To establish the relationship between the progression of sarcopenia and apoptosis we examined apoptotic gene expression in plantaris muscles (Pl) from 8 mo old (n=8), 30 mo old (n=8) and 35 mo old (n=6) male rats by real-time PCR. Pl mass declined from 368 +/- 7 mg at 8 mo to 333 +/- 7 mg at 30 mo (P<0.05) and 210 +/- 15 mg at 35 mo of age (P<0.05). BAX, Bcl-2, and Apaf-1 expression decreased by 62-74% at 30 mo and by 90-96% at 35 mo of age (all P<0.05 vs 8 mo old). In contrast, the expression of Caspases 3, 8, and 9 and AIF increased 3- to 5-fold at 30 mo (NS) and 7- to 50-fold at 35 mo of age (P<0.05). There were significant (P<0.05) correlations between Pl mass and Caspase 3 (r(2)=-0.60), Caspase 9 (r(2)=-0.58), Caspase 8 (r(2)=-0.50), and AIF (r(2)=-0.48). Thus, our results show that the expression of some genes involved in apoptosis increase with aging in Pl and correlate with progression of sarcopenia (Caspase 3, Caspase 9, Caspase 8, and AIF), whereas others decline with aging (BAX, Bcl-2, and Apaf-1).