Grab the bar and do reps til failure and tell me you don't have a sick pump. Your muscles get bigger from rebuilding tiny tears. It triggers your muscles to heal and repair bigger so that next time the stress on your muscles is reduced. You can tear them by heavy weight or high reps. Don't quote me because I don't pretend to know very much about muscles, but from my understanding high weight is for size and high reps is for conditioning. I think this is true because lifting does two things. Tears fibers and uses the muscles fuel. High weight means there is tearing but the amount of energy it pulls from your muscles overtime is less than High reps. High reps until failure is no doubt tearing fibers, but more reps means more fuel is being burned overtime. Say you lift for 10 seconds 8 reps heavy weight. But then lightweight high reps lifting for 2 and a half minutes. It's like it's literally sucking your muscles dry creating the separation and striations. It may not be correct but that's how my brain came to make sense of the difference between high reps and heavy weight. If your on gear however, the muscles synthesize protein better and create ATP(I think) which is the energy muscles use. So you literally repair quicker. So if your on gear the difference between heavy weight and high reps becomes almost negligible. Which is why I think you see 300 lb mass monsters curling light weight (at least compared to what you would think due to their size) for high reps. They are putting there muscles through stress, and concentrating on squeezing and contracting the muscles as much as they can. Which simply can't be done if the weight is too heavy. Even if you can lift it. I work out at home by myself. Forces me to have no ego and in my opinion less prone to injury. I could use a spot occasionally on some lifts, but I think I'm doing okay for what I'm able to do.