You're Pumped After a couple of sets, the muscles you're targeting should feel full and hard. This is the pump, the best feeling you can have in a weight room without getting arrested. You see the results of your work. The pump also serves an important physiological purpose. The movements that trap blood in your muscles also generate lactic acid.
Lactic acid helps produce growth hormone.
Growth hormone is thought to help your muscles grow bigger and your fat cells shrink, since it mobilizes fat for energy. The last thing you want is for hunger to kick in before your workout's over. When you use muscle protein for energy, you're making your muscles smaller instead of bigger. We can't support you in that endeavor. Not Trashed Your muscles will let you know when you've hit it just right.