Being busy is not an excuse to not do something about your health. According to a recent study, you can maintain your fitness and even improve your health by dedicating at least four minutes every day to exercise.

For the study, a group of 26 overweight and sedentary (but otherwise healthy) middle-age men did tests three times a week for 10 weeks. The tests was to compare the effects of doing four four-minute high intensity intervals (running at 90 percent of maximal heart rate) with doing just one four-minute session.

The findings showed that both groups had the same health benefits, whether they exercised for 16 minutes or just four per session.
At the end of the program, the men had increased their maximal oxygen uptake, or endurance capacity, by an average of 10 percent or more, with no significant differences in the gains between the two groups.

Metabolic and cardiovascular health likewise had improved in both groups, with almost all of the men now displaying better blood sugar control and blood pressure profiles, whether they had exercised vigorously for 16 minutes per session, or four minutes per session, and despite the fact that few of the men had lost much body fat.
The key to all this is to get your heart rate up, which researchers say can be done simply by sprinting up multiple flights of stairs or even walking very briskly.