I don't think I've seen a squat as tenacious as Priscilla Ribic's 546lb. world record in 2006. Then I recently saw Tony Cardella squat 826.7 at the 2003 IPF World Championships. (To watch, go here and click on the 125kg squats. Cardella's is 1:50 in.)
It wasn't the heaviest squat of the day for the 275s. Great Britain's Clive Henry squatted 925.9 (starts at 5:06), which had a remarkable context as well. (Henry was on the verge of bombing out, missing his first attempt at 881.8 and second at 925.9.)
But watch Cardella struggle for nearly six seconds to lift the weight, and you will see what tenacity is.