Lean body mass is a misnomer (and DEXA scans aren't reliable). Lean body mass = Total Body Mass - Fat Mass That's "lean body mass," but it's not 1:1 "muscle m

Lean body mass is a misnomer (and DEXA scans aren't reliable). Lean body mass = Total Body Mass - Fat Mass That's "lean body mass," but it's not 1:1 "muscle mass," because bones, organs, and etc. do not constitute as skeletal muscle, but still take up weight. And muscle mass itself is a misnomer, because the actual weight of your muscle protein is not 1:1 to the actual weight of your entire muscles. Most people think muscle is made out of protein, but while that's true, it's not the main way you muscles get "bulk." The main compound that gives muscles "bulk" is water. Usually that's because your muscles have hydrophillic compounds like glycogen (stored sugar), electrolytes like potassium and sodium, and creatine. These latter compounds draw the water into the muscle, and make up for most of its weight and size. All these compounds get used up during exercise, so your muscle hold less water, and it's technically "consumed" during exercise, and needs to be replenished after. A coincidental fact is that once these stores are depleted, they become "super-sensitizied" that means they're much more likely to take up compounds out of the bloodstream than before. So, exercise depletes them, but if you eat enough after, you can fill them up to be bigger than where they were before.