I came across some online explanation claiming it's tougher overall for females to build up arm power versus leg power. The main reasons involve starting out with far less upper-body muscle tissue plus distinct patterns in how the nerves trigger contractions there. Legs begin closer to male levels in raw power output, while arms lag further behind from the outset. Everyday activities keep the lower limbs active through basic movement and supporting body weight, which builds extra staying power over time. Arms tend to handle only lighter precision work instead. Muscle makeup also plays a role, with more endurance-oriented fibers showing up in the legs to help generate force more readily. On top of that, the shoulders, back, chest, and arms simply hold less tissue to work from, so visible changes require steady increases in demand.
I keep hearing that tirz leads to big muscle loss unless you eat tons of protein and lift. I want to get stronger instead. My legs have improved a lot on the leg press, but my biceps have not moved at all. I do full body weights twice a week plus yoga and running. My legs look more defined while my arms still look skinny. Could I be dropping muscle only upstairs? I'm 35, 5'4", started at 240 now 210, on tirz since 3/9/26.