What movements happen at this joint?
Extension happens at the trunk when you straighten from bending at the waist, increasing the angle between your chest and your thighs. As you can see Biggie is doing, you can slightly hyperextend your back past neutral.
What muscles make these movements happen?
The muscles that extend your trunk are mainly your erector spinae, posterior muscles that pull the chest back up when they contract. Also back there are the multifidi, which act to stabilize the spine during trunk extension, lateral flexion, and rotation.
What exercises make these muscles work?
Squats and deadlifts, two of my favorites, work the erector spinae as do prone back extension exercises like supermans. Birddogs work the multifidi.
