We examined the effects of endurance treadmill running on the oxidative capacity in specific plantaris muscle fiber types in young (5 month) and senescent (25 month) female Fischer 344 rats. Both young and senescent animals were trained at 75% of maximal O₂ consumption for 1 h/day, 5 days/wk for 10 wk. Densitometric analysis of succinate dehydrogenase (SDH) activity in type I, II a and II b muscle fibers was determined using a computerized image-processing system. SDH activity was found to be increased in all three fiber types in both the young and senescent trained animals compared with their sedentary counterpart.
　However, SDH activities of Type I and II a fibers in senescent rats were more responsive to endurance training than in young rats. The results indicate that the senescent plantaris muscle maintains its oxidative capacity to adapt to endurance training.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE