An astronaut’s maximal oxygen intake (VO_2max), along with cardiac function, decreases during space life; and many astronauts experience unhealthy weight loss due to energy imbalances. In fact, excessive exercise may promote an energy deficit. Moreover, a typical scheduled exercise program (2.5 hours per day) appears to be excessive for time-pressed astronauts. Hence, more efficient exercise programs need to be developed for future space missions. With this background, the study of “high-intensity interval aerobic exercise training (HIAT)” was initiated. The HIAT protocol in our study consisted of 3 sets of 3-min high-intensity cycling with 2-min active rest between sets. Two intervention studies conducted with sedentary male adults revealed that VO_2max improvement by HIAT was significantly higher than improvement by moderate-intensity continuous aerobic training (MICT); and that cardiac function significantly improved in HIAT, but not in MICT, even though the exercise duration and volume of HIAT (15 mins, 180 kcal) were substantially lower than those of MICT (42 mins, 360 kcal). Further studies on general workers with metabolic syndrome also showed the superior effect of HIAT to MICT on VO_2max. Studies conducted on astronaut health may provide clues to solving lifestyle-related public health issues because the microgravity environment is similar to physical inactivity in reducing the load on the heart. Lack of time is a significant barrier to exercise habituation in our time-pressed society. Therefore, time-efficient exercise may contribute to the prevention of health risks not only in astronauts, but also in working adults in a modern society with time constraints and sedentary lifestyles.