A week of daily hard skiing will take a lot more out of you than you would think. Don’t forget also that the improvement comes as the muscles rebuild themselves in the days after exercise.
When I go away for two week overseas trips with absolutely zero exercise my legs always feel surprisingly strong on my return; it’s the cardio-vascular side tha deteriorates. I actually think that during the summer when I’m out twice or three times a week on the roadie including a very fast hooligan ride Wednesday evenings, I’m in a state of permanent tiredness and struggling to recover. Only a professional cyclist’s regime of balanced diet, physio and supplements would help overcome the tiredness – or being 30 years younger!