A little, but only with very long, intense stretching, and far less efficiently than lifting. In one trial, an hour of calf stretching every day for six weeks thickened a calf muscle about as much as a short lifting routine1. Across 25 studies of more ordinary stretching, the effect on muscle size was unclear and close to zero2.
What was studied
Static stretching means holding a muscle at a long, stretched position without moving. Muscle growth in these studies was measured as muscle thickness: how deep the muscle is, read from an ultrasound scan. Range of motion means how far a joint can move.
Two papers carry most of the weight, and both were read in full.
The long-stretch trial. Warneke and colleagues randomised 69 recreationally active adults (30 women, 39 men, mean age 27.4) into three groups of 231:
| Group | What they did | Time per week |
|---|---|---|
| Stretching | calf of one leg held at maximal stretch in a brace, 1 hour a day, every day, 6 weeks; stretch pain 7–8 of 10 | about 7 hours |
| Lifting | calf raises on a leg press, 5 sets of 10–12 to failure, 3 days a week; about 15 min a session | about 45 minutes |
| Control | usual activity | none added |
The weekly times are our arithmetic from the paper's protocol.
The meta-analysis. Arntz and colleagues pooled 25 studies with 710 participants, all measuring muscle size by ultrasound2. The typical single stretch lasted 60 seconds (range 20 seconds to an hour)2. Twelve of the studies were on the calf muscles.
In plain terms: one trial pushed stretching to the extreme; the review looked at stretching as most studies do it.
What the studies found
Extreme stretching grew the calf about as much as lifting. In the medial calf muscle (the inner head of the gastrocnemius), thickness rose from 19.55 to 21.06 mm with stretching (+7.7%) and from 19.25 to 20.87 mm with lifting (+8.4%), while the control group did not change1. The stretching and lifting groups did not differ (p = 0.979)1.
Medial calf muscle thickness before and after 6 weeks · mm
Before After
Lifting still did better in the other calf muscle. In the lateral (outer) head, only the lifting group grew clearly (+8.5%); the stretching group's +4.7% was not different from control1.
Strength rose in both. Isometric strength with the knee straight rose 18.0% with stretching and 13.4% with lifting, not different from each other, against 1.8% in the control group1. The authors note the test was isometric (pushing against a fixed plate), which sits close to what the stretching group practised1.
Ordinary stretching: an unclear effect. Across 25 studies, the pooled effect of static stretching on muscle size was a standardised mean difference of 0.118, with a 95% prediction interval from −0.233 to 0.4692. A standardised mean difference is the change measured in units of how much people normally differ; 0.118 is trivial. A prediction interval shows where a new study's result would likely land, and this one includes zero. The authors call the effect "unclear" with a "trivial point estimate", while noting that the range of the prediction interval leaves room for a modest benefit2.
Static stretching and muscle size, pooled across 25 studies · SMD
Time under stretch mattered. Longer single stretches and more stretching time per session, per week and in total were linked to larger gains, and trained people showed larger effects than recreational or sedentary ones2. Range of motion, by contrast, clearly rose (0.698, a moderate effect)2.
In plain terms: stretching can add some muscle, but the clear results came from doses far beyond a normal stretching routine.
What it does and does not mean
It does not mean stretching replaces lifting. In the calf trial, the stretching took about 7 hours a week against about 45 minutes of lifting, for similar growth in one muscle and less in the other1.
Weekly time spent for similar medial calf growth · min/week
It does not mean every muscle responds the same. Most studies used the calf. A 2024 trial of the chest in 81 active people found 15 minutes of stretching a day, 4 days a week for 8 weeks, gave strength and muscle-thickness gains not different from a 3-day-a-week lifting routine3. The authors still concluded that the equipment and long durations needed limit its use to "special circumstances"3.
It does not mean a few stretches after the gym add size. Typical holds of 20 to 60 seconds sit at the low end of the time-under-stretch range, where the review found the smallest effects2.
The studies are not independent. The meta-analysis includes the same research group's long-stretch trials, so the two main sources partly overlap.
The chest-trial authors discuss mechanical tension (the pulling force on muscle fibres) as the likely driver3. That is an explanation, not something these trials measured.
In plain terms: stretching can build a little muscle in special setups; lifting builds it in a fraction of the time.
What this looks like in practice
The studies that found growth used long daily stretching, often with a brace, and supervised protocols13. The lifting groups that matched them trained a few times a week with hard sets. For growth, what is known about lifting (sets, effort and range of motion) is covered in how many sets per muscle group per week and what progressive overload is. Stretching right before a heavy set is a separate question, covered in should you stretch before lifting.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Warneke et al., *Eur J Appl Physiol*1 | 69 recreationally active adults; calf; 6 weeks | 1 h/day stretching grew the medial calf about as much as lifting (+7.7% vs +8.4%) | 2023 |
| Arntz et al., *Sports Med Open*2 | 25 studies, 710 healthy people | Unclear, trivial effect on muscle size (0.118); range of motion rose clearly | 2024 |
| Wohlann et al., *Eur J Appl Physiol*3 | 81 active people; chest; 8 weeks | 15 min/day stretching, 4 days a week: gains not different from lifting | 2024 |
| Warneke et al., *J Sport Health Sci*4 | Panel of 20 stretching researchers | Consensus: stretch training does not add substantively to muscle growth | 2025 |
| Siegel et al., *Sci Rep*5 | 49 recreationally active people; thigh; 4–5 weeks | 15-min hip flexor stretches thickened the rectus femoris | 2026 |
Limits worth knowing
- Mostly the calf. Twelve of the 25 pooled studies were on the calf muscles2.
- Short studies. The calf trial lasted six weeks; most studies were short, so long-term effects are unknown.
- Ultrasound thickness, not whole-muscle size. Thickness at a few spots stands in for the whole muscle; no study here measured muscle volume.
- Not highly trained people. The calf trial included recreationally active adults, and its authors say nothing can be stated about highly trained people1.
- One research group dominates. Several of the long-stretch trials come from the same group.
- Abstracts only for the chest trial, the 2025 consensus and the 2026 thigh trial.
Latest research
The newest study we opened is a 2026 randomised trial on the thigh5. Forty-nine recreationally active people either did nothing extra or did 12 sessions of 15-minute supervised hip flexor stretches over 4 to 5 weeks. Muscle thickness rose in the rectus femoris (the front thigh muscle that crosses the hip), with inconsistent results in the outer thigh5. It is the first such result for the quadriceps, in a small group over a short time. It widens where stretch-related growth has been seen, but it does not compare stretching with lifting.
The short version
- Ordinary stretching had an unclear, near-zero effect on muscle size across 25 studies.
- Very long, intense stretching (an hour a day) grew one calf muscle about as much as lifting, at about nine times the weekly time.
- More time under stretch went with more growth, and range of motion rose clearly.
- An expert panel agreed stretch training does not add substantively to muscle growth.
Educational overview only — not medical advice.
