What are some guidelines for proper stretching?

As you stretch, remember that it isn’t supposed to hurt. Stretch until you feel mild tension, then hold that position. As your muscles relax, you may be able to stretch a little bit more, but don’t overstretch. Also, if you have moderate or proliferative retinopathy, avoid stretches or exercises that place your heart lower than your waist or that cause you to hold your breath and strain, which can raise your blood pressure.