Intensity is usually described in terms of failure. You need to work close to failure for a good level of intensity. That’s how I understand it. Back squats present a bit of a problem in that regard, because going to failure is a safety issue. For some of my lifts, like OHP or pull ups, I actually will reach true failure at the last rep of two of the last set of two. I actually try to hit that failure threshold so I know I’m keeping a good intensity level. I can’t really apply that approach to squatting. If I do squats every workout with a 50/50 chance I may fail in a final set, I’m just asking for disaster.
Generally, I use tempo as a failure gauge. That works well for squats too. But one thing I have noticed with squats that I don’t feel the same way with other exercises is a heart rate increase. I’m lifting in the 5-7 rep range now and my heart rate doesn’t go up like it did in the past with 10-12 rep range or body weight exercises. Except for squats. When I do a set of 5 - heavy for me - squats my heart rate can go up in a surprising way. Not quite aerobic level, but pretty high.
My two questions are: is that heart rate increase normal for squats? and can that be used as an intensity gauge?
I’m not sure about the exact rates. My resting heart rate is around 50-55. The squat heart rate I’m taking about is probably around 100-120. (I only measured it once.) I’m 52 years old, and according to the US Navy method I’m about 10% body fat. So, pretty fit.
I can add detail if it would help.