I exercise every day, that way there's no bargaining with myself about whether or not I'll exercise. I can't say to myself "I'll skip today and exercise on Sunday instead," because I exercise today and Sunday and every day in between. Exercising is a struggle for me and I've found it's easier to do it consistently if it is just part of my daily routine.
Here is my weekly routine:
Mon: 1 hour with personal training (mostly weights with some cardio)
Tues: 1/2 hour cardio on gym equipment and 15 min abs
Wed: 1 hour with personal training (mostly weights with some cardio)
Thurs: 1/2 hour cardio on gym equipment and 15 min abs
Fri: 1 hour with personal training (mostly weights with some cardio)
Sat: either a group circuit training class at the gym or 1 hour swimming
Sun: 6 mile run (about 1 hour)
That said, it is possible to overtrain. The article
Preventing Overtraining - When Less is More on About.com describes how to know when you are exercising too much. I was doing an hour of pretty high intensity cardio (a 7 on Paige Waehner's
10-pt perceived exertion scale) on Tues and Thurs and I finally just decided it was too much. I was hungry all the time, exhausted when I finished my cardio, and I had to eat so much that I wasn't losing weight. By dropping my cardio back to 1/2 hour, I've been able to reduce the calories I eat, I'm no longer so hungry, I feel energized when I finish my cardio, and I'm losing weight again.