The current five-day format emerged from the days when Hobie Cat supplied boats. The same format is still used at the worlds, where there are supplied boats.
There was usually a 3 day (Fri-Sun) lead-in event, most often the Women's. Otherwise, the leading weekend was used for travel.
The first three days were a round-robin with boat rotations between every race. There was a party on Wed night where the fleet was cut in half (the Wed night gala at most events is still called the "Cut Party" for this reason).
The final two days, the leading half of the fleet raced, the back half got to sightsee. The trailing weekend was reserved for travel.
The format is still used, even though Hobie hasn't provided boats since 1989 (2005 being an exception).
Is it physically demanding? You betcha. However, at the 17 North Americans in San Francisco Bay, the average wind was 15+ knots and the average age was 56
! Despite that, there was more attrition from broken boats than broken sailors. I think after the second day, you kind of hit a groove where the post-race physical discomfort just doesn't get any worse. Of course, NSAIDs (like Advil) are in high demand.
I've done 8 days straight (14s followed by 16s in Syracuse) and last year I did a weekend regatta on the way home from the 16s. I'm 47 and far from being in shape. Yeah, I was tired, but I learned a lot, had a lot of fun and I even was awarded a can of "Road Kill Stew" for being a total road warrior by the folks at Canandaigua Yacht Club.
In another week, I'll be on the road to compete for 3 days (14's), run race committee for 5 days (17s and 18s) then home, only to turn around in 7 hours to go run race committee for another 4 days (NACRA F17 North Americans). Three days later, I'll head back to NY (6 hour drive) to do a weekend event with my wife on the 16.
You're younger and more in shape than I am, Madge! Quit yer bitchin!