The senescence accelerated SAMP8 mouse is a model for sarcopenia and provides an opportunity to study the effects of lifelong dietary composition on the loss of physical function with age. We studied the effects of trans-fatty acids (2 % of total energy, TFA diet) on the loss of strength and aerobic exercise capacity (VO₂peak) with age. SAMP8 mice were studied at two ages (young, 25 weeks; old, 60 weeks) and on two diets (control vs TFA). Body composition, grip strength, VO₂peak, blood metabolites, and biochemical parameters were assessed. Body weight, fat mass, and body fat percentage all increased with age (p < 0.05) but were not significantly impacted by diet. There was a significant age-related decline in total grip strength as well as that normalized to fat-free mass (FFM) (p < 0.05) with a further decrease at old age in these metrics of strength on the TFA diet vs control diet (p < 0.05). Total VO₂peak exhibited no change with age or diet, but when normalized to FFM, VO₂peak exhibited age and TFA-related declines (p < 0.05). Intramuscular triacylglycerol (p < 0.05) and collagen content (p < 0.05) significantly increased with age, while blood triacylglycerol was increased by the TFA diet (p < 0.05). These data further characterize the SAMP8 mouse as a model for sarcopenia and indicate that dietary fatty acid composition can impact the degree of this age-related loss of physical function.