Originally Posted by
Carbonfiberboy
There's a reason that racing cyclists warm up at a moderate pace on their trainers before the start. Just sayin'. It used to be possible to hold a TT on a public road near me It. It started at the base of a short, steep hill. Before the start, I'd do a few loops up that hill and down a slightly circuitous route just before my number came up. That really helped. It's not a matter of HR. It's a matter of arteries and muscles. They take a little while to come up to "operating temperature." Starting up a hill cold will affect your whole ride. Not a lot, but it's noticeable to me, just like it is to those pros.
I agree it's good to warm up if one needs peak performance for a event that comes early in a ride. Or for the entire event if it's a race where you must start out as the best you can possibly be.
I don't think there is anything unhealthy about just getting on the bike and almost immediately going up a hill that gets ones HR up. I took the OP's question to be more about whether it was detrimental for health than a timed performance issue .