The reason for increase heart rate & breathing hard is that I tend to combine exercises w/out breaks. I will do 10-13 of assisted pull-ups & then 12-15 of standing calf raises (machine). I will complete 3 sets of each, working back & forth alternately.
I ST for about an hour. Typically, 12 different exercises with an overall full body focus (upper, lower, core).
And yes, I get tired. So I'm not sure if I'm taking the muscle groups as far as I should go...to gain / build strength. Overall I know I'm getting stronger because I'm using heavier weights!