I've got a 12hour tomorrow, and on a track that is fastest with weight forwards, I'm 6' 2", sitting froglegged for two hour stints result in some funky feeling legs. Lower back is definitely my weak point though. I did a 24hour kart race on an indoor track earlier this year, 3 driver team, 1 1/2 hour stint limit was in the rule books, my team was the ONLY team to not have any driver pull in early, we were also the first team to complete the race with only three drivers, anything less than four has failed to finish in the history of the race.
I feel your pain. Arms, ribs, legs, etc, that goes away for me when I work out and am in shape, but long runs ALWAYS end up with lower back pain for me.
You really wanna talk tiring, try this.
This is what I looked like slightly after half way of my first 24hour, I didn't know if my team of seven could make it.(we did.)
STARK contrast is in this photo taken after doing it as three person team. Working out and being fit makes a HUGE difference. I was aprehensive about this event as I caught walking pnemonia two weeks and a day before the event, I finally got rid of the congestion day of the event. Sucks as I wasn't able to workout/practice like I'd of liked to, and not feeling well the day before a race is good reason for apprehension.(My lower back was KILLING me)
Really really comes down to the track, and kart. If you slide it out, you load the inside rear wheel, which means a lot of extra friction coming out of the corner(solid differential). I steer with the brake in a few situations, but if I'm trying to get a good exit speed, I brake in a straight line, release right as I feed in a huge turn in, reduce turn in, stay lifted, then feed on the gas. Rolling as much weight off the inside rear gets the best exit.
Indoor karting has sets of corners where shedding speed and going a little sideways in will help set you for the next corner, but when I race outdoors, it KILLS momentum, you want to hang the inside rear just off the ground, and hold it there.