Limited data exist concerning exercise training-induced alterations in skeletal muscle oxidative and antioxidant enzyme activity in senescent animals. Therefore, the purpose of this study was twofold: 1) to examine the exercise training-induced changes in oxidative and antioxidant enzyme activity in skeletal muscle of old rats; and 2) to critically analyze the relationship between oxidative and antioxidant enzyme activities in skeletal muscle in both trained and untrained senescent rats. Female Fischer-344 rats (approximately 24-mo-old) were divided into 1) exercised trained (ET; n = 10) and 2) sedentary (S; n = 6) groups. The ET rats performed a 10-week training program of treadmill exercise (approximately 60 min, 5 days/wk). Training significantly (p less than 0.05) improved VO2max (delta 22.8%) in the ET rats above their age-matched controls. Further, the ET group had significantly elevated (p less than 0.05) activities of succinate dehydrogenase (SDH) in the soleus and red gastrocnemius (RG) muscles as well as greater (p less than 0.05) 3-hydroxyacyl-CoA dehydrogenase (HADH) activity in the RG when compared to the S group. However, training did not alter (p greater than 0.05) HADH activity within the white gastrocnemius (WG) or soleus muscles. Activity of the antioxidant enzyme, glutathione peroxidase (GPX) was higher (p less than 0.05) in the soleus and RG in ET rats when compared to the S rats; in contrast, training did not alter (p less than 0.05) GPX activity in the WG. Finally, the correlation coefficients between SDH and GPX activities (combined ET and S groups) for the RG, WG, and soleus muscles were r = .73, .17 and .36, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)