I visited a friend the other day for whom I built a rod in 2007. I won't get into what brand of rod, length, or any of that. He told me it was his favorite and he had caught hundreds of fish on it, mostly bass. I picked up the rod, as I usually do, to see how I've changed in the years and I noticed that it seemed to have a really slow action. I remember the rod well and can tell you that I don't remember the action being as slow as it is now. Not even close. There could be other reasons as to why it felt different but it lead me to a ponderance.
Can extensive usage put wear on the action of a rod? Has anyone ever taken CCS data on a newly built rod and then come back after years of use and compared new CCS data to the original? If so, any difference? If there was a difference, what could be the driver(s): graphite content, taper, wall thickness?
Just a thought.

Are you talking action or speed? Every time you flex a rod you fatigue it to some minute degree. Old glass rods with polyester resins fatigued quick enough under often and hard use that they indeed changed over several seasons. Carbon fiber rods aren't prone to such noticeable changes, although they certainly do fatigue just like everything else.

It should be a fairly simple thing to rig up a test stand with a windshield wiper motor and load/unload a blank through many thousands of cycles. Count how many occur in a minute and you'd know how many cycles it would eventually take for you to record a difference in ERN, CCF or even AA. Could be an interesting experiment, although I suspect you're going to have to get into the hundreds of thousands of cycles before you record much of any difference.

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That's strange. I guess I've alway thought of graphite as replicable carbon chain that's very durable. Guess that doesn't mean as much when the resins are fatiguing. Are the resins the weak link here or do we have the resin to thank for being more of a shock absorber? I've always thought that fatiuing is only something to worry about with bamboo - which actually takes a visible set - which can be straightened with some coersion. Which brings up another interesting question: If graphite blanks can fatigue, are they capable of being manipulated into being straightened by some method if they're slightly crooked to begin with?

You don't need to worry about this with a carbon fiber rod blank. As I said, it happens - carbon does fatigue, but it takes a truly tremendous number of cycles to reach a point where you'd ever be able to tell it with your human senses. Put it out of your mind, or run the above test to put your mind at ease.

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To get me to believe that rod action can change with age (modern graphite rods) will take a before and after CCS measurement. Other than doing that, it is all conjecture.