I have been riding since 1971, touring and racing. This year something has crept up on me that I never experienced before. If I sprint for a stop sign or do hard pulls at the front or jam a short hill my legs feel like they are about to explode. Not sure if it is lactic acid build up or something else.
It is to the point that I am forced to rest after a sprint or hill, and my pulls are very short indeed.

Physical Age 55. Is this what is suppose to happen? I stretch every day and before/after each ride. What is going on? Ideas?