Participants
This study was conducted during the COVID-19 pandemic and included eight individuals with mild to moderate ID (five males and three females; age 22.25 ± 2.71 years; IQ 66.25 ± 9.50). Detailed participant characteristics are presented in Table 1. Inclusion criteria for participants with ID were: (a) a documented diagnosis of mild to moderate ID, (b) enrollment in a 4-year federally approved postsecondary transition program, (c) little or no prior experience in badminton or racket sports, (d) medical clearance through the Physical Activity Readiness Questionnaire (PAR-Q), and (e) for those in the badminton group, maintaining at least 80% attendance across the 15-week program to ensure adequate exposure to the intervention. Exclusion criteria included severe or profound ID, medical contraindications identified by PAR-Q, and failure to meet the 80% attendance threshold for inclusion in post-intervention analyses.
Four TD exercise partners (female undergraduate students, aged 19–21) were recruited using the same sport-experience criteria. Participants with ID and TD partners were recruited through convenience sampling at a university in the Southeastern United States. All participants with ID were capable of independent living and completed at least one college-level course each semester, indicating the ability to comprehend instructions and express emotions during the badminton program. All participants provided informed consent, and the study was approved by the University Institutional Review Board (IRB-21-193).
Procedure
This study used a quasi-experimental pre-post design. Anthropometric measures (i.e., height, weight, and BMI) and PAR-Q were first used to screen by the researchers. The IQ level of each participant with ID was reported from the University transition post-secondary program. During the pre-test session at the University Recreation Center, graduate and undergraduate student research assistants evaluated the participants’ physical well-being (Body mass index (BMI), maximal handgrip, 30-s chair stand test (30CST), 6-min walk test (6MWT)), social well-being (the short-form UCLA Loneliness Scale (ULS-8)), and mental well-being (forward digital span test and knock-tap test).
Four participants with ID and four TD participants were enrolled in an adapted and inclusive badminton class for one credit hour. TD participants served as exercise partners. The class met twice a week for 50 min per session, over a period of 15 weeks. An additional four participants with ID were recruited as the control group and did not receive any intervention. They continued with their regular daily routines throughout the duration of the program and did not receive any intervention. A certified adapted physical educator led the activities (teaching schedule and activities are listed in Table 2). With a background in Kinesiology and specialized training in adapted physical education, the instructor has worked across school, community, and research settings to promote motor skill development, physical fitness, and social engagement among individuals with ID. This class was held during the COVID-19 pandemic. All participants, exercise partners, and the instructor wore masks and maintained social distance for health and safety concerns. After fifteen weeks of training, the participants’ health and well-being were evaluated with the same tests during the post-test session at the University Recreation Center. The post-test session was scheduled and conducted by researchers at the same time and place as the pre-test session to eliminate possible confounding effects (e.g., temperature, flooring surface, sunlight) on the results.
Measures
BMI, maximal handgrip, 30CST, 6MWT, ULS-8, forward digital span test, and knock-tap test were used to evaluate obesity, muscular strength, muscular endurance, feeling of loneliness, working memory capacity, and inhibitory function, respectively, of participants with ID before and after the 15-week intervention.
Physical well-being
Obesity BMI is a measure of obesity status based on height and weight that was applied to participants. The formula is = kg/m2 where kg is the participant’s weight in kilograms and m2 is his/her height in meters squared. A BMI of 25.0 or more represents overweight, while the healthy weight range is between 18.5 and 24.9.
Muscular strength Maximal handgrip strength of the dominant hand was assessed using a hydraulic dynamometer. Participants stood naturally and held the dynamometer and flexed the elbow at an approximate 90° angle, with the forearm in a neutral position and the wrist positions between 0 and 30° dorsiflexion and between 0° and 15° ulnar deviation [28]. Participants were instructed to clench the handle as strongly as possible for at least 5 s for each trial. A total of three trials were performed. The test–retest reliability of adults with ID was excellent (ICC = 0.94) [29].
Muscular endurance 30CST was used to measure lower limbs’ muscular endurance. Participants were requested to sit in the middle of the chair, with hands placed across their shoulders at the wrists, and both feet flat on the floor. When the “go” instruction was given, participants rose to a full standing position and then sat back down again. They were to repeat this for 30 s. During testing, participants also needed to keep their backs straight and arms against the chest. The test–retest reliability of adults with ID was moderate (ICC = 0.72) [29].
Cardiovascular endurance 6MWT was used to assess cardiovascular endurance. Participants were requested to walk back and forth in the hallway and walk as far as possible in 6 min. The distance covered over a time of 6 min was recorded as the outcome performance. The test–retest reliability of adults with ID was excellent (ICC = 0.98) [30].
Social well-being
Feeling of loneliness The ULS-8 Scale contains 8 items (e.g., I am an outgoing person, I can find companionship when I want it). Each item has a 4-point Likert scale, with answer choices of 1 (never) to 4 (always). The total score ranges from 8 to 32 points, with higher scores suggesting a higher degree of loneliness. In this study, the internal reliability of the ULS-8 was 0.88. To our best knowledge, this was the first time that the ULS-8 was used in adults with ID.
Mental well-being
Working memory capacity The forward digit span test was used to measure working memory capacity. Participants were told they were going to play a number game. They were told a series of numbers first and then they needed to repeat the numbers to the examiner. The test was started at two digits. The longest span was 8 digits. Memory demands increase when participants are required to repeat longer sets of numbers. Two trials were given for each digit span level. The test was stopped after participants answered both trials at one level incorrectly. The internal reliability of the forward digit span test for adults with ID was 0.89 [31].
Inhibitory function The knock-tap test was used to assess inhibitory function. First, participants were required to knock with their knuckles on the table when the examiner tapped and vice versa. Next, participants knocked when the examiner showed the side fist, banged with the side fist when the examiner knocked, and did not move when the examiner tapped. The total correct responses were recorded as the performance outcome. The Knock-Tap test is a subtest of the NEPSY [32] and its internal reliability is from 0.61 to 0.70. The knock-tap test had been used to assess inhibitory function in adults with Down syndrome with some levels of ID [33, 34].
Intervention
Badminton group Participants with ID and their TD partners would meet at university indoor badminton courts that used a total of approximately 15 weeks, two times per week, 50 min each time. The training content was developed with reference to Badminton World Federation (BWF) Shuttle Time Lesson Plans (https://shuttletime.bwfbadminton.com), with consideration for the mental and physical conditions of people with different disabilities. Each time, the participant with ID would be assigned to practice with a TD partner. The goal of this class was that each participant with ID was able to play inclusive badminton doubles with a TD partner.
As seen in Table 2, each session consisted of a warm-up period of jogging and dynamic stretching exercises, followed by badminton practice, and ended with static stretching exercises. The main activity period included forehand and backhand grips, backhand serving, net and lunge, net rally, clear, drop, and smash. Activities included comprehensive practice with TD partners and were supplemented by games developed by BWF Shuttle Time Lesson Plans for badminton skill development.
In addition to individual skills, participants were also introduced to basic doubles rules and game strategies. These included understanding court positioning (front-back and side-by-side formations), effective communication between partners, and tactical movement patterns such as switching positions during a rally. Game-based activities emphasized teamwork, serve and shot placement to build game awareness within a doubles match.
Several teaching strategies were integrated into the program to make badminton more accessible and enjoyable. Equipment was adapted by using textured racket grips and larger shuttlecocks to support better control and visual tracking. Rules and court size were simplified to reduce complexity and physical demands. Instruction relied heavily on visual guides and structured, predictable practice routines to build comfort and confidence. Participants were paired to promote social interaction, and the program emphasized effort, progress, and positive reinforcement (e.g., praise and rewards) to boost motivation and self-esteem.
At the end of each activity session, the pictorial Physical Activity Self-Efficacy Scale was administered to assess participants’ perceived confidence in performing badminton-related activities. The scale consists of four items, each rated on a 4-point scale ranging from 1 (not confident at all) to 4 (very confident), with higher scores indicating greater self-efficacy.
Control group The control group maintained its original school schedule and activity habits during the intervention.
Data analysis
Statistical analysis was performed using SPSS 27.0 (SPSS Inc., Chicago, IL, USA). Considering the insufficient power and violation of the assumption of normality due to the small sample size, the Mann–Whitney U test was used to compare pre- and post-intervention differences between the badminton group and the control group for each outcome variable. This non-parametric test is similar to the parametric independent t-test in which the median values were used. The effect size of each outcome measure was calculated using r. According to guidelines by Cohen [35] as small effect: r r r > 0.5. The alpha level of statistical significance was set at p
