This study will test the hypothesis that Botulinum toxin A (BOTOX®) treatment reduces pain and disability in subjects suffering from sub-acute low back pain due to an identifiable muscle strain or back trauma occurring 6 to 16 weeks prior to enrollment. The study will also delineate the duration of medication effect and control for any placebo or mechanical trigger-point injection effect by employing a prospective, double-blind, placebo-controlled design.