Reproducibility of Acute Changes in Range of Motion Following Short-Term Static Stretching of the Hamstrings and Gastrocnemius.

Background and Objectives: Acute responses to exercise interventions may vary within individuals across repeated exposures, potentially limiting the interpretation of individuals as "responders" or "non-responders". This study investigated whether acute changes in range of motion following short-term static stretching are reproducible within individuals. Methods: Twenty-six healthy young adults completed two identical sessions separated by one week. Flexibility was assessed before and after static stretching using the Sit-and-Reach Test (SRT) and ankle dorsiflexion range of motion (ADF ROM). The intervention consisted of three 30 s static stretches for the hamstrings and gastrocnemius. Results: Baseline measurements showed excellent reproducibility (SRT: ICC = 0.98; ADF ROM: ICC = 0.95). SRT performance and ADF ROM increased significantly after stretching (p < 0.001), with no evidence of a systematic difference in the mean response between visits (time × visit interactions: p > 0.05). Reproducibility of individual pre-to-post change scores was moderate by point estimate but imprecisely estimated (SRT: ICC = 0.74; 95% CI: 0.50-0.88; ADF ROM: ICC = 0.57; 95% CI: 0.25-0.78). Conclusions: Individual change scores showed limited reproducibility. The design cannot separate measurement error, normal day-to-day variation, and variability specifically attributable to the stretching response. Classifying individuals as "responders" or "non-responders" based on a single acute stretching session should therefore be approached with caution.