Exploring the Impact of Swimming on Body Mass Index and Body Fat in Individuals with Down Syndrome: A Meta-Analysis

Abstract

The aim of this study is to assess the effectiveness of swimming training in reducing body mass index (BMI) and body fat percentage among individuals with Down syndrome (DS), utilizing a meta-analysis approach. We conducted a systematic search for studies examining the clinical impact of swimming training on individuals with DS. Inclusion criteria encompassed studies involving DS patients who underwent swimming training for a minimum duration of 4 weeks. The primary focus was to compare changes in BMI and body fat percentage from baseline to post-training. Our analysis incorporated four studies comprising a total of 48 participants. The results demonstrated that swimming training lasting from 8 to 36 weeks did not significantly decrease BMI among DS patients, with a weighted mean difference (WMD) post-training of −0.428 (95% confidence interval (CI): −1.721–0.865) and an I² of 0%. Subgroup analysis based on age or duration (≥33 weeks or 8 weeks) also showed no notable decrease in BMI. Conversely, the analysis of body fat percentage demonstrated a significant decrease, with a WMD of −2.946 (95% CI: −5.056–−0.837). Subgroup analysis indicated a consistent reduction in body fat percentage across all duration groups. Swimming training does not lead to a significant reduction in BMI among individuals with DS. This outcome may be attributed to concurrent muscle gain alongside decreased body fat, resulting in a notable decrease in body fat percentage.

1. Introduction

Down syndrome (DS), a subgroup of intellectual disability, arises from an additional copy of chromosome 21, leading to various physical and cognitive difficulties [1]. In addition to the physical and cognitive challenges mentioned earlier, individuals with Down syndrome often face multiple intellectual disabilities and other health issues. They typically exhibit varying degrees of intellectual disability, which can affect their learning abilities and daily life skills. Moreover, they may have congenital heart defects, hearing or vision problems, a weakened immune system, and hypothyroidism. These multiple challenges necessitate increased medical and educational support to help individuals with Down syndrome manage their daily lives. Notably, individuals with DS commonly exhibit elevated body weight and body fat percentage, alongside distinct alterations in muscle mass and fat distribution, as evidenced in several studies [2,3,4].

The causes of weight gain in individuals with DS are complex and involve multiple factors. Physiological factors contributing to obesity in DS include decreased muscle tone, reduced levels of leptin, systemic inflammation, metabolic disorders, or a slower metabolism [3]. Furthermore, individuals with DS often experience a decrease in resting energy expenditure, providing a physiological basis for their susceptibility to weight gain. Additionally, the presence of comorbidities and unhealthy dietary practices can exacerbate weight gain in this population [5]. Additionally, cognitive challenges unique to DS may affect awareness and the ability to adopt healthy eating habits and engage in moderate exercise. Reluctance to participate in physical activity, often stemming from patient refusal, emerges as a significant factor contributing to excessive weight among individuals with DS [6].

The efficacy of land-based aerobic exercise in managing body mass index (BMI) among individuals with DS remains a topic of debate, yielding inconclusive findings. Conversely, aquatic activities like swimming often exhibit higher adherence rates among populations with decreased muscle tone [7,8]. Water-based exercises offer a convenient and accessible setting, potentially fostering increased participation and compliance. This underscores the importance of investigating the potential advantages of swimming as a means to enhance overall health in individuals with DS.

Swimming, a widely embraced form of exercise, presents itself as a straightforward and economic activity. In comparison to pursuits such as jogging or weightlifting, swimming typically garners greater compliance. Evaluating the impact of swimming on BMI and body fat in DS patients holds significant importance. Our objective is to amalgamate existing randomized controlled trials (RCTs) through a meta-analysis to ascertain the effects of swimming on weight and body fat management in this population. Many recent studies have demonstrated the benefits of swimming for individuals with Down syndrome. The article by Querido et al. [9] points out that swimmers with Down syndrome exhibit a level of physical fitness close to European fitness standards, which is significantly higher than that of typical individuals with Down syndrome. Specifically, water-based exercise has been shown to benefit individuals with intellectual disabilities in terms of cardiorespiratory endurance, muscular endurance, speed, static balance, and agility [10,11]. Running, which is also considered a common aerobic activity, is believed to significantly improve the benefits of treadmill training for patients with Down syndrome in Kamińska et al.’s system review [12].

When assessing obesity, BMI and body fat percentage serve as cost-effective and time-efficient measures that effectively gauge patient health [13,14]. In public health, they are considered the most important indicators for measuring obesity. Height and weight measurements, among the parameters monitored, are straightforward and expedient. More complex measurements such as skinfold thickness, waist circumference, and hip circumference necessitate specialized training and entail varying degrees of error. Furthermore, there is a scarcity of RCTs in this domain. Although waist circumference is a valuable indicator, it is seldom included in studies, likely due to the aforementioned reasons. After discussion and consideration, we decided to focus this meta-analysis on BMI and body fat.

In conclusion, the underlying factors contributing to weight gain susceptibility in individuals with DS are complex and encompass multiple domains. One of the primary aims of this meta-analysis is to investigate the potential of swimming as a beneficial intervention to positively impact BMI, body fat, and pertinent health outcomes among individuals with DS. We will focus the scope of the study on the effects of swimming on body fat and BMI in individuals with Down syndrome and conduct a meta-analysis. Our aim of this meta-analysis is to investigate the potential of swimming as a beneficial intervention to positively impact BMI, body fat, and pertinent health outcomes among individuals with DS.

Before conducting this research, we believed that swimming would have a significant effect on reducing body fat. As for BMI, considering that swimming increases muscle weight, we hypothesized that it would remain stable or decrease.

2. Materials and Methods

Our study protocol adhered to the guidelines outlined by the Preferred Report Items For Systematic Reviews and Meta-analysis (PRISMA) [15]. This article includes studies published before August 2023. Our research started in September 2023, with plans to collect data for one month, analyze the data for one month, and check for missing articles and write the paper for one month. We planned to complete this by February 2024 and begin submission.

2.1. Literature Search Strategy

We conducted searches on various databases including Scopus, Google Scholar, Cochrane Library, China National Knowledge Infrastructure, and PubMed using specific search terms such as “Down syndrome”, “swimming”, “swim”, “aerobic”, “exercise”, and “water”. Additionally, we manually searched original studies to identify any articles that might have been overlooked by the database searches. The search strategy is in the Supplementary Materials. We also examined the citations in the literature we identified. Our inclusion criteria encompassed original articles published in peer-reviewed journals from the earliest available records up to August 2023. There were no language restrictions imposed (see Figure 1).

2.2. Inclusion and Exclusion Criteria

We applied the following inclusion criteria to determine the suitability of studies for inclusion in our meta-analysis: (1) studies that enrolled participants diagnosed with DS, (2) studies that included a swimming training program lasting at least 4 weeks, and (3) studies that included measurements of BMI and body fat. It is well-acknowledged that exercise impacts the body over a period of time. Therefore, we chose 4 weeks as the standard in our study to ensure that the exercise intervention could produce significant effects.

Studies that did not meet the following criteria were excluded: (1) nonRCTs studies and (2) studies for which the full text could not be obtained or for which no data were available even after contacting the authors

Our primary objective was to compare BMI or body fat levels before and after swimming training. We utilized the weighted mean difference (WMD) to assess the effectiveness of the training.

2.3. Study Selection

Two researchers (H.-T.K and C.-C.Y) independently reviewed the titles and abstracts of all identified studies. Subsequently, a full-text evaluation of potentially relevant studies was conducted to determine their compatibility with the inclusion and exclusion criteria.

2.4. Data Collection and Risk of Bias Assessment

Following the selection of studies, two independent researchers (H.-T.K and C.-C.Y) extracted relevant data. These included details such as study design, first author, publication year and journal, study location, patient demographics (gender, age), duration of follow-up, specifics of the swimming training regimen (progression and frequency), and measurements of BMI and body fat during each follow-up period. The risk of bias for each included study was assessed by the same researchers using the Cochrane risk of bias tool and it was categorized as “low”, “unclear”, or “high”. A study was deemed to have a high risk of bias if at least one domain was rated as high risk.

The initial selection of studies was made by the two reviewers based on their relevance to our inclusion criteria (H.-T.K and C.-C.Y). Any discrepancies were resolved through discussion, with eligibility ultimately determined by mutual agreement. Subsequently, data extraction and qualitive assessment of the included studies were conducted by the same reviewers.

2.5. Data Synthesis and Analysis

Our study adhered to the PRISMA criteria ²³ in reporting our findings. For articles that provided data categorized into various treatment groups, each set of data was considered as separate treatment arms for analysis. All analyses were carried out using the Comprehensive Meta-analysis (CMA) software version 3. Pooled estimates along with their corresponding 95% confidence intervals (CI) were calculated. Statistical significance was determined when the p-value was less than 0.05. Significant heterogeneity was defined as I² > 50.0%. Initially, a random-effects model was employed before proceeding to quantitative analysis. Heterogeneity was quantified using the I² statistic. We anticipated that heterogenicity might stem from differences in training duration, follow-up duration, participant age, and the country of origin of the study. Therefore, predefined subgroup analyses for patients were conducted based on these factors. Additionally, funnel plot and Egger’s tests were utilized to evaluate the potential presence of publication bias.

3. Results

3.1. Study Search and Characteristics of Included Patients

Figure 1 illustrates the process of study selection. Initially, a total of 1951 studies were identified through electronic searches across all databases. Following the removal of duplicates, 657 articles remained. Of these, 1201 studies were excluded based on title or abstract screening. Reasons for exclusion included ineligible study design, duration <4 weeks, inclusion of water sports other than swimming, lack of disclosure regarding the swimming project method, and incomplete data on BMI or body fat. Ultimately, four articles meeting the predetermined inclusion and exclusion criteria, comprising a total of 48 patients, were included in this meta-analysis.

Table 1. Characteristics of included studies.

First Author	Country	Population	Study Design	Duration	Patients	Mean Age a	Outcome	Training Program
Suarez-Villadat, 2020 [16]	Spain	Adolescents	RCT	36 weeks	15	13.93 (1.23)	BMI, body fat	Total 50 min, HR b 110–180, twice a week
Naczk, 2021 [17]	Poland	Adolescents	RCT	33 weeks	11	14.9 (2.35)	BMI, body fat	Total 70–90 min, three times a week
Boer, 2020 [18]	South Africa	Adult	RCT	8 weeks	13	34.2 (5)	BMI	Total 30–40 min, three times a week
Malayeri, 2020 [19]	Iran	Adolescents	RCT	8 weeks	9	12.2 (2)	BMI, body fat	Average 33 min, six times a week

^a: Age is presented as means ± standard deviations. ^b: HR: Heart rate.

presents the characteristics of the included studies.

3.2. Quality Assessment and Risk of Bias

The assessment of risk of bias [20] is presented in Table S1. The overall risk of bias among the included studies was varied, with half of them demonstrating a low overall risk of bias, while the remaining half exhibited an unclear overall risk of bias. Specifically, two of the included studies were rated as having some concerns regarding deviations from intended intervention, while the other two were deemed to have a low risk in this regard. Consequently, two studies were categorized as having some concerns in terms of overall risk of bias, while the other two were considered to have a low risk.

3.3. Outcomes

A pooled analysis of all four studies was conducted to examine the overall changes in BMI before and after swimming. Additionally, three studies investigated changes in body fat. The results of the included studies are presented in

Table 2. Subgroup analysis of weight mean differences based on age and training duration.

Subgroup	Weight Mean Difference	95% Confidence Interval
BMI: pooled	−0.428	−1.721 to 0.865
Duration
33–36 weeks	−1.118	−2.709 to 0.472
8 weeks	0.915	−1.304 to 3.134
Age
Adolescents	−0.408	−1.831 to 1.016
Body fat (%): pooled	−2.946	−5.056 to −0.837
Duration
33–36 weeks	−0.57	−1.124 to −0.015

. The WMD post-treatment in terms of BMI changes was −0.428 (95% CI: −1.721–0.865). Regarding the heterogeneity of the included studies, the I² value was 0% (Figure 2).

To explore whether the duration of swimming training among individuals with DS might act as a confounding factor, a separate pooled analysis was performed. The WMD obtained from this subgroup analysis for durations > 33 weeks was −1.118 (95% CI: −2.709–0.472), with an I² value of 0%. For the subgroup with a training duration of 8 weeks, the WMD was 0.915 (95% CI: −1.304–3.134). In the subgroup analysis comparing BMI changes between adolescents and adults, the WMD for adolescents was −0.408 (95% CI: −1.831–1.016), with an I² value of 12.667% (Figure 3 and Figure 4).

We further examined the data pertaining to body fat, with analysis incorporating only three studies. The WMD was −2.946 (95% CI: −5.056–−0.837), and the I² value was 0% (Figure 5). Subgroup analyses were conducted for durations ≥ 33 weeks. Within this subgroup analysis, two studies were included, yielding a WMD of −0.57 (95% CI: −1.124–−0.015) and an I² value of 0%. As the sole study involving adults did not provide data on body fat percentage, it was excluded from the outset, resulting in the omission of age group categorization in our analysis.

Among the three studies, control groups without any additional therapy were present. The WMD for BMI was 0.132 (95% CI: −0.246–0.510), while the WMD for body fat percentage was 0.151 (95% CI: −0.283–0.585). Both demonstrated slight increases but lacked significant differences (

Table 3. Subgroup analysis of weight mean differences of control groups.

Subgroup	Weight Mean Difference	95% Confidence Interval
BMI: pooled, control (3 studies included)	0.132	−0.246 to 0.510
Body fat (%): pooled, control (2 studies included)	0.151	−0.283 to 0.585

). Weighted mean differences in body fat percentage from pooled data showed in Figure 5.

The included studies exhibited no significant publication bias in terms of overall WMD. The p-values on the Egger’s test were 0.976 and 0.296 for pooled analyses of BMI and body fat, respectively. The funnel plots for the WMD of post-swimming training are depicted in Figure S1.

4. Discussion

To our knowledge, this study represents the initial investigation into the clinical effectiveness of swimming training in reducing BMI and body fat levels among individuals with DS.

4.1. Novel Findings

In our study, we discovered that a swimming program spanning 8–36 weeks did not lead to a reduction in BMI among individuals with DS, as evidenced by our CMA. Despite the common association of regular swimming with positive weight management outcomes, factors such as the adherence level specific to individuals with DS and durations shorter than 36 weeks played significant roles. When considering these factors, our study highlights the inability to achieve a decrease in BMI.

Furthermore, subgroup analysis based on age and exercise duration from the four studies indicated that although the group with a duration > 33 weeks showed a relatively larger WMD, the difference was not statistically significant.

However, a different trend emerged regarding body fat percentage. Our analysis revealed a significant alteration in body fat percentage following the swimming exercise program, both in the overall pooled analysis and in the subgroup analyses. This indicates that the swimming program may indeed be effective in decreasing body fat percentage among individuals with DS.

4.2. Clinical Implications

There is a clear need for alternative strategies to improve body composition and overall health among individuals with DS. While effective methods for controlling BMI and body fat percentage exist for the general population of obese individuals, implementing these approaches becomes more challenging for individuals with DS due to factors such as hormonal regulation, cognitive limitations, and adherence challenges. Water-based activities, especially swimming, have been recognized as attractive options for individuals with intellectual disabilities or children, as they are more appealing and easier to adhere to. Therefore, investigating the effects of swimming on individuals with DS holds significant importance.

Although our study did not find any notable differences in BMI, recent insights indicate that when considering health factors such as cardiovascular diseases, strokes, and other risks, body fat percentage may hold more significance than BMI [21]. There are two reasons to explain this unexpected outcome. First, the calorie-burning efficiency of swimming may not be as pronounced as other aerobic exercises such as treadmill running or jogging [22], and some studies underscore that swimming may increase appetite [23]. Second, the lack of BMI reduction could be due to a decrease in body fat accompanied by an increase in skeletal muscle mass. Despite the absence of significant changes in BMI, our meta-analysis revealed a notable reduction in body fat percentage. This indicates that the absence of BMI reduction may be offset by a simultaneous increase in skeletal muscle mass alongside a decrease in body fat. Consequently, swimming training spanning 8–33 weeks shows promise in significantly improving baseline health in individuals with DS.

Therefore, when family physicians or occupational therapists engage in swimming training for individuals with DS and observe no significant decrease in BMI, they can now be reassured by the findings of this meta-analysis that such an outcome falls within the expected range. This is because body fat percentage may have already decreased. This newfound understanding can enhance their confidence in continuing the current training regimen.

In summary, our findings hold significant clinical implications as they may impact decision-making regarding training options for individuals with DS. Furthermore, our provision of valuable data will help inform the methodology for future research in this area of training interventions.

4.3. Comparisons to Other Studies

This meta-analysis comprised four RCTs, involving a total of 48 participants. Our results indicated a decrease in the standard mean difference of BMI to −0.428 following swimming treatment. It is well-established that adults and adolescents with DS exhibit higher levels of total and regional fat compared to those without DS. Consequently, due to their elevated body fat proportion, they are at an increased risk of various serious health conditions such as diabetes, hypertension, and coronary diseases [24]. Aerobic exercise plays a crucial role in combating obesity in individuals with DS. In addition to the studies included in our meta-analysis, several other investigations have explored this aspect. Our findings are somewhat consistent with those of Malgorzata Charmas et al. [22], who conducted a 12-week swimming study involving healthy young women, concluding that the program did not lead to a decrease in BMI levels.

To our knowledge, there has been no meta-analysis specifically addressing the impact of exercise on weight and body fat in individuals with DS. Régis B Andriolo et al. [25] conducted research on aerobic exercise training programs aimed at improving physical and psychosocial health, observing improvements in various parameters such as knee extension and flexion, maximal treadmill grade, and ergometer resistance, but they did not include BMI or body fat. Additionally, a study conducted in 2022 demonstrated significant differences in BMI and body fat between exercise and control groups following a 22-week basketball program [26].

Two other studies yielded similar findings to our study. The study by FJ Ordonez et al. [27] demonstrated a decrease in body fat of up to 3.9% following 10 weeks of jogging, while BMI remained similar. Similarly, the study by P.H. Boer et al. study [28] indicated that 12 weeks of cycling and walking at an intensity of 70–80% of VO2 peak improved leg strength and walking distance but did not lead to a reduction in BMI.

If the scope is expanded to include all populations with intellectual disabilities, there are more similar studies, and the results are also intriguing. Several studies have found that swimming three days a week for 8–33 weeks, with each session lasting 30–90 min, can lead to weight loss [17,18]. However, other studies have found that swimming weekly does not affect weight [29,30]. Similarly, some studies have shown that swimming can lead to a decrease in BMI [15,17,18], while others have concluded that swimming for 45–60 min, 2–3 days a week for 12–16 weeks, does not impact BMI [29,31,32]. Our study focuses on Down syndrome. If we disregard the differences in DS biological fields and only consider intellectual disabilities, these contradictory results support our viewpoint that the reduction in weight may not be significant in water activities for individuals with intellectual disabilities. This may be related to the increase in muscle mass and a higher appetite caused by lower water temperatures. If limited to individuals with Down syndrome, the article by Querido et al. [9]. points out that swimmers with Down syndrome achieved better results in all test categories, including body fat and weight. At the same time, they also hypothesized that the impact of swimming on individuals with intellectual disabilities might be less significant compared to other forms of exercise.

Additionally, we should also focus on other barriers that discourage individuals with intellectual disabilities from engaging in exercise. Jacinto et al. [33] have proven that intellectual disability and exercise difficulties are related to three factors: (i) family members, (ii) individuals and (iii) society. There are many different challenges that contribute to obesity in individuals with intellectual disabilities, not just physiological factors. Therefore, in addition to focusing on exercise itself as we have in this paper, reducing the difficulty of exercise for individuals with intellectual disabilities might be even more important.

4.4. Strengths and Limitations

The current meta-analysis presents several notable strengths, primarily its pioneering effort to provide a comprehensive pooled analysis of the clinical effects of swimming programs on individuals with DS, specifically focusing on BMI and body fat. Given the limited research available on the clinical efficacy of swimming interventions for this population, our findings represent a significant advancement for future studies and offer valuable guidance for healthcare professionals responsible for individuals with DS.

Moreover, it is important to highlight that existing trials often suggest a decrease in BMI among individuals with DS following swimming interventions. However, our thorough comparative analysis has revealed a more nuanced understanding. By incorporating measures of body fat percentage and skeletal muscle mass, we have provided a robust explanation. This insight can enhance confidence in maintaining current training regimens, reducing concerns regarding short-term BMI fluctuations. Notably, our approach includes a unique subgroup analysis of training duration, an aspect not previously explored in similar research endeavors. Additionally, an advantage of our study is the absence of such limitations in our English publication.

However, there are several limitations that warrant discussion. One limitation is the restricted number of studies included in our meta-analysis, comprising only four RCTs. The possibility exists that our observed outcomes could have been influenced if a larger number of RCTs had been included. Nonetheless, it is important to emphasize that the limited number of recruited studies is attributable to the scarcity of research in this area, with a predominant focus on land-based exercise interventions. For instance, there is a greater abundance of RCTs and meta-analyses concerning treadmill interventions for individuals with DS. Therefore, due to the limited studies included, our results can offer valuable insights but cannot provide definitive conclusions regarding the clinical effects of swimming for individuals with DS. We must acknowledge that including land-based aerobic exercises, such as running, in our research would lead to broader and more practical conclusions. This will be the objective of our team in future studies.

Another limitation of our study is the explanation for the absence of BMI decrease. While it can be speculated that a reduction in body fat combined with an increase in skeletal muscle mass contributes to BMI maintenance, the lack of data on skeletal muscle in all four studies only allows for an indirect rather than a direct demonstration of this point. Additionally, our study solely investigates BMI and body fat, overlooking factors such as balance, coordination, and cognitive abilities, which are equally vital for the health of individuals with DS [34,35].

Moreover, there was variability in the control of diet and exercise programs among the four studies included in our analysis. While we recognize the importance of dietary control in reducing body fat, the dietary restrictions differed across these studies. Additionally, although the duration of swimming in exercise programs generally showed minimal variation, discrepancies were noted in swimming techniques and styles. For example, the efficiency of the butterfly stroke and breaststroke can vary significantly [36].

Furthermore, due to the limited number of cases, our study did not conduct subgroup analyses based on race and gender. As a result, we were unable to confirm any differences in fat-burning efficiency during swimming among different ethnicities.

5. Conclusions

Our meta-analysis investigated the clinical impact of swimming programs lasting 8–36 weeks on individuals with DS, utilizing BMI and body fat percentage as key metrics. Our findings indicate that these swimming programs did not result in a decrease in BMI among individuals with DS, consistent with previous research. This pattern persisted even when considering studies with durations > 30 weeks. However, there was a notable decrease in body fat percentage. This discovery offers healthcare professionals greater confidence in implementing swimming programs, as the absence of BMI reduction is understandable, with the focus being on reducing body fat percentage. Future research, particularly exploring the composition of body fat and muscle, is warranted.