Here are three simple six-week training programs designed for people who don’t have time to go to the gym and/or don’t want to buy exercise equipment:
I found the first one in a Lifehacker article last year. Since then, the site owner decided to expand (copy-paste :P ) the program to work on the abs and the thighs.
I’d like to give couple of comments about the programs. First off, always keep in mind that working out a body part will remove fat from it i.e. targeted fat loss doesn’t work. You’ll need to control your calorie intake for that. At most, these exercises will tighten/tone their respective body parts preventing the loose skin and fat from sagging.
The other thing about these programs is that the sit up and squat challenges are too easy compared to the push up challenge. This is because the muscle groups used in those exercises are large and as such, respond quickly to exercise. Heck, in my summer weight training class back in college, we were doing 4 sets of 500 crunches at the end of the 5th week.
On the other hand, push ups use both large muscle groups (chest, abs, and to a smaller degree, back) and small muscle groups (shoulders and triceps). Unless your push up stance is wide (which puts more effort on the chest) your progress will be hampered by the relatively slower responding shoulder muscles and triceps. Expect to repeat some weeks for 3 times or more.