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Limited Evidence for Flexibility as an Independent Predictor of Health Outcomes in Adults: A Systematic Review and Meta-Analysis of Prospective Studies

This systematic review and meta-analysis of 45 prospective studies involving over 48,000 adults found that while greater baseline flexibility is weakly associated with reduced risks of future pain, disability, and frailty, current evidence provides limited support for flexibility as an independent predictor of broader health outcomes due to methodological limitations and low certainty of evidence.

Original authors: Lewis Ingram, Grant R. Tomkinson, Bethany Gower, Noah M. A. d’Unienville, Terry Boyle, Justin J. Lang, Hunter Bennett

Published 2026-07-02

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CC BY 4.0

Original authors: Lewis Ingram, Grant R. Tomkinson, Bethany Gower, Noah M. A. d’Unienville, Terry Boyle, Justin J. Lang, Hunter Bennett

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body is like a high-performance car. For years, mechanics and drivers have agreed that to keep this car running smoothly, you need to check five main things: how fast the engine runs (cardiorespiratory fitness), how strong the pistons are (muscular strength), how long the engine can run without overheating (muscular endurance), how much fuel you're carrying (body composition), and how well the wheels and suspension can turn and bend (flexibility).

While we have plenty of data proving that a strong engine and powerful pistons prevent the car from breaking down, this new study asks a simple question: Does having "bendy" wheels actually predict if the car will break down in the future?

Here is the story of what the researchers found, using simple language and analogies.

The Big Picture: A Search for Proof

The researchers, led by Lewis Ingram from Adelaide University, acted like detectives. They didn't just look at one or two cases; they went through a massive library of scientific studies (45 studies involving over 48,000 adults) to see if people who were naturally more flexible stayed healthier as they got older.

They were looking for a direct link: If you can touch your toes today, will you be less likely to get sick, hurt, or die tomorrow?

The Findings: A "Maybe," but a Very Weak One

The results were surprisingly quiet. Here is what they found, broken down by category:

1. The "Bendy" Connection to Pain and Walking

The Claim: People with better flexibility had a tiny, tiny reduction in the risk of future pain, disability, or trouble walking.
The Analogy: Imagine you have a rubber band. The study suggests that a slightly stretchier rubber band might be barely less likely to snap than a stiff one. The difference was so small it was almost invisible (statistically negligible).
The Catch: The researchers couldn't be very sure this finding was real. The "evidence quality" was rated as "very low." It's like trying to read a sign through a foggy window; you think you see something, but the glass is too dirty to be certain.

2. The "No Connection" Zones

The Claim: Flexibility had no link to heart disease, diabetes, muscle diseases, or injuries.
The Analogy: It's like checking if the color of your car's paint predicts whether the engine will fail. The study found that being "bendy" doesn't seem to protect your heart or stop you from getting a broken bone any more than being stiff does.

3. The "We Don't Know" Zones

The Claim: There wasn't enough data to say if flexibility helps prevent falls, death, or if it makes people more active.
The Analogy: It's like trying to predict the weather with only three cloud photos. There simply weren't enough studies to draw a conclusion.

Why Is the Evidence So "Foggy"?

The authors explain that the reason we don't have a clear answer isn't necessarily because flexibility is useless. It's because the studies we have so far are flawed.

The "Ruler" Problem: Imagine trying to measure "bendiness" with 44 different rulers. Some studies measured how far you could reach forward; others measured how much your hip could turn. Because everyone used a different tool, it was hard to compare the results. It's like trying to build a puzzle where half the pieces are from a different box.
The "Follow-Up" Problem: Many studies didn't follow the people long enough or didn't track them carefully enough to be sure.
The "Gold Standard" Missing: For heart health, we have a "gold standard" test (like a stress test). For flexibility, there is no single, perfect test that measures "whole-body bendiness."

The "Too Much of a Good Thing" Twist

The paper also hints at a strange possibility: More flexibility might not always be better.

The Analogy: Think of a suspension bridge. If the cables are too stiff, the bridge snaps. But if they are too loose, the bridge sways uncontrollably and becomes unstable.
The authors note that people with "hypermobility" (being too bendy) often have their own set of health problems. This suggests the relationship might be a "Goldilocks" curve: you need just the right amount of flexibility, not too little and not too much.

The Bottom Line

The study concludes that current science does not strongly support the idea that flexibility is a crystal ball for predicting future health.

While being flexible might offer a microscopic shield against pain or walking difficulties, the evidence is too weak to say for sure. The authors argue that flexibility remains a "mystery component" of fitness. It's not that it's useless, but rather that we haven't done enough high-quality research to prove it works.

In short: If you stretch, you might feel good, but this study says we don't yet have enough proof that stretching alone will keep you from getting sick or hurt in the future. We need better, clearer studies to solve the puzzle.

Technical Summary: Limited Evidence for Flexibility as an Independent Predictor of Health Outcomes in Adults

Problem Statement
Flexibility is recognized as one of the five core components of health-related physical fitness, alongside cardiorespiratory fitness, muscular strength, muscular endurance, and body composition. Despite its inclusion in international physical activity guidelines and its presumed relevance to overall health, the evidence base supporting flexibility as an independent predictor of future health outcomes remains underdeveloped compared to other fitness components. While cardiorespiratory endurance and muscular strength have strong, consistent meta-analytic support for predicting health, the degree to which flexibility independently associates with health outcomes has not been comprehensively assessed. This gap has fueled debate regarding the clinical and public health relevance of assessing flexibility and prescribing stretching interventions. Previous reviews, such as Marín-Jiménez et al., were limited by non-exclusive focus on flexibility, inclusion of other motor fitness tests, and reliance on a small number of primary studies.

Methodology
This study is a systematic review and meta-analysis of prospective cohort studies, registered with PROSPERO (CRD420251029178) and reported according to PRISMA 2020 guidelines.

Search Strategy: A systematic search was conducted across MEDLINE, Embase, Emcare, CINAHL Complete, and SPORTDiscus from January 2005 to April 2025.
Eligibility Criteria: The review included prospective cohort studies involving apparently healthy adults (≥18 years) at baseline. Studies were required to objectively measure flexibility or joint range of motion (ROM) and report associations with future health outcomes (e.g., mortality, disease incidence, physical performance, quality of life). Special interest groups (elite athletes, clinical populations, pregnant individuals) were excluded.
Data Synthesis: Forty-five studies (n=48,020 participants) were included, with 25 studies contributing to meta-analyses. Health outcomes were categorized into eight domains: self-reported pain/disability, musculoskeletal disease, cardiometabolic disease, mobility limitations/frailty, falls, mortality, injury, and physical activity levels.
Statistical Analysis: A three-level random-effects meta-analysis was performed using R, accounting for dependency within cohorts. Effect sizes (ORs, HRs) were converted to Risk Ratios (RRs) where necessary. Heterogeneity was assessed using $I^2$ and $\tau^2$ .
Quality Assessment: Risk of bias was evaluated using the CLARITY Group tool (7-item checklist), and the certainty of evidence was graded using the GRADE framework.

Key Contributions and Results
The analysis synthesized data across 45 prospective studies with a median follow-up of 6.0 years.

Self-Reported Pain and Disability: Greater flexibility was associated with a statistically significant but negligible reduction in the risk of future self-reported pain and disability (RR = 0.99; 95% CI: 0.98–1.00). Heterogeneity was negligible ( $I^2$ = 0.7%).
Mobility Limitations and Frailty: Greater flexibility was associated with a negligible reduction in the risk of future mobility limitations and frailty (RR = 0.98; 95% CI: 0.96–1.00). Heterogeneity was negligible ( $I^2$ = 0.2%).
Musculoskeletal and Cardiometabolic Disease: No significant associations were found between flexibility and the risk of musculoskeletal disease (OR = 0.73; 95% CI: 0.37–1.44) or cardiometabolic disease (RR = 0.94; 95% CI: 0.76–1.16).
Injury: Flexibility was not associated with injury risk (RR = 0.76; 95% CI: 0.35–1.68), though substantial heterogeneity was observed ( $I^2$ = 88.1%).
Narrative Syntheses: Due to insufficient data for meta-analysis, results for falls, mortality, and physical activity levels were synthesized narratively. Evidence was insufficient to draw definitive conclusions for these outcomes, with some studies showing associations that disappeared after adjustment for confounders.
Certainty of Evidence: The certainty of evidence was rated as very low to low across all outcome domains. Downgrading factors included serious risk of bias (e.g., inadequate follow-up), inconsistency of results, indirectness of evidence, imprecision, and publication bias.

Significance and Claims
The paper concludes that current evidence provides limited support for flexibility as an independent predictor of health outcomes in adults. While statistically significant associations were found for pain/disability and mobility/frailty, the effect sizes were negligible, and the certainty of evidence was very low.

The authors argue that these findings challenge the assumption that flexibility is a core component of health-related fitness with established prognostic value. The lack of robust evidence suggests that the current inclusion of flexibility in health guidelines may be based more on tradition than on empirical data linking it to future health. The authors posit that the observed lack of association may reflect methodological limitations in existing studies—such as the absence of a standardized "gold standard" flexibility test, heterogeneity in measurement tools (44 different tests identified), and inadequate follow-up—rather than a true absence of biological association.

The study emphasizes that flexibility remains under-researched compared to other fitness components. It calls for high-quality prospective studies with standardized assessment batteries to clarify whether flexibility has genuine clinical and public health relevance. The authors caution against interpreting the negligible effect sizes as proof of clinical utility and highlight the need to investigate whether an "inverted U" relationship exists, where excessive flexibility (hypermobility) might be detrimental to health.