Impact of Customized Content in 3D Virtual Reality Motionless Imagery Exercise through Avatar on Emotional Well-Being, Cognition, and Physiological Response

Abstract

People in situations where physical activity is difficult face limitations in participating in exercise to maintain health. Participation in exercise is especially difficult when social non-face-to-face situations such as infectious diseases occur. This causes various social problems. Background: The study developed a 3D virtual reality (VR) Motionless Imagery Exercise through Avatar (MIEA), provided customized content such as companion avatars, and aimed to verify its effects. Methods: This study was conducted using a randomized block design experiment. The participants were 40 healthy adults (20 experiment and 20 control group) aged between 19 and 49 years. Both groups engaged in interventions three times per week for 20 min over six weeks. Data obtained from measurements of emotional well-being, cognition, and physiological responses before and after the experiment were analyzed. Results: The experimental group showed significant improvements in emotional well-being compared to the control group, particularly in trait anxiety, resilience, stress, and positive affect. The similar physiological responses observed in the experimental group resembled exercise-induced responses. Verbal memory and working memory in the experimental group improved more in the experimental group than the control group. Conclusions: The results showed the effectiveness of a 3D VR MIEA, indicating its positive impact on exercise outcomes. Furthermore, the provision of customized content including companion avatars was validated to enhance emotional well-being. This suggests that incorporating content-driven companion avatars in developing virtual reality exercise programs can evoke emotional effects.

1. Introduction

Physical activity enhances physical health and positively impacts mental well-being. In particular, changes through physical activity have been reported to improve emotional anxiety, stress, and depression, and physical activity has a positive effect on mental health promotion. In addition, physiological changes in which inflammation in the body is reduced through physical activity are also observed [1,2]. As such, physical activity plays an important role in improving our psychological, emotional, physiological, and immunological functions. Despite the positive effects of physical activity, there are often situations in which participation in physical activity is restricted or physical activity persistence is not maintained, and this problem can be helped by using virtual reality technology, which makes the human senses feel as if they are in a virtual environment. Virtual reality (VR) technology has revolutionized how individuals interact with their sensory perceptions and engage in physical activities through embodied VR devices, mimicking real-life actions [3]. Embodied VR programs have comparable results to traditional physical activity by enabling direct bodily movements. On the other hand, the applicability of current VR programs is limited to scenarios involving physical activity, which poses challenges for individuals with limited mobility or those unable to move such as older adults or patients. Imagery training, a technique involving the mental simulation of training experiences to address this limitation, has gained attention as an alternative exercise method that does not require physical movement [4,5,6].

Neuroscience research has shown that the human brain cannot differentiate between physical training and mental imagery training, making imagery training an effective tool to enhance the performance of athletes [5,7,8,9]. Expanding on this concept, developing virtual exercises based on imagery training might benefit the general public and rehabilitation therapy settings [7,10]. On the other hand, some individuals may find imagery training challenging due to the difficulty of holding visual images through imagination (visual image holding) [11].

Imagery training was made more accessible by developing a program named 3D VR Motionless Imagery Exercise through Avatar (MIEA) to facilitate engagement and ease of use for inexperienced individuals. The program aimed to enhance the psychological and physical effects of physical activity, even though physical movement is not required. Moon et al. (2023) [12] observed improvements in cognitive function and changes in physiological responses after 6 weeks of 3D MIEA. However, emotional well-being did not show significant changes, likely due to the absence of physical movement and associated hormonal changes such as endorphin release [13]. Therefore, improving emotional well-being is crucial for such motionless imagery exercise programs, which this study aims to address through content supplementation.

In addition to activities through physical movement, a way to promote emotional change is to strengthen external factors such as companions or motor environments. Exercising with a partner has enhanced exercise effectiveness and efficiency [14]. Furthermore, exercising with a companion increases engagement in exercise activities [15]. Virtual companions (avatar), controlled with superior abilities compared to the actual players, have been introduced as a new form of exercise, offering advantages in sustaining physical activity and inducing emotional well-being [16]. Human interactions through media resembling interpersonal relationships have also been suggested to affect the sustainability of the physical activity [17]. This new program incorporates personalized avatars to enhance a sense of ownership and allow for adjustments in immersion and character representation.

If we develop a new program that will allow subjects to customize an individual’s own avatar, companion avatar, place and time of exercise, it is expected that their emotional well-being will be improved while maintaining the existing exercise effect.

Therefore, this study aimed to develop a new 3D MIEA that incorporates elements to evoke emotional well-being while retaining the positive changes in cognition and psychobiological responses observed in the previous program and verify its effect. That is, to verify that the features of the new 3MIEA—companion avatars, customized avatars, and self-selected exercise environments—are effective.

2. Materials and Methods

2.1. Participants

In this study, the sample size was determined using the statistical program G-power (latest ver. 3.1; Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany), based on the effect size (f) of 0.26, α of 0.05, and a power (1-β) of 0.95. The analysis resulted in a total sample size of 40 participants. Forty healthy adults (20 male and 20 female) between the ages of 19 and 49 were recruited (see

Table 1. Demographic characteristics.

Variables		Experimental (n = 20)		Control (n = 20)
Characteristic	Categorize	Frequency	Percentage	Frequency	Percentage
Age (years)	M (SD)	30 (7.69)		29.40 (7.43)
Sex	Male	10	50	10	50
	Female	10	50	10	50

). The eligibility criteria for participation were as follows: (1) males or females aged 19 to 49 with healthy neurological and physical status; (2) no medical, neurological, or psychiatric history; (3) no ongoing rehabilitation program for cognitive or emotional disorders; (4) no frequent experience of nausea, dizziness, or history of vestibular disorders such as Meniere’s disease; (5) not participating in any other experimental studies; (6) able to understand the study without difficulty; (7) no visual or auditory abnormalities or skin diseases; and (8) currently not participating in individual physical activity. All participants were asked to maintain routine activities without regular exercise, and all participants provided written informed consent prior to participation. No one dropped out of the experiment and the participants who completed the experiment were paid approximately USD 80. Institutional Review Board (IRB) of Korea National Maritime and Ocean University approved the ethics of this study (approval No. KMOU IRB 2021-02) before study implementation.

2.2. Procedures

The current study utilized Microsoft Office Excel 2017 (Microsoft Corporation) for the randomized block design. Specifically, in the study, only sex and age were controlled, and subjects were randomly assigned sequentially. This study was a single-blind experiment. The experiment was conducted with separation between the researcher conducting the study, the individual creating the avatars, and the licensed psychologist responsible for administering the pre- and post-psychological tests and measuring the physiological responses.

The participants were recruited through online communities and bulletin boards in local communities. Those who met the inclusion criteria for the study were requested to visit the laboratory. Subjects participated in 18 exercise interventions (three times a week for six weeks, 20 min per session. In this study, the exercise intervention period was designed for 6 weeks by modeling studies verifying the effects of an aerobic exercise intervention such as running, which have been conducted in previous research. Specifically, various exercise intervention studies related to physical, cognitive, and emotional changes through aerobic exercises such as jogging have been conducted for approximately 6 to 8 weeks [18,19,20]. The exercise intervention period was designed based on these models. Pre-tests were conducted for all participants before the first visit and prior to the intervention. The post-test was conducted after the completion of the sixteenth session of the exercise intervention (after the seventeenth session including the pre-test). The virtual reality imagery exercise lasted for 20 min for the collection of physiological data, while the emotional well-being and cognitive function assessments took approximately 40 min, resulting in a total duration of about 60 min. Pre- and post-tests were conducted using the same methodology. Therefore, the participants experienced 3D MIEA in the lab twice, and the remaining 16 times on their own through the equipment provided.

However, the participants in the experimental group visited the laboratory once more to create their own avatars (see Figure 1).

The participants experienced a five-minute virtual reality program (not exercise based) to determine if they experienced cybersickness before experiencing 3D MIEA, then the experiment proceeded accordingly. All participants practiced until they were able to operate the equipment and the program. All participants were intensively instructed to focus mentally on their avatar, particularly the legs, during the execution of the virtual exercise to achieve a psychological synchronization and embodiment of their avatar’s actions. All participants were individually provided with VR devices to execute the 3D MIEA during the exercise intervention phase following the pre-experiment. The provision of VR devices offered the participants safety and temporal and physical advantages. To enhance the participants’ engagement in the study, they were guided to report to the researchers via SMS after the exercise intervention. Efforts were made to increase the participants’ research participation rate. The experiments were conducted by one of the researchers, while a licensed psychologist, separate from the exercise intervention, conducted the cognitive and emotional assessments.

In the experiment, the experimental group had three main differences between the control group. The experimental group used a self-made avatar, but not the control group. The experimental group was provided with companions such as other people or dogs and could select them, but not the control group. Finally, the experimental group could choose the day, night, and exercise place, but not the control group. The participants in the experimental group used customized avatars in 18 sections without change, but other companion avatar types, exercise places, and times could be selected and used differently each time.

The control group was provided with designated avatars corresponding to their gender but without a companion avatar, and the program was provided in the same manner as the experimental group.

2.3. Content Development

A 20-minute program was developed using Unity, a 3D VR development platform. The participants could choose the location, day or night setting, and companion avatar type. In the experimental group, customized avatars were created by the participants themselves using Reallusion’s Character Creator 3.

The companion avatar was the first important point included in the program development. To improve the effectiveness and efficiency of exercise performance and increase emotional trust, partner avatars were provided [14]. Similar age groups (both male and female) were incorporated to reflect positively. In addition to human companions, avatars of two types of pet dogs, large and small breeds, were included as companion avatars. The second important factor in the program development was the choice of exercise location and time. Even in virtual reality exercises, if only fixed exercise locations and times are provided, it can diminish the sense of realism and engagement while experiencing it [21] (see Figure 2). The third point was the customization of an individual’s avatar. An avatar represents the user’s appearance in the virtual space and serves as a means of self-expression, allowing the individuals to identify with their virtual bodies [22]. A specific method of creating avatars including options for height, skin color, body shape, facial features, hairstyle, clothing, and other detailed physical composition aspects enabled the participants in the 3D VR MIEA to embody their appearance.

2.4. Apparatus

This study utilized the Oculus Quest 2 VR device. The Oculus Quest 2 weighed 503 g and provided a resolution of 1832 × 1920 pixels, making it lightweight and offering wireless operation without needing a computer, ensuring user convenience. The system had a head-mounted display (HMD) and two hand controllers. Measurements of electrophysiological responses were conducted using the Procomp Infiniti device (Think Technology Ltd., Montreal, QC, Canada).

3. Measurement

To assess anxiety, a questionnaire that Kim and Shin adapted for reliability and validity in Korean from the Spielberger scale was used [23,24]. The STAI consists of 20 items measuring state anxiety and 20 items measuring trait anxiety. There are ten reverse-scored items for state anxiety and seven reverse-scored items for trait anxiety. The Korean version of Ryckman’s Physical Self-Efficacy Scale was used [25]. The Physical Self-Efficacy Scale consists of 22 items organized into two factors: perceived physical ability and physical self-expression confidence. The response format for the questionnaire is a 6-point Likert scale ranging from “Not at all true” (1 point), “Slightly untrue” (2 points), “Somewhat untrue” (3 points), “Somewhat true” (4 points), and “True” (5 points) to “Completely true” (6 points). The Korean version of Reivich and Shatte’s resilience scale was used [26]. Recovery resilience is defined and structured as a manifold phenomenon consisting of nine types across three forms. Each item is rated on a 5-point Likert scale, where higher scores indicate greater levels of recovery resilience. The Stress Response Inventory (SRI) was used to evaluate the stress response [27]. The stress response questionnaire measures overall psychological maladaptive reactions and is composed of sub-factors including depression, tension, anger, somatization, fatigue, discouragement, and aggression (e.g., “Everything seems bothersome”, “Feeling unable to cope”, “Experiencing indigestion”). Respondents use a 5-point Likert scale format, with a total of 39 items.

Finally, the Positive and Negative Affect Schedule (PANAS), developed by Watson et al. and modified for the Korean language version, was used [28]. The PANAS consists of 10 items measuring positive affect (PA) and 10 items measuring negative affect (NA). Each item is rated on a 5-point Likert scale ranging from “Not at all” (1) to “Extremely” (5), assessing mood over the past week.

Regarding cognitive function assessment, The Korean version of the Stroop Color-Word Test was used for evaluating the attentional response inhibition [29]. In the Stroop test, three reading conditions were utilized: the word reading condition, the color reading condition, and the color–word reading condition. Performance in the word reading and color reading conditions reflects the ability of the participants to correctly read the names of colors or identify the color of ink in which “XX” is printed, respectively.

The Korean-Auditory Verbal Learning Test (K-AVLT) from the Rey memory test was used for assessing working memory [30]. The K-AVLT, which tests memory, involves the immediate recall of a list of 15 words repeated five times, followed by three stages of measurement: delayed recall and delayed recognition.

The digit span task from the Korean-Wechsler Adult Intelligence Scale-IV was also used to evaluate working memory and executive function [31]. The digit span task involves listening to sequences of numbers and immediately repeating them forward, backward, and in numerical order. These three conditions consist of eight items each, and the maximum possible total score across the three conditions is 48 points.

Furthermore, the Controlled Oral Word Association Test (COWAT) was used to evaluate the executive function [32]. The Controlled Oral Word Association Test (COWAT) is a neuropsychological assessment that evaluates frontal lobe function. In the semantic fluency task, participants are required to generate as many words as possible within one minute that belong to semantic categories such as “animals” and “supermarket items”, and one point is assigned to each word. In the K-AVLT and COWAT, different word lists were used in the pre-post test to exclude the learning effect. A licensed clinical psychologist performed the neuropsychological evaluation.

Electromyography (EMG) of the left brachioradialis muscle (EMG A), quadriceps femoris muscle (EMG B), and temporalis muscle (EMG C) as well as electrocardiogram (ECG), blood volume pulse (BVP), and skin conductance (SC) were performed to assess the changes in the electrophysiological responses. The Biograph Infiniti software system (version 6.5.0) was used to measure the ECG data from beats per minute, EMG data from mean muscle relaxation values (μV) during the measurement period, BVP data from pulse per minute, and SC data from mean values (μs) during the measurement period.

For preprocessing, the participants had an adaptation period of five minutes to stabilize after attaching the sensors used to measure the physiological responses. Data were collected during a baseline period (five minutes), a VR experience period (20 min), and a resting state period (three minutes). For statistical analysis, the data were constructed by subtracting the mean value during the resting state period from the mean value during the VR experience period. One skilled experimenter measured the physiological signals.

Statistical Analysis

This study analyzed 40 participants who completed the entire experimental process for statistical analysis. Descriptive statistics (mean and standard error) were calculated for all measurements and demographic information. IBM SPSS 22.0 for Windows (SPSS Inc., Chicago, IL, USA) was used for the analysis.

The changes in emotional well-being, cognitive function, and electrophysiological responses were analyzed using repeated measures analysis of variance (RM-ANOVA), with the pre-post tests as the assessment factors and the experimental and control groups as the group factors.

The Greenhouse–Geisser corrected F-statistic was used in RM-ANOVA if the result of the sphericity test was significant. The significance level was set to p < 0.05. The effect sizes were considered small, medium, or large, according to Cohen’s criteria based on the value of partial eta squared: 0.01 or larger for a small effect size, 0.06 or larger for a medium effect size, and 0.14 or larger for a large effect size [33].

4. Results

4.1. Emotional Well-Being

The changes in emotional well-being observed with the anxiety, physical self-efficacy, resilience, stress response, and PANAS scores, which are reported in

Table 2. Results on emotional well-being.

Variables	Group	Pre-Test	Post-Test	RM-ANOVA (F-Value)
				Time (p-Value)	pη2	Group (p-Value)	pη2	T × G (p-Value)	pη2
State anxiety	Experimental	44.00 ±9.11	33.45 ±6.61	19.622 (0.000) ***	0.341	0.238 (0.629)	0.006	2.624 (0.114)	0.065
	Control	40.05 ±10.38	35.15 ±9.99
Trait anxiety	Experimental	45.25 ±8.39	32.55 ±6.04	35.653 (0.000) ***	0.484	0.619 (0.436)	0.016	7.133 (0.011) *	0.158
	Control	39.75 ±9.69	34.90 6.75
Physical self-efficacy	Experimental	81.50 ±13.63	93.55 ±13.57	12.438 (0.001) **	0.247	0.089 (0.767)	0.002	2.258 (0.141)	0.056
	Control	86.20 ±15.17	91.05 ±13.10
Resilience	Experimental	80.35 ±10.38	93.55 ±10.36	10.445 (0.003) **	0.216	1.844 (0.183)	0.046	11.268 (0.002) **	0.229
	Control	91.05 ±12.79	90.80 ±11.14
Stress	Experimental	36.50 ±28.54	9.85 ±16.87	16.187 (0.000) ***	0.299	0.938 (0.339)	0.024	4.537 (0.040) *	0.107
	Control	21.80 ±20.62	13.60 ±22.44
Positive affect (PANAS)	Experimental	23.10 ±8.45	34.80 ±8.56	7.965 (0.008) **	0.173	0.165 (0.687)	0.004	11.416 (0.002) **	0.231
	Control	28.45 ±10.99	27.40 ±11.44
Negative affect (PANAS)	Experimental	18.10 ±6.51	11.65 ±3.03	31.865 (0.000) ***	0.456	4.506 (0.040)*	0.106	2.223 (0.143)	0.055
	Control	14.40 ±4.97	10.65 ±2.30

NOTE. Values are M ± SD. * p < 0.05, ** p < 0.01, *** p < 0.001. T × G: Time × Group Interaction, pη2: partial eta square.

. The RM-ANOVA results showed that for the state anxiety (F = 19.62, p < 0.001) and trait anxiety (F = 35.65, p < 0.001) sub-factors of anxiety, all participants showed a decrease in their anxiety levels from pre-test to post-test. Furthermore, there was a significant effect (F = 7.13, p < 0.05) for trait anxiety in the interaction between the time and group. Physical self-efficacy increased in the post-test compared to the pre-test (F = 12.43, p < 0.01). Regarding resilience, there was a significant effect for time and group interaction (F = 11.26, p < 0.01). In stress response, there was a significant effect for time and group interaction (F = 4.53, p < 0.05). In the positive affect of the PANAS scale, there was a significant effect for time and group interaction (F = 11.41, p < 0.01). In the negative affect, all experimental participants showed a decrease in negative affect over time (F = 31.86, p < 0.001), and a significant effect for group changes (F = 4.50, p < 0.05).

4.2. Cognition

Changes in the cognitive function were observed with the Stroop test, K-AVLT (immediate recall, delayed recall, and recognition), the digit span task, and the COWAT, the results of which are reported in

Table 3. Results on cognitive function.

Variables	Group	Pre-Test	Post-Test	RM-ANOVA (F-Value)
				Time (p-Value)	pη2	Group (p-Value)	pη2	T × G (p-Value)	pη2
STROOP	Experimental	73.05 ±7.68	74.40 ±8.00	13.712 (0.001) **	0.265	24.572 (0.000) ***	0.393	0.143 (0.708)	0.004
	Control	63.10 ±4.72	64.20 ±4.91
Immediate recall (Rey–Kim Test)	Experimental	47.50 ±9.67	49.25 ±9.62	5.583 (0.023) *	0.128	4.891 (0.033) *	0.114	6.259 (0.017) *	0.141
	Control	43.10 ±5.06	46.05 ±4.79
Delayed recall (Rey–Kim Test	Experimental	10.55 ±9.30	11.25 ±1.44	28.500 (0.000) ***	0.429	10.614 (0.002) **	0.218	0.792 (0.379)	0.020
	Control	9.30 ±1.08	9.80 ±1.10
Delayed recognition (Rey–Kim Test)	Experimental	13.55 ±1.70	13.85 ±1.49	10.106 (0.003) **	0.210	0.056 (0.815)	0.001	0.404 (0.529)	0.011
	Control	13.70 ±1.12	13.90 ±1.02
Digit Span Task	Experimental	34.55 ±4.52	36.55 ±3.59	10.584 (0.002) **	0.218	13.650 (0.001)**	0.264	4.704 (0.036) *	0.110
	Control	31.50 ±2.87	31.90 ±2.69
COWAT (semantic fluency)	Experimental	48.50 ±8.15	48.65 ±8.09	2.623 (0.114)	0.065	1.338 (0.225)	0.034	0.054 (0.818)	0.001
	Control	46.20 ±3.59	46.40 ±3.21
COWAT (phonemic fluency)	Experimental	66.20 ±15.30	66.00 ±15.09	0.977 (0.329)	0.025	0.007 (0.935)	0.000	0.109 (0.774)	0.003
	Control	66.45 ±5.71	66.35 ±5.67

NOTE. Values are M ± SD. * p < 0.05, ** p < 0.01, *** p < 0.001. T × G: Time × Group Interaction, pη2: partial eta square.

. There was a significant effect in all measurements except for the semantic fluency (p > 0.05) and phonemic fluency (p > 0.05) of COWAT between the pre- and post-tests. Furthermore, there was a significant time and group interaction in the immediate recall of K-AVLT (F = 6.259, p < 0.05) and the digit span task (F = 4.70, p < 0.05).

4.3. Physiological Response

Changes in the electrophysiological responses were assessed by measuring the ECG, EMGs (EMG A, EMG B, EMG C), BVP, PULSE, and SC, the results of which are reported in

Table 4. Electrophysiological response changes in both the experimental and control groups.

Variables	Group	Pre-Test	Post-Test	RM-ANOVA (F-Value)
				Time (p-Value)	pη2	Group (p-Value)	pη2	T × G (p-Value)	pη2
ECG (beats/min)	Experimental	0.74 ±5.10	2.26 ±5.24	1.396 (0.245)	0.035	0.407 (0.527)	0.011	0.149 (0.702)	0.004
	Control	0.42 ±4.59	1.19 ±3.33
EMG A (μV)	Experimental	0.12 ±0.69	1.47 ±4.30	0.920 (0.344)	0.024	0.154 (0.697)	0.004	2.651 (0.112)	0.065
	Control	0.73 ±1.73	0.39 ±1.71
EMG B (μV)	Experimental	1.24 ±1.23	3.59 ±2.03	43.701 (0.000) ***	0.535	0.687 (0.412)	0.018	5.206 (0.028) *	0.120
	Control	1.48 ±1.15	2.63 ±1.83
EMG C (μV)	Experimental	1.34 ±1.21	3.72 ±1.53	34.912 (0.000) ***	0.479	22.951 (0.000) ***	0.377	14.295 (0.001) **	0.273
	Control	0.45 ±1.76	0.97 ±1.10
RESP (beats/min)	Experimental	−0.41 ±1.15	−0.22 ±1.10	1.816 (0.186)	0.046	0.854 (0.361)	0.022	4.408 (0.042) *	0.104
	Control	0.41 ±1.68	−0.49 ±1.03
SC (μV)	Experimental	−0.79 ±1.47	1.01 ±2.89	3.318 (0.076)	0.080	0.154 (0.697)	0.004	4.101 (0.050)	0.097
	Control	0.02 ±1.45	−0.07 ±0.83
BVP (pulse/min)	Experimental	1.42 ±3.58	5.81 ±16.08	2.50 (0.122)	0.062	1.962 (0.169)	0.049	0.023 (0.881)	0.001
	Control	−1.83 ±15.58	1.78 ±3.66

NOTE. Values are M ± SD. * p < 0.05, ** p < 0.01, *** p < 0.001. EMG A: left biceps muscle, EMG B: left rectus femoris, EMG C: left gastrocnemius. T × G: Time × Group Interaction, pη2: partial eta squared.

. The results showed the significant effects of time for EMG B (F = 43.70, p < 0.001) and EMG C (F = 34.91, p < 0.001), while most of the other measurements did not show statistically significant results (p > 0.05). Significant effects were observed in the group differences for EMG C (F = 22.95, p < 0.001). Significant interactions between time and group were found only in the EMG B (F = 5.20, p < 0.05), EMG C (F = 14.29, p < 0.01), and RESP (F = 4.40, p < 0.05). On the other hand, no significant effects were found in the interactions between time and group for most of the other measurements (p > 0.05).

5. Discussion

The purpose of this study was to observe changes in 3D MIEA’s emotional well-being and cognitive functions and the electrophysiological responses in healthy adults. In particular, the aim was to observe whether content activation through companion avatars, customized avatars, and virtual environment manipulation functions improved emotional well-being that the monotonous program (previously developed) did not have. The key findings are as follows. (1) Substantial effects were observed in anxiety, resilience, stress, positive affect, and negative affect. (2) Significant changes were seen in physiological responses of EMG B, EMG C, and RESP. (3) Significant effects were observed in Stroop, K-AVLT, and the digit span task.

Regarding emotional well-being, this study revealed changes in state anxiety, trait anxiety, physical self-efficacy, resilience, stress, positive and negative affect. In particular, significant enhancements in emotional well-being were found explicitly in trait anxiety, resilience, stress, and positive affect within the experimental group compared to the control group, with the magnitude of change dependent on the temporal difference between the pre-test and post-test assessments. While previous research has often focused on direct physical movements in exploring the emotional effects of exercise [33,34], this study introduced a novel finding by demonstrating positive emotional effects through virtual reality technology and visual mental imagery, even in the absence of physical movement. These results suggest that providing a companion avatar can improve emotional well-being akin to those achieved through actual physical activity.

Over the 6-week intervention period, both state and trait anxiety levels exhibited a reduction across all groups between the pre- and post-tests. This reduction was particularly notable in the experimental group, where introducing a virtual exercise companion avatar appeared to contribute to decreased anxiety levels. This aligns with previous research indicating that exercise and virtual reality interventions can mitigate anxiety [35,36,37]. Physical self-efficacy was also evident in all groups over time, which is consistent with previous studies demonstrating the positive effects of exercise on self-efficacy [38,39]. Importantly, providing a 3D VR MIEA with a companion avatar showed discernible impacts on emotional well-being as much that we have from general exercise.

Resilience increased after intervention in both groups and more significantly in the experimental group. This underscores the positive influence of the intricate exercise environment offered through user and environmental settings and exercise partners on resilience. This aligns with previous research indicating the potential for environmental interactions to enhance resilience [40,41]. Furthermore, the stress analysis indicated statistically significant changes over time and interactions between time and groups. The experimental and control groups experienced a reduced stress post-experiment relative to the pre-experiment, with the experimental group experiencing a more pronounced reduction. Incorporating a partner avatar in the experimental group likely facilitated social and emotional well-being akin to that experienced during partnered physical exercise, aiding in stress reduction through social support [42]. Furthermore, the potential for stress reduction through physiological regulation such as enhanced oxygen consumption and metabolism from exercise was evident.

The positive and negative affect analysis revealed significant changes over time, with a significant effect of time and group interaction for positive affect. This highlights the importance of affective function, which extends to mental health and influences behavior similar to cognition and physical activity [43]. These findings align with previous research showing that a positive affect contributes to positive emotional states and diminished negative affect, affecting the psychological states directly [44,45].

The discussion on improving cognitive function is as follows. Regarding cognitive function, improvements were noted in subdomains such as response inhibition, language memory, working memory, and executive function. In particular, the experimental group showed significantly greater language and working memory enhancements than the control group over time. These findings resonate with prior research highlighting the positive impacts of exercise and VR exercise on cognitive functions such as reaction inhibition, working memory, and language memory [46,47,48]. Although the improvement in the experimental group was greater, an improvement was also observed in the control group. This was seen as the effect of both groups experiencing motionless virtual reality exercise. This becomes clearer when looking at the results of the researchers’ existing studies [12]. In the previous study, the control group of the current experiment was the experimental group, however, the cognitive function was slightly improved in the group who experienced 3D MIEA, but was not observed at all in the control group who experienced VR only without exercise content. These results were observed more significantly in the elderly group experiment. These results underscore the potential of 3D VR MIEA to influence cognitive functions, even without physical movement.

The discussion of physiological responses through motor imagery is as follows. An examination of the physiological responses, particularly electromyographic (EMG) data, indicated significant time-dependent changes in certain muscle groups. In particular, introducing the experimental protocol led to significantly greater electromyographic changes in specific muscle groups post-experiment than pre-experiment. These findings align with the theory of motor imagery, wherein the brain and muscles experience analogous electrical stimulation during mental imagery as they do during actual movement, suggesting an enhancement of motor memory [49]. Moreover, using a 3D VR MIEA for synchronized movement with a partner can be considered an embodiment, wherein visually presented movements are perceived as one’s own through VR. This explains psychoneuromuscular theory, suggesting that mental imagery facilitates muscle and neural activation similarly to the actual movement [50]. The experimental group’s augmented muscle activation further emphasizes the influence of a co-avatar on the left rectus femoris and left oblique muscle activation, which is indicative of the potential of this VR exercise paradigm to enhance physiological responses similar to actual exercise.

Limitations

This study had some limitations. This study was conducted on samples of a specific age group. Therefore, the results of this study should not be applied directly or generalized to the general population. Additionally, in the experiment in this study, although the research participants were encouraged to participate in 3D MIEA and report their experiences via phone or text message after each exercise session, measuring the degree of immersion in the avatar during each exercise session was difficult. Future studies will use technologies such as eye-trackers to address this limitation. Additionally, meaningful results could be derived through a dynamic analysis method of the collected physiological data, but no such analysis was performed. In the future, research using this analysis will be conducted.

6. Conclusions

In conclusion, the results underscore the potential of virtual reality technology and imagery training to induce emotional well-being, enhance cognitive functions, and evoke a similar pattern of physiological responses arising from actual movements.

This study focused on emotional well-being, cognitive improvement, and physiological responses through companion image training using customized avatars, which showed changes similar to the positive effects of exercise. Participants experienced a similar experience to the exercise in real situations in the visual environment of the participants. First, in emotional function, both the experimental and control groups showed significant improvements in anxiety, physical self-efficacy, resilience, stress, and emotional state, and the experimental group’s emotional state was significantly improved in characteristic anxiety, resilience, stress, and static emotions. Second, in cognitive function, both the experimental group and the control group showed significant improvements in response suppression, language memory, and working memory, and the memory improvement in the experimental group was significant in the immediate recall of language memory and working memory. Third, in the electrophysiological pre- and post-comparison, both groups showed significant differences in the left great retirement muscle and the left non-abdominal muscle, and the change in the experimental group was also greater in time and group interactions in the left great retirement muscle, left abdominal muscle, and RESP.

Future research will extend these results by exploring ways to apply the program to patients with emotionally challenged depression or older adults with cognitive impairment. Furthermore, an investigation into the long-term sustainability of these effects and the potential for synergies when combined with traditional exercise regimens is needed. Overall, this study contributes to our understanding of the potential of virtual reality interventions to promote overall well-being and health outcomes in diverse populations.