The purpose of the present short review was to evaluate the relationship between the percent increase in Vo_2max (% Vo_2max) and intensity, duration, frequency, period of training, the initial fitness level (Vo_2max) and age, as a reexamination of various studies on different populations with different protocols regarding endurance training. Close connection was recognized between the magnitude of improving Vo_2max and the duration and period of training in male and the frequency of training in female. More important factors found to improve Vo_2max were initial fitness levels of the individuals in male and female, i. e., one with lower initial scores showed a greater percent increase. Furthermore, the present study had shown that minimum training thresholds for improving Vo_2max were 40-50% Vo_2max for intensity, 20-30min/session for duration, 2-3 sessions/wk for frequency and several weeks for period of training.