Immersive Virtual Reality-Based Exercise Intervention and Its Impact on Strength and Body Composition in Adults with Down Syndrome: Insights from the InDown Pilot Project

Abstract

This pilot study examined the feasibility, usability, and physiological effects of a high-intensity exercise program delivered through immersive virtual reality (IVR) in adults with Down syndrome (DS). Twenty participants (mean age: 29.85 ± 9.37 years) completed a 12-week intervention using the FitXR exergame on Meta Quest 3, with two sessions per week. Usability, safety, and personal experiences were assessed via the System Usability Scale (SUS), Simulator Sickness Questionnaire (SSQ), and Game Experience Questionnaire (GEQ), while body composition and strength were measured using bioelectrical impedance analysis and standardized tests (handgrip dynamometry, Five Sit-to-Stand Test). Results indicated excellent usability (SUS: 92.88–95.03/100), minimal cybersickness (SSQ: 2.12 → 1.98/48), and high adherence (90%). Positive experiences increased significantly, with no negative experiences reported. Lower-limb strength has been considered as a primary outcome, which has shown to improve significantly (p = 0.018; Cohen’s d = 0.89), whereas upper-limb strength and body composition changes were minimal. These findings suggest that IVR-based exercise is a safe, engaging, and feasible strategy for promoting physical activity and enhancing functional strength in adults with DS. Further controlled trials with longer duration and nutritional strategies are warranted to optimize body composition outcomes.

1. Introduction

Down syndrome (DS) is the most common genetic cause of intellectual disability, resulting from a genetic abnormality where chromosome 21 is either partially or completely duplicated (Trisomy 21) [1,2,3]. DS is associated with neurological motor disorders and is currently prevalent, occurring in approximately one in 800 births in the USA [3].

Individuals with DS present with distinctive physical and cognitive challenges, including hypotonia, ligamentous laxity, and limited muscle strength [2,4]. These musculoskeletal issues contribute to limitations in motor function, affecting resistance, mobility, and balance [2,4]. The associated decline in physical function and loss of muscle mass hasten the onset of premature aging and functional deterioration in adults with intellectual disabilities [1,4].

A significant health concern for this population is the high likelihood of sedentary lifestyles and an increased prevalence of overweight or obesity compared to their typically developing peers [3,5]. Rates of obesity tend to escalate as individuals with DS progress from adolescence into adulthood [3]. This predisposition is reinforced by medical risk factors, such as a lower metabolic rate and reduced resting energy expenditure [1,3]. Comorbidities, including obstructive sleep apnea and hypothyroidism, may further contribute to weight gain [3]. Although resistance training lasting at least two weeks has been shown to enhance upper- and lower-limb muscle strength in individuals with DS, greater gains are observed in younger participants (under 20 years old) [1]. Critically, resistance training alone does not typically yield significant changes in fat mass or waist circumference [1].

Given the challenges of maintaining physical activity and the necessity for interventions to address strength and body composition, there is a clear need for strategies that motivate sustained exercise participation [3]. Exergames—digital games requiring physical activity to play—have emerged as a compelling technological solution [5,6]. Virtual reality (VR), particularly its most advanced form, immersive virtual reality (IVR), provides a gamified, inclusive, and adaptable environment for exercise [5,6]. IVR uses a Head Mounted Display (HMD) to project a fully artificial environment, effectively transforming exercise into an interactive experience [5,6]. This approach can help overcome common barriers like lack of motivation and access to appropriate facilities [3,5].

In research comparing immersive VR exercise to identical screen-based alternatives in healthy individuals, IVR demonstrated marked psychological and physiological benefits [6]. Participants engaged in an IVR exercise chose to exercise at a significantly higher intensity, evidenced by increased oxygen consumption (VO₂), compared to the screen-based equivalent [6]. Furthermore, IVR sessions were associated with greater enjoyment, higher positive affect, and lower negative affect [6]. In clinical populations with neurological conditions, training incorporating VR has been reported to result in greater improvements in function and quality of life than conventional therapeutic approaches [6].

The adoption of VR and exergaming technology has generally been successful and acceptable among individuals with intellectual and developmental disabilities (IDDs) [5]. VR physical activity games are perceived by adults with IDD as enjoyable and successful, and they value the ability to modify the options to suit their individual requirements [7]. Technology-based interventions have been shown to increase motivation and enhance physical activity indicators, such as heart rate and energy expended, in adults with IDD [5,6,7,8].

Specifically, regarding immersive technology, a study utilizing IVR exergaming (stationary bike paired with an HMD) with high school students with IDDs (which included a participant with DS) demonstrated a functional relation, leading to a significant increase in exercise [5]. The intervention successfully tripled the total time students engaged in physical activity per session compared to the baseline [5]. The participating students consistently expressed a strong preference for the VR exergaming condition [5]. However, while short-term feasibility is established, continuous at-home compliance often requires external support, and video support alone has shown limited long-term adherence [3].

In the context of DS and VR interventions, most studies have focused on non-immersive systems such as Nintendo Wii (Nintendo Company Limited, Kyoto, Japan) or Xbox (Microsoft Corporation, Redmond, WA, USA) with Kinect Sensor [9,10,11,12,13,14,15,16,17,18]. Evidence from these investigations indicates significant improvements in functional balance [9,14,15,16,18] and dynamic balance [9,17], with the latter showing a reduction of 3.65 s in Timed Up and Go (TUG) test performance. Regarding muscular endurance [9,13,17,18], analyses revealed a significant positive effect favoring VR-based interventions to enhance the capacity for sustained effort. Conversely, in the domain of static balance, assessed through posturographic parameters under eyes-open and eyes-closed conditions, no statistically significant differences were reported [12,14].

In contrast, studies employing full-immersion technology for the development and improvement of physical parameters (strength, balance, speed, aerobic endurance, etc.) remain scarce [19] as most focus on cognitive and behavioral parameters [20,21,22]. However, immersive virtual reality (IVR) has demonstrated considerable effectiveness in improving physical parameters such as balance, agility, and muscular endurance [23], frequently surpassing the results of conventional therapy. Furthermore, full immersion has been shown to encourage users to perform higher-intensity exercise, thereby optimizing oxygen consumption (VO₂) and promoting reductions in body fat, weight, and BMI when incorporated into resistance training programs [4,6]. These physical benefits, combined with improvements in coordination and functional autonomy, position RVI as a superior technological alternative for psychomotor development in this population.

Recognizing the need for effective and motivating interventions to address the low muscle strength and unfavorable body composition associated with Down syndrome, the present study aims to examine the usability, safety, and subjective experiences of a three-month high-intensity exercise program delivered via IVR, as well as its effects on strength and body composition in adults with Down syndrome. Accordingly, the primary contribution of this study is methodological and applied, as it provides novel evidence on the feasibility and safety of a long-term high-intensity immersive virtual reality exercise intervention in this underexplored population.

2. Materials and Methods

2.1. Study Design

A prospective study was conducted using a single-arm pilot clinical trial design. This approach was chosen to assess the usability, safety, and feasibility of immersive virtual reality as a tool for promoting physical exercise in a group of young adults with DS, prior to implementing larger and controlled studies. All participants in the trial were volunteers and received the same intervention. The study did not include a control group or randomization, which classifies it as quasi-experimental. The trial was carried out between May and July 2025.

2.2. Participants

The study sample consisted of 20 adults with DS (Trisomy 21, translocation Trisomy 21, or mosaicism), aged 17 to 44 years. The group included 14 males (mean age: 31.43 ± 9.04 years) and 6 females (mean age: 26.17 ± 9.89 years). Participants were recruited through the Down Syndrome Association of Pontevedra, which informed its members and their families about the research and technological innovation project and invited them to participate. Inclusion criteria: mild to moderate intellectual disability as reported by parents, ability to follow simple verbal instructions in Spanish or Galician, and adequate physical condition to engage in a high-intensity exercise program. Personal, family, or medical authorization was required for participation. Exclusion criteria: individuals who had participated in a high-intensity exercise program within the previous three months; those with concurrent medical conditions such as juvenile chronic arthritis, autism, unrepaired congenital heart defect; or a history of violent episodes, elopement, aggressive behavior, or antisocial conduct; presenting severe visual or auditory disturbances, vertigo, psychosis or uncontrolled epilepsy that would prevent the sessions being carried out.

The study was carried out following the ethical principles for medical research on human subjects according to the Declaration of Helsinki, and was in compliance with all the provisions established in the Organic Law 3/2018—concerning Personal Data Protection and Guarantee of Digital Rights (Organic Law 3/2018, of 25 May)—according to which strict confidentiality of the data, as well as the results of the tests performed, must be maintained. In addition, the study was approved by the local ethics committee and registered under the identification code CEIHG 2023-00125. All participants signed the corresponding informed consent form, and they, plus their relatives and guardians, were all informed in detail about the study, its aims, and its benefits.

2.3. Intervention Program

Participants completed a 12-week high-intensity interval training (HIIT) program delivered in IVR environments, with two sessions per week. The intervention was supervised by exercise and health professionals and conducted in the gym facilities of the participants’ center (Figure 1). For the training program, we used the Meta Quest 3 device (Meta Platforms, Inc., Menlo Park, CA, USA) for IVR, along with two handheld controllers and a projection screen that allowed the staff to see participants’ performance in real time. The exercise sessions were implemented using the FitXR software (developed by FITXR LIMITED, London, UK; version 3.7.88; available in the library at www.meta.com, accessed on 15 January 2026) following the protocols described in previous studies [24,25]. FitXR was selected for its ease of use among individuals with no prior IVR experience [24]. The Combat Studio module of FitXR was employed, featuring martial arts-inspired workouts. The handheld controllers simulated boxing gloves, enabling participants to perform punch combinations on spherical targets while dodging blocks through squats and lateral movements. Three difficulty levels were used, progressively increasing in complexity based on movement speed: Beginner (5 min), Intermediate (7 min), and Advanced (9 min). Exercise intensity was determined using the Rating of Perceived Exertion (RPE; 6–20) and was established at a high-intensity level (16–17). This assessment was performed at the conclusion of each session. Throughout the sessions, participants wore a chest strap heart rate monitor (Polar H10, Polar Electro Oy, Kempele, Finland) to monitor their heart rate levels, which were required to reach a minimum of 70% of their maximum heart rate. Maximum heart rate was estimated using the formula proposed by Fernhall et al. [26]: MHR = 210 − (0.56 × age) − 15.5. Exercise intensity variables were used solely to monitor adherence to the prescribed protocol and were not considered dependent outcome measures; therefore, they were not systematically recorded during the intervention.

2.4. Outcome Measures

The evaluation of the different parameters under investigation in this project was carried out twice (pre- and post-intervention assessment). In addition, an intermediate assessment was included (2 weeks after the start) to ensure good adaptability to the virtual tool by the participants.

To evaluate the usability, safety, and personal experiences of the IVR hardware and software used in the project, the following instruments were employed:

• System usability, using the System Usability Scale (SUS). The SUS is a widely used survey designed to quickly and easily assess the usability of a product or service. It consists of 10 items rated on a 5-point Likert scale, generating a score out of 100. The Spanish version of the SUS was administered immediately after the intervention [27].
• The safety of the immersive experience. Simulator Sickness Questionnaire (SSQ). We assessed using the SSQ, adapted and validated for Spanish [28]. This tool is widely applied to measure cybersickness frequency in the general population [29]. The questionnaire was completed immediately after the intervention.
• Personal experiences with the Game Experience Questionnaire (GEQ–Post-Game Module) [30]. This module consists of 17 items scored from 0 (“not at all”) to 4 (“extremely”), grouped into four dimensions: positive experiences, negative experiences, tiredness, and return to reality [31].

The evaluation of IVR exergame effects on body composition and strength was carried out through different tests:

• Body Composition. Body composition was assessed using the Tanita MC-780 analyzer, which provided fat mass (FM), fat-free mass (FFM), muscle mass (MM), and total body water (TBW). We performed a segmented body composition analysis for the trunk, upper limbs (right and left), and lower limbs (right and left). Sex, age, and height were entered into the device, with height measured using a SECA stadiometer (SECA, Germany; accuracy: 0.1 cm). Data collection took approximately 20 s. Body mass index (BMI) was calculated as weight (kg) divided by height squared (m²). VFR was estimated indirectly and expressed on a scale from 0 to 59, where 1–12 indicates healthy visceral fat levels, and 13–59 indicates excessive levels. This BIA technology has been recently validated in adults with varying levels of physical activity [32].
• Muscular Strength. Upper-body strength was measured using a handgrip dynamometer (Jamar, Sammons Preston Inc., Bolingbrook, IL, USA). Participants performed the test in a seated position to enhance focus, an adaptation shown to have no significant effect (p > 0.001) compared to standing in individuals with DS [33,34]. Lower-limb strength and functional capacity were assessed using the Five Sit-to-Stand Test (5STS) [35]. Participants began seated with their backs against the chair, arms crossed over their chests, and feet firmly on the floor. They were instructed to complete five sit-to-stand cycles as quickly as possible. A visual demonstration and verbal encouragement were provided. A familiarization trial preceded two recorded attempts, and the mean time was used as the final measure [36,37].

2.5. Data Analysis

Descriptive statistics with means/standard deviations (SDs) and frequencies/% were used to summarize the demographic and clinical characteristics of the participants at baseline (n = 20). The results related to the usability and applicability of the immersive virtual reality headset and the exergame used in the Project were collected during the second and twelfth weeks of the intervention, following the protocols and interpreting the results based on the normative values established by the authors of the evaluation tools. Regarding the parameters related to the effect of the intervention program on strength levels and body composition, it should be noted that they were collected at two points: week 0 (Baseline) and week 13 (Post-intervention). Paired-sample two-sided t-tests were conducted to determine if there were statistical differences in the body composition variables and strength levels at the two evaluation points (baseline–post-intervention). To minimize the risk of Type I error due to multiple comparisons across strength and body composition variables, the Holm–Bonferroni correction was applied to the resulting p-values. Furthermore, the lower-limb strength was defined a priori as the primary outcome, while the remaining variables were considered secondary or exploratory. The normality of the distribution of the variable values was previously verified using the Shapiro–Wilk test. Statistical analyses were performed using SPSS (v.29, IBM Corp., Armonk, NY, USA). All tests were two-tailed, and a p value < 0.05 was the criterion for statistical significance. Given the nature of this feasibility study, a formal sample size calculation was not conducted. However, based on prior literature and considering the number of people with DS, a sample comprising 20 patients was considered suitable for assessing feasibility and examining the impact of the exercise intervention on secondary outcomes.

3. Results

A total of 20 adults with DS participated in the study, and none dropped out.

Table 1. General characteristics of the study participants.

	n = 20
	Mean	SD
Age (years)	29.85	9.37
Gender, female (%)	70.00	-
IVR Experience (%)	0.00
Height (cm)	153.29	9.23
Weight (kg)	64.47	16.18
BMI (Kg/m2)	27.88	5.86
Degree of intellectual disability, Mild (%)	80.00	-
Overweight (%)	20.00	-
Obesity (%)	40.00	-
Dominant hand, Right (%)	75.00	-

BMI: body mass index; IVR: immersive virtual reality.

shows the main characteristics of the sample.

Table 2. Usability, safety, and personal experiences regarding IVR intervention.

Variables	Intermediate Assessment 2 Weeks After the Start (n = 20)			Post Intervention Assessment (n = 20)
	Mean ± SD	Min	Max	Mean ± SD	Min	Max
SUS (0–100)	92.88 ± 18.15	76	100	95.03 ± 14.55	78	100
SSQ (0–48)	2.12 ± 1.15	0	7	1.98 ± 0.98	0	5
GEQ
Positive experiences (0–4)	3.01 ± 1.05	1	4	3.65 ± 0.85	2	4
Negative experiences (0–4)	0.00 ± 0.00	0	0	0.00 ± 0.00	0	0
Fatigue (0–4)	0.95 ± 0.66	0	2	1.35 ± 0.87	1	3
Return to reality (0–4)	0.25 ± 0.17	0	1	0.16 ± 0.10	0	1

GEQ: Game Experience Questionnaire; SSQ: Simulator Sickness Questionnaire; SUS: System Usability Scale.

, shown below, shows in detail the analysis of usability, safety, and personal experiences. Based on the findings, after two weeks of intervention, the mean score on the SUS was 92.88 ± 18.15, with values ranging from 76 to 100. This initial result already reflected a highly positive perception of the tool, placing it within a range considered excellent in terms of usability. At the end of the 12-week intervention, the mean SUS score increased slightly to 95.03 ± 14.55, remaining within the same high range (78–100). Although this increase was moderate, it confirms that participants’ perception of the program’s ease of use and usefulness remained consistently high throughout the intervention. The stability of these values suggests the viability of this experience (exergame) and the IVR system used.

Regarding safety, assessed using the SSQ, the results were equally encouraging. After two weeks, the mean score was 2.12 ± 1.15 (range: 0–7). By the end of the 12 weeks, the score decreased to 1.98 ± 0.98 (range: 0–5). These low values indicate that the intervention was well tolerated, with no increase in symptoms associated with dizziness, nausea, or discomfort. The reduction observed in the final measurement reinforces the idea that the program (exergame) and the IVR system did not generate relevant adverse effects and that safety was maintained throughout the intervention.

With respect to personal experiences, evaluated using the GEQ, changes were observed in the dimension of positive experiences. At two weeks, the mean score was 3.01 ± 1.05 (range: 1–4), while at the end of the 12 weeks it increased to 3.65 ± 0.85 (range: 2–4). This increase reflects an improvement in the participants’ satisfaction, enjoyment, and motivation, suggesting that the intervention was perceived as attractive and rewarding. In contrast, negative experiences remained nonexistent in both assessments, with a constant score. This finding is particularly relevant, as it indicates that no participant reported unfavorable sensations, frustration, or rejection toward the program at any point. However, we must be aware of the limitations imposed by the sample size used. The fatigue dimension showed a slight increase over time: at two weeks, the mean was 0.95 ± 0.66 (range: 0–2), while at the end of the program it rose to 1.35 ± 0.87 (range: 1–3). Although this increase suggests greater perceived effort in the final phase, the values remained low, indicating that fatigue was moderate and did not compromise continuity or acceptance of the program. Finally, the return-to-reality dimension presented low scores in both assessments, with a slight reduction from 0.25 ± 0.17 to 0.16 ± 0.10. These values suggest that participants’ transition after the experience was smooth, without difficulties in reintegrating into their usual context. The fatigue dimension showed a slight increase over time: at two weeks, the mean was 0.95 ± 0.66 (range: 0–2), while at the end of the program it rose to 1.35 ± 0.87 (range: 1–3). Although this increase suggests greater perceived effort in the final phase, the values remained low, indicating that fatigue was moderate and did not compromise continuity or acceptance of the program. Finally, the return-to-reality dimension presented low scores in both assessments, with a slight reduction from 0.25 ± 0.17 to 0.16 ± 0.10. These values suggest that participants’ transition after the experience was smooth, without difficulties in reintegrating into their usual context.

Overall, the usability and safety outcomes indicate that the program achieved high usability and safety from the early weeks through the end of the intervention. Positive experiences increased progressively, while negative experiences remained nonexistent. Although perceived fatigue rose slightly, participants continued to report an overall favorable experience, a well-tolerated intervention, and a positive impact on their general perception of the program. These findings reinforce the notion that the intervention was not only technically safe and effective but also enriching from the users’ subjective perspective. The combination of high usability, absence of adverse effects, and improvement in positive experiences is an indicator of the viability and acceptance of this exergame and the technology used. However, we must be cautious in our conclusions because this is a pilot study with a small sample size.

Regarding the effects of the exercise program delivered in immersive environments through the FitXR exergame, the intervention consisted of an average of 21.56 ± 2.44 sessions per participant, based on a planned schedule of two sessions per week (Mondays and Thursdays), resulting in a mean adherence rate of 89.83%.

Primary outcome—lower-limb strength: After 24 sessions of high-intensity training, lower-limb strength showed a statistically significant improvement (p = 0.018), with a large effect size (Cohen’s d = 0.89) (

Table 3. Evolution of strength parameters after the IVR-based program.

	Baseline (n = 20)			Post Intervention (n = 20)			Paired t Test	Holm-Adjusted p-Value	Cohen’s d
	Mean ± SD	Min	Max	Mean ± SD	Min	Max
Upper-body strength, dominant hand (kg)	23.44 ± 8.95	8.00	38.00	26.25 ± 7.38	15.00	39.00	t = −0.970; p = 0.340	0.680	0.34
Upper-limb strength, no dominant hand (kg)	23.31 ± 7.52	11.00	38.00	23.81 ± 7.47	10.00	39.00	t = −0.189; p = 0.852	1	0.07
Lower-limb strength (s)	13.01 ± 3.59	7.31	18.43	10.48 ± 1.85	7.14	13.41	t = −2.504; p = 0.018	0.018	0.89

).

Secondary (exploratory) outcomes: For all secondary outcomes, positive trends with small-to-moderate effect sizes (d = 0.07–0.34) were observed; however, none reached statistical significance after Holm–Bonferroni adjustment (all adjusted p > 0.05) The main results of body composition parameters are shown in

Table 4. Evolution of body composition parameters after the IVR-based program.

	Baseline (n = 20)			Post Intervention (n = 20)			Paired t Test	Holm-Adjusted p-Value	Cohen’s d
	Mean ± SD	Min	Max	Mean ± SD	Min	Max
Weight (kg)	64.47 ± 16.18	40.00	98.90	64.70 ± 16.38	40.20	98.20	t = −0.040; p = 0.968	1	0.01
BMI (Kg/m2)	27.88 ± 5.86	20.10	41.20	28.05 ± 5.91	20.20	40.90	t = −0.084; p = 0.934	1	0.02
Fat Mass (Kg)	15.92 ± 9.06	4.20	32.50	14.94 ± 8.63	3.20	31.00	t = 0.314; p = 0.756	1	0.07
Fat-Free Mass (Kg)	48.55 ± 9.50	35.80	67.40	49.76 ± 9.75	35.00	67.20	t = −0.356; p = 0.724	1	0.08
Muscular Mass (Kg)	46.09 ± 9.06	34.00	64.10	47.24 ± 9.29	33.20	63.90	t = −0.356; p = 0.724	1	0.08
Total Body Water (Kg)	36.16 ± 6.48	26.80	52.30	37.05 ± 7.07	26.70	49.20	t = −0.386; p = 0.702	1	0.09
Trunk
Fat Mass (Kg)	8.73 ± 5.53	0.70	18.90	7.43 ± 5.47	0.60	19.10	t = 0.665; p = 0.511	1	0.15
Fat-Free Mass (Kg)	27.71 ± 4.54	20.90	35.30	26.30 ± 4.56	19.50	35.20	t = 0.875; p = 0.389	1	0.20
Muscular Mass (Kg)	26.40 ± 4.39	19.90	33.80	25.04 ± 4.42	18.50	33.70	t = 0.871; p = 0.391	1	0.20
Upper Limb
Fat Mass, left (Kg)	0.84 ± 0.62	0.20	2.30	0.94 ± 0.66	0.20	2.30	t = −0.415; p = 0.681	1	0.09
Fat-Free Mass, left (Kg)	2.65 ± 0.85	1.20	4.60	2.71 ± 0.75	1.60	3.70	t = −0.220; p = 0.827	1	0.05
Muscular Mass, left (Kg)	2.49 ± 0.79	1.10	4.30	2.56 ± 0.71	1.50	3.50	t = −0.236; p = 0.815	1	0.05
Fat Mass, right (Kg)	0.78 ± 0.60	0.20	2.20	0.83 ± 0.49	0.30	2.00	t = −0.256; p = 0.800	1	0.06
Fat-Free Mass, right (Kg)	2.73 ± 0.97	0.80	4.80	2.81 ± 0.86	1.70	4.60	t = −0.271; p = 0.788	1	0.06
Muscular Mass, right (Kg)	2.57 ± 0.91	0.70	4.50	2.64 ± 0.80	1.60	3.70	t = −0.247; p = 0.806	1	0.06
Lower Limb
Fat Mass, left (Kg)	2.81 ± 1.73	1.00	7.20	2.91 ± 1.56	0.90	6.40	t = −0.172; p = 0.865	1	0.04
Fat-Free Mass, left (Kg)	7.66 ± 1.74	5.60	11.20	8.70 ± 2.16	6.00	12.70	t = −1.502; p = 0.143	1	0.34
Muscular Mass, left (Kg)	7.24 ± 1.64	5.30	10.60	8.24 ± 2.04	5.70	12.00	t = −1.538; p = 0.135	1	0.34
Fat Mass, right (Kg)	2.74 ± 1.75	0.90	7.20	2.91 ± 1.53	0.80	5.80	t = −0.290; p = 0.774	1	0.07
Fat-Free Mass, right (Kg)	7.81 ± 1.71	5.60	11.50	8.99 ± 2.07	6.20	12.60	t = −1.748; p = 0.091	1	0.39
Muscular Mass, right (Kg)	7.39 ± 1.62	5.30	10.90	8.52 ± 1.95	5.90	11.90	t = −1.786; p = 0.084	1	0.40

.

Body composition (exploratory): Following the IVR program, most body composition parameters showed minimal and non-significant changes. In accordance with multiplicity control, none of the variables met the significance threshold after Holm–Bonferroni adjustment (p_adjusted = 1.000). Small-to-moderate effect sizes for leg muscle mass (d = 0.34–0.40) are reported as exploratory signals and should not be overinterpreted in the context of this pilot design. This suggests that while high-intensity training may initiate hypertrophic trends, the 24-session duration or the inherent lack of sensitivity in conventional BIA may have prevented these changes from reaching statistical significance in this specific population.

4. Discussion

This pilot study evaluated a high-intensity exercise program delivered through immersive virtual reality in adults with Down syndrome, showing excellent usability and tolerability of the platform, high adherence (90%), and a significant improvement in lower-limb strength with a large effect size, while changes in body composition were minimal after 12 weeks. These findings are consistent with previous literature indicating that immersive exergames can elicit moderate-to-vigorous exercise intensities accompanied by positive affect and enjoyment, which may enhance adherence, and that in populations with Down syndrome, early adaptations are more commonly observed in muscle strength than in body composition when no dietary intervention is included [1,6,38,39]. Importantly, the study was powered to detect changes in the primary outcome (lower-limb strength), whereas secondary outcomes, including body composition, were exploratory, did not survive correction for multiple comparisons, and should therefore be interpreted cautiously and considered hypothesis-generating. The small-to-moderate effect sizes observed for muscle mass suggest potential hypertrophic trends that warrant confirmation in adequately powered trials with longer intervention durations and more sensitive body composition assessment methods.

SUS scores (93–95/100) are well above the reported average (68) and fall within the “Excellent” category, suggesting an outstanding user experience maintained from week two to the end of the intervention [40]. Similarly, low and decreasing SSQ scores (2.12 → 1.98/48) indicate good tolerability and minimal cybersickness; although absolute SSQ interpretation requires caution due to heterogeneity and the debated “zero baseline” assumption, the observed profile is consistent with a safe exposure for this population [41,42]. In older adults and rehabilitation contexts, evidence further supports that, with ergonomic and task adjustments, IVR can be implemented safely in vulnerable groups [43]. The increase in positive experiences (GEQ) alongside the absence of negative experiences reinforces that immersion and contingent feedback inherent to exergames enhance positive affect and motivation—core dimensions of the GEQ [30]. Recent controlled trials show that, compared to conventional or 2D conditions, sessions in FitXR/BOXVR are associated with greater enjoyment and often physiological responses comparable or superior to traditional exercise, especially in modes requiring vigorous intensity [6,39]. The observed adherence (89.8%) aligns with qualitative analyses identifying instructor support, equipment provision, and motivational feedback as key facilitators for continuity in virtual programs for individuals with disabilities [5,44].

The main finding was a significant improvement in lower-limb strength (large effect size), while upper-limb changes were small/non-significant. This asymmetry is physiologically plausible in DS and consistent with meta-analyses and RCTs reporting robust gains in knee extensors after ≥4–10 weeks of resistance or combined training, with moderate-to-large effect sizes, whereas functional improvements in gait or stair climbing may require longer periods [1,2]. In high-intensity IVR, boxing/fitness movement patterns (punches, pivots, squats) impose repeated loads on the lower limbs, reaching moderate-to-vigorous intensities and favoring neuromuscular adaptations; conversely, upper-limb improvements typically require progressive external overload (dumbbells/bands/machines) and periodization to achieve hypertrophy or greater strength gains [6,39].

Despite the high intensity of the exercise program, monitored by RPE (16–17) and heart rate (minimum 70% of HRmax according to the Fernhall equation), changes in weight, BMI, and fat mass were minimal. Overall, the results suggest that the IVR program did not produce substantial changes in overall body composition; however, a positive trend was observed in lower-limb muscle mass, with moderate effect sizes (d = 0.34–0.40), which may indicate emerging benefits in strength and functionality. These findings are consistent with current literature, which suggests that body composition in DS responds more slowly to physical stimulation and generally requires a combination of structured progressive overload (≥2–3 days/week), adequate weekly volume, and dietary intervention (controlled energy deficit) to achieve clinically meaningful differences within 8–12 weeks; often, ≥24 weeks are needed [4,38,45]. Furthermore, the absence of substantial changes in body composition should be interpreted considering the inherent limitations of bioelectrical impedance analysis (BIA) in individuals with DS. This is primarily due to the unique anthropometric morphology of this population, characterized by shorter limbs and a wider trunk, as well as the current lack of validated predictive equations specifically tailored for this group [46]. Consequently, conventional BIA may lack the necessary sensitivity to detect subtle tissue variations. When coupled with the slower metabolic response typically observed in DS, these findings suggest that future research should prioritize the use of Bioelectrical Impedance Vector Analysis (BIVA) or dual-energy X-ray absorptiometry (DXA) for a more precise and reliable assessment [46].

The findings of this study highlight several practical considerations for implementing IVR exercise programs in adults with DS. First, it is essential to consolidate high-intensity training through objective monitoring—such as percentage of heart rate reserve (% HRR), heart rate variability (HRV), and ratings of perceived exertion (RPE)—while progressively increasing task difficulty and prioritizing game modes that demand power and intermittent work [6,39]. Second, to optimize strength development, particularly in the upper limbs, practitioners should integrate external overload (e.g., resistance bands, free weights) two to three times per week, complementing the IVR stimulus for lower limbs and aligning with current resistance training guidelines for individuals with Down syndrome [1,2]. Additionally, when the goal includes changes in body composition, incorporating a nutritional strategy—such as a moderate energy deficit combined with adequate protein intake—becomes critical [4,38]. Finally, maintaining behavioral support mechanisms, including instructor guidance, real-time feedback, and graded goal setting, is recommended to sustain adherence and engagement throughout the intervention [5,44].

Limitations

Despite the promising results, this study presents several limitations that should be acknowledged. First, the single-arm design and the moderate sample size (n = 20) limit causal inference, as observed effects—particularly for secondary outcomes—may reflect regression to the mean, natural variability, or measurement error rather than true intervention effects, and reduce the ability to detect small changes, especially in body composition outcomes [1,38]. Accordingly, findings beyond the prespecified primary outcome should be interpreted as preliminary and hypothesis-generating, which underscores the need for future randomized or controlled studies with adequate statistical power.

Moreover, the 12-week intervention period may have been insufficient to induce significant changes in fat mass in the absence of a concurrent dietary intervention, as improvements in functional and compositional parameters in adults with Down syndrome often require medium-term programs (≥24 weeks) [2,38]. This limitation informs future research directions, suggesting that longer intervention durations and combined exercise–nutrition approaches may be necessary to capture meaningful changes in body composition.

Although the program was designed to elicit high-intensity training stimuli, the segmental dosing for upper limbs may have required more specific overload to induce hypertrophy or greater strength gains, highlighting the need for optimized resistance prescription in subsequent trials [1,39].

Additionally, interpretation of cybersickness using the SSQ remains challenging due to variability in its application and the debated zero-baseline assumption, which may affect comparability across studies [41,42]. Finally, a notable limitation concerns the use of BIA for body composition assessment. Its accuracy may be compromised by the distinctive morphology and muscle hypotonia associated with Down syndrome, which affect electrical conductivity and the validity of standard prediction equations, potentially leading to overestimation of fat mass [46,47]. As a result, BIA may lack the sensitivity required to detect subtle compositional changes in short-term interventions, further supporting the use of more sensitive assessment methods and longer follow-up periods in future research [46,48].

Finally, the generalizability of these findings is limited by the use of a single commercial exergame and a specific hardware configuration; further research should confirm whether similar outcomes can be achieved with other platforms and devices [28].

5. Conclusions

The preliminary results of this study show that people with DS can carry out a high-intensity interval training protocol, and moreover, do this in an immersive virtual environment. These findings suggest that IVR-based exercise is a safe, engaging, and feasible strategy for promoting physical activity and enhancing functional strength in adults with DS. Further controlled trials with longer duration and nutritional strategies are warranted to optimize body composition outcomes.