Discipline: Biological Sciences
Subcategory: Physiology and Health
Karina M. Matos Fernandez - University of Puerto Rico at Ponce
Co-Author(s): Millard F. Reschke, Neurosciences Laboratory, NASA Johnson Space Center, Houston, TX, USA
The human body has the ability to adapt to extreme environments, prolonging survival. Exposing the human body to prolonged periods of weightlessness induces adaptive modifications to the neurovestibular system that must be readapted upon a return to the Earth?s gravitational field. Astronauts returning to the Earth’s gravitational field begin a readaptive process that will often impair their ability to stand, walk, turn corners, jump and climb stairs. Returning to a normal functioning state may take hours, days or even weeks depending on the length of time spent in an environment weightlessness. Readaptation has a serious side when survival demands immediate action, such as immediate evacuation of the spacecraft. In an emergency, adverse effects can include the astronauts? ability to stand up, walk or jump from the craft. These adverse effects are particularly dangerous if returning crews land in the water where wave motion and spacecraft attitude do not allow for easy identification of the vertical are apparent. Therefore, the objective of this study is to understand the nature, extent and duration of the readaptive process. Of particular interest is the control of reflex processes in the major postural muscles, that have or may be altered. We hypothesize that the Functional Stretch Reflex (FSR), a spindle-shaped burst of electromyographic (EMG) activity in the postural muscles associated with preparation for landing when the astronauts returning from long duration space flight jump from a step located 20 cm above the floor. Specifically, what contributes to an observed loss of balance in crewmembers that causes them to fall backwards from almost any height. In order to gain a better insight on the underlying mechanisms we began the analysis of the output from the major postural muscles: gastrocnemius, anterior tibialis and soleus to evaluate their contribution to the FSR reflex response. The data used was collected as a part of many measurements made during the experiment known as the ?Field Test?. Jump tests from the 30 cm platform were performed preflight and postflight (as close to the landing of the Russian Soyuz spacecraft as possible). Measurements were made on raw EMG data by using MATLAB. Preliminary results shown that there is an earlier onset of the FSR postflight compared to preflight jumps and a tendency showing an increased flight-time in postflight when compared to preflight. In addition, activity from the anterior tibialis muscles appears to be earlier in onset and longer in duration in when postflight EMG activity is compared to preflight activity. Although the implications of these results are not conclusive, the extended duration of the anterior tibialis contraction could mean an increase in dorsiflexion, influencing the backward fall observed in postflight tests. They represent alterations in the onset of medial gastrocnemius reflex and extended dorsiflexion of the anterior tibialis that, in turn, affects the astronaut?s ability to maintain an upright posture after a jump.
Funder Acknowledgement(s): I thank the Universities Space Research Associaton for providing the funding for the research and the Space Life Sciences Summer Institute for the opportunity. I would like to acknowledge Marissa Rosenberg, Ph.D. and Chris Miller, Ph.D., NASA for their technical help.
Faculty Advisor: Dr. Millard F. Reschke, email@example.com
Role: Created a code by using MATLAB to visualize and analyze the electromyographic data gathered from three muscles.