From a personal perspective I can say it's just routine. I get used to training every day and I like training with intensity (more sprint than endurance) but alas after years of repetitive strain injuries I have toned down the training load. It was unhelpful in the long run anyway as I would train for 9 months then need to sit out for 3-6 months and be back at square one (usually shin splints). My body (knees especially) aren't thanking me for it but it's nothing that can't be fixed without a good chiropractor and lots of cross training (mainly cycling and weights but yoga/pilates, running and swimming too).

I learnt a lot from how a buddy who is/was a world class 24 hour mountain bike racer trains. His view is long term, building up fitness slowly over years. I do admit I find it much harder to maintain routine now that I have pulled back the training load.