When it comes to stretching your spine and the back of your legs, keep two things in mind: position and patience. This forward bend, using a block, will help relieve tightness in your lower back as well as stretch your calves and hamstring muscles. Remember: There's a direct relationship between flexibility and strength. The more range of motion your muscles have, the more strength and power they can generate.
1) Sit upright with your legs extended in front of you. Sit evenly on your buttock bones. Place an upright yoga block between your upper calves. Press your heels forward. Point your toes upward. Inhale as you raise the crown of your head upward, lengthening your spine and lifting your chest. Slowly bend forward by hinging at the hips. Rest your forehead on the yoga block and place your hands alongside your legs. Take five or six slow, full breaths.
2) Once you are comfortable with this stretch, you can progress to a more advanced version by reaching your hands around your feet. Bend your elbows out to the side as you fold deeper into the pose. To get more out of this stretch, make sure you slightly rotate your thighs in, and keep your knees straight. Hold and take five or six slow, full breaths.