Twenty-eight studies (n=1,338) were included, of which 23 were RCTs.
The studies were generally of a poor quality: the scores ranged from 2 to 8 out of a possible 10 (mean score 4.3). Only 6 studies scored between 6 and 8 points. Most studies reported point estimates and variability for outcomes, methods used for statistical analysis and randomisation. Flaws included a lack of allocation concealment and a lack of blinding of the participants, therapists and outcome assessors.
Stretch position.
All stretching positions showed gains in ROM motion compared with the control groups. The minimum gain in ROM was 5.2 degrees with straight leg raise/seated; the greatest gain reported was 14.3 degrees with straight leg raise/standing; and the range of means for the control groups was -2.9 to 3.0 degrees, based on 11 studies.
Stretching technique and duration.
Studies using static stretching showed greater gains than studies using PNF. Four studies directly compared stretching techniques. No technique was found to be consistently better than any other. The studies showed improvements with static stretching compared with dynamic stretching (1 study) and slow-reversal-hold compared with a static intervention (1 study). There was no significant difference between static and ballistic exercises (1 study) or between PNF and static exercises (1 study).
Four studies directly compared stretching duration. Studies showed that durations of 30 seconds and 60 seconds were equally effective and better than 15 seconds (1 study); one stretch daily for 30 seconds was as effective as one stretch daily for 60 seconds and three stretches daily for 30 or 60 seconds (1 study); six stretches daily for 10 seconds were as effective as two stretches for 30 seconds (1 study); and three stretches for 15 seconds were as effective as nine stretches for 5 seconds (1 study).
Warm-up.
Two higher quality studies (scores 6 and 8) assessed the effects of warm-up exercises but neither found any effect of warm-up exercises on the ROM with stretching.