Training intensity is today's topic of conversation. Being that I enjoy teaching people how to become stronger, eat healthy and smash goals monthly, training intensity is something that is a learned behavior. Intensity to me is not the same as it is for you. This is partly due to that fact that we all perceive things differently. There are a lot of factors when you talk about training intensity from the speed in training, weight used to perform the movement and the desired outcome. Knowing which "intensity" you want to create an adaptation for is going to be the golden ticket to success.
So what is training intensity? To be fair, intensity is subjective. So instead of trying to identify it, I want to look at it in terms of training. For starters, intensity of load is where I want to start because it's the easiest to understand. Think of a barbell, with 100 pounds on it. If i would say I want you to do back squats at 75% of 100 pounds and then do singles at your 95% of 100 weight, 75% is less intense than 95%. Agreed? So going with this concept, the intensity of this training at the 95% is very high whereas the 75% is hard but manageable.
Next is your effort in training. A lot of group fitness classes will define themselves as "intense" training. This is referring to the amount of work you are putting in and how difficult it truly is. A lot of times lifters will you s a RPE scale or the rating of perceived exertion, So in terms of lifting, a 10 out of 10 on the RPE scale means you hit failure. A 7 out of 10 means that you might have 3-4 reps in the tank. Knowing the effort and training intensity is going to help you with overloading your training to get stronger as time goes on.
Intensity also plays on your neural, muscular or metabolic effects. So sets of 1-3 are going to be more neurally intense. Doing sets of 6-10 have more muscularly intensity. Sets of 20 or more might be primarily metabolically intensive although the muscular effort is often still quite high. If you are a bodybuilder, contraction of the muscle is also another form of "intensity" that should be considered. While the intensity of load or weight may actually be fairly low, the intensity of effort and concentration are both high.
Reviewing this information, it's safe to say that you need to look into your training. You SHOULD be struggling your final few reps if you are going for a high intensity of training. You shouldn't feel like you have much in the tank left over. However if your training is a lower intensity day, you don't want to cross into the high intensity threshold and create an over stimulus.
Vary your intensity and your results will also start to increase and change to adapt to the intensity variable!