Maximal oxygen uptakes were determined by means of treadmill run for a sister marathon runners aged 8 and 9 years. They began to running exercise before 5 years. And they keep on running everyday about 10-15 kilometers. Their best performance; elder (YC): 3 hour 43 minute 46 second, younger (RC): 4 hour 15 minute 44 second.
　The following results were obtained:
　1) Their maximal oxygen uptake; YC was 1.413 l/min (52.3 ml/kg・min) RC was 1.226 l/min (49.1 ml/kg・min).
　2) During the marathon pace running they utilized about 70% of their maximal oxygen uptakes with a heart rate of 150-160 beats/min.
　3) Their physical fitness of structural and functional growing were good.
　4) During the daily running their heart rate was 150-180 beats/min, it level like an ordinary girl who play out-door activity with her friends.

DESCENTE SPORTS SCIENCE Vol.27/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE