The purpose of this study was to characterize the-effects of two different dietary antioxidant supplementations and chronic repetitive loading exercise on biomarkers of oxidative stress in aged rats. Aged Fischer 344 Brown x Norway rats (30 months) were randomly assigned to either a diet supplemented with Vitamin C (2% by weight) and Vitamin E (30,000 I.U.) (N = 4), curcumin (1% by weight) (N = 5) or normal (unsupplemented) rat chow (N=4). The dorsiflexors of one limb in all animals was loaded 3 times per week for 4.5 weeks. The contralateral limb served as the intra-animal control. Additional control aged (30 months, N=4) and young adult rats (6 weeks of age, N=6) underwent the training protocol, but received the non-supplemented diet. The tibialis anterior muscle (TA) was removed and assayed for biomarkers of oxidative stress that included: the ratio of reduced glutathione to oxidized glutathione (GSH/GSSG), which is a measure of redox status, malondialdehyde (MDA) which is a biomarker for lipid peroxidation, 8hydroxy-2'-deoxyguanosine (8-OHdG), which is a marker of oxidative damage to DNA, catalase concentration, and cytosolic hydrogen peroxide (H2O2) levels. The data indicate that compared to control muscles, repetitive loading significantly increased catalase activity and lowered MDA levels in the TA. Non supplemented chronic exercise significantly increased cytosolic H2O2 levels in the TA of old rats, but decreased the cytosolic H2O2 levels in the TA of young adult rats. Supplementation with Vitamin E & C significantly increased the GSH/GSSG ratio and decreased cytosolic H2O2 levels in muscles of old rats. Supplementation with either Vitamins E & C or curcumin attenuated the increase H2O2 levels in the exercised TA muscle of old rats. Supplementation had no effect on catalase concentration. The results suggest that both antioxidant supplementation and repetitive loading exercise can improve the pro-oxidant status in muscles of old rats, but that they may work via different mechanisms.