Part 2 (randomized, double-blind, placebo-controlled) Prior to the initiation of Part 2, a review of safety and efficacy data from Part 1 will be conducted to determine whether cohorts for one or both muscles will be pursued in Part 2, as well as the recommended dose level for each muscle. A total of up to 40 new patients (20 patients per muscle) may be enrolled and randomized (3:2) to receive either ACE-083 (n=12) or placebo (n=8) unilaterally or bilaterally (if both sides are affected per inclusion criteria) to either the TA or BB muscles (but not both). The SRT will meet to review Part 2 patient safety data after the first 10 patients reach Day 43 in the study and approximately every 3 months thereafter.