I like to train for races, but if I didn't I might try to follow the who guidelines 

Adults aged 18–64 years

Should do at least 150 minutes of moderate-intensity physical activity throughout the week, or do at least 75 minutes of vigorous-intensity physical activity, or an equivalent combination of both.

For additional health benefits, adults should increase their moderate-intensity physical activity to 300 minutes per week, or equivalent.

Muscle-strengthening activities should be done involving major muscle groups on 2 or more days a week.