Statistically improbable words 5

What I read this week:

Traditional Coast Guard boot camp when I was a grunt in the 1960s was twelve weeks, versus the Army's nine-week stint. This was because people who came into the Guard were usually in suboptimal physical condition and because we had more instructional classes, such as semaphore and maritime law.

(From Lee Gutkind's book on creative non-fiction, You Can't Make This Stuff Up)

If some study found that Coast Guard graduates are in worse physical shape than Army graduates, what is the cause?