How long should I rest for?

The idea of resting and varying the intensity and volume of your training so that you balance recuperation with improved performance and/or muscular gains is called "periodization" and I think it is easily one of the most important concepts in exercise science.

I would refer you to the work of Tudor Bompa, who used this system to help his athletes win several Olympic medals and other competitions - I was lucky enough to attend York University in Toronto, where he was a professor and I have used periodization ever since...

I usually arrange my training in cycles so that I start each cycle lifting a nice, easy, manageable amount of weight (about 65% of my 1-rep max) and don't go anywhere near failure on the lifts and gradually increase the weight each week until I go two weeks without improvement (no increased weight lifted or reps completed) and then I take a week or two off and start the whole cycle again.

The best duration for these cycles is probably 6 to 12 weeks but it depends upon how long you've been training (the longer, the shorter should be your cycles), your age, recovery ability, how much training you do per week, etc.

In your case, you may have left the "time off" too long so I would suggest at least 2 weeks. Just as importantly, you should resist the urge to "hit it hard" when you get back and try using the progressive cycling described above. Not only will you be stronger at the end of each "cycle" but you'll find you get far fewer injuries.

Remember, you are actually going to get BETTER results by adding a week or two of rest into your program every few months. It's difficult for many people to accept that resting is actually productive but it is very difficult to argue with the results of periodization training.

I agree with Mark, although i undertand it to be productive to rest i find it difficult from a psychological stand point and find it very hard to rest longer than 2 days.

During this rest period (1-2 weeks) should cardio be maintained or should it be complete rest during a mass building program?