I agree wholeheartedly with reflexes. It's always remarkable to watch an obviously declined fighter insist that he still has them. We our own best deceivers.
Workrate decline is related to loss of reflexes, especially for counterpunchers. Guys talk about seeing the openings and no longer being able to pull the trigger. RJJ is a perfect example. He relied almost exclusively on his superior reflexes, and once they were gone, he was completely finished, with nothing to fall back on.
Bigcat said it pretty well; it's far easier for a fighter to maintain stamina and fitness to an older age than it is reflexes, which are more physiological functions. Both reflexes and stamina could be tied to workrate, so I suppose it all goes together. We could at least agree that power is usually the last thing to go?
Good point. It is definitely hard for a 40 year old at a weight like 160 to keep up with a 28 year old at 160. Hopkins' reflexes are also not what they used to be, but to me he was ALWAYS a frustrating fighter to watch, even in his prime, due to his style.
Common sense is reflexes. Anybody after 40 years of age has vision problems. Stamina, speed, timing and everything else would decrease but sight is the first one to go. RJJ is an example of this. He does still have the speed, (hands and feet) the movement, the skills and everything else but I am pretty sure he dosn't see the punches coming the way he used to, and that's why I think he doesn't react the same way anymore.
Got to echo the majority here, speed and reflexes go first. The old adage is that power goes last, but that can also be affected by reductions in speed and timing.