Based on mitochondrial aging theory, oxidative stress plays a major role in aging and age related degenerative diseases. Since oxygen consumption and ROS (reactive oxygen species) rate increase during aerobic exercise, we supposed that heavy aerobic training can lead to enhance mtDNA deletion. Two experimental groups of adult male Wistar 14848 rats with 2 month-age were trained by running on a treadmill for 3 months (5day/wk, E40: N=10, 40 m/min, 20 min, E20: N=10, 20 m/min, 40 min, and slob=6%). mtDNA deletion of soleus muscle in these groups were compared with that in two control groups (Con1: N=10, aged 2 months and Con2" N=10, aged 5 months) and two sedentary groups that participated only in aerobic exercises at the end of the study (CE40: N=10, 40m/min, 20min, CE20: N=10, 20 m/min, 40 min, and slob=6%). Multiplex PCR products based on the agar (2%) indicated that mtDNA deletion (4.6kb0 induced by heavy aerobic training in E40 group. This deletion was not shown in other groups. This result was confirmed by sequencing analysis.