Monday mornings set the tone for the week, but I guess that goes without saying. For my workout schedule, if I don't get a run in on Monday morning the whole week feels a bit off kilter. I always fear falling behind my goal of running or exercising 5 times per week. Missing the Monday workout means I'm behind the eight ball and can only miss one other day all week! That's too daunting and makes it easier to rationalize that I can write off this week and concentrate on next.
But if I get my early morning run on Monday then I get to work with the feeling that I'm already ahead of the curve. I don't need to rush home and try to get a run in before dark, or break up my day with a lunchtime visit to the fitness center for a boring treadmill session. The little pains I feel climbing the stairs to the 3rd floor each morning remind me that I've already accomplished something today, this week, this year.
From a fitness standpoint it's probably not a huge thing. I often hike both days of the weekend, so I'm already getting a good amount of exercise. Sunday is really the first day of the week according to my software tracking but that's not they way my lazy self rationalizes it. I've found that I can't give my self a sliver of justification to avoid exercise. The best Monday mornings are: wake up, put on running gear that I set out the night before, put on the MP3 player to some loud fast music, and be out the door less than 10 minutes after the alarm goes off.
After that, the rest of the week is up to me.