The purpose of this study was to investigate whole muscle and single muscle fiber adaptations in very old men in response to progressive resistance training (PRT). Six healthy independently living old men (82±1 y; range 80-86 y, 74±4 kg) resistance trained the knee extensors (3 sets, 10 repetitions) at ~70% one repetition maximum 3 days/wk for 12 wks. Whole thigh muscle cross-sectional area (CSA) was assessed before and after PRT using computed tomography (CT). Muscle biopsies were obtained from the vastus lateralis before and after the PRT program. Isolated myosin heavy chain (MHC) I and IIa single muscle fibers (n=267; 142 pre; 125 post) were studied for diameter, peak tension, shortening velocity and power. An additional set of isolated single muscle fibers (n=2215; 1202 pre; 1013 post) was used to identify MHC distribution. One repetition maximum knee extensor strength increased (p<0.05) 23±4 kg (56±4 to 79±7 kg; 41%). Muscle CSA increased (p<0.05) 3±1 cm² (120±7 to 123±7 cm²; 2.5%). Single muscle fiber contractile function and MHC distribution were unaltered with PRT. These data indicate limited muscle plasticity at the single fiber level with a resistance-training program among the very old. The minor increases in whole muscle CSA coupled with the static nature of the myocellular profile indicate that the strength gains were primarily neurological. These data contrast typical muscle responses to resistance training in young (~20 y) and old (~70 y) humans and indicate that the physiological regulation of muscle remodeling is adversely modified in the oldest old.