Background <p>Static stretching is widely accessible across the lifespan and commonly prescribed to improve flexibility. However, whether flexibility improvements following chronic static stretching are moderated by participant characteristics or the targeted muscle group in lower-limb remains uncertain.</p> Objectives <p>We primarily aimed to determine whether the effects of chronic static stretching on flexibility are moderated by age, sex, training status, baseline flexibility, and muscle group.</p> Methods <p>We searched PubMed, Web of Science, and Scopus for randomized controlled trials published before June 2025 that examined the chronic effects of static stretching on lower limb flexibility outcomes (compared with non-stretching or passive control conditions) in healthy populations. Meta-analysis was performed using a random-effects model, with effect sizes expressed as standardized mean differences corrected for small-sample bias (Hedges’ g). Subgroup analyses were conducted to examine the potential moderation by age (children and adolescents vs young vs middle-aged vs older adults), sex (male vs female), training status (athlete/trained vs recreationally active vs sedentary), baseline flexibility (with tightness vs without tightness and not reported), and muscle group (knee flexors vs knee extensors vs ankle plantar flexors). Methodological quality was assessed using the Physiotherapy Evidence Database (PEDro) scale, and potential small-study effects were evaluated using Egger’s regression test and trim-and-fill analysis.</p> Results <p>Seventy-nine studies (n = 3287) were included in the analysis. Chronic static stretching produced a moderate improvement in flexibility (Hedges’ g = 0.851, 95% confidence interval 0.710 to 0.991; SE = 0.0718; Z = 11.845; <i>p</i> &lt; 0.001), with substantial heterogeneity (τ² = 0.249; I² = 66.1%). No significant moderating effects were observed for age, sex, training status, baseline flexibility, or target muscle group. Egger’s regression test indicated potential small-study effects (<i>p</i> &lt; 0.001); however, trim-and-fill analysis did not impute any potentially missing studies and the adjusted pooled estimate remained unchanged. The mean PEDro score was 6.15 ± 0.90 (range 4–8), indicating moderate-to-good study quality.</p> Conclusions <p>Chronic static stretching yielded significant, moderate improvements in lower-limb flexibility; however, substantial heterogeneity and potential small-study effects were observed. These effects did not appear to be meaningfully moderated by age, sex, baseline flexibility, training status, or target muscle group. Overall, chronic static stretching may improve lower-limb flexibility across diverse healthy individuals and target muscle groups, although the results should be interpreted cautiously given the heterogeneity, potential small-study effects, and methodological variability among the included studies.</p>