Carbonfiberboy 

This discussion, like so many on BF, has gone all crazy. About the cardio danger of exercise, I'd just mention that the American standard heart disease diagnoses method is called a heart attack. It's just to expensive to screen everyone. If you want to pay for it yourself, go for it, but it's several thousand dollars for a full workup. I got lucky and had an minor heart issue, which combined with a sympathetic cardiologist, got me that workup. My cardio says, "Don't worry about it. Do what you want." And that's for a guy (me) with known heart issues. So there's that.

Next, I'd like to address the issue of lifting to failure. I definitely do not squat to failure. That's just stupid. There are youtubes of that. However when I rep out my last set of squats, I go until I can tell that doing one more would be a bad idea. I've been sick and for three weeks hadn't been in the squat rack until yesterday. I did my first two sets and did not do a third. My hams told me to quit while I was ahead. I also don't do leg extensions to failure because I do them after squats and my legs hurt so bad that I have no need to hurt them more than just enough. But everything else to failure. Sled is fine going to failure. Anything where you can set the weight down on a stop or drop it. Benches always to failure. Dumbbell work not always to failure, sometime just to adequate pain. That said, dumbbells and cables are good places to have a try for that last rep.

Next, that silly discussion about joints and their injuries: What keeps your joints in good condition is keeping them in good alignment. It's when they go out of alignment that they get injured. That's the reason that weight training helps prevent joint injuries.

Powerlifters don't have to train to failure because they spend the whole afternoon in the squat rack doing endless sets. They have plenty good fiber recruitment. They "only" go to 90% of 1RM because they do sets, not 1RMs. Which reminds me: don't do barbell squats except in a rack.

All the above said, I work out with a guy who's been lifting heavy all his life. He says, "Never squat over 500 lbs. It's just not necessary. Going too heavy will mess up your joints in time." However, this is a thread about weight training for cyclists. I don't think any of us should be squatting more than double their body weight. BW X 1.5 is probably plenty.