD F P
Gas analysis
Rf (cycles / min) 28.47 (1.06) 26.03 (1.12) 6.025 0.022
VT (l) 1.22 (0.09) 1.11 (0.07) 6.861 0.015
VE (l/min) 34.08 (2.71) 28.11 (1.60) 7.141 0.013
VO2 (ml/min) 1395.02 (101.14) 1201.15 (66.15) 8.545 0.007
VCO2 (ml/min) 1241.64 (98.66) 1013.77 (61.30) 11.396 0.003
HR (bpm) 122.99 (25.1) 113.72 (24.11) 6.571 0.017
Rectus femoris
Right SmO2 (%) 67.74 (18.47) 76.01 (10.52) 4.891 0.037
Right THL (g/dl) 11.99 (0.48) 12.03 (0.47) 0.490 0.491
Left SmO2 (%) 71.86 (14.43) 75.06 (11.13) 1.283 0.269
Left THL (g/dl) 11.91 (0.52) 11.88 (0.60) 0.094 0.761

IVC, immersive 360-degree virtual cycling; VCHMD, virtual cycling with head-mounted display, Rf, respiratory frequency; VT, tidal volume; VE, ventilation; VO2, oxygen consumption; VCO2, carbon dioxide production; HR, heart rate; SmO2, muscle oxygen saturation; THL, total hemoglobin.


Table 3

Comparison of usability between IVC and VCHMD

Variables IVC VCHMD F P
SSQ (scores)
Nausea 19.08 (20.60) 38.54 (41.07) 8.408 0.008
Oculomotor 14.85 (15.54) 47.60 (33.86) 35.954 < 0.001
Disorientation 12.24 (19.40) 61.24 (49.05) 28.134 < 0.001
Total 18.10 (18.87) 55.05 (41.65) 27.412 < 0.001
SUS (scores) 72.40 (15.30) 61.00 (18.22) 14.371 0.001

IVC, immersive 360-degree virtual cycling; VCHMD, virtual cycling with head-mounted display; SSQ, simulator sickness questionnaire; SUS, system usability scale.


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