PRINCIPAL INVESTIGATOR(S) : Joseph T. Baker, Arnauld E. Nicogossian, G. 



Wyckliffe Hoffler, Robert L. Johnson, and Jerry R. 

 Hordinsky 



EXPERIMENT TITLE/NUMBER : Changes in the Achilles Tendon Reflexes Following 



Skylab Missions 



PROGRAM/MISSION : Skylab 3, 4 



CLASSIFICATION : Human 



DISCIPLINE(S) : Musculoskeletal, Neurosensory 



OBJECTIVES : To assess possible neuromuscular alterations following extended 

 spaceflight by conducting measurements of the Achilles tendon reflex duration 

 and its associated muscle potential. 



PROTOCOL : Each of the crewmembers participated in 3 preflight and six 

 postf light tests. The crewmember positioned his right knee on a firm support, 

 with additional support as necessary to achieve relaxation of the 

 gastrocnemius muscle. A relative displacement transducer was attached to the 

 plantar bearing surface. Muscle potentials were taken. The Achilles tendon 

 was struck several times as a warm up. To elicit reproducible and well 

 inscribed tendon reflexes, the Achilles tendon was struck every two seconds 

 for thirty seconds with a percussion hammer. No reinforcement maneuver was 

 used to augment the reflex. 



EQUIPMENT : Relative displacement transducer, silver electrodes, FM magnetic 

 tape . 



RESULTS : Crewmembers of Skylab 3 and 4 exhibited a significantly shortened 

 reflex in the immediate postf light period. A compensatory prolongation of the 

 reflex duration was exhibited between 4 and 12 days after recovery followed by 

 a gradual return to the preflight values. In general, the muscle potential 

 interval corresponded with the increase and decrease in the reflex duration. 



CONCLUSIONS : The changes in reflex duration may be due to the servofeedback 

 system of the postural muscles in which they must suddenly resume upright 

 support of the body in a one-g environment after weeks of inactivity. An 

 attendent strain and stretch in these muscles results in an overstimulation of 

 the neuromuscular system causing initial decrease in reflex duration. As the 

 muscles regain strength and mass, there occurs an overcompensation reflected 

 by increased reflex duration. When a normal neuromuscular state is reached, 

 the reflex duration returns to baseline value. 



PUBLICATIONS : 22, 23, 24 



