the lumbar spine is designed to rotate 13 degrees. this is like the short (hour) hand on a clock going from 12:00 to 12:30! it’s nothing.
this link explains more on great trunk/core training:
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i am big fan of dr stuart mcgill:
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he does not like them at all and with him being a leading expert on spinal biomechanics i pretty take his suggestions for face value.