Introduction

In the last twenty years, research interest on parasport had growth exponentially likely due to an increase in the number of parasports events and competitions1. One of the targeted population includes subjects with Intellectual Disability (ID) as they are generally less active and exhibit higher levels of sedentary behaviours than the average of not-ID population2,3. Indeed, Dairo and colleagues4 showed that about 90% of individuals with ID did not reach the suggested amount of physical activity per week recommended by the World Health Organization5.

Physical and mental health problems in adults with ID are significantly associated with sedentary behaviours6 and, consequently, have a negative impact on health-related determinants (i.e. body composition, cardiovascular and muscular endurance, flexibility and muscular strength)7. In particular, it has been shown that approximately the 80% of people with ID are overweight or obese and have a body mass index (BMI) higher than the average population3. These abovementioned factors may contribute to an increased risk of suffering physical dysfunction, cardiovascular diseases or chronic health problems8. Moreover, individuals with ID are likely to show lower level of cardiovascular endurance9, muscular strength10, muscle coordination and balance control11 compared to the general population. Additionally, many individuals with ID have issues with postural stability, movement planning, and speed12, which could negatively impact on their daily life activities and independence.

Considering the physiological and psychological issues that individuals with ID might cope with, engaging in physical activity and sport activities could represent a valuable tool for both social inclusion13 and fitness enhancement14,15, improving their motor, communication, social and cognitive skills12,16.

Several researchers suggested that physical activity and sport intervention programs positively contributed to the overall person development (physical, psychological, cognitive, and social development)12,16 and life quality improvements in individuals with ID10,14. Despite these evidences, Barnes et al.3 reported that the most common physical activity that a large sample of adults with ID referred to do is merely walking, which might not be sufficient to fulfil the above described social and physiological needs of people with ID when walking is alone without others17.

Team sports, compared to individual training, could not only improve fitness level but also increase interactions among participants. In the field of parasport research, basketball is the most analysed sport1 and it has been investigated in several studies with subjects with ID18,19,20,21,22. Indeed, basketball practice, which includes many of the basic motor skills such as running, jumping, shooting, change of direction skills and defensive and offensive skills22, represents an effective training for both cardiovascular endurance23 and muscular strength9,20 in population with ID.

Two different settings have been commonly used in basketball training for people with ID: the specific or the inclusive activity. In the first arrangement, sport is designed exclusively for persons with ID, and is based on the protective role of a specific educational institution24. On the contrary, in the inclusive setting, people with ID train together with people without ID in the same context25. The role of the inclusive context is the promotion of social inclusion throughout the sport activity26 where athletes with and without ID compete together in the same team, such as in the Special Olympics Unified Sports19,21,27. Playing with peers without ID could increase the perception of sport competence in athletes with ID28 and could improve the self-awareness of their physical limitations19. In addition, the inclusive sport practice aims to impact on individuals without disability. Indeed, the first goal of the Unified Sports, is to create a context where all athletes are challenged to improve their skills, regardless of their physical and mental health conditions19.

Still now, barriers in the development of inclusive fitness contexts are due to prejudices and preconceptions of people without disability29. A recent report on perceptions of people without disability about integrated sport, showed that around two thirds of people had no knowledge of what the term ‘inclusive sport’ means. Moreover, they stated that the major benefit of inclusive activities in people without disability is the social and personal enrichment, whereas individual sport skills and fitness improvement were not mentioned among the hypothetical benefits of inclusive sports30. In general, the major concern in people without disability, regarding the integrated sport, is the common thought that training with teammates with ID is less effective than a regular sport environment and could under challenge their training level31. Baran and colleagues32 investigated the effect of 8 weeks of Unified Sports Soccer training in athletes with and without ID. The authors found that the program was effective in increasing fitness and soccer skill performance of all athletes, even if in a more modest degree than those with ID32.

Although the research on inclusive sport has growth in the last few years, to our knowledge there is a lack of studies that analyse the improvement of both people with and without ID during inclusive sport practice32,33. Moreover, some recent reviews showed that only few studies on physical activity and ID the effects of sport interventions on people with ID34,35, suggesting the need to focus on this assessment area. In addition, studies with long training intervention programs are needed to understand the long-term benefits on fitness improvement in both people with and without ID7,10.

Thus, this study had three different aims. The first aim was to evaluate the effects of 9-month basketball training on fitness level of athletes with ID comparing non-inclusive setting, inclusive setting and sedentary persons with ID (control group). The second aim was to evaluate the potential role of the inclusive basketball training on fitness level of athletes without ID. The third aim was to assess the correlation of each fitness variable with subjects’ ID levels. We hypothesized that subjects with higher ID level have the poorer gross motor control that could affect performance on physical fitness tests, resulting in lower fitness level.

Methods

Experimental approach to the problem

A repeated-measures experimental design was used to quantify the effects of inclusive basketball training intervention on fitness and health of athletes with and without ID. The experimental protocol was conducted in four consecutive steps. In the first step, all subjects with ID underwent a medical-psychiatric examination conducted by a mental health staff to assess their diagnosis of ID, in order to define their level of intellectual functioning and of corresponding functional abilities (i.e., levels of adaptive functioning), and abilities in communicating36. Moreover, all participants underwent a compulsory physical examination including a general medical history and sports-related history, with a standardized questionnaire followed by supplementary questioning; a physical examination; an electrocardiogram at rest performed and interpreted by a specialist in sports medicine37. The physical examination was performed for determining the participants’ athletic eligibility.

In the second step, all subjects were assessed before the specific intervention period (Pre) through fitness and coordinative tests.

In the third step, all players of both inclusive (INC) and non-inclusive (N_INC) groups participated in a 9-month basketball specific training program of 3 h per week (2 times × 90 min). Each basketball training session consisted in four phases which could be adapted following the specific coaches’ goals during the same training session (Fig. 1). Each phase required a different type of weight training and conditioning program for players to follow and it was designed to prepare players for the rigours of training and game play38. Details on basketball training are described in the Appendix 1. During the same 9 months, the sedentary control group (CG) participated in a recreational and leisure activity program, focused on artistic, logic and/or cooking activities (artistic lab, logic lab and/or cooking lab).

Figure 1
figure 1

Training session schedule.

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In the fourth step, all subjects were assessed after the specific intervention period (Post) through the same fitness and coordinative tests performed in the second phase.

Subjects

A total of 99 subjects with ID (36 females, 63 males) and 14 subjects without ID (5 females, 9 males) volunteered to participate in the study. The 14 athletes without ID and 38 athletes with ID and (no-disability group) were randomly assigned to inclusive sport group (INC), 38 athletes with ID were randomly assigned to non-inclusive sport group (N_INC) and the remaining 23 participants with ID were randomly assigned to the control group (CG; not attending to any sport).

All subjects with ID lived at home or in group settings, and none was institutionalised. They were classified as having mild (28.3%), moderate (29.3%), and severe (42.4%) ID. All participants were recruited from sports clubs (athletes) or social cooperatives in Rome (control group). All athletes had to be exclusively involved in the project “Sport anch’IO” [ME are sports too]. Inclusion criteria were being adults, never having participated in inclusive sporting activities. For participants with ID, having a neuropsychiatric diagnosis of mild, moderate, or severe ID, not having physical and/or sensory disabilities. Exclusion criteria included having profound ID. The study was approved by the Ethics Committee for Transdisciplinary Research (CERT) of Sapienza University of Rome (ricerca ID n. 7/2022 revisione 2 del 20.02.2023) in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. Written informed consent was obtained from all participants and from their parents or their legal guardians (if indicated) after a detailed description of the procedures was provided.

Measurements

Before recording anthropometric measurements, fitness and coordinative test scores, all subjects had a variable number of familiarization sessions. The number was related to the speed with which the participants got used to the field tests.

Anthropometric measurements, physical fitness and coordinative abilities were evaluated through modified and validated test battery for individuals with ID. All the tests had a high reliability in people with ID (ICC range 0.90–0.99)9.

Pre- and post-intervention participants’ weight, height, body mass index (BMI) and body fat were assessed. Weight and height were measured using a scale and a stadiometer to the nearest 0.2 kg and 0.1 cm, respectively. Biceps, triceps and suprailiac thickness was measured to the nearest 0.2 mm using a calliper (Harpenden, St Albans, UK) on the right side of the body. All skin folds were taken three times by the same experimenter to ensure consistency in results with the average of the three values used as a final value. To predict body fat (%FM) the equation described by Durnin and Womersley39 was selected for this investigation.

Pre- and post-intervention participants’ physical fitness variables were assessed: cardiovascular endurance (VO2max) (step test), explosive leg power (standing long jump test), hip joint flexibility (sit-and-reach test), forearm muscular strength (hand grip test), upper-body and trunk muscular strength and endurance (push-up and sit-up tests, respectively), and agility and speed of lower limbs (shuttle run 10 × 5 m test)9. Moreover, pre- and post-intervention participants’ coordinative abilities were assessed: balance ability (flamingo test), motor coordination (timed up and go test), coordination and speed of upper limbs (plate tapping test)9. Details on test protocols are described in the Appendix 2.

Statistical analysis

An a priori power analysis to determine sample size was completed using G*Power 3.1.9.7 software. The Type I alpha (error level) at 5% and a Type II beta (error level) of 5% (or a power of 95%) were set a priori. This analysis showed that for the medium effect size of 0.25 and an error probability of 0.05 with a power of 0.95, the sample size would need to be N = 66. Thus, the target size of the sample recruited for this study was greater than 66 participants. A sample of this size will provide the study with the requisite power needed to provide valid results40.

Descriptive analysis

All results were expressed as mean ± standard deviation.

Inferential analysis

Individuals with ID

Data were analysed using a mixed-model analysis of variance (ANOVA) with group as between-participants factor and time as within-participants factor. The main effects of group (three levels, INC vs. N_INC vs. CG), time (two levels, pre vs. post) and the interaction between them (time x group) were assessed. Bonferroni post hoc analysis was subsequently performed to interpret data results when significant main effects and interactions were observed. Partial eta squared was used to calculate the effect size of the different variables (partial ƞ2 = small ≥ 0.01, medium ≥ 0.06, large ≥ 0.14).

A bivariate correlation analysis (Spearman correlation coefficient) was performed to examine the relationship between ID levels (1 = mild, 2 = moderate, 3 = severe) and all parameters measured at baseline and their changes (∆) following the intervention period.

Individuals without ID

A paired t-test comparison was conducted on each variable to examine the intervention effect (pre vs. post) in the no-disability group. Cohen’s d was used to calculate the effect size of the different variables41.

Improvement degree (∆) analysis among trained groups

For each athletes’ variable evaluated after the intervention, we calculated the absolute variation (∆) with respect to its preintervention value (postintervention value—preintervention value). The analysis of variance (one-way ANOVA) was then performed to examine the effect of intervention (three levels, INC vs. N_INC vs. no-disability group) on the absolute variation in each variable, followed by post hoc analysis (Bonferroni adjustment) to determine effects within the three intervention groups.

Statistical significance was defined as p < 0.05. Statistical analysis was performed with SPSS Version 27.0 statistic software package.

Results

Individuals with ID

The ANOVA revealed a significant main effect of time on weight, BMI, cardiovascular endurance, balance ability, forearm muscular strength, upper-body strength and endurance, trunk muscular strength and endurance (p < 0.01), a significant main effect of group on explosive leg power, forearm muscular strength, strength, upper-body strength and endurance, trunk muscular strength and endurance, agility and speed of lower limbs, coordination and speed of upper limbs (p < 0.05) and a significant time x group interaction on weight, %FM, BMI, balance ability, hip joint flexibility, upper-body strength and endurance, trunk muscular strength and endurance, motor coordination, agility and speed of lower limbs, coordination and speed of upper limbs (p < 0.05) (Table 1).

Table 1 ANOVA results in anthropometric, fitness and coordinative ability variables.
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Specifically, both INC and N_INC groups significantly improved weight, BMI, balance ability, upper-body strength and endurance, trunk muscular strength and endurance, agility and speed of lower limbs, coordination and speed of upper limbs while CG group significantly worsened weight, BMI, trunk muscular strength and endurance, motor coordination, agility and speed of lower limbs, coordination and speed of upper limbs after the intervention (Table 2).

Table 2 Pre- and post-test (mean values ± SD) in INC group, N_INC group and CG group.
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Explosive leg power and forearm muscular strength were significantly affected by the group regardless of the time, showing that CG performances were significantly lower than INC and N_INC athletes’ performances (76.1 ± 38.1 vs. 108.7 ± 41.8 vs. 88.7 ± 52.2 cm; p < 0.05 and 16.8 ± 16.6 vs. 40.5 ± 22.8 vs. 38.1 ± 23.2 kg; p < 0.05, respectively).

The application of Spearman’s correlation analysis indicated that ID level was significantly correlated with 10 of the 13 parameters measured at baseline (Table 3). Moreover, correlation analysis indicated that ID level was positively correlated with the coordinative changes (timed up and go test ∆) following the intervention period (p = 0.03, R = 0.28), revealing that people with lower ID obtained higher ability score in motor coordination.

Table 3 Correlation coefficients between ID level and variables measured at baseline.
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Individuals without ID

No-disability group significantly improved weight, %FM, BMI, cardiovascular endurance, hip joint flexibility, forearm muscular strength, trunk muscular strength and endurance, motor coordination, agility and speed of lower limbs, coordination and speed of upper limbs after intervention (Table 4).

Table 4 Pre- and post-test (mean values ± SD) in no-disability group.
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Improvement degree (∆) analysis among trained groups

Improvement across intervention for each trained group (INC, N_INC, no-disability group) was analysed using absolute variation (∆). ANOVA revealed that no-disability group showed the higher reduction of %FM comparing with both INC and N_INC groups (F2,80 = 8.48, p < 0.001, ƞ2 = 0.175), N_INC group showed the higher improvement of balance ability (F2,64 = 4.10, p = 0.021, ƞ2 = 0.114) and upper-body strength and endurance (F2,81 = 3.81, p = 0.026, ƞ2 = 0.086) comparing with no-disability group and finally, INC group showed the higher improvement of agility and speed of lower limbs (F2,84 = 3.84, p = 0.025, ƞ2 = 0.084) and coordination and speed of upper limbs (F2,79 = 6.69, p = 0.002, ƞ2 = 0.145) comparing with no-disability group and N-INC group, respectively (Table 5).

Table 5 Variation (∆) of each measured parameter in INC group, N_INC group and no-disability group (mean values ± SD).
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Discussion

Individuals with ID

The first aim of the present study was to evaluate the effects of 9-month basketball training on fitness level of individuals with ID comparing inclusive setting, non-inclusive setting and sedentary people.

Results showed the positive effects of physical activity and sport training on fitness level of subjects with ID since athletes of both INC and N_INC groups significantly improved in most of the anthropometric, fitness and coordinative tests after the basketball training period. In particular, they significantly improved their weight status compared to CG. Thus, these data suggested that physical training could prevent weight gain, a common condition in persons with ID, and also could favour the loss of fat mass. These findings on the positive role of sport training on body weight management in individuals with ID were in line with those of previous studies9,27,42. However, the loss of body weight depends on training volume and intervention duration43. A more limited intervention time than considered, could not be able to produce a weight or BMI decrease32. Conversely, the sedentary CG increased their weight and BMI. Inactivity and inappropriate eating habits may be the major causes of the weight gain of CG and, in general, of the high obesity rates of individuals with ID that is usually greater among people with ID than those without disability9.

After basketball training period, athletes showed significant improvements of balance ability, trunk muscular strength, agility and upper-body speed. Previous studies showed that sport and physical activities induced significant improvements in numerous fitness outcomes such as muscle strength15,20,32,42,44, movement speed45 static and dynamic balance42,44, flexibility42,44, walking speed and agility44 in people with ID.

Graham and Reid2, in their 13-year longitudinal study, reported that the magnitude of fitness decrease over time in people with ID is higher than the one expected in the general population. Thus, sport activity plays a crucial role in physical health maintenance slowing down the typical fitness decline of this special population.

Even if the key role of sport participation in people with ID appears widely shared, Cuesta-Vargas and colleagues46, in their observational study, concluded that there were not meaningfully differences between the sportspeople and non-sportspeople with ID in strength, balance, aerobic fitness, and flexibility. These findings could be explained by measurements issues. In fact, as the authors themselves pointed out46, using specific tests for people with ID might have led to different results of fitness scores. Thus, according with existing literature18,47, we suggest that this type of studies should mainly include tests specific for individuals with ID than fitness test batteries used for the general population.

Our findings revealed that people with a low ID level showed better scores in fitness tests than people with severe ID level. These results were in line with previous studies on motor coordination9, sport skills18 and muscle strength48.

Moreover, correlation analysis between fitness performance improvement after intervention and ID level revealed that ID level was positively correlated with changes in motor coordination alone, suggesting that the rate of enhancement in fitness performance after a sport training program seems not to be directly correlated with ID severity. In the literature, there are many works with contradictory results on this topic. Guidetti and colleagues18 found that after a 4-month basketball training, athletes with mild and moderate ID achieved higher improvements in sports ability compared to individuals with more severe ID. In agreement with them, Wu and colleagues49 reported that subjects with mild ID showed the highest effectiveness on anthropometric outcomes after a 6-month fitness program. Moreover, Isık and Zorba50 found that 12 weeks of hemsball training were more effective in increasing the motor proficiency of adolescents with moderate ID compared to peers with mild ID.

The individual response to training could be the key to explain the different improvement rate of athletes with different ID levels.

Individuals without ID

After 9 months of inclusive basketball training, no-disability group significantly improved most of the measured parameters. In particular, subjects without ID showed a significant improvement of their weight status differently from the other intervention groups. Most of the research studies focused on integrated sport reported the effects of sport training in people with ID and did not pay attention on its effects in people without ID19,25,28 However, Baran and colleagues32 found no significant changes in body composition of subjects without ID who participated in 8 weeks of integrated soccer training. Authors argued that a longer intervention period was needed to obtain significant changes in body composition parameters. Authors also reported that an integrated soccer program was effective in improving soccer skills performance in both individuals with and without ID32. In agreement with them, Castagno and colleagues21 found improvements in basketball skills after 8 weeks of Unified Sports program in all participants with and without ID. In our study, we did not assess the specific basketball skills, however we supposed that the significant improvement of cardiovascular fitness, flexibility, strength, dynamic balance, agility and motor coordination could positively affect sport performance. Previously, Stanish and Temple51 found that a peer-guided exercise programme for adolescents with ID was effective in increasing some fitness-related outcomes also in their peers without ID. In particular, they found significant improvements in BMI, arm strength and walking speed of participants without ID after 15 weeks of individualized weight, aerobic and flexibility training together their peers with ID51. Despite these positive results in line with the results of our study, it should be considered that the peer-guided inclusive setting is very different from a team sport setting, where all participants play together and interact within the group toward the same goals. Therefore, involving in the same training group individuals with and without ID does not limit but favours the beneficial effects that training induce on people without ID. However, further studies are needed in order to evaluate the effectiveness of inclusive sport training on fitness and on specific sport skills of people without ID.

Improvement degree (∆) analysis among trained groups

Previous studies have investigated the impact of inclusive and/or non-inclusive settings in physical activity programs for individuals with ID. However, these studies primarily addressed psychological aspects such as perceived social stigma52, self-esteem21, and social inclusion26. To date, there has been limited research on fitness- or sport-related outcomes within inclusive and/or non-inclusive settings25,32,51. Ninot and colleagues25 analysed the effects of 32 months of integrated and segregated swimming training in adolescents with ID. The study showed a performance improvement over time in both intervention groups with no significant differences between the two settings. Other studies confirmed the effectiveness of integrated sport training in improving sport skills and fitness outcomes32,51.

Our analysis of fitness tests’ variation across intervention revealed a similarity between the two INC and N_INC groups, while the no-disability group showed the higher improvement in some fitness test comparing with INC and N-INC groups. These results suggested that it is the training itself to lead the athletes’ performance improvement rather than the type of training setting.

Limitations of the study

Subjects with severe ID could have experienced difficulty in the understanding of some tasks during fitness assessment. Therefore, despite the continuous supervision and feedback provided by trainers and investigators, casual errors in fitness measurements could have arisen. Another limitation of the study is the lack of assessment of sport skills of both people with and without ID. A third limitation results from the lack of assessment of further psychological and social aspects that could be positively influenced by inclusive sport practice. Moreover, no effects of participants’ demographic characteristics, cultural sensitivity and environmental factors could be accounted for in the analyses. The relatively small number of athletes without ID and the unequal distribution of males and females within the three intervention groups could have affected the inclusive basketball training. Finally, a limitation results from the lack of assessment of exercise volume and from the lack of monitoring of exercise intensity during basketball training.

Conclusion

Findings of the present study showed that inclusive basketball training improved fitness level of athletes with ID, decreasing health risks. Moreover, our results novelly showed that inclusive sport training induced beneficial effects also on persons without ID.

Therefore, the present study adds new evidences related to the positive impact that sport training could have on physical fitness of population with ID. In fact, regardless of the sport activity setting, 9 months of sport training induced significant improvements in fitness level of individuals with ID compared to sedentary peers with ID. Moreover, considering the positive effects that inclusive sport settings could have for social inclusion, we suggest that inclusive training could be a valid way to promote physical and psychological health of people with ID. Finally, results of the present study showed a significant improvement of fitness and coordinative test also in athletes without ID, going beyond the common thought that inclusive sport settings could be ineffective to enhance fitness level of people without ID. Future studies are needed to investigate different strategies for social inclusion of people with ID through inclusive sport, in order to evaluate the impact that fitness enhancement could have on sport skills during unified sports matches and competitions.