The purpose of the present study was to examine the utilization of fatty acids (FA) and muscle substrates by skeletal muscle in young, middle-aged, and old adult rats under hyperglycemic-hyperinsulinemic conditions. Male Fischer 344/Brown Norway rats aged 5, 15, or 24 months underwent hindlimb perfusion with a medium of 20 mM glucose, 1 mM palmitate, 1000 µU/ml insulin, [1-¹⁴C] palmitate, and [3-³H] glucose. Glucose uptake and palmitate delivery were similar among age groups. Palmitate uptake (nmol^.g^-1.min^-1) and oxidation (nmol^.g^-1.min^-1)as well as muscle protein concentration of FAT/CD36 and FABP_PM were significantly increased (p0.05) in 24-mo- versus 5-mo- and 15-mo-old animals. When compared to 5-mo- and 15-mo-old animals, pre- and post-perfusion muscle triglyceride (TG) levels were significantly (p<0.05) elevated 72-145% in red and 112-129% in white muscles of 24-mo-old animals. Palmitate uptake was associated with total pre-perfusion TG concentration (r² = 0.27, p<0.05) and total TG synthesis rate (r² = 0.68, p<0.05). These results indicate that under insulin-stimulated conditions, FA uptake is significantly increased in old animals, which is associated with increased rates of TG synthesis and may contribute to the accumulation of TG in muscle of old animals.