Anything more than a walk around the park for an elderly person. Hiking maybe.
A person who is 20 lbs overweight should not be running a marathon until they have lost the weight. Training for a marathon requires 10 mile runs or longer with the feet and legs and body slamming against the pavement for hours at a time. That extra 20 lbs beats down on the joints.
Heck, even sitting on a bike seat may seem low impact but I believe that it is no coincidence that my serious back problems were the result of my very long rides that summer. Sitting for 3-4 hours on a bike seat is not good for the back.
Now if you are in fit and muscles are strong then the muscles will hold the frame together. That might have been my problem — my abdominal muscles were not strong.
“Anything more than a walk around the park for an elderly person.”
Is 72 elderly?
It's interesting that there are now three global studies that show that virtually every type of exercise extends life span except one. Marathon running. The extended steady state cardio tends to kill you off earlier. Short intense bursts are much better for your heart. Remember, Jim Fixx who started the running craze in the 70's with his book "The Joy of Running" - kicked off in his 40's while running. That's why I limit my runs to 5K and when I'm ripping up I rely on interval and circuit training.