Just had a conversation today with a dear old friend who does a lot of running. We both agreed that you just have 'off days'.
Now, I know this isn't strictly an answer to the question but it's like this for me; as others have implied in regard to short absences, if I have anything up to five days without a ride it sometimes gives me a boost; almost like a welcome back from the bike, because your legs have missed me. Anything over and a few conditions that aren't quite right - a headwind or crosswind and it feels like a struggle. Saying that, I don't really know it any other way than to have gaps between riding and what I'm more interested in is the effect, not being a commuter, that riding everyday would have on me...?
This week for instance I did 83 miles on Tuesday, 47 on Wednesday and 35 yesterday. This isn't usual for me despite an average of 150 or so a week. Well, when I left yesterday my legs felt like crap despite adequate recovery, a bath and all the usual routine stuff I do. I found that after an hour in the saddle however, I was right as rain. (I sometimes find that my legs are aching after a day's work - I'm a part-time cabbie and full-time father - but rather than cycling making it worse it seems to sort it out).
I know I'm rambling here but I'm becoming more and more analytical of the little details that could be reason enough for having a bad/slow/gruelling ride even when all other things seem equal: sleep, attitude, food and fuel, weather conditions, windspeed and direction.
Somebody once said to me that if you only cycle once a week you don't improve. I tend to agree but only because the more you cycle, the more you are likely to know how to cope with 'off days'; headwinds, tiredness etc. Then again, sometimes you think you have all the ingredients for a perfect ride - teetotal the night before, healthy food, a good night's sleep, recent service on the bike, right mental attitude...hang on, why is this hill so damn hard? I did this yesterday, after a few jars, less food, no energy gels with more wind and rain...?
I know I'm posing more questions but they interest me.