7Seated Hamstring / Side Bend
Sit with your back straight, your right leg extended out to the side, your left leg bent.
Keeping your back straight, exhale and lean forward toward your extended leg while lifting your left arm over your head to stretch your waist. Hold for twenty seconds.
The best time to stretch is after your workout, because this is when your muscles are warm and you can stretch the connective tissues (the ligaments and tendons) more deeply and with less risk for injury.
If you stretch when your muscles are cold (for example, as soon as you wake up in the morning), you have much more limited flexibility and higher chances of hurting yourself.