Then what you need is stronger abs, not a more muscular back. The abs support the lower back and help maintain its alignment. Work your abs and stretch your hamstrings and you'll stop putting your back out.
Trimble has a really good "Intro to GPS" Tutorial which covers how pseudo-random codes are used. The entire tutorial is here:
http://www.trimble.com/gps/fsectio ns/aa_f3.htm
while the section on pseudo-random codes is here:
http://www.trimble.com/gps/howworks
It even discusses jamming (briefly).
"Religion is something left over from the infancy of our intelligence, it will fade away as we adopt reason and science as our guidelines." -- Bertrand Russell
