This study assessed the effects of long-term consumption of the United States Recommended Dietary Allowance (RDA) for protein by older people who were sedentary or performed resistive training (RT) on body composition, skeletal muscle size and protein metabolism, and if the number of muscle groups trained influenced the muscle hypertrophy response to RT. Twelve men and 17 women (age range 54-78 years) completed this 14 week controlled diet and exercise study. Throughout the study, each subject completely consumed daily euenergetic menus that provided the RDA of 0.8 g protein kg(-1) day(-1). From study weeks 3-14 (weeks RT1-RT12), 10 subjects (four men, six women) performed whole body RT (WBRT), nine subjects (four men, five women) performed lower body RT (LBRT) and 10 subjects (four men, six women) remained sedentary (SED). Both the LBRT and WBRT groups performed knee extension and flexion exercises, and the WBRT group also performed chest press and arm pull exercises (three sets per exercise at 80 % of one repetition maximum, 3 days per week for 12 weeks). From week 2 (baseline) to week RT12, muscle strength increased in muscle groups trained in the LBRT and WBRT groups, and was not changed in the SED group. From baseline to week RT12, whole body muscle mass and protein-mineral mass were not changed, fat-free mass (P = 0.004) and total body water (P = 0.013) were decreased, and percentage body fat was increased (P = 0.011) in these weight-stable older people, independent of group assignment. The RT-induced increases in mid-thigh muscle area (from computed tomography scans) were comparable in the LBRT and WBRT groups (2.13 +/- 1.26 cm(2) and 2.17 +/- 1.24 cm(2), respectively), and were different from those in the SED group, which lost muscle area (-1.74 +/- 0.57 cm(2); group-by-time P < 0.05). From baseline to week RT12, 24 h urinary total nitrogen excretion decreased (P < 0.001), nitrogen balance shifted from near equilibrium to positive, whole body leucine oxidation (from the infusion of L-[(13)C]leucine) decreased (P < 0.05) and net (postabsorptive vs. postprandial) leucine balance (P < 0.05) increased from near equilibrium to positive, with no differences in responses over time among the three groups. In conclusion, the number of muscle groups trained did not influence whole body protein metabolism or RT-induced muscle hypertrophy in older people. Most of these data are consistent with a successful adaptation to the RDA for protein. However, research should continue to question whether the decreases in fat-free mass and total body water observed in all subjects, and the decrease in mid-thigh muscle area in the SED group, are physiological accommodations, and whether the RDA for protein might be marginally inadequate for older people to maintain skeletal muscle.