a-c, Greater hindlimb ischemia, use impairment, tendency for decline in native collateral diameter (before FAL), and reduced collateral remodeling after FAL. d, Aging impairs ischemic angiogenesis. e, Baseline muscle atrophy (average muscle fiber cross-sectional area) in aged mice. No ligation-induced atrophy at day-7 after FAL in this moderate ligation model. Decline in baseline collateral diameter and subsequent outward remodeling contribute to findings in Fig 1; less ischemic angiogenesis may also contribute to reduced recovery of perfusion on day-3 and day-7 after FAL.