Remodeling of skeletal muscles is regulated by matrix metalloproteinases (MMPs). Functional genetic polymorphism (PM), modulating the expression of some MMPs, might be associated to different body composition and muscular strength improvement after exercise. Genetic PM of MMP-1 (G+/- at -1607), MMP-3 (5A/6A at -1171) and MMP-9 (Cytosine-Adenine microsatellite=(13-27)CA) repeats, around -90), body cell mass (BCM), extracellular water (ECW) and isometric maximal extensor strength (MES) of both legs were determined in 17 old sedentary women at the beginning and at the end of a 24 week physical exercise program. A 12 and 72% increase in BCM and MES, respectively, and 11% reduction in ECW were observed at the end of the program. Carriers of G-insertion in MMP-1, PM increased their BCM (7 kg vs. -1.5, p=0.007) and lost ECW (9% of total body water vs. 0.1%, p=0.004) more than the non-carriers; homozygote for 21 or less CA repeats/allele in MMP-9 PM gained more MES (115 N, interquartile range=IQR=63-132) than carriers of longer microsatellites (63 N, IQR=40-86, p=0.028). MMP-3 did not show any association with body composition and exercise-related strength changes. Exercise in elderly women increases BCM and strength, these changes are associate to specific MMP genotypes.