Flexibility Emerges as a Hidden Powerhouse of Fitness in Adults With Intellectual Disabilities

Flexibility has long been the neglected sibling of physical fitness, overshadowed by strength, endurance, and body composition in nearly every health-related assessment. Now a new cross-sectional study of adults with intellectual disabilities suggests that this overlooked quality may be far more central to overall fitness than many researchers have assumed, with measurable links to balance, muscle performance, and walking endurance.

The study, published in the Journal of Autism and Developmental Disorders, was conducted by Fatih Mirze and Cihat Demirel of Muş Alparslan University in Turkey. The researchers set out to answer a deceptively simple question: how does flexibility relate to the other components of physical fitness in adults with intellectual disabilities, and do those relationships shift depending on sex, age, or the severity of the disability?

To find out, the team recruited 106 adults between the ages of 18 and 40 and assessed them with the SAMU DIS-FIT battery, a test suite specifically designed and validated for people with intellectual disabilities. The battery covers four domains: body composition, motor performance, musculoskeletal fitness, and cardiorespiratory fitness. Flexibility itself was captured with two distinct measures, the classic Sit-and-Reach Test, which probes the hamstrings and lower back, and the Functional Shoulder Rotation Test, which evaluates the mobility of the shoulder girdle through a rotational movement pattern.

The choice of two flexibility tests matters. Trunk and hip flexibility, as measured by the sit-and-reach, and upper-body joint mobility, as measured by shoulder rotation, reflect different anatomical regions and different functional demands. By including both, the researchers could test whether flexibility behaves as a single unified trait or as a multidimensional component whose various expressions connect to fitness in different ways. The answer, according to the data, leans strongly toward the multidimensional view.

The results revealed a familiar pattern of sex differences in some domains but not in others. Men outperformed women on the Timed Up and Go Test, a measure of mobility and dynamic balance, as well as on the Handgrip Test, the Timed Stand Test, the 30-second Sit-Up Test, and the 6-minute Walk Test. Yet when it came to body composition and to both flexibility measures, the sexes were statistically indistinguishable. That absence of a flexibility gap is notable, because in the general population sex differences in hamstring extensibility are often reported, with men typically showing lower sit-and-reach scores, a difference that has been attributed largely to variations in stretch tolerance rather than tissue properties.

Age and disability severity told a clearer story. Participants aged 19 to 29 posted more favorable values than their older counterparts across most parameters, and participants with mild intellectual disability consistently outperformed those with moderate intellectual disability on most measures. These gradients matter for practice: they suggest that fitness declines and disparities are already detectable in early adulthood within this population, and that the degree of disability shapes physical capacity in ways that assessment protocols and intervention programs must account for.

The core of the study lies in the associations between the two flexibility measures and the rest of the fitness profile. Both the Sit-and-Reach Test and the Functional Shoulder Rotation Test were negatively associated with the Timed Up and Go Test, meaning that more flexible participants completed the mobility task faster. Better flexibility was also linked to stronger muscular performance and to greater walking endurance on the 6-minute Walk Test. The Functional Shoulder Rotation Test carried an additional association, correlating negatively with body composition, so participants with more favorable body composition tended to show greater shoulder mobility.

These findings carry weight because they intersect with an ongoing debate in exercise science. In 2020, a prominent paper in Sports Medicine argued that flexibility should be retired as a major component of physical fitness, contending that its health relevance was overstated and its evidence base thin. That argument was largely built on data from the general population. The new results from adults with intellectual disabilities complicate the picture. In this group, flexibility does not appear to be a decorative extra; it travels with balance, strength, and aerobic capacity, the very qualities that predict independence and quality of life.

The stakes are high for this population. Previous research has repeatedly documented that adults with intellectual disabilities show lower physical fitness than their peers without disabilities, spend more time in sedentary behavior, and face elevated risks of chronic disease. Physical fitness in this group has even been shown to predict five-year survival in older adults, and gait quality is closely tied to fitness levels. If flexibility is woven into that web of associations, then stretching and mobility work may deserve a more deliberate place in exercise programs designed for people with intellectual disabilities, rather than being treated as an optional warm-up ritual.

The authors conclude that flexibility should be addressed alongside other fitness components through a holistic approach to assessment and intervention. Because the study is cross-sectional, it cannot establish whether improving flexibility would directly improve balance, strength, or endurance; the associations could reflect an underlying general physical activity effect, shared biomechanical factors, or causal pathways in either direction. The datasets are not publicly available due to privacy and ethical restrictions, though anonymized data can be requested from the corresponding author with ethics approval. Still, the message for practitioners is concrete: when evaluating or training adults with intellectual disabilities, measuring flexibility at both the trunk and the shoulder, and designing interventions that develop it in concert with strength and aerobic work, may capture a dimension of fitness that standard batteries have too often left out.

Subject of Research: Associations between flexibility and physical fitness parameters in adults with intellectual disabilities

Article Title: Associations Between Flexibility and SAMU DIS-FIT Physical Fitness Parameters in Adults With Intellectual Disabilities: A Cross-Sectional Study

Article References: Mirze, F., & Demirel, C. (2026). Associations Between Flexibility and SAMU DIS-FIT Physical Fitness Parameters in Adults With Intellectual Disabilities: A Cross-Sectional Study. Journal of Autism and Developmental Disorders. https://doi.org/10.1007/s10803-026-07521-y

Image Credits: AI Generated

DOI: 10.1007/s10803-026-07521-y

Keywords: flexibility, intellectual disabilities, physical fitness, SAMU DIS-FIT, Sit-and-Reach Test, shoulder rotation, balance, muscular strength, cardiorespiratory fitness, cross-sectional study, exercise intervention, developmental disabilities