Deb, I've been meaning to send you a link to this article since you posted about wanting to do JASR in a few months. It's by Dr. Eades of Protein Power, but it's about weight/resistance training that's especially easy on joints and tissues. But the most interesting section to me was this:
"When you run a few hundred yards (assuming youâ€™re out of shape) you end up puffing and panting and with your heart pounding. You assume that your heart and lungs arenâ€™t in good working order, and you assume that if you start a regimen of regular jogging or other aerobic exercise that in due course your heart and lungs will get in better shape. If you do pursue such a course, you will find that indeed you do breathe less hard and your heart doesnâ€™t pound, so you assume that both your heart and lungs are in better condition. The truth of the matter is that your heart and lungs are about the same as they were when you startedâ€“what has improved is your muscular fitness. Let me explain.
"In the conditioning process the place where the rubber meets the road so to speak is at the level of oxygen entry into the muscle cells. As muscle cells work, they need oxygen. In an unconditioned muscle oxygen doesnâ€™t get into the cell particularly efficiently. Consequently, your body, in an effort to get more oxygen to the working muscle cells, pumps more blood (your heart pounds) that contains more oxygen (thanks to your huffing and puffing). As your muscles become more conditioned, what happens is that the bodyâ€™s ability to get oxygen into the muscle cells becomes much more efficient. After your muscles are conditioned and you run a few hundred yards, your heart doesnâ€™t pound and you donâ€™t pant because your muscles are getting plenty of oxygen because of the conditioning effect in the muscles themselves. It has nothing to do with your heart or lungs."
I actually tested this myself and it works pretty well!
https://proteinpower.com/drmike/2006/04/ 17/slow-burn-fitness-for-boomers/ 9 days ago