When it comes to squatting and deadlifting strength, the thoracic extensors play an even greater role in stabilizing the spine than the abs. And while many lifters perform accessory movements for the quads, hams, gluteals, and abs, most don't do any accessory work for the erector spinae. That's a mistake.
For years powerlifting experts such as Louie Simmons and Dave Tate have stressed the importance of targeting the erector spinae, especially when it's an inherent weak link for the lifter, but until now we haven't had any research to back up their methods.
A recent study by Fisher et al. showed that performing the Romanian deadlift (RDL) didn't improve lumbar extension torque, but lumbar extension training was found to improve both RDL performance and lumbar extension torque.
This shows that performing isolation movements for the spine can directly improve deadlifting performance. According to Hamlyn et al., the lumbar erectors fire harder during squats than deadlifts, but the thoracic erectors fire harder during deadlifts than squats.
Needless to say, both the lumbar and thoracic spine need to be incredibly strong to hold the pelvis in place and prevent the spine from buckling during heavy squat, deadlift, and good morning variations.
In the video are eight go-to-exercises for accessory erector work. When you perform thoracic extension exercises, it's very important to do them properly. You want to move mostly at the thoracic spine and not so much at the lumbar spine.
While the lower back does flex slightly when performing thoracic extension exercises, trying to maintain a lumbar arch ensures that it doesn't round excessively and that the vast majority of motion comes from the upper back. Moreover, the lower lumbar spine and pelvis will remain stabilized with any lumbar motion occurring in the upper lumbar spine.
A variety of barbell, safety squat bar, chain, kettlebell, band, and dumbbell exercises can all be used to develop upper back strength.