HEIGHT INCREASE, NEUROMUSCULAR FUNCTION, AND BACK PAIN DURING 6-DEGREES HEAD-DOWN TILT WITH TRACTION

Background: Spinal lengthening and back pain are commonly experienced by astronauts exposed to microgravity. Methods: To develop a ground-ba sed simulation for spinal adaptation to microgravity, we investigated height increase, neuromuscular function and back pain in 6 subjects al l of whom underwent two forms of bed rest for 3 d. One form consisted of 6 degrees of head-down tilt (HDT) with balanced traction, while the other was horizontal bed rest (HER). Subjects had a 2-week recovery p eriod in between the studies. Results: Total body and spinal length in creased significantly more and the subjects had significantly more bac k pain during HDT with balanced traction compared to HER. The distance between the lower endplate of L4 and upper endplate of S1, as measure d by ultrasonography, increased significantly in both treatments to th e same degree. Intramuscular pressures in the erector spinae muscles a nd ankle torque measurements during plantarflexion and dorsiflexion di d not change significantly during either treatment. Conclusion: Compar ed to HER, HDT with balanced traction may be a better method to simula te changes of total body and spinal lengths, as well as back pain seen in microgravity.