I've been sore for 4-6 days on several occasions. Worst one was an ~8 hour 3-on-3 floor hockey tournament where my team made it to the finals. We played some 8 games total, all of which included crazy amounts of sprinting. The next day, my 15 minute walk to class took an agonizing 45 minutes. My legs literally buckled when I tried to walk on stairs, so I had to drag my ass around using the railing. I had to use the handicap bathroom stalls so I could hold onto the hand rails and lower myself onto the toilet. Other bad ones included my first heavy squat session after a month+ off (quads completely cramped up) and my first time doing lots of GHD sit-ups (sneezing and laughing became incredibly painful).