I totally agree on the value of rucking. I have a Wild Gym ruck and wear it every day while walking my dog 2 or 3 or 4 miles. I am a 68 year old female so I am in the "use it or lose it" stage of life.
I had been walking the dog daily for years since I retired, but adding the ruck pack last May has made all the difference. The nice thing about a ruck pack is how easy it is to gradually ramp up the weight by doing a varied mix of weight plates. I have a 5,a 10,and a 20 lb. weight plate. I started with 15 lbs, moved up to 20 after a few months, moved up to 25 at New Years, and plan to be up to 35 by May. That will equal the weight of my backpack's summer setup.
One way I know it is helping is when I go on a dayhike with my dayhike setup, which is 15-20 pounds, and I can do a ten mile dayhike with no issues.