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 you lean back a bit, your legs can push harder at the knee even though your muscles aren't working any harder—this might be because of how your body is positioned, not because your brain is sending stronger signals to your muscles.

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 changes depending on the position.