This simple stretch can really help with lower-back pain as well as reduce tight muscles in your lower back (and hamstrings). If you ever do a tough session on a Roman Chair [1], you'll definitely want to stretch out your back. I like to call it the Fetal Position Stretch because you'll look like you're in the fetal position when you're in mid stretch. Here's how you do it:

• Lie on your back with your knees bent.
• Slowly hug your knees to your chest until you are in the fetal position.
• Hold for 30 seconds and repeat as needed.

Source [2]