Erector Spinae is a muscle group located in the back, between the shoulder blades and hips. It consists of three individual muscles that work together to extend, flex, and rotate the torso while maintaining posture.
In contrast, Comfort et al. (2011) compared the front and back squat with the same absolute load of 40 kg to the superman exercise and reported no difference in lower erector spinae muscle activity. (strengthandconditioningresearch.com)
The prone trunk extension (superman) exercise is an effective exercise and displays very high levels of erector spinae muscle activity when performed with maximum lumbar extension. (strengthandconditioningresearch.com)
Comparing squat variations, Schwanbeck et al. (2009) explored lower erector spinae muscle activity in the back squat with either a barbell or in a smith machine with the same relative loads (8RM). (strengthandconditioningresearch.com)