When people sit at different angles—leaning forward or backward—their brain sends the same signal to their thigh muscles to squeeze as hard as possible, even though the strength they can produce...

If you're sitting reclined back a bit (like leaning back in your office chair), your leg muscles can push a little harder than if you're leaning forward—by about 5 to 11%—at least in healthy adults.

When healthy guys push with their legs, the electrical activity in one specific thigh muscle (vastus lateralis) goes up steadily with how hard they push — unlike two other thigh muscles — so it might be a better way to measure how much force their whole quad is producing.