To be healthy, we're supposed to exercise at least x hours a week, one can read here and there. But does it depend on the person? Does it have to be divided into daily pieces or can it safely be packed into saturday + sunday for instance? And what would be the safest figure for the minimum weekly amoung of exercise for securing optimal health?
According to the 2008 Physical Activity Guidelines for Americans, you need:
Once you have safely progressed from the above recommended level without injury, gradually increase to:
There has been some more recent information that this activity level alone is not enough if you sit for prolonged hours. The suggestion is that you need to take regular activity breaks from sitting in addition to the above exercise recommendations to lower your risk of cardiometabolic disease.
The idea of packing all your activity into the weekend would not be optimal. Doing so could also increase your risk of injury and not give you the health benefits of regular activity. It is best to schedule your routine into your daily life. The above guidelines are to improve your health. As your health and fitness level improves you will want to re-evaluate and adjust your activity level.
The Bare Minimum of Exercise
Major health science organizations recommend a minimum of substantial aerobic activity and several strength training workouts per week. For instance, the CDC says that according to the evidence,
(If I may interject here: the recommendation of "brisk walking" has been criticized for being easily subverted into plain walking. They really mean brisk. It's got to be moderately intense--a hike, not a stroll.) Anyway, the CDC's recommendations continue:
Note the section on that page titled "For Even Greater Health Benefits". The minimum really is the minimum!
Similarly, the World Health Organization recommends: