Today is a passive rest day after a very difficult 68-miler yesterday with some members of my group (I'm a 54-year old woman). I agreed to do this ride against my better judgment --- my longest recent ride was 40 miles a month ago, and my standard weekly 40-milers have tapered off due to other weekend obligations. I have ridden a few metrics but not since last year. I work full time and go to the gym several times a week, but my endurance bike rides have been infrequent.
I ended yesterday's ride feeling completely, totally drained. In the last 5 miles I desperately wanted to stop riding. The last mile was grueling. I believe I ate and drank enough during the ride ---- my 2 water bottles were nearly empty (one of them included a little O.J.) and all 3 food bars in my pack were eaten 1-2 bites at a time throughout the ride. On our stop for lunch, I had a double latte and a Nutella banana crepe, figuring the eggs in the crepe would provide a little protein. I believe I did not bonk, but experienced extreme fatigue due to exceeding my current fitness level. The weather was cool and I did not feel overheated.
Last night, I was ready for bed at 7:30 (my usual bedtime is around 10:00). I slept almost 10 hours. Today, my muscles are not very sore but very stiff. I feel less fatigue, but still drained. A very mild headache comes and goes. I am hydrating (water) and eating well. Tomorrow, I plan to take an easy walk (30-45 minutes), or another passive rest day running some errands.
QUESTIONS: I'm wondering how to know when it's time to begin endurance training again after this type of fatigue, and if it is reasonable to take yesterday's mileage into account and put my current baseline mileage somewhere between 40 (my previous long ride) and yesterday's 68 miles. I need to train for a similar ride in early August, a recreational ride of about 88 miles. I want to ride and finish well without feeling completely drained.
Any suggestions would be much appreciated.