The Hand Posture Analyzer (HPA) system is designed to collect kinematic and force data on human upper limbs (hands, wrists and forearms) onboard the International Space Station (ISS). Kinematics is the science of motion. In human movement, it is the study of the positions, angles, velocities, and accelerations of body segments and joints during motion. The kinematic studies on the movement of the hand and wrist in microgravity, collected while manipulating both virtual and concrete objects, was researched to assess the approaching, reaching, and grasping mechanics of the hand and fingers without the effect of gravity. Also, a fatigue assessment of the forearm was done to determine how the control of grip force was affected by the exposure to weightlessness.
The absence of gravity causes many inconveniences, generically referred to as “space motion sickness,” but collected data have shown crewmembers normally adapt to microgravity in about a week. The main objective of HPA is the assessment of upper limbs performance, specifically the holding or grasping movements, and muscular function since the upper limbs are the principal means of work and locomotion onboard the space station. Daily tasks and movements, as well as physically demanding extra-vehicular activities, can have a significant effect on the hand causing muscle fatigue. This degradation of muscular-skeletal performance can be easily recognized on the upper limb. Another aspect is the adjustment of the brain and motor control system to microgravity on the upper limb, affecting not only bio-mechanics but in general the psycho-physical conditions. Overall, tests showed prompt recovery after short-term flight and loss of force up to 40% after 6 months in space. These results provided a quantitative evaluation of the performance of the upper limb and provided the base to develop countermeasures (e.g., tools to facilitate adaptation and make working in space easier) against the impairments due to change in gravity.