The hamstrings are a set of three muscles in the back of your thigh. They attach in the lower half of your bottom down to behind the back of your knee. The job of the hamstrings is to bend your knee and to move your hips backwards. Tight hamstrings can lead to lower back tension and vice versa. The more you sit, the tighter your hamstrings become.
Sitting can give you a bad back! Tight hamstrings will just add more unnecessary tension to your lower back, inhibit your ability to bend forward and affect the ease with which you can walk. They are muscles that are easy to stretch, with a dramatic effect on your day to day living.