The sample size calculation was based on the exergame study of Martin-Niedecken et al [9], which, although not identical in design, also focused on an HIIT exergame. With an effect size of d=0.73, guided by cardiac responses reported in their study, we aimed for 80% power and a 5% significance level. This necessitated at least 11 participants per condition or group to provide objective, quantifiable data critical for evaluating exercise intensity and effectiveness. G*Power software (Heinrich-Heine-Universität Düsseldorf) was used for this transparent and reproducible calculation. However, due to the convenience of the sample, this study increased the participant pool to 30 healthy individuals aged 18 to 30 years, consisting of both male and female medical students from the Federal University of Rio Grande do Sul School of Medicine (Table 1). Recruitment was conducted through advertising on social networks and within the university community. Participation in the research was entirely voluntary, with students given the option to freely choose whether to take part. Nonparticipation did not result in any detriment to their university activities, ensuring that the right to choose was fully respected without any prejudice or consequence. Maximal HR was calculated using the 220−age formula [24].

Participants were required to be healthy and free of major health issues, including severe psychiatric disorders, cardiovascular diseases such as congenital heart defects or arrhythmias, serious chronic conditions like uncontrolled type 1 diabetes, binocular vision anomalies, or upper and lower limb neuromuscular restrictions. Additionally, individuals with recent muscular injuries, flu-like symptoms, or any infectious conditions that could hinder HIIT performance were also excluded. Participants were classified as gamers or nongamers based on their self-reported video gaming habits. Nongamers were defined as those who reported playing less than 1 hour of video games per week over the past 2 years [25], a criterion that did not include experience with VR gaming, given that everyone reported having no previous experience with VR exergames.

All participants provided written informed consent prior to participation in the study. The study protocol was reviewed and approved by the Federal University of Rio Grande do Sul Institutional Review Board (approval 59636722.1.0000.5327). Data collected during the study were anonymized to ensure participant confidentiality, and all privacy measures adhered to institutional and legal requirements. No financial compensation was provided to participants, as participation was entirely voluntary and without any expectation of remuneration.

The study was conducted using a crossover design consisting of 3 visits. During the first visit, participants were introduced to the Move Sapiens exergame on the Oculus Quest 2 VR device (Meta) and the 12-exercise HICT. The familiarization session involved participants completing a half session of the exergame, which included 6 blocks of 16 seconds of exercise, followed by 20-second pauses. Additionally, participants performed 10 seconds in each of the HICT exercises. For the randomization of activities, the Research Randomizer tool (Social Psychology Network) [26] was used to generate a random sequence for each participant. This tool is specifically designed for research purposes and provides a reliable method for randomization [26], involved either the Move Sapiens exergame or the control exercise condition (HICT). All sessions occurred within the School of Medicine at Clinics Hospital of Porto Alegre, performed 48 hours apart, and at consistent times of the day to control for circadian variation. On test days, participants were instructed to abstain from other exercises and to avoid alcohol and caffeine for 12 hours before testing. These restrictions were emphasized during the study briefing and reinforced through reminders sent to participants 24 hours before each test session. Compliance was self-reported by participants upon arrival on test days.

Mint chewing gum was provided as a preventive measure to mitigate any potential initial discomfort related to motion sickness during the first visit [27], which served as a familiarization with the VR equipment and protocol. This was intended to help participants acclimate to the VR environment. No formal scale was used during the familiarization session; only anecdotal records about discomfort with VR were kept, and no participants reported any symptoms of motion sickness. Consequently, chewing gum was not provided in subsequent VR sessions, as the initial preventive measure appeared sufficient to alleviate any discomfort during the first exposure.

After each session, participants completed the Simulator Sickness Questionnaire, which uses a 0‐ to 3-point scale to measure simulator sickness symptoms across nausea, oculomotor, and disorientation subscales. This 16-item questionnaire rates symptoms from 0=none to 3=severe, enabling the evaluation of specific issues like stomach awareness, eyestrain, and dizziness. Responses provide subscale and total scores, quantifying the overall impact of simulator sickness [33]. Subjective perception of effort was recorded at the end of the test using a 6‐ to 20-point RPE scale [34]. The SIMS was used to evaluate both intrinsic and extrinsic motivation among participants, featuring 16 distinct items: (1) I think this activity is interesting, (2) I am doing it for my own good, (3) I am supposed to do it, (4) I do not see any good reasons for doing this activity, (5) I think this activity is pleasant, (6) this activity is good for me, (7) it is something I have to do, (8) I do this activity but do not see its value, (9) this activity is fun, (10) it aligns with how I choose to live my life, (11) I feel obligated to do it, (12) I do this activity but do not know what I gain from it, (13) I enjoy this activity, (14) this activity is important for me, (15) I feel forced to do it, and (16) I do not see what this activity brings me [35]. This comprehensive questionnaire is segmented into 4 motivational factors: intrinsic motivation, identified regulation, external regulation, and amotivation. Each factor is represented by specific items that participants respond to, rating their level of agreement or how applicable each statement feels to them on a nuanced 7-point scale. This scale ranges from 1=does not apply at all to 7=completely applies, facilitating a detailed exploration of participants’ motivational states across various situations. The 16 items are designed to capture a wide range of motivational attitudes, from personal interest and enjoyment (intrinsic motivation) to compliance with external demands (external regulation) and lack of motivation (amotivation).

HR was measured continuously during each 7-minute training session using an HR monitor (Polar H10) and was used to calculate average and peak HR. Blood samples were collected from the fingertip and immediately analyzed on a radiometer (ABL 800 flex, Radiometer; Radiometer Medical ApS) to determine blood lactate. Blood collections were performed twice: before the exercise and 5 minutes after the end of the exercise [36].

Data were analyzed using the RStudio software (version 2023.12.1, Build 402; RStudio PBC), and the significance level was defined at P<.05. Linear mixed models were used for all the analyses with condition (2 levels: HIIT VR vs HICT) as a fixed factor and participant ID as a random factor. Mean and peak HR as well as postexercise blood lactate were adjusted for baseline values with their addition to the model as a covariate. This was done to account for initial individual differences. This model was used due to its robustness to data missing at random. Data are represented as estimated means (emmeans) and 95% CIs, except stated otherwise. Cohen d was used to calculate effect sizes for objective and subjective data, offering a standardized way to evaluate the practical significance of the observed effects. For Cohen d calculation, a transformation from Student t values to Cohen d was performed:

Cohen d classifications are interpreted as follows: a value below 0.2 indicates a very small effect, above 0.2 indicates a small effect, above 0.5 indicates a medium effect, and above 0.8 indicates a large effect.

The findings from this study underscore the efficacy of VR HIIT exergaming to increase physiological measures such as HR and increase perceived exertion without reducing intrinsic motivation when compared to traditional HICT. This demonstrates that VR HIIT is not just effective in providing physical exercise benefits akin to those of HICT but also has the potential to maintain acute motivation for exercise. Despite the greater perceived exercise intensity, intrinsic motivation did not decrease, given the sensory stimuli of the VR environment. The immersive nature of VR HIIT, marked by interactive and engaging elements, may contribute to these positive outcomes [21,22]. This aligns with previous studies showing that VR exergaming effectively increases enjoyment during a single bout of HIIT in untrained individuals [14] and improves mood [16].

Lactate levels were substantially increased following both exercise sessions but were significantly higher in the HICT condition compared to the VR HIIT. This can be attributed to the nature of HICT, which typically incorporates a higher volume of strength exercises and calisthenics using body weight [32]. Such activities are known to facilitate a greater accumulation of metabolites due to the anaerobic nature of the exertion, leading to higher lactate production [37]. Despite this, the VR HIIT condition also achieved substantial blood lactate concentrations, indicative of significant metabolic stress [23,38]. Notably, this was achieved alongside higher values in HR during the exercise, suggesting that this VR HIIT boxing protocol effectively stimulates cardiovascular and metabolic responses even in the absence of traditional strength and calisthenic exercises [8]. Our HR results demonstrated that the VR HIIT boxing protocol achieved vigorous intensity levels comparable to the “Supernatural” VR fitness game’s flow and boxing modes. These modes are associated with significant caloric expenditure, ranging from approximately 12.01 to 13.11 kilocalories per minute, with metabolic equivalent of task values of 11.44 for flow and a peak of 12.49 for boxing at higher intensities. [20].

Importantly, the VR game, although a distinct exercise modality from HICT, induced metabolic stress like that of an exercise model validated to be performed independently [32]. This finding underscores the potential of VR HIIT to offer a comparable physiological challenge to HICT, leveraging the immersive and engaging qualities of VR technology to simulate a validated exercise environment effectively.

The exercise intensity within the VR setting is inherently self-selected, despite the game design being crafted to encourage engagement at the highest possible intensity levels [9,21]. Similarly, exercise intensity is also self-selected for HICT, as every type of exercise involves motivation, volition, and intensity self-regulation. The incentive to increase intensity in the game was a better score achieved via the greatest number of punches within the HIIT blocks [21,31]. The stimulus of the VR game may have led to increased effort during the activity, leading to increased HR. Whether this leads to greater health benefits or increased engagement in exercise over time remains to be investigated. Evidently, how to increase motivation response in VR is a considerable question ahead [39]. The foremost challenge lies in the evolution of game design, where the objective is to increasingly leverage game mechanics and sensory stimuli to foster higher motivation among users [21,22]. However, it is important to acknowledge that the novelty of VR may initially boost motivation and engagement, potentially skewing performance in the short term [40]. This effect underscores the need for creating more compelling and immersive experiences that not only draw participants in [39] but also encourage them to exert themselves more vigorously during the exercise [9,14]. This endeavor requires a nuanced understanding of human motivation and behavior, alongside a mastery of VR technology, to craft experiences that are both engaging and physically demanding [41].

Integrating HIIT with VR in the study demonstrated a notable safety profile, with no adverse effects reported, particularly concerning motion sickness. The intersection of HIIT and VR with continuous innovation [42] represents a promising approach, particularly for improving engagement and motivation in exercise routines [21,43]. By combining the cognitive and physiological benefits of HIIT with the immersive qualities of VR, this approach holds the potential for a holistic method that addresses physical health. While this study did not specifically examine mental health special populations, the immersive and engaging nature of VR HIIT suggests potential applicability for these groups. This is particularly relevant for youth populations, such as patients with attention-deficit/hyperactivity disorder [44,45], who may benefit from such a different and multifaceted approach to exercise [21,46]. While the study confirmed safety among 30 medical students with heterogeneous physical activity levels, the findings are specific to this group. More research is needed to determine the effectiveness of VR HIIT exergames for these kinds of patients.

This study acknowledges certain limitations, primarily its reliance on physiological markers, such as HR and blood lactate levels, and subjective motivation assessments [47]. The study uniformly administered the Simulator Sickness Questionnaire after the exercise across both experimental and control conditions. While this approach maintains comparability, it does not capture baseline symptom levels [48]. We chose to compare an HIIT VR protocol to a traditional HICT protocol, which may have led to some of the differences observed.

The study uniformly administered the SIMS after the exercise across both experimental and control conditions. While this approach maintains comparability, it does not capture baseline motivation or symptom levels [48], limiting our ability to assess changes in motivation due to the exercise protocols themselves. Additionally, the choice of highly active participants, who likely had high baseline motivation, may have introduced a ceiling effect, making it difficult to detect significant changes in motivation between the VR HIIT and HICT conditions. This limitation should be considered when interpreting the null findings in motivation, as the participants’ pre-existing motivation levels could have constrained the potential for further increases. Importantly, we do not infer any superiority of either exercise type despite some differences in physiological responses, and further research should make comparisons between our VR HIIT protocol and other non-VR HIIT protocols.

The data derived from this study do not necessarily suggest that VR HIIT will be better adhered to over the long term nor that it will generate similar or better results when applied in a prolonged context. This points to a significant area for future investigation, emphasizing the need to assess the long-term adherence to, and effectiveness of, VR HIIT programs [16,39]. Despite these constraints, the findings contribute valuable information on the physiological responses to VR HIIT. Although the study did not show significant changes in intrinsic motivation, it demonstrated that VR HIIT does not reduce intrinsic motivation compared to HICT. Since subjective motivation plays a crucial role in determining whether participants will continue to engage in an activity [39,49], future research should aim to enhance subjective motivation and examine its impact on long-term adherence and engagement.

VR HIIT achieves acute significant increases in key physiological measures, affirming its effectiveness as an exercise modality comparable to traditional HICT in terms of likely long-term physical benefits. The combination of VR and HIIT has proven to be safe, with no adverse effects, and has maintained intrinsic motivation despite greater perceived exercise intensity due to the sensory stimuli provided by the VR environment. Additionally, VR HIIT’s capacity to deliver immersive and tailored exercise experiences presents promising applications in therapeutic contexts, particularly for populations with specific needs where conventional exercise methods may fall short. While this study demonstrates the immediate benefits of VR HIIT, future research is essential to evaluate the sustained engagement and long-term health outcomes associated with this modality. Investigating its impact over extended periods will be crucial to fully understand the breadth of VR HIIT’s benefits and to optimize its application for various exercise and therapeutic needs, particularly in clinical populations.