My workout usually consists of three sets of each exercise, 6-10 reps (depending on the exercise). I try to push myself to do as many reps as I possibly can in *each SET*. In fact, I keep track of all reps/weights and at each workout try to do at least one more rep per exercise or more weight. Sometimes I will add an extra rep in the first set, and exhaust myself, rest for the usual 60 seconds, and then do the last two sets at the same # of reps from the last workout.

Recently, I started to wonder if working to failure means only pushing yourself to that point where you can't do another rep for *only the LAST set*. So which is it? What should I be doing?

Thanks in advance.

Yes, the latter is much less likely to result in overtraining. I would try to stop at the point where you could do another rep and avoid failure altogether.

As the weights get heavier, training to failure becomes more and more of a strain on your recovery ability, and IMHO, eventually gets counterproductive. Olympic lifters never train to failure and make excellant strength gains.

Also realize that you can't add weight and/or reps every workout forever. At some point you are happy to add weight to the bar on a monthly basis.

I totally agree with Robert

Yep, what Robert said. Working to failure will really overtax you in the long run. As the great Mistress Krista of stumptuous.com says, it's best to leave one or two reps in the tank at the end of a set.