Biceps brachii regional shear modulus following elbow flexion exercises at different muscle lengths.

When you move your arm backward, it stretches your biceps because the muscle runs over your shoulder joint — and when you move your arm forward, the biceps gets shorter.

This scan can see how stiff your biceps get before and after a workout, and might help track muscle changes without needles or surgery — especially for guys who lift weights regularly.

Shear wave elastography is a technique that can accurately measure changes in muscle stiffness in the biceps after intense eccentric exercise in trained men, with consistent results when the same person repeats the measurements.

After heavy bicep workouts, most guys show reduced muscle stiffness in a specific part of the bicep—especially when the arm is stretched out—meaning that area might get worked harder during certain movements.

In men who regularly lift weights, the biceps muscle becomes stiffer when the shoulder is moved from a bent position to a straightened position, due to the muscle being stretched longer.

After performing heavy bicep curls with the shoulder extended, the lower part of the long head of the biceps muscle shows a larger decrease in stiffness compared to other parts of the muscle, indicating it experiences more mechanical strain during the exercise.