I remember those 5BX and XBX booklets too! My dad swore by them! Maybe because he was in the Air Force, and posted to the Aleutian Islands off Alaska, which sounds exactly like the kind of remote place the exercises were made for!
I saw in the recent articles on Prince Philip that he was a fan. It made me want to try the exercises again, except maybe not sit ups - those have been discredited, i think?
Now i'm curious to see how much similarity the BX programs have with sun salutations!
Cheers
Shirlea