Final answer:
A bicep curl with a supinated grip is often more difficult than with a pronated grip due to biomechanical leverage and the greater force requirement from the bicep muscle for the supinated position. This is because of the torque generated by the distance of the weight from the elbow pivot point when supinated.
Step-by-step explanation:
The question refers to whether a bicep curl with the radioulnar joint in a supinated or pronated position is more difficult. When comparing the difficulty of the two exercises, the bicep curl with the radioulnar joint supinated is often found to be more challenging. This increased difficulty in the supinated position can be attributed to a couple of factors. One, the bicep muscle has a decreased lever arm when the arm is supinated, resulting in a greater force requirement to lift the same weight. Second, the supinated position is mechanically less advantageous for the muscles involved. Torque plays a crucial role in understanding this. Torque, which is the rotational equivalent of force, will be greater when lifting a weight with a supinated hand position because the dum/bbell is further away from the elbow pivot point.
In terms of biomechanics, the supinated position is the anatomical position where the palm faces upwards, and this requires the bicep to exert more force as compared to when the palm is facing downwards or backwards (pronated). This is due to the involvement of additional muscles and the biomechanical position of the bones and muscles in the arm. With the bicep being closer to the pivot point than the weight in the hand, the force applied by the bicep has to be greater to generate the necessary torque to lift the weight.
However, whether an exercise is more difficult can also depend on individual strengths and weaknesses, as well as technique and form. That said, generally speaking, a supinated bicep curl often requires more force and is thus considered more difficult than a pronated bicep curl.