Though most health organizations recommend getting at least 30 minutes of exercise a day, a Taiwanese study of 416,000 adults found working out for just 15 minutes per day is beneficial. Getting 90 minutes of exercise per week cut the subjects’ risk of death by 14% and increased their live expectancy by three years compared to those who did no exercise. Those who say they don’t have enough time for exercise should either start taking the stairs, or convince themselves that they have a bad knee.