Kingpole, and others,
Squats are the real deal and so is power walking. If anyone has a physical limitation that would preclude doing squats, then Kingpole’s suggestion is quite valid - and here’s a little twist to accelerate the conditioning effect:
Wear a weighted vest when you walk - or, wear one and do a couple sets of squat jumps or other calisthenics.
I have found that wearing a weighted vest that allows you to gradually increase the weight in the vest as you build conditioning is a terrific (and safe) way to build both muscle mass and aerobic conditioning - simultaneously. I wear a cardio monitor by Polar when I power walk. Mon/Wed/Fri are weighted vest days (currently maxed the vest at 50 lbs - distance 3 miles - time 42 minutes - avg pulse rate 128 - max PR 142). Tues/Thurs are regular days - no vest.
Regular exercise has a big effect on releasing growth hormone and the big T.
Walking is great for me because it’s low impact.
All the Best,
MrTiPS