Standing Forward Fold

The standing forward fold is the most direct hamstring stretch there is, and it reaches further than its simplicity suggests. Folding forward from a standing position with the legs straight lengthens the hamstrings, but also the calves and the fascia running up the back of the body, which is why it often relieves a stiff lower back as much as tight thighs. The instruction to keep the legs straight is what makes it work, and it is also where most people compensate. If the hamstrings are tight, the pelvis stops rotating and the lower back rounds to make up the difference, which moves the stretch off the muscle you were aiming at. Allow a small bend at the knees if that happens: a slightly bent knee with a long spine stretches the hamstring better than a locked knee with a rounded back.