Exercise Frequency and Duration
Exercise has many long term benefits in terms of improving survival, and maintaining fitness. When an exercise physiologist looks at fitness, they assess it by measuring "VO2max". This refers to oxygen consumption, and is affected by how efficiently we use oxygen when we exert ourselves. When we are exerting more energy during exercise, our VO2 is increased, and when we are fit, we are able to acheive a higher "VO2max" (the maximum amount of oxygen we can consume per unit of time) than when we aren't. If you compare our ability to improve our VO2max, and our exercise patterns, you can generate graphs, such as though below. I have used the graphs presented to me by Barry Franklin, PhD, while I was in med school at Wayne State. He sent me copies at my request to use in the early 1990s for educational purposes. They illustrate quite well the relationship between exercise duration and frequency on VO2max. You can see where the recommendation of exercising 20-30 minutes, 3-4 times a week come from. These times and frequencies are where the graphs show maximum benefit in terms of fitness (VO2max) and effort expended. This doesn't mean you don't get any benefit from lesser amounts of exercise in terms of fitness, nor that you can't get more aerobic benefit by doing more. However, it is important to note that fitness does not necessarily relate to longevity benefits of exercise. I will be exploring this issue in a future web page.