Source notes

Spending longer in a stretch does not necessarily buy a proportionally larger gain in flexibility. The researchers pooled controlled studies comparing static stretching, where a position is held, with no stretching. Across 189 studies involving 6,654 adults, flexibility improved after both single sessions and repeated training. Their dose analysis suggested gains levelled off around four minutes per muscle group in one session, or ten minutes per muscle group across a week of training. Participants averaged about 27 years of age, so the evidence mainly describes younger adults rather than an evenly distributed sample of all ages.

Those times are estimates from comparisons across studies, not proven limits for every person or joint. The authors explicitly question whether the apparent plateau reflects a biological ceiling or the shortage of studies using very long stretches. The single-session dose relationship was not statistically significant, despite the fitted curve suggesting a peak. Repeated training produced a clearer dose relationship, and people starting with poorer flexibility generally improved more.

How Does This Show Up in Real Life?

For someone trying to improve flexibility, the useful question is how much time a particular muscle group receives, rather than how long an entire stretching routine lasts. The authors propose using cumulative stretching time to plan sessions, with ten minutes per muscle group per week as an evidence-based starting reference for longer-term improvement. That is not ten minutes for the whole body. They also found no clear overall advantage from pushing stretching intensity higher, so their practical guidance does not require stretching into pain. However, intensity was inconsistently described across studies, and some direct comparisons favoured stronger stretches. These findings concern range of motion. They do not establish that the same routine prevents injuries, improves sporting performance or addresses a painful movement problem.

Study quality varied, and the analyses showed potential publication bias and inconsistent results. Evidence certainty was rated low for immediate effects and moderate for repeated training. Most studies concerned hamstrings or calf muscles, while older adults were less studied. Repeated programmes typically lasted about six weeks; the analysis does not establish how long improvements persist after stretching stops.

The paper offers a useful planning reference, with more confidence in stretching improving flexibility than in any exact universal dose. Treat its time estimates as provisional findings from the available studies, and keep the goal of increased range of motion separate from other hoped-for benefits.