This is an old training maxim - "Listen to your Body" - it means that no matter what, no matter that you did more last week then this, that you haven't been pushing yourself or that you have done similar workouts before - if your body starts complaining then pay attention.
Trouble is your body whispers. It gives hints. The signs are slight, and you're going to have to get good at listening for the murmurings. Because if you ignore them then the next thing will be full-blown injury or over-training or illness.
And having a rigid training plan can also be a problem. You become so fixed on completing the workout assigned for that day you don't even bother listening out for the signs that things aren't right. A weekly plan with workouts set out for each day puts lots of pressure on the training cyclist - after all, if you start cutting a workout here and there, well, soon you won't be doing anything, will you?
But if your body is complaining then you have already done enough. Congratulations, you're pushed yourself far enough that it's starting to complain. Hang back, let your body recover and come out storming when fully recovered. That's the real secret - sometimes you need to do nothing to get better...
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