I've trained every exercise of every workout to failure, and this was how I could guage whether or not I needed to increase the weights... Not training to failure is something completely new to me so I'm not quite sure how I would know to increase the weight used unless I had some sort of failure mechanism to know if my strength has gone up or not... How should that guy know when to increase?
When the weight feels easy enough, increase it. Hell, you can increase it every time you hit all your target reps, but some may wait a bit so they are insured continued progress.
Glenn Pendlay offers up his advice:
Add weight every session until you feel like taking a big load off and starting again. At that time your goal is to beat the weight you used on the previous cycle with that exercise. Your workouts over time would then look like a saw-tooth wave with ever-increasing amplitude.
when you start anything new, be it a new workout, new exercise, or new rep range in your training, start conservatively... judge how much you increase each week by what you feel you are capable of. at some point you wont get all the reps... then you would stick to the same weight the next week, and hopefully get all the reps or at least get closer... if you get them all, add a couple of pounds for the next time. If you go a couple of weeks without getting closer to succeeding with all your reps... then make a change. change to 1 work set, change to 5 work sets, change the reps, just make some change. and, start over with that new rep range, or new number of work sets, again with a weight that is comfortable, and again make steady increases, follow the same progression you did the first time. if you have one week where you actually do LESS than the week before... then immedietly change something and start over. there should be NO subjectivity when selecting weights or deciding when to move up, NO going by how you "feel". if you get all the reps the week before, you move up, simple as that. if you dont get them, you try again with the same weight. if you go nowhere for a couple of weeks or decrease, you change the nature of the workout.
now, when done correctly, this is largely self regulating. thats why it works so consistently. it you follow the rules, its hard to screw up. when you get to really hard weights doing a certain thing, it is certainly more stressfull than during the first couple of weeks you did it... this extra stress each week spurs the body to adapt. at some point, most often when you have been doing the same exercise and rep/set scheme for a month or two, and are not getting all your reps week after week (in other words, going to failure) the body just wont adapt to it anymore. so you make a change, and after this change, for a time, the workouts arent as stressfull, but still they are increasing each week and eventually youll be going full out again, and eventually you will go to failure again, and at first this will spur progress, then progress will stop, and it will be time to start over again... thats about as clear as i can make it. but one other thing... you are NEVER trying to go to failure. you are ALWAYS trying to make all your reps. failure is just that, a FAILURE to complete your workout. if this happens a couple of times in a row, you change the workout.