why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs

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why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs
why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs
why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs
why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs
why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs
why do some bodybuilders have straight backs and other bodybuilders have really indented lower backs