How to build muscle (the smart way) — 6 reps is a magic number for most of my clients. Why Because it’s uncomfortable. “Hit muscle failure BELOW 8 reps” This is one of my favorite mantras for intermediate level clients. Because most people are lying to themselves. They’re believing that they are working harder than they actually are. 10, 12, and 15 reps are hard, but not because you’re working hard... but because they BURN. You stop because it’s uncomfortable, not because it’s working...