Muscle architecture adaptations to static stretching training: a systematic review

Key points

1. 01Resting fascicle length increased trivially overall (SMD = 0.17, p = 0.042); fascicle length during stretching increased by a small amount (SMD = 0.39, p = 0.026).
2. 02High stretching volumes (total greater than 5400 s) and high intensities (at or near point of discomfort) were required to produce fascicle length gains; low volumes and intensities had no effect.
3. 03Muscle thickness increased only with high-intensity stretching (SMD = 0.27, p = 0.021); overall there was no significant change (p = 0.18).
4. 04Fascicle angle (pennation angle) was unaffected by stretching regardless of volume or intensity.
5. 05Meta-regression confirmed that both total stretching volume (p = 0.02, R2 = 0.76) and intensity (p < 0.04, R2 = 0.52) independently moderated fascicle length gains.

How it was conducted

Design

Systematic review and meta-analysis of RCTs and controlled trials (PRISMA guidelines, PROSPERO registration CRD42021289884)

Databases searched

PubMed Central, Web of Science, Scopus, SPORTDiscus (searched July 2022)

Studies included

19 studies (14 RCTs, 5 controlled trials without randomization)

Participants

467 healthy participants; mean age 21.1 +/- 1.6 years; 342 males

Intervention

Static stretching training lasting 3 weeks or longer, targeting lower limb muscles

Primary outcomes

Fascicle length at rest and during stretching, fascicle angle, muscle thickness

What they found

• Fascicle length at rest (overall): SMD = 0.17, 95% CI 0.01 to 0.33, p = 0.042, I2 = 24.15%
• Fascicle length during stretching (overall): SMD = 0.39, 95% CI 0.05 to 0.74, p = 0.026, I2 = 46.90%
• Fascicle angle (overall): SMD = 0.08, 95% CI -0.07 to 0.22, p = 0.30, I2 = 0.00%
• Muscle thickness (overall): SMD = 0.11, 95% CI -0.05 to 0.28, p = 0.18, I2 = 33.22%
• High-volume fascicle length (>= 5400 s total): SMD = 0.29, 95% CI 0.09 to 0.49, p = 0.004; low-volume: SMD = -0.06, p = 0.60; subgroup difference p = 0.024
• High-intensity fascicle length: SMD = 0.28, 95% CI 0.08 to 0.47, p = 0.006; low-intensity: SMD = -0.05, p = 0.72; subgroup difference p = 0.042
• High-intensity muscle thickness: SMD = 0.27, 95% CI 0.04 to 0.51, p = 0.021; low-intensity: SMD = -0.11, p = 0.30; subgroup difference p = 0.016
• Risk of bias was low in 83.9% of all assessed criteria; GRADE evidence quality was high
• Egger's test showed no publication bias for any outcome (fascicle length intercept = 0.525, p = 0.313; fascicle angle intercept = -0.743, p = 0.292; muscle thickness intercept = -0.195, p = 0.802)

Limitations

• All 19 included studies targeted only lower limb muscles (15 of 19 focused on the ankle joint), limiting generalizability to other body regions.
• Sex-specific effects could not be examined because only one study reported results separately for females and most studies included collective values.
• Stretching intensity was classified by perceived discomfort and pain ratings rather than objective measures, introducing inconsistency across studies.
• Only two studies measured muscle cross-sectional area, preventing meta-analysis of that outcome.

Why it matters

For patients

People who want to use stretching to improve muscle size or function need to stretch at high intensity (to the point of discomfort) for extended total durations, well beyond the brief warm-up stretches typical in everyday exercise.

For clinicians

Prescribing static stretching for morphological muscle adaptation requires high volume (total duration greater than 90 minutes across the program) and high intensity; short or pain-free protocols are unlikely to produce structural change.

For readers

This meta-analysis provides the clearest evidence to date that static stretching can remodel muscle architecture, but only under demanding dose conditions that differ substantially from typical sports practice.