Implementation and ground validation of a facility for functional and structural analysis of proximal upper limb muscles in microgravity.

The study of the activity of the proximal muscles of the upper limb and in particular of muscles acting on the gleno-humeral joint in microgravity condition has a special interest because: 1. The upper limbs play a major role in posture and locomotion for the subject living in the space station; 2. Muscle fatigue may have a significant effect on the hand and upper limb, for the ordinary work on board and in particular for the extra-vehicular activities (EVA); 3. Crewmembers may be at risk of shoulder injury during space walks because of decreasing muscle and tendon mass during long-duration space-flight. In this study a facility was developed to follow the changes in mass and force of proximal upper limb muscles. The facility is composed of a dynamometer, composed of a handle connected to a load cell, indicated as Pullgrip Dynamometer (PGD), and a specific software able to record force measurements and to drive the testing procedure (indicated as MAAT protocol). PGD was designed in a way to be easily mounted on the inner wall of the ISS. The results obtained in the testing session demonstrated that PGD and MAAT can reliably: 1. Discriminate between subjects in relation to the level of muscle strength develop in a pull effort applied on the PGD; 2. provide data for correlation between force and muscle size; 3. Evaluate the weight of the proprioceptive feedback in comparison with visual feedback to determine precision of force generation; 4. Evaluate muscle fatigue. The validation of the facility based on PGD and MAAT provides support to the plans to utilize them in experimental studies on alteration of proximal upper limb muscles on board of the International Space Station (ISS).