Evaluation of a sitting light volleyball intervention to adults with physical disabilities: Qualitative study using social–ecological approach

Background: This study was part of a 15-week sitting light volleyball (SLVB) intervention programme which examined the effectiveness of the intervention on physical and psychological attributes of adults with physical disabilities (PWPD) in Hong Kong. SLVB was a new sport, combing Paralympic volleyball and light volleyball. Gaining an in-depth understanding of the perceptions and experiences of PWPD in the SLVB intervention is critical to further develop SLVB as a PA intervention and sport. Using a social–ecological model (SEM), (a) the participants’ experiences regarding the intervention were assessed and (b) the suitability and feasibility of the SLVB intervention to PWPD were qualitatively examined. Methods: Twenty participants (mean age = 53.52 years standard deviation (SD = 9.02), 60% female participants; 25% had at least a college degree) attended our semi-structured interviews. Results: Using content analysis, their experiences at the individual or intrapersonal level (physical and psychological health, enjoyment, novelty, competence autonomy); interpersonal levels ( socialization, teamwork, social support); organizational and community levels (perceived sport venue environment, venue accessibility, safety, dissemination of information, and community facilities); and policy level (resources allocation by the government) were obtained. The participants also commented on the suitability and feasibility of the SLVB intervention for PWPD, contents and coaching, modified rules, duration of session and scheduling, and number of participants and coaches. Conclusion: This qualitative study identified several themes for engaging PWPD in SLVB, and demonstrated that adopting a multilevel approach to intervention in SLVB has positive outcomes to participants. In general, SLVB is suitable and feasible to PWPD. The study contributes to an in-depth understanding of the experiences among PWPD in the SLVB intervention, which is very critical to the further development of SLVB in terms of a PA intervention and sport.

study to examine methods to promote participation in sports by PWPD. Schools for PWPD expressed concern regarding the decrease in types of sports and number of courses offered to them.
Furthermore, only students with relatively high levels of motor ability and cognitive function were selected for participation in existing sports programs [3]. The HKSAR Government advocates sport for all, including PWPD; accordingly, in recent years, the HKSAR Government has increased the allocation of resources to support the development of sports for PWPD. The expenditure on development of sports for PWPD for the year 2018-19 was estimated to be $70 million, which is an increase of more than 50% over the previous year, and it includes hosting local large-scale sports events for PWPD [4].
In addition to promoting existing sports programs, practitioners and researchers [3] are recommended to develop new physical activities (PAs) for PWPD. Light volleyball (LVB) is a relatively common PA for older adults in China [5]. Compared with the traditional ball, the LVB is bigger (with a diameter of 80-83 cm vs traditional volleyball of 65-67 cm), lighter (100-150 g vs 250 g), and travels at a lower velocity; furthermore, the LVB remains airborne for longer than the traditional ball, which increases the rally time between players during the games. Additionally, LVB can be played in a standard badminton court. Team composition is 10 members as a team with five players on court.
The height of the net for men and women is 2 m and 1.8 m, respectively. Studies in China have indicated that older adults gain physical and psychological health benefits by practicing LBV regularly [6,7]. Leung and colleagues [8] conducted a 15-week LVB intervention to evaluate its effectiveness in improving physical and psychological attributes among adults aged ≥60 years in Hong Kong. The control group (CG) showed significant improvements in agility, cardiovascular endurance, upper and lower extremity muscle strength, and PA enjoyment when compared with the participants in the rouliqiu (RLQ) group and those in the LVB group [8]. The participants in the LVB group also demonstrated higher cardiovascular endurance, upper extremity muscle strength, and PA enjoyment than participants in the RLQ group. This pilot study suggested that future studies should investigate the effect of LVB on the health of other populations with relatively low fitness levels (e.g., PWPD).
Sitting volleyball (SVB) is an official paralympic sports event. Similar to traditional volleyball, an SVB game comprises two teams of six players each on a smaller playing court with a size of 10 m × 6 m.
The height of the net is approximately 1.15 m for men's teams and 1 m for women's teams. Unlike traditional volleyball, the SVB player's position is determined by the contact of the buttocks on the floor or the playing court (play while sitting on the floor), which is also a parameter for assessing any fouls. The British Paralympic Association [9] stated that SVB is faster than the Olympic indoor game because of the modified rules of the game (such as a low net height). Thus, SVB is a fast, high-level competitive team sport, demanding power and agility, which is only suitable for PWPD with a very high sports competence.
Considering the high speed and high sports competence requirements of SVB and extending the aforementioned work, the objectives of the SLVB intervention were to develop a new sport and provide additional PA opportunities to PWPD in Hong Kong and to improve the physical and psychosocial health of PWPD. Sitting Light Volleyball (SLVB) is a newly modified sport from LVB and SVB for PWPD. The bigger and lighter ball used in SLVB makes it more accessible to PWPD with a low fitness level (slow speed and long reaction time). Furthermore, the light weight of the ball results in considerably less soreness in the shoulders, arms, palms, fingers, and forearms than that caused by the traditional ball. SLVB is a safer non-contact team sport that can be played in a standard court with a size of 10 × 6 m or in space-friendly badminton court, which is smaller than a standard volleyball court. The smaller court enables the promotion of SLVB for PWPD in sports facilities in Hong Kong that normally have limited space. Team composition is 12 members as a team with six players on the court. Notably, it is optional to have one non-disabled player. SLVB is played in a sitting position (i.e., sitting on the floor) and has modified rules, such as allowing the ball to bounce at most once in each pass. Being playable, easier to learn and control, SLVB is relatively accessible for those with muscular degradation and motor disabilities. Leung and colleagues [10] conducted a 15-week SLVB intervention in 2018 and examined its effectiveness in improving selected physical and psychological attributes in PWPD in Hong Kong. The study results revealed that the SLVB intervention group, compared with the controls, had significantly higher cardiovascular endurance, body composition, and PA enjoyment.
Furthermore, the SLVB intervention effectively enhanced the participant's quality of life in the areas of role limitations due to physical health or emotional problems, body ache, social functioning as well as mental health [10].

Objectives
This study was part of the SLVB intervention. Gaining an in-depth understanding of the perceptions and experiences of PWPD in the SLVB intervention is critical to further develop SLVB as a PA intervention and sport. Using a social-ecological approach, in this qualitative study, the participants' experiences in the 15-week SLVB intervention were examined and the suitability and feasibility of the SLVB intervention content to PWPD were evaluated. These results were necessary for organizing SLVB-related activities in a community setting in the future.

Social-ecological approach
This study adopt deductive content analysis that data was analyzed based on Social-Ecological Model (SEM) [11]. This model has been used to create more physically active communities [11], in a framework of studies in sustainability of PWPD empowerment projects in Nairobi, Kenya [12], to evaluate multiple effects on participating in PA in old age [13], and to define social inclusion of people with intellectual and developmental disabilities [14]. SEM helps in understanding the multifaceted and interactive effects of personal and environmental factors that determine behaviors and identifies behavioral and organizational leverage points and intermediaries for health promotion within organizations. SEM has five nested hierarchical levels, namely individual, interpersonal, community, organizational, and policy or enabling environment. Individual factors refer to the personal factors, such as fitness levels, which affect the likelihood of participating in a PA. Interpersonal factors refer to the relationships, culture, and society with whom the individual interacts (e.g., social support).
Organizational factors are institutional rules and methods to implement and promote PA, including organizational capacity (such as professionals in PA and therapy) of non-government organizations (NGOs) to organize structured and PA programs that are suitable to PWPD. Community factors represent PA promotion through collaboration between parties (e.g., NGOs and academic institutions).
Policy factors include policies regarding the allocation of resources for health and access to health care services and restrictive policies (e.g., high fees for health services) or lack thereof.

Semi-structured interviews
In this qualitative study, data were collected using semi-structured interviews (conducted in Cantonese) after the 15-week SLVB intervention. The semi-structured format is a frequently used interview technique in qualitative research [15] and in the health care context [16]. Semi-structured interviews were used to collect information on (a) the participants' experiences regarding the intervention were assessed and (b) the suitability and feasibility of the SLVB intervention to PWPD. A set of interview questions was pilot-tested on five PWPD and investigators involved in the study (See Appendix 1 for sample questions). The interviewers adapted a flexible approach and, when necessary, altered the question sequence and/or asked some probing questions to facilitate in-depth conversations about the SLVB intervention. Because they combine a predetermined set of open questions with opportunities for the interviewers to further explore particular themes or responses, semi-structured interviews were used to understand the working of the SLVB intervention, its effects, and areas of improvement. This qualitative method of inquiry does not limit interviewees to a set of predetermined answers (unlike a structured questionnaire) and allows them to discuss and raise issues that the interviewer may not have considered. This method assisted the interviewees in describing complex phenomena and the interviewers in collecting information on SLVB, immediately clarifying the information collected, and ensuring optimal use of the limited interview time [17].

Procedures
The study was conducted between September and November 2018. All research activities were reviewed and approved by the University Institutional Review Board (REC/18-19/0378). Additional details and results of the SLVB intervention can be found elsewhere [10]. A cover letter stating the details of the study (e.g., aims and procedures) was given to the partner non-government organization (NGO) serving PWPD in Hong Kong. After receiving the agreement of the person-incharge of the NGO, recruitment was conducted by the NGO through social media (e.g., WhatsApp) and by advertisements in their bimonthly magazine. With the enrolment of the potential participants, details of the interviews (the time and venue) were confirmed. The interviewees were informed about the confidentiality and details of the study, namely the objectives of the study, their involvement, and potential risks of participation in the study) and their right to leave the project at any time. Upon signing, participants agreed to participate in the study. All interviews were conducted by the principal investigator (KML) and a trained research assistant at a meeting room of our partnered NGO. The two interviewers were female, knew about sports and exercise (especially in LVB), and trained in qualitative research methods as well as interviewing skills. Field notes were also made during and after the interviews. All interviewees had no prior relationship with interviewers, except conducting pretest and posttest measures. Other than interviewers and interviewee, no one was presented at the meeting room. All interviews were audio-taped for further data analysis. A HK$100 supermarket cash voucher was given to the participants to acknowledge their contributions to the study. The interviews averaged 40 min (range = 20-77 min).

Participants
Twenty-three participants who participated in our SLVB intervention were purposively invited to attend our qualitative interviews. Three participants refused due to personal reasons, so 20 interviews were conducted, and saturation was reached. No repeat interviews were carried out. The interview participants (n = 20; 12 women, 25% with a college degree or higher) had a mean age of 53.52 years (standard deviation [SD] = 9.02). They were both completer and non-completers (i.e., the attendance of interview was less than 80%). Their attendance was 66.11% in average in our SLVB intervention.
Participant characteristics are summarized in Table 1 Data analysis All interviews were transcribed ad verbatim and checked against the co-investigators' notes. The transcripts were qualitatively analyzed using thematic analysis (TA). TA is one of a cluster of analytic approaches for identifying patterns of meaning across a qualitative dataset. Both theory-driven and deductive TA were used in this study to analyze data and consolidate them into meaningful themes, following the process suggested by Biddle et al. [18]. A coding team comprising two individuals (KML and CYM) read all transcripts and developed a codebook, which was iteratively refined throughout the coding process and with reference to the SEM. Each transcript was coded independently by two coders who used the latest codebook. At regular intervals throughout the coding process, a reliability check of the coding was conducted in the team. Any differences were resolved through a consensus.
The final codes were determined by KML, who ensured that transcripts coded earlier reconciled with the most current codebook.
The raw data extracted for TA included participant quotations and our interpretations of these data.
The participants' experiences and perceptions of SLVB interventions were coded deductively with reference to the SEM framework. Measures used to improve the trustworthiness of the analysis included inviting both completer and non-completers to the study, and asked participants' interpretation of the data so as to increase the result's credibility. The 32-point consolidated criteria for reporting qualitative studies (COREQ) was used to reporting the results [19].

At the individual or intrapersonal level
Physical and psychological health. Reduction in lumbar spine pain and improvements in upper limb muscles, reactivity, and body coordination were the positive outcomes perceived by the participants.
One of the male participants (M4) expressed that SLVB helped reduce lumbar spine pain: "In the past three months, I often sat on the floor while playing SLVB. Eventually and "It demands reactivity and synchronization of the players…. As such, I think it is good for building our brain and body." In addition to physical health, potential improvements in psychological health (positive mood and fewer worries) and quality of sleep were mentioned by a few participants.
A female participant (F5) said, ""Playing SLVB causes me to have a good mood. I become worry-free while focusing on the ball," she added (F5). "I would tell them that SLVB is something I never came across before. Playing SLVB is very joyful and a sort of exercise. I seldom exercised before I retired," expressed a female participant (F2).
Another female participant (F4) said, "In general, I found SLVB fun-full to play with." One male participant (M3) expressed, "It is surely good. I saw that they were very happy to play SLVB. It was impactful, at least psychologically. The sports ground was full of happiness and laughter.
They cheered when they served a good ball. They laughed when someone hit a ball beyond the lines. The class started at four. We arrived 30 min earlier to practice so that we can play better." Novelty. Because SLVB was new to the participants, they were curious and eager to find out what it is, how it is played, and whether they could play this form of PA, which is for a healthy and strong body.
One female participant (F1) expressed, "Curiosity drove me to join the project. SLVB was new to me.

At the interpersonal level
Socialization. Other than physical and psychological health, the interviewees also described the social interaction effects of joining the SLVB intervention, namely mixing socially with others, discussion and exchange of information within teams, extension of social circles from one that mainly included wheelchair-bound friend to one that included volunteers, coaches, and the organizing team Support from peers, friends, family members, coaches and volunteers as well as peer pressure were evident during the SLVB intervention. Support from peers and friends was described by one of the female participants (F2): "Some of my classmates are very friendly. They are proactive to say "hello" to me and even invite me to play with them in a small group. They told me some tricks of playing SLVB, which had helped me do better." She added, "I didn't tell others except for my old friends. They said that wow, you were awesome!". Family support, which was crucial to engaging the participants in PA, was mentioned by many participants. One male participant (M2) said, "Most of them encouraged me to do so. My wife supported me too, even though she was more introverted than me." "Yes, they (family members) were very supportive. They said that it was good for me to go out and play more. They told me not to stay at home alone." Echoed by a female participant (F2). "I felt that I have become more proactive than before (in knowing friends and social interactions)." She (F2) Volunteer support was appreciated by a female participant (F4): "I am very thankful to those ball-boys and girls. (They were very co-operative, right?) Yes, absolutely. We played, and the balls were everywhere. They helped picking the balls for us quickly. They did a great job."

At organizational and community levels
Perceived sport venue environment. Comfort, privacy, spaciousness, and convenience of the venue affected the participants' engagement in the intervention.
One male participant (M4) exclaimed, "Superb, superb! Unlike other playgrounds, there were no other players except us. I liked very much the privacy and comfort this playground gave me." Sufficient space was necessary to accommodate numerous wheelchairs and participants' belongings.
One wheelchair user (F1) commented, "The playground is big, and the indoor environment is ok." One male participant M(6) commented on the sports ground: "It is convenient and comfortable inside the center. It is big enough to place our wheelchair and the air-conditioner is great. There is a restroom and drinking water on 1/F." Venue accessibility. As many participants were wheelchair users and have walking impairments, accessibility concerns were at the heart of the discussions. Parking space. Availability and proximity to disabled parking spaces are essential to engage in PA.
One female (F4) participant said, "We drove to the venue. We got to wait for a parking slot downstairs." She (F4) added, "They are (small). Sometimes we parked at the public car park downstairs which was always full. It was difficult to get space." However, for some participants with higher mobility, they can park at a normal though smaller parking space. One male participant (M2) said, "Given my mobility, I can manage to off-load or upload my wheelchair even though the parking lot is a bit narrow. No big deal." Nevertheless, some participants were not discouraged by the accessibility issues. "I met many of the players on other occasions. Some are old friends, and we chat with each other sometimes. The changes are that many of them had become proactive to play SLVB although the venue was quite inconvenient to them, given the steep road, insufficient parking spaces, etc." Commented by one male participant (M3).
Safety. Safety is a concern when playing sports, particularly for PWPD and people with relatively low fitness levels. When asked about the potential risks of playing SLVB, a male participant (M3) expressed, "Every sporting event has its own risk. SLVB players may strain their muscles; they may fall on the floor and get hurt if they don't play it properly. At their ages, the chance of hurting themselves is higher. It would be troublesome if they hurt their hands." The disability conditions of the participants posed a potential risk of playing SLVB.  Table 2. The Social Ecological Model developed using the aforementioned findings is presented in Fig. 1.

Suitability and feasibility of our SLVB intervention elements
Suitability. SLVB is played in the sitting position and is relatively less vigorous and intensive; hence, it is perceived to be suitable for PWPD. Project contents and coaching. In general, the project contents were perceived to be adequate and progressive, and the caring approach adopted by the coaches was appropriate and made instructions easy to understand.

Discussion
This qualitative study aimed to explore participants' experiences regarding the intervention by using SEM and examine the suitability and feasibility of our SLVB intervention to PWPD.

Participants' experiences of participating in the intervention
Using SEM, this qualitative study yielded five levels of themes that influenced PWPD to engage in the SLVB intervention. They were physical and psychological health, enjoyment, novelty, competence, and autonomy (at the individual or intrapersonal level); socialization, teamwork, and social support (at the interpersonal level); perceived sport venue environment, venue accessibility, safety, dissemination of information, and community facilities (at the organizational and community levels); and resource allocation by the government (at the policy level).

At the individual or intrapersonal level
Physical and psychological health. Exercise and PA are an effective way to improve people's physical and psychological health. The most frequently cited outcomes of this study were perceived health when playing SLVB. Partaking in the intervention resulted in many health benefits, including reduction in lumbar spine pain, strengthening of upper limbs, and improved reactivity, eyesight, and hand-eye coordination. Potential improvement in psychological health (positive mood and fewer worries) and quality of sleep were also mentioned by a few participants. These aligned with the results of the meta-synthesis, where health was substantial concept. The potential for improvement in health and well-being motivated engagement in the intervention, and these improvements facilitated an ongoing physically active lifestyle [20].

Enjoyment.
In the literature, people participating in sports activities and organizations exhibit a significant positive correlation with happiness and have a higher level of happiness than do people engaged in other leisure activities, such as listening to music, going to church, and watching television series [21][22][23]. Feedback from the participants of the present study indicated that promotion of SLVB in the form of group participation in PA could uphold the subjective happiness of PWPD. Participants expressed an overall perception that they felt happy and joyous (individually and as a group) when playing SLVB, which was consistent with the findings of a previous study that enjoyment was mentioned most often in PA activities and was evident in group activities as well as independent activities [13].
Novelty. The uniqueness of SLVB (using a bigger, lighter, and softer ball and with modified rules such as allowing the ball to bounce at most once in each pass) is noteworthy and brings novelty (outcome) to the participants. SLVB being new to them, the participants were curious and eager to find out what it is, how it is played, and whether they could play this form of PA, which is for a healthy and strong body. This was consistent with the finding of Krops et al. [2] that diverse or new activities were one of the themes regarding PWPD's perspectives about an effective community-based PA intervention.
Competence and autonomy. Competence and autonomy were two of the basic psychological needs in the self-determination theory [24]. These needs must be satisfied to foster well-being and health.
Competence is to seek control of the outcome and experience mastery [25]. Deci [26] found that giving people unexpected positive feedback on a task increases their intrinsic motivation to do it because the positive feedback fulfills people's need for competence. Many of the participants expressed that they derived a sense of competence from serving a good ball, scoring a point for his/her team, mastering the skills of playing SLVB gradually, receiving positive feedback from the coaches, and even helping peers progress. The sense of "can do" was expressed evidently by a female participant (F4) who exclaimed that she felt happier because she made it and she could play SLVB. In his fifties, one male participant (M4) reflected proudly that he was one of the top players within the team, being appraised by the coaches for applying well the taught techniques. This intervention even brought positive changes to participants' thoughts about the role of exercise in their lives.
Autonomy is the want to have self-control of one's own life and to be someone; however, Deci and Vansteenkiste [27] noted that this does not mean becoming independent of others. In the process of rehabilitation, PWPD faces such barriers as acting independently, their mobility being regulated by external aspects which causes the feeling of being unable to control their own body, self, and life [28]. The participants in the present study positively reflected that they attained body autonomy and a sense of freedom by playing SLVB. They had higher mobility when sitting on the floor and were able to hit the ball at different positions and were not limited in their space and action by the wheelchair. Some players could play SLVB with just one hand despite their impairments. Sense of freedom was perceived as a crucial motivator for getting involved in SLVB.

At the interpersonal level
Hills and Argyle [21] showed that sports provide sociability. Gatab and Pirhayti [30] indicated that people participating in sports associate with each other by teamwork, social communication skills and strengthened social development. The results of the present study indicated that social interaction effects (, teamwork, and social support) made the SLVB intervention effective.
Socialization and teamwork. These themes coincided with the relatedness of the selfdetermination theory. Relatedness is the wish to interact, interconnect with and to feel affection for others [31]. Cooperation and interaction during the mock games (a crucial element of the SLVB intervention) engendered socialization and communication skills. Our findings revealed that the intervention had multiple socialization effects on the participants, namely learning how to interact with each other, following instructions from the coaches, and mix socially with others; extending from playing SLVB to other types of PA; and enlarging one's social circle to include not merely wheelchairbound friends but also coaches, the organizing team, and volunteers who helped picking and feeding balls to participants. Similarly, teamwork also enhanced the relatedness of our participants. SLVB is group-based PA requiring teamwork to win a game. Mutual inclusion, cooperation, team spirit, combined action as a group, and winning as a team were perceived from the SLVB intervention program.
Social support. Consistent with previous studies that have shown different types of social support for PA were a significant component of the interventions [29], support from peers, friends, family members, coaches, and volunteers was evidenced from the SLVB intervention. Peer support facilitates a sense of feeling that members matter to one another and to the group as people shared their experiences with others [20]. This was consistent with the research results that participants were associated with buddies who rendered support by motivating them and making them feel welcome at the activity [2]. However, peer pressure was perceived by a few female participants during mock competitions despite good peer intention to encourage them to serve well. They felt stressed during service because if they could not serve successfully, points would be deducted. Peer pressure can be counter-productive if not managed appropriately and in a timely manner.

At the organizational /community levels
The diverse environment in which PA took place also influenced participants' engagement in the intervention. For example, the culture of the environment and facilities enable continued exercise. By contrast, inaccessible facilities and transport inhibit continued exercise [20]. Participant's experiences of the environmental factors influence how they feel and act. Dynamic, multidirectional relationships exist among various SEM levels [32]. Our findings revealed that comfort, privacy, and spaciousness of and accessibility to the venue were necessary for engaging PWPD in PA.
Perceived sport venue environment. To encourage participation in PA, venues need to warm, clean and proximal to home [13]. Our results indicated that comfort (e.g., room temperature, drinking water facility, and attitude of the security guards), privacy, and spaciousness of the venue (spacious enough to accommodate participants' wheelchairs and their belongings) were crucial for engaging PWPD in PA.
Venue Accessibility. Despite that a supportive environment that is culturally accepting of differences is crucial for PWPD to maintain a physically active life, PWPD face multiple environmental and social obstacles that inhibit them taking part in sports and PA [33]. Many participants are wheelchair users who drew considerable attention to accessibility issues. Our findings revealed that if concerns regarding steep roads leading to the venue, and availability and proximity of parking spaces, not satisfactorily addressed, the PWPD will not be encouraged to engage in PA.

Safety.
The disability PWPD poses a potential obstacle in PA. Safety is certainly a concern when playing sports, particularly for PWPD and people with a relatively low fitness level. Considering the different categories and levels of disabilities of the participants, our findings revealed that they were vulnerable to loss of balance, falling, and injury. They might strain their muscles and even experience abrasion while dragging or moving their legs on the floor because their legs were powerless. At their age (i.e., average 53.32 years), the chances of injury were higher. Nevertheless, the use of proper techniques (e.g., teaching them how to prevent falling as well as teaching them to fall properly) and protective gears (e.g., elbow-ankle and knees supporters to protect their ankles from abrasion) can reduce potential risk.

Dissemination of information.
In terms of the importance of communication, participants should be allowed to communicate with each other by means of multiple ways to meet individual preference and capabilities (phone or email) [20]. The participant opined that a specific WhatsApp group should have been used by the responsible party to disseminate relevant information such as change of venue and training schedule. A range of resources should be drawn upon to disseminate PA information through more engaging means.
Community facilities. Inaccessible facilities are obstacles to continue exercise [20], and our findings too revealed that lack of wheelchair-friendly and wheelchair-accessible facilities in the community (public sports complex or NGOs) discouraged participation in SLVB in the future.

At the policy level
Resource allocation was identified as one of the difficulties among NGOs at promoting sports in the community. Among the many elements influencing participation in PA at an old age, the importance of affordable activities has a strong evidence base [34,35]. However, this intervention project was funded, and participants could attend all the sessions free of charge. Thus, the element of affordability was not included in this qualitative study.

Suitability and feasibility of our SLVB intervention contents
Because SLVB is played while sitting on the floor, it is less impactful and less intensive than wheelchair basketball. Furthermore, it uses a bigger, lighter, and softer ball (compared with SVB) and lower net and is expected to be easier to learn and control and more suitable (expected outcomes) than traditional volleyball for those with motor disabilities and muscular degradation. The interview results revealed the expected outcomes that SLVB was considered by many participants (both female and male) to be suitable for PWPD mainly because it is played in a sitting position and was less vigorous and intensive than wheelchair basketball; therefore, a player's hands would not be hurt easily. Nevertheless, due consideration must be given to the different categories and levels of disabilities of the participants while mapping out an intervention program for PWPD. Their comments about the rules of SVLB also reflected that our modification to SVB and LVB seemed reasonable to them.
Regarding the intervention, participants were satisfied with its content, coaching, time, and class size.
Adaptable activities like SLVB are important so that people can proceed at their own pace within an activity [13]. The results of this qualitative study indicated that flexible scheduling was an important element of the intervention program. As far as possible, it should take into consideration participants' family days, other training sessions (like wheelchair basketball), and work schedule. In addition, participants preferred longer and flexible training sessions.

Conclusion
To the best of our knowledge, this qualitative study was the first of its kind to examine PWPDs' experiences of participating in a 15-week SLVB intervention and the suitability and feasibility of the SLVB intervention to PWPD. Using SEM, this qualitative study yielded five levels (individual, interpersonal, organizational, community, and policy levels) of themes that influenced PWPD to engage in the SLVB intervention. They were physical and psychological health, enjoyment, novelty, competence, and autonomy (at the individual or intrapersonal level); socialization, teamwork, and social support (at the interpersonal level); perceived sport venue environment, venue accessibility, safety, dissemination of information, and community facilities (at the organizational and community level); and resource allocation by the government (at the policy level). As suggested by SEM, these levels of themes are interrelated. For instances, enjoyment at individual levels in fact might come from socialization at organizational level at our SLVB intervention. In general, it demonstrated that adopting a multilevel approach to intervention in SLVB has positive outcomes for the participants.
Regarding our study strength, both participants who completed or did not complete the intervention program were invited for interviews, which enhanced the vigor of this study. Also, the study was theory driven as a framework to guide the study. However, the study has a few limitations. First, exit instead of interim interviews were conducted, which inhibited interim improvements of the intervention program. Second, all participants came from the same partner NGO, which might lead to group-think. Furthermore, our findings provided insights into a few issues important for mapping out future SLVB intervention programs, namely designing the project contents with due considerations disability conditions (for instance, teaching them how to fall properly in view of their disability conditions), using protective gears (e.g., supporters for elbows, knees, and ankles) to reduce the risk of hurting their hands and legs, being sensitive to and timely handling of peer pressure, and having a specific communication channel (e.g. WhatsApp group) for dissemination of information among the participants. In addition, this qualitative study also identified a few areas for future studies to explore whether better engagement effects on SLVB could be attained by recruiting samples from multiple NGOs with more participants and an equal sex ratio, flexible scheduling that takes into account participants' family day or other schedules, working out an optimum ratio between the number of coaches and players.
Taken together with the limitations and recommendations, the findings contribute to an in-depth understanding of the perceptions and experiences among PWPD in the SLVB intervention, which is very critical to the further development of SLVB in terms of a PA intervention. Furthermore, our results could be used for establishing the experiential aspects of SLVB and accounting for the suitability and feasibility of organizing SLVB-related activities in a community setting in the future.

Ethics approval and consent to participate
All research activities were reviewed and approved by the University Institutional Review Board.
Written informed consent was obtained from participants prior to study commencement.

Consent for publication
Not applicable.

Availability of data and material
The datasets generated and analyzed during the current study are not publicly available due to ethical restrictions but are available from the corresponding author upon reasonable request.

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