Hamstrings and Achilles Stretch
The common standing, bend forward at the waist and touch your toes hamstrings stretch and/or bending forward with one straight leg extended up on a bench hamstrings stretch can cause a bulging disc or a "slipped disc" in your lower back, so avoid them like the plague! Instead, while lying on your back, place a towel around the ball of your foot, pulling equally with both hands. Gradually bring the almost straight leg towards your head while pulling the foot towards your chest. This is also a good stretch for the calf muscles and achilles tendon.
Dr. Paul R. Copeskey, DC, CCFC
Dr. Paul's Hamstring and Achilles Stretches