Different people’s bodies respond in different ways to overtraining, particularly when training indoors, and the symptoms can move around as you get older. Outdoors, I’m much more likely to spend lots of hours just grinding my legs away and thinking “Hey, I need to take a break. My legs are too tired.”
But when training intensely indoors, I tend to get sick and burned out before I start feeling deep fatigue in my legs. Lots of people have trouble with their sleep, carry around excess stress or exhaustion, and all sorts of other symptoms that show up before the legs start screaming. In my early 50’s, it took some time to understand and get a better sense of how my body coped (or didn’t) with indoor training stress over the long haul, and it’s different than the outdoor season.