Originally Posted by waterrockets

Just curious why you're thinking it's leg muscle? I always thought that if you had enough strength to run up a flight of stairs then you had enough strength to win the Tour... at that point it's just a question of endurance. Heck, look at The Chicken's legs...

So when you're riding just above FTP, do your legs die more than your lungs? I'm at the point where all systems fail pretty evenly