In male bodybuilders, the top part of a big thigh muscle reacts more to hip position than the lower parts when the knee is bent slightly, showing that the muscle doesn't work the same way from top to bottom.

When male bodybuilders flex their knees at a 30-degree angle, the upper part of a specific thigh muscle gets stiffer if their hips are straighter, suggesting how stretched the hip is can change how the muscle works.

When male bodybuilders flex their knees and push without moving their legs, the front thigh muscle feels stiffer than a neighboring muscle — and this difference depends on how much the hip is bent.

For male bodybuilders, changing the knee bend doesn't really affect a key thigh muscle's stiffness if the hip stays in the same position — but changing the hip position does seem to matter more.

When bodybuilders push hard with their legs, the stiffness in a key thigh muscle changes depending on leg position—but the usual muscle activity sensors (EMG) don’t pick up these differences, suggesting they might miss some real muscle behavior.

When male bodybuilders do leg extensions with their hips bent at 80 degrees, the lower part of their front thigh muscle works harder than the middle part, according to MRI scans.