The biceps brachii begins roughly from the shoulder joint. As for radial tuberosity, here? On one side of the forearm? What about when the muscles are close to being fixed and shortened? At the stop, the forearm will rotate out, then the elbow joint will bend, and then the shoulder joint will be extended under the guidance of the tripod. Therefore, it is the biceps brachii resistance training that exerts resistance on this series of movements. Because I can't see your movements, I can only guess? You may be doing partial flexion to lift your shoulders and wrists, especially after 90, that is, using deltoid or pectoral muscles to stretch your shoulders and make your humerus move forward and upward. Is it only a common reason to bend the wrist, shorten the arm and change the center of gravity? So it's not necessarily your problem? The general correction method is wall bending? Try to keep your arm against the wall when you turn a corner, that is, try not to let your arm be too far away from the wall, and leave a little more at each corner? Explain that the wrist can only go down beyond the forearm midline after the deltoid or pectoral muscle is forced too hard? Up to the midline, try to avoid wrist bending.
Figure 1 shows the approximate position of biceps. Near fixed contraction? Is the forearm everted and then close to the shoulder when the shoulder is not moving? Then the big arm will be slightly raised? Other movements are basically relays.
Figure 2 shows that the so-called median line can only be lower than? Not higher than
Haven't typed so many words for a long time? If it works, adopt it? If you don't understand, just ask.