For many people, a diligent effort over a period of weeks might well increase your range of motion. In 2011, a nicely done experiment by Marshall et al showed that regular hamstring stretching substantially increased range of motion in normal university kids. Specifically, after “a 4-week stretching program consisting of 4 hamstring and hip stretches performed 5 times per week,” their range increased about 16˚ or 20%. That’s a real result. For whatever it’s worth. Regardless of what it does for flexibility, stretching remains amazingly useless for nearly any other popular or clinical goal. See Quite a Stretch. And see the next post for more discussion about the implications of this study: Plasticity versus tolerance.
“A randomized controlled trial for the effect of passive stretching on measures of hamstring extensibility, passive stiffness, strength, and stretch tolerance”