Mechanisms underlying range of motion improvements following acute and chronic static stretching

Key points

1. 01Acute and chronic static stretching both produce a small reduction in overall stiffness (Hedges g approximately 0.42 and 0.37 respectively).
2. 02Stretch tolerance (maximum tolerable passive resistive torque) increases only after chronic stretching (Hedges g 0.74), not after a single session.
3. 03Neither acute nor chronic static stretching changes muscle fascicle length, even up to 24 weeks.
4. 04Acute reductions in stiffness are only significant at moderate or high stretching intensities and in individuals with normal baseline flexibility.
5. 05Long-term range-of-motion improvements are significantly associated with both decreased stiffness and increased stretch tolerance, suggesting dual mechanisms drive chronic adaptation.

How it was conducted

Design

Systematic review, multilevel meta-analysis, and multivariate meta-regression

Databases searched

CINAHL Complete, Cochrane CENTRAL, Embase, Emcare, MEDLINE, Scopus, SPORTDiscus (searched up to June 2023)

Included studies

65 randomised and non-randomised controlled trials

Participants

1542 adults (71% male; mean age 26.1 plus or minus 11.0 years)

Primary outcomes

Stretch tolerance (maximum tolerable passive resistive torque), stiffness (MTU, muscle, tendon, shear wave elastography), fascicle length

Secondary analysis

Multivariate meta-regression examining associations between stiffness or stretch tolerance changes and ROM improvements

What they found

• Acute static stretching: small positive effect on overall stiffness (Hedges g = 0.42, 95% CI 0.21 to 0.63, p < 0.001) with substantial heterogeneity (I-squared = 57.9%).
• Acute static stretching: no significant effect on maximum tolerable passive resistive torque (g = -0.25, 95% CI -0.01 to 0.51, p = 0.05) with negligible heterogeneity.
• Acute static stretching: no effect on fascicle length (g = 0.11, 95% CI -0.26 to 0.47, p = 0.52) with negligible heterogeneity.
• Acute stiffness reduction was only significant at moderate intensity (g = 0.42, p = 0.04) and high intensity (g = 0.40, p = 0.003), not at low intensity; it was also significant only in those with normal baseline flexibility.
• Chronic static stretching: moderate positive effect on maximum tolerable passive resistive torque (Hedges g = 0.74, 95% CI 0.38 to 1.10, p < 0.001) with substantial heterogeneity (I-squared = 65.4%).
• Chronic static stretching: small positive effect on overall stiffness (Hedges g = 0.37, 95% CI 0.18 to 0.56, p < 0.001) with moderate heterogeneity (I-squared = 30.0%).
• Chronic static stretching: no significant effect on fascicle length (g = 0.26, p = 0.95) with negligible heterogeneity.
• Effects of chronic static stretching on stiffness and stretch tolerance were not moderated by stretching intensity, intervention length, baseline flexibility, or sex (all p > 0.05).
• Chronic ROM improvements were significantly associated with decreased overall stiffness (g = 0.59, 95% CI 0.08 to 1.10, p = 0.03) and increased maximum tolerable passive resistive torque (g = 0.74, 95% CI 0.41 to 1.09, p < 0.001).
• Acute ROM improvement (moderate positive effect, g = 0.52, 95% CI 0.36 to 0.69, p < 0.001) was not significantly associated with maximum tolerable passive resistive torque or overall stiffness in the meta-regression.
• Chronic static stretching produced a large positive effect on ROM (g = 0.85, 95% CI unreported range, p < 0.001) with moderate heterogeneity (I-squared = 61.3%).

Limitations

• GRADE analysis rated the certainty of evidence as low or very low for all six outcomes, mainly due to risk of bias, inconsistency, and potential publication bias.
• Subgroup analyses for moderators such as specific muscle group, training status, and age could not be conducted because too few studies were available for each category.
• Female-only cohorts were underrepresented; the maximum number of female-only studies for any single variable was three, limiting sex-specific conclusions.
• Stretching intensity was classified from qualitative participant descriptions of discomfort rather than an objective standardised method, introducing potential misclassification.

Why it matters

For patients

People doing stretching programs should expect improved flexibility over time through both reduced muscle-tendon stiffness and an increased ability to tolerate the discomfort of stretching, rather than through changes in muscle fibre length.

For clinicians

When prescribing static stretching to increase range of motion, clinicians should appreciate that acute effects depend on stretching at moderate or high intensity, while long-term improvements are driven by both reduced stiffness and increased stretch tolerance, with implications for timing around sports performance and when to prefer eccentric training instead.

For readers

This is the first meta-analysis to use regression to directly link specific mechanistic changes (stiffness and stretch tolerance) to range-of-motion gains from static stretching, but the low certainty of evidence means findings should be interpreted cautiously and more high-quality primary research is needed.