Why is it easier to flex the right elbow when forearm supinated?

When the forearm is supinated, the biceps brachii muscle is in a more advantageous position to flex the elbow. This is because the biceps brachii muscle crosses the elbow joint at an angle when the forearm is supinated, which allows it to generate more torque. In contrast, when the forearm is pronated, the biceps brachii muscle crosses the elbow joint at a more acute angle, which makes it less effective at flexing the elbow.

Here is a more detailed explanation of the biomechanics of elbow flexion:

* The biceps brachii muscle is a two-headed muscle that originates from the shoulder joint and inserts on the radius bone in the forearm.

* When the forearm is supinated, the biceps brachii muscle is in a position where it can generate more torque on the radius. This is because the line of action of the biceps brachii muscle is more perpendicular to the radius when the forearm is supinated.

* In contrast, when the forearm is pronated, the line of action of the biceps brachii muscle is less perpendicular to the radius. This means that the biceps brachii muscle is less effective at generating torque on the radius when the forearm is pronated.

* As a result, it is easier to flex the elbow when the forearm is supinated because the biceps brachii muscle is in a more advantageous position to generate torque.