The five objectives examined during this study were:
(1) Determine how long-duration space flight altered the anticipatory neuromuscular activity associated with arm movement.
(2) Perform proof-of-concept research to determine whether foot sensory input modified neuromuscular responses during space flight.
(3) Determine the time course of adaptation during long-duration space flight to foot sensory input as measured by patterns of neuromuscular activation.
(4) Determine whether long-duration space flight modified anticipatory neuromuscular postural activity in the immediate postflight period.
(5) Determine whether modifications in anticipatory neuromuscular postural activity associated with long-duration space flight were correlated with postural instability immediately after landing and during the recovery period.
The BPAS vest assembly was used inflight to collect electromyogram (EMG) and acceleration data during a series of arm raises. EMG signals were obtained by placing an electrode on a muscle, and flexing the muscle. Acceleration data were obtained by placing the accelerometer wrist assembly on the right wrist, and then raising and lowering the arm. Voice data was obtained by speaking into the TEAC data recorder microphone. All data were stored in the TEAC data recorder for ground-based analysis.
Four test conditions were utilized inflight: 1) 15 arm raises while free floating, 2) 15 arm raises while free floating with the addition of foot pressure, 3) 15 arm raises while attached to the Mir support surface, and 4) 15 arm raises while bungeed to the Mir treadmill. Foot pressure boots were worn during test conditions 2 and 3. Force plate and motion analysis data were not obtained inflight.
This integrative approach helped determine whether returning crewmembers were able to perform the appropriate coordination patterns required for complex movements as efficiently as before flight.
All subjects demonstrated decrements in postural control associated with voluntary arm movements. Center of pressure (COP) measures indicated that two postural control strategies were evident after space flight. Some subjects increased the magnitude of COP motion despite a decrease in arm acceleration features. This increased COP motion brought these subjects closer to the limits of their base of support, thus jeopardizing their stability. Other subjects displayed compression of the COP motion after space flight. This fact, combined with decreased arm acceleration suggested that these subjects chose to minimize their COP motion to stay clear of their base of support boundary. For all subjects, data indicated that the precise neuromuscular activation patterns necessary for optimal arm movements were not produced after space flight.
Inflight data indicated that the addition of foot sensory input (i.e. provided by pressure to the feet) resulted in neuromuscular activation, which was not normally present without foot pressure. These results strongly suggested that inflight foot pressure may be used as a countermeasure to retard muscle atrophy and maintain the health of neuromuscular reflex loops. Muscle activation patterns associated with the "bungeed to treadmill condition" were dissimilar to those observed during arm movements made in 1-g. This finding was important because the bungee cords were calibrated to create a load equivalent to the subject's body weight (i.e. 1-g loading), but the altered activation patterns suggest that bungee loading was not biomechanically equivalent to a 1-g condition. Thus, for movement tasks, it would be inappropriate to compare responses observed during inflight bungee loading with those observed on Earth. Additionally, adaptations in neuromuscular activation patterns associated with different inflight support conditions indicated that the sensory-motor system maintained it’s response flexibility even after 130 days in microgravity.
In conclusion, the evidence suggested a wide response range of the movement control system to space flight, and the ground-based Posa test could be utilized to characterize this response range. The ability to generate the neuromuscular activation patterns characteristic of preflight movement was compromised after space flight. In addition, evidence from the application of inflight foot pressure confirmed previous findings that neuromuscular activation was enhanced during free-floating arm movements.