Historically, it has been considered that the loads assumed by the elbow joint are distributed 57 % by the humero-radial joint and 43 % by the humero-ulnar joint. These data come from the study conducted in 1964 by Halls and Travill (Halls and Travill, 1964) by simulating extrinsic load on the hand of 3 specimens fixed in extension and full pronation of the elbow plus varus/valgus block. The role that was given to the radius head in the transmission of force was very relevant.

Some subsequent studies maintain this line. Hwang et al.(Hwang et al., 2018), also applying external load and the elbow in extension but also evaluating different rotations of the forearm, obtained humero-radial/humero-ulnar transmissions in neutral 58 % / 42 %, in pronation 54 % / 46 % and supination 57 % / 43 %. For these authors, rotation has little influence on the force distribution (Hwang et al., 2018, Morrey et al., 1988).

However, other studies obtained different results (Morrey and An, 2005, Chantelot et al., 2008, Lim et al., 2008). The study by Chantelot et al.(Chantelot et al., 2008), also performed in extension and varying the rotation position of the forearm but also allowing physiological valgus contradicts these data. This study indicates that 23 % of the transmitted force that travels through the humero-radial does so in neutral, 11 % in pronation and 6 % in supination. The study emphasizes the humero-ulnar joint and specifically the coronoid process, which assumes 60 % of the total load.

Similarly, a study by Morrey et al.(Morrey and An, 2005) found that in extension, 40 % more passes through the humero-ulnar joint than through the humero-radial joint. In 90° flexion, the load passes almost equally through the humero-ulnar and humero-radial. Another study by Wai Lim et al.(Lim et al., 2008) even states that in the flexion position of 90°, due to ligament laxity, the head of the radius can move away from the capitellum when applying a varus moment so that up to 93 % of the axial force is transmitted by the humero-ulnar joint.

On the other hand, the vast majority of studies that study the load transmitted by the elbow joint focus on extrinsic loads (Halls and Travill, 1964, Hwang et al., 2018, Morrey and An, 2005, Chantelot et al., 2008, Diab et al., 2005), those generated by forces when supporting actions such as falling, hitting or pushing. The role of intrinsic loads, those generated by our muscles when contracting to perform an action, has been largely ignored.

Some experimental models have been developed that consider the role of the musculature in the generation of loads and simulate muscle contractions (Morrey et al., 1988, Amis et al., 1979, Amis et al., 1980, Ofuchi et al., 2001, Cohn et al., 2014).

Using this type of model, Morrey et al. in 1988(Morrey et al., 1988), in a study in three anatomical pieces, concluded that the forces transmitted at the level of the humero-radial joint during muscle contraction should be considered lower than what had been established. The largest amount of force generated by the muscles studied (Biceps and Brachii) and transmitted to the elbow is produced at the beginning of flexion (0° to 30°) and is greater in pronation than in supination for the humero-radial joint. In addition, with the elbow in extension, the load is greater by the region of the coronoid, while as it moves towards flexion, it moves towards the olecranon.

We have not found in the literature studies that have studied the loads generated by the muscles with which we perform manual activities of any kind, the epitrochlear and epicondylar muscles. These, due to their anatomical location, generate load transmissions at the elbow level while mobilizing the forearm, wrist and hand.

To try to define which loads travel through the elbow joints, we designed a study in which the individual contraction of the epitrochlear and epicondylar muscles was simulated and the transmission of force exerted on the elbow joints was recorded. To do this, we have used a workbench that we had used in our previous study of joint forces in the elbow (Casanova Canals et al., 2019).