The Collaborative International Dictionary of English v.0.48:
Flabbily \Flab"bi*ly\ (fl[a^]b"b[i^]*l[y^]), adv. In a flabby manner. [1913 Webster]WordNet (r) 3.0 (2006):
flabbily adv 1: in a flabby manner; "the old man's muscles were sagging flabbily"