We evaluated changes in the dynamic and isometric strength in the newly weakened quadriceps muscles and asymptomatic triceps muscles of 6 patients with postpolio muscular atrophy (PPMA) after 10 weeks of progressive resistance strength training. Alterations in muscle size were determined with magnetic resonance imaging. Serum creatine kinase levels were measured throughout training, and histological signs of muscle injury and changes in muscle fiber size and types were assessed with muscle biopsies before and after training. Exercise training led to an increase in dynamic strength of 41% and 61% for the two knee extensor tests, and 54% and 71% for the two elbow extensor tests. Up to 20% of the improvement was maintained 5 months after cessation of training. Isometric strength, whole muscle crosssectional areas of quadriceps and triceps muscles, and serum muscle enzymes did not change. No destructive histopathological changes were noted in the repeat muscle biopsies, and no consistent changes in muscle fiber size or fiber type percentages were observed. These results demonstrate that a supervised resistance training program can lead to significant gains in dynamic strength of both symptomatic and asymptomatic muscles of PPMA patients without serological or histological evidence of muscular damage.