PEDERSEN, PREBEN K., and KURT JØRGENSEN. Maximal oxygen uptake in young women with training, inactivity, and retraining. Med. Sci. Sports. Vol. 10, No. 4, pp. 233-237, 1978. Six young, healthy, sedentary females performed intense endurance training at a constant training stimulus (HR = 170 beats x min-1) twice a week in two 7-week periods separated by seven weeks of inactivity. Inactivity was defined as a period without scheduled exercise but with necessary daily activities. An increase in V̇o2max (10-14%) and in training intensity at target heart rate (24%) were observed in both periods (p < 0.001). Considering the intensity and duration of the program these gains are similar to those reported previously in women and men. The training response was the same in the two periods. Thus, there was no indication of beneficial effects during retraining from the previously performed activity. After the inactivity period V̇o2max, as well as the work intensity at target heart rate, did not differ significantly from the pretraining observations. Thus seven weeks with no training was sufficient to neutralize the effect of a conditioning program of similar duration.