These reasons are different from the goals of using muscle, which include: increasing blood flow and volume, warmth, increasing caloric expenditure and balancing blood chemistry. The point in all this is that narrowing to a simple focus can make it easier to stay on track with goals. If your goal is to build muscle then you can identify the minimum you need to do to trigger the body that it needs to create more muscle.
For instance, the average American loses 1/2 pound of muscle a year after the age of 20 and each pound of those muscles require 35 to 50 calories each day to maintain. At this rate, by the age of 40 the average American's metabolism will have decreased by 2450 to 3500 calories every week. This 3500 calories number is important because it is the same number of calories in each pound of body fat. Simple math to make it clear why so many Americans might be adding body fat as they age.
The simple solution to this is muscle. By maintaining the muscle you continue to need the calories. If your body believes that muscle is necessary it will not get rid of it. Research on the minimum amount of exercise that you need to do to maintain the muscle is not as definitive with the aging body. In our early 20s we maybe have to exercise at the same intensity once every 10 days but that for most of us is not enough as we get older. In fact the minimum gets progressively more frequent as we age. And, of course, everyone is different but certainly the guideline only applies if you already have the muscle and are using it at the same amount of effort. Less intensity of work and allowing your body to cheat (ie leverage on joints) will enable the body to shed muscle even if you are exercising on a frequent interval.
While convincing your body to build muscle is not as easy as reminding your body to keep it, it is necessary if your goal is to benefit from any of the perks of having more muscle. The process of training with the objective of building muscle can be intensive and challenging. In a motivational movie like Rocky the entire training phase can be packed into a short montage. In real life, the process might not be as exciting and, again, this is where I find the distilled goal to be helpful. By determining the therapeutic dose of exercise that your body needs to trigger the building of muscle, you achieve your goal in the most efficient way.
Exercise covers a broad spectrum of activities from the very general to the targeted and specific. My focus has been on creating the most effective ways to build and use muscle because, frankly, much of our quality of life is dependent on muscle.
As always, let me know how I can help.