One quick stretch won't move your hamstrings

Hamstring stretching is one of the most widely prescribed interventions in training rooms and rehabilitation clinics, yet how much of it is actually needed to change range of motion has stayed vague. People with clinically confirmed hamstring shortening are routinely given a hold of a few seconds before exercise, without knowing whether that amount can shift anything measurable. This review set out to map the relationship between total stretching volume and range-of-motion gains, to test whether that relationship is linear, and to separate stretching modalities. It also asked whether a single session behaves like a programme.

The authors searched MEDLINE, Web of Science, SPORTDiscus, CINAHL and SCOPUS for randomised controlled and crossover trials in healthy participants with no active musculoskeletal injury and clinically confirmed hamstring shortening. Eighty-four studies met the criteria, covering 3008 non-athletes and 1059 athletes. Range of motion was measured by active knee extension, passive knee extension and straight leg raise. Random-effects meta-analyses pooled mean differences, and separate dose-response meta-analyses related total stretching time to change in range of motion. Risk of bias was rated with RoB 2 and certainty with GRADE.

In non-athletes, static stretching beat no intervention on active knee extension by 9.03°, passive knee extension by 8.44° and straight leg raise by 12.11°. Proprioceptive neuromuscular facilitation improved active knee extension by 10.10° against no intervention and carried a small 3.18° advantage over static stretching. In athletes, static stretching improved active knee extension by 9.00°. The dose-response curves were nonlinear: a brief 1.5-minute single session did not exceed the 12° minimal detectable change for active knee extension, while repeated stretching delivered over at least 1 week with a cumulative volume of 70 minutes was more likely to pass that threshold.

That stretching increases range of motion is not new; what this adds is the shape of the dose-response and a modality comparison in people whose hamstring shortening was clinically confirmed. It complicates the popular idea that a short pre-session hold produces a meaningful change, because the gain from a brief single bout sat below the measurement threshold the authors used. It also positions proprioceptive neuromuscular facilitation as only slightly ahead of static stretching rather than dramatically better. Open questions remain: most included trials had bias concerns, certainty ranged from very low to high, and the review looked at range of motion rather than performance or injury outcomes.

The signal here is about accumulation rather than intensity of a single effort — repeated stretching across at least a week was the pattern most likely to produce a change big enough to detect. It is also a reminder that a measured improvement has to clear a minimal detectable change before it counts as real, which is why very short one-off doses looked unimpressive. The choice between static stretching and proprioceptive neuromuscular facilitation appears to matter far less than whether the stretching keeps happening. None of this speaks to whether extra range of motion changes how you perform or how often you get hurt.