Many of us want to know "how much exercise is do I need?" and probably more to the point is, "how little exercise can I get away with doing, to maintain or improve my overall health and fitness?" (well, I'll at least speak for myself!)
According to the American College of Sports Medicine (ACSM), who sets the standards for national guidelines on exercise and fitness, they publish a "position stands" with concrete information regarding frequency, intensity and duration of each type of exercise (i.e., cardiorespiratory, strength/resistance, flexibility, endurance, etc). I have summarized their published national guidelines below (note: these have not been updated since 1998; I welcome fitness experts to chime in with newer --published-- information:
Definition of Fitness:
The ability to perform moderate-to-vigorous levels of physical activity without undue fatigue and the capability of maintaining this capacity throughout life.
Aerobic Training
Frequency: 3-5 days/week
Intensity: 55%-90% of max heart rate
Duration: 20-60 minutes of continuous or intermittent exercise (10-minute "bouts", accumulated throughout the day DO COUNT!!)
Bottom line:
Aerobic endurance training fewer than 2 days/week, for less than 10 minutes, is insufficient for maintaining or developing fitness.
Resistance Training
Frequency: 2-3 days/week
One "set" of 8-12 repetitions of each exercise, including 8-10 various forms of exercise for each major muscle group
Flexibility Training
Frequency: 2/3 days/week
Performing both static and dynamic techniques to develop range of motion is ideal
The above information is just quick summary from the two published articles (each includes 14-20 pages!) from the two articles (reference below) that you may view online.
So, now the real question: do you follow any of these recommendations in your weekly/daily lifestyle currently? If so, is it religiously or sporadically, or somewhere in between?
[Source: POSITION STAND, ACSM
The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults, June 1, 1998]
[Source: Circulation
The American College of Sports Medicine and the American Heart Association Physical Activity and Public Health: Updated Recommendation for Adults http://circ.ahajournals.org for online version of journal article]