A few days ago I was chatting with my friend about what I consider to be 'acceptable fatigue.' The conversation stemmed from talking back and forth about how tired we were. The first question is: when does 'being tired' become detrimental to your goals?
I've spent a lot of time asking this same question and I usually don't get the answer until I've overdone it and find myself fairly shelled. This is not to say that I intended to wear myself out, but rather, I underestimated the cost on certain training blocks and/or sessions. Over time I accumulate enough real world data (by this, I mean, how I feel) to know how to place workouts appropriately.
This past round of training I have experimented with new sessions in an attempt to breakthrough on various levels. While the sessions themselves went well I found myself needing nearly 72 hours to fully recover from them as opposed to the 24 or 48 hours that I had anticipated. While this might not seem like a big deal, I find that it is. Something that takes so long to recover from cannot become a weekly staple in your training plan. It might become something you do monthly or every few weeks knowing that the cost will be high (but the return might be worth it). Trying to make it a weekly staple will cost you too much fitness loss when compounded week after week.
Another question: when is it ok to train tired?
This question is a bit complicated because we are almost always somewhat tired. I see two primary thinking patterns amongst folks I know:
1. Do the best that you can every day. Some days will be better than others and that's ok.
2. Only train at the prescribed power, pace of the session or shut it down.
My own line of thinking falls somewhere in the middle of those. There are certain days when I know that my level of fatigue from past sessions might not allow me to execute workouts perfectly based on the intensity guidelines (i.e. goal pace/power). In my mind, being off by a couple percentages is ok. Being off by huge margins (and subsequently feeling awful) is not.
A practical example:
1. I am planning to ride long intervals continuously between X and X+30 watts with a target of sitting around X+15. I had hard training the 24 or 48 hours beforehand and can only really manage hanging around in the X to X+5 range. In this case, I roll on. I might also take more breaks/recovery intervals to try to keep power up. I adjust the workout so that I can still manage to hit the target numbers. (For ex: I might ride 8 x 10 minutes on 5 min rest instead of 4 x 20 on 5 min rest).
2. I am planning to ride long intervals continuously between X and X+30 watts with a target of sitting around X+15. Getting anywhere near that range is a massive struggle; my legs burn, my HR is depressed (or elevated) and I'm cranky. The only option is to ride easy. In this case, I go home or cut the session short.
It takes time to know when you are simply tired and need a longer warm up (or an adjustment to the session); and when you really need to shut things down to regroup. I never do things perfectly and I'm constantly trying to learn how various sessions and training blocks affect me. All this is in hopes that one day, when there aren't many seasons left, I might just get it right.