Anything which gets you panting for 1/2 hour, three times a week (EVERY week that is, and not just the week before the medical) will keep the circulation in good order.
Plenty of room for interpretation there.
Convenience is a key issue - if I have to drive to the pool / gym, pay, get changed, do the stuff, shower, get changed, drive home, it adds another hour on to the 1/2 hour's panting.
Cos I live in the back of beyond, cycling or running in the local woods and paths is fave. Running is much harder work.
Result - Arnie Schwarzenegger from the waist down, everything else stick insect.
sd